Go back to home

Avgas and ignition timing

Author
Post
Essentials Only Full Version
wayovermyhead
Enthusiast
  • Total Posts : 23
  • Scores: 3
  • Reward points: 2873
  • Joined: 2012/05/01 17:46:45
  • Status: offline
2012/06/26 00:04:15 (permalink)
0

Avgas and ignition timing

Hi all,
So the car i just bought has a pretty worked and stroked Pinto. The CR is pretty high but i'm not sure what it is exactly. It's currently running on and tuned for Avgas by the previous owner (who has run it on 98 but didn't do any of the timing/tuning on it so is no help). Already it's more hassle than it's worth for me and my goal is to use the car for tarmac rallys in the future so 98 pump fuel will have to do at some point.
Does anyone have any experience with running Avgas vs pump fuel in a high compression engine and generally what did you learn?
Specifically, how much timing would one need to take out when going from 100Avgas to 98pump fuel.
I know a dyno is the best way to work it out, but if there is a good enough rule for timing of these two fuels relative to each other it'd be a great help.
Cheers,
Llewellyn
#1


3 Replies Related Threads
    mud
    Supporter
    • Total Posts : 588
    • Scores: 12
    • Reward points: 2753
    • Joined: 2011/08/01 11:02:49
    • Location: Crescent Head NSW Australia
    • Status: offline
    Re:Avgas and ignition timing 2012/06/26 13:31:50 (permalink)
    0
    My last Pinto was built for avags with a comp ratio of over 12:1.
    If I remember rightly (some years ago now) we set it on the dyno on a number of occassions around the 28-33 degree mark. While no pinging was evident on the dyno it never lasted more than a few stages on an event.
    Hot spots would develop in the cylinder (usually no.3) and blow the headgasket. After 4 times of this I gave up and stuck it in the shed for 6 years.
    It's now having a new engine built by LotusMk1 for normal 98 pump fuel.
    Hope you have better luck than I did!

    Tar's for getting there. Dirt's for racing!
    #2
    spigot
    Enthusiast
    • Total Posts : 153
    • Scores: 4
    • Reward points: 2753
    • Joined: 2011/08/01 11:02:49
    • Location: North QLD Australia
    • Status: offline
    Re:Avgas and ignition timing 2012/06/27 21:16:39 (permalink)
    0
    Cranking psi is the biggest indicator of timing. On a mild motor with 175psi you can run 16deg initial with 35 deg all in by 3500rpm no problems.

    If its over 200psi you may have to reduce that to 30 deg as a starting point. I would always try and have at least 12 deg at idle.
    #3

    wayovermyhead
    Enthusiast
    • Total Posts : 23
    • Scores: 3
    • Reward points: 2873
    • Joined: 2012/05/01 17:46:45
    • Status: offline
    Re:Avgas and ignition timing 2012/06/28 09:29:33 (permalink)
    0
    Thanks guys, some usefull info there. Spigot as you suggested i'll check my cranking pressure and go from there. If anyone else has any experience, I would love to hear it also.
    #4
    Jump to:
    © 2025 APG vNext Trial Version 5.1