Boost -vs- Octane requirement - Page 2 - Rennlist - Porsche Discussion Forums

Notices

Boost -vs- Octane requirement

 
Old 11-01-2001, 12:07 AM
  #16  
TurboGuy
User
Thread Starter
 
Join Date: Oct 2001
Location: Colorado
Posts: 41
Post

Adrial not sure what boost he was running but it was his own # 41 951 race car. He has tons of mods including the Garrett GT25 ball bearing turbo. See his web page at Technodyne for all the info. Ice ya the numbers seem high to me also but again this means zero detonation. If Chris at Technodyne is correct the cars would be in bad shape without our knock sensors so maybe there is something to the data. I believe that Porsche originally recommended 91 octane and set the boost at around .75 bar at 2300 rpm. I know of nobody that has had a blown head gasket under those conditions.
TurboGuy is offline  
Old 11-01-2001, 07:00 AM
  #17  
Danno
Super User
 
Danno's Avatar
 
Join Date: Jul 2001
Location: Santa Barbara, CA
Posts: 14,077
Post

Yeah, I've been running 1.0-bar of boost for over a year now using 91/92-octane gas without any problems. One of the biggest issues is the flatness of your fuel-curve under all conditions. Even the stock computer can't maintain that. So you end up with a situation where you get a nice, safe 11.5-12.5:1 air-fuel ratio from 2000-5500rpm (full-throttle), but then it gets lean to 13.0-13.5:1, which then causes detonation. Which leads you to believe that 92-octane gas is insufficient, when in reality, the problem is with your fuel-mixture.

Adding octane (95+) would quence the detonation, but your configuration is still not optimal. If you were to fix the top-end mixture to 12.5:1 air-fuel, then you can run 91-octane AND make more power than the lean/95-octane combo.
Danno is offline  
Old 11-01-2001, 10:22 AM
  #18  
TurboGuy
User
Thread Starter
 
Join Date: Oct 2001
Location: Colorado
Posts: 41
Post

The only input number that the software requires that I kinda winged was (VE) Volumetric Efficiency. I used a value of 75 this number does change with engine rpm. A lower value of say 65 will deliver lower octane requirement numbers. Anybody out there know the correct value ? I normally run 93 octane with 1 bar and one plug colder this last weekend I put some 110 race fuel in and WOW !!! What a rush Turbo's really like high octane.
TurboGuy is offline  

Thread Tools
Search this Thread

Contact Us About Us Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: