Originally Posted by hammertime
Mark, I didnt want to start a pissing match on drr asking this question so I will ask on here its a bit more civil
I wonder if you have ran the bigger cfm billet main bodies say like 1600cfm vs a holley 1250 main body. Reason I ask, what I see is a lot of power on the dyno and can never get them to be as fast on the track under acceleration. Same goes for my injection (2100cfm terminator) we've been able to make awesome power on the dyno with my combo (25hp avg and 30trq avg better) but yet it does not run faster on the track.
This is my first carb this large, so I can't give you a definite answer yet. I do know BLP has run a few different sizes across their 673 Sonny's engine, the 2.600 throttle bore is what they ended up with.
The issue with any big carb is providing a strong enough metering signal to maintain CONSISTENT fuel metering at the lower RPM's. Most will show more peak power and carry father past peak torque, a good clue is how peak torque is affected. If you gain there and have the gear and converter optimized chances are it will gain. There is a balance point with any engine as to having enough pressure differential at the booster to help with atomization and how low you can go to see gains from pumping losses. Every engine is different, and throw in different port and combustion chamber designs, ignition systems, engine temps and fuel used you can change a lot an in some cases not appear like much. My SB2 ran the best with a 1250 over a smaller carb, my friends pump gas 540 runs as well with a 1050 as anything bigger. The difference is in the port designs, compression, and fuel. Low compression and pump gas despite being made to work together are not the best combination for a race car. Vaporization characteristics of pump gas sucks... and low compression doesn't help. A smaller carb creates more vacuum under the carb, creates a better pressure differential, and that aids atomization and vaporization. Burn the fuel more completely you need less, and make more power.
The engine this carb is going on is for the challenge at BLP, it's a 622 Steve Schmidt engine with 11° Big Chief Heads, these are high velocity Pro Stock style heads. It should be an extremely efficient engine with a VE at least or over 110%, and hopefully my choice on size will be close. I found some interesting things on the flow bench, I'll see if they will help a little as well.
As far as injection I don't have any experience there, but I suspect much the same there with vaporization. A TB too large will have less vacuum to assist in vaporization. You might try raising fuel pressure and cutting back on jet size to compensate if that is possible. Consider how air conditioning works. Pressurized freon goes through a restriction and drops pressure. The liquid freon changes to a gas, and the temps drops. Methanol already does that to a degree, but if you can vaporize the fuel better you may not need quite so much and gain some more power. Of course other factors are involved, for one look at the ignition the Top Alcohol cars use. You need a very strong ignition to light the fuel when you start adding more. The right heat range plug, the right engine temps...