Which is faster?

[rcfanatic]

A stock 325i or a 325e with i head? Assuming pistons, rods, etc are left alone. Just wondering if the added displacement of the 2.7L bottom end trumps the higher CR of a 325i, or if it's the other way around. I've seen a couple of curves on this forum, but it would be nice having a dedicated thread comparing the two by experiences and general discussion about peak torque, hp, power bands, 1/4 mile times, etc. Total area under the power curve..

Edit: For the poll let's say both cars are running 3.73 diffs

[2.5-12]

stroker is for sure quicker. even the Eta bottom end and rods were ludicrously over-engineered.

[Aptyp]

forgot the most important piece of that puzzle...


DIFFERENTIAL

E's have 2.79 and 2.93, but I's have 3.73 and 4.10

[rcfanatic]

Great point, I was wondering how long it would take for someone to bring that up. So let's say they are running the same diff

[2.5-12]

also, if you use an i head (correct me if I am wrong) on a normal ETA bottom end, you need Seta or I pistons so they don't hit the valves.

[5KWattson]

nope they clear, it enlarges the combustion camber and lowers the compression due to the I head has a combustion camber that mates with I pistons the E pistons are more concave which creates no other problem rather than lower compression

[Aptyp]

Really depends on the work then.

327i will have barely more torque, than 325i and will have lower compression. Than you have dual-mass flywheel... 325i would still be faster, than a backyard 327i. Chipping an E would probably be faster as well.

[5KWattson]

i think the chipped E with the I swap dont nicely would be a tad faster depending on tire,clutch,flywheel, and driver...its the higher TQ of the E that would make it close

[rcfanatic]

Power is torque x angular velocity (rpm). So if E with I swap makes more torque over the same rpm range - that would equal more power.. right? You have to figure that a stock eta starts to redline at 4500 rpm and an I at 6250. I've never seen the two stock curves side by side, but I'd be willing to bet that *up to* 4500 the eta makes the same if not more total energy than an I. Anyone have stock curves??

[5KWattson]

the I head on a E block can only be done with the I electronics so there fore it r3v's just as high...but as stated above there are other factors that work against the poor 2.7i flywheel,gearing and driver error

[2.5-12]

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

[rcfanatic]

Only downside is heavier flywheel (assuming same diff), but would like to hear from people who have driven both or have dyno sheets

[rcfanatic]

Well, upon quick calculation the eta compresses a tiny bit more air as well - even with the lower compression ratio

8.4CR x 2.693L = 22.6L
8.8CR x 2.494L = 21.9L

The 8.4CR value was taken from Kenika65's 2.7i swap writeup

http://www.r3vlimited.com/board/showthread.php?t=100939

So yeah, eta makes more power with I head and motronic 1.3, excluding drivetrain factors

[Wh33lhop]

Well, upon quick calculation the eta compresses a tiny bit more air as well - even with the lower compression ratio

8.4CR x 2.693L = 22.6L
8.8CR x 2.494L = 21.9L

The 8.4CR value was taken from Kenika65's 2.7i swap writeup

http://www.r3vlimited.com/board/showthread.php?t=100939

So yeah, eta makes more power with I head and motronic 1.3, excluding drivetrain factors

:???: that is not really how it works

If you really want to calculate full intake charge, it's (CR/(CR-1))*displacement, but that really doesn't tell the whole story anyway... of course the eta "compresses more air," it's both larger displacement and smaller compression ratio, both of which mean the intake charge will be larger. The calculation you are making is a little more meaningful than intake charge volume but it is still a very rough figure of merit.

[nando]

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.