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i have posted this before in another thread, but if this gets stickied it could do far more good here.. and i am sure this is mostly for 97-03, but the basic principle of how to mod safe is the same
here is a write up on a local board to me.. kinda long. but lots of good info..
First off, I have two GTPs basically, a 96 with an L67 Swap (98-99 PCM setup), and a 97 GTP. So i have seen my fair share of modding issues. My hope is that other vets here will dispense their knowledge as well.
Here are the questions we always here from newbies, these are the same questions we asked when we first got into our cars, the answers were different back then. Now through experience and through a maturing after market for our cars, we can provide better advice to YOU then what we had to start with.
I want to start modding, where do i start?
the FIRST thing you should do is a tuneup. If your transmission is slipping, get a new one or get it rebuilt. mods kill transmissions. Its a fact. If you don't like it, buy a car thats already fast from the factory, a GTO or a Vette is a good choice, get your wallet ready! Replace worn belts, spark plugs, plug wires. Run some fuel injector cleaner through your tank. I personally recommend a 'GM Top Engine Clean' Google it and learn about it. Do a coolant flush. Replace your worn out dexcool coolant especially if you are over 75,000 miles. Fix your brakes. To go fast, you will need to stop too. Replace your fuel filter. Don't even think about ignoring it. If you need convincing, pm Chris Metzger. Stop getting cheap fuel. Get your gas from BP, Shell, or someone reputable. Actively search out and find 93 octane. Don't settle for 92. Don't even think about mid grade or regular. If you do, don't even think about modding your motor. Step up to some synthetic oil, it lasts longer and you will make more HP just from that. Change it every 3000 miles. I suggest running autolite Spark plugs. start with 103's. Gap them to 50 until told to do otherwise . Change them every other oil change or every 6 months which ever comes first.
What is the best FIRST MOD for a GTP?
The answer used to be a 3.4 or 3.5 Pulley, or maybe an intake. While pulleys are inexpensive, and powerful mods, they do not work well for everyone and there is a reason for that. Some STOCK GTPs may already be experiencing problems with Knock Retard. This is an issue common in modded cars, but in stock ones as well. This is in a nutshell, your engine computer pulling power out of the engine in order to save it from chipping a piston, breaking valves, flipping lifters or anything else that can go wrong. Knock is defined as your gasoline exploding in your engine before your spark plug is supposed to ignite it. That means while your piston is on its way up in the chamber, theres an explosion trying to push it back down. What is a piston to do? it can't go back down yet! The only thing it CAN do is overcome that explosion and attempt to survive, or send chips of aluminum into your exhaust. Your computer can detect this through a special microphone called a knocks sensor listening for tell tale signs of a knock. Based on how much knock is heard, the computer pulls timing out. This slows the motor down just a bit to reduce internal heat which is the cause of knock. If the internals of your engine are hot enough, and the incoming air is hot enough and dense enough...then its like throwing gasoline on a fire thats already burning!
The m90 supercharger on your car is made to produce boost, but does so in such a way that also produces heat. Basically the m90 is sending large, pressure cooked clumps of air into your poor little 3.8!!! a stock GTP has a 3.8" pulley and this means that the amount of air (boost) and the temperature of that air are pretty low. About 6-8 lbs of 'boost' is normal for a stock M90 supercharger with a 3.8" pulley. Smaller pulleys spin the supercharger faster at any given engine RPM. This means the boost will go up, and so does the heat! the smaller the pulley the more heat and boost go into your 3800.
So lets say your engine has some issues with knock. When you punch the gas pedal you are getting a couple of degrees of knock. How do you know? theres no magic light on your dash that tells you this is happening. So you assume you don't have a problem? no put a 3.4 pulley on your supercharger. Now you have more knock...so you basically just took a dangerous situation and made it worse! you may be making your car a little faster, maybe even SLOWER! as your computer starts pulling time to save itself from disaster. Why would you do this?
So the first mod, is not a mod. Its called a scanner. You need something to tell you and give you feedback on what is happening inside your motor. You wouldn't want a doctor to perform surgery on a patient entirely based on what he feels like doing without getting good information first... like an MRI, taking samples, or speaking with the patient. in the same way, you shouldn't make changes to your motor without getting a good diagnostic first. Plug in a good engine scanner and see what your PCM already knows.. If you have some KR or not.
Even better than a scanner. Get a tuner... they scan also. You also won't need a computer 'mod.' You can make more horsepower AND get better gas mileage. Not only that, you will also learn absolutely priceless information about your car. You can make a change and see how the car reacts. See how adding more fuel at the right times can make KR go away. Or how less fuel can make more power. Or how timing in certain situations makes more power, or better gas mileage. Don't like the way your car bogs down going uphill? theres a fix for that. the POWERTUNER is my official, without a doubt FIRST MOD recommendations. Do you already have another car sitting in your parking lot that you would like to play with? don't be shy, "DHP Powertuner's" or "HP tuner's" will work on MANY different cars. Maybe your Mom's, your girlfriend's, your winter beater and even your truck may be a good candidate for some tinkering.
I have KR, now what? Good question...here is a quick list of 'early' mods you can do:
Mods that effectively and consistently REDUCE KR:
Downpipes. This is the piece that connects your exhaust manifold to your exhaust 'cat-back' and typically will replace your stock CAT with a high-flow unit and will remove the terrible, imfamous "U-bend" The stock downpipe is restrictive and keeps your motor from pushing the hot, spent air out effectively. It is too restrictive even for a stock GTP. and even worse for a GTP with a 3.4 pulley! Downpipes are cheap, new engines are not. Less than $200 will get you one. Your gas mileage will improve, and you will quickly notice the better sound in your exhaust and the 10+ HP it makes on a bone-stock GTP.
Intercooler. As stated earlier, your M90 supercharger makes heat. A LOT of it. an Intercooler deserves a longer explanation but the short of it is that it will get rid of much or all of the knock you already have and produce 10-40 HP depending on your other mods! Intercoolers cost more, $600-$1300 and require other modifications to be completely effective.
Heads, CAM, Rockers. These CAN reduce KR. it really depends on what you are doing already. Rockers are cheap, but only install them if you have already done a downpipe swap. It doesn't make sense to push out more air if there is no where for that air to go! same goes for CAM or heads. They don't make a lot of sense if your exhaust is restrictive.
Headers, PEMs, Powerlog. These are mods that replace your factory exhaust manifold peices. Careful through, headers require a DIFFERENT downpipe than the one you will need for stock manifolds. Doesn't makes sense to buy a downpipe for you stock manifolds, then buy another one if you decide to get headers.
As the above will show, it makes sense to plan your modifications. If you want run 11s, its a completely different game than running low 13s. I will explain further below.
I Don't have KR, Now what?
Get the downpipe anyway! if you don't have any KR on a stock GTP, you WILL with a 3.4 pulley. It is extremely well documented and pretty much a guarantee. The stock downpipe is VERY restrictive. If you put more air into the engine, and it still can't get rid of it...it doesn't make much sense, does it!
OK, i got the downpipe, Whats next?
Scan again, you should see an improvement. If you have no KR, now its time for a 3.4 pulley! Now it gets interesting.
If you have some KR now, see the list of 'KR' reducers... Then put on a smaller pulley and so on. Don't put a smaller pulley on if you have too much KR! a few blips of less than 1 degree is OK. 1 degree or more...go see the list. When you get down to a 3.1 pulley, get ready to get bigger fuel injectors and a fuel pump 'rewire'. As you are adding more air to the motor, you will also need to make sure the fuel can keep up.
I want to run low 13s. Maybe a 12.99. And my budget is tight. $2500 over the next year or two.
You are basically saying you need to get up to 300 Wheel HP. stock you are making approx 200 Wheel Horsepower (240 at the crank), You need to make 100 HP, i can help you do it! Mod in this order. This is purely my advice. I'm not going to make you follow it. And there are many ways to get this done with different mods. These are just the ones that myself and others have done, and wished we had already done.
1. DHP Powertuner or HP Tuners. $400. You will make up for some of this in gas mileage if you do this right! Give yourself a couple of months to learn and use this item. Get a downpipe if you want instant gratification. there is no harm in it and you will make almost as much power from this as though you were putting on a 3.4 pulley. If you have 97 year GTP. get the downpipe first anyway. 97's are a bit of a black sheep when it comes to computer tuning, so be ready and read up on it while you enjoy your downpipe.
2. Downpipe w/Cat. $200. Get the 3". more is better . Have an exhaust shop weld it up for you. Get the 2 1/2" if you need to be able to unbolt your exhaust. Not really necessary though.
3. Modular pulley system. get a pair of pulleys together to save some money! $300/2 pulleys and hub. Get a 3.4 and a 3.0 pulley. put the 3.0 in your glovebox to show off to others! Install the 3.4 Pulley. Pay someone to have the hub put on, or rent a puller. Learn how to use it first! By this point you will be making about 240 WHP, running high 13's and you might have a few blips of knock. Don't worry, its not the end of the world!
4. Rockers or a CAM. 1.9 ratio rockers( ~$400 with hardware) are for the faint of heart. If you have the guts, get the cam (~$800 with hardware). Get an XP. Its very streetable, sounds awesome, and makes gobs of horsepower. If you go with rockers, get the bigger stage 2 intercooler next, since you will have to make up for the slightly lower airflow with more/cooler boost to make the same power. You may want to get a 2.8 or 2.9 pulley instead of that 3.0 if you decide to do this.
5. Short Stack Intercooler, Fuel Injectors, fuel pump rewire. $850. (add $500 for stage 2 intercooler) Now you can put on your 3.0 pulley! You shouldn't have much or any knock, and you may need to adjust timing to make it all work happily or to make the remaining horsepower to get that 12.99 pass. Your power tuning skills and knowledge by this point should be ready to handle the new injectors and added boost. You will also notice that you are making on the edge of 300 HP, running low 13's on street tires, maybe even high 12's if you can find some cash for some slicks! You've either spent about $2500 by now or you have already replaced your transmission and waiting until the next year.
6. Notice whats off the list so far? Intake and Exhaust. Your stock airbox and your stock cat-back exhaust can handle up to around 300 HP just fine. There is no need to change them except for the sound, or if you plan on making more HP later on. You will not make more horsepower with these mods. If you anything, you will trade torque for horsepower. That means you might get better times at the track, but your throttle response will lag. You also don't need transmission mods like shift kits. These aren't going to help with anything except driver enjoyment. There are a couple of 'free mods' you can do to make your shifts very firm, and the power tuner can help you get the most out of what you have as well! Save the shift kit and 'poly motor mount' money for a dead transmission someday instead
7. So by now you have spent about $2500 or so. What to do next? well to get the edge you can now add an intake and exhaust to your to do list. You should also consider some of the throttle body options. Make sure all of the 'free mods' have been done as well. Look at different things you can do to improve the handling of your car. You will probably notice that at 100+ mph your car feels the road like wet hands feel a squirming fish. Handling upgrades can improve your times a tad too! get some slicks. If you want to run 12s, they are a necessity. Unless you make gobs of horsepower from a giant turbo, you will want these. A Ported supercharger would be nice. You can do it yourself if you have the tools, or buy one. A power log would be inexpensive and helpful (PEMs are a bit of a waste compared to this option) the Powerlog mod can be done at any time and be helpful anywhere. If you have more money to spend. Get some heads put on. You will now be able to make mid 12s within reach, and 320 WHP. But is that 20-30 HP worth $2000? If it is, it is the next mod for you.
I want to run 11s and stay supercharged.
My advice.... Start with the power tuner. Then get headers. Plan on stage 3 or better heads, get an XPZ cam. stage 2 or 3 intercooler. At somepoint either get an L36 (GT Block) or rebuild the motor with some oversized and higher compression pistons. Don't worry about forged pistons, they just take more parts out with it when they break. Get anything you can. Exhaust, Intake...Electric Water pump. Injectors. Gen V blower, NOS. Go all out. This is tough to do with an M90 but can be done, and 10s are not out of the question and this has been done before. Prepare to break your transmission, get a rebuilt/beefed up unit, and prepare to break that too. Plan on spending anywhere from $4000-$6000 just in engine mods. $3000 on a transmission at some point. Buy as much as you can from other members/2nd hand to keep costs down. Many people try this and give up, so buy their parts cheap and try it yourself.
I don't have many mods yet and I want to run 11s or 10s and thats it.
Get a turbo setup. A big one. Just call ZZP up, tell them you want to run 11s, they will hook you up. At this point its better to just plan on spending about $10,000 and just have a turbo setup put together and get a transmission that can handle it. Don't spend 10,000 getting close to 11s, then 10,000 again to actually get there thats dumb in hindsight. Plan ahead!!!! Look at brandon jane's car...you are just a turbo kit away from mid 11's. and a transmission away from it running again after that 11 second pass.
My Ode to the XPZ Cam
11.5's huh? suuuure.... look at what everyone runs with the XPZ.... compare that to the XP, the VS. Why aren't us XPZ cam owners just steam rolling the competition with mid and low 11s, or even 10's like Zoomer?? After all, you really can't do an XPZ setup without getting heads, headers etc. All mods that advertize 20, 30, 40 HP gains with 'supporting mods'
Look at this dyno graph. At first i thought 'hey look at that!' 410 HP and its right accross the power band! it doesn't 'peak' out like a lot of other dyno graphs i'm used to seeing...which means that 410 hp is going to last for a couple seconds at WOT, not for just an instant just before my next shift.
No wonder he ran 10's, that's nuts! its also what sold me on it.
"Stage 3 blower, Gen 2 intercooler, 2.55" ZZP Gen 2 MPS, Comp pushrods, modified INTENSE S3 heads "
So now i have almost exactly the same setup as Zoomer's major mods. Stock bottom end, even stock lifters like he had, Intense Stage 3 heads, .... modified?? how so?, Stage 3 blower, stage 2 intercooler, a 2.8 pulley with not a lot of timing before the 'KR monster' comes out to play. Now im curious where my other 90 HP is supposed to come from (im guessing im at about 320)? ricer math would say 'hey, i should be at 700 HP by now'
It just goes to show that just because a self-sponsored, experienced individual can run 10's and 400 HP, doesn't mean you will. Alas. I don't know all the secrets. I wish i did, cause they are worth 90 hp at this point.
Hey Zoom, you're running another setup now. What's your secret, i mean send me your PCM dump...what did the car weigh? what magical tweaks did you do? what TB did you have, what exhaust setup? theres no way that with my current 'KR cieling' that i'm going to make 90 more hp with my current tuning knowledge. I figured hey, i can find 10 or 15 more no problem, but 90??!?!? Now my goals are only for an 11.99 pass, maybe some more if get some n2o some day. It just sucks that i have so far to go and yet someone else out there with similar mods is well beyond that!
So, whats the point of my rant? i have several points. Don't be afraid to ask for help when you need it. I ran a 12.6 and i'm asking for help, where to next?, and don't chase someone elses dreams, just because Metzger ran a 12.3 with an XPZ non-intercooled doesn't mean i'm going to. Hell the best i could do Non-IC was 13.0 and I had 'better' mods than he did. Don't beleive everything you hear, and never underestimate the power of knowledge. Money will get you the stuff, your experience and knowledge will take you the rest of the way...I just hope i can find mine!!!
Mods you don't need.
.....I bought a DHP PCM, then an AFC, payed someone to help me tune it instead, got a happy knob, or an ICCU.... then finally got a powertuner. A powertuner REPLACES the need for an AFC, ICCU, a PCM upgrade, a happy Knob...etc. Either spend $400 realizing you need a powertuner or spend $400 to get the power tuner...the choice is yours!
.....I have a 3.5, 3.4, 3.3, 3.25, 3.1, 3.0, 2.9, 2.8, 2.7 pulley and on two different pulley systems. If I could make a suggestion, your troffy case is the only useful place for all these pulleys. They look cool, but i bet you are using the smallest one you have and the rest are useless. The 3.4 is a good early mod. If your goal is low 13s, high 12s. Get an inexpensive modular pulley system, a 3.4 and a 3.0 pulley. You can compensate for more boost by adding timing. a 3.4 pulley with 23 degrees of timing advance is just as good as a 3.1 with 12 degrees. If mid 12s or 11s are your goal. Immediately get a ZZP 8-rib system and don't be cheap! Plan ahead on a 3.4, a 2.8 and a 2.5 pulley as you mod up.
....I spent $XXX.xx on a intake and exhaust setup thats loud and dirty. Do you want a loud car? Thats cool. Do you want more power? spend the money on something else. Your stock intake and stock cat-back exhaust sounds pretty darn good with other mods. You can hear that supercharger whine over the top of all that noisy air. Save money on fix-it tickets. Get a K&N panel filter and call it good until you make enough horsepower that it becomes an issue.
....I bought rockers, then decided to get a cam, then decided on a different cam. SET GOALS!! I can't stress that enough. If you want 12s, don't expect to do it with rockers or a VS cam alone, it can be done, but don't limit yourself unless you have specific tastes. A VS cam is great choice for a daily driver but you will need an intercooler to get to those 12s.. XP is a bit nastier on the street but still OK. XPZ is really no worse than an XP but requires a lot more money to work. In each of those two cases 12's are possible without an intercooler.
....Less is better. In hindsight, i could get a car into the 12s with about 6 mods and a power tuner. Injectors, XP Cam (& supporting hardware), SS intercooler, 3.0 pulley, Downpipe, Slicks, Powertuner. All of those mods can be done in two weekends for about $2500. After about $2500 i spent all kinds of money on an XPZ setup only to stop at 13.00 because one mod was useless without the other. I also payed a lot of money for a custom PCM, then an ICCU, and both are pretty much useless now that i have the powertuner. Your other mods, your supporting mods can all come later so that they make more sense. The exhaust you waited on will now be worth 4 or 5 hp, an intake may be good for 3 or 4 and so on. the right throttle body, a powerlog...add another 5 or 10. Now you can make huge progress for pennies by comparison! Those little mods that would have done nothing for you before are now suddenly worthwhile investments. If you had spent all your money on those before only to improve by a .1 on your 1/4 mile times you would feel pretty discouraged i bet. Sucks improving from a 14.9 to 14.8. But now that extra .1 means the different between a 13.05 and a 12.95, thats much more satisfying!
_________________  2001 white gt coupe with enough crap to make it run mid 13's with 3 bad pistons 2002 40th GTP sedan mostly stock
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