M42 internals modification questions - BMW Forum

Autotechnica · 03-10-2004, 02:55 AM

I want to free up more high end in my '94 M42. The M42 E30 intake manifold had a larger diammeter manifold and the motor had a higher rev limiter and seemed to pull harder at higher RPM's than the E36 M42. I tried to swap the E30 M42 intake manifold into my car, but the hood wouldn't close. There's a difference of how the motors were mounted on the E30's and E36's.

Anyways, I want to match the intake ports with the intake plenum and throttle body, smoothen and enlarging the intake manifold divider/entries. I'm wondering if the intake manifold on the E36 M42 is a restriction and whether doing this modication will help free up some high end. Not to worry whether or not the gains are worth it. I'm basically getting it done for free.

Here's my concern. If the manifold outflows the head I'll loose power. If the head outflows the manifold and I enlarge it, I'll gain power. I assumed since the E30 M42 maifolds were larger in diammeter that the E36 M42's smaller intake manifolds were outflowed by the heads. Is it possible to only enlarge the shorter intake runners?

Any help would be greatly apprecaited. And I do realize that normally matching the intake plenum with the ports is done after headworks and cams. But like I said, it's no problem to do it since it's free.

Thanks,

Bryan

Furious · 03-10-2004, 02:58 AM

hey bryan welcome to BMW-forums.

hey guys welcome this guy and hopefully someones got an answer for his question,

yeah thats right Bryan , i dont .hahaha

Autotechnica · 03-10-2004, 03:07 AM

Thanks for the warm welcome! Looking forward to swapping info with all of you

Bry

bimmerfan620 · 03-10-2004, 10:45 AM

hey welcome brother.......hope you enjoy the forums....

Your going to notice a significant gain in power by porting the intake manifold, but not as much power as if you were to take the head off and completely port & polish it. See your head is where the most of the flow is needed to flow as much and as smooth as possible. With having a ported intake manifold, you are increasing it's ability to ram air into the head faster, thus less restriction, but at the same time the maximum gains are prohibited from being reached until the head is ported as well. So you see, porting the intake will make a difference now, and even farther down the road when you choose to port the head and possibly stick performance valve-train components. I can only say, do it, but make sure it's done right. If the ports are abnormally sized out of proportion, you will have a problem with the consistency of the flow, ie. the disturbance will create problems. Anyway, thats my way of putting what you are asking for.. Anything else, feel free to ask...

ps - porting out the intake manifold, will not cause you to lose power if you don't port out the head.....

Autotechnica · 03-10-2004, 01:28 PM

Thanks for your advice. I agree with how improper consistency will cause disturbance. However, you will have to see where the bottleneck is. Let's say the head flows 250CFM, no matter how big you port the intake manifold, the only amount that will flow to the engine will be 250CFM. Porting the intake manifolds too large will only slow down the air going into the intake ports if the previous statement is true.

So if I start porting the intake manifold now, it can either gain some power (minimal) or lose power.

It is a gray area between flow and velocity of an intake manifold. Sometimes guys would gain power by increasing the runner length, or shortening it. I just need to know that the restriction is the intake manifold and not the heads.

Thanks for your advice.

Bryan

WickedBimmer · 03-11-2004, 05:46 PM

hey bryan, and welcome... quick question for ya...
what model is ur car? makes a diff with the compression and airflow being either the 4 cyc or the 6 cyc... makes a diff as far as the parts etc...

i really like all ur mods on ur site.. good job!

do u have any more pics of ur car?
thanks

Wicked Bimmer

Autotechnica · 03-11-2004, 06:28 PM

Quote:

Originally posted by WickedBimmer@Mar 11 2004, 07:26 PM
hey bryan, and welcome... quick question for ya...
what model is ur car? makes a diff with the compression and airflow being either the 4 cyc or the 6 cyc... makes a diff as far as the parts etc...
i really like all ur mods on ur site.. good job!
do u have any more pics of ur car?
thanks

Wicked Bimmer

It's a late model M42 OBD 1 318i (1.8L 16V DOHC), same year and model as your car, but in 4 door. "Engine" dyno'd not "Chassis" dyno'd at 164HP@6500RPM and 160lbs*ft@4500RPM. Stock 318 is 138HP@6000RPM and 129lbs*ft@4500RPM.

Anyways, thanks for the compliments. It's nice to be noticed for the mods rather than a flashy body kit and big wheels. I'll get more pictures in the summer. I live near Furious. Like him, I have to deal with salt and snow on my car constantly during the winter season. I have a bad habbit of taking pictures only when my car is dirty

I'll snap some nice ones in the summer. I've actually had a lot done during the winter. I haven't been able to try out some of my suspension/chassis mods properly because I'm on 15" winter wheels, plus no traction in the snow :wink

cheers,

Bry

Autotechnica · 03-11-2004, 06:38 PM

LOL, I just realized there was a mistake in my "subject" heading. I'm not stupid! I do realize that porting the intake manifolds and throttle body does not constitute as being internal modifications :wink

Thanks, just wanted to clear that up so you guys don't think I'm a dummy.

Bry

Furious · 03-11-2004, 08:12 PM

hey Bry my mechanic with the 318 said hes never heard of anyone doing this but he said it is possible to port it out, however there isnt much you can really take out. he said hed have to see again (next time he takes one apart) but last he could remember (not like hes ever thougth of it to begin with) that there wasnt much to take off of it.
he also said that you have to get it done pro, he said any mistakes could actually cost you HP.

Autotechnica · 03-11-2004, 09:34 PM

Quote:

Originally posted by Furious@Mar 11 2004, 09:52 PM
hey Bry my mechanic with the 318 said hes never heard of anyone doing this but he said it is possible to port it out, however there isnt much you can really take out. he said hed have to see again (next time he takes one apart) but last he could remember (not like hes ever thougth of it to begin with) that there wasnt much to take off of it.
he also said that you have to get it done pro, he said any mistakes could actually cost you HP.

Thanks Mark,

Looks like I should go and have a talk with your mechanic. It's difficult to find any mechanic who drives a 318. He should more or less be able to solve all my problems with my car hopefully.

After reading that, I'm somewhat turned off by porting the mainfolds. My friend does really good work on Honda's, but who knows. You get power gains with $80 headers for Honda's.

Bry

Furious · 03-11-2004, 11:53 PM

no worries well go talk to him , they will solve all your problems.