engine and drivetrain M10B18 Head mill

[Shifty1426]

Hi Guys,

how much we can mill the head with 1,8i in it? Without losting liveproof of that engine. I'm triyng to get bigger CR without race pistons or b20 crank. Is there any other chance to get bigger CR? I've find that 121ti head have smaller combustion chamber, but i'dont know if it will work with modified stock pistons.Thank you :-)

[TobyB]

Good question.

 

My GUESS is that you can pretty safely mill the same 1mm that you can usually get away with on the E12/21.

That should give you about a point of compression, give or take.

 

But just like those heads, the first thing to touch is probably going to be the intake valve, so that will depend on your

cam and it's timing.  Then you could cut clearance pockets into the pistons, if needed, which isn't too hard.

 

At 1mm, it's worth using an adjustable timing sprocket to get the cam timed properly again.

Sometimes, you can adjust cam timing just a bit, and gain some valve- to- piston clearance.

 

As to the 121 head, you'd have to check to make sure the 1.8i dome fits into it.  It might.

(or need at most minimal modification)  And yes,

that will boost compression considerably, at the cost of combustion efficiency, as it's more shrouded than the 1.8i.

 

Gotta say, tho, the 2l crank is about the cheapest way to make a 'stroker' there is-

and if you need pistons anyway, Ireland Engineering makes a 1.8i piston with a higher pin that

fits.

 

Just a guess,

t

 

[GazM3]

You can also consider a thin cometic MLS like I did.  You can skim the head also but have to watch piston to valve clearance.  Adjustable cam gear makes sense.  The extra compression is really worthwhile on our engines.  Makes them feel more responsive.  

[Shifty1426]

Toby B: if i use 121ti head, that i need to modify 1.8i pistons, becase they have very big p dome on them. 

 

The reason why i post this is, that only one 2.0 crank in our country is ONLY chamge for rear whole axle from e21 323i not for sell :'(. 

 

First i'm trying to make it budget. I don't have problem to put some staff on cnc machine or something like that. Problem is to find some 2.0 crank or 121ti head. Easiest think is to mill the head and use thin head gasket. I want to use it with 292 cam. One friend said to me, that i need to have at least 11:1 cr to be most efficient with that cam. Is that right? 

 

I want to build funnier m10 engine. But stay N/A. 

[TobyB]

Nope- you'll notice a 292 from stock compression on up.

 

In our country, the 1.8i head got a small round dome in the middle- I bet your 1.8i pistons are quite a bit higher compression than ours...

 

Yes, mill the head and use a 292, and you'll notice it!

 

t

 

[Shifty1426]

I know that i notice it, but best effeciency is with compression 11:1 or more, this is the deal...but on the other side...for me....This project is 90% street project and 10% track/race project....so is it worth it to try to go 11 or more cr?Or 10,5:1 with 292 some head work, bike carb and programmable ignition will be enough?

[TobyB]

11:1 is more in the 304-316 range-

292 is a very 'mild' cam for that high a compression ratio. 

I think 10:1 is probably just fine.

 

How is your fuel?  Much over 10:1 and you run the risk of losing power to detonation,

as in, you will have to retard timing to keep the engine from detonation, and that will cost

more power than it gains.

 

I ran 11.x:1 with 100 octane avgas, and that was pretty stable-  I never saw evidence of

any detonation.

 

hth

 

t

 

[Shifty1426]

 

We have here 92, 95 and 98. For now with stock i run 95, and with modified i will run 98 probably or 95 and retarded timing. I want to use programable ignition unit based on a/f sensor so detonation should be fine. 

 

So best will be 292 cam and cr around 10:1. So if i mill head 0,5mm that should be ok, right? Stock engine have 9,5:1 i think. 

 

I was scared about detonation because i want to use this engine 90/10 street/track and 11:1 is very big for street driving. 

[TobyB]

Quote

So best will be 292 cam and cr around 10:1. So if i mill head 0,5mm that should be ok, right? Stock engine have 9,5:1 i think. 

 

You're lucky.  I think we got 8.3:1.

 

Yes, 292 at 10:1 with good gas should be a good fit for mostly street.  

When you go to the track, do take a look at your spark plugs once in a while just

to be sure it's not detonating.  

 

t

 

[Shifty1426]

Ok, thank you very much :).  How much hp do you think that this setup should have?

 

m10b18 within keihin cvk carbs (39mm), 10:1 cr, 292 cam, ported polished head, lightened flywheel, ignitech ignition unit, supersprint manifold. Engine will be fully rebuilded. 

[TobyB]

Oh, at least a hundred!

 

Honestly, no idea- you already started off ahead with your euro pistons.

 

But the compression bump and cam will add 15-20 to what you started with...

 

t