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How much boost on flat top pistons?

I ordered a .140" cometic, it should knock the c/r down to around 8.6-1, depending on how much comes off the head. Now my concern is getting the timing belt on.

You will be giving up squish, which is actually worse...
 
this isn't the 60s, you have a after market ecu, just get it tuned and run the higher compression. it will be so much nicer to drive. no need to knock your compression into the ****ter
 
You will be giving up squish, which is actually worse...

I've already been down this road with the B21, it worked very well. If the wire hadn't pulled out of the old ass Volvo EV1 connector and burned a pencil eraser sized hole through the cometic and the head I'd probably still be running that setup.
 
I cc'd the head and it appears to be 49.7cc's. my thinnest feeler gauge .008" was a little tight, so I'm assuming John V is correct at the pistons being in .007" , this gives 10.94-1 on the summit calculator. I'm going to get the head skimmed and check it again. I'll probably order up a cometic thick enough to reduce the CR below 9-1. The pistons appear to be forged, but I'm no expert, I'll have the machinist look at one when I drop off the head.

Did you include the stock head gasket thickness in the calculation?
 
Math is important if you don?t want to keep trying to make it work. Math lets you do it once.
I asked about the gasket because the CR return on the calculator surprised me. It ran good, but we never got it tuned.

Eh, no point in today?s era. Better fuel, tuning, etc. 7.5:1 is kinda useless unless you just wanna throw boost at it
that?s what we are trying to do, numb-nuts. The more you pressurise it, the longer it gives a good push on the down stroke. And we have a big open chamber with hardly a quench pad in sight.
You can get away with a lot if you keep the octane up and the tune conservative (and fat). But that?s not how you make big power.
 
New rings showed up today, ITM from Rock Auto, not chromed like machinist said I would get. He said hit the bores with 320 grit and assemble the pistons/cylinders with ATF . Should I do something different with the rings not being chromed? I will try to assemble the bottom end tomorrow with new big end rod bearings and turbo drain welded in oil pan. Machinist recommended .024"-.025" ring gap, this is ok per Haynes manual specs as well.
 
New rings showed up today, ITM from Rock Auto, not chromed like machinist said I would get. He said hit the bores with 320 grit and assemble the pistons/cylinders with ATF . Should I do something different with the rings not being chromed? I will try to assemble the bottom end tomorrow with new big end rod bearings and turbo drain welded in oil pan. Machinist recommended .024"-.025" ring gap, this is ok per Haynes manual specs as well.

Dang, I guess I better pack up that thing and get a mailing address and get it sent, huh?
 
Math is important if you don’t want to keep trying to make it work. Math lets you do it once.
I asked about the gasket because the CR return on the calculator surprised me. It ran good, but we never got it tuned.

that’s what we are trying to do, numb-nuts. The more you pressurise it, the longer it gives a good push on the down stroke. And we have a big open chamber with hardly a quench pad in sight.
You can get away with a lot if you keep the octane up and the tune conservative (and fat). But that’s not how you make big power.

Yeah numb-nuts, and mordern fuels and tuning allow you to run higher compression with higher boost, making a much better daily driver.

Of course your error margin goes way down with higher compression, but something tells me OP isn’t making lots of power anyway.
 
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