CR
 

Maybe a stupid question,but is there a way to determine the compression ration of a motor without tearing it down??

NO ! This Wallace CR calculator shows the specs you must know, in order to figure CR. :)

http://www.wallaceracing.com/cr_test2.php

http://www.projectpontiac.com/ppsite...tio-calculator

Basically the same thing, but has some explanations for each measurement.

You could guesstimate, assuming stock components.

Or you could use one of these; http://store.katechengines.com/whist...ster-p174.aspx

They use it to tech "limited" engines in circle track racing, haven't seen or heard of one being used anytime recently in dirt track racing, although it is mentioned in some dated rules, asphalt/road course racing may be a different story, they may be used currently.

Wouldn't you be able to calculate compression ratio by pulling two rockers off a cylinder, attaching a fitting to the spark plug hole, filling it with fluid at BDC, rotating to TDC while capturing the expelled fluid .. then

Total fluid at BDC - amount of fluid expelled at TDC = volume of combustion chamber.

(Amount of fluid at BDC + volume of combustion chamber) divided by volume of combustion chamber = compression ratio ??

Basically just CC'ing the whole cylinder as a working unit.

Yes

Interesting device. Must use pressure pulses or some kind of resonance to determine the volume of the chamber at TDC. Similar to the changes in sound made by blowing on a bottle with different levels of water inside.

http://store.katechengines.com/whist...ster-p174.aspx

Well, hey, if these things work as advertised, that changes everything ! All you have to do is buy one or find somebody else who has one, to check your CR.

Anybody have one or know somebody who does ? :confused:

Did a search on it, it's fairly well known that it exists ... but most people, like us, are like WTF? How does it work.

However it works, my bet is that with the latest hardware and electronics a smart person could produce one for a fraction of the cost. I have zero facts ... but the design looks kind of dated.

It's got to work on the principle that a known volume of air of ANY shape, well behave in a certain way, at certain temps.

I think pulling a head is easier than paying $2,300.

or put 2300 towards new heads since you are taking them off

My brother Dan has one and it does work well as advertised. We use it at the Pure Stock Drags to check suspect cars out that seem to be running too well. It has been verified to be within 0.1:1 on every engine that Dan builds (yes, he CC's all the heads he rebuilds and Whistles the engine after break-in). It is a very interesting contraption, I mean device.

Dennis

Sounds like a great device to have, for any high performance engine building shop, or anyone who does a lot of high performance tuning, for others.

Hey, you could charge guys, to check their compression, just like they charge for dyno time.

It would help in choosing a cam, for an engine of unknown specs. :)

There is also another neat little device, which I saw used by the tech guys at a dirt track. It is a small scope, on the end of a flexible shaft(sometimes called a flexible borescope). You feed it in thru a spark plug hole. You can look up at the valves & combustion chamber, or down, at the top of the piston. At the dirt track, they were using them to look for illegal oversize valves, and illegal pistons.

One of these could be used to ID the pistons in a Pontiac engine. Might also help get a real ruff idea of deck height--not sure about that ? :confused:

https://www.google.com/webhp?sourcei...e%20borescopes

You can buy a decent little video borescope from Milwaukee at Home Depot ... I use mine all the time .. about $200.

Recently I was able to look into the lifter oil feed holes to see if the oil gallery was clean ... it wouldn't fit into the holes, but got close enough I could see what I wanted to see. Also has built in light at the end.

Every shop should have one. The units with the small camera head, like the Milwaukee will fit into a spark plug hole no problem, around 7mm diameter camera head.

They take some getting used to and only focus on things well within a couple of inches or so, not like you are going to put it into King Tut's chamber and see the whole room :)

I'm not advocating using or owning one, just that it exists. You need to know the displacement of the engine for accurate compression #.
So max allowed displacement is usually used when checking limited engines.
And I've "heard", ahem, a length of a wire tie sucked into the intake port lodged between the intake valve and seat before the rockers are removed will give whistler (and the tech inspector) fits.

On to the bore scope, they are paraded around too while checking limited/spec engines.
I recall a spec SUPR Brodix head engine being checked with a scope and the tech inspector saying "interesting..long pause...everything looks good here, button it back up". I won't get into all that was going on inside there, but the obvious externally was the angle mill, based on the deck thickness measurement holes drilled in the front of the heads, one had about 1/4" of material under it.... and the other was cut in half!
Engine rules in limited dirt tract racing are useless unless enforced correctly. The flood gates aren't open, their long gone.
The GM crate engine series like FASTRAK and RUSH/NE SMITH are better with track able seals and heavy fines, punishments for infractions inside the seals for re builders as well as owners and drivers.
:focus:
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Captain, the head casting # and cubic inch/block casting will likely give you a decent guesstimate if it's likely stock components. Let me know if I can help.
HTH :cool:

Quick look with a borescope would tell you what type of piston ..dish, flat, dome, how many valve reliefs ... might even be able to still read the bore size engraved on the top of the piston.

A given Bore, stroke, CR, and Intake Close point will yield a consistant cranking PSI. assuming a good sealing cylinder. good luck duplicating that many variables..