Compression test blues.

[clutterbucker]

So here I am, after 2 and a half months of getting crap together, getting the M20 out, buying random parts (for and not for the engine swap), the M50 was just about ready to go in. Before putting it in, a compression test, we decided, would be wise. Probably should have done it earlier:
One cylinder pulled a 75psi. CRAP.

Now, I like to look at this as an oppurunity more than a road block. We decided to put the M20B25 back in for a year while I scrounge up money for rebuild/upgrading. What should I do while I'm in there replacing piston rings over the next year. I was almost thinking of an S50 head maybe? I have to overbore 1mm and get new pistons...so do you think higher compression could be fun?

Post your suggestions as to how I might upgrade the top end (I'd like to leave the bottom end where it is) of the engine now that I have the time to think and save up.

I'm going to try to get the guy that sold me the engine to pay for new rings, and possibly some of the pistons, but we'll see about that.

Thanks in advance for any suggestions.

[grapedrink]

I would do a leakdown test on that engine before you do anything further on it. Compression in my mind really doesn't tell shit other than the engine turns over and there is enough to fire a piston. On the M50 depending on mileage I would say anything under 10% would be good.

[clutterbucker]

What do you mean by 10%? Within 10% of where it's supposed to be? It's 75psi, and should be around 200.

If cylinder 5 is only holding 75psi, and should be holding 200psi, I'd say that's a pretty good reason to rebuild right? Essentially missing one cylinder would make the M50 more or less as powerful as the M20 it's replacing! What a waste!

I'll do a leakdown test, but I fear everything may just need to be replaced while I'm in there.

[nando]

if the compression is that low something is definetly wrong. but it could be as simple as a headgasket, not neccesarily the whole motor in need of a rebuild. I think a leakdown test can show you exactly whats wrong though, so it might be worth it. if it's just the headgasket I'd replace it and throw the motor in the car, unless you really want to build it.

[clutterbucker]

"unless you really want to build it"

I suppose I was sort of looking for an excuse, and what better excuse to upgrade than something going wrong.

So what are the most cost-efficient ways to get more power from an M50 (I've already decided on new pistons). What compression ratio is safe/good? What S50 upper engine parts are a direct fit, and with which of these things could I keep my ECU? I'm not looking for 250whp, just some zest.

Higher comp pistons and S50 Cams?

(I have a 1994 m50)

edit: I just realized that some of these questions are probably answered in other threads, so feel free to ignore this post