Edited for you reading pleasure.

Exactly how much do 4.10's help out the modular engines? The reason I'm asking is because a friend of mine with a '00GT and myself in my '88 RS dynoed our cars today and the #'s weren't quite what we were expecting.

'00 GT - 235rwhp at 5500rpm and 261rwtq at 4200rpm

'88 RS - 275rwhp at 5200rpm and 352rwtq at 3200rpm

The #'s just didn't add up to us. Everytime we've raced its dead even and one of us will inch past the other on the top end. The cars weigh almost the same, 3405 for the GT and 3435 for my car. Granted, anything can happen on the street but if I'm making 40 more hp and 90 more ft-lbs of torque than he is, I don't think I should have any problem smoking him but that doesn't happen. So assuming the dyno is accurate, which I honestly don't think it is, the only thing I can think of that lets him hang with me are the gears.

Mods of both cars:
'00 GT: CAI, Hooker LT's, Hooker x-pipe, Magnaflow Magnapack system, 2800 stall coverter, Transgo shift kit, 4.10's, pulley's, aftermarket TB, some sort of 3-stage prom, aluminum drive shaft, Eaton Limited Slip

'88 RS: 357cid, AFR190's, LT4 Hotcam, SuperRam upper and lower, Holley 52mm TB, Accel 24# injectors, Harland Sharp 1.6RR, Edelbrock headers, Yank 3200, 3.27's, Ed Wright mail order prom, gutted maf, Edelbrock cat-back

Sorry about the long post but this is really messin' with me.

 

It's hard to say why he would keep up as there are many variables that come into play beyond simple numbers.
4.10s will help him immensely off the line but limit his top speed. What's your rear gear ratio and are you certain your posi is working?
I'm thinking you need a bit more tuning, personally. Mail order proms are alright, I guess, but they don't compare to someone (or yourself) sitting in your car doing runs and programming to EXACTLY what your car is doing.
Another issue is those edelbrock headers.. They're too small. Your engine can't breathe as well as it could with larger headers. Unfortunately your choices are limited due to the constraints of the thirdgen engine bay and inherent drawbacks of long tube headers in thirdgen apps. SLP 1 3/4" shorties might help a little but it's hard to say, although even the more common 1 5/8 have more surface area than the 1 1/2" edelbrocks.
Although I question the validity of his dyno numbers due to the fact that 00 GTs came with comparable numbers stock I'd have to say that he simply has better exhaust. True duals with longtube headers and an x pipe vs 1 1/2 into a 2" y pipe through what can be assumed to be a stock cat as a 3" high flow was not listed with a 2 1/2" catback (I think that's the internal diameter of the Edelbrock, I could be thinking of another system, regardless the point is still valid)
What can be done about it? How much money do you have? The cheapest thing is probably a cutout before the cat. Head over to the PROM tuning board and learn to tune your own car, there are many skilled chip tuners on the board. Make sure everything is running well, if the numbers are correct then you should be the winner but his just plain don't add up.

 

I pm'd you earlier, but I have a little more to add. I think he needs to try it without the chip. What elevation are yall running at?His mods dictate a low 13 second car and his dyno numbers are WAY down for what they should be.

 

Inwo, you hit just about every problem my car has. It runs alright with the prom I have but it's NOT at its best. The headers are, well they're Edelbrock headers. I'm running a gutted cat. The Edelbrock cat-back is supposed to be a 3in system but I haven't measured the actual internal diameter.

I have a stock 9bolt rear with 3.27's and the posi is working fine. Lauching isn't too much of a problem, I cut 2.0 60' times but the car has seen 1.8 60' and 12.80's in the 1/4 with different tires. When I race my friend's GT from a dig I can get him by a car due to his spinning but I can't pull away at all. From a roll, all bets are off.

This is Houston, we're just about at sea level here but it's always humid as hell. The GT ran 13.5 at 100 on a 1.9 60' before the LT's so yeah, now it should be a legitament low 13 sec car. I know that loose converters tend to sap more hp but we expecting to see at least 250rwhp out of the GT.

I'm starting to think he's got hidden shot of N2O or something...

 

LTs will give him a ton of power. My LTs were the best mod I did!!!

 

Joe, sounds like your dyno #s are screwed. You both should be higher.
I don't think longtubes will get your bud to trap 106 as you currently do, so at a track you should pull him up top.
I could see him getting to 103 maybe, but to 106 is like a 60hp gain which aint gonna happen with just LTs on that car.
Makes me think dyno=poo:lala:

 

It don't add up in my mind, either. The way I see it, if anything, he should get the jump off of the line and you should real him back in. Those dyno numbers for his car are crap. 235rwhp is stock as said above. He is making at least 250rwhp as you expect. I still don't see how he could be running 106+ like you. What speed have you raced him up to?

Chris

 

We've run from a dead stop up to 80 mph. I got him by a car off the line due to his spinning and the fact that I'm on DR's. I wasn't able to pull anymore and stayed a car ahead of him till we let off at 80. Then from a 40 roll up to 110. Pretty much dead even the whole way. He says he was inching by me at 100 but I didn't see it.

Yeah Paul, we were estimating the GT to trap around 103 too. At the track we could probably cover the 1/8th in the same amount of time but yeah, I should walk away past that. We'll see what happens when we get out to HRP, hopefully pretty soon.

And yep, I think that dyno is crap too but at least it was free.

 

anyone consider that they may be using a mustang dyno? they usually show a little less hp to the wheels than a regular dyno.

 

Not a Mustang dyno. This was on a Dynojet.

Something I neglected to metion was that these runs were done in 2nd gear. I know thats the wrong gear but we were not allowed to dyno in our 1:1. This is our schools dyno so we had to do it they way they wanted us to, even if its the wrong way. I don't know how this would effect the output but I'm sure it has something to do with these screwed #'s.

 

amazingly with exception of turbo cars gar and gear ratio effect is almost nil...

 

Two things come to mind. Total gear ratio and torque converter. The dynojet has a hard time with stall converters for some reason. Was your converter locked and his not? And his gear ratio and tranny more than overcome lower HP.

Also that aluminum driveshaft helps more than you think. Lower recipricating weight is a real good thing

 

A higher stall converter with auto will show less RWHP, he should be quite bit higher than that really. I would guess that he has near 260+ rwhp if it was a 5spd. A guy I know has stock manifolds still on his 99 GT 5spd with 3.90's, ProChamber H, cold air, and slicks and ran a 12.81@103 with it. I'd guess that car would be pretty quick with those mods. An auto loses more HP to the wheels anyway and the converter will screw it up big time on the dyno. Go to the track and compare times. Sounds like a low 13 car to me though.

 

definitely, rims and tires too.

 

the converter wasn't locked on Br's car, won't lock at wot in 2cd gear, don't know about the GT.
I figure with a locked converter he could be looking at closer to 300 rwhp, which was my goal when I started. so I hope to see him get it.
Also, the runs may have been made in limp mode. there were some computer probs right before the run that weren't cleared, that may have hurt.
Also, these aren't corrected #s, its in Houston so very close to sea level, but wicked humidity and heat right now.

 

Thanks for typing all that Paul, I didn't feel like it.

No, the converter on the GT wasn't locked either. We're through with dynoing, at least on that dyno anyway. I guess we'll just have to let out timeslips tell the story when we get out to the track.

 

Well I dynoed the RS again. This was a 3rd gear pull with the converter locked.

295rwhp at 5000rpm
348rwtq at 4000rpm

Best torque, 355rwtq at 3800rpm on a 2nd gear pull.

I can live with these #'s for a while.