[Jay S]

I will post the head flows next. But here is some explanation on compression.


There is not much special tuning like jetting or special ignition curve’s on this engine. It isn’t hard to tune. At least NOT YET. The massively ported single plane intake and headers I have on it right now put peak power well past 6000 RPM. I expect there could be some tuning challenges as I make changes that tend to narrow back up the power band, like a dual plane intake, or possibly exhaust manifolds. Right now I don’t even know how many RPM’s it can run…It buries the Tach. 6000 is a good place to stop for now.

For the ignition the distributer and curves are original. The initial timing is 14, with 38* total. It is running NGK plugs with a 7 for heat range, pretty cold plugs. I like to keep the operating heat range for spark plugs on the cold side if possible.

Porting heads for more flow, bigger port CSA’s, big inductions, big headers and exhaust, combined with the right cam, can work at pulling more air into the engine. More air pulled into the engine from those things can cool the air&fuel charge, and make it more dense and less prone to preignition.

The cam on this engine has an LSA of 114, but the way it is ground with the long closing ramps it acts like it is a 116 LSA. To reinforce that, the heads are ported in such a way the LSA acts quite a bit wider also. The heads are ported to shift some of the air flow from scavenging to cylinder fill. When the heads flow a great at low lifts it has a similar effect of narrowing up the LSA of the cam. If you left the compression low, and lost the low head flows from porting, the porting would be hurting power. The compression helps the top end power a lot, off setting the loss of power from less flow at during scavenging. The camshaft and the head flow are matched up to the compression. The end result is a smooth long power band, that is not very picky on carb settings or shift points. Cranking it over when starting your would never guess it has that much compression. I have done some cams in engines that by the way they act you would guess the engine to have 11:1 compression, but are only in the 9s. This combo is opposite of that, it is at 11 and it’s manors act like it only has 9:1.