351 c Compression question

[3514boltstang]

Anybody know what the compression ratio would be on a 1973 dished pistons Cleveland with 4 bbl open chambered heads?too low to make decent power?thanks

 

[Jeff73Mach1]

about 8-1

 

[3514boltstang]

about 8-1

How about t using closed chambered?at least 9:1?

 

[Jeff73Mach1]

I put closed chamber heads and a cam in my 73 and got 300 at the rear wheels before I dropped a valve. Depends upon the condition of the bottom end and your goals

If you are willing to rebuild, pop up pistons can make the stock block and heads capable of significantly more power.

My opinion is that 10:1 compression is really about the baseline for building respectable power but then again, I tend to overbuild

 

[3514boltstang]

I put closed chamber heads and a cam in my 73 and got 300 at the rear wheels before I dropped a valve.  Depends upon the condition of the bottom end and your goals

If you are willing to rebuild, pop up pistons can make the stock block and heads capable of significantly more power.

My opinion is that 10:1 compression is really about the baseline for building respectable power but then again, I tend to overbuild

Ok,this motor was rebuilt not too long ago and was punched .030 over but stock style dished so I'm looking for the easiest way to make a eecent motor

 

[73pony]

If you are not looking at doing popups or at least flat tops, then CC heads would get the compression ratio up to where you need to be. Once you determine your course of action on this front you will need to decide on a different cam. When I was starting mine I called comp cams and discussed in detail what I was doing and what I was shooting for and we came up with a custom grind. I also went full roller valve train as the cam they spec'd would destroy a flat tappet in no time. I believe the stock dished pistons have are 8 cc's. Hope this helps.

 

[3514boltstang]

If you are not looking at doing popups or at least flat tops, then CC heads would get the compression ratio up to where you need to be. Once you determine your course of action on this front you will need to decide on a different cam. When I was starting mine I called comp cams and discussed in detail what I was doing and what I was shooting for and we came up with a custom grind. I also went full roller valve train as the cam they spec'd would destroy a flat tappet in no time. I believe the stock dished pistons have are 8 cc's. Hope this helps.

Ok,thanks for the help.

 

[Robsweden]

Hi

You can use flat pistons and shave the heads down to 67-68 cc. It should give you about 9.5.1 of course heads should be shave in both directions.

Regards Rob

 

[3514boltstang]

Hi

You can use flat pistons and shave the heads down to 67-68 cc. It should give you about 9.5.1 of course heads should be shave in both directions.

Regards Rob

Thanks,the biggest issue is that I don't know enough about motors to feel confident changing pistons,is it difficult?spany special tools involved?thanks.

 

[Robsweden]

Hi

It all depends, but changing pistons is not that difficult.  Tools depends, Pistonring compressor, torque wrench, the machineshop  can replace  the piston to the rod.

Regards Rob

 

[4Vforever]

If the bore is good I'd change the Pistons to flat tops, rehone to suit new Pistons and for the new rings, deck the block to zero deck height, decide on the compression ratio you want and mill your heads to suit. Nothing at all wrong with open chamber heads and those who say there is don't know the Cleveland head design at all. Also compression isn't the be all and end all it once was I've read about a few builds over the last few years. One of them was a 9.0:1 comp ratio hydraulic roller cam engine making over 550HP. If yours are the 73 small valve open chamber heads, then even better. I'm using those same heads on my street engine build and helping a couple of others with theirs. I spoke with a guy not long back that's been using those heads for decades in the class he races in very successfully and also laughs how people think these heads are junk and loves them because they're cheap as no one that doesn't know their potential doesn't want them. He does by his Pistons semi finished on the dome and keeps his finished dome design a very closely guarded secret. No need to purchase other heads.

 

[3514boltstang]

If the bore is good I'd change the Pistons to flat tops, rehone to suit new Pistons

and for the new rings, deck the block to zero deck height, decide on the compression ratio you want and mill your heads to suit. Nothing at all wrong with open chamber heads and those who say there is don't know the Cleveland head design at all. Also compression isn't the be all and end all it once was I've read about a few builds over the last few years. One of them was a 9.0:1 comp ratio hydraulic roller cam engine making over 550HP. If yours are the 73 small valve open chamber heads, then even better. I'm using those same heads on my street engine build and helping a couple of others with theirs. I spoke with a guy not long back that's been using those heads for decades in the class he races in very successfully and also laughs how people think these heads are junk and loves them because they're cheap as no one that doe

thanks

sn't know their potential doesn't want them. He does by his Pistons semi finished on the dome and keeps his finished dome design a very closely guarded secret. No need to

thanks for the info.

purchase other heads.

 

[downwardspiral]

For the sake of not creating a new thread.. How high is too high for 93 pump gas? I just picked up my buddy's rotator that he said was either 10:1 or 10.5:1 which I believe to be the safe limit. Going off this I am assuming the deck clearance to be ~.015 with a .040 gasket. Now this was calculated with 4V heads, assuming a 62cc chamber volume. I have a built set of Aussie heads which would put the chamber volume at 58cc and the compression at 11.1:1 (assuming it is 10.5:1 w/ a 62cc chamber). That's too much, right? Now I was thinking I would just run a thicker gasket, but to get it to 10.5:1 I would need a .060 gasket, which would kill the quench effect from what I'm reading. I am going to measure the deck clearance but want to figure out as much as I can now. Also does quench really die at .050" clearance and would it be dangerous?

 

[Don C]

The static compression ratio is a starting point, but the dynamic compression ratio is what tells you what fuel you need to run. With quench heads and a decent cam 11:1 may be OK on pump gas. This should help:

https://www.7173mustangs.com/thread-engine-and-compression-calculations

 

[downwardspiral]

The static compression ratio is a starting point, but the dynamic compression ratio is what tells you what fuel you need to run. With quench heads and a decent cam 11:1 may be OK on pump gas.

https://www.7173mustangs.com/thread-engine-and-compression-calculations

I should have mentioned I am going to run a lumpy solid roller to bleed off a little dynamic compression.

That calculator is more of an answer than what I was looking for.. thanks! ::thumb::