2.7i Pros and Cons

[jeffnhiscars]

I've put a lot of effort I. To deciding on intake and head layouts, but now that my 731 is in the shop it's time to discuss exhaust. I fully intend to go dual when the parts appear but I'm more interest in the exhaust manifold and down pipes.

Does anyone have side by sides with b27 and b25 exhaust manifolds ?

Given that I have a 731 what reasonably priced header options do I have ?

Should I just mate a stock b25 to the ETA manifolds ?

Etc etc

[digger]

different person with shot bearings

[Red_liner740]

Who said I was pulling the engine ?

You said the rod bearings are shot. How else will you rebuild it?

[jeffnhiscars]

you should get there with a proper tune

I do hope you are right :)

[digger]

I'm going to throw another curve at this never ending discussion. I'm about to put a 731 head off of a b23 on to my chipped but otherwise bone stock ETA. The head will have new +2 valves, new intake guides, a mild port, 323 intake & cam & b25 TB.

All the externals will be stock ETA and I'm hoping to dyno it as is and then after the head is on. This will be with all ETA externals other than the TB.

Anyone think I'll get b25 hp ?

you should get there with a proper tune

[digger]

i would find a good used engine and swap it, screw building a stock b25 when the cost to do a 2.8L is a relatively small difference

[jeffnhiscars]

If youte gonna go through the trouble of pulling the engine, might as well go 24v. They are dirt cheap now.

Who said I was pulling the engine ?

[Red_liner740]

If youte gonna go through the trouble of pulling the engine, might as well go 24v. They are dirt cheap now.

[jeffnhiscars]

I'm going to throw another curve at this never ending discussion. I'm about to put a 731 head off of a b23 on to my chipped but otherwise bone stock ETA. The head will have new +2 valves, new intake guides, a mild port, 323 intake & cam & b25 TB.

All the externals will be stock ETA and I'm hoping to dyno it as is and then after the head is on. This will be with all ETA externals other than the TB.

Anyone think I'll get b25 hp ?

[nando]

I would just rebuild the 2.5 bottom end unless you happen to have a seta laying around. the compression is a little lower but not significantly. as far as the extra displacement, it's only .2 liters. the stock injectors would work fine.

[crappycoco]

I'm in the same boat as OP. Bearings are shot - I also get the dreaded knocking. Took it to GAS in Berkeley, they told me the bearings are on their way out, but head is good.

So if I understand correctly:

- an ETA engine with an i head is bad, because the compression drops, due to inadequate pistons?

- a SETA engine with an i head is good, no compression drops or other problems? Do the 15lbs injectors keep up with the increase in displacement? Need to update the ecu map?

From what I've read up until now, the bottom end swap can cost you from 2-3k, but most of those estimates are based on the fact you're upgrading a SETA engine with an i head. What about our case? If you already have an b25 engine with everything, but just need to swap out the bottom end?


Edit: nvm, found this: http://www.e30tech.com/forum/showthread.php?t=48288

[digger]

You can't get any worse than a stock eta.......A 2.7i should make about the same power as a b25 if it's not high mileage and you fit the same induction as a b25 with a custom tune. Many m20 builds even big $$$ ones never get a custom tune and that's where many seem to lack. If you want more power you need breathing mods but the low compression means you need to limit how much duration you throw at it.

Also a small amount of compression doesn't make much difference at all, it's not like going from 8.8 to 11:1,people seem to get hung up on it

[Regnar75]

^ you missed the point man, people here are discussing whether to go 2.7i or rebuild his cammed m20b25, I think it would be difficult to find anyone claiming the 2.7i build is not an improvement over an ETA, and even more difficult to find someone who has done the conversion and wants to go back.

just read the 2.7i thread, its stickied in the m20 section


unless i missed you checking the sarcasm button?

[UgkNW*]

I was thinking about getting a 885 head for my 86 325e but after reading this....

It's pretty much pointless because the difference you would see you loose to the fact of compression.

[IronFreak]

True - but even the seta engines with 885 heads don't really end up with that much more power than a B25.

I'd agree with that. But from the position the OP is in, I think swapping in the 2.7 if its in good shape is a better route than rebuilding the 2.5.