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Unit 5302 · 06-02-2001, 10:01 PM

Oh, I'm not saying the headers, H pipe, exhaust combo will hurt the 1/4 mile time. Adding just headers on a bone factory car will in most cases, though.

The explanation in physics is right above your last post.

An H pipe will add a legitimate 15-20hp. That is serious extra power. Stock your 5.0 won't pull worth crap at much higher than 5000rpms, when you add all the exhaust mods, you get it to flow better up top, but you lose low end.

The reason you may not feel it is because of your gears. The 3.55:1 gear ratio you are currently running allows you to stay in a more narrow rpm range allowing you to utilize the extra topend power the exhaust creates. Not to mention the additional torque multiplication involved with going from factory 2.73's to 3.55's which offsets some of the torque loss.

I could compare your experiance to the 150 experiances of other 5.0 drivers who've experianced the loss of low end torque phenomenon, too.

As far as the dyno, was it at the same temp, was the car at the same temp, same humidity? Was the additional 8hp and 10 lb/ft at the previous (and reoccuring max horsepower rpm)? Or was the original dyno showing a max hp at 4200rpm and the new one showing 4500rpm? If that's the case, what's the increase at the previous max, the new max, and avg?

It all gets technical, but if the old headers made

178hp@3800, 183hp@4000, 187hp@4200, 185hp@4400, 179hp@4600, 171hp@4800, 166hp@5000

new headers
164hp@3800, 173hp@4000, 183hp@4200, 193hp@4400, 183hp@4600, 174hp@4800, 169hp@5000

The new headers would have added a peak 8hp increase, but overall they wouldn't have helped anything, plus they would have moved the powerband a little higher hurting low end performance on a stock geared car pretty bad.

Adding an H pipe and freer flowing exhaust might make your numbers look more like

158hp@3800, 170hp@4000, 188hp@4200, 200hp@4400, 201hp@4600, 191hp@4800, 183hp@5000

Serious low end losses occur with those mods, but if you have gears, or solid traction and you can keep the car in it's powerband, you'll certainly improve your times.

It really helps in the 4500-5500rpm area for flow, but much above 5000rpm most stock 5.0's are restricted by their heads/intake. That pretty much negates the higher rpm gains much above 5500rpm.

I experianced a huge performance increase with my hi flow H-pipe and 2.5" exhaust. I'm relatively certain, had I chosen to use the 1 5/8" headers I had, my low end would have been deystroyed because of my stock gears (2.73) and my T-5z's 2.95:1 1st gear ratio. It's already too tall, with the 3.35:1 1st gear of the standard T-5 I had, I could launch very hard (with street tires) and it would use every bit of traction out of the hole. Now it's very, very hard to manage to get the proper launch. I either bog badly, spin badly, or spin a little, then bog a little.

------------------
1987 GT 5spd.
D&D Performance "Z" spec T-5
Dynomax 2.5" Super Turbo system
BBK 2 1/2" H-pipe with cats

06-02-2001, 10:01 PM	#13
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	Oh, I'm not saying the headers, H pipe, exhaust combo will hurt the 1/4 mile time. Adding just headers on a bone factory car will in most cases, though. The explanation in physics is right above your last post. An H pipe will add a legitimate 15-20hp. That is serious extra power. Stock your 5.0 won't pull worth crap at much higher than 5000rpms, when you add all the exhaust mods, you get it to flow better up top, but you lose low end. The reason you may not feel it is because of your gears. The 3.55:1 gear ratio you are currently running allows you to stay in a more narrow rpm range allowing you to utilize the extra topend power the exhaust creates. Not to mention the additional torque multiplication involved with going from factory 2.73's to 3.55's which offsets some of the torque loss. I could compare your experiance to the 150 experiances of other 5.0 drivers who've experianced the loss of low end torque phenomenon, too. As far as the dyno, was it at the same temp, was the car at the same temp, same humidity? Was the additional 8hp and 10 lb/ft at the previous (and reoccuring max horsepower rpm)? Or was the original dyno showing a max hp at 4200rpm and the new one showing 4500rpm? If that's the case, what's the increase at the previous max, the new max, and avg? It all gets technical, but if the old headers made 178hp@3800, 183hp@4000, 187hp@4200, 185hp@4400, 179hp@4600, 171hp@4800, 166hp@5000 new headers 164hp@3800, 173hp@4000, 183hp@4200, 193hp@4400, 183hp@4600, 174hp@4800, 169hp@5000 The new headers would have added a peak 8hp increase, but overall they wouldn't have helped anything, plus they would have moved the powerband a little higher hurting low end performance on a stock geared car pretty bad. Adding an H pipe and freer flowing exhaust might make your numbers look more like 158hp@3800, 170hp@4000, 188hp@4200, 200hp@4400, 201hp@4600, 191hp@4800, 183hp@5000 Serious low end losses occur with those mods, but if you have gears, or solid traction and you can keep the car in it's powerband, you'll certainly improve your times. It really helps in the 4500-5500rpm area for flow, but much above 5000rpm most stock 5.0's are restricted by their heads/intake. That pretty much negates the higher rpm gains much above 5500rpm. I experianced a huge performance increase with my hi flow H-pipe and 2.5" exhaust. I'm relatively certain, had I chosen to use the 1 5/8" headers I had, my low end would have been deystroyed because of my stock gears (2.73) and my T-5z's 2.95:1 1st gear ratio. It's already too tall, with the 3.35:1 1st gear of the standard T-5 I had, I could launch very hard (with street tires) and it would use every bit of traction out of the hole. Now it's very, very hard to manage to get the proper launch. I either bog badly, spin badly, or spin a little, then bog a little. ------------------ 1987 GT 5spd. D&D Performance "Z" spec T-5 Dynomax 2.5" Super Turbo system BBK 2 1/2" H-pipe with cats