Group K says no timing bump for pump gas

[SharkB8]

I am replacing my 633cc Superjet engine with a 701cc, and while its out I thought I would have Group K perform their mild Sleeper package on it.

Apparently I have to have the 633's cdi box modifiied for use with a 701. Fine.

I thought that maybe an MSD enhancer would solve the problem (would it?) and also give me a little extra power due to the change in ignition timing.

I asked Harry Klemm about this and he said that, to ensure compatibility with pump gas, "no" ignition timing change would be best.

http://www.pwctoday.com/showthread.php?t=194664

So you can't run an MSD enahncer on a Sleeper? I am surprised. Any comments?

 

[SuperJETT]

Harry is very conservative, very.

 

[crammit442]

I am replacing my 633cc Superjet engine with a 701cc, and while its out I thought I would have Group K perform their mild Sleeper package on it.

Apparently I have to have the 633's cdi box modifiied for use with a 701. Fine.

I thought that maybe an MSD enhancer would solve the problem (would it?) and also give me a little extra power due to the change in ignition timing.

I asked Harry Klemm about this and he said that, to ensure compatibility with pump gas, "no" ignition timing change would be best.

http://www.pwctoday.com/showthread.php?t=194664

So you can't run an MSD enahncer on a Sleeper? I am surprised. Any comments?

I'd agree with him about no additional STATIC advance. I don't think he was suggesting that the enhancer not be used.

 

[SharkB8]

So it wouldn't be ludicrous to put an msd enhancer in a Sleeper 701...?


Is the potential problem that you might get detonation at higher revs? I can use a little octane booster.

 

[kevbo]

GroupK mods are designed to run at full power for long periods on cheap gas. This makes them mild by freestyle standards. An enhancer can make a small difference in throttle response if you constantly toggle the throttle (like most people). High compression and early spark timing have become very common but nobody is running these WFO for very long.

 

[SharkB8]

I know zero about engine tuning, but it surprises me that detonation is a problem at higher RPMs. I read about a deto test that Honda did - as the engine approached 20,000 RPM (WFO by any standard) the octane requirement fell to somewhere in the 60's. This obviously wasn't a SuperJet motor but it led me to believe that deto is less likely at higher RPMs, everything else being equal. (That is defintely how it works in my old chevy truck!)

In any case, is it reasonable to expect that a Sleeper with an MSD enhancer would be ok for full throttle operation while racing around buoys with friends if I buy the best pump gas and add some octane booster?

 

[Matt_E]

Detonation is absolutely a problem at higher RPMs, rather than lower.
This is especially true on a motor without knock controls (such as most any 2-stroke engine)

 

[SharkB8]

I searched around for that article and finally found it. Here it is in case anyone finds anything useful in it. At the very end of the page, Item 8 refers to the high-RPM test Honda performed.

http://www.factorypipe.com/t_deto.php

 

[restosud]

yes,it's true that at higher rpm's the octane rating can be lower.the only problem is that jet ski motors don't turn those high rpm's.

 

[SuperJETT]

That article is only referring to operation above 12,000 rpm on that particular engine. Jetski engines turn nothing close to that.

I know zero about engine tuning, but it surprises me that detonation is a problem at higher RPMs. I read about a deto test that Honda did - as the engine approached 20,000 RPM (WFO by any standard) the octane requirement fell to somewhere in the 60's. This obviously wasn't a SuperJet motor but it led me to believe that deto is less likely at higher RPMs, everything else being equal. (That is defintely how it works in my old chevy truck!)

In any case, is it reasonable to expect that a Sleeper with an MSD enhancer would be ok for full throttle operation while racing around buoys with friends if I buy the best pump gas and add some octane booster?

 

[kevbo]

Jetski engines dont compare very well to other types. You will find that they are a lot easier to burn up.