scippy

iTrader: (3)

I'm running AV 100LL fuel through my Arizona Speed & Marine EFI's they're are atop my BBC 575's .......all my stuff is circa 1996 stock.....I've read where AV gas burns leaner for a given jet size (carburetor) ~ or ~ injector pulse width
for ( EFI's) compared to auto gas..............realizing AV gas is not formulated like auto gas ........specific gravity is much less than that of auto gas, formulated for longer shelf life and has a slower burn rate ie. flame speed..........To combat
running too lean which could burn valves and melt pistons, because I have EFI's , how do I get a slightly longer pulse width for my injectors?

SB

iTrader: (1)

I thought it was tuned for 89 octane gas and you've been running it on avgas ?

I'm missing something I think.

underpsi68

You need to install a wideband to see actually what is happening.

You might have to adjust timing also. Time to read the plugs.

GPM

After the wideband, you may be able to just increase the fuel pressure to make an across the board change.

Trash

Yes the stoich is higher for AV gas or race gas. I've run VP110 and 91 octane and saw the difference. I simply have two different tunes if I need to go back to VP110.

If you can retune the fuel table that would be the best solution. Fuel pressure increase as GPM suggested is another method but one I'm not a fan of. The issue you have is you are held hostage to AZSM's tune.

What ECM are you using?

Rookie

iTrader: (4)

I agree why would there be any reason to run AV 100LL. I thought we covered that in another thread.
I think a nice AFR is necessary.

scippy

iTrader: (3)

So my engines are 9 :1 comp. & if there tuned to 89 octane what damage would occur by continuing to use AV gas?.......burnt exhaust valve?......using it was a decision simply for it's shelf life.
I still have 50 gals left from it's initial fill up ...boat has only been used 5 hours since buying it........maybe a dumb reason to have used AV gas in the first place, but I'm sure auto gas would have
turned to varnish by now!........If it's too complicated to tune for AV gas with AS&M EFI's (not sure about ECM).....Thought the remedy would be pulse widths for injectors to compensate for AV
then auto gas would be less complicated!

zz28zz

A buddy that worked at the airport in the late 70's ran 117 octane in his crotch rocket. Turned his 2 year old chrome header pipes blue on the first tank. He re-jetted and fattened it up but still the pipes kept getting worse. He eventually discovered it was because it burns too slow. Mixture was still burning when exh valve opened. Granted his eng was turning 10-12K rpm, but the effect is still there. Wide band is great for dialing in mixture but not sure if it would help much in regards to detecting slow flame-front speed. EGT sensors might be a good idea if your going in that direction.

As for adj pulse width, my experience is purely automotive but what a lot of people did (including me) was change the fuel inj size in the s/w. If you're afraid you're running lean, adj fuel inj size to a lower value. Computer will use a longer P/W to make up for the "smaller inj".. This will shift everything at once so small steps. Then you go over to the fuel table and fine tune using the wide-band. Once you get that dialed-in, you start messing with the timing table, now the mixture is off again, so back to the fuel table, now it's surging, back to timing table, then you notice the fuel press is off, fix that and start all over.

I'd highly advise anyone doing this to save test-drive data-logs with corresponding notes documenting any changes, check fuel pressure often and be damn sure you don't have a vacuum leak (long sad story).

articfriends

iTrader: (1)

Unless you have unlocked, tunable ecus, increasing "pulse widths" is not a option. If you COULD tune your efi , first you need accurate 02 data, without it your just pissing in the wind. If you actually think it lean overall, as Gary mentioned, you could turn up your regulator and take pressure up 5 psi or so which would richen the tune every where, Smitty

articfriends

iTrader: (1)

Ive dynoed 9-1 motors and made more power with 89 octane then 93 sometimes so besides "shelf life" is there any other reason you'd run 100 octane, dry fuel?