Stroker Questions

[PeaveyBassist]

I'm thinkin bout doin a stroker project and searched around on the forum. I have a 325i right now. I'm lookin for a list of things I would need. I only have one car, so a whole new motor would be cool :)

1. Complete m20b25 head
2. m20b27 block
3. Super ETA pistons or m20b25 pistons ( top shaved 2-3mm)
4. m20b27 crank

Is that really all you need? Or is there more to do? I figure do the stroker, then get SMT6 a little down the road to get the most power out of it :) Is there anything else I need?

Will

[Jordan]

Why build a stroker with super eta or shaved i pistons? buy some real pistons.

[PeaveyBassist]

I'm on a budget. Can you get custom pistons for under $500? If so... where?

Will

[modifiede30]

Based on what you have, that should suffice since you can use all of the existing electronics, intake, etc from the 325i. I'd recommend that you do a complete overhaul of all internals, balance, and polish, and magnaflux the crank and rods.

You need to really think about what you're trying to acheive by this project. A stroker based on the components you've listed won't provide much more power than what a stock 325i will produce. HOWEVER, the stroker will provide a much different torque curve, which, depending on intended use, could be very beneficial.

A few other things you should consider. Shave the head to BMW specified maximums. If you're willing to be a bit more aggressive, you might also want to deck the block by a very small amount. The combined effect of these can increase compression while not interfering with timing or piston/valve clearence issues. You should be able to get to stock 2.5l compression figures by doing this.

If you have a super eta intake, it might be worthwhile to see what performance is like, since the torque potential can be maximized, although this would limit top end potential a bit.

If you intend to spend more time at the top rpm levels, but need more low end torque for slow corner exits, it is also worthwhile to drop in a more aggressive cam - I would say anything above 275 would begin to nullify any benefit of the longer stroke. A better cam will just add to the higher rpm torque/hp that can be acheived, but keep in mind low end will suffer as soon as the cam is more aggressive than the original super eta cam.

If you intend to be at the top end of the rpm spectrum all the time, spend your money on modifications to the 2.5l engine, and drop the stroker project. You'll get more out of the 2.5l using add-ons than trying to stroke it if you intend to use it at higher rpms all the time.

[PeaveyBassist]

This will pretty much be daily driving...all the time. Wont see any autox/track time in the near future. Maybe in a year or 2 or something, but not soon. I would like more low end torque in the 325i. Mostly I just think a stroker project would be a fun thing to do. More torque down low would be fun around town though :)

Will

[modifiede30]

This will pretty much be daily driving...all the time. Wont see any autox/track time in the near future. Maybe in a year or 2 or something, but not soon. I would like more low end torque in the 325i. Mostly I just think a stroker project would be a fun thing to do. More torque down low would be fun around town though

I'm not sure that you're intended purpose for this engine requires a stroker. I'd do some searching for other options to increase torque for the 2.5l. It would be just as fun to do, and it will be much more efficient in terms of time.

[PeaveyBassist]

What other options are there? Only thing I know of off the top of my head is SMT6(some piggyback unit) or just a chip. Would a turbo with low boost be a better option? Only around 6psi?

Will

[modifiede30]

I'm not a big fan of turbos. What has been done to the engine so far?

[PeaveyBassist]

Nothin has been done. Total stock m20b25 :)

Will

[modifiede30]

I'd throw a chip in, intake, open up the exhaust a bit, and see if you like it better before you go building an engine or do any major modifications. Long tube headers might help as well but those are expensive. Shorty headers are cheap but they don't do anything for low end torque.

[PeaveyBassist]

Would a simple cat-back exhaust system work ok? As far as intake stuff goes, is there really anything you can do short of MAF?

Will

[modifiede30]

Really depends on what you're willing to spend or devote time to. You could do the megasquirt, dump the AFM altogether, and tune the engine yourself. Or you could do the standard items (exhaust, chip, intake/filter). Intake options are a bit limited on these cars unless you fabricate up an individual throttle body setup. Some M30 AFM's will work correctly with a stock M20 but if you have to play with the electronics, you'll need someway to correctly adjust the fuel to compensate. Split second could work, but I've not heard of great success with these.

[Jon325i]

Enhancing an M20B25s low end performance....

JC Chip....cost effective and easy to do.

4.10LSD....the lower gearing puts the sweet spot of your torque curve at lower speeds

Exhaust....very little gains to be made here. Its more of a sound enhancement

Cam....something like the IE Sport Cam or Schrick 272, both are mild upgrades which retain civility in your motor

That's about all for the bolt-ons I can think of. A stroker M20 can be built on the cheap. An '88 SuperEta shortblock and "i" head is one such option. The standard eta shortblocks have different shaped piston crowns that will create clearance problems with the combustion chamber on the "i" head. If you sourced up a SuperEta shortblock from either an '88 325 or '88 528 (they are the same thing) that had automatic trannys then these are likely to be good cores to start with. Of course, their maintenance history will need to be taken into consideration.

Jon

[PeaveyBassist]

So the IE 272 cam (reground) would be ok? It costs $190, but if you return the stock one you get $130 back, which means the new cam only costs you $60. What kind of expectations can I have with a new cam? What exactly does it do? Basically...cam and engine management (chip or MS or SMT6) would be good then. I dont wanna put in a 4.10 diff.

Will

[modifiede30]

The standard eta shortblocks have different shaped piston crowns that will create clearance problems with the combustion chamber on the "i" head.

I don't believe clearance is the issue as much as compression. Stock eta pistons would produce compression numbers around 8.5:1 - not optimal unless you turbo the car. Super eta compression is better but still not optimal. Shaving and decking can be done to improve this.

I'm also a bit skeptical that a more agressive cam is going to do anything for low end torque. A chip, yes, but the cam will likely have the opposite effect.