M10 block build, help with configuration, if you would...

TLDR version - what seems best?:

1. Use a larger bore on the block with flat top pistons in order to use any M10 head, but compression will be between 8.3 and 8.6, with a 292 cam.

2. Just get some domed pistons in standard bore (or overbore) for the head, figure 9.5:1, and run it.

Luck with this car has not been that great, 3 or 4 to 1 down time to run time over the 2 decades I've had it. Heads are getting harder to find in good condition, I went through 2 different head castings, both cracked at the #3 chamber, and the head I have now has some pitting on the flat part of one of the chambers.  So, a bit sporty with some of the hard parts.

Taking pros and cons to help me decides, but I'm starting to lean towards #2....  Any help is appreciated.

What I thought was a clean 2.0 block isn't once you look a little closer and remove carbon from the pistons - turns out it ALSO has some p to v issues on #1, and the piston looks a little off center in the bore, as though there's a ring issue.

So, it's time to build up a block. Both the 2.0 and 1.8 will need a bit of over bore to take scarring out of a couple cylinder walls. How much is TBD, but...

- are there any issues running a 91 or 92mm piston?

- I'm thinking of flat top pistons so if I run in to any head issues in the future, I can get any head and throw it on.

Thinking of running a thinner head gasket to get couple tenths more compression...

- Any issues running an 040 or 045 head gasket (stock is 051)?

Ireland Engineering does not recommend a thinner head gasket.

I know that it'll retard the cam timing, but I have their 3 or 4 position adjustable sprocket, so I can get most if not all of it back.

I know thinner gasket means pistons closer to valves (and I have their 292 regrind), but I saw a dude with flat tops and valve reliefs (turbo build), so that's a solvable problem.

The larger bore gives me a little more compression on the same gear all else equal, and a 92mm bore on my E21 head gets me gives 8.8-1 with a stock 051 gasket, if Summit Racing's compression calculator is to be believed. It gives a tenth more for each thinner gasket (so 9:1 with an 040). Each mm smaller bore drops compression a couple tenths...

Thoughts and suggestions?

I don't know that I have much useful feedback here, but what are you trying to achieve? What induction are you planning? Naturally aspirated, yes? Is the head full thickness, or has it been skimmed?

You have their cam and adjustable cam sprocket and they suggested against the thinner headgasket. I'd likely see what their recommendations are and follow them. 

Although if I were building a BMW engine, I'd likely be calling Metric Mechanic or VAC Motorsports. 

In reply to 02Pilot :

I think mostly just to know whether or not I'm ok running a 92mm piston (stock is 89mm, so pretty large overbore), and what's the thinnest HG I should run. 

CR winds up being +/-  9:1 with the big piston and my current head (E21),  E12, and a 121, and about 8.5 if I wind up with a 1.8i head.

So, the questions posed to Ireland (where I'd get pistons from) are, is the 92mm bore ok, and how thin a HG is too thin. 

Thought (hoped?) the gang here might have insights.

In reply to z31maniac :

I've asked, they've not gotten back to me in a couple days now....

ГУЛАГ мальчик УР следующий said:

In reply to 02Pilot :

I think mostly just to know whether or not I'm ok running a 92mm piston (stock is 89mm, so pretty large overbore), and what's the thinnest HG I should run. 

CR winds up being +/-  9:1 with the big piston and my current head (E21),  E12, and a 121, and about 8.5 if I wind up with a 1.8i head.

So, the questions posed to Ireland (where I'd get pistons from) are, is the 92mm bore ok, and how thin a HG is too thin. 

Thought (hoped?) the gang here might have insights.

Can you get ahold of the cam card for that camshaft grind? 

It would be nice to be able to calculate the dynamic compression ratio. 9:1 with a 292 cam sounds like dynamic would be too low to me. 

In reply to ГУЛАГ мальчик УР следующий :

I wish I had something helpful to offer. Have you posted this over at 2002FAQ? There are some serious M10 gurus over there.

Trent said:

ГУЛАГ мальчик УР следующий said:

In reply to 02Pilot :

I think mostly just to know whether or not I'm ok running a 92mm piston (stock is 89mm, so pretty large overbore), and what's the thinnest HG I should run. 

CR winds up being +/-  9:1 with the big piston and my current head (E21),  E12, and a 121, and about 8.5 if I wind up with a 1.8i head.

So, the questions posed to Ireland (where I'd get pistons from) are, is the 92mm bore ok, and how thin a HG is too thin. 

Thought (hoped?) the gang here might have insights.

Can you get ahold of the cam card for that camshaft grind? 

It would be nice to be able to calculate the dynamic compression ratio. 9:1 with a 292 cam sounds like dynamic would be too low to me. 

 

I'd thought about that, but several guys on the 2002FAQ board as well as another forum where a guy's brother runs it at auto-x, all of whom had 8 or 8.5:1 motors were pretty happy with it, one or two of whom came from a 284.

Keep in mind those are advertised durations, so at the 050 lift standard, probably like 230 degrees and less. 

My 284 is a Schrick, the 292 regrind is supposedly patterned after the Scrick, all of which are 70s designs, so I'm guessing should work ok. 

I'd have to get the specs on the regrind for sure, but according to Dr. Schrick's website, both cams have the same LSA, which is why one dude in particular said the difference below 3500 wasn't very noticable, but night and day above that. 

As I think about it, I'm trying to solve a problem I don't yet have (on the "new" parts); but, 2 cracked heads (one a 121, the other a 1.8i) at the #3 cylinder make me paranoid.

I've got a nice set of aluminum pistons for a 121 head that are paper weights (from 2 decades ago - dang I'm old), I don't want to do that twice.

I am starting to think I should just get some 9.5:1 slugs for the E21 head and let it fly, but my luck on this car had never been great.

Decisions, decisions....

02Pilot said:

In reply to ГУЛАГ мальчик УР следующий :

I wish I had something helpful to offer. Have you posted this over at 2002FAQ? There are some serious M10 gurus over there.

I have not, but if I deviate from my current plan, it'll be OBE.

I'll think on just getting the right pistons for the head v. flat tops that I can run with any head and go from there.

ГУЛАГ мальчик УР следующий said:

In reply to z31maniac :

I've asked, they've not gotten back to me in a couple days now....

I don't know if you're saying IE hasn't gotten back to you or the other two. 

Although, I suspect other companies might not care about giving you advice for a competitors product.