427 Carb Jet Sizing

[jhv48]

Good idea.
Roush 427 SRTW.
Altitude is at sea level.
Carb is a ProSystems 850 DP.
Mains are 76/86
Squirters are both .045

Runs slightly rich, but is freakin wild when you let it loose.
Mileage is 10 around town and 12 on the open road with a .80 fifth gear/ 3.46rear end.

My goal is to lean it down a bit but not sure where to start. Squirters seem quite large to me but there is no hesitation on throttle tip in or steady cruise at light throttle.

Still, after reading the setups on quite a few others, (with similar engine sizes and double pumpers) I'm thinking of taking the mains to 72/80 and the squirters to .37. and, yes, I would make one change at a time but how in the hell do you gauge the secondary mixture without a wideband? It's not like I can put my foot into it AND try to watch a vacuum gauge at the same time. I'm too busy trying to go straight!

And I already had it on the dyno where they tuned it for max power. That's where the current jet sizes came from. Not sure that's best for every day driving. It seems like I'm pouring a lot of fuel into those cylinders during normal driving.

Thoughts.

[blykins]

Power valve size?

[jhv48]

Originally Posted by blykins

Power valve size?

6.5 power valve

The dyno tuning was done on a chassis dyno.

I had the same thought about over carbing, but the engine came with a 770 Street Avenger and when I ordered the new carb from ProSystems, I asked the same question and he recommended the 850 DP.

[mrmustang]

Originally Posted by jhv48

Good idea.
Roush 427 SRTW.
Altitude is at sea level.
Carb is a ProSystems 850 DP.
Mains are 76/86
Squirters are both .045

Runs slightly rich, but is freakin wild when you let it loose.
Mileage is 10 around town and 12 on the open road with a .80 fifth gear/ 3.46rear end.

My goal is to lean it down a bit but not sure where to start. Squirters seem quite large to me but there is no hesitation on throttle tip in or steady cruise at light throttle.

Still, after reading the setups on quite a few others, (with similar engine sizes and double pumpers) I'm thinking of taking the mains to 72/80 and the squirters to .37. and, yes, I would make one change at a time but how in the hell do you gauge the secondary mixture without a wideband? It's not like I can put my foot into it AND try to watch a vacuum gauge at the same time. I'm too busy trying to go straight!

And I already had it on the dyno where they tuned it for max power. That's where the current jet sizes came from. Not sure that's best for every day driving. It seems like I'm pouring a lot of fuel into those cylinders during normal driving.

Thoughts.

Regardless of what others without chassis dyno experience will say, I'll start off with the fact you are over carb'd....

650-750CFM double pump will alleviate some of your issues, spending a few dollars more to get it tuned and tweaked on a chassis dyno (not engine dyno as you cannot take in to account the effects your drivetrain has on your engines tune) and you'll really wake up your engine.

Having spent days with my cars on chassis dyno's, after first listening to my engine builder tell me what I needed based on his engine dyno, I can tell you what I stated above is FACT and not conjecture......


Bill S.