euro eta questions

[2mAn]

Im trying to get clarification on a few things.

I found someone selling some high comp euro eta pistons and I'm considering getting them, but in my research I found this thread

http://www.e30tech.com/forum/archive/index.php/t-103356.html

"Early Eta's up until Sept. 1985 had a compression ratio of 11:1. The blocks of these engines is stamped 27 6KA. From 9/86 the compression ratio was dropped to 10.2:1 and these engines are stamped 27 6EB."

Ive cut and pasted the post im most concerned about. Theres a year between to the two dates listed, I'm assuming it's a simple typo and 9/85 is the cutoff time. Is this true?

What was the power difference with the higher CR?

Why?

Well, I'm considering building a motor with a 731 head and the euro eta pistons, but being my car is an 86, maybe im already fortunate enough to have the high comp pistons. It's not likely, but I figured it doesnt hurt to ask.

While we are on the subject, has anyone built an m20b27 with the high comp pistons and a 731 head?

Thanks

-Simon

[e30trooper]

id like to know some of this info to. I know of a euro eta around here. Might be worth it to pull those pistons :D

[cheapshot]

I cant comment on the year gap but I can add to your question about a high compression 731 2.7i. Mark Welch, a bmw builder here in town, put one together with 10.5:1 pistons and a 288 cam and it screams. I drove it about a month ago and immediately sourced a 731 head for my eta. It is at the machine shop now and I will be doing the same thing as soon as its ready to be picked up. The motor he built wasn't a straight eta head swap, it has a forged crank and custom pistons, both of which should make no hp difference.

Wait, is your car a euro car? If not, it should have the 9:1 pistons.

[1fastm50]

why not use the 885 head instead of the 731 head?

[2mAn]

the 885 head has nice big ports, but the design of the stock eta pistons and the design of the 885 chambers arent designed for each other. the super eta is another story, but most of us dont have super eta's. the 731 head is designed with the same type of combustion chamber and there is also no loss in compression. combine that with a piston that increases compression and it should be a nice torquey combo.

[cheapshot]

why not use the 885 head instead of the 731 head?

You absolutely can use the 885 head. As the OP stated though, you will loose compression. You can counteract this by shaving the head and the block and using a thinner HG. From what I can tell, this will net you around 8.5:1 CR with the stock eta pistons. Not bad at all but there is considerable expense and down time in going that route, unless of course you have a spare motor. The 885 head does flow better than the 731 but from what I have seen, with the CR of the 731 and eta bottom, the hp at the wheels are relatively the same. I decided to go with the 731 instead of the 885 to avoid pulling the motor completely out and machining the block. If you are building a motor to drop in or are not worried about downtime or cost, I would go with the 885 set up mentioned above.

[wakdog]

I have recently built a 2.7L M20 for track use:

ETA bottom end with Euro 10.2:1 pistons
731 head ported
Hartge throttle body (63mm butterfly as far as i am aware - 3mm bigger than b25 tb)
Match ported b25 intake manifold
Custom extractors -> 2.5inch exhaust
1.5L surge tank with bosch 044 pump
22lb injectors
AFPR running 3.5bar
Megasquirt 2 ECU

Here is a shot of the dyno graph:



(not really sure whats up with the jump and dip in power but it isnt noticable while driving...)

This setup is running a stock cam atm, im in the process of getting a 288 degree cam for it which should give me a decent chunk more power, but as it is there is soooooo much torque and it is so usable, also the fact its in a 2250lb car helps...

[2mAn]

whats the torque curve look like? im curious to see what the cam does as well

[cheapshot]

wakdog, build thread??

[wakdog]

ill make a build thread when i can get round to taking some photos, car is constantly evolving so i may as well start it now...

[cheapshot]

Do it! Also, were you running the b23 or b25 cam?

[2mAn]

UPDATE: I spoke with someone who has more knowledge. Apparantly the 11:1 setup might have problems with piston to valve contact when using the 731 head. Ideally this would be the setup to use because I see no point in installing higher comp pistons when using a stock 200 head. My goal is a car with an abundance of low end torque and a powerband that pulls to 6000rpms min. I have both pieces lined up (euro eta pistons and a ported 731 head), but theres a few things holding me back from splurging on it, mainly the fact that I have two other projects and my eta is my daily. im sure wakdogs build thread would convince me to do it...

[acolella76]

I have recently built a 2.7L M20 for track use:

ETA bottom end with Euro 10.2:1 pistons
731 head ported
Hartge throttle body (63mm butterfly as far as i am aware - 3mm bigger than b25 tb)
Match ported b25 intake manifold
Custom extractors -> 2.5inch exhaust
1.5L surge tank with bosch 044 pump
22lb injectors
AFPR running 3.5bar
Megasquirt 2 ECU

Here is a shot of the dyno graph:

(not really sure whats up with the jump and dip in power but it isnt noticable while driving...)

This setup is running a stock cam atm, im in the process of getting a 288 degree cam for it which should give me a decent chunk more power, but as it is there is soooooo much torque and it is so usable, also the fact its in a 2250lb car helps...

This could DEFINITELY be improved by using an 885 head instead of a 731 head. My old stroker had flat top pistons, an 885 head, and a 272 cam and put down 8whp less than you, and that is without a tune!

The compression lost by using an 885 head vs a 731 head is so negligible it's not even funny, and especially with higher compression pistons there is no reason not to go with an 885 head.

[wakdog]

My biggest issue with my setup is going to be valve clearance with these 10.2:1 pistons, looking at the lift of the schrick 288, im not 100% that its going to work with my current pistons.

The main reason im using the 731 head still is that I had it running on my 2.3L motor before and it cost me nothing... If i picked up an 885 head id want to clean up the ports and make it nice before using it, and in Australia an 885 head goes for big $$$. What ill probably do is track this setup for 12 months or so and maybe source an 885 head and some custom pistons that will allow me to run a proper cam....