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Old 05-31-2010, 12:33 PM
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blower motor help!!

allright here goes nothing...last spring built a dart 406 dart engine, 215 64cc dart heads,dished forged pistons,crank plama moly rings, hbeam rods comp cams roller blower cam msd ign...all the goodies..almost 20 grand worth! engine sucks!! put it together last year,seems to run good but having a overheating issure...changed waterpumps,radiators,fans ,themostats,restrictor plates.ect.ect.ect.finally with a big enough rad and twin fan, got it to were i can drive it for a little while...egts seem to be real high!!melted a poly motor mount,burn out header and collector gaskets quick..went to copper, headers will glow red hot after 30-40 sec held at 2000 rpm..go 2 exits down the highway and get off the exit and at the first light will go from190 to 230 before the light changes?have a fresh 671 with 2 650 holley vac sec.carbs.have the timing at 30 primary jets r up to 77's!!! carbs have pv block offs???? only running 5 lbs boost 12% underdriven.had the engine apart twice with no apparent issues? took it to baker eng in april to put on the chassis dyno...335hp terrible!! wich was at 3000rpm hp flat after that, found secondarys wernt opening...got home and found a missing oring in one of the vac secondary pods..afr was around12-1 they said a little lean but not terrible...it seems to start making serious exhaust heat almost immediatly...?got it jetted almost to high? how can it show lean and be puffin black smoke? not sure were to go now....nobody really seems to know...even the shop that did the machine work and put the short block together..?seems like there is a big problem? was told to go to cooler plugs but dont see that making a huge diff..this is my first forced induction motor..but not a idiot...lol really sick of getting the run around...just want to be able to drive and enjoy it!!!! please any help would be greatly apprciated...maybe someone around here that knows what they r doing that I can take it too? thanks!!

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Old 05-31-2010, 12:53 PM
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what cam?

base timing at idle?
Did you verify true TDC on the balancer timing tab using a piston stop?

Serious exhaust heat ='s retarded timing.
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Old 05-31-2010, 01:58 PM
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comp cams part #12-704-8 .575lift 255/262 duration 114lode sep.solid roller have really messed with timing one way and then the other without huge changes in temp only the way it runs..seems to like around 16 at idle and 30 full adv thats were they got the most power out of it at baker anyway...335 at the wheels..disgusting..
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Old 05-31-2010, 06:28 PM
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16 deg base timing for this motor is not near enough.

30deg is about right for WOT under boost, on pump gas.

But blower motors want a ton of idle advance, especially with a big cam.

The motor wants a lot more advance at idle and low speed.
Do not assume the timing tab is correct.
for true TDC on the timing tab using a piston stop and correct as required .... then....
With a dished piston you will ahve to make your own piston stop out of a spark plug body and weld in a a 5/16" steel tube with a bend in it.
Bend the tube and trim the tube length as required to get piston contact before TDC. Be sure to back off both valves on #1 cylinder completely before installing the piston stop.

Lock out the distributor mech advance curve and set the locked/frozen timing at 30deg BTDC at idle. The locked timing does not advance with rpm. 30deg at idle 30deg at max rpm WOT. Reset the carbs and install fresh plugs.
Remove both carbs , flip them both over and look at the throttle blades. and reset the throttles pri and sec idle transfer slot exposure so they are all 8 barrels even at idle. approx .020" of idle transfer slot exposure at idle.
reinstall the power valves. 10.5" rated, Go to stock jetting +6 jet sizes for a starting point.

You are using the wrong carbs. You should have two 750 DP carbs.

Holley makes 750 blower carbs for this. So does Demon. Edelbrock 750's work fine with a few mods.

vac sec carbs on the blower motor will require joining the vac sec housings with a a vacuum hose. Holley makes a special va sec housing lid for this.
But you are wasting your time money power and performacne on 650 Vac sec carbs on this motor.

Just get the DP carbs. 750 or 800cfm.

What plugs are you using?
Where the Dart heads drilled for the 400block steam holes?
On the back of your blower intake manifold are there rear water ports?
Do a engine compression test to verify the engine is not fubared. reset the valve lash to .018" in .020" ex ,engine dead cold.
What ignition box?

Last edited by F-BIRD'88; 05-31-2010 at 07:01 PM.
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Old 05-31-2010, 07:00 PM
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it has accell shorty header plugs, we have checked true tdc probably 15 times they even did it at baker, after the first pull. I do have the vac lines for the secondaries routed together..what is a good point to start with base jetting, i will lock out the timing at 30 since havent done that yet..the carbs have pv block offs in them? I will also put in 10.5 pvs..and reajust the trottlle plates.i bought the blower and carb setup complete off ebay,said to only have 5-8 hours on it..all seemed like new, he said he played with the carbs a little and that was it.. sent the blower to dmpe to be freshend up...they said it was in great condition...can i put metering blocks and *** hardware on these and make em double pumpers? I am not rich, lol a new set of dp mech sec blower carbs arnt cheap! will try your suggestions this week, any others would be GREATLY appreciated, what would be a good cooler plug to run? thanks
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Old 05-31-2010, 07:04 PM
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sorry missed a few questions, yes the heads were drilled for steam holes,yes there r water ports on the back of the manifold, and yes I have tried looping them together with little to no change..have checked comp...all cyls show good all within 10psi and i think the cam calls for .o20 and.024 and thats were i set em..running a msd6al with a manual timing control box, + or - 7deg. either way...i am only puttin 87 octane in it? should i jump up?

Last edited by 1957chevyguy; 05-31-2010 at 07:10 PM.
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Old 05-31-2010, 07:13 PM
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Those carbs will need extensive idle and off idle circuit air fuel curve recalibration for the blower. Will need replaceable screw in style air bleeds,main well emulsion jets and PVCR's and idle feed restrictions.
You want functional power valves preferably with boost referenced signal source. (from the intake manifold below the blower.)
An the know how and tools to calibrate them correctly.
You will have $$$$double$$$$ in the carbs and likely a engine rebuild after farting around with them compared to getting the right 750cfm blower carbs to start with. You cannot convert a vac sec carb to DP. Why do you think the guy put it up on ebay He could not get it running right. You are not rich... How many engine rebuilds can you afford from cooking that motor?
Sell the carbs, get a paper route and buy two HP body style 750cfm blower carbs from Holley or Demon or a blower motor specialist like Oddy's or BDS or Dyers.

ya keep running that 87 octane buddy .....what are you on crack guy???
What turnip truck did you just fall off of?

get a friggin clue.

Connecting the water port at the back of the intake manifold on the drivers side to the water bypass on the top of the water pump helps a lot on 400's.
Put the thermostat back in. Get a real (mechanical clutch) fan with full fan shroud. You will need 4000- 5000cfm of fan air flow for this motor.

Last edited by F-BIRD'88; 05-31-2010 at 07:24 PM.
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Old 05-31-2010, 07:30 PM
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87 octane will kill your engine.

To drive on the street, you need real blower carbs intended for that purpose. Or even just one big carb.
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Old 05-31-2010, 07:53 PM
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If the headers are glowing that quick you are either too lean or timing is retarded or the exhaust is way to restrictive. I agree with F-Bird on the carbs but I am not convinced it is your whole problem. If your A/F was 12 that should not be glowing the headers. I would certainly check the timing. You can not run regular gas, you need premium.
What are you running for exhaust?
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Old 05-31-2010, 09:08 PM
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allright thanks for the info...and the insults....i am not claiming to be a expert..this is my first forced induction setup..sorry didnt know..so the 87 octane is out...lol. The exhaust consisits of sanderson superman 1 3/4 full lentgh, 3 in pipes ele.cutouts and flowmasters. also have a nice 4 core alum triple pass rad. with flexalite 292 mega fan...twin pullers that r rated at 4500cfm...the "pros" at baker reset the timing, played with the air bleeds,did 4 pulls went from 310 to 335, but that was before we got the secondaries working.still wonderin what plugs you guys suggest for this app.
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Old 05-31-2010, 09:37 PM
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"Engines that are detonating will tend to overheat, because the boundary layer of gas gets interrupted against the cylinder head and heat gets transferred from the combustion chamber into the cylinder head and into the coolant. So it starts to overheat. The more it overheats, the hotter the engine, the hotter the end gas, the more it wants to detonate, the more it wants to overheat. It's a snowball effect. That's why an overheating engine wants to detonate and that's why engine detonation tends to cause overheating."

Replace the 87 octane swill w/some honest race gas and drive it. See if the overheating doesn't diminish.

Remember the need for more initial timing, w/o exceeding about 32 of total timing.
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Old 05-31-2010, 10:29 PM
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Air to fuel ratio is actually rich! You said it was 12:1 and that means less air therefore more fuel. Another common side effect of "too rich" is hot/glowing headers. I agree with cobalt. Bump up your fuel octane. Also, use the air bleed screws to lean out the mix at idle to see what happens. That is easy to change. Use a temp gun and watch your temps.

Your ignition timing sounds like it is at a good place to start. I set most blown small blocks at 16-18 initial and 34-36 total. You want it fast and in full below 3k. However, Like fbird said if the balancer mark is off. You won't get it right and it could be retarded and would do the same thing as rich idle. I would tweak the air bleeds before bumping up the timing. You will do more damage to the engine under load and driving with too much timing. At idle in park a lean mix won't be so bad.

As for the afr;shoot for 13:1 to be on the safe side. That will give you plenty of power when not under boost and a safe ratio when you are. Remember you only make boost at WOT and under load. Therefore you won't make any in park. Just curious how much and what rpm did you start making boost while on the dyno?

Also, you can try and drive the car with the belt off. A blower shouldn't increase the heat in the motor more than 20'. Drive it hard like you did with the blower and let us know what happens. Good luck!
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Old 05-31-2010, 10:35 PM
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from bds web site The ignition system and advance curve are very important to a blower motors longevity and performance. The general rule for ingnition timing in a blower motor is as follows: Initial advance at idle should be set at 16-26 degrees with the total advance of approximately 32-36 degrees, all in by 2500-3000 RPM. It is very important to verify the advance curve. Locked out magnetos or distributors are recommended for racing applications only. Improper curves may cause a variety of problems including overheating. Spark plugs should be one or two heat ranges colder than the recommended stock factory plug (never use extended tip spark plugs). The colder plugs need to be used due to the higher cylinder pressure created by supercharging; higher cylinder pressure means more heat. Ignition management systems that can vary the timing according to engine requirements are a good idea to help keep the engine from killing itself with detonation and to keep performing at its maximum.
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Old 05-31-2010, 10:42 PM
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oops.....didn't catch part about them playing with the air bleeds. Might need to reset transfer slots and air bleeds. If the cam is crazy might have to go as far as drilling some holes in the butterflies. Set em up like fbird said. Also,where is your reference lines for the power valves plumbed?
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Old 06-01-2010, 01:09 AM
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First, simply lose the carbs you have. It's not that vac sec and small carbs won't work but you have already found that they are really mis-matched for your motor. It will take a lot of work and knowledge to make them work. If you can't do it yourself it will cost more than 2 new carbs will. Get a pair of 750 DP blower Holley carbs. Your will save yourself one big pile of trouble right from the start. You can probably bolt these on and set the idle speed and mix and go have fun.

Why are you running a blocked power valve?? (OP) no good reason for this. Trying to jet up for this is difficult as it is let alone with a blower.

Get an AFR gage and install it. I run 12.2 AFR most of the time in my 355 SBC and it runs just fine. I already have nearly 4000 miles total on it and I have been to (driven to ) 30 events already this year. I drive it nearly every day just like a daily driver. It never gets above 210 even on 96 deg days in traffic. I've still got the same plugs in it I had last year. AC Delco stock heat range. I average around 12 mpg on our back road cruises.

As noted above, lots of advance at idle, not too much total, all in by 2000 or so....simple. If you haven't got this, do it first. You already have plenty of rad just get the carb situation under control. You may have to have the headers Jet Hot coated. I did mine and it helped a lot with under hood temps. I wrap selected areas to protect nearby items.

BTW, playing with the airbleeds without really knowing what you are doing and without a good AFR and data recording is simply asking to cause problems.

There is no need to run race gas in these on the street if your compression ratio is in the 8 to 1 area. I've even run 87 just to prove it can be done. Yes full 6 psi boost.
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