High compression issue

[air blair]

 

[tstewart]

A person posted...he used vp110. Vp110 is not "stated". In spec sheet to b oxygenated. U then state 3 jet sizes... About an oxygenated fuel ??? More confused people now, I'm not, but words (incorrect) will mislead some down a bumpy trail.

 

[tstewart]

Wish that pic was there before

 

[Big Kahuna]

A person posted...he used vp110. Vp110 is not "stated". In spec sheet to b oxygenated. U then state 3 jet sizes... About an oxygenated fuel ??? More confused people now, I'm not, but words (incorrect) will mislead some down a bumpy trail.

It's really simple. If you make a change to your dome size. You may need to re-jet. Just adding race gas is not the answer. Is that hard to understand? Out of here.

 

[Brian_216]

I never saw vp110. Only c12 and such sold around here. We do have a station with sunoco 110 at the pump.

Here is an interesting read. It's old but good. It's a lot to read but really valuable info when you start getting into understanding 2 strokes further than the next guy.

http://www.2strokeengine.net/gordonjennings/twostroketunershandbook.php

I wish I could find the article about burn rate, detonation, timing and squish and how they all relate. It was really in depth.

 

[BruceSki]

And we sit and wonder how engines get blown up all the time...

We know why. Just hate to admit we were playing with poop.

 

[Brian_216]

With the high comp domes what was the corrected compression ratio of that engine? And what did the squish measure out at?

 

[air blair]

With the high comp domes what was the corrected compression ratio of that engine? And what did the squish measure out at?

I have no idea, i had a head i got on a trade put an oem gasket on checked compression at 110 ish figured anything over 190 needed a little race gas. Couldnt tune it in at all. Got a good plug color but in beginning the braaaap was goofy. Squish a proper compression thats just more than i really wanted to know on a little ol' backup engine. So i toned her down with ada head 40 cc domes now.

We know why. Just hate to admit we were playing with poop.

Poooooop is what poop does. Ive been guilty in my past i baught a 650sx and was told it needed 93 octane cause of shaved head. At that time i was a newby to jetskis and just ran cheap gas and the cheapest oil i could buy. I paid the price on that one jacked that engine right up within 15 gallons. That was about 4 or 5 years ago. I'm a pro now. Lol

 

[augustaf]

So i put a 210-220 compression westcoast head on a 760. Race gas was used. It hit well but not well enough. Suspected blow by as i didnt have a girdle kit on it. I changed my head back down to get 160 compression. Braud band brap now when before it was almost a rev limited braap. Like braaaa-aa-aaaa- ap. Now braaaap! Understand?

Never knew that westcoast had domes for a 760. Your ADA would do nicely with 37cc domes, 93 pump gas on a 760 - that is if your 760 means 84 bore , not 81 + 5mm stroker.

 

[DAG]

Changing domes will "never" change your fuel/air ratio. Why do ppl say you may need to rejet for a dome change?

 

[Big Kahuna]

Changing domes will "never" change your fuel/air ratio. Why do ppl say you may need to rejet for a dome change?

Christmas of 1999 I got a cast R&D head. Installed it. Made it around the corner (5-10 minute run) and stuck a piston. Why. Makes more heat. How do you control the heat. Higher octane and/or more fuel. I was running 92 octane. That not the issue. I was also running the same settings as I ran with stock head and B PIPE.

 

[DAG]

I didn't think about the added heat, can defiently see how it would add more heat. if you keep your pisser temp properly adjusted the jugs and pistons will expand together, wouldn't they?

 

[fastgtfairlane]

when you change domes to add more compression, you go to a higher octane fuel to combat the additional heat.. depending on what higher octane fuel you run you may need to rejet.. and using cranking compression to determine what octane fuel you run will cause a seizure quicker than anything else.. rejetting isnt really a bad idea for extra insurance but not always necessary..

 

[DAG]

Care to add numbers for the statemen above

 

[fastgtfairlane]

numbers for what?

 

[Vortex]

I wouldn't hesitate to jet up 5 sizes, I did that after I installed a mod chamber pipe an k&n's while still using the stock head. What ignition are you running? Msd?

 

[air blair]

What goes on under the head is interesting. Engine gurus have that figured out. I for one have tinkered with high compression. Felt different issues. Some things should be left to the pros. I'll bump up to 190 comp. And know that my setting must be right on and no air leaks or kaboom. For example i forgot to tighten a a.m. airfilter clamp it popped off carb and leaned out one cylinder when i b lined it home as a storm approached. Boom. I generrally stay within high grade pump gas range for a better than stock power hit(190). I have used low grade octane for a high compression head and smoked another one before. It usually comes down to my fault some how but on another note ive had engines just straight blowup for other reasons not my fault. I usually like to know what happened so i don't do it again. These days i always run a msd enhancer or comparable. Pre/post detonation is the key in the kaboom. That gas needed to explode at the right time