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RacerX

Highest Engine Compression Ratio on Pump Gas

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typo, meant 36 sorry, i edited it.

 

But isn't this true? I'm no expert on cylinder heads or anything related to engines, but after spending hours reading up on this stuff, particularly quench areas and things of that sort, this was the impression I had, that the more modern style combustion chambers don't require nearly as much timing, and were also much less prone to detonation. I don't know if they are less prone to detonation BECAUSE of the reduced timing needed, or if these two are independent. Granted it was a while ago I read this stuff.

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Not to burst any Bubbles here, (I made a funny huh?), that is not a Typo, (“trippintl0”, you were correct about our L-series using such a wide range of total timing figures, even if you didn’t know it, and you were pretty close on the rest of it. Keep reading up). 46 degrees is totally realistic and not uncommon for high output open chamber dished piston N/A L-28’s. That doesn’t mean that much timing is a good thing, actually it indicates the chamber is quite inefficient, but the open chamber dished pistons combos require that much timing for maximum output and they do produce some impressive power, even with their inefficient chambers. With the squish chamber of the P-79/P-90 and flat top pistons, (like Bubbles application), the chamber is much smaller so the flame front doesn’t have as far to travel, even with its slight squish design, that also helps chamber efficiency, hence less ignition timing is required. In my opinion, 35 degrees seems a little conservative for an N/A P-90 flat top combo on 110 octane race fuel. I’m not saying yours is not ideal but you might be leaving a little more power on the table. It has been my experience for most P-90/P-79 flat top piston combos, around 37-38 degrees is where the engine prefers to run on pump gas, but this is dependant on many factors which could influence it to a little more or less timing. With the even smaller, more efficient, better squish chamber of the MN-47 or P.Reiths welded N-42 chamber pictured here, ideal optimum total ignition timing could be as low a 34-36 degrees.

 

Chamber flow efficiency, plug location, squish, fuel octane, cylinder pressure, all dictate how much ignition timing an engine will require/can take for maximum output and also how much timing it can take without destroying itself, (detonation resistance). Some are more efficient than others. Even within the L-series family there are drastic variations as to what ideal timing is depending on the cylinder head and pistons used.

 

 

Head2Medium.jpg

 

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