m20 stroker confusion....

[modifiede30]

The compression ratio of a standard 2.5l is 8.8:1. The super eta is at 8.5:1. Mathmatically, if you drop the 2.5l down to an 8.5:1 compression ratio, you will only loose 1% of your max hp, which equates to around 2hp if using stock figures.

If you mate the more aggressive cam of the 325i and the ability to reach 6900 rpm's, these engines become much closer to each other in terms of performance if you ignore where the max torque kicks in.

The super eta stroker in most cases doesn't necessarily produce more hp or torque than a 2.5l, it just moves the power band to a more desirable location. If you're running the car on the street, having torque available much sooner is very nice. If you're on a track with sharp corners that require the engine to drop below 4500 rpm's, again, the stroker is nice to have.

However, if you're driving on tracks that have long sweepers or use it on the drag strip, I'm not sure the stroker is a great choice. I think to some extent, the reason for building one of these should be its use, not so much that you want to create more power, since it really doesn't unless you buy a kit or have significant machine work or customization performed.

There are many other options to consider when building a stroker from stock parts if you're willing to spend some time doing calculations and spending money on machine work. There are other pistons that will work if shaved, that can be used in combination with other rods to achieve similar results.

[Sean]

I think what would be interesting would be to take a NORMAL eta, and do some major headwork on it (this is what I think Josh (eurospeed)) is doing.

You pretty much make a normal eta head into I spec - create the extra oil journals, cam, springs, etc.

Then you'd technically have a 9.0:1 (or whatever the normal eta's are at) stroker. Which, would still be fairly modest in terms of compression, but would be a nice little engine.


Does anyone have dyno curves for a 325i engine versus a Super Eta stroker? I'd be interested in seeing it.

Here's something I just thought of - I have a complete 325i engine sitting in my garage, 182,000 miles on it, and I think it ran pretty good. But, I WAS going to tear it down and put the top end on my Super Eta to make the stroker. However - you bring up something about. I can either do that, or just swap the engine in, and essentially have the same amount of horsepower - right?

I'm thinking I'll probably still do that, switch the top end onto my Super Eta, cause the low end torque would be more fun at an autocross. But, it's something I could do, since it's the same amount of horsepower.

[modifiede30]

The only way to make an eta head the same as a 'i' head properly would be to install all new valve seats. I was thinking of doing this to a 'i' head using a combination of m30 and m20 valves to increase size. I was quoted costs in the range of 1500 - 2000. Just isn't worth it.

[modifiede30]

Here's something I just thought of - I have a complete 325i engine sitting in my garage, 182,000 miles on it, and I think it ran pretty good. But, I WAS going to tear it down and put the top end on my Super Eta to make the stroker. However - you bring up something about. I can either do that, or just swap the engine in, and essentially have the same amount of horsepower - right?

Not quite. If you use the super eta head, you need to exchange a few parts - springs and cam. If you have the 'i' head, and don't want to do anything with the heads, just swap them. However, like I said before, to increase compression a bit, have it shaved - and if you can, have it ported.

[NC325iC]

I think what would be interesting would be to take a NORMAL eta, and do some major headwork on it (this is what I think Josh (eurospeed)) is doing.

You pretty much make a normal eta head into I spec - create the extra oil journals, cam, springs, etc.

Then you'd technically have a 9.0:1 (or whatever the normal eta's are at) stroker. Which, would still be fairly modest in terms of compression, but would be a nice little engine.


Does anyone have dyno curves for a 325i engine versus a Super Eta stroker? I'd be interested in seeing it.

Here's something I just thought of - I have a complete 325i engine sitting in my garage, 182,000 miles on it, and I think it ran pretty good. But, I WAS going to tear it down and put the top end on my Super Eta to make the stroker. However - you bring up something about. I can either do that, or just swap the engine in, and essentially have the same amount of horsepower - right?

I'm thinking I'll probably still do that, switch the top end onto my Super Eta, cause the low end torque would be more fun at an autocross. But, it's something I could do, since it's the same amount of horsepower.

you should swap the heads then maybe give her some boost some day then youd have a power house

[Sean]

I think what would be interesting would be to take a NORMAL eta, and do some major headwork on it (this is what I think Josh (eurospeed)) is doing.

You pretty much make a normal eta head into I spec - create the extra oil journals, cam, springs, etc.

Then you'd technically have a 9.0:1 (or whatever the normal eta's are at) stroker. Which, would still be fairly modest in terms of compression, but would be a nice little engine.


Does anyone have dyno curves for a 325i engine versus a Super Eta stroker? I'd be interested in seeing it.

Here's something I just thought of - I have a complete 325i engine sitting in my garage, 182,000 miles on it, and I think it ran pretty good. But, I WAS going to tear it down and put the top end on my Super Eta to make the stroker. However - you bring up something about. I can either do that, or just swap the engine in, and essentially have the same amount of horsepower - right?

I'm thinking I'll probably still do that, switch the top end onto my Super Eta, cause the low end torque would be more fun at an autocross. But, it's something I could do, since it's the same amount of horsepower.

you should swap the heads then maybe give her some boost some day then youd have a power house

Which is what I have been considering lately...just not feasable money wise.

A few years from now, I'd like to rebuild. So, I'll just swap heads as is, and run it like that.