Quote:
Originally Posted by Juho
I've already started modding it; welded combustion chambers and took the valve seats out. Bigger valve seats and valves coming, so it's possible to make the ports better.. intake port requires the most work since I'm trying to change it for 'high tumble flow'.
On factory lean burn engines, are there some clear differences in combustion chamber? Atleast Honda Insight has valve disable function(?) and intake ports made for swirl flow; which is quite odd for a 4 valve head (per cylinder) but understandable when it's disabling the other intake valve making it act more like a 2 valve head.
So in my case it's clear it's best going for tumble flow.
Compression ratio is another thing. Because I'm running the engine on E85, it's possible to benefit of quite extreme compression ratio.
I'm targeting to around 14 to 15:1 ratio, which should still work with the small cams.
Any thoughts/ideas?
If I find the previous threads related to lean burn engines with useful information, I'll post their links here.
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Welcome to the forum!
I'm not aware of combustion chamber differences. I know all lean burn Hondas use a high swirl design, and they can lean out to something like 1.7 lambda and run smoothly.
The Insight also doesn't fully disable one valve - it still opens it fractionally, to prevent fuel from pooling on the backside of the valve. It's really the asymmetrical valve opening that helps. And, above ~2800rpm, both valves become locked together and open fully, to allow the engine to breathe at higher RPM.
I wouldn't worry about knock at moderate to low loads. Even if it does knock (and it isn't likely to), it isn't likely to be dangerous, with cylinder pressures being so low.
What method did you use to determine your ignition timing?