M20 building questions

[clutterbucker]

I have an M20B25. What is the maximum bore. I'd like to do something like 89mm but I fear that 5mm may be wayyy too much. I think my ctlinder walls are scratched up and basically ruined, so i figure hey, why not make the displacement a bit larger and fix the problem. Buying new pistons woul dbe important then, too.

So, what is the maximum safe bore and the best piston to suit it. Has anyone ever done this?

[Madhatter]

200 thou is a big big big rebore. I doubt you need much more than 20 or 30 thou to clean up the bores either.

How do the ireland engineering 3L's come about?, with the standard stroke of 81mm, 89mm bore would give you a 3L engine.

Edit: Seems it's a crank change. Pistons only say 1mm oversized.

[clutterbucker]

yah I dont feel like giving in to a crank change. I want to bore out as much as I can, but I fear it won't be all too much.

Would a 2.7i be just about as expensive as a bit of an overbore?

[clutterbucker]

ya know, I just looked on the ireland engineering website at their 3.0L stroker kit. It's only 2500, and that doesnt sound too bad, i think I cn afford to spend 3500 grand total in a year or two. woo hoo, this is going ot be fun. Anyone have any suggestions. What are your realistic dreams in terms of NA building....I'd love to be a guinea pig.

[Madhatter]

Nothing against the kit but for $2500 you could start looking at a DIY turbo install and produce more horsepower still.

[DSchultz325e]

or throw in an m50, possibly even s50.

[e30Matt]

I'd stroke it first... stroke = more torque = more of a felt change in daily driving.

or throw in an m50, possibly even s50.

[nando]

a bore out isn't going to give you much power, and you're limited to 1-2mm max. stroking is the only way to go, 2.7l cranks are cheap but you do need custom pistons (or '88 325 pistons)

[PanamaE30]

or throw in an m50, possibly even s50.

Honestly if I had the money right now I'd build up the M20..

Why? Because for one, it came with the car and my car is staying as "original" (at least in intent) as possible.

Not to mention the fact that I love the valve chatter :P

[Digitalwave]

or throw in an m50, possibly even s50.

Honestly if I had the money right now I'd build up the M20..

Why? Because for one, it came with the car and my car is staying as "original" (at least in intent) as possible.

Not to mention the fact that I love the valve chatter :P

What does that have to do with how much the M20B25 bottom end can be bored out?

[PanamaE30]

I was simply noting the fact that maybe clutterbucker would prefer to keep his M20 instead of the M50 as suggested in my quote.

[Stu]

The maximum you can safely bore it is 1mm to 85mm. You might be able to go to 86mm for a short-use track motor. Why would you not want to stroke it? You're going to need custom pistons anyway, it would be stupid not to swap cranks at the same time and setup the motor properly.

[clutterbucker]

Yah I'm slowly realizing that. Well, let's see. An M50 would put out 190hp...correct? Not worth an extra 10hp in my eyes (I figure a chip, intake, and exhaust gives me 10hp on the m20). An S50 is extremely expensive and really NOT that much better than a stroked M20. It seems ot me that leaving most of the original parts in there would mnake the car more realiable.....would I be wrong if I said this? Swapping in the M/S50 and all it's new parts would be a bitch and probably take a lot longer. Correctr me if I'm wrong.

[BahnE30]

last time i checked 170 + 10 gives me 180. not like your M20 makes those numbers anyway

plus with the M/S50 motors your starting out way farther ahead. 24 valves more displacement and the potiential is much greater with an M20 your only going to make maybe 210 at the Wheels tops probably nopt even that

[Charlie]

Aqquiring an M50 requires an initial investment, paying shipping/finding a method to transport it, and a good bit of extra storage space. He already has an M20 block.

Something that us "real world" modders like to think about.

-Charlie