donyue

I have a question for all the engine experts out there. Is it worth the cost to have a MSD Pro-billet distributor re-curved and Quick Fuel SS 750 mechanical secondary carb tuned by a professional on a custom built, dyno'd crate engine?

I know that the Quick Fuel carb can only be tuned properly when the engine is actually installed in the car because factors such as location altitude, weight of car, type of trans, exhaust configuration etc. have direct affect on the correct carburetor setup.

For the carb, I have already changed the jets, changed the air bleeds, and changed the power valve from the stock box configuration based on air fuel readings obtained from my installed AEM wide band A/F gauge, but should the MSD distributor need to be re-curved on a dyno'd engine that has already been run in and tested?

Just wanting to make sure I'm not wasting money on a custom tune that is not going to yield significant results.

Thanks for the feedback!

Don

7T1vette

Depends on what you expect from the engine. If you want to squeeze every available ft-lb of torque out of your engine, you need the timing to be optimized throughout the [effective] operating range of the engine. Actually, that means to stick the engine on a dyno and spend a few hours figuring out what timing yields max power at various rpm settings. That data would define the timing curve that would need to be transferred to the MSD box.

Don't know if you are "in" for that level of effort...or not.

cagotzmann

Save your money and take it to the track and tune it yourself

Tune for max mph for a 1/4 mile run

2 benefits. You learn how to tune it yourself and enjoy running the car at the track.

You don't need to worry about 1/4 et this saves your clutch and other issues with hard launches.

cardo0

Well optimizing/tuning a carbed car is not a simple question to answer. Most everyone has there own method(s). So ill just try to help with a kinda rough draft.

Something to note is an engines power is much more sensitive to timing than mixture meaning u can vary the a/f quite a bit and have almost the same results. Yes there is an optimum mix but power output is much more forgiving of mix than timing. Also to note is a carb has no temperature compensation or air density compensation for changes in air density so what was optimum in mid summer maybe quite different from what is optimum in the winter. But again the range of a/f mix is much more forgiving.

So the modern way of tuning is with an a/f monitor and usually a dyno. But it is taken for granted a dyno is used to hold an rpm to "fill in the blocks" for timing and mix. A carb really doesnt have any blocks to "tune" as only the CCC qjets used an ECM for tuning at cruise rpm. So a simple inertial dyno or even 1/4mi pulls is all that maybe needed to tune a carb'd car. I think some a/f monitors can capture data runs/pulls with rpm displayed by themselves if u choose that method. So now its a matter of optimum pwr on a dyno pull or optimum time in the 1/4mi. Many feel a tune "on the road" better reveals the airflow and drag of the car but thats an argument ill let pass.

Timing a car w/distributor and carb is gonna be different because once u have it "all in" thats what u get where as a EFI car can still make timing changes all the way to max rpm. Most dizzy's are all in before 3000rpm. But it does make it simpler to find your max timing by just a run or pull and adj the initial timing (bump the initial) to give u a different max timing number and find the sweet spot. Once u have the optimum "all in" timing value u can dial in the timing curve using your own ingenuity and im sure everyone will have there own method there.

Well that maybe be general but if u have any specific question just let us know. Good luck and let us know what works for u - it helps us all.

donyue

Thanks for all the replies.

From what I gather it really is not worth taking it to the professional as he does not have a dyno and will only recurve the distributor and setup the carb based on air fuel readings from an air/fuel gauge.

So as long as I can find the sweet spot in my timing to have it all in by 3000 rpm then the carb tuning should not be overly difficult since I already have an A/F gauge permanently installed in the car. This forum is excellent for all the help that is supplied.