[F-BIRD'88]

way better air flow into the carb with the blower hat installed.
Those choke horns are going to mess up the carb metering with the blower hat installed.
Cut them off and do the boost reference mod on the body.
Don;t cut off the bowl vent boss. just shorten and angle cut the bowl vent tubes a bit.

The choke horns got to go. You may need anti pull over style accelerator pump shooters.
(observe with a mirror @WOT on the dyno. (binoculars and a mirror or video camera in the dyno cell above the carbs) you can observe the vac sec action on the dyno too.

When you get the carbs dialed in you will see and not want to waste time and money on EFI.
Blower motors are very very street friendly drivable when the carbs and ignition curve and boost retard are dialed in correctly.

I cannot download and listen to the video until tomorrow at college.

[mustang 671]

this are the timing figures i have at the moment . they need fine tuning but are getting it ideling at 850-900 rpm which im happy with . especially with the lupmy cam i have .

[F-BIRD'88]

So is your buddy going to bring you back some shiny new Holley 750HP Blower carbs?

That cam is not "lumpy" Thats a sissy cam..LOL
You ar choking that poor blower motor with that tiny cam.

[mustang 671]

no not at this stage. i like the vac sec on a blower , as the blower can decided when they come on and i get better mpg around town etc. once dialled in they will be fine ,

regarding the cam , i specifically got this crane "supercharger cam " from them as it was a good moderate to fair ride cam for my set up. i didnt want a mad unrelistic cam. dont agree i am choking it. yes i agree there are bigger duration higher lift blah blah cams out there. but i want a reliable daily driver not some unrelistic strip car.

i have contacts in the film industry and concierge so i do want to use it commercially . something that would be more uncomfortable with a big arse cam.

again a matter of opinoin and not fact as are alot of mods on cars.

did you have any thoughts on my question earlier on my c6 oil capacity with a front mounted oil cooler ?

cheers shaun

[mustang 671]

thanks cobalt for sending the diagram on the transtion slots . that fixed that problem , top man

[mustang 671]

Originally Posted by cobalt327

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.

cheers for the advise !!

[cobalt327]

You are quite welcome, Shaun. I'm still following this thread and will add when appropriate. I'm sure you'll get this sorted out and before you're done you'll be driving a BEAST!

Mark

[ProStreetRob]

Been following this thread and learning a lot
Hope you get it all worked out 671 and I have to agree with that cam not sounding to lumpy, hell mine fires like once every few seconds
I also have to agree with the sideways carbs, they fit and look quite well if done right, here's mine

Only sound file I have is my buddy backing it down his driveway

Only sound file I have is my buddy backing it down his driveway

Unfortunately you really cant hear the motor in that

Best Of Luck and hoping to hear you got it all figured out shortly

[mustang 671]

hi all .

been working on the car again today . so i pumped twice from cold. choke off secound turn of the engine and off it went. kept it for 1500 rpm for a moment and then it happily idled at 900 rpm.

looking forward to the dyno in a coulpe of weeks .

i will jump to another subject concerning my brakes. and will come back to you all when i get some updates after the dyno and i hope to get a video and some figures for you !!

last question until i come back to you.

currently i have millers running in oil. and i have now had the engine running and idleing for a bit. whats your opinions on keeping this oil in for when i go to the dyno ? i am in the mindset of running in the engine quickly and not over 1500 odd imiles as most stupid manufactures advise. bed the rings in quick under load before its too late. i have seen the evidence to make my mind up. so with that said would you recoomend this oil as it will alow this or a semi synthetic as the running oil i have is mineral !!

cheers all - and amazing advise.

[mustang 671]

hi all . had the engine running for a while today . sorted out my brakes but my alternator still isnt charging.

however the car didnt want to start when hot . and i got a back fire through the exhausts ( not the blower - that never happens now ) as i have a wasted spark system im thinking my mixture is too rich ??

am sure this will be sorted when im off to the dyno and they plug in their lambda sensors.

any ideas ? i didnt pump the throttle. went to catch a couple of times but nout . all good from cold . just when its hot

expect the pv will neede to be changed .

cheers

[cobalt327]

Originally Posted by mustang 671

hi all . had the engine running for a while today . sorted out my brakes but my alternator still isnt charging.

however the car didnt want to start when hot . and i got a back fire through the exhausts ( not the blower - that never happens now ) as i have a wasted spark system im thinking my mixture is too rich ??

am sure this will be sorted when im off to the dyno and they plug in their lambda sensors.

any ideas ? i didnt pump the throttle. went to catch a couple of times but nout . all good from cold . just when its hot

expect the pv will neede to be changed .

cheers

If you wire in an ignition interrupter, that will help the hot start problem.

It works by allowing the engine to be spun by the starter, w/o the ignition enabled. Then after the engine is spinning nicely, the momentary switch is released allowing the ignition to become hot and the engine fires.

[mustang 671]

that sounds a good plan . as i havent been to the dyno yet i hope it will be just a fueling and timing issue slightly off ?

also is this normnal on a blown motor ? do they suffer from this ? i have 1x stage colder plugs than normal

[cobalt327]

Originally Posted by mustang 671

that sounds a good plan . as i havent been to the dyno yet i hope it will be just a fueling and timing issue slightly off ?

also is this normnal on a blown motor ? do they suffer from this ? i have 1x stage colder plugs than normal

You can take a good look at the plugs to see if they show signs of fouling. I wouldn't call it normal, at least not for a sorted out tune up. But seeing as how you're just beginning to get a handle on this, I'd say it wasn't that unusual. Especially if its only been idling and no real load/heat put on it. Before changing anything on the tune up, try the interrupter first. If you still have the same issues then you can get further into it.

[F-BIRD'88]

It likely backfired thru the mufflers cause yu keep letting it idle slow, when cold.
(this allows unburned fuel to enter the exhaust system)

2000+ rpm when you first fire it up. Keep the rpms WELL up until some heat gets into the blower. its not a taxi cab.
Blower motors need to "warm UP"

The simple dash mounted ignition power interupt toggle switch will allows easy cranking/starting when the engine is hot.

The vac sec carbs are not the best for the blower motor and will not save you gas
or do any of the other things you think they will.

Double pumpers work a lot better. Preferabily Holley 750 blower carbs with boost referenced power valves and 4 corner adjustable idle circuits, set up specificly for a roots blower.
+ down leg boosters and adjustable idle and hi speed air bleeds.

You will only getr so far with those carbs on it. They are not blower carbs.

Change the plugs, oil and filter before you go to the dyno session. Bring extra spark plugs and good fuel with you. bring holley carb gaskets, etc etc.
coat all carb gaskets wth vasoline or PAM cooking non stick spray so they don't stick and you can reuse them.

if/when you idle the engine in the garage, it is rebreathing its own exhaust gas and will load up and foul the sparkplugs. Blower motors need to be driven, not idled.

[F-BIRD'88]

Be aware your pump gas is no better than ours here. Different rating standard.
Your 98 octane pump gas is research method only. Ours is R+M/2. (92-94)

Yours is 92 at best. Go easy on the spark advance, on pump gas.

If you want to see how much power it can really make use 110+ unleaded racing gas.
Now you can put some timing and boost to it.

Do not confuse the two different tuneups.
if you are going to run it with a blower scoop on, get rid of the choke horns on the carbs.

Other wise the air fuel ratios will be a lot different when you are driving it with the hat on.
you will have wasted your time dynotesting . Tear down the carbs and do them right, before the dyno test. Cut the choke horns off and boost reference the power valves and make sure the vac sec system is A-1. It will run a whole lot nicer with the powervalves functional and properly boost referenced. Until that is done don;t expect it to drive nice. Expect short spark plug life and a bockey engine.