731 head for NA eta?

[whitebulat22]

I have an 86 ETA and in a perfect world it will be making 250 WHP through natural aspiration in the future. Since the 885 head doesn't match the eta pistons and drops compression a fair amount I've been thinking about trimming down a 731 head to more easily reach compression around 11 to 1.

I'm trying to do as little work and money spending as possible so I'd rather not go get some I pistons. I know the 885 is a superior design but is a 2.7i + 731 with a big cam / valves, high compression thinned head (I'm buying head studs of course) and a full computer tune realistically and reasonably gonna be able to get near my goal?

[kickinindian]

just get a junkyard b25, add s52b28 crank, mild cam, squid tune, and you still wont get 250hp...m20s do not make alot of power NAed.

but what i just explained has been pretty fun for me so far feels like the engine that should have been in the car

[digger]

I have an 86 ETA and in a perfect world it will be making 250 WHP through natural aspiration in the future. Since the 885 head doesn't match the eta pistons and drops compression a fair amount I've been thinking about trimming down a 731 head to more easily reach compression around 11 to 1.

I'm trying to do as little work and money spending as possible so I'd rather not go get some I pistons. I know the 885 is a superior design but is a 2.7i + 731 with a big cam / valves, high compression thinned head (I'm buying head studs of course) and a full computer tune realistically and reasonably gonna be able to get near my goal?

its alot of effort to get a 731 up to scratch but its certainly possible to make 250whp in absolute terms using a "731" head as a start point.

However you are dreaming if you think it can be done with little work or money. you are talking complete new induction system and exhaust plus extensive head work, new valvetrain etc and probably new pistons at the end of the day. you'd not really want to use ETA rods either as with a relatively small m20 you will need to turn 7-8k rpm to make those hp targets and this might be well above the standard rods.

[M-technik-3]

Or just go 24V

[nando]

is a 2.7i + 731 with a big cam / valves, high compression thinned head (I'm buying head studs of course) and a full computer tune realistically and reasonably gonna be able to get near my goal?

No.

[Gary Horneck]

You can get to 200, but getting past 200 is a big job. I make 25hp more with a 885 head over the 731 on my eta. Compression is fine. Car is a beast.

[whitebulat22]

I accept my fate that 250 wheel isn't happening without a full built motor or just a different one. 200 is plenty enough for me honestly but just for sake of future ventures is building a bottom end for my car able to accept the revs needed gonna be significantly more expensive than a full swap? 24v or LS etc. doesn't seem to me like it'll match the at least 3k figure I feel I'm gonna need to hold the NA power and in fact both seem like a lot less, does this match your guys' past experiences?

Ex. something ridiculous like an S54 in an e30 would create my dream car and it's starting to seem like that's similarly priced to what I would need for a NA m20 getting close to stock power.

[Gary Horneck]

I did nothing to my bottom end, other than rings and bearings, (its a 235k e lower end), and my fuel cut-off is 7,000. How much higher do you need to rev?

[nando]

I doubt it would even be 200. you haven't mentioned how you will tune it.

Gary, I'd love to see a dyno of your motor.

[ForcedFirebird]

I doubt it would even be 200. you haven't mentioned how you will tune it.

Gary, I'd love to see a dyno of your motor.

I believe it. 20-ish whp seems like a common gain for an eta with 885 head for me. Strongest stock eta we dyno'd was 124whp with just accy delete and open exhaust, same motor made 145whp with 885 head (and 178wtq o.0). Typical 2.7i is in the 140's (about the same as a tired b25). Fresh b25's have been in the mid to upper 150's.

Pretty sure I have the dyno plots saved if you would like to see them.

[whitebulat22]

I'm thinking 7k revs via performance head and 272 ish cam and thinned head compression will be enough to make me plenty happy for the time being if my non forged crank and normal rods can take that. I guess my long term goal is to experience a hot m20 while not undergoing budget breaking bottom end work that will leave me too poor for any future engine swaps I might want to pull off.

In which case how often are m20s able to pull this off without engine building? I have about 150k miles. Thanks for sharing allyour experience guys.

[ForcedFirebird]

I have about 150k miles.

That's nothing lol. The odometer in my car has been broken at 174k miles for at least the PO and I (dunno, 5-ish years), I daily drive it, drive it to/from/on various Florida road courses and it still has plenty of life left.

Don't worry about trying to shave the head for compression, the gains are negligible. You would have to shave an extreme amount, just take off enough to clean the gasket surface and be done with it.

[digger]

I'm thinking 7k revs via performance head and 272 ish cam and thinned head compression will be enough to make me plenty happy for the time being if my non forged crank and normal rods can take that. I guess my long term goal is to experience a hot m20 while not undergoing budget breaking bottom end work that will leave me too poor for any future engine swaps I might want to pull off.

In which case how often are m20s able to pull this off without engine building? I have about 150k miles. Thanks for sharing allyour experience guys.

you wont need to rev to 7k with a basic 2.7 and cam, 6500 will be plenty as the power will have peaked by then.

[SkiFree]

poorly cobbled together m20s do not make alot of power NAed.

Fixed. As has been proved by digger and many others. If done properly, the M20 is very capable. The problem is kids cobbling together parts not made to work together. Recently I've been comparing it to nissan's L-block in terms of displacement via stroke and bore sizing (slightly more bore and slightly less stroke).

[ForcedFirebird]

If done properly, the M20 is very capable. The problem is kids cobbling together parts not made to work together.

It's not just kids. Internet persuasion for "popular" parts plays a huge role.