My Custom GT750's

Suzukidave · Post by **Suzukidave** » Sat Feb 19, 2011 5:32 pm

Thanx Kevin ...Looks like i really need to think about a wider squish but i wonder now what the compression will be like set this wide . I guess there is one way to find out .. Richard you didnt happen to keep a note on this info when you did the trapped head volume figures long ago ?

tz375 · Post by **tz375** » Sat Feb 19, 2011 11:06 pm

Dave,

We worked on 1.2mm and remember that the squish band is very narrow. If it were wider we would need it to be much deeper. 1.4mm (0.055") would drop compression from 6.9 corrected to 6.8 and would drop MSV from by 10%

I agree with DF that a high squish velocity is not necessarily ideal in a motor with such low trapping efficiency, but I suspect that the issue here is that as MSV rises, so does combustion chamber turbulence and flame propagation speed and that meas you have to retard the timing at the top end.

This is a street motor rather than a racer and slight loss at the very top end would be a small price to pay for stronger mid and low end IMHO.

Suzukidave · Post by **Suzukidave** » Sun Feb 20, 2011 4:43 pm

As always Richard thanx for your thoughts so 1.2mm ( .047~.048") it is .

Suzukidave · Post by **Suzukidave** » Mon Mar 14, 2011 3:00 pm

Finally got around to checking the squish as it sits right now and ended up pulling out the copper head gasket to do the check as it alone added .032" to the stack so with the head bolted back down and the 2 base gaskets and spacer in place but no head gasket i get .101" across all cylinders . Looks like the shave job i had done to clean up the head and base surface of the block is right on the money . So with everything added up i get a measurement of .133" and i need .047~.050 so looks like the block top needs another .085 decking to get it at .048"

tz375 · Post by **tz375** » Mon Mar 14, 2011 3:51 pm

Nothing wrong with your calculator Dave. I would take off 2.0mm/.080" which should leave it about 0.1 -0.2mm wide so it's a touch on the safe side.

Suzukidave · Post by **Suzukidave** » Mon Mar 14, 2011 4:04 pm

Good advice as its easier to take a shave off later than to figure out how to add it back on

Suzukidave · Post by **Suzukidave** » Tue Apr 05, 2011 2:57 pm

Got the cylinder back and the machine shop didnt do a very good job on the decking leaving cut marks and some area's of tool chatter . I spent a good hour wet sanding down the deck till it was nice and flat n smooth . Put the top end on and rotated the piston around to TDC and things LOOKED much better

Suzukidave · Post by **Suzukidave** » Tue Apr 05, 2011 3:01 pm

But then when i bolted the head on with the copper gasket in place this time i find out they must not have machined off the full .080" as the squish is still even all across but at .060" .. still too wide

.. i guess better too wide than too narrow so back apart and back to the machine shop again for a ( better this time i hope ) .010" skim .

water cooled · Post by **water cooled** » Tue Apr 05, 2011 3:24 pm

Dave, maybe Cometics has thinner copper sheet that you could try before re-decking. I might do the same and try a thinner gasket...worth a phone call. BTW, what's going on with that bolt hole between the two cylinders? Is that an insert? Did you relocate that hole for some reason...

Suzukidave · Post by **Suzukidave** » Tue Apr 05, 2011 3:31 pm

Hi Kevin , i called the machine shop and caught them before they closed up shop and told them the story . they said if it was there mistake they would skim off the extra .010" no charge .. i said to them this time the surface really needs to be smooth . the hole between the bores is the stud hole as it needed to be removed for the decking .

water cooled · Post by **water cooled** » Tue Apr 05, 2011 3:39 pm

the stud hole looks like it was drilled out and an insert put in...i havent seen that before... and the 10mm bolt holes look tapped??

Suzukidave · Post by **Suzukidave** » Tue Apr 05, 2011 3:47 pm

I had tapped all the stud holes so i could get the block off . maybe with this 72 block the insert for the stud was cast into the block .

tz375 · Post by **tz375** » Tue Apr 05, 2011 6:35 pm

Dave, that's correct. I have a couple of 72 blocks and there's an insert screwed in for that stud. On later blocks it's cast in place IIRC

Suzukidave · Post by **Suzukidave** » Wed Apr 06, 2011 8:39 am

I must have messed up somehow on the first cut figures as this morning we measured the block height and compared the figures to the before and indeed they had cut off .080" from the deck surface , somehow my figures are off by .010"

i cannot figure that one out .

Suzukidave · Post by **Suzukidave** » Fri Apr 15, 2011 5:41 am

I just cannot win , i got the block back and did another trial assembly to check the squish and even after the .010" removed the test shows i am still .005" too wide . This is getting expensive as the last decking was a super smooth finish it was another 40$ .. i have around 150$ in machine work now just to set the dang squish

My Custom GT750's

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