Author Topic: Turbo M42 questions (Read 5365 times)

Boosted E30 · « **on:** August 23, 2008, 04:01:40 PM »

I just finished my m42 turbo build and have some issues. im running the Autronic Sm4 system, 42lb injectors, turbonetics turbo hot side is .48 i dont know the specs on the compressor side, internal wastegate.

Heres what i need help with the turbo starts spooling at around 2800rpm and on 5-7psi full boost is around 3500rpm but if i go up to 12psi or more i dont get full boost until around 5000rpm which i dont think is right. and the boost keeps building as rpms increase and then around 5500 the boost starts to bounce (if i set it at 14psi it drops to 12psi and then back up to 14psi again) i have tried different wastegates or just setting the boost with the wastegate but its still does the same. i have a greddy profec b spec2 boost controller and i played with all the settings on that nothing changes.

i also put in the cometic steel head gasket and head studs from Vac motorsports its 3 or 4mm thick and im wondering does the camshaft timing change? if so by how much does anyone know? this is my first turbo car and no one i know has done the M42 so help and ideas would be appreciated.

Also does anyone have a turbo manifold for this engine mines not the greatest. also what size should my exhaust be (down pipe to muffler)

bearsbmw · « **Reply #1 on:** August 23, 2008, 09:13:31 PM »

do you have a blow off valve?

bar73k · « **Reply #2 on:** August 24, 2008, 08:27:07 AM »

sounds like your boost controller is not set up correctly e.g. boost bouncing up and down

i have the same boost controller, once set up they work great

Boosted E30 · « **Reply #3 on:** August 24, 2008, 11:49:31 AM »

ya i have a tial bov with 7psi spring. i played with the gain and set gain settings as many ways as i could nothing changes it did it even without the boost controller.

nuvolarossa · « **Reply #4 on:** August 24, 2008, 12:03:59 PM »

you tried other internal wastegates, right? ( the other wastegate actuators were same psi as the first one?)

ose30 · « **Reply #5 on:** August 24, 2008, 12:41:37 PM »

Looks like your WG does not work properly. What comes to the cam timing 3-4mm additional gasket thickness does effect it. Adjustable cam gearing can help on this.

halcron · « **Reply #6 on:** August 25, 2008, 12:48:44 AM »

For your downpipe, its the bigger the better!! Get at least 2.5-2.75 inches. If you are able to use 3 inches, thats even better

strypt · « **Reply #7 on:** August 25, 2008, 03:10:47 AM »

Why aren't you using Autronics internal boost control? It's working very good plus you have the opportunity to set boost level vs throttle or RPM's or gear or...

Regarding the head gasket, like ose30 said it affects your cam timing but all M42's have adjustable cam gears so when you assembled your engine what did you set them at?

Boosted E30 · « **Reply #8 on:** August 25, 2008, 07:37:40 PM »

yup tried different acctuators, all that right now the exhasut is 2 1/4 but i will be changeing that to 3" once i get my new manifold. and the cams i set like your supposed to #1 intake and exhaust pointing towards each other and the back of the cams where its square is flat/flush with the head like its supposed to be so i dont think cam timing is the issue it was just an idea. i think the wastegate is the problem. i dont have the autronics boost controller hooked up i know it can do that though but you would still need a solinoide valve to controll the amount of boost pressure the wastegate gets right??? I talked with the guy i got my turbo from at majestic turbo today hes looking into it but ill probably just end up changing the turbine side of my turbo cuz how long it takes to spool up doesnt make sence and the turbo is mechanical so either it works or it doesnt and mine half ass works. What turbo would you guys recommend couple ppl said to use GT28rs or a GT2871 would that be ok?? like i said this is my first turbo car and no one else i know has done this engine so its been a hit and miss build but it hasnt worked properly from day one. So i am now gonna change my manifold turbo and do a big exhaust all the way back and we'll see what happens i guess.

strypt · « **Reply #9 on:** August 26, 2008, 01:51:08 AM »

Yes you'll need this little baby

Sounds like you got your cams about right, although I'd suggest you try and turn the intake cam slightly CW (seen from front of engine) and exhaust slightly CCW. Exact position will have to be found in dyno but this will give you a start.

I also suggest you change that DP before changing turbine etc, 2 1/4" is way too small and will affect your spool and if your backpressure is too high you'll have problems with controlling the boost aswell.
Remove the hood and exhaust and just put one 90 deg 3" bend straight up and go for a ride, quick and easy

Boosted E30 · « **Reply #10 on:** August 26, 2008, 07:18:41 PM »

ya i figured the DP and rest of the exhaust is to small so i did try just running the DP open but nothing changed. But i didnt try putting a bigger pipe on. but i gotta wait till i get a new head gasket cuz mine leaking so i figured ill just wait till i get my new manifold and head gasket and send my turbo out to get redone cuz my car will be down anyways for a couple weeks now so i may as well do it all and hopfully be done with it.

If i would have known about that solenoid i would have bought that instead of my greddy boost controller but to late now. as for my cams i will try that when i put in the new head gasket