Compression ratio N/A

[NineEleven]

Hi guys.

First of all what's a good safe CR for my car. i'm running on solex c40 addhe carbs, bigger intake and exhaust ports. Best fuel available is RON 98 (belgium)

And how much do i need to take off my cilinderhead to get to that CR? I don't have to tools to measure the CC of my cilinderhead.

thnx

[SkiFree]

By US standards I believe that's a hair over 93 octane. A nice compression ratio with that octane would be 9.5:1 (maybe 9.75:1 but the noticeable difference would be minimal).

For how much material to take off the cylinder head? NONE! NEVER shave the cylinder head to gain compression.

[nando]

you should be able to run 10-11:1 on high grade fuel, no problems. best to pair it with a decent cam, though.

One way to increase would be to bore and stroke the engine. ;)

[Wh33lhop]

Shaving your head will also screw with your cam timing. If you're going to play with your CR, do it the right way and play with the bottom end.

[TobyB]

About 1mm from stock will bump you into the 9.3-9.5 range, ASSUMING your car
came with the 'low dome' 8.3 pistons we got here.

Yeah, you're not 'supposed' to, but it's how I've done 3 of 3 race motors. Honestly,
most older M10's have been cut .5mm or more, so I just started with ones that were
already at 128.low thickness.

And yup, using an adjustable cam gear's a good idea, and keeping your timing chain parts
in top shape's required, since you're about at the limit for what the stock setup can
compensate for...

t

[solo318]

First thing we need to know is what the engine came from. The e21 motors were 8.3:1 (U.S.) the 83,84 e30 m10 was 9.3:1 (U.S.) and the 85 and on e30 M10 was 9.0:1 (U.S.) I'm not sure what the euro cars had but 9 to 9.5:1 compression is easily safe.

[NineEleven]

I didn't change the CR. I already have 9,5:1 so i could only screw my engine up by going to high. I'm not installing an other camshaft anyway. I just wanted a bit more hp from the carbs and the fact that they are adjustable unlike the oem pierburg mf'er...

Next week or so i'm planning put the engine back together. New gaskets or seals everywhere. Just no work done on the crankshaft or pistons. I measured compression and all 4 cilinders had around 12,5 to 13 bar. The person that did a little work on the head noticed that some valves didn't seal properly. but he fixed that. assuming that 'leak' would cause me to lose a little bit of pressure my engine's bottom should be a 100%. It's also to expensive or to much work to just replace the bearings and or pistonrings for no good reason. i'm on a limited budget and lack tools to do the job.

[Hey_You]

You don't have a torque wrench?