How To Find Piston Dome Volume

[datzenmike]

Update: I emailed Arias pistons about the pistons and included a link to this thread. This was the reply:

 

"unfortunately, I can't find the correct information for the pistons, no serial number to find it and the only thing I can tell you is that the pistons for these engines don't usually come with high compression and the most you could have on these pistons is about 3.5cc... which would give you about 11:1 compression ratio. I have seen the pictures and with a 45.0cc combustion chamber, you could have as much as 5.0cc but that would be about max. to give you a point of reference, 86.0mm bore with 86.0mm stroke and 45.0cc combustion chamber, .040" gasket, would give me about 10:1 with a flat top piston..."

 

86 bore and stroke open chamber head and 3.5cc dome = 10.73

 

86 bore and stroke open chamber head and 5cc dome = 11

 

86 bore and stroke open chamber head and flat tops = 10.11

[banzai510(hainz)]

spend the money and run them!!!!!!!!!!!!!!

 

Hang writes.

i sold the same set, it would produce ~11:1 in a stock L20b w/an open chamber head.

 

 

"the writting is on the wall NOT to use them"

[datzenmike]

11 to 1 is like the X wife. Hard to live with and glad when we separated!!!! Someone else is learning that right now!!!! :lol:

[dimedriver]

Sell them on ebay or dime-quarterly for more than you paid for them. Im sure someone with a 510 setup for SCCA GT1,2,3,4 will like them.

Make sure you list them as for "racing only".

Then get the over bored L18 4cc dish pistons for $80 from summit racing.

Or even the L28 flattops.

 

-Avery

[banzai510(hainz)]

L18 4cc is more than enough if those pistons are still avail on a L20

 

with a closed chamber head and that MIGHT still need good gas 91oct or above

[Eric p]

I'm interested in buying these if you still have them.

[Eric p]

Anyone know Logical? I've tried PMing but no response.

[Eric p]

OR anyone know if he sold these pistons?

[DanielC]

To check the compression ratio, you need these. Plexiglas, or acrylic plates, and a burette. one of these plates fits a Datsun L-engine, the other fits a Ford 390 FE engine.

Here is a close up of the burette.

 

First, you need to do a trial assembly of the block. This is especially important, with oddball part combinations. This will also sort out impossible combinations, like putting a L-18 crankshaft in a L-20 block. The deck height will also be obvious.

 

Once the block, piston, and connecting rod are assembled, find TDC. If no part of the piston sticks up above the deck, put the plate on the block, and use the fluid of choice to fill the area between the plate and the piston. Check under the piston for any leakage. Tap on the plastic plate, to help move air bubbles to the fill hole in the plate.

 

If the piston sticks up above the deck, and these pistons probably do, you still have to assemble the parts. Find TDC, and then move the piston down. It might be easier to calculate volumes using 10 mm measurement to move the piston, to keep all your measurements in one system.

 

The diameter of the piston is different from hot to cold, and different across the pin boss, and 90 degrees to it. Use the bore for the diameter, assuming the piston clearance to the bore is correct.

 

 

One (and there are many) factor that affects detonation of the engine is quench area. If the piston top surface is within a very close, but not touching distance to the cylinder head, the closeness of the cool piston, and cylinder head suck heat out of the flame front as it travels in this area. This slows down, or quenches the flame.

The peanut head, with flattop pistons does this. This is why a peanut head can run a numerically higher compression ratio, than an open chamber head, and not detonate.

[Eric p]

Thanks Daniel. Got that spec'd out but still need to find those pistons... Logical has to be out there some place and/or those pistons are...?