2.3 cam or 2.5 cam?

[yrureadingthis]

Hello,
Looking to build another 2.7i. I currently have a super eta and 2.3i out of a e30. I was wondering if the cam out of the 2.3 would be a better cam then the 2.5. I've already built a super eta w/ the full "i" top end and a 10lb. alum. flywheel and loved it. Was wondering if the 2.3 head and intake would be a good choice for better performance on a super eta? I'm not totally clear on all my facts with the 2.3 head. It's hard to find info on these motors. any help would be greatly appreciated. Thank you.
Joe

[Motorsports]

i've been doing a little reaserch of my own because i want to do the same but using the 325i head and intake. but i found a few things that might help you out. The head of the 323 is the same as the 320 which is the "731" head. which means it has much bigger inlet ports than the eta. It has the same size valves though which are 40mm inlet and 34mm exhaust. the combustion chambers are the same from the eta's 200 head so by fitting the "731" head in keep the same exact compression ratio.

[Madhatter]

yeah but he said a super eta. The chamber is different and so are the pistons. Putting the head on a super eta should result in the same problem as doing it on a 325i, the pistons will hit the chamber. Besides, the super eta head is a better flowing 885 head anyway, so unless you worked the 731 head to get it to flow as good (or better) than the 885 head, there isnt any gain to be had.

[SpecM]

the b20/23 cam has a higher duration, but smaller lift than the b25 cam

[Madhatter]

what is the advertised cam lift of a stock 325 cam?

[yrureadingthis]

Cool. Thank you. Now With more duration the upper rpm range will be stronger right? So if the 2.5 cam has more lift that means more flow which means more horsepower? Then what is the advantage of more duration? Just the power band is moved further up to work with a higher revving motor?

[digger]

has anybody actually profiled both cams to definitively show the difference?
Everyone seems to think using a 2.3 cam is the way to go but i have yet to see anything published online to warrant this but i have see documents which show the 2.5 to be bigger in both lift and duration.

[Madhatter]

its not in duration. even the factory manuals say it isnt. lsa is wider on the 323i cam, timing is different too.

[SpecM]

I say use the b25i cam

[digger]

its not in duration. even the factory manuals say it isnt. lsa is wider on the 323i cam, timing is different too.

you don't really want a wider LSA unless you want less midrange and smooth idle..........almost all the performance cams go narrower and those that don't usually don't for a very specific reason.

[E30 Wagen]

I'm planning on swapping a 731 head on my relatively low mileage eta block. Will a b25 cam work in a 731 head? I've done a lot of reading about this swap but don't think I've read a straight forward answer to that question. Are there are any gains from this? Or, would it be better to a run a completely stock 323i 731 head?

After reading about all this, the tentative plan for my eta is this:

eta block
731 head from later 323i
b25 cam, dual valve springs
I intake and exhaust
325i afm, ecu (173?)

My main goal is a steady power band, i'm less concerned with getting more horsepower at a high rpm.

[yrureadingthis]

I've done a little research on the differences of both cams and here are the specs i got.


2.3 2.5
duration 264 256
lsa 110 108
Lift 6.58mm 10.1mm

I found this online. Can't remember what site I found it on. Glad I wrote it down. hope this helps.

[E30 Wagen]

I've done a little research on the differences of both cams and here are the specs i got.


2.3 2.5
duration 264 256
lsa 110 108
Lift 6.58mm 10.1mm

I found this online. Can't remember what site I found it on. Glad I wrote it down. hope this helps.

Thanks. I guess my question now is to figure out which one would be best for a daily driver. I just want a very smooth running engine with steady power.

[digger]

I've done a little research on the differences of both cams and here are the specs i got.


2.3 2.5
duration 264 256
lsa 110 108
Lift 6.58mm 10.1mm

I found this online. Can't remember what site I found it on. Glad I wrote it down. hope this helps.

there is something wrong with those lift numbers

[accident]

Thanks. I guess my question now is to figure out which one would be best for a daily driver. I just want a very smooth running engine with steady power.

Fuck smooth idle. My 83 Rabbit was way over-camed, and while it idled rough, when it was actually moving it was like butter.