3.4 questions

[Craig 930 RS]

Does a 3.4 @ 9.8:1 compression - made from a 3.2 - REQUIRE twin plugs? I have a 3.2 coming with rebuilt top end and am going to have the bottom end rebuilt........and need advice!

THX,
Craig
www.RennStore.com

[1fastredsc]

I doubt it, although i believe you'll be limited to strictly using premium as far as pump fuel's go.

[ttweed]

Craig-

If you use a relatively "hot" cam, with high overlap and duration, and don't push the timing advance too far, you shouldn't have excessively high combustion chamber pressures from 9.8:1 compression, and should be able to use premium pump gas in it with single-plug ignition without risking detonation. Keeping the engine cool will help as well (big oil coolers are helpful). The original 2 liter 911S engine had 9.8:1 compression (as do the Euro Carrera 3.2s) and they run well on premium.

The weak point of the 3.2 is the rod bolts. If you are going to run the engine hard, use Raceware or ARP bolts when you do the bottom end.

[ChrisBennet]

Originally posted by RennStore
Does a 3.4 @ 9.8:1 compression - made from a 3.2 - REQUIRE twin plugs? I have a 3.2 coming with rebuilt top end and am going to have the bottom end rebuilt........and need advice!

THX,
Craig
www.RennStore.com

I did some research on this and I think you should be OK with a true 9.8:1 compression motor and premium fuel.
Porsche's stated compression ratios are higher than actual measured compression ratio. For example, a 3.6 has a stated compressoin ration of 11.3:1 but a true/measured ratio of 10.4:1.
I don't know if Mahle uses the "Porsche method" or not.
-Chris

[CJ]

I have done this conversion along with C2 cams and have not had any problems.

[89911]

I'll further the question, "Would going with twin plugs offer and advantages, ie lower octane, higher compression, smoother idle, better milage?" I may be going this route and am most likely do the twin plugging while it is apart.

[ChrisBennet]

Originally posted by 89911
I'll further the question, "Would going with twin plugs offer and advantages, ie lower octane, higher compression, smoother idle, better milage?" I may be going this route and am most likely do the twin plugging while it is apart.

Having done a twin plug 3.4 I would say it isn't really cost effective. Fun yes, but cost effective, probably not. If you are going to twin plug you should up the compression to 10.5:1 if you can get 93-4 octane where you are.

Twin plugging a 3.2 runs about $2000: Andial splitter box $600, used dual distributor $250-400, twin plugging heads ~$400, extras plug wires $200?, sheet metal mods, custom chip $400-450, 2nd coil, bracket for two coils.

-Chris

[89911]

Still got the parts?

[ChrisBennet]

Originally posted by 89911
Still got the parts?

I think Tod Holyoak had a splitter box for sale. I'm going to rebuild my own 3.4 when I get a chance...
-Chris