CamTom12 wrote:

blackrock wrote:A good electronic ignition system would help push the detonation limits; the guys I know who do that don't really know where the timing limit is until it's too late. That gets expensive in a hurry! They rebuild, back off the timing a little and hope for the best with the new rebuild. I'm sure there has to be a better way, but they haven't found it. That is with an LS1 engine and they are notorious for detonating, anyway.

I'm curious what setup your buddies are running...

I built an LS1 with 11.2:1 SCR and ran ~25° timing at WOT. I used the stock engine management, just reworked the maps to fit the engine alterations. Still runs great, 5 years later on 93 octane. Thanks to a great combustion chamber design, LS1's are pretty resistant to detonation.

The LS1 has a good knock sensors in the valley, I'm not sure why someone wouldn't use them.

They run SDS and can vary the timing with a rotary switch on the panel. I think they also tried to run 85 octane mogas. Didn't work out too well. they avoided the stock system because they didn't think the shut down/limp mode could be disabled. They did try knock sensors but then abandoned them. I don't remember why.

dirtstrip wrote:I had this discussion about altitude and auto fuel with Ly-Con Visalia when reworking my 180 (HP) to 10:1 pistons. I got the go ahead with the following advice. The manifold pressure is the gauge to watch and is the early warning system on detonation, which is what we are trying to avoid. Low density altitude ops, cold temps and WOT with low octane would give the worst combination. They suggested limiting 26 or below manifold pressure to provide the saftey net.

I'm definitely no engine expert, but was thinking along the same lines. IN THEORY even if the engine has a 8.5:1 or greater compression ratio if a pilot operated either at high altitude or carefully restricted the manifold pressure to below a set limit you should be able to run mo-gas in a normally asiprated engine like a Pponk Continental O-470-50 or an Cont. O-550. By limiting your MP to a set limit, either with the throttle or by operating at altitude you should be able to keep the cylinder compression ratios below the point that would cause detonation. Every 1 inch reduction of MP should reduce the power and the compression ratio by 3.5%. Am I missing something here?

I have a 180 with the P-Ponk conversion and I researched this very topic and found the STC specifically calls for 100LL.

blackrock wrote:

CamTom12 wrote:

blackrock wrote:A good electronic ignition system would help push the detonation limits; the guys I know who do that don't really know where the timing limit is until it's too late. That gets expensive in a hurry! They rebuild, back off the timing a little and hope for the best with the new rebuild. I'm sure there has to be a better way, but they haven't found it. That is with an LS1 engine and they are notorious for detonating, anyway.

I'm curious what setup your buddies are running...

I built an LS1 with 11.2:1 SCR and ran ~25° timing at WOT. I used the stock engine management, just reworked the maps to fit the engine alterations. Still runs great, 5 years later on 93 octane. Thanks to a great combustion chamber design, LS1's are pretty resistant to detonation.

The LS1 has a good knock sensors in the valley, I'm not sure why someone wouldn't use them.

They run SDS and can vary the timing with a rotary switch on the panel. I think they also tried to run 85 octane mogas. Didn't work out too well. they avoided the stock system because they didn't think the shut down/limp mode could be disabled. They did try knock sensors but then abandoned them. I don't remember why.

Tell them to look into HPTuners or EFI Live. Retains stock sensors, wiring, ecu, etc. but also allows full modification of the fueling/timing/management tables. I did away with the maf and narrowband O2 sensors to run speed density tuning (with a standalone wideband O2 sensor) and completely tuned around any emissions related limp modes.