TO EVERYONE that is making or has made a stroker.

[Sean]

With the stock eta crank you have to machine 7.43mm off the piston to return it to the deck. Thats 3mm of crown plus the 4.43mm of dome the 325i pistons have. Everyone thought it was only 3mm, and thats true if you only look at compression heights vs rod length, but then they forgot there is a big bloody dome in the way so the 3mm figure is totally worthless.

Cant remember who it was, but it happened to someone on e30tech, have a search for the thread, otherwise you need to try and remanufacture the dome shape once you have been cutting to fit back within the combustion chamber, then you need to start asking yourself if the change in piston crown is going to effect squish areas within the head (given the 885 has a different chamber design).

So, do you suggest NOT shaving the top of the I pistons, or is it just really really sketchy?

[Madhatter]

well, the dome shape is matched to the combustion chamber, so it might not be as efficient (meaning a slight loss in horsepower) as you hoped, and 2) you want to make sure you have your machinist check the pistons against the head (there are differences in the domed dish design). If you dont take enough out of them you are going to end up with a very large mess.

[nando]

US spec 325i pistons have a dish, not a dome.. at least mine did. 8.8:1 ftw!

[nando]

shorter rods dont rev as high? 130mm rods in my 323i with a 6600rpm factory rev limit would tend to suggest otherwise.

your 323i doesn't have an 89.6mm stroke either, now does it? ;)

[nando]

Are the S50 rods as strong as the 325i rods? I wanna use S50 rods with the modified I piston to help lighten it up a bit. I can get a whole set for $150 - so I figured why not.

you don't want to use light rods with a heavy piston.. think about it. Jim said you want your rods to be about 15% heavier than your pistons, with a heavier piston and lighter rod, you're liable to break something. if you want to go the budget route, stick with the i rods.

and we'll see what mistakes I'll make I guess.. but at least there have been plenty of people before me that I can learn from. really the bottom end of my motor will be pretty basic, I'm just going for the 86mm bore rather than the standard 85mm. as long as it doesn't explode in the first 5,000 miles I'll be happy :D

[Sean]

you don't want to use light rods with a heavy piston.. think about it. Jim said you want your rods to be about 15% heavier than your pistons, with a heavier piston and lighter rod, you're liable to break something. if you want to go the budget route, stick with the i rods.

and we'll see what mistakes I'll make I guess.. but at least there have been plenty of people before me that I can learn from. really the bottom end of my motor will be pretty basic, I'm just going for the 86mm bore rather than the standard 85mm. as long as it doesn't explode in the first 5,000 miles I'll be happy :D

Yea, that's true.

I asked Jim real quick today what he thought of the I piston idea, and he said it was trash. It's a real big risk to do it, specially shipping them out like I am planning. if they do work, I'm almost positive they won't handle any type of boost.

So...hate to say this...and I really do - I'm basically back to my original thought. SuperEta stroker or slap down money for custom pistons or MM ones, and get S50 rods.

If I did MM pistons, I'd never get to play with boost. If I got custom pistons, I could play with boost - but I haven't the slightest idea where to go to get custom pistons made AND I'm worried I wouldn't get the right specs to them and end up with an incorrect piston. Back to the stroker idea, I'll have a fun little engine - yea not the best - but a pretty reliable engine that will last me good until I'm out of college. Then, when or if I ever get the money, I could always boost it.

Yea, the SuperEta stroker is not the best designed - but I could maybe have the machine shop lighten the rods a bit (MAYBE) and hope for the best. Deck the block .020" and put er' together and have some fun with it. That would leave me more room for buying a standalone and learning from an engine on my own, before jumping to the big stuff. Not to mention, I could always boost it when I could afford to blow an engine - ahve some fun with it! lol

I'm pretty indecisive aren't I? hmm

And with that, I'm bringing everything back to the machine shop and moving forward with my budget stroker. I'll let you guys know how it goes. :D

[nando]

well, at least you learned something.. just get a damn motor put together! ;)

hoping my pistons come today. I hate waiting around for UPS trucks..

[Sean]

well, at least you learned something.. just get a damn motor put together! ;)

hoping my pistons come today. I hate waiting around for UPS trucks..

Right on!

I talked to Jim a bit more, and told him that I decided just to go this route. He seemed a bit dissappointed. But, honestly...I just don't have the cash. I could spend a grand on other stuff that's a bit more important than an extra 20 hp. ;)

[rwh11385]

anyone want a long stroke motor?

http://forums.bimmerforums.com/forum/showpost.php?p=6688706&postcount=41

i'd rather have a 6950rpm b25 than a 6450rpm stroker, but that's just how I am. Are we making that much power that high? No, but it sure helps to have that much tach while at the track.

[nando]

that's why I'm sticking to 81mm ;)

[DrMcDave]

get some JE pistons from IE w/ whatever comp ratio you want. You'll save a few hundred and be able to choose your CR. I or s50 rods and eta crank/td crank. would make for a nice bottom end.

i'd like to see how much power can be pulled out of a stock bottom end m20. worked head, itb's and fuel management, headers blah blah. guesses?

[rwh11385]

get some JE pistons from IE w/ whatever comp ratio you want. You'll save a few hundred and be able to choose your CR. I or s50 rods and eta crank/td crank. would make for a nice bottom end.

i'd like to see how much power can be pulled out of a stock bottom end m20. worked head, itb's and fuel management, headers blah blah. guesses?

yeah, if you are afraid to machine pistons, get custom ones which should be perfect.

i've always been curious. but think about the $/benefit. hot cammed 325 non-vanos would be a fun car for J-prep IMO

[Madhatter]

US spec 325i pistons have a dish, not a dome.. at least mine did. 8.8:1 ftw!

They dont, dished dome, take another look its a unique piston design. Dome with a large dish cut out of them. Do know how to read mahle piston information like has been posted about the place?

KH = compression height
UH = height above crown (in this case a dome)
VT = depth of depression (in this case, the dish cut out of it)

your 323i doesn't have an 89.6mm stroke either, now does it? ;)

No, but if you go back to his post he said short rods arent strong enough in long stroke, which is just isnt true. If shorter rods werent good in longer strokes (then referred to the 325i) why would they use shorter rods in an engine with a longer stroke than the 325i if that was the point he was making? Forgive me for trying to post something relevent to the engine family. There are of course engines like chrysler 6's, they run low rod ratios too and produce quite a lot of power (and torque). without any problems

[Madhatter]

big list of custom pistons, take your pick (though i prefer JE)

je
cp
ross
arias
wiseco

and thats just off the top of my head.

[Sean]

Although I would absolutely love to get custom pistons - if I was going to do that, I'd want a longer stroke and want to be putting more into it.

I'll just stick with my budget stroker, and have fun getting stuff out of it with bolt ons and tuning, possibly turbo later on.

Should last me at the very least, 4 years. :D