MALS is considering a simple way to check engine compression ratios without pulling the head. Anyone have a system that is usable? We have found charts with factory cc's listed and have possibly figured a way to inject premeasured amounts Marvel Mystery Oil in through the plug while at TDC. Then extract the biggest part before replacing the plugs and creating a "hydraulic" situation. A minute amount of MMO shouldn't harm a motor when refired. Questions are..........Do they consider cc with the spark plug in place? How much would .005-.010 in head milling effect the stock cc? Has anyone considered this as a viable way to check compression ratios? Obviously this would be done AFTER bore and stroke have been verified. If someone could call me or email be with some input, I would really appreciate it. We are experimenting to see if we can use this as part of our tech system. Thanks in advance........Phil Heavelow (913) 371-5152 or jmillwright@kc.rr.com

You guys allow aftermarket pistons right?

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We allow stock configuration aftermarket pistons. Presently we have a 240 psi max on the compression to work with. I have been told manipulation of valve timing might present a false reading though. To me........compression reading is a compression reading. But we are looking for another method to verify that motor has a stock compression ratio without a major effort to find this out. We check weight, all tranny gears, bore and stoke, compression, bore scope observation for excessive valve relief and fuel. We also can check to make sure the cams have stock lift. If anyone has any experience with this please feel free to contact me. Thanks again.

I guess that's what I really like about "stock" engines, no real way to spec them, and be certain you've caught everything someone can do to a "stock engine", ask Joe Gibbs. Measure the bore and stroke, and as far as I'm concerned, that's it, unless you want to work all night and the next day, teching engines, these things are so borderline, another .010 off the block makes it a hand grenade looking for a place to explode anyway, that puts the piston/deck at about .020, which is almost a certain piston/head crash. JMHO! Bob

Hi Phil

Guess you guys are still chasing your tails with that guy with a funny sounding engine running off and hiding from the rest of the racers?

Honest Dad himself

The issue is all aftermarket pistons have altered domes, you can put just as much compression on oem with the right cam timing and a mill.

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Hi Dad......Naw......not chasing him or them anymore. We are finally getting things controlled here it seems. Pretty equal playing field and the guys are doing great. Now.....both MALS and MLS are utilizing the same motor rules. We were just trying to come up with a better and quicker way to check actual compression since things can be "sorta" manipulated to give false readings.

TQ29m........we are simply trying to come up with a few basic checks to "convince" racers to not step outside the box on stock motors. We do not want to enforce a major teardown and inspection. We just would like a have simple workable procedures in place to check obvious points where HP can be gained. I am sure someone can work around even these checks and cheat the system. Can't stop everything. But it still amazes me after all my years in racing different classes that someone would intentionally cheat his fellow competitor and be able to live with himself. When you have no honor.....that must not be a problem?

So......someone with some insight..........it this cc check a total waste of time or does it have some validity? Someone shoot some holes in it if there are any. One of my concerns is the viscosity of the 5w Marvel Mystery Oil changing enough in a warm motor that there might be some "leak by" of oil. That tells me the procedure needs to proceed as rapidly as possible. Also carbon build up on the guys running gas might be an issue.

Phil - I have a gauge that screws into the spark plug hole. Is that what you are looking for? That would check compression......but then you said something about cc's. Wouldn't a bore and stroke check cc's?

Phil

Like Andy said valve timing does have a lot to do with cranking compression pressure. Longer cam duration (RACE CAM) and and or closing the intake valve Later in the timing event (RETARDING CAM) will lower the cranking compression. It can't make any compression until the intake valve closes at slow cranking speeds. The AMSA tried compression checking many years ago and found it didn't work.

Actual compression ratio depends on two measurements. The total volume of the cylinder measured at bottom dead center including the volume of the combustion chamber to the bottom of the plug hole. Then you need to measure the volume at top dead center all the way up to the bottom of the plug hole. Divide the first reading by the second reading and you get compression ratio. Just measuring the Volume at TDC only probably won't get what you are looking for. Also the cylinder has to be perfectly vertical (you would have to hang car from a crane). I bought a 300cc graduated cylinder 10 years ago to try this out. Valves opening and closing and in-trapped air are your big problems. I was able to measure displacement with this set up by only using only part of the power stroke and a known stroke measurement taken mechanically.

You have a bore scope already, a JE or Wisco piston does not look like a stock piston, they are not supposed to, the machine work is much better, the crown of their piston is not like the stock one's because they all raise the CR just a little, a good reason for buying an aftermarket piston, for that reason one would be hard pressed to find an after market piston with a stock CR.

The best way I know to tell you how to spot an engine with altered compression ratio is to observe the top of the piston. Almost all 4 valve M/C pistons have a little round spot machined into the piston just below the spark plug. They also have 2 lines going across the piston crown cutting the valve relief on the top of the piston, the distance from the little round machine spot to the lines on the valve relief will get closer as you raise the crown of the piston and the compression ratio.

All you need to check a head for milling is a 6 inch caliper, remove the valve cover find an exposed portion of the head where it meets the block, measure from that spot to the machine surface for the valve cover and the milled head will stick out like a trd in the punch bowl.

Frankly I can not understand why a group would allow after market pistons and be worried about compression ratios.

If this guy is still bothering you guys, what I would do is go in the infield set up two cones one at entrance to turn #1 and one at the exit of turn #2. Have someone clock him between the two cones only, and then have them clock the next fastest guy, is there a difference in their times?

Honest Dad himself

Chris...........we have a compression gauge system but thanks. Some have convinced me to NOT totally rely on that motor compression test due to valve timing manipulation. We are trying to simply check the cc's of the combustion chamber after we have verified bore and stroke are stock. We have the factory spec on the chamber cc's to most motors/years with only a few to go. This way the correct cc of 5W oil could be injected at TDC. We have to determine the exact level that factory spec considers. I am assuming with the plug in place but no one has verified that yet. I can test the theory on my stock ZX-10 and my stock R-1 to see where the pre-determined oil amount is meant to come out and go from there. Just looking for a fairly simple way to check compression other than with a gauge. We will have the plugs out and at TDC at some point anyway. I already have the accurate syringes, oversized needles and suction device to extract the oil when we are done. If the oil rises above a specific level or comes back out the spark plug hole....................."You got some splain'n to do Lucy!" I just was looking for someone to shoot holes in this idea so I can sleep a nights again and quit thinking about it.