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Originally Posted by SPF2245
Thanks for all the replys...when the motor is shut down, I can hear the fuel boiling in the carb after a slow ride. I have considered other carb related problems and will adress those with a quality dyno check and tune.
Greg,
Thanks for the info on the pro-systems carbs...I've about had it with the Holley supplied by Roush...it's been nothing but a PITA, I knew I should have gone to FI, oh well live and learn.
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First I'd like to say I'm not an expert, but have gone through a useful learning curve from using the forum here and while searching the net and picking minds of assorted individuals.
My car was delivered with a Holley 750 double pumper. It's a very good carb if it's jetted and set up properly. Mine wasn't due to the engine installer's selection of tuning options. He did a beautiful job putting the engine in, but it ran lacking. Looking for the easy street and not knowing how to tune a carb myself at the time I went out and purchased a Holley 870 Avenger vacuum secondary from a local performance shop. I actually bought it thinking it might be a good idea for around town because I saw it was landing on top of other Roush 427Rs that were coming out of the location were my car came from. Granted I do have a single plane manifold with less low rpm vacuum than that of a dual plane intake at low RPM, but I'm 99.9% certain the Cobra is too light for that vacuum secondary. Holley seems to think so as well. I tried every secondary adjusting spring option all along with a combination of jet options. I used an actual car in motion testing device to graph power and G values and acceleration. I had lag invariably when I nailed it from a roll. The top power isn't bad once you're banging off gears, but that lag sure does suck if you want to go from a roll.
When I ordered my first Pro-Systems carb I told Patrick I want to go fast in a straight line. He pretty much knew what was up with the set up for the Roush 427R and asked what's your zip code. He tuned the carb to the actual density altitude at that time in my location. Mine was tuned dead on. I got the carb, put it on and it absolutely hammered with lightning throttle response, was smooth always and works beautifully on my single plane intake manifold at low RPM. If you can't get a 2500 lb ride rolling from 2000 rpm with 350 wheel ft lbs of torque at that rpm you need to release the emergency break.
Here's my dyno sheet with the Pro-Systems carb and a couple changes including exhaust options I changed. Note the punch at a bit over 2000 rpm and how the torque comes on. That's at the wheels and a zero smoothing on the graph with no games for representation of having smooth power.
