 Comression ratio advice, 6 cylinder motor build |
|
|
|
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG.
This site is not affiliated with Porsche in any way. Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners. |
|
|
| team914 |
 Apr 22 2023, 04:06 PM
Post
#1
|
|
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 |
   |
 
|
  |
Replies
| Retroracer |
Apr 22 2023, 05:11 PM
Post
#2
|
|
Senior Member Group: Members Posts: 616 Joined: 7-July 13 From: Bend OR Member No.: 16,100 Region Association: Pacific Northwest 
|
Sounds like a nice build! I'm +1 on the "conventional wisdom" of <10:1 on single plug/high street petrol - the Dempsey book suggests as much - but I've never tried to build & run a high compression -6 motor daily, so what do I know?
HOWEVER: there are a few Porsche specialists on your time zone which might be worth a phone call for recommendations / guidance: Design 911 in Essex, and Tuthill Porsche in Oxfordshire. Both have run older 911s in competition/ historic rallies all over the UK, so can't hurt to ask. - Tony PS. post pics of the build pls? (IMG:style_emoticons/default/smile.gif) |
|
|
|
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 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 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 |
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:
|
Lo-Fi Version | Time is now: 9th June 2024 - 12:02 PM |
Invision Power Board
v9.1.4 © 2024 IPS, Inc.