'2.7' vs '2.8' stroker

[mkcman17]

wanted some input as to some stroker options. plan on rebuilding my motor as a summer project, and want to up the displacement while it's apart.

i already have an eta crank, clean and ready to go. however, i'm under the impression that without custom pistons i'm limited to a lower cr. are there any rod/piston combos that would yield a better n/a cr?

i am talking to a guy about picking up an m52 crank, which with minor adaptation, can run b25 pistons and eta rods for a 2.8L and 9.7cr.

obviously it would be 'cheaper' to stick with the eta base, but is it worth the extra money/adaptation for the 2.8?

[e30trooper]

Mike, to fix the compression drop when using a 2.7l block you use a 323i head , it keeps the etas compression to 9.1:1 , with a 325i head it drops to 8.1:1 (ish) that is good for boos. Or find some SETA pistons ( 88 325 ) only. Plenty of ways to do it.

[mkcman17]

I'm cheap, ben. I'm not buying a new head when my current 885 is very clean. super eta pistons or rods?

[e30trooper]

I'm cheap, ben. I'm not buying a new head when my current 885 is very clean. super eta pistons or rods?

Super eta pistons , rods , and eta crank with your head.

Theres 1XXXXXXXXXX's threads on it

[e30trooper]

you need these ,http://www.r3vlimited.com/board/showthread.php?t=197325

[mkcman17]

I know the 2.7 has been covered, but I'm asking vs the m52 based 2.8

And why the hell would I want a 731 head?

[The Humjet]

731 heads flows less and 885 heads has lower cr so whatever route you take it won't make a difference on the day when your car is put on the dyno as each cylinder head you use with the eta block has its faults. I'm currently in the middle of a stroker swap myself and since the 731 head is cheaper here in Australia I've gone for that, but ill be fitting larger valves from the 885 head so I can get the higher cr and better flow.

From what I heard 731 heads arnt very common down where you are so I'd just keep your current head and throw it onto the eta block, although it does result in low cr it will do just fine and would be a decent improvement over your current engine, unless you want to get custom pistons and up the cr which I think is a waste of money as turbocharging that setup will be more worthwhile

[Danny]

You could just get custom pistons with the eta crank and i rods and make a 2.8l.

[The Humjet]

would have to bore the block to get that result?

like mkcman17 mentioned earlier he is short on money so be thing to do is buy an eta block from the junkyard recondition it with new bearings and rings and plop his 885 head ontop and then he is good to go. And if you want more power you save up for a turbo and then the only thing that can keep up with him is a big booster

[mkcman17]

Although i've yet to ride in a stroker vehicle, i've heard that doing a basic 2.7 will still get pulled on by healthy b25s. It's not that I want to cheap out on the motor, but I have plans to swap in a couple years if I still have the car/things dont change.

[Pedaaa]

Don´t use eta pistons for your 2,7. With those you can´t get a really good performing engine.

Use your eta crank and rods.
Then get some 325i pistons. With that combination you need to mill off your block for 2mm.
Because of this modification, you need to get a adjustable cam gear, to get the right timing again.

If using non-cat 325i pistions you will get a CR of 10,3
If using cat 325i pistons you will get a CR of 9,4

either way this combination will give you way better performance than any eta-piston combination can do.
(Thats the typical way the 2,7L engine is built in europe)

[Sirotto]

Don´t use eta pistons for your 2,7. With those you can´t get a really good performing engine.

Use your eta crank and rods.
Then get some 325i pistons. With that combination you need to mill off your block for 2mm.
Because of this modification, you need to get a adjustable cam gear, to get the right timing again.

If using non-cat 325i pistions you will get a CR of 10,3
If using cat 325i pistons you will get a CR of 9,4

either way this combination will give you way better performance than any eta-piston combination can do.
(Thats the typical way the 2,7L engine is built in europe)

You correct my bad! :oops:

[Pedaaa]

No, the pistons will not hit the head, because you are using the shorter 130mm eta-rods!

You think of using the 135mm i rods, only then the pistons will hit the head...

With eta crank (81mm) + eta rods (130mm) + i pistons , your pistons will be located 2mm too low at top dead centre.
Therefore you need to machine the block off 2mm.

It definitely will works this way.
(i know what i am talking about, i have such an engine 186rwhp, 214hp)

This combo is definitely a more efficient stroker than any eta piston 2,7 conversion could ever be:
Eta-Pistons + 885 head: way too low CR, only good for turbos
Eta-pistons + 731 head: too small valves, too less flow
super eta pistions + 885 head: too low CR, similar like the solution above, but still not good.

[The Humjet]

Never heard of that setup before but it does sound interesting and if your saying you have done this before then I would have to trust you on that theory, with the adjustable cam gear is that used to re-tighten the loose cam belt due to shaving the block? sorry if its a dumb question I don't know how adjustable cam gears work.

Still for me I'd get a eta block keep it like that for a bit and collect parts for a turbo build it isn't really worth spending money on a NA m20 IMO

[mkcman17]

what about custom 137mm rods? I've driven turbo m20s, and they're absolutely bonker...just not what I'm looking for at the moment.