Pump Gas and 2.0L

[Nordschleife]

I dropped my engine... and that got me thinking about pump gas + 2.0L deep cylinder heads...

For planning purposes, and as I ponder my next move... what is the maximum compression ratio for a 1968 2.0L engine running 93 octane pump gas? My cams are currently Crane P-296 (similar to S) and pistons are 911E 2.0L with standard 66mm crank and con rods in very early magnesium case. Ignition is a single plug (JB Racing) distributor w/ MSD 6AL.

In other words, is a compression bump to 9.5:1 or 9.8:1 advisable/worth the effort given I want to run it on 93 octane gas?

Also, is a swap to 1970 911T cylinder heads + opening up ports to something larger than 32mm worth the trouble? Especially if I raise piston compression at same time? The 70T 2.0L heads = larger valves than '68 SWB also.

Thanks in advance for sharing your recommendations & experience.

Andy

[gsjohnson]

I'm running 2.2 PCs with E pistons and Dougherty DC30 S-Mod cams in my 68 2.0. I skipped the 2.2 heads and I wonder if I missed the boat as well not doing the 2.2 heads at the time. Although, the motor runs strong on 93 with no ill-effects.

[Nordschleife]

The 2.2L "bump up" makes all the sense in the world, especially for a 2.0L. But I'm hoping to stay at the lower displacement, even though the cylinder head design is suboptimal.

I'm guessing the shallower 2.2L heads can run more compression at 93 octane than the deeper, more shrouded 2.0L heads?

[gsjohnson]

Let me make a correction. We can only achieve 91 octane here, but still no ill-effects with my engine configuration. It is my understanding that there is a compression bump with 2.2 heads on the 2.0. I believe that only the 70T came equipped with the carbureted 2.2 heads.

[Jim Breazeale]

Let me make a correction. We can only achieve 91 octane here, but still no ill-effects with my engine configuration. It is my understanding that there is a compression bump with 2.2 heads on the 2.0. I believe that only the 70T came equipped with the carbureted 2.2 heads.

71T, as well

[John Fusco]

Ive got 2.2 E pistons and cylinders - the original Solex cams - and 2.0 heads (flycut)
I always try to put 93 in it but not easy to find in Maine so I have run 91 and even 89 and no knocks.

No issues and with original 5 speeds pulls very nicely for street driving, and for my level on the the track as well.

[Nordschleife]

Do you think 9.8:1 would be too much for 93 octane gas with single plug 2.0L heads then? I'm currently at 9.1:1 with my 911e (1969) pistons...

[gsjohnson]

Do you think 9.8:1 would be too much for 93 octane gas with single plug 2.0L heads then? I'm currently at 9.1:1 with my 911e (1969) pistons...

I'm confused...How do you plan to achieve 9.8:1 compression with the 2.0 heads?

[SIMI BOB]

I think you need to check the compatibility of the 2.0 pistons with the 2.2 heads. I think the piston may hit the head, and there is no provision for the 2.2 head gasket on the 2.0 cylinders. According to my posting here about a year ago, a 2.0 engine with 2.2 cylinders will be way down on compression. Remember that a 2.2 piston only adds about 34cc to the volume of each cyl, and the 2.2 piston dome is very shallow. Also, I see no way you are going to get 9.8:1 compression with "E" pistons, and have you checked the price lately for 2.0S P/C's?
If you are going the 2.2 piston route anyway, I would bolt up one cylinder with the 2.0 head and check the volume of the combustion chamber at TDC, by measuring volume added thru the spark plug hole. Remember to add the volume of the combustion chamber measured above to the cylinder volume before you divide it by the combustion chamber volume. Then you will know what your compression ratio will be. See my posting below, especially the reply by Ed Mayo.
I finally had Walt at Competition Engineering (in California) Port a set of 2.2 heads to "S" specs to put on my engine and basically ended up with a 2.2S engine.

http://www.early911sregistry.org/for...837#post620837
Bob B

[Nordschleife]

No 2.2l, only 2.0L... I've unfortunately confused with my "911e" reference I believe. Bob is certainly correct that 2.0 pistons would not match up well with 2.2 heads.

Current set-up is 2.0L pistons (911e 2-liter 1969, not later 2.2L) at 9.1:1 compression in original 2.0L cylinders and with original 1968 2.0L heads.

Proposed set-up is new 2.0 pistons (J&E or Carillo-CP most likely) at a higher compression ration to-be-determined (depends on finding a compression that can run on pump gas), with the existing 2.0L cylinders and 2-liter 911 heads from 1970-1971 2-liter 914-6T engine. Cams are currently Crane P-296 (similar to 'S') and with JB Racing single plug distributor.

My "beer math" estimate is that I could go as high as 9.8:1 maximum compression on 93 octane with the proposed set up. Instead, if the 911sRegistry Technical Forum general consensus is that 9.5:1 is probably the maximum compression(given today's 93 octane pump gas with its typical ethanol component), then honestly it may not be worth it to change out the existing 9.1:1 pistons. Unless I were to machine the heads for twin plugging of course.

Thoughts?