I'm Really Stumped Here

I raced a buddy's modded GTP the other day. Lost by 3 car lengths up to 95 mph. I added a 10% pulley, and took the back half of the exhaust off past the resonator, and i tied a car that he tied. Car felt fast and strong. Last night and today i changed the gears to 3.55's, raced him again and lost by the same 3 car lengths again. He hasnt changed anything. How can my car run the same with gears, pulley and less exhaust as it does stock?!?!? It has only seemed to have gotten slower since the gears, but they are installed properly. I have no idea wtf is going on. What could cause the car to be down on power?!?!?! The only problem is a leak in the thermostat housing, since i installed a 180 when i did the pulley. Frick, i couldnt even pull from a stock prelude today at speed. Something is definantly wrong

Is your belt slipping on the 10%?

ANother thing to consider with the 10%, Along with making more power, it is also sapping more power to turn the blower now, AND it is heating the air more.

You may be making more power when you first start up, BUT after you run around for a bit that 10% is heatsoaking the intercooler, so you are making less power after a bit of running.

Was your car warm when you ran the GTP? Try a couple of hard runs up to speed, then pull over and see how hot your intercooler is. If it is hot, you might want to look into an intercooler fan, or backing off to a 5% pulley, or if you are serious, stepping up to a better intercooler.

I know when I had a 10% on, after a couple blasts into the boost the intercooler was so hot you could barely hold your hand on it. This actually happened to me on the Dyno once. They tried making a couple pulls (had trouble getting the tach pickup straight) and warmed the engine. Once everything was set the did a pull, and measured 170 RWHP. I was shocked, took a look under the hood and damn near burned my hand on the intercooler. We cooled it down with some ice (not cold, just back to around 70 Deg F) and tried again, 202 RWHP. 30 HP difference from a hot intercooler, that was heated from just a couple aborted dyno runs.

455Poncho: I'm glad you posted this because I'm about to buy either a 5 or 10% pulley. Also, years ago I had a 1974 Grand Prix and I really loved that car! I was young and didn't have the money to keep it going so I had to get rid of it after owning it fo a few years... It also had a two-tone paint: mettalic purple and gray. Nice car!

Andy 94SC: This is interesting about the 10% pulley. So should I deduce that with a stock intercooler (even with an IC fan) maybe I should just go with a 5%? Sounds like with the extra hp drain and the extra heat of a 10%, a 5% would be a better choice...

Thanks!

I'd say it really depends on your driving style. I think the 10% will make more power, for a short while, then you have to wait for things to cool back down before you get full power again. If you really only need full power for short bursts once in a while the 10% might be good. But if you are going full throttle at every stop light, the 5% might give you better overall performance, in other words the performance is a bit lower than the 10%, but it might last longer. Better for more consistant back to back runs.

I suspect that if Ponch was dogging on the car a bit before racing the GTP that he could have heat soaked the intercooler, thus been stuck with stock, or worse performance.

The thing is, smaller pulleys are the quick and easy solution to getting more air in the engine, but they can come with the heat and parasitic drawbacks. Other solutions to getting more air, such as blower porting, and nice big intercoolers, are much more expensive, but don't have the same drawbacks. All three of these solutions compliment each other nicely though. A ported blower, or better intercooler will help the heat problem of the 10%.

Freeing up the front part of the exhaust is a good idea too.

hey 455poncho... looked at ur car site and saw the pics, u must have a lot of money to blow on tires!

So maybe I'd be ok with a 10% then... I've got the MPII ported blower, raised top, and plenum from MP, plus I finished the top half of my exhaust with ported stock manifolds and hi-flow cats/downtubes. 76 maf and 75 tb.

Thanks Andy, and sorry for hijacking your thread, Mr. Poncho!

Thanks for the advice. I had driven the SC accross town just before i raced him. I just put down 184 hp and 293 ftlbs of torque on a mustang dynamometer. I also put 3.55's in, and i think im holding the gears to long. Believe it or not, shifting before 5 grand really seems to speed the car up

motocross_masta said:

hey 455poncho... looked at ur car site and saw the pics, u must have a lot of money to blow on tires!

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I've always got money to blow when it comes to tires I think im in the mood for another huge one in the SC before i do the back brakes

joenintiesc said:

455Poncho: I'm glad you posted this because I'm about to buy either a 5 or 10% pulley. Also, years ago I had a 1974 Grand Prix and I really loved that car! I was young and didn't have the money to keep it going so I had to get rid of it after owning it fo a few years... It also had a two-tone paint: mettalic purple and gray. Nice car!

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The GP is a neat car for sure. Takes someone who has experience it to appreciate it. Mine has a big solid camshaft (594 in lift, 587 exh lift. duration 255 in, 266 exh), extensively ported D-port pontiac heads, forged rods and pistons, and lots of other goodies. Should run pretty good once its all assembled, even though the car is a tank.

If u have any pics of your GP, post them or send them to jpage@shaw.ca

people dont get that stock 2:73s are faster to the quarter mile than other gears on a 5-speed(who knows with slicks). Most of these cars arent meant to rev, and the lower gears raise the rpms past the power band, the 10% causes too much drag at higher rpms, I thought the 10% was a waste on mine(made no difference 0-60).

I have had or have 2:73s, 3:08s, 3:27s and 3:73s installed and lost over .5 seconds with 3:73s. I was power-shifting also (never let off gas when shifted when I timed them)

AsScLoWn said:

people dont get that stock 2:73s are faster to the quarter mile than other gears on a 5-speed(who knows with slicks). Most of these cars arent meant to rev, and the lower gears raise the rpms past the power band, the 10% causes too much drag at higher rpms, I thought the 10% was a waste on mine(made no difference 0-60).

I have had or have 2:73s, 3:08s, 3:27s and 3:73s installed and lost over .5 seconds with 3:73s. I was power-shifting also (never let off gas when shifted when I timed them)

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So the car feels slower because it is slower

Hmmm, dont know what to do now. I dont wanna take it all apart again just to put 2.73's back in. Do 3.27's help over the 2.73's Assclown?? Stupid me thinking bigger gears are better

they might from a roll, not off the line, I think the IRS doesnt like the "shock" from the lower gears also, the 2:73s kind of bog it and transfer the weight. I do have a recently rebuilt 2:73 diff though if you really want one . I only have lower gears because I power shift it and snap engine mounts and output shafts

AsScLoWn said:

they might from a roll, not off the line, I think the IRS doesnt like the "shock" from the lower gears also, the 2:73s kind of bog it and transfer the weight. I do have a recently rebuilt 2:73 diff though if you really want one . I only have lower gears because I power shift it and snap engine mounts and output shafts

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LOL. Have u tried the 3.27's or 3.08's?? how are they??

I have 3:08s now, I cant go back to the 2:73 diff because I dont feel like changing the trans output shaft speedo gear

I tried the 3:27s twice, still kind of on the low side

AsScLoWn said:

I have 3:08s now, I cant go back to the 2:73 diff because I dont feel like changing the trans output shaft speedo gear

I tried the 3:27s twice, still kind of on the low side

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This really suprises me. Cant u just shift sooner??!?!

I've got 3.31s, and I like them. I am kind of suprised you only made 184 HP on the dyno.

then you have no 1st gear

Oh I have a first gear. Its a creeper gear. I use it for uprooting Oak trees, and towing 4X4s out of mud pits.

Seriously though, I am happier with the 3.31's than the 2.73s. I really don't know anyone who has slowed down going from the stock gears up a size or two. The closest I heard of was a guy who went to 3.73's in the 5-speed, his 1/4 times (with other mods) were as bad as my stock times.

Hmmm.....

Well guys,
The truth of the matter is that it is very hard to get any performance gains from bigger gears if you are running "stock". I went to 3:73's in my stock AOD SC and the car actually ran slower. When you start adding HP into the equation, you can get the full benifit of a good set of gears. Otherwise you are just "pissing in the wind". Traction is really a factor too "especially from a dead-stop".
Just my .02

DB91