difference in 351C-2v heads

[Don C]

The only thing I see is the 1.5cc dish volume. Even the notches for the valves is more than that. Everything else looks good.

 

[Ron Tanzi]

Thanks for all those numbers! It’s given me a decent understanding of the whole compression calculating thing.

I filled in a couple of “could be” numbers and got 9.1:1. This is with forged pistons from a fed mogul kit and .02 piston to deck height (so could be less still):

What do you think? Looks correct? (but not optimal perhaps?)

My 72 2V with open chambers that I measured were 76 cc per chamber,Trw flat top pistons (2 valve reliefs),standard Fel-pro head gaskets. 0 deck height, .030 overbore ended up calculating out to 9:3:1. I am at peace with it. Ron

 

[Vinnie]

The only thing I see is the 1.5cc dish volume. Even the notches for the valves is more than that. Everything else looks good.

The pistons are from this kit:

https://www.summitracing.com/parts/fem-csmhp732-311/kitcombocontents/make/ford?prefilter=1

 

[Don C]

Interesting, most with two valve reliefs are at least 3.0cc, the single relief Keith Black are 2.0cc.

 

[Vinnie]

I'm trying to fill in this calculator:



I couldn't find the piston crown diameter for the piston I might use (https://www.summitracing.com/int/parts/slp-l2379f30/overview/). Did I guestimate it correct? I have no clue to the actual diameter of a piston but surely it's not the bore size of the block...

 

[Stanglover]

For what it's worth, Keith Black KB 177 Hyperutectic flat top pistons have a compression height of 1.67" Stock are 1.65". That extra .020" will give you zero deck height. and up your comp ratio. With open chambers, it will not likely get any compression pinging.

I had these piston in my M code closed chamber and at zero deck, 4.030" bore with a .039" compressed head gasket, it pinged like crazy at approx. 10.6:1 on 91 octane Shell gas. Head gasket choice will also change comp ratio.

Due to other circumstances, I dropped to KB 148 13cc dished top pistons, still at zero deck, but a more manageable 9.4:1. This is with CC heads of course. The rest of pinging elimination is down to timing and fuel choice.

Below is the chart for my engine. If you Google Keith Black pistons or UEM piston, you should find this calculator. What I found is different calculators give slightly different results. Mine ranged from 10.56 to 10.89. There are other considerations that are not taken into account with the basic calculators, so these are a guide only.

Geoff.

 

[Don C]

I'm trying to fill in this calculator:



I couldn't find the piston crown diameter for the piston I might use (https://www.summitracing.com/int/parts/slp-l2379f30/overview/). Did I guestimate it correct? I have no clue to the actual diameter of a piston but surely it's not the bore size of the block...

It should be closer to 4.028 to 4.0285.

I believe the figure they are looking for on the piston ring height is the distance from the top of the piston to the top of the first compression ring.

I would also use 0.00 on the advance/retard.

 

[Don C]

I'm prejudiced, of course, but I still prefer my spreadsheets for these calculations. I know what formulae were used and the results of each calculations are shown. I added the calculation for the volume between the top ring and the top of the piston. It only adds 1cc, or less in most instances, and for most calculations will only change the static compression ratio by 0.01, or less.

Dynamic compression ratios are also available in the second tab. I also added some camshaft intake valve closing angles for comparison.

If you want to see what formulae I used, all you have to do is unprotect the sheets, they are not password protected.

https://www.7173mustangs.com/thread-engine-and-compression-calculations?pid=199290#pid199290

 

[Vinnie]

Don, thanks for reminding me of your sheets! I filled them in and both SCR and DCR are 100% identical, nice!

Big thank you to you