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View Full Version : Requesting 325i Head Rebuild Advice


Spalding
07-14-2006, 11:38 PM
I have a euro import 325ic that needs some head work. It’s an 03/87 build date.

I am considering the following:

• Upgrade to larger North American E30 radiator
• 272 Cam
• Port/Polish the head with matched intake
• Header
• Remus exhaust
• M50 or S50 injectors
• Chip: Mark D or Turner

The bottom end appears strong and still has a nice factory cross hatch in the cylinder walls.

So, I am curious if these modifications are a good idea? Is the return on investment in terms of horsepower and torque worth it? I want to avoid modifications that are going to cost a lot and give me 2 horsepower.

Lastly, is there any reliable way to determine if the European M20b25 is different than the North American version? I have read conflicting reports of higher compression and flow improvements in the head.

Here is a pic of my car:

http://members.shaw.ca/e30/Alpina.jpg

Jordan
07-15-2006, 07:34 AM
There is absolutely no point doing a P&P, cam, and headers on a 2.5l bottom end.


compression varies, but your head is the same as every other 325i.

static
07-15-2006, 09:33 AM
save some dough and go turbo for significant hp/$ ratio.

i heard m20 heads don't flow very well

you can also stroke it to 2.7 or just swap for a (better) M50/S50

BTW, car looks very nice! What bodykit is this?

Spalding
07-15-2006, 11:53 AM
There is absolutely no point doing a P&P, cam, and headers on a 2.5l bottom end.

Is there any point doing a chip with a stock head & bottom end? Are the gains really close to 14hp?

Spalding
07-15-2006, 11:57 AM
save some dough and go turbo for significant hp/$ ratio.

i heard m20 heads don't flow very well

you can also stroke it to 2.7 or just swap for a (better) M50/S50

BTW, car looks very nice! What bodykit is this?

I am familiar with the swaps and how much better the hp/$ ratio is. I want to keep a factory look to my car so they are pretty much a no go. I have been thinking about a stroker rebuild but done right the money is big and the hp seems to be 230 max. So that ratio is not good at all.

The kit is a front euro spoiler and m-technic sides and rear apron / spoiler.

Thanks!

///M-TRD3
07-15-2006, 12:26 PM
Is there any point doing a chip with a stock head & bottom end? Are the gains really close to 14hp?

I always hear nothing but good things about chipping M20's, and that they are much more responsive and therefore feel like a power increase.

Mark D for the win, altho I cant say how much of a difference it is between his 91 oct. chip vs. the 93oct. rated for bigger injectors.

Hopefully someone can chime in and say if the drive/power difference between the two is noticeable enough to warrant the "little" more you'll pay at the pump. *th-up*

Jordan
07-15-2006, 12:44 PM
Chipping is very worth while on a E car.

Not so much on a I car, but still OK.

You don't get 14hp gains. You get 1-3hp gain at the peak, and will maybe see 14hp gain under the curve. Basicly they give you more power throughout the power band, and as the rpm varies so does the gain. All chips are typically rated as the max gain @ xxxx rpm.

IE take a stock m20's figures:

168hp@5800
160tq@4300

and a JimC chip (for example) has a claimed gain of:
+15hp@5000
+15tq@5000

You honestly won't notice any real difference on a otherwise stock I car. When I say stock I mean no internal modifications. Most boltons are worthless, and are no better then stock.

You can make a m20 make alot of power, but not without alot of work, and a sizeable chunk of change.

Spalding
07-15-2006, 01:15 PM
Ok. The whole goal with this car is small and tasteful modifications.

Since the head is off and needs to be rebuilt is there anything I should consider doing? I don't want to waste my money on useless changes.

I am already replacing all the worn components. Hoses, water pump, t-belt, filter, plugs, wires, motor mounts etc will all be done.

Should I buy new injectors or have the existing ones cleaned and flow matched?

///M-TRD3
07-15-2006, 01:58 PM
Jordan do you think theyre would be a noticeable difference or benefit to go with the 93oct. Mark D and upgrade to bigger injectors, over his normal 91 oct. chip upgrade?

Jordan
07-15-2006, 03:04 PM
I've never had the 91 chip in anything.

Back before I built my stroker I had his 93oct chip in my 2.5L m20 with extensive headwork. It was a notable gain. (the chip)