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problems with running my supercharged 351w

47K views 176 replies 14 participants last post by  Mustang671 
#1 ·
hi all , have been posting for a while as i have been finishing my 67 eleanor mustang . i have a 351w supercharged engine with a 6/71 weiand super charger , spec below .

high volume canton sump with windage tray and scraper
high volume oil pump
re-ground balanced crank
crane supercharger crank specs are -- fair to moderate ride,3pm 3.400-3.800 cruise rates at 8.5-1 max
degrees duration 226d @ .05"
degrees advertised 286d @ .05"
lobe seperation 112d
open and close intake 6d and exhaust 40d
gross lift .502"

hydraulic lifters on roller rockers
forged rods with hyperutectic pistons ( keith blacks)
edelbrock performer heads (need to find the spec but are good for a blower)
high volume engine run fuel pump
weiand 6/71 blower with 2x holley 600 vac secs carbs

what i need help on now is your opinions on what jets i should be using as a starting point in the primarys and secoundaries ?

currently i have .72 in the primary metering blocks and .78 in the secoundaries .

i have adjusted the timming to be 28d advanced with a idle of 22d advanced ,
the problem i am having is the carbs are spitting and when the engine finally runs its lumpy as hell ( i know its got a lumpy cam but its more so than it should be )

it will not idle and i have to keep the revs high ( say 1500 to 1800 ) but it is still rough at that rpm

do you have any idea on if my jets are too big ? it doesnt change when i adjust the air mix screws . they are currently out 1 turn .

i have a omex ecu and can adjust the timing very easily ,

i have got to 2 x boses ready for lambar sensors for when i get it dynoed and have also fitted 2x heat sensors in the exhaust manifold ,

but before that i just want to get it running on idle , also i cannot start it with the choke on . i have to have the flaps on the carbs open, which tells me it needs lots of air -which i have heard most supecharged engines and high lift cam engines never use the choke ??

am getting really frustrated as the car is 99% finished and i just want to get it on the road for 6 weeks or so to get some miles on it before the snow and ice come in december . then i can store it up till spring and adjust and fix any problems.

boo hoo:confused:

cheers shaun
 
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#2 · (Edited)
Couple basics

The engine needs a lot of initial timing, and a short (relatively speaking) mechanical timing curve, or possible locked out timing. DETONATION HAS TO BE AVOIDED AT ALL COSTS! If it detonates under a load, the engine will be toast- especially w/cast pistons.

The carbs need to be boost referenced. If there's no response from the idle mixture screws the primary throttle blades are open too far. Adding initial timing can help this just don't let the total timing get too high when you add initial. You might need to go richer from baseline if the carbs are stock. Baseline jetting can be found here.

To start it give it a couple pumps of the throttle (cold) and w/the throttle CLOSED, crank it up. Do not pump the throttle while cranking, do not partially open the throttle while cranking.
 
#3 ·
thanks for the info - much appreciated. i take your points and will apply them and double check the timing and also the primary throttle blades are closed .

thanks for the link to the carb spec sheets.

its hard for me to work out what jets i should have as they dont list it for a application but only for a specific carb model or part number.

so with a 351w with 30 thou over bore and this supercharger and with 2x 600 vac sec holleys. is there a close idea of what jets i should be using ?

i have seen around .62 for fronts and i have .72 but also have 2 carbs. so do i go lower as i have 2x carbs ? ie 2x lower than .62

very confusing and i want to get it somewhere there before going to dyno etc. i am sure with a bit of help and advise i should be able to get it to idle and run fairly normal. under small load before going on the road

also you say to lock the timing out etc. i havent got a dizzy. i have a ecu with a chart that i am able to enter actual timing numbers into. so for example what timing would you advise on the following rpm's ?
450
800
1200
1500
1800
2200
2600
2800
3000
3400
3700
3900
4200
4500
4700
5000
5200


as i can put any figure against those rpm's but i can also go above the scale and add differnt figures for engine load. so ie 10% engine load could be 28 btdc but at the same rpm with engine load at 70% that wouldnt be the same figure ?

thanks shaun
 
#8 · (Edited)
thanks for the info - much appreciated. i take your points and will apply them and double check the timing and also the primary throttle blades are closed .

thanks for the link to the carb spec sheets.

its hard for me to work out what jets i should have as they dont list it for a application but only for a specific carb model or part number.

so with a 351w with 30 thou over bore and this supercharger and with 2x 600 vac sec holleys. is there a close idea of what jets i should be using ?

i have seen around .62 for fronts and i have .72 but also have 2 carbs. so do i go lower as i have 2x carbs ? ie 2x lower than .62

very confusing and i want to get it somewhere there before going to dyno etc. i am sure with a bit of help and advise i should be able to get it to idle and run fairly normal. under small load before going on the road
Like TI said above, baseline the carbs and let the plugs tell you what it needs. In many cases- unless it's a competition only engine and vehicle- the jetting will not be radically different from stock. Select the power valve by the vacuum the engine has, read below the blower

also you say to lock the timing out etc. i havent got a dizzy. i have a ecu with a chart that i am able to enter actual timing numbers into. so for example what timing would you advise on the following rpm's ?
450
800
1200
1500
1800
2200
2600
2800
3000
3400
3700
3900
4200
4500
4700
5000
5200


as i can put any figure against those rpm's but i can also go above the scale and add differnt figures for engine load. so ie 10% engine load could be 28 btdc but at the same rpm with engine load at 70% that wouldnt be the same figure ?

thanks shaun
Use a curve instead of locked timing if possible. You will usually find that using a relatively large amount of initial timing along w/a relatively quick curve will work very well for you. Only in cases where the amount of timing needed at idle is within a few degrees of the total timing would you consider locking the timing at one setting.

AFA giving you numbers to go w/each rpm, the numbers can be plotted on a graph. It might start out at about 18-20 degrees at idle, ramping linearly up to about 30-ish degrees at 2600-2800 rpm. This is w/the engine under a light load. Now, this is not written in stone. While these numbers should be safe (no detonation), still be on guard for detonation, and increase the amount and/or rate of advance slowly, evaluating each change as you go. I would strongly recommend you start a tuning log or journal to keep tabs on each change and the result. Don't rely on memory!

You need to compensate for engine load by pulling out advance as the load increases- just like a vacuum advance would. Hopefully your ignition is vacuum referenced so it can sense the engine load.

I looked around and found the graph below which can give you an idea of how engine load should affect timing. Remember, load is estimated by the amount of vacuum the engine makes at whatever rpm it is running.

The numbers on the graph are just a representation, your engine will likely have different amounts for how much vacuum you have at idle and at what vacuum the advance is all removed. Also the amount of advance change may need to be different than the ~2.5 degrees per in/Hg vacuum shown on the graph:



How much boost are you planning on using? What bolwer drive ratio?

What is the static compression ratio? Plan on using the very best pump gas available (or E85, but that's a whole 'nuther ball o' wax). You may need to blend race gas w/pump gas.
 
#4 ·
high volume engine run fuel pump

weiand 6/71 blower with 2x holley 600 vac secs carbs

it will not idle and i have to keep the revs high ( say 1500 to 1800 ) but it is still rough at that rpm

do you have any idea on if my jets are too big ? it doesnt change when i adjust the air mix screws . they are currently out 1 turn .
The first thing you'll want to do is to get the fuel pressure under control. Some fellows forget this all together and other fellows think it doesn't matter. Carburetors are not like fuel injection. More pressure will not make more horsepower. The filling of the fuel bowl is controlled by a needle and seat arrangement that is sensitive to pressure and although Holley carbs can stand just a little more pressure than, for instance, the Carter AFB/Edelbrock design, you can still introduce only about 6 1/2 psi MAXIMUM PRESSURE into the carb inlet before you overpower the needle and seat and blow raw fuel into the intake manifold. I generally recommend a maximum of 5 psi just to be on the safe side. With carburetors, you need to concentrate on high volume, not high pressure.

What you'll want to do is to tee off at either of the carb inlets and run a small copper line back to the firewall, then up past the hood lip and to the cowl. On the cowl, temporarily mount a mechanical 0-15 psi liquid-filled fuel pressure gauge so that you can monitor the pressure going into the carbs by reading the gauge through the windshield as you drive. The better the quality of the gauge, the better the resolution you will get from it. The mounting system for the gauge won't have to be fancy unless you intend to make it permanent. You can make do with duct tape and tie wraps just for getting the pressure under control, then removing the line and gauge. Personally, I would want to keep it there permanently, but that's just me.
 
#5 ·
thanks for the reply . i have done all of this and i have just installed a red top holley electric pump . then pressure reg and a fuel pressure guage. i am showing 6psi and will take your point and lower it to 5.5psi just to be on the safe side . whats your thoughts on the jets and timming ? cheers
 
#6 · (Edited)
Cobalt327 offered up valuable information in his post #2. He may have gotten busy and can't come back to follow up right now. Here is the information from the Holley engineers about boost-referencing the carbs. He gave you a link, but I don't know if you saw it.

"QUESTION What is a Manifold Referenced Power Valve?
ANSWER Nothing will kill a blower or Nitrous engine quicker that a lean condition. You want plenty of fuel available for the engine to use .There is a thing you need to know about the power valves on a roots style blower engine. The power valve is installed to keep the engine from loading up and running rich at an idle. On a naturally-aspirated engine the engine vacuum at idle will hold the power valve closed. When you step on the gas the throttle plates open and the engine vacuum drops as you accelerate. When the vacuum drops below the rating of the power valve, it snaps open and richens up the main system. On a blower with the carb mounted above the rotors there is constant vacuum all the time even under wide open throttle. The power valve will never open and you will have a lean condition. To remedy this there is a modification you can have done that is called manifold referencing the power valve. You plug the vacuum feed hole in the baseplate for the power valve. Then you drill a hole in the side of the main body into the hollowed out vacuum chamber for the power valve. You then insert a vacuum nipple in this hole. You will run a vacuum line to the lower intake manifold from the new vacuum nipple. Now you will have vacuum on the power valve at an idle, and when you hit the gas as the boost builds, it will force the power valve to open and richen up the main system. This can be done by most carb modifiers or even yourself. We offer quite a few different size blower carbs with this already done. Consult you local Holley dealer or our Techline for the correct application."

Here's what Holley has to say about ignition timing.....
"Blower engines like timing advance. If the initial timing advance is not enough it will cause issues. Most blower engines will run between 12-20 degrees of intial timing and a total of 30-32 degrees. You do want a fairly fast timing curve. All the timing should be in by 2500-2800RPM.This is just a guideline. All engines are different. The other main cause is a lean running engine. Make sure the carbs are tuned correctly for the setup and that there are no vacuum leaks. Remember the blower moves a lot more air through the engine so it needs more fuel as well!"

I went through the Holley site and found this technical info as well. I highly recommend reading through it a few times.....
http://www.holley.com/data/TechService/Technical/Supercharger Tech Info.pdf

If this were my project and I had no means of finding out what jets to run in the carbs, I would run the ones that came in the carbs out of the box, then I'd be on top of reading the spark plugs if I had not equipped the exhaust system with oxygen sensor(s). But just let me say here that if I were you, I'd be on the phone to the Holley engineers and I'd have every last detail of your combination written down and in front of me before I made the call.....
Holley Performance Products
You have far too much money invested here to be making guesses.
One last thought regarding air supply. When I'm asked about air cleaner requirements, I generally suggest 14" diameter by 4" tall for a naturally-aspirated street motor up to 406 cubic inches and 6500 rpm's. That gives the motor 175 square inches of filter area and insures that the air cleaner will not be causing excessive vacuum at the carb inlet. The motor has to inhale easily through a well-designed intake system and the motor has to exhale easily via a well-designed exhaust system if it is to make good power.
Your motor, depending on boost, could easily pass 1.7 times the air that a naturally-aspirated motor of the same displacement would pass, so if it were my project, I'd opt for air cleaner element area of 1.7 times 175, or 300 square inches. There will be others who will disagree with this, but that's the way I'd do it. Actually, I'd look for a large oval element to enclose both carbs and make my own base and top lid. Maybe a diesel element of some kind.
 
#7 ·
thanks alot for this info. it really helps . i have booked it in with a company to have it rolling road as is, i havent got the time to try to fix something that they will know excatly what it is. they stock all the parts required to boost ref the carbes . i will take the notes with me to re-assure myself of what they are doing - will keep you posted and also post a video of when i get it running correctly. thanks again shaun
 
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#10 ·
i have the carbs set up back to back ( as thats how i bought them with the billet linkeages ) i have converted the front one to have 2 x metering blocks and the rear one only has a primary metering block as there isnt room for the secoundary one . so at least i can jet 75% of it . will need to double check on id of air ways etc .
 
#9 ·
guys this is great thanks so much . i have this weekend to get all of these tips in place for next wednesday .

ok compression ration is 7.48 to1
i have a 14 psi max ratio on the pulleys . ( so weiand say )

i had to have a new pulley machined to fit over my rattler harmolnic balancer to save space so thats why the top one it larger than normal . bottom pulley is 45 and top is 51 teeth so its 0.88 so its being underdriven.

i can regulary get hold of 98 octane gas .

thanks t bird for the tech stuff . just what i needed. i have 6.5 power valves . so they must be getting pulled open all the time ?

so my .72 in the primary also seem to rich ?

will check my plug gaps . i have just been sold a cooler plug from champion and i havent gapped them . i wonder what they are factory set at ?

i have larger headers and also nice elderbrok victor heads . so feel confident on them . what about my air filters and scoop . i hope i am not restricting air flow ?

i have a ecu so will have to speak with them regarding boost and timing retard box and how that will work with it ?

what about colour for fuel squirt cams ? and colour of spring on sec's ?

also the vac sec's have 2x air tubes coming out of them and are fixed to the manifold "below " the supercharger !! is this where it should be plumbed in to read vacum to open the vac sec's?

thanks guys . good job !!
 
#13 · (Edited)
The carbs are referenced for secondary opening if connected to each other. Could be boost referenced if connected below blower. The vacuum would need to fall below 6.5 in/Hg to have the power valves open, so there's almost no chance they're opening all the time unless there are other problems. Take a vacuum reading below the blower and use that to see what power valve you need. If the vacuum is excessively low, there could be other issues that need attention. If the carbs aren't boost referenced, the power valves will stay shut.

You have secondary metering blocks w/changeable jets, I take it?

If you are .88 underdriven, w/a 355 cid engine, and a blower displacement of 411, I'm getting about 11 psi. Still a good bit of boost for a street vehicle. With the static CR you have, that puts the effective compression ratio at about 13:1 at max boost, so you may well need to blend in race gas. Remember no detonation, else the pistons will fail.

Boost formula I used:
[(25.58) times (Blower Displacement) times (Blower Drive Ratio)] minus 14.7 divided by the engine displacement in cubic inches equals the theoretical boost in psi.
 
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#12 ·
ok - explain what you been by locked timing ? and 36 d btdc locked timing ? i havent a dizzy and have to do everything by the way of imputting figures on a graph, i can change it exactly so not a problem - but i think you mean locked timing in the way of when i get to say 3000 rpm the timing curve is flat and for eg 36d btdc remains flat along the higher rev range so a flat ign line for that rev range being 3000 and above ?
 
#11 ·
i only have the 2x pulleys . so do i restrict the rpm for now or get another pulley ? of just keep a eye on the boost guage as im not too sure if it will produce 14psi ?? with my pulley ratio

thanks on the springs .

the tubes come out of the sides of the vac sec's and join together with a t piece then go into the back of inlet manifold below the charger.

also the ball bearing in the vac sec have been removed to both carbs .

will look for the part number on the carbs.

now i get these numbers confused. i have converted the front one - is it 4150 to 4160 or 4160 to 4150 ? as i have added metering blocks and the rear carb has a metering block to the primary
 
#14 ·
the primarys are .72 and sec's are .78 so do you think they should be changed to .80 ? as i have .80's

will check the number on the metering block

yes i thnk i have converted from 4150 to 4160 with the addito of the metering blocks.

to be honest i am saving up for fuel injection so if i can hold off i will use the current carb bodies and fit injectors into the inlet manifold. but probably a job when i have some money saved up
 
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#16 ·
Locked out timing is locked. It is fixed it does not advance with rpm. No ECU control.
You need a electronic boost ignition retard box. Not some ECU from a EDI system. Get a clue or it will be a very short ride.

Locked timing is the same at idle as at max rpm. No mechanical advance ---no ECU timing control.
Blower motors do not use the same timing curve as a N/A car. ECU from a EFI system will not work.
remove or disable.....
i have this ecu so i can get spot on figures and not a dizzy set up . so i can put into the ecu what figures i want. i havent pulled this from a car. its a completey open map that i can add figures to . i cannot remove as i no longer have a dizzy , i have a toothed wheel on the crank and a sensor to count the teeth etc for timing. so what figures would you reccomend. i posted a chart on page 1 asking the question ?
 
#18 · (Edited)
Sounds about right. A lot of boost for the street, you should consider lowering it.

Please tell us what the tubes from the carb are connected to (I think you said to the intake below blower), and where the vacuum ports are located on the carb itself. A carb w/an added on boost referenced power valve port looks like the one shown below:

 
#21 ·
Yea they are fine if u have none but I can assure u with what u are saying u are not keeping detonation at bay with kb cast piston a little is to much they will shatter dont know wby anyone would put that kind of money into a engine place a blower on it and not use forged piston they are not that much more but yea if u get carbs replaced or figured out and lower boost psi they will live for a little while wouldnt run but bout 6 maybe 8 psi and if set up worked when u got it why mess with it what was the problem
 
#24 ·
U r right detonation is not good in any engine seen a many kb pistons in pieces and alot of other brands but with forced induction thats like beating on a piston with a hammer I would.love.hear ur reason why kb hyper were better than forged if u all ready had them the only reason ive ever heard of someone wanting go with any cast piston hyper or not was they didnt want spend the extra money ive seen it to many times in engines the hyper wont last with much boost not for long
 
#25 ·
not sure if you have got the wrong end of the stick there , i choose against them not for costs as i had them already . look at what a forged piston does to a block when it cracks compared to a cast one. the chances of either cracking etc in my engine and from what i have seen and discussed with many engine builders are pretty much the same. yes forged are harder and will take a more hammering, but not the hammering "i " am talking about . with no detonation and 12 psi a kb hyperutectic piston is more than capable of handling 800 bhp . i have seen it for my own eyes and over here @ santa pod they are doing it every weekend . yes there will also be others running forged, thats up to them . i am happy with 500 - 600 bhp with what i have,

the main thing ( reason for the post ) is to work out what problems i am having @ my carbs, do you have any advise for that ? and also in ignition ?
 
#26 ·
fyi -idontdrivericeieatit-

interesting read on Hypereutectic -vs- Forged Pistons


Hypereutectic pistons are used in some original equipment engines. They are favored because of reduced scuffing, improved power, fuel economy and emissions.

Hypereutectic 390 refers to a unique aluminum piston alloy that contains dissolved and free silicon. The material can be T6 heat treated to high strength and stiffness. Non-heat treated 390 hypereutectic alloy aluminum has slightly less strength than conventionally cast F-132 aluminum.

With this in mind, we caution the reader about the use of non-T6 heat treated O.E. design hypereutectic pistons for high performance. Silvolite and others do make replacement-type hypereutectic pistons that are worthwhile for stock replacement applications. Original equipment design is almost never suitable for performance applications.

The KB line of hypereutectic pistons were designed around the 390 alloy. The result is a high performance part intended to give the performance engine builder access to the latest in piston technology.

Forgings have long been the mainstay of the performance business and did well in the big cubic inch engines of the 60’s. Now, with focus on peak cylinder pressure timing, ring sealing dynamics, cylinder air tumble and swirl, combustion chamber science, and extended RPM ranges, we need to consider some new piston options.

The KB T6 hypereutectics are considerably different than the forgings. The KB pistons have shown improvement in power, fuel economy, cylinder sealing, service life, and cost effectiveness. The reduced thermal expansion rate allows the piston to be run with reduced clearance. A tight piston is less likely to rock, make noise, and burn oil. A rocking piston wears rings and increases blow-bye. The close fit of the KB piston allows the piston rings to truly seal, minimizing blow-by.

The design flexibility enjoyed by the KB series of pistons has an advantage over present day forging practices. The die for a forged piston must be designed so it can be easily removed. This limitation makes it difficult to make a light weight piston without sacrificing strength.

The KB pistons' utilization of the permanent mold with multiple die parts allows undercut areas above the pin hole and material distribution in the skirt area that stiffen the entire piston unit. The forged piston requires thick skirts to achieve comparable piston rigidity. A rigid piston rocks less in the cylinder and improves ring seal.

The forged pistons' thick skirts add weight. The design of KB pistons gives us the option to build the lightest pistons on the market.

Some current KB pistons are not super light for several reasons. If the piston is to be used as a stock replacement, more than a 10% weight reduction will mandate that the engine be re-balanced.

Common sense suggests that the introduction of a new product be extra strong at the initial release. As the product becomes accepted, weight reductions are scheduled as regular product upgrades, as justified with actual race testing.

There will always be a market for custom forged pistons. Small runs of forgings are more economical than small runs of permanent mold pistons because of the complexity of permanent mold tooling. Where quantities justify, expect to see future KB pistons developed that are lighter and stronger than anything else on the market. Machined head profiles are easily changed with our CNC equipment so we will stay current with new cylinder head developments. Volume production is expected to keep the price reasonable.

Our pricing policy has given the impression to some that we are building an economy, or in between, piston. The truth is, we are striving to build the "State of the Art" piston that is best, regardless of price. Reasonable pricing is just an added benefit.


- if the instaltion instruction are followed exactly these pistons i feel are very good. ( i am not comparing them to forged ones - i dont want forged ones ) but if people are suffering from kb hyperutectic pistons cracking braking rings and shattering then clearly there is another problem with either the instalation and or the tuning of the engine. maybe detonation maybe timing. who knows. but it is always difficult to listen to people saying they brake they arent any good but clearly they work and clearly kb wouldnt invest millions in creating this, etc if there principal idea was floored. its not . it depends on what you want from your piston and how you intend to drive. i made the decision not for a money saving ( it was only a £100 odd quid ) i didnt want to put some old age old trusted piston that hadent had any new tooling or desing in it since the dinorsaur age when there was fantasastic new designed material that wanst like stone and actually absorbed slight problems and can give a bit. which on a blown engine is a good idea and especially where i live as from day to day the humidity and temperature change withinn 24 hrs.

i also have a brand new electric power steering pump instead of a clunky old one and a brilliant ecu that can have anything changed to it, thats what i like to use. new types of techynologies . good luck to forged
 
#27 ·
Never said kb hyper are bad they are not but where the problem with them are they are harder let me repeat that kb hyper are harder than forged piston thats where problems with detonation comes in a forged piston will bend and warp if it gets to bad a hyper will not it will shatter in a million pieces if u dont have any detonation yes u should be. Ok but with the carbs like they are what I saying is wouldnt run it at all if the carbs are not right. U will have problem and I dont know anybody running 800 hp with hyper piston its not the installation with pistons thats the problem u got it right its running and detonation that is the problem it dont take much for somebody get little off hit detonation and have problem some are not smart enough not to drive it not saying that you im not just saying a forged is way more forgiving that any hyper if u have a problem
 
#28 ·
As far as carbs go I would either take them to somebody that knows what they doing and have been doing it for years or buy tge right carbs for the job or save money to. Buy the fuel injection you really want no advice on ignition im one them dinosaur that dont like or want fifty million sensor or computers on my car I got gas I got spark and im drivin mine quits I dont need computers to fix it I can fix in matter of min because there can on be a couple things wrong thats how I like it mines never been down for days.OR weeks chasing a problem
 
#31 ·
They don't usually use a tube from the carb base back into the intake. All the vacuum the carb needs comes from the throttle plate and/or the throttle bores of the carb, making them basically 'internal'.

You are correct- just plug any unneeded ports.

The carb's ported vacuum port is on the side of the metering block. As you know, ported vacuum is not present at idle, it comes on as the primary throttle plates start to open. BTW, the instructions will often say to use ported vacuum for the vacuum advance but in many cases manifold (full time) vacuum works better. You have no need for a vacuum advance port anyway so this is a moot point.

The small vacuum port(s) down on the baseplate will usually be manifold vacuum sources. The larger ports on the baseplate are used for the PCV system (usually the front port) and for the power brake booster vacuum (usually the rear port). The power brakes could use an intake manifold mounted port instead of the carb port.

Hope this helps, but if I've misunderstood you or missed the point, just let me know.;)
 
#32 ·
cheers guys .

yep that has put my mind at rest . i will plug all vacum lines and agree i will not use the vacum off the primary metering block as intake vacum is always better .

i am going to get another top pulley to reduce the psi down to 8 and then build up at a latter stage ( if needed ) also my power brakes are off the intake .

i have spoke with the guys at the dyno shop that i am going to see a week wednesday and they stock all the bits in need for the holley .

so this weekend im going to tidy up . gap my plugs ( what do you recommend for my application ? or will stock factory set do ? they are champion )

i am going to stip the carbs down and give them a good clean out and make sure they are flowing correct etc . also i still think i have a fuel leakage . possibly fronm the power valve ? being a 6.5. will this oen and over fuel or would i need to be putting the enginbe under load for it to open ?

it is really lupmy and will not repsond to mix srcew adjustment , i am going to un hook the billet linkage and double check they are not holding open the butterflys just slightly etc .

any things to look for when im cleaning out the carbs ?

cheers guys
 
#33 ·
0.032"-0.035" max on the plug gap.

The way the PV is supposed to work is it will stay shut until the engine load causes the vacuum to drop to below the PV rating, at which point the PV opens and enrichens the air/fuel mixture to help overcome the load the engine is under.

So, check to see what the vacuum reading below the carb and above the blower is. If this reading is less than the number on the power valve, the power valve will be open and the engine will be overfueled. The engine doesn't need to be under a load for there to be fuel coming in from the power valve. If the vacuum at idle is lower than the power valve rating, there will be excess fuel, for example. This might be part of the reason you have a rough, 'lumpy' idle.

But since the carbs aren't boost referenced, the PVs should be shut- even when you want them open. That is, unless one or both PVs are ruptured from a backfire or old age. Newer Holley carbs have backfire blowout protection for the PV- if it's functioning properly. If not or if the carbs don't have blowout protection for the PV, then they could be damaged allowing fuel in when it isn't needed. If the wrong PV gasket is used, or two gaskets are accidentally used, there can be a fuel leak. Just things to look for when you take them down for cleaning.

If the initial ignition advance is too low, that will also account for a poor quality idle, and can cause the primary butterflies to be open too far. If the butterflies are open too far the engine will be pulling fuel in from the transition slot of the carb instead of running mainly on the idle circuit. If the timing is advanced at idle and the carb curb idle screw is backed out to close the primary butterflies, the idle mixture screws should become functional.

Sometimes the secondary butterflies need to be cracked open farther than "normal" to add bypass air to get the idle back to normal. Sometimes you even see where the primary throttle blades have been drilled w/small holes in them to add bypass air, although this is seldom really needed if the other methods (secondary bypass air and increasing the timing at idle) are used.

Something else to look for when you first pull the carbs is to see what the transition slot looks like. It should be between a "square" and a slot about 0.040" long. If this is too long, that's when the engine will be trying to idle on the transition circuit instead if the idle circuit. Photo below shows what I'm referring to.



If the carbs aren't boost referenced, I wouldn't want to run it on the dyno. The dyno loads the engine heavily, and w/o the PV adding fuel it can go lean. You have to be sure that the PV's were working when the blower is making boost and the vacuum drops.

This is a concern to me because of the small carbs. If you had a pair of 750 cfm carbs you might not need boost referencing at low boost levels- but this would need to be verified before loading the engine.

A 65 PV might open later than you need. It wouldn't surprise me for you to end up w/an 85, as an example.
 
#34 ·
I forgot to mention that if you had to dyno the engine w/o boost referencing the carbs, you can remove the PV and use a plug made to block the PV off. Jet the carb up about 7-8 jet sizes to compensate for not having the PV installed. This will work on a race-only engine or for a wide open dyno pull. On the street it will not work because the air/fuel ratio will be too rich much of the time.
 
#35 ·
thanks for all your comments.

i have had a great day - took cobalts advise and when i stripped the carbs down the primary throttle plates where open more than the diagram you showed ( in the link ) so i reduce it to where it showed, also i turned the scre in on the base of the carb to open the secoundary plates just so slightly to allow a bit of air flow. i replaced the base gaskets (carb to supercharger ) and replace the pv with the new ones i had - although still being 6.5 ,

the dyno shop are going to measure the vacum first and and try to get it nearer ( if needed ) i also gave the carbs a through clean and blow out , seems to have sorted it as its now idling at 1135 rpm . still lumpy bit is as smotth as i could get due to the high lift cam - i didnt run it for long - prob a couple of minutes . as i dont want to wreck anything - i want the dyne shope to use their lambda sensors and heat sensors etc to see what mix im getting .

i had a few silly problems which wasnt helping - end of sprak plug lead was exposed and shorting onto the exhaust headers .

ok the specs on my carbs are .

- on the top of the carb horn - 1850-5 0209
i have converted them to have sec metering blocks although i cant fit in the rear of the front one due to them being back to back.

primary jets - 70
sec jets - 78

shooters .25
R107 booster

.65 pv ( for now )

both carbs have a orangey brown cam for the acc pump shot

i have a pair of each jets from 70 to 80 .

regarding the ecu not being needed - thats really up to personal prefernece, clearly as long as there is a spark then it will run. however when i go fuel inj the ecu will come into its own. also i can run some much more off of it. electric fans. rev limiter , wide band lambda sensors , water meth , launch control , and i can monitor any faults and the ecu will log these for fine tuning, which is a huge difference with that and a dizzy run engine. i dont want to be some where between by timing light a turening the dizzy a degree or so. with the ecu it can be exact , not a tiny bit out , thats the beauty of the ecu.

t bird , i know you keep referring to a ecu . not sure if you understand exactly it is i have. its not something i have pulled from a efi engine , i cant turn this off. i dont have a dizzy anymore due to the height of my supercharger. it wont fit - i have a dummy dizzy to run the oil pump . i particulay wanted this system due to its huge amounts of options and parameters.

its hard to explain te difference. ( i am sure you know the concept of a ecu ) but i have something that xrays the engine and reports the findings and a dizzy is like a blind massager who relies on hear and feeling, all you can do with a dizzy is stobe to time , pull plugs , and adjust approx. ( i know you can get close ) with the ecu i have a 100% safety net. once set uo this will not allow the engine to break. it will just shut off and repost a error. its what i want after spenging £10k plus on the enigne.

so if you state timing figures can you please be exact - ie. locking timing out , what does that mean ? i cant do that .

i will take a pic of my ignition chart which i can do what i want with and then i think you will be clearer.

thanks for all your help guys. nice to finally hear it idle a a sensible rpm :)
 
#36 ·
below is my ign table. i can put in what figures i want



below if a 3d table of the above graph . i can pull this about to change the table above.



below is my main start and run chart whchi i view what the engine is doing, i can also add other section when i need them like lambda sansors. fuel inj etc.



below is a line chart of the first 2x ign charts. again i can pull this about to change the ign curve etc



lastly a short video of it diling at 1135 rpm. ( dont worry about the smoke - its old oil on the exhaust wraps that i spilt just burning off ) i paniked and turned the engine off. all ok :)



what your thoughts on exhaust header wraps ? always get mixed opinions on them. if you speak with exhaust guys they like them because they flow the wate gas better ? but others say not good as they kill headers ?

cheers shaun
 
#37 ·
what your thoughts on exhaust header wraps ? always get mixed opinions on them. if you speak with exhaust guys they like them because they flow the wate gas better ? but others say not good as they kill headers ?

cheers shaun
Your engine control unit sounds like it should work fine once the other areas are covered.

Have you used a vacuum gauge to take a reading at the base of the carb yet? You could use one of the manifold vacuum ports for this if you wanted. I'm just curious- but this can wait until the guys at the dyno shop get tuning on it.

As you know the 1850-5 Holley was originally a 4160 and it had a secondary plate instead of a block until you converted it to a 4150-type set up. For reference, the original 134-9 secondary plate your carbs came with had a secondary orifice equivalent to a #64 jet. So if you are now using a 78 secondary jet, this should be plenty- it would prolly be enough even w/o the power valve. If you added the power valve to it, you'd have the equivalent of about an 85 jet in the secondaries!

Also for reference, here's a Holley numerical listing showing the factory specs, etc. And here's a chart showing the relationship between plates and jets.

Header wraps are OK, if you were to use stainless steel headers, the wrap wouldn't cause rust. If you use mild steel I'd prefer ceramic coating inside and out. But anything that'll keep the underhood temps down and the exhaust gas hot inside the header (and the gas velocity up) will be a good thing, overall.
 
#38 ·
I haven't read the vacum pressure yet , will do next weekend , I have called off the dyno shop for another week so I can get cleaned up , will let you know what it is , thanks a lot for your help , the other thing is even though I have cleaned the carbs out the new needle valves let by every now and then , with a tap on the adjutment nut it stops it , my regulator is set for 6 psi , so you think I should drop it ? If so what to ? ,

I also was pumping too much fuel in , it was spitting out and blowing unburnt fuel back , so I closed the choke half way and left it for 30 mins , then just cranked with not touching the pedal and it started staright away , but it does like the choke off , I presume these blown motors like a lot of air flow ,

Its all new to me
 
#39 ·
It should hold 6-1/2 psi w/o overpowering the needle and seat. You might need bigger, higher flow needle and seats. What you don't want to do is lower the fuel pressure too much so the WOT pressure stays as high as possible. It's not unusual to see 6-1/2 to 7 psi under WOT conditions on an engine making boost. The last thing you want is for it to go lean.

You probably won't need to use a choke. Cold, two or three pumps, foot off the pedal and crank. Hot, no pumps, foot off the pedal, and crank.
 
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