New Dyno results

[Superdave]

the cutouts were right where the cat would go, they replaced my X pipe.

I took them off last week and just installed some straight pipe in there for now, the car is going to the strip a few times then it will be undergoing a few changes.


Here is the graph for the open cutout run:




and for anyone who goes to the dyno, have them save the images to a USB drive instead of printing them out.. MUCH better

[IsaacHayes]

Don't know where Dave's are. But wherever they are, they are too close! It obviously needs time to merge all the pulses so they can pull on the others.

[3400-95-Modified]

I have a short length of pipe before my cutout... its not right after the collector...

[merlot566jka]

^ yes sir!

[IsaacHayes]

I'm sticking with my theory that it needs some length of pipe to keep pulling out the gasses vs just open collectors.

[Superdave]

I'll post up the dyno sheet from that run tonight.. lol

[merlot566jka]

ill dissagree!

not trying to say your wrong, but i dont think its as exagerated. at lower rpm, possible. but at 2500 and up, i dont see enough time for it to happen. i do see it pulling out all the spent gas and bringing in a fresh charge.

what i gather from what you said, would be like having an overlap cam on a supercharged engine... i just dont see there being enough scavenging force to draw out enough of an intake charge to cause a dip in overall performance...

that said, ill blame it on incorrect resonance tuning, or factors out of our control for resonance tuning.

maybe im way off...but i dont think so....otherwise i would have kept my mouth shut )

[IsaacHayes]

Right. Not disagreeing.

[sprucegagt]

Just saying it's a possibility. How many people here have equal length 32" long headers on a modified big cam 3500? We don't know the limits of the engine or exhaust system and it is possible to have a set of headers scavenge so well that they can pull a bit of the intake charge straight out the exhaust port during cam overlap.

[IsaacHayes]

Hmm, possible that it sucked so much air out of the cylinder that it created a vacuum in the cylinder before compression? heh. I'd say that the pipe right after the collector isn't a restriction, and that it probably helps pull everything out. Now when you get down to the axle and start getting into some of the bends and really long pipe length, then it would be a restriction.

[sprucegagt]

all the local trans shops refused to touch the HM282.. lol


Yes, i hit about 98 Kpa depending on the weather at WOT. The engine loves the 75mm TB

my exhaust setup is matched to the engine almost perfectly flow-wise.

I think your headers may have been over scavenging with the cutouts open. It just doesn't make sense to me to loose velocity because you lost restriction?

[3400-95-Modified]

My next route is the 3.69 gears for my car... 3.42 may be too low with this converter, we'll see.

[Superdave]

all the local trans shops refused to touch the HM282.. lol


Yes, i hit about 98 Kpa depending on the weather at WOT. The engine loves the 75mm TB

my exhaust setup is matched to the engine almost perfectly flow-wise.

[IsaacHayes]

The 90 GTZ has a shorter 1st gear too though. Just swap the 4th into your v6 getrag...

Yeah the headers probably need some pipe after the collectors for a decent stretch to keep the velocity going. But there is a beretta that has just a 3400 swap and ran a 14.something with a cutout on stock manifolds. Picked up power because of extra flow, where you lost power because you killed some velocity. Crazy how different designs react. I wonder at which point you should open the cut outs in the exhaust as to not kill the velocity but yet get rid of any potential restriction from bends going to the rear axle/mufflers. Probably won't pick up that much power to be worth it.

Did you ever get higher than 92 kPa with the bigger TB Dave? I noticed from my logs I never get higher than that, but that may be due to other things. Soon I will go from 52mm to 65mm. Big jump LOL.

[Superdave]

3.61 FDR in mine, with LSD

i had the 3.94 diff for a while, i had a hard time breaking into the 13's with it though. I really want to find a '90 GTZ tranny with the 3.61 FDR and the better 1.03 4th.