Expansion/stretch of engine internals

Hi all,

Trying to figure out minimum quench distance I can run in a possible upcoming engine build. Anyone know how much a hypereutectic alloy piston will expand vertically as it gets hotter vs a 4032/2618 alloy? Additionally, any guesses on how much a 4340 steel rod will stretch at a maximum of 7000 rpm? Piston rock is not really a consideration as I've found a technique to reduce it to a minimum. I read an article by Kevin Cameron (I think) a while back where motorcycle racers were testing minimum quench distances and landed around .020 inches or about 0.5mm. This was at over 16000 rpm using high quality materials but I have a feeling in my application there is a chance it can be reduced further. Just something I've been thinking about, let me know your thoughts.

Thanks,

Demetri

Hmmm, my response seems to have disappeared.

Anyway, it would help if you gave some info' on the engine, use, and fuel?

Some good info in this discussion on speed talk covering quench. On page 10 of 22 they talk about different piston materials and there expansion, also piston/rods stretch at rpm. Hope it helps.

[url=https://www.speed-talk.com/forum/viewtopic.php?t=65624&start=135]https://www.speed-talk.com/forum/viewtopic.php?t=65624&start=135

Accidentally deleted my reply to Gord.

M52TU, street use, 93 octane. Trying to figure out how much things expand so I can run the closest clearance without smacking the head.

Maybe this helps, these are rough numbers, this is a generalization, a lot more things need to be taken in account, but there is information online for more exact numbers.

a common accepted corrected starting test temperature for differential correlation is 32C /89.6F

so we will assume that your starting Temp is 90F, I will make all calculations in imperial you can convert everything to metric if you want this in metric

The formula for Thermal Growth = ( Hot Temp - Cold Temp ) x Length x coefficient of expansion

Carbon steel = 0.0063 mils / Aluminum = 0.0124 mils / Cast Iron = 0.0059 mils / per inch per 100F

Note: I put cast Iron for a reason that a lot of people miss when calculating this for an engine

Lets say you have a 6" long rod and a 1.5" Piston compression Height

Lest say you run your engine oil to 250F normal operation

It follows as this:

Conrod Thermal Growth = ( 90 - 250 ) 6 x 0.0063 = .006"

Piston Thermal Growth = ( 90 - 250 ) 1.5 x 0.0124 = .0029" called .003"

Rough Thermal Growth for those to pieces are .009" @ those conditions

Note 1: no your piston don't run at 800*F or more temperature, it would destroy if it was like that

Note 2: each alloy has a coefficient of growth, to be more accurate you need to know them, you need to know as well what you highest oil temperature will be.

Basically these parts run a little higher than your oil temperature, I don't know how much more.

This was fantastic and exactly the kind of information I was looking for. I know silicon content affects the growth, just not how much. I will look into it to see if there is a worthwhile clearance reduction benefit of hypereutectic vs 4032 vs 2618. Any thoughts?

I only can think it will be marginal ( maybe I'm wrong ), but Hypereutectic pistons will not tolerate mishaps on tuning as well as Forget pistons, read your spark plugs to make sure your timing is where it should be, and use high octane pump gas.

Be Careful with carbon buildup on you piston and chamber with tight quench on street applications. get you a cheapo Bore-scope and check the buildup every 5000Km, it will be good to eliminate your EGR to minimize carbon buildup, run generous size lines and vent points to the catch can if you eliminate the EGR from your engine.