Closing up the squish band clearance on my modified head! My testing continues....

[joeak47]

I've been gone for a while. I've had time to test a few more things...

I re-machined the squish band hemi head i made a few moths ago. I reduced the squish band clearance from my original .066 thousandths to .072 thousandths.

WHAT A DIFFERENCE 30 thousandths of an inch will make!!! I probably won't go much more,but who knows. I beleive that I'm getting into the danger zone.

I also removed my oil injection,so I could test pre mix ratios,and different jetting. We'll see where this goes too.

Right now I'm testing Maxima castor 927 at ...20 to 1 (I know what your thinking),and I have noticed a power increase from running more oil in the mix. I believe its creating a better ring seal. The difference in power is very,very noticeable compared to 32 to 1 that I tested before this batch of fuel.

I'm still running that "Cheap cast piston" that everybody loves to hate....with zero issues.

The testing continues.

 

[Awk08]

Re: Closing up the squish band clearance on my modified head! My testing continues...

as always...good tests/info Joe,
keep 'em coming

 

[sicivicdude]

Re: Closing up the squish band clearance on my modified head! My testing continues...

Did you run this setup at high temperatures for long periods of time?

Also, what's your cranking compression on this head?

 

[scotj77]

Re: Closing up the squish band clearance on my modified head! My testing continues...

leavin us hanging here with not much input. no compression, engine temps??????

 

[joeak47]

Re: Closing up the squish band clearance on my modified head! My testing continues...

I'll get all sorts of info tomorrow.

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

danger zone is farther out then most think. im running 180psi and something like .030 squish on crappy 91 octane pump gas, 3mm stroker blaster.

 

[Surfrjag]

Re: Closing up the squish band clearance on my modified head! My testing continues...

i find that hard to beleive zedicus.. any more info on that motor?

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

wifes blaster, 35 a/s pwk, clamp on air cleaner, 4 degree advanced timing. forged wiseco piston, i think 67mm, been a while since i had it apart since i built it. porting and head done by c-leigh racing.

no easy way to prove the fuel unless you want a clip of me mixing it at the pump and pouring it in the quad.

 

[sicivicdude]

Re: Closing up the squish band clearance on my modified head! My testing continues...

180 psi and .035" of squish clearance with a timing advance? Either you have defied the laws of physics, that's 191 octane gas you're running and the "1" label just got rubbed off (joking obviously), or that engine is bound to be short lived.

I've had trouble with predetonation on 93 octane fuel at 170 psi at 100degF and .048" squish. <---that's "tight" for a pump gas engine....

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

not really, your just thinking inside of the box (cylinder) hehe. and timing itself can't really alter preignition.

did i mention i run a bcpr5ey plugs? most people would say that is WAAY to hot.

 

[sicivicdude]

Re: Closing up the squish band clearance on my modified head! My testing continues...

I'm fairly certain that your piston will agree at some point.

I'm about as "out of the box" thinker as it gets around here but consistent personal testing has told me otherwise.

My previous engine setup was head done to 170psi with .048" squish running on pump. I would go out and "play" on the dragstrip and after the 4th or so good hard run it would start to ping. So again, either you've defied laws of physics, you haven't run that engine hot enough long enough to find out otherwise or there's a lot more to the story. The numbers don't lie, compressing certain grade PON gasoline to a certain amount of thermal energy will cause it to spontaneously combust (preignite).

Timing will have something to do with preignition... it will cause the piston crown to run hotter from the last combustion cycle so any hot spots on the piston will ignite the incoming charge as it's compressed.

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

the answer is in the heat and amount of fuel, not really the static psi or even the squish. though more squish and more static psi is more torque. the is a point where it will cause issues with top end power.

and blasters are air cooled so i consider my set up on the safe side. ive ridden it in 110 degree heat and never had any trouble

its been running with this set up for a couple years now.

 

[sicivicdude]

Re: Closing up the squish band clearance on my modified head! My testing continues...

So you're running a 450 mainjet to dampen out the fire? Straight divergent coned exhaust pipe so no backpressure charge gets back to the engine? Your wife rides it and never takes it over half throttle? You're stationed in Siberia where it never gets above 55degF ambient?

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

details. don't assume.

keihin A/S carb, its not overly rich, my wife puts around most of the time and i don't like fouled plugs. thats not to say it doesnt get ripped on too. and when its 110 degrees outside it doesnt matter if its WOT or just off idle, the engine on an air cooled bike is going to get HOT.

the design of the fuel charge, and the carb and the reed have more to do with cooling then the fins on the head. ive ran this blaster pinned to the hilt through sand on days it was so hot the wind would peel the skin off your face.

now things like piston to wall clearance and ring end gap come into play, and a forged piston and how it handles heat different then say, the crappy cast pistons i run in my banshee cuz with its craptastic 120psi engine i could run 85 octane in it and be safe.

 

[sicivicdude]

Re: Closing up the squish band clearance on my modified head! My testing continues...

For an occasional rip you can get away with that setup and especially putting around here and there, no problem at all. Run that engine hard two times around a TT track or a few times up a drag strip back to back and you'll hear that engine just a knockin'. I was able to get my BBK to knock in the back yard doing relatively small "laps". The predetonation really becomes evident if you don't give the piston crown adequate time to cool down after a long hard "shoot" up a hill or around a lap.

So I should say "Run hard consistently, 165psi static compression, .050" squish gap on clean fresh 93 octane is the 'accepted' standard for an engine with no pre-detonation problems."

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

i dont think you read the entire post. the river bottom here is sand, its MILES from bridge to bridge and goes between towns. it can be WOT for longer then a tiny TT track and it would take 20 trips down and back on a drag strip to come any where near the length we run up and down the dry river bead.

its my wifes blaster, that doesnt mean other people dont ride it. i like to take it out and school some of the punks on their 450's with their baffles removed. makes them look foolish.

 

[Awk08]

Re: Closing up the squish band clearance on my modified head! My testing continues...

as we've always said on here....every engine and situation is different !!!!!

 

[mmajay]

Re: Closing up the squish band clearance on my modified head! My testing continues...

as we've always said on here....every engine and situation is different !!!!!

I must add whats the other famous saying here?? PIcs or your lieing???

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

the air and fuel cool the engine too, expansion chamber wave will pull the heat out after the burn. but you cant just dump it to atmosphere, that blaster has an fmf pipe with a stock can. that is actually there on purpose. the fmf is not the most loved blaster pipe, but its tune and wave design work perfect for this engine.

an engine is an air pump, cool air and fuel in, hot air and burned fuel out.

 

[zedicus]

Re: Closing up the squish band clearance on my modified head! My testing continues...

i posted a pic of the psi gauge, i can borrow an infrared temp gun and take a vid of me putting fuel in the blaster.