Hey guys, need some help here. I have trick flow power port 195s 72cc, with 14cc dish TMeyer pistons. Trying to figure out my safe compression.
the math shows with the set up now 9.89:1 static compression, factor in with the dynamic compression calculator, intake closing at 26deg. ATDC, 600ft elevation, puts me at a 9.58:1.
If I deck them down to 68cc and put it up to a 10.25 will put it up to 9.81:1 compression. I want to run this thing on no more than 89 being its alum heads shouldn't be any issue. How much higher can I go? Help?

Thank you guys,
Curtis

 

Hi Curtis,

I assume you're trying to determine safe compression ratios in order to avoid detonation (pinging) on the lower octane fuel, and to maximise power.

Your static compression ratios (SCR) look like they could be right, but the dynamic compression ratios (DCR) look incorrect, and I think it's the intake valve closure(ICR) timing of 26* which is incorrect (for the calculation).

Are you using the advertised timing or 0.05'' timing ?

What is the camshaft part number ?

What engine is it ?

What is the bore size ?

What is the deck height ? (Piston head (flat part) to block surface distance)

What is the compressed thickness height and bore of the head gasket ?

What is the compression height of the pistons ? (Piston head to centre of pin)

Are the piston dishes round or 'D' shaped ?

The answers will help to determine the actual SCR, DCR, and cranking pressure, but equally important, the squish.

With ally heads, you could go as high as say 10.5 :1 SCR with the correct squish and quench on 89 octane and avoid detonation, but only as high as say 9.7 : 1 with an inefficient squish and quench !

Cheerz4now,
Nick

 

Cam card states IN opens at -10BTDC, IN closes at 26ABDC at .05, cam is from Camcraft Cams part # HR31-9604-12A4.
This is a 400 ford, 4.03 bore, TMeyer 0deck height pistons with 14cc dish. MLS head gaskets, .041(I thought .039) compressed, 4.065 gasket bore, no D shape just lower on exhaust side(not like a windsor)

Thanks
Curtis

 

Hi Curtis,

Using the 0.05' cam timing will always give crap figures !
If your engine was assembled and you had a degree wheel and dial gauge you'd actually see that the valve was still open at 26*.

That said, I looked at Camcraft's website but could get no info on your cam.
They seem to use an advertised duration of 0.004'' which would be far more useful than the 0.05' timing.
If your cam card has the LSA, ICL and both 0.05' and advertised durations, we can work out the IVC at 0.004'', otherwise phone Camcraft.

The 0.041' head gasket compressed thickness drops your SCR by +/-0.04, so with 68cc heads the SCR would be 10.22.

Out of curiosity, 70cc heads would give an SCR of 10.02.

The squish of 0.041' is perfect. (Just double check valve to piston head clearance.)

You want an IVC of +/- 64* (not at 0.05' lift) which will give you a DCR of +/- 8 : 1 and a CP of +/- 161 with 68cc heads.

In a nutshell, you need the advertised IVC to make a decision on the head cc's to use, or different cam.

Laterz,
Nick

 

1119121600.jpg photo by Curt408 | Photobucket
Compression is fine with 72cc on pump gas. Coming together, going to try to get block and rotator to the machine shop next week(they had issues with something there said to wait). Oiling mods(Tmeyer set up) are done, Trick flow raised intake runners .100tho. also so had to match the roof of the spacer plates and waiting to build floor with either tig or alumaloy. Opened the runners on the intake to match the spacers funny seeing a windsor intake with a cleveland size port. Going to smooth the runners on the heads due to not liking the "fast as cast" roughness too rough for me. I have to cut flanges off the windsor short tube headers TIG weld them to the cleveland flanges and send them out and thats done.
There is more pictures on there of the 400, I will take more soon been working on it after work all week just too tired to take pics when I'm done.

Curtis