compression 200psi

[Matt_E]

Riding style plays a big part here.

For me personally, I need to be able to go WOT for at least 10-20 seconds without trouble.
As such, I cannot run 190+ psi on a stock bore with stock ignition.

Sure, if you've got throttle control and will not go WTFO more than a couple seconds, run 230psi on pumpgas all you want.
Not for me. :biggthumpup:

 

[chunky]

took the head of to have a look for detonation
how does this look (if you can tell from these pics)

 

[Matt_E]

Don't see deto

 

[waxhead]

hey i ran 225 on my hx with pump gas

i just made sure it got rid of the timing up top


you can make an engine live like that as long as you can control the timing

 

[chunky]

you can make an engine live like that as long as you can control the timing

but with stock timing at the minute could it be harmful if i was riding wot for short periods of time on a regular basis??

 

[Matt_E]

How short?

If you want to ride WOT or even close to that on stock timing, don't go past 190-200psi.

 

[chunky]

was thinking of getting the advent ignition fitted.
if my timing was advanced would it then be ok to run 93 octane with 200psi?
what way would the timing affect the 200psi with the 93 octane?
know very little about this as you can probably tell!!

 

[Matt_E]

It's impossible to tell you the whole story with all the variables getting thrown in here.

Yes, you can run 200 PSI on pumpgas on a stock ignition if you ride careful.
You can run 200PSI on an Advent, just set up the curve right (advance down low, retard on top)

 

[chunky]

got it.

 

[chunky]

Either have your domes recut to 38cc and the squish corrected for the 84mm piston size or just buy some new domes. This will give you about 180psi or so depending on your porting.

if the domes i have now are putting out 200psi, what all would have to be done to the dome to get it to put out, say, 185psi?

 

[sjetrider]

decrease your compression via domes or get 110 octane fuel before you even ride again IMO. No way I would risk that in any situation. Domes = $80.00
Complete top end & boring plus domes $350.00 min. and pray it doesnt destray a cylender/ crank or cases too.

 

[Matt_E]

Figure out your mechanical compression ratios and go from there.

 

[chunky]

took the squish reading on both cylinders
front of front cylinder is 0.050
back of f/c is 0.045
front of b/c is 0.050
back of b/c is 0.053

do these squish readings seem ok for the compression that is being put out?

 

[Matt_E]

Yes....rule of thumb is 0.045 min for pumpgas on that bore and pistons.

 

[chunky]

so if i wanted to lower the compression for this set of domes, would i need to get the radius of the dome machined again or would i be able to lower the compression by altering the squish, if you know what i mean?
or would the whole dome need altered in this case?

 

[Matt_E]

I don't know...an engine builder would.

 

[chunky]

thanks for your advise

if any engine builders on board feal free to chime in!

 

[waxhead]

i run 50 thou on my boats 0r 1.1 mm squish
yes on the stock ignition you will be pushing your limits

if your squish is to tight and then yes you can reduce your compression ratio by machining squish to correct clearance

 

[chunky]

if your squish is to tight and then yes you can reduce your compression ratio by machining squish to correct clearance

in this case then if i took the squish to 55 thou would this make a noticable difference in compression and if so is it possible to say how much?

 

[Speedfreak]

If you have an o-ring head then throw a gasket in there to check the compression. Measure the gasket and add that to your squish. I'm like Waxhead I like squish to be at 50 thou or maybe 52 to play it safe. But having too much squish will only lower compression and HP it won't cause any problems.