2.7i 731 head build

[Wanganstyle]

so what makes the 731 a worthwhile upgrade? if they have smaller ports then surely the laws of physics would say that the 885 would make more power cos it can shift more air?

sorry to be a drag. just interested in what must be a good upgrade some reason. need to make sure i choose the right head for my build.

731 is a head that happens to match the early style eta pistons to allow bottom end to stay full eta and have reasonable compression for running NA. It can be worked but if you have 885 next to it the 885 is more advanced, flows better stock vs stock.

I refreshed a complete 1985 Hardy and Beck 327"s" euro engine with built 731 head and euro bottom end with balanced 2,7L crank+rods and 10.5:1 pistons. This combination makes easy going power in the midrange, the cam is mild. Long tube Hardy and Beck headers fitted for proper vintage sound.

Don't expect more RWHP than a stock usa late model 325i unless you are changing the cam. The power range just drops down even lower in the rev range, a 3.46 final drive would be more proper setting than the OEM g260+3.73.

I dyno'ed last Dec with very mild timing setting; my own custom mapped garbage fuel chip (91 octane california garbage fuel).

The mapping chart is similar to a stock 325i but needs to be mapped adjusted differently for timing and fueling vs a 885 head setup. Hope mrkd has a running 2.7L euro 731 engine in cdn to map in person instead of experimenting remote on somebody's fresh built motor.

[e30leigh]

731 takes a fair bit of work to be worthwhile over the 885.

the 885 flows a fair bit more but ports are quite a bit larger so not suited for small cc M20

731 came in e30 323i and late e30 320i

so what makes the 731 a worthwhile upgrade? if they have smaller ports then surely the laws of physics would say that the 885 would make more power cos it can shift more air?

sorry to be a drag. just interested in what must be a good upgrade some reason. need to make sure i choose the right head for my build.

[2mAn]

he is running long tube headers which I hear don't really make much of a difference. Realistically I am hoping to get somewhere around 145-150 whp. Stock I will be lucky to make 100 whp.

Ive heard long tube headers are good for torque. Ill know first hand once I install the set thats sitting in my trunk.

I dyno'd my car bone stock and made 90whp and 133ft/ lbs of torque. I also was hoping for 100whp :( Ill be back on the dyno once the headers are on. Ive got an ebay chip, and 2.5" exhaust with no cat right now. Chip made a big difference, exhaust was minimal but it sounds so much better now

[Gary Horneck]

Well I will wait and see then. Not really into doing the harness swap. Sometime this season the 323i carbureted manifold will be going on, with a Holley 4160. A MSD 6AL will control spark, making the ECU an ugly paperweight.

[I got it, yes!!]

Yes there is, he gets sick sometimes, so be patient. His chip is definitely worth it if you dont feel like doing the whole harness swap.

[Gary Horneck]

So there is actually a MarkD chip for this swap? I emailed him about it and never heard back. Its not on the MarkD website.

[I got it, yes!!]

Also, I had the swap before the chip, and it was still fun, that chip just wakes it up even more!

[I got it, yes!!]

I have a 731 head, eta block, 3.73 LSD,with the MarkD Chip(for this swap) for the 027 ECU. I love it. I have walked(just for reference) a stock 325i E30. (He maintained it well). As stated in the above link, it makes drivability much better and is just plain fun!

[Gary Horneck]

I just finished my 1987 325e - 2.7i/731. The 731 head was off a 1984 323i EU, recently rebuilt, and I have the 4-barrel intake that goes with it also (but not installed yet). TB and intake from a 325i, adjustable FPR @ 65lbs, stock injectors, CAI. Running a Dinan chip in the 027. With the 3.73 lsd, it gave it a nice mid-range boost, which is what I wanted. The car is a dedicated Autox/Rallyx car so its either floored, or not floored. Would be nice to have it rev to 6k, but @ 5300k its doing about 50, so its a nice upgrade.

[pantelones]

I don't have any first hand experience, but I have some useful information...

http://www.e30tech.com/forum/showthread.php?t=52085

[2mAn]

watching this as i have similar plans for my eta, but with the higher comp pistons (11:1)

[MrNatural]

2.7i 731 head build

731 came in e30 323i and late e30 320i[/quote]

actually they came in the e21...

http://e21.tricord.be/e21/about.php

[digger]

731 takes a fair bit of work to be worthwhile over the 885.

the 885 flows a fair bit more but ports are quite a bit larger so not suited for small cc M20

731 came in e30 323i and late e30 320i

[e30leigh]

this is all very interesting.

sorry for the ignorance. but the 731 head are they off the 320's?

im asking as im building a motor. its a 2.5 turbo. kinda off topic. not to steal away from this. but i was going to run an 885 head. but might rethink if they 731 is ment to be higher flowing?
i assume thats the reason behind using this head? am i right in thinking they can be found on 320's? i think i have both an 885 and 731 sitting on the bench at work.

thanks for the help. and good luck with your build man. sounds very interesting.

[MrNatural]

Here's my .02....I've done a bit of this for my '87 eta. I got a euro 320 head (same casting as eta 200) with a 260 degree cam and dual valve springs about five or six years ago (Couldn't find a 731) had it decked and valves ground slapped it on with a 3.25 lsd and it ran pretty good, quick take off and pulled pretty hard to about 70 but nothing extreme. Finally got around to the motronic 1.3 upgrade and all the i stuff...wow! It's like a different car. I haven't dyno'd it but it pulls very hard. When you guys do the ecu upgrade you'll see the results. No need to to chip the eta computer (I've done that) it's not that big of a gain compared to the 173 ecu.