You gonna have to use a higher octane fuel. Personally, I thought about the higher comp pistons. I talked to John Noonan at JE pistons ( a famous top speed record holder) and he told me that the gains (2-3 rwhp) are not worth the money and the labor, plus the use of higher octane fuel. He told me to stick to head mods and leave the bottom stock. I thought about it and it makes sense. I know of another hawk rider that detonated his engine with high comp pistons, caused it to seize and he crashed.

 

That doesn't sound right. Why does JE even offer the pistons for the VTR? Because they need it, that's why. The power gains by themselves, more than 2-3 by the way, might not justify the cost for some people. Any modifications done to the heads would be limited by the compression of the stock bottom end. It's a cumulative effect, and the compression should be the first step.

His comments are also suspect because he brought up needing to use higher octane fuel. Even at 11.5:1 you can safely run 92 octane (side note - the guy who melted his engine had aftermarket pistons PLUS milled heads. Who knows what his compression actually was. I think he also had jetting issues too, which is not the fault of his engine configuration). Do the math and figure how much $.20 more per gallon of fuel amounts to over a year. It's pretty insignificant.

Ask John Noonan what compression HIS bikes run. I doubt it's stock.

 

Hey Killer, I reckon you need cams to go with your other mods. My info is that this really works well together on the VTR. Cams or pistons on their own don't work anywhere near as well as the combo does. I know a guy who has both and he is very happy.

 

Yeah, I realized this as soon as I got mine back together. They weren't in the budget for this round of modifications, but they'll find their way in pretty soon. What cams did your friend use?

 

Good question. Being in Australia our options are a bit more limited than yours. I will see if I can find out if he knows what the shop that did the job used.

 

Higher compression is needed with more radical cam timing. 11.5:1 is getting close to the limit with stock cams with pump gas. With milled heads, I was pretty much at the limit for 92 octane fuel with Stage 1 cams (Moriwaki). That's mainly due to the fact that the cams do a good job of filling the cylinders at midrange engine speeds. The engine is well tuned from the factory for street use on pump gas and factory ignition timing. If I were to build another one (and I really want to) I would pretty much do all of the same things. Probably would not deck the heads for a street engine. And I woudl test various ignition timing settings.

Jamie's right. I was jetted for high altitude. Judging by the coloration of the intake valves on teardown. I was running pretty lean at sea level. the added heat probably contributed to detonation.

I'm not sure how long it had been detonating. I didn't hear it. Engine seizure was not the cause of my crash. the pistons were free in the bores when I tore it down. But the 2nd compression ring was pinched in the ring groove and the bore was mildly scored.

 

I found out he had a custom grind done here in Australia, so not much good for you I'm afraid. Last time I heard Moriwaki stuff was still availale.

 

Thanks Shayne. I know of at least one Hawk owner here in the states who had a custom grind done by WebCam, so that's a possibility.