What should I be looking for when I start tracking back pressure, is it a certain % of intake pressure, where is the limit that you say this is too much exhaust restriction? I know lower is better but what are some numbers that are typical of a 700-900 turbo buick?
If the clearance volume is minimized the cylinder will start to fill sooner because the pressure will equalize closer to tdc. You would see it as lower manifold pressure and likely increased exhaust pressure even though it less boost its likely a measurable amount of power increase. Just because the intake valve is opening doesn't mean there's positive flow. There's so many factors. At least with logs you can tell if something you did helped. Switching turbines, compressor cover or ex housing, changing valve overlap, switching crossover or manifold cross section, ran in better air, etc. something's you can control and some you can't carry easily. Exhaust pressure to intake in a 900hp turbo regal could be 1:1 or 2:1 depending on the turbo and the rest of the combo. Turbobitt's car has 9 sec power with boost in the mid teens. Exhaust pressure is about even with manifold pressure at that point. If you're not pigeon holed on the turbo you can get a tremendous amount of mass flow through the engine. Using nitrous with larger than what you typically see posted about and a good wastegate and electronic boost controller can really help a lot. You're not going to get many who figured out all these relationships posting their timing data, CR, or cam lobes, separation or installed locations. Usually the turbo is the limiting factor and is run all in. The comfort zone must be exited or there's no way to get ahead of them. Sometimes it's back to the drawing board.
Got it bison, need to think about this a bit Till I fully understand it. Thanks for taking time to reply, I'm just trying to get a little bit smarter and get to another level. I try to learn something new every day weather its at work or has to do with the race car stuff.
If you don't mind, spill the beans on your current combo and best et's
Turbobitt This is The first this car has been on the road since 98. Back in 97 I ran 10.22@ 132 with a 206 cam ported iron heads and an old lt 72 p trim turbo stock mass air+ecm. The car in its current as of today configuration Is 233 inch 012 stage 2 block, 8.2-1 compression 3.400 bms crank, 6.500 carillo rods, champion aluminum heads flow was 239 on the intake, stock ported intake, T/A stainless headers and 3 1/2" downpipe, 96# injectors, hpq 71 dbb precision turbo and custom garret cored armstrong stock location cooler. Cam is Intake 224*/.578" exhaust 212*/.534" 113lca solid roller. installed at 108*. 1.6 rockers that measured at 1.65. The car went on the dyno in november so I have no ET for this set up yet. On the dyno [mustang] after sorting out some stuff It ended up at 680 hp peak at 6200. When we layed into it at 70 mph the converter flashed to 6000 and the hp was pretty flat up to 6500. Injector duty cycle was 80%. 11.4-11.6 a/f 19* timing. Fast xfi. We need to get back on the dyno as we simply ran out of time and the car is put up until nicer weather now. This was thru the full exhaust system. There is some more left and not sure on the converter yet but it ran very strong on the street the little we did get to drive it. Not a purpose built engine but it will get leaned on to see what it has.
Thanks jerryl I will find it.
Yes its on the money, It picked up 12 hp going from 18* to 19*. We just ran out of time and have to wait a couple months now. Thanks for the input. we are switching the mustang over from f2procharger to nitrous car this winter. shooting for 4 digit power.
This is why next time I buy Pistons it will be at least 9..5:1
