# So did any of you guy's know that adding performance parts will make your car slower?



## 04bottlefedGTO (Feb 28, 2011)

PLEASE HELP ME OUT!!! 

Okay.. So bear with me here because this is a really long story. But I really need someones HELP for ease of mind or something.

So first off.. I got my 04 GTO m12 about 4 months ago. It has had 3 owners, me being the 3rd. The 1st owner was an older man about the age of 50 something. Well he had it up to 14,000 miles. The 2nd owner had it up to 18,000. Then I was the next. Well I recently meet the guy that owned it first. THIS IS AN IMPORTANT PART. He told me he had it dyno tune. 

Next off.. I always knew my GTO was a bit faster than others stock for some reason. I guess because of the dyno. But anyways I got use to the speed so obviously it was time for MODS!!

Well I have put a Cold air intake, exhaust cat-back (Cats are back on now), SLP Underdrive pulleys, 3:90 Motive Rear end gears, and a SCT flash tuner since then.

Well here is the ISSUE...

When my car was COMPLETELY stock with the dyno before any of those mods at all, I would cross this bridge on my road going 15 and stomp on it and hit 115 MPH right before I passed a church. I know you have no idea how far that is. But they are not far apart at all. But now get this. AFTER ALL OF MY MODS, ON THAT SAME BRIDGE GOING 15 AND STOMPING ON IT (same temperature, same tires, same driver, same everything.) I ONLY HIT LIKE BARELY 85, maybe 90. It doesn't feel sluggish or anything, but I can tell a pretty major difference in power. And I don't mean a good difference. It's like when I stomp on it, the power wants to release, but something just isn't letting it. Something is just holding it back. Maybe I need another dyno tune after all the mods. Idk.. 

Can one of you guys please tell me what the heck I did to deserve this?LOL :confused   What's wrong with my car?


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## 87GN06GTO07IRL (Aug 10, 2009)

04bottlefedGTO said:


> Well I recently meet the guy that owned it first. THIS IS AN IMPORTANT PART. He told me he had it dyno tune.
> 
> Well I have put a Cold air intake, exhaust cat-back (Cats are back on now), SLP Underdrive pulleys, 3:90 Motive Rear end gears, and a SCT flash tuner since then.
> 
> Can one of you guys please tell me what the heck I did to deserve this?LOL :confused   What's wrong with my car?


You took off a dyno tune to replace it with a canned tune. Get a dyno tune and you'll be good.


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## motoristx (Apr 27, 2010)

ya, I don't like those little flash tuners for this reason. There are so many variables that they don't touch on, and one little thing like changing the exhaust can throw a good tune off. 

do everything you want to do that will affect the tune (cam, intake, exhaust, fuel too!) and then do your tune once your happy with the mods you wanted to add. it sucks going back every time you add something, but thats the best way to gain the most potential from everything you add.


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## Falco21 (May 11, 2010)

The above two posts are your answer. Nothing is like a custom tune. Especially not those handheld canned tunes. Motoristx is correct about tuning it after all those mods, but the question is if you plan on modding that far, and spending the money. If your like me or many people on here, you do things little by little and then when you have some extra cash your gonna add in the major mods (Cam, Heads, Fuel System, etc.) If your not looking to do these things any time soon, I would say get the tune, then when you add these into the mix, get it again. You should ask the previous owner where he got it tuned though, after the first time going to a dyno, they give you a discounted price for all the other times you go after that. Maybe the shop will cut you some slack since your car has been there once before. Worth a shot.


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## svede1212 (Nov 1, 2005)

I'd also take it easy on the road or you'll be the last owner too. . .


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## amtrucker22 (Apr 12, 2011)

Did you change the speedometer from KM to MPH?  j/k

I agree... Get it dyno tuned.


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## GuatoLT1 (Jul 22, 2009)

First off whats an m12? Secondly i dont want to sound rude but what made you replace a professional dyno tune with a half ass prorgammer. Third you said your car went 115 before, now only 85? A dyno tune would not make your car go 30mph faster then a stock GTO. Some thing else is wrong. Bring it in to your local shop have them run baseline number and see what your putting to the wheels. Do you smell any type of clutch fluid? Your clutch could be going out.


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## Thumpin455 (Feb 17, 2010)

You put 3.90 gears in it, that will make a difference in your top speed as well as your top end acceleration. If you go back to the stock gears you will find it pulls harder from a roll than it does with the 3.90s. The deeper gears are more for getting your car moving off the line, after the first 60' to 100' they arent helping you anymore. The lever is just too short. To utilize the deeper gears the way you are, you need to increase the RPM range your engine can turn, which will be wasting bottom end torque.

I know that sounds like complete BS, especially if you are used to small engines like Gen I 350 sbc or 4 and 6 cylinder imports, but that is how it works with larger V8s like the LS1/LS2 and especially so with the 400 and 455 V8s some of us have in our older GTOs. The overdrive gears will give you back your cruise rpm, but the ratios for each of the other gears are now much shorter and that affects your acceleration exactly how you have described it. I would put the stock gears back in and lighten the car instead, you will get much more for the effort that way.

If you want to build a car that will be devastating from a roll, you want more highway like gears, it keeps the engine in the power band much longer so you get more work out of it. Its the same reason you dont need nor want 4.56 gears in a car with turbos or a blower, you are wasting all that torque if you have it geared too deep.

Also retuning it would probably help.


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## HP11 (Apr 11, 2009)

GuatoLT1 said:


> First off whats an m12?


Without going into all of the eplaination since it seems to cause arguments, the simple answer is that an M12 is the version of the T56 transmission used in the 04-06 GTO.


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## svede1212 (Nov 1, 2005)

Thumpin455 said:


> You put 3.90 gears in it, that will make a difference in your top speed as well as your top end acceleration. If you go back to the stock gears you will find it pulls harder from a roll than it does with the 3.90s. The deeper gears are more for getting your car moving off the line, after the first 60' to 100' they arent helping you anymore. The lever is just too short. To utilize the deeper gears the way you are, you need to increase the RPM range your engine can turn, which will be wasting bottom end torque.
> 
> I know that sounds like complete BS, especially if you are used to small engines like Gen I 350 sbc or 4 and 6 cylinder imports, but that is how it works with larger V8s like the LS1/LS2 and especially so with the 400 and 455 V8s some of us have in our older GTOs. The overdrive gears will give you back your cruise rpm, but the ratios for each of the other gears are now much shorter and that affects your acceleration exactly how you have described it. I would put the stock gears back in and lighten the car instead, you will get much more for the effort that way.
> 
> ...


A change in gears from 3.46s to 3.91s don't have the pronounced effect you state. I have 3.91s and can get to the next "powerband" a little quicker than I did before. In my car that does 0-100 in a tick over 10 seconds that's not a problem. You'll find that as the gears go up so does your time in each one. Most of that time is spent in 3rd and 4th gear. When I changed gears 1/4" times got better from the launch but traps remained about the same.


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## 04bottlefedGTO (Feb 28, 2011)

GuatoLT1 said:


> First off whats an m12? Secondly i dont want to sound rude but what made you replace a professional dyno tune with a half ass prorgammer. Third you said your car went 115 before, now only 85? A dyno tune would not make your car go 30mph faster then a stock GTO. Some thing else is wrong. Bring it in to your local shop have them run baseline number and see what your putting to the wheels. Do you smell any type of clutch fluid? Your clutch could be going out.


It says under the hood on the tag, m12 transmission. I was told it was a type of transmission in corvettes. Or what the guy below said. And the reason I bought a tuner was because I had NO IDEA about the dyno before I did all that to my car. Dealerships never tell you anything lol. But I met the 1st owner of the car at a gas station one night and that's when I found out about the dyno.


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## 04bottlefedGTO (Feb 28, 2011)

I really appreciate all the help guys. I'm going today to get it dynoed. Hopefully that will fix everything. Thanks!!!


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## pocketmaster (Feb 26, 2010)

HP11 said:


> Without going into all of the eplaination since it seems to cause arguments, the simple answer is that an M12 is the version of the T56 transmission used in the 04-06 GTO.


LOL....oh I remember that guy!!!!!!!!!!


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