Which is faster?

[5KWattson]

I have about four 2.7i dyno charts.. only one of them is close to an M20B25, the rest are all lower in HP with a bit more torque. I think a good condition, strong running M20B25 will still be faster.

going to agree with you on that...i just didnt have a "good condition, strong running m20b25" ever haha

[Aptyp]

well, an I head on the e bottom end should yield E torque with I revs... right? whats the downside?

wrong, E has more torque due to intake plenum design and single exhaust... Which are both restriction when you're looking for top-end horse power.

[2.5-12]

wrong, E has more torque due to intake plenum design and single exhaust... Which are both restriction when you're looking for top-end horse power.

even still, added stroke and displacement *should* yield more hp.

my M20B25 runs very strong but I have been in a stroker 2.7i and that thing seriously booked.

[Syncro325is]

I think my I car definitely revved faster than my 2.7i(885head, I flywheel, 4.10, 86eta block and internals, low compression) I built it for boost, but am breaking it in N/A. Its definitely no slouch, and is not tuned for the stroke yet, but I still feel like my I motor was quicker.

Edit: I will report back when I put the stroker tune on it.

[2.5-12]

the stroker I rode in had a super ETA plenum and 19lb phase 3 ford injectors, stock I ECM though, I still stand by it being quicker than either of the 2.5i cars.

[Aptyp]

the stroker I rode in had a super ETA plenum and 19lb phase 3 ford injectors, stock I ECM though, I still stand by it being quicker than either of the 2.5i cars.

I like your gradual concessions. Just admit you don't know what you're talking about. There's a very specific question at the top of this thread without tons of speculations.


Metric Mechanic and Korman 2.7I builds are a lot faster, too...

[2.5-12]

I like your gradual concessions. Just admit you don't know what you're talking about. There's a very specific question at the top of this thread without tons of speculations.


Metric Mechanic and Korman 2.7I builds are a lot faster, too...

I will concede that the question being polled about: whats faster, a good M20B25 or a stock ETA everything with an i head on it? an I will be faster, yes.

I was talking about a different engine effectively, so yes. what I am talking about is irrelevant to this thread but I won't admit I don't know what I am talking about because I don't believe that statement is true.

[rcfanatic]

Nando, can you post your dyno sheets? I personally don't care either way which makes more power, but I bring it up because it puzzles me. How an engine with the same head, electronics, and lower displacement can make more power than the larger disp engine. I believe the CR and disp basically cancel each other out, so is it because the I has a better exhaust and lighter flywheel?

[morerevsm3]

I have a 327i, 2.7 bottom end, and 323i head, 325i intake manifold and throttlebody, as well as loom and ECU, 19Lb injectors, tuned length headers, 535i AFM etc...and is slower in a straight line than several 325i's, all with 3.91 diffs on a racetrack, I am putting a stock 325i in mine to get it faster

[rcfanatic]

323i head? From an E21?

[Iain]

Australia got Euro models (incl. E30 323i)

[morerevsm3]

Australia got Euro models (incl. E30 323i)

correct, 731 head from euro 320i/323i

[Wh33lhop]

I believe the CR and disp basically cancel each other out

Again, it's not quite that simple.

[nando]

Nando, can you post your dyno sheets? I personally don't care either way which makes more power, but I bring it up because it puzzles me. How an engine with the same head, electronics, and lower displacement can make more power than the larger disp engine. I believe the CR and disp basically cancel each other out, so is it because the I has a better exhaust and lighter flywheel?

because it loses compression, and because it has no quench area (VERY important on a hemi engine!), and because the rod ratio isn't optimised for the head/intake, and because everyone who does it is using a stock ECU with the stock or off the shelf chip, etc. etc.

here are the charts. Pay attention to the shape of the torque curve, which is a little more important than peak to peak numbers - especially since these are all on different dynos on cars from around the world. But the difference is still obvious.

this is a straight 885 head swap:


this one even has forged 9:1 pistons. Look how fast the torque drops off in the high RPM area. that's probably due to the rod ratio..


this one is even built with a cam - alpina 27x for 96kw/128hp, schrick 288 for 102kw/136hp


here's a 260,000 mile, M20B25 with a dinan chip, otherwise stock:


here's another bone stock M20B25


and anyone will tell you, a SpecE30 built M20B25 will make 150-160whp, all with stock parts.

The case for the 885 swap is obvious - you already have an eta, and you have the parts for the head or got them cheap. No harm in that. But it's still not going to be faster than a B25, unless you get lucky or their engine is worn out..

[rcfanatic]

Awesome - thanks for the dyno sheets and explanation. I think that pretty much puts it to rest