[johnta1]

It's best to do your own due diligence.

Google it, research it if you don't understand it.

[johnta1]

One example:

From HO Racing book a graph showing the CR change percentage:
(nothing to do with me so don't shoot the messenger again)

CR Change

[Tom Vaught]

Originally Posted by johnta1

One example:

From HO Racing book a graph showing the CR change percentage:
(nothing to do with me so don't shoot the messenger again)

CR Change

LOL! How can we assume stuff when the graph only goes to 13 to 1?
Not very easy is it John. Same deal for percentage changes with 16 to 1 engines and 930 hp engines.
Bet Craig would have killed for a 930 HP engine when he and Kern wrote the book. So then you have to
go with real data like single cylinder engine testing where a full sweep of the engine's compression ratios
is done and the power levels documented.

It was a basic Generic question and we gave generic answers, so how about we call this one a TIE?
So what data did you base your calculator program on? Smith, Vizard, Speed Talk?

Tom V.

[johnta1]

Tom, ask Craig maybe?

Really if you knew anything about it, you would know that basically anything more than 13:1 CR the advantage to gaining HP is vastly dropping.

LOOK at the curve!

It's starts going straight up almost at 13:1, continue the graph and the percentage is practically nil.
(from 13 on up)

Ask any of the big guys, I didn't decide this.

Just admit you are wrong.

[Tiger Paw]

My Comp engine was 15.6-1 for a reason. In an engine with ports limited by CSA compression is way to get that power back.

[greggutknecht]

It would be nice to know cam spec also to compare to to other builds.I just dynoed my 541 and it makes over 900 on pump gas with around a 700 lift cam.And its not a happy dyno my buddy dyned there went to the track and showed 15-20 horse more.

[slowbird]

Originally Posted by Tiger Paw

My Comp engine was 15.6-1 for a reason. In an engine with ports limited by CSA compression is way to get that power back.

Compression is your friend, quite a few guys are 16+

[greggutknecht]

A lot of comp does sound nice.

[Dragncar]

Mikes was 18-1, he could have probably run that thing on diesel. Highest I have ever heard of. What is the highest you can run BTW ?

[slowbird]

Originally Posted by Dragncar

Mikes was 18-1, he could have probably run that thing on diesel. Highest I have ever heard of. What is the highest you can run BTW ?

You can run as much as you want if the fuel can take and your ability to tune it is up to the task. The more compression you run the small the tuning window.

[Tiger Paw]

13ish-1comp ratio thinking is from when engines were small, chambers were big and required big domes. The big domes were the limiting issue. Things have changed since, most noticeably engine size and secondly but more importantly chamber volume.

[slowbird]

Originally Posted by Tiger Paw

13ish-1comp ratio thinking is from when engines were small, chambers were big and required big domes. The big domes were the limiting issue. Things have changed since, most noticeably engine size and secondly but more importantly chamber volume.

Ya chamber size/shape has really help with the compression increase. With the way things are today imo 12:1 to 14:1 is no mans land, cant run pump gas and you arent not taking full advantage of race gas.

[Dragncar]

Heads I will have by Friday,Lil Jacks old E heads, then Gachs, now mine were run by Gach at 12-1 with 93. Made 880 with off the shelf Comp cam. Said it rattled a little bit. But about put it on the bumper, got off, still ran 147 MPH.
Fresh from Gabbys shop, 404, Ti valves. Going to be fun.
Mine will be a true Ca 91 octane engine. 11-1, 11.5 max. But I can make a easy 800+ or 1000 if I want to turn up the CR and cam.

[Tom Vaught]

NASCAR has been running engines for many years with high compression ratios because the fuel is a spec fuel, the tuners are very sharp, and high compression gives better F.E.

Tom V.

[charlie66]

Why is 18 to1 the limit ? Is it different then a turbo with high boost? I have a motor with 43 psi going through it. What to do think that compression is ? way more the 18 to 1 for sure.. and it responds with more power every time the pressure is turned up..

I think Mike was on to something..

RIP Mike.. .

[Tiger Paw]

Charlie, while the math says 18-1, cam events greatly effect the actual. In reality there only a window of time where vol eff is around and/or above 100%. That's what John and Mike were doing, using cams among other things to allow them to use that cr.

As far as your boosted combo, maybe Tom can more accurately explain how and why.

[GTO Dan]

If you are running n/a trying to make as much power as you can and are already buying race gas why wouldn't you run as much compression as you can.

[Tiger Paw]

Absolutely! But it's a slippery slope and a screw up or problem can ruin it all. You'll have a second or so recognize and react. That type testing isn't for the faint and must be snuck up on.
Personally I'd recommend to avoid that high cr for 99.9% of you guys. Gamblers, rich guys and unlimited racers only.

[Tom Vaught]

Originally Posted by GTO Dan

If you are running n/a trying to make as much power as you can and are already buying race gas why wouldn't you run as much compression as you can.

X2

Tom V.

Charlie, some say (like Corky Bell - a Turbo and supercharger expert and book writer) that the cylinder pressure (if the engine is built right) will only increase about 15-20% but the mass flow thru the engine goes up a great deal and the push on the piston is longer so you make a lot more power from a COMBINATION of parts to the puzzle. You did good Charlie.

[charlie66]

Originally Posted by Tiger Paw

Charlie, while the math says 18-1, cam events greatly effect the actual. In reality there only a window of time where vol eff is around and/or above 100%. That's what John and Mike were doing, using cams among other things to allow them to use that cr.

As far as your boosted combo, maybe Tom can more accurately explain how and why.

So are you saying with the right cam 18 to 1 will drop to a lower cylinder pressure?