 Comression ratio advice, 6 cylinder motor build |
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| team914 |
 Apr 22 2023, 04:06 PM
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#1
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Newbie  Group: Members Posts: 3 Joined: 5-April 20 From: Ireland Member No.: 24,102 Region Association: Europe  |
Hi,
I am planning to build a 6 cylinder street motor for my 914/6 factory replica. My original 84mm barrels were worn, so I elected to machine the barrels to 84.5mm and have bought a set of 84.5mm Wossner pistons. With a 70.4mm crank, the compression ratio is stated at 10.11:1 with the pistons out of the box. I intend on using Weber carbs, E cams and an E distributor/123 Distributor. My machine shop engineer has recommended reducing the compression ratio from the 10.11:1 to a more suitable figure. The petrol quality in Ireland is poor, typically 95 octane, and we now have a compulsory addition of 10% Ethanol added (E10)! Any advice greatly appreciated |
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| r_towle |
Apr 23 2023, 05:05 PM
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#2
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Custom Member Group: Members Posts: 24,588 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States 
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For a Daily Driver, I would suggest 9.5:1 to ensure cooler running on worse fuel.
We don’t drive them daily We don’t race the (really) So build it to last do 15 years from now it still runs great. I have 240k on my 84 3.2 powered 911. Easy to run I am building a 3.2 to similar specs because 200 hp in a 914 is more than I need. |
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Posts in this topic
team914 Comression ratio advice Apr 22 2023, 04:06 PM
mepstein You want to measure the actual compression ratio a... Apr 22 2023, 04:15 PM
nditiz1
You want to measure the actual compression ratio ... Apr 22 2023, 05:55 PM gereed75 The general wisdom says 9.5:1 is the max you can d... Apr 22 2023, 04:44 PM porschetub
The general wisdom says 9.5:1 is the max you can ... Apr 24 2023, 05:02 PM Retroracer Sounds like a nice build! I'm +1 on the ... Apr 22 2023, 05:11 PM rgalla9146 Summit racing has an easy to use compression ratio... Apr 23 2023, 06:24 AM Krieger You do need to cc your heads. Apr 23 2023, 08:57 AM rgalla9146
You do need to cc your heads.
OOPS. Yes, th... Apr 23 2023, 09:30 AM ogdougy I would also add that some piston manufactures wil... Apr 23 2023, 10:49 AM Krieger
I would also add that some piston manufactures wi... Apr 23 2023, 01:49 PM targa72e As others have said you need to CC the heads, figu... Apr 23 2023, 10:12 PM gereed75 The "9.5 compression" JE's i got wer... Apr 23 2023, 10:50 PM |
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