Competition Compression Ratio Question

[J.Davy]

Just wondering what most of the Pullers/Dragracers run for compression. Is there a standard drop in ratio for each increment in boost?I am not sure if that makes sense but for example if 60psi is ideal for a engine running 18 to 1 then would 70 psi be ideal for 16 to 1 and so on?

 

[RMalone]

Wow someone finally the stumped the hardcores!! Great question, but alas I'm way to ignorant to answer it.

 

[J.Davy]

Maybe it is a secret. lol,Hope not.

 

[DRadzierez]

Up to 70 lbs stock----70 to 100 lbs 14 to 1----over 100 lbs 12 to 1 compression.

 

[J.Davy]

Thanks for the info. Is 14 to 1 streetable?If so how about in the winter?How about 12 to 1?

 

[CumminFast]

The real question is what is your definition of streetable?

 

[DRadzierez]

14 to 1 is streetable but winter may be an issue. 12 to 1 you will need either to start all year every time.

 

[Jim Fulmer]

I run about 15. 5 and can bump start at will but I haven't had it in cold weather yet, not below freezing.



Jim

 

[J.Davy]

Is there any point in going higher than stock?

 

[B.G. Smith]

Is there any point in going higher than stock?

?????Stock on my 99 is 16. 5:1, how do you rerate them to say 12:1? Are we still talking about diesel engines???? bg

 

[J.Davy]

I am not sure but i read somewhere around here that the third gens are 17 or 17. 5 to1. In regards to my question about going higher than stock,I was wondering if there might be a gain in bottom end or ease of cold starting or a gain in h. p. at a lower boost number. As for getting down to 12to1 I think all you have to do is change the pistons. I believe that the all out competion trucks run that low.

 

[B.G. Smith]

I am not sure but i read somewhere around here that the third gens are 17 or 17. 5 to1. In regards to my question about going higher than stock,I was wondering if there might be a gain in bottom end or ease of cold starting or a gain in h. p. at a lower boost number. As for getting down to 12to1 I think all you have to do is change the pistons. I believe that the all out competion trucks run that low.

Ok, I think I missed the point, the fog is lifting or is that diesel smoke. It makes sense that if you make the combustion chamber bigger (lower the ratio) and ram more air (higher boost) in there that you would also be able to add/burn more fuel for more umph. Can also understand if you get it too low that in cold weather it won't fire off. My apologies. bg

 

[Pourinthecoal]

Great question. Curious as to whether or not this correlates with Cetane rating in Diesel. A higher compresions ratio should make things more efficient during low-boost situations. I'd like to hear more from you experts out there.

 

[Devan Manis]

How come in a gasser they higher the compression, but in a diesel we want to lower it?

 

[COMP461]

Compression is part of the equation in making big diesel power. The CR Cummins in over 17 to 1 stock. If you are going to effectively rise to intake track pressure to something around 60 lbs then a drop in compression will help. Above that and you will need to drop it even more. I believe at some point the compression and big boost number will cause the motor to expend excessive amounts of energy to push the piston to TDC on the compression stroke. Reducing this to the optimum number will let it put more of that power out the flywheel. The way a motor makes power is from expanding oxidizing gasses. If you start at a much higher pressure then needed to fascinate this action to its most efficient point of producing maximum peak cylinder pressure at the right time, say 15 to 20 degrees ATDC , then you are wasting power. Anything produced much after that point is totally worthless in making an appreciable power gain. So all the fuel in the world after that point is not going to make power, but will produce a carburized partially oxidized mixture, that did not release its stored energy. Or in other terms SMOKE



Now for the real answer, I would on most 600 hp or below street engines put a thicker head gasket on when you O-ring, and when you get serious and put a cam in the motor, cut the pistons. This will make the best power you could possible use. Some where in the neighborhood of . 025 to . 040 is enough, to clear a good street cam and drop the compression ratio a full point.



Cams, If you aren’t doing cams you way behind the power curve, the best cams out there now are for either John Russin at Buddha power, or Bullet Racing cams. Everything else is just these two groups reverse engineered stuff, and is out of date with the new stuff being worked on so when you want to buy one of these so called new cams that are the be all to end all cams , remember these are two to three year old designs . The newest stuff is light years better. But it is only a mater of time before some of the reverse engineering pros on here will con some one, LIKE ME in to being helpful and selling them a grind and then copying it.



You know who you are, and you know if funny the big be all to end all cam, you copied and now are marketing is one of John Russin 3 to 4 year old design cam I had laying around after progressing to the next 3 or 4 cams John has helped me with. The Cams John is now doing are dramatically better on spool up and power.

 

[J.Davy]

How come in a gasser they higher the compression, but in a diesel we want to lower it?

Gasser,s are the same when it comes to boost. You typically lower compression the more boost you run. The owner of the company I work for grenaded his 6. 0 liter chevy running 9. 5 to 1 0n pump gas @ 6psi boost. Now he is running 8 to 1 with no detonation.

 

[Devan Manis]

makes sense thanks.

 

[KLockliear]

The CR Cummins in over 17 to 1 stock.

17. 3:1 for all the 3rd gens. 17. 3:1 for the HO 2nd gens, 16. 5:1 for the SO 2nd gens.

Cams, If you aren’t doing cams you way behind the power curve, the best cams out there now are for either John Russin at Buddha power, or Bullet Racing cams. Everything else is just these two groups reverse engineered stuff, and is out of date with the new stuff being worked on so when you want to buy one of these so called new cams that are the be all to end all cams , remember these are two to three year old designs . The newest stuff is light years better. But it is only a mater of time before some of the reverse engineering pros on here will con some one, LIKE ME in to being helpful and selling them a grind and then copying it.

Ya know, for all the typing you spew out, at some point you should see about getting some facts. I'm not knocking any vendor out there, but YOU sure are. Get the facts before you post.

 

[pwerwagn]

Everything else is just these two groups reverse engineered stuff

hmmmm, I find it kinda hard to believe that EVERYTHING else is a reverse engineered copy of their cams.

 

[COMP461]

17. 3:1 for all the 3rd gens. 17. 3:1 for the HO 2nd gens, 16. 5:1 for the SO 2nd gens.



Ya know, for all the typing you spew out, at some point you should see about getting some facts. I'm not knocking any vendor out there, but YOU sure are. Get the facts before you post.

not all are doing it , just one ,



and most of the time my facts are right. I have always tried to point out smoke and mega mental mirrors