m20 with small mods: what gains can be expected?

[u3b3rg33k]

I would definitely put bumping the CR on my list of engine mods. I believe MM's nutty N/A M20 pulls off a 12:1 CR on hi-test.

If I was going to build it myself, and not have proprietary knowledge to throw at it, I'd port the exhaust ports, put on REAL long tube headers (not ebay knockoffs/shiny replicas), port the intake / port match the gasket, and extrude hone / port the intake manifold. I'd also bump up the CR as high as reasonably possible on pump gas. Not only will you get better torque, but you'll also have slightly more efficient engine, which I don't think is ever a bad thing.

From what I've read, going +1 on the intake valves is really only useful as a last mod, not a first mod. As in doing it by itself yields nothing positive.

[iXguido]

Was that motor running on race fuel? And is it a stroker or a b25 still? Would I be able to run my motor on premium if I wen with 11:1 CR? Also from the list of work you posted above I don't see anything about a cam. Would you just use a stock cam?

[lennon]

yes you can run an 11:1 m20 on pump gas, and yes you should definitely use a hotter cam with that higher compression.

[nando]

for 11:1 you need something like a schrick 288. Definitely not a good idea on a stock cam - you'll probably run into detonation issues on pump gas. Probably highest with a stock cam I'd go is 9.5:1. Generally CR goes with your cam. I have 10:1 with a schrick 284/272, which is matched decently. a 288 at 10:1 might be a bit overcammed.

for exhaust definitely don't waste money on ebay headers. Other than being shiney and lighter, there's no performance advantage. It's not just close to equal length, primary length or diameter that matters. The merge has to be properly built to really get good velocity scavenging, and quality merges cost money. that's why the "ultimate" headers for an M20 cost like $2000 (BTB from the UK).

Of course at that price you might look into building your own. Der Affe is doing that right now I think, he's aiming for 28-30" primaries if he can fit.

[iXguido]

for 11:1 you need something like a schrick 288. Definitely not a good idea on a stock cam - you'll probably run into detonation issues on pump gas. Probably highest with a stock cam I'd go is 9.5:1. Generally CR goes with your cam. I have 10:1 with a schrick 284/272, which is matched decently. a 288 at 10:1 might be a bit overcammed.

for exhaust definitely don't waste money on ebay headers. Other than being shiney and lighter, there's no performance advantage. It's not just close to equal length, primary length or diameter that matters. The merge has to be properly built to really get good velocity scavenging, and quality merges cost money. that's why the "ultimate" headers for an M20 cost like $2000 (BTB from the UK).

Of course at that price you might look into building your own. Der Affe is doing that right now I think, he's aiming for 28-30" primaries if he can fit.

I already have a set of Racing Dynamics headers. Are those good enough you think? What kind of fuel would I have to run with 11:1? What about 12:1?

[nando]

you can probably do pump gas with 11:1 and the right cam.. don't know about 12:1. keep in mind with every point increase in CR, there is a diminishing return in performance. You probably won't benefit from 12:1 if you have to retard the timing a bunch.

[u3b3rg33k]

I took another look at MM's M20 PDF, and it turns out I was wrong, their engine has an 11:1 CR, not a 12:1 CR.

http://www.metricmechanic.com/pdfs/metric-mechanic-m20-engine-booklet.pdf

[digger]

waste of time going above 10:1 on stock cam you'll be retarding ignition timing so much as to be worse off. On a B25 a nice 270 odd at 10:1 should a good match.

To get higher CR you'll need custom pistons in which there are a myriad of cranks to choose from the will do wonders

[stinkydriverx]

For how much money your looking at spending with those mods. You might as well just boost it. Seriously though, you will see much more power. The stock m20 from what I hear and read is a very reliable engine on boost as long as you keep it roughly >10psi. And there are a few chip tunes that run on 7psi or so, for really cheap. Look into it IMO!

[qbuilt]

I agree, an N/A m20 is very cool, but if all your really after is more power, a simple well built turbo setup will give you more power and similar reliability as a full blown N/A m20 would.

[e30polak]

You're climbing up the wrong tree as far as your power goals. With the money you're looking to spend on the m20 - either do a proper stroker kit if you're hell-bent on keeping that motor, or turbo it.

If you really want reliable NA power, you should look into one of the 24v engines. Much better bang for your buck. If you're worried about weight, then source the aluminum block m52 out of a z3 (it's lighter than an m20!).

I will be getting an m20 powered e30 as a DD soon. I'm simply looking to do the 2.7i stroker set-up with some gasket matching, a MAF kit, free flowing exhaust. That will be a fun DD, especially with my 3.46 LSD and the 260! :D