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Metal Guru
Join Date: May 2001
Location: Beverly Hills, Michigan
Posts: 2,526
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Flieger is correct about the high dome pistons found on normally aspirated 911 engines. There are advantages for our flat dome turbo engines also.
Twin plugs get the flame front started from both sides of the cylinder (the stock single plug is at one end) so the mixture burns faster. Twin plugs are good for a little bit of torque (since you can run a little less timing advance) and .5 point of static compression (a faster burning mixture is less likely to auto-ignite).
If I were building a race engine or already had EFI and was doing a rebuild, I'd do it. On my CIS car it wouldn't be worth the extra expense.
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Paul B.
'91 964 3.3 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, H&R Coilovers, ESB spring plates- 210 lb
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