Ok, finally got the top end swap done. To anyone that wants to do this, be ready for some labor. Took me a good 60 hours to complete the disassembly and install. I have had many problems with it... including fuel injectors spraying fuel everywhere, broken bolts, o2 sensor crapping out, shredded s/c belts etc., but the end result...totally worth every bit. The car hauls now with only around 5-6 pounds of boost.

I am also having the same shifing problems that drummerboy is having though. It doesnt want to shift out of first, and when it does, it is very slippy. But the car will not get traction until around 50-55 mph!!

Tune is coming on saturday at our local mod day, hopefully then it will be just right!!

Sounds awesome.

What did you do about your PCM programming?
It sounds like you're running 4t65e-HD programming. Makes sense cause the HD shift tables won't WOT shift till like mid 40 mph... which probably exceeds the rev limiter for fuel and/or spark (theres two different tuner-adjustable rev cutoffs. one cuts fuel at a certain rpm and the other cuts spark).

I just did a top end on my YZ125. Took about an hour and I was back on the trails....

Be careful parking it on hills, you never know when that kickstand will let loose.

har har

You mean "kick the bucket"


Rolling down a hill is a walk in the park for this thing. It's hit trees, had the engine flooded in a pond, been stuck in mud, flipped over, crashed doing wheelies, been ghost-ridden (not on purpose), and blown 3 top ends in 3 years.

The YZ is very unlike the wimpy GTP.

Perhaps the YZ is a sadomasochist and the GP wasn't?

Sweet man.. well I replaced the TPS on my throttle body and my shifting issue is gone... I did however have to replace the MAF sensor which was $175...

But it sounds like you had a bit of bad luck compared to me. I pulled the motor and everything, and the entire job was about 3 solid workdays, so maybe like a 25-30 hr deal total? And that included the cam install...

But man, it really is worth it. The first time I opened it up and heard the S/C scream, I was grinning from ear to ear. At WOT, I'm consistently pushing 8 psi, and I even saw a burst of 10 psi once... maybe it's that cam that's helping me?

Also you installed Pacesetters right?

yes, i installed pacesetters. Im not pleased with the sound of the car now, the crossover bolts were too short, and the exhaust clamps they sent were a joke (broke on the interstate).

I have a random shudder at idle now. The engine convulses slightly. There were no misfire SES codes so it must be something else. Any ideas?

Also, i will have pics up pretty soon

Dude, I don't like my exhaust tone anymore either. I didn't install Pacesetters but I have the Powerlog/Rear Ported Manifold, 3" DP and a custom catback with Dynomax superturbo mufflers, and it sounds pretty boss at idle but when revving it up or driving it's very raspy...

I'm thinking about buying some stock mufflers that don't have a sound chamber and throwing those on. I dunno though. Maybe it will grow on me? Are you getting any codes at all? My engine also shudders slightly but as you know I cammed it... so that's probably why.

drummerboy, do you have a resonator? If not, you might want to throw a glass pack on and see if that helps.

im not sure what im going to do about the exhaust.

But about the codes, lol...im throwing 10 of them. None of them explain the shuddering though.

You got a bunch of codes? Sounds like I ended up luckier than you. Hey I've been meaning to ask, did you reuse your L36 MAP, or are you using the L67 2 bar MAP sensor? That's the only thing that's been giving me problems and I can't figure it out.

I dont mean to sound like a jerk here but you guys have kind of made yourselves the guinea pigs of this project. I hope you do get it all straightened out cuz this seems like a very cool power adder for less than some of the other options out there. When you do get it ironed out I'm confident you will be the top resource for info for what/what not to do on this upgrade. two big thumbs up guys

p.s. exhaust on these cars is a real crap shoot isnt it?...I'm getting ready to try another set myself. I've spent more on the exhaust system on this car than any I've ever owned.

10 codes are they all related, what are they?

Having the wrong MAP sensor could cause a lot of issues... it depends on what the PCM is programmed for as to whether you should use the 1bar or 2bar sensor. Ideally you want the 2 bar for the M90'd setup so the PCM has more information to go from when in boost.

Since I have a '97 and thus the 4T60E tranny, my top end swap tune could not flash over to the GTP files, so I have to reuse the L36 MAP sensor. It isn't a big deal, it just means that at WOT, the voltage that the PCM reads is locked in at one single value. I did ALOT of research into this issue and also talked to several guys on clubGP that have done top-end swaps on 97 GT's, and they said unless you swap trannys, this is the best method.

i dont remember all of them, but they were all fixable. at least most of them. I deleted the Egr which set two codes, and there were others that were simple.

i used the L67 MAP

i dont mind being the guinea pig! I learned a lot and had a lot of fun doing it! Thanks for the props!

and yes, the exhaust is a guessing game. I just had it the way i wanted it, and now i hate it with the pacesetters!

Ok, i know it took a few weeks, but i finally got the car perfect, so i got some pics for you guys!

Sweet it looks nice...

Awesome man. There's a lot of top end swaps now.

Great pics. I got a question about the above one: Is that right after head removal or just before gasket reinstall? I'm still trying to figure out how anal I need to be about prepping the surface.

BTW, looks like the red theme is popular lately.

Only two, on this site at least!

Looks fantastic man! Nice work!

this is just after head removal. Just scrub the surface real clean prior to putting new head gasket on. Be very particular, i would not chance it. And make sure the arrows face the front of the motor (towards the belt).

Becareful not to scratch or gouge the mating surfaces. Otherwise you'll have troubles down the road.

i used a scotch brite pad and just scrubbed it gently, but firm. almost to the point i could see myself in the reflection!

whats all the small read wiring for? seems like it has no dirction and is wrapped around everything lol.

Probably oil pressure switch or some other sensor/doodad.

yeah, that is for an oil pressure gauge. it is now zip tied and hidden better than that

nice job on a scale of 1-10 what is the difficult of doing this? is there any book or thing you follow?

scale of one to ten, I give it an 8. Plan on a weekend for the job and then several days after that of troubleshooting, etc. This was my first significant mechanical job I've done on a car and it was quite the project. If you're not confident in your ability to do automotive work, don't do it.

x2. i would give it an 8 or so. You have to remove the heads, balancer, etc. Save your pennies and do a turbo or the ZZP SS M90 Kit, which is easier installation

You don't have to remove the balancer for a top swap do you? I wouldn't have if the cam didn't need to go in.

the crank pulley has to come out in order to run the 2nd belt. The pulley for the L36 only has one set of grooves for the acc. belt, not the s/c belt

Oops. The S/C belt grooves never popped into my mind.

So, you don't need to swap the balancer for the top swap, only if you want boost, right?

Yep. If you just want to use the S/C as a "hi-flow redesigned upper intake manifold", then no need to swap the crank pulleys!