 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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| rgalla9146 |
Apr 23 2023, 06:24 AM
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#2
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Advanced Member Group: Members Posts: 4,563 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None 
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Summit racing has an easy to use compression ratio formula on their site.
You'll have to measure deck height and provide other info that is probably included with your pistons. Wossner is a high quality brand. Good choice. 9.5 is a reasonable target. You'll have to use the best pump gas available CR can be adjusted incrementally by raising the barrels with thicker than stock base gaskets. This method is also reversable. You've got a beautiful plan. Good luck Rory (IMG:style_emoticons/default/clover.gif) |
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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 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 r_towle For a Daily Driver, I would suggest 9.5:1 to ensur... Apr 23 2023, 05:05 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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