2.7i Raising Compression?

[Luis325]

What is a safe way to raise the compression on my 2.7i?
I have stock 1986 ETA bottom with 885 325i head, and intake manifold. And wanted to raise the CP for more power. Im not planning to boost the car...

I was told to mill the head .20??

Thanks!!

[MrSpectre]

I or SETA pistons

[Luis325]

SETA i think they are the ones that came in the 1986 325es...

[jmc1590]

SuperETA in a '86 325es, no. At least not acording to RealOem. Did you do the e2i swap? If so, you should remember if the pistons were dished (std eta 9:1 pistons) or slightly raised (seta pistons, 8.5:1).

Based on your info, you compression should be right about 8.3:1. As far as raising the ratio, you have a few options:

1) Seta pistons: Not a huge gain, but piston is developed for the head.
2) i pistons: Require modification. Crowns need to be shaved down. Without modification, will strike your head.
3) Euro eta pistons: High CR flat top pistons. You'll lose about a point of C/R due to the i head.
4) Custom pistons: Tell them what you have. Tell them what you want.

[Luis325]

Im new to this... im still learning.
Ok i have the Std ETA pistons, With an 885 head. from a 1986 325es. With 1989 325i intake manifold,injectors, etc. and motronic 173ECu..

Me question is can i raise the C/R by milling the head?
And do i have to change the pistons i have?

[nando]

mill the head and get an adjustable cam gear - there's a thread about them in the feedback forum.

[jmc1590]

Yes, milling the head will raise your compression. In the situation that you mentioned earlier, .020" (or .5 mm) will add about .3 to your compression. (My math says in the range of 8.6:1). The only thing to watch for is the more you mill the head, the more the cam timing changes. If you mill too much, you'll need an adjustable cam gear to get your timing corrected.

[Luis325]

Ok so if I mill .020" ill be fine?
The truth is i did this setup to gain more power NA then the standard 325e engine.. But im finding out know that the compression is going to be very low for NA... But i dont want to boost the car, i like NA, and its a track car...
thats where milling the head option comes in to play. .
327i swap with a .020" head mill with a Comforti ECU chip, headers and full race exhaust
should provide better HP ???

I plan on adding in the future 272 or a 284 cam with 19lbs injectors.

Thanks for the help.

[nando]

you will definitely want an adjustable cam gear in that case

the 284 has enough lift on the intake side that checking valve clearance at TDC (and before/after) is critical. the 272 has more room but you still want to check it. You may consider enlarging the valve reliefs on the pistons 1-2mm before you put the head on.

[884door]

I doubt you could run a 284 cam with a milled head without custom pistons, the valves would probably hit the pistons.

[Luis325]

Ok but for a 272 cam i wont have any problems with .020 milled head?
And it should give me some decent power NA?

How much power can be had from my setup NA( with stock i cams)?

[Luis325]

LOL sorry for all the questions ive been reading allot of the posts and there so many ways to do the 327i swap and me not knowing much about C/R, etc im all confused.

[nando]

cutting the valve reliefs deeper isn't that big of a deal. you will want to check for clearance before you do your final HG torquing though!

as far as power, I don't really know. it's not going to make much more "peak" power than a stock 325i, because although the displacement is slightly higher the VE will be the same if you use the same cam. You will get more low end torque though, which means a fatter powerband in the low-rpm area.

[Luis325]

Ok! thanks,
So a 272 cam would help me allot in power?
At least its gonna have more power than an e...LOL

I guess my next step would be then to mill the head .020" cutt the valve reliefs , get a 272 cam and 19lbs injectors with a mark D chip a header and im good to go???

[Paukert11]

Rm racing has a good cam gear for cheap. http://www.r-mracing.com/catalog/pro...5719737e8d0dcd