Squish band taper

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Yamablue

Member
Joined
Mar 7, 2004
Messages
221
Location
Ham Lake, Mn
I just measured the squish band on my 02 viper with a Peak head and the 23cc inserts. It appears the squish band is parallel to the piston at 0.053" from the cylinder wall to the dome. Is this what I want to do, or do I want to have a slight angle to it. I was thinking of chucking up the inserts and adding 2 more degrees to the total angle which would put it around 10. I would also like to pull a layer out of the opticool gasket to get the piston to head around 0.045" and gain back some of the compression from the cut. Is there any reason why this wouldn't be a good idea?

Also, are there any problems with pulling the Opticool head gasket appart. It appears the center layer is just a stainless shim, is that the one I would want to eliminate, as the others have the sealing ribs? Thanks.
 
I'm runnning 91 non oxy, but I'm also using an SRX/Viper High RPM box. I would think I could handle pulling a shim out since I'm going from 21 cc on the mag/center (OEM) to the 23cc inserts with better cooling. I'm more concerned about the parallel squish than than the compression. Thanks for the gasket info.
 
you should take trapped volume measurements, w/the head installed on the engine, to get your UCCR and CCR figured out. also, i would want to run a pump gas viper, on a squish band any tighter than .055" or so, w/todays poor fuel. i thought the last time when i measured up a viper piston crown, that it measured 9deg?? if that's right, then i would personally like to see a 11deg band angle for pump gas. 2deg over piston crown angle is a good start.
 
Piston crown is closer to 8 degrees. So what would be better 0.048" at the cyl wall and 0.064" at the radius of the dome with the band at 0.420". Or would .058 at the wall and 0.072" at the radius be better. Either way the OEM pistson dome is about 8 degrees and the head is cut at 11. Again, premium non-oxy and SRX CDI.
 
well, between your choices, the tighter squish is better for having less mixture between squish band and more in the "bell" of the head, but i wouldn't run that setup w/93 oct, or for the trails, etc. i was on my TSR, and played w/your numbers. i also just used 6.6:1 CCR (stock for center and mag cyl's) for you, even tho you have a peak head, as i don't know for sure if your 23cc is flat plat volume, or installed trapped volume.

so, saying that you have .42" (10.67mm) wide squish band, or 52.4% squish area, 12.5:1 UCCR, 6.6:1 CCR, 30.2mm ATDC exh port opening or 81.435*, 20.16cc trapped volume, and .058" (1.473mm) squish clearance, you would see 25.6MSV (squish velocity) @ 8700 rpm. TSR's estimate of fuel is 91 octane.

now, if you reduce the squish clearance to .048" (1.22mm), you will end up reducing the trapped volume .95cc, thus upping your UCCR and CCR. now, you would have 6.88:1 CCR, 13.07:1 UCCR, 19.21cc trapped volume, and increasing the MSV to 30.1. now TSR says 94 octane.

personally i would leave the squish at .058", but that's just me i guess.
 
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Thanks for running the rough numbers. I believe it is the flat volume as it was for my old 22 and 21cc chambers. Does it matter/help for the velocity that the band is now tapered instead on parallel to the piston crown?

Also, how were the factory dome measured, flat or trapped volume?
 
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Yamablue said:
Thanks for running the rough numbers. I believe it is the flat volume as it was for my old 22 and 21cc chambers. Does it matter/help for the velocity that the band is now tapered instead on parallel to the piston crown?

Also, how were the factory dome measured, flat or trapped volume?
Click to expand...

tapered?? do you mean how your squish band angle is 2-3deg greater than piston crown angle? if so, that's the norm and for a pump gas trail machine, i wouldn't want to see the squish band angle to be less than 2 deg over piston crown angle. you can go tighter, but that's left for higher octane, "built" motors. also, the cc volumes that yamaha has posted in the service manuals, is suppose to be trapped or installed volume and not flat plat volume.
 
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