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Once I get some time, I'm going to do a compression test.
A little back story as to "why"....
Based on the amount of oil being pushed into the catch can and based on several dozen stock and non-stock acceleration data points (ie 55-75mph, 65-90mph, and 80-100mph) on the same track in similar weather,.....something ain't right! For instance, a car that supposedly has an extra 150whp should be quicker 80-100mph vs the stock engine than 0.2sec
My question....
Compression tests on "normal" cars are easy. The C7 is a PIA due to the fuse box on the passenger side. Ideally I'd like to remove it once in order to pull the plugs and then put it in place so I have power to spin the engine over. However, it looks like I'm going to have to remove it every time I move the compression gauge to the next cylinder. I do have headers so access is a bit better. I think a compression test is about the only thing I've never done on this car!
Has anyone found otherwise or have suggestions? I haven't found/seen an easy to use "Remote Start" for a C7...anyone found one?
If the compression test looks good....probably do leak-down as well....I'm going to run it on the dyno. I'm not worried about absolute numbers but rather magnitude. In other words if it's at 430hp.....that's an issue.
I don’t use a mechanical gauge anymore but a “relative compression” test done with a labscope..takes less than 5 minutes and can even be done without opening the hood.. I look at the compression relative to each other to get a quick look…if I need some compression psi numbers I’ll use my pressure transducer hooked up to an easy cylinder to remove a plug and then get a psi reading on one cylinder…
as far as a remote start just do a clear flood crank…hold the gas pedal to the floor and keep it down while you try starting the car…it will only crank…no injector pulse…something like an intermittent sticking valve (misfire) may not be seen with a mechanical compression test which can lead to a misdiagnosis..in this situation I’d crank the engine over 10-15 seconds.
if you have access to a lift you can reach the back 2 plugs on both sides from underneath. might bleed a little from the heat shield but its doable
I don't have a lift but I do have a Quickjack so there's at least a little room. Not so much concerned about the plugs as being able to thread the hose for the compression gauge into each sparkplug hole without needing to remove the fuse box every time...which is just an invitation to break something.
I don’t use a mechanical gauge anymore but a “relative compression” test done with a labscope..takes less than 5 minutes and can even be done without opening the hood.. I look at the compression relative to each other to get a quick look…if I need some compression psi numbers I’ll use my pressure transducer hooked up to an easy cylinder to remove a plug and then get a psi reading on one cylinder…
as far as a remote start just do a clear flood crank…hold the gas pedal to the floor and keep it down while you try starting the car…it will only crank…no injector pulse…something like an intermittent sticking valve (misfire) may not be seen with a mechanical compression test which can lead to a misdiagnosis..in this situation I’d crank the engine over 10-15 seconds.
I appreciate the input but unfortunately I don't have a lab scope.
Having said that.....1, 3, 5, and 7 are easy plugs to remove. I may remove those 4 for a relative comparison.
I had a plug wire pop off on track on cylinder 5. I'm concerned I washed down the cylinder wall and trashed the rings. If my theory is correct, then on a relative basis to cylinders 1, 3, and 7 the compression test should show that. I'd prefer to test all the cylinders but starting off with a quick check may be good enough. Just making up numbers.....if three of the cylinders show 200psi and #5 shows 150psi...no need to do anything else. Time to freshen the motor over the winter I'm not a fan of the current cam in it anyway, so 2 birds with 1 stone.
I remember that the car does have symptoms of blow-by compared to a stock engine, but I know yours isn't stock.
You could buy multiple compression gauge adapters, then you can limit the fuse box removal. Remove it, install the hose/s into obscured cylinder/s, re-install fusebox for testing everything. Then you just remove again once to remove the hoses, re-install spark plugs.
An alternative would be to energize the starter independent of the underhood fuse panel, since you don't need ignition or fuel to work. Never used a remote starter switch on a C7, but the starter doesn't seem special.
Endoscope into the cylinder at BDC would be useful to inspect cylinder walls.
Stock valve covers but with a custom catch-can setup from GSpeed that includes a drain-back to the pan so in reality what I'm draining is only part of what's blowing by. Oil pump is stock. The bottom end (crank, pistons, rods, rings) is stock.
I've driven on the street with it and after a couple hundred miles...nothing in the catch can and no signs of oil leaks. It's just the high rpm stuff on track and being down on power. No way a car that at one point dyno'd >550whp (actually 570whp) should have only a couple more miles per hour at the end of various straights on a track I've run numerous times. To wit, my personal best lap time is barely better with the current engine than the stock engine.
Stock valve covers but with a custom catch-can setup from GSpeed that includes a drain-back to the pan so in reality what I'm draining is only part of what's blowing by. Oil pump is stock. The bottom end (crank, pistons, rods, rings) is stock.
I've driven on the street with it and after a couple hundred miles...nothing in the catch can and no signs of oil leaks. It's just the high rpm stuff on track and being down on power. No way a car that at one point dyno'd >550whp (actually 570whp) should have only a couple more miles per hour at the end of various straights on a track I've run numerous times. To wit, my personal best lap time is barely better with the current engine than the stock engine.
Still N/A? What's done to the car?
I'm a bit lost on the catch can drain back, how do you know how much its collecting if it's being drained back to the pan?
The catch can system has a primary can with a drain line and then a line to a secondary can to capture anything that doesn't drain to the engine. After a 20-25 minute track session, I'm draining 500+ml from the secondary can. That means there's a whole lot more draining back into the engine. Waaaaaaaaay too much. Pretty sure this is a piston ring issue. I just want to verify it before I yank the engine.
In the pic below you can see the primary can and the stainless steel braided drain-back line below it running to the engine
The secondary catch can is behind the driver's side front tire and it has a vent line that runs to the rear bumper just in case it needs to spit anything out
If you don't have a dragy, you should get one to compare times after modding or changing settings/setups.
I was asking about mods because I was wondering if you had a blower installed and were getting heat soaked. I know you said you were going to do a compression test; I would start there and just do the easy cylinders and see what I came up with.
If you don't have a dragy, you should get one to compare times after modding or changing settings/setups.
I was asking about mods because I was wondering if you had a blower installed and were getting heat soaked. I know you said you were going to do a compression test; I would start there and just do the easy cylinders and see what I came up with.
This is definitely a mechanical issue. With the PDR and Pi Toolbox I can see times, acceleration rates, etc and it all says the engine is barely above stock power levels so I'm not guessing or estimating time differences, I see it in the data. I've overlayed sessions and the current engine really doesn't pull away from the stock engine. There's only one configuration change to the engine....stock to the current configuration, no in-between. I also have a multitude of dyno runs, all showing >550whp. Unless multiple dynos and multiple runs on those dynos are off by >100whp.....something is broke.
Unfortunate downside to race tracks....sometimes things break I just want to pinpoint it before ripping the engine out of the car.
The interesting thing is that it doesn't blow oil out the exhaust. I took a GoPro and mounted it looking backwards. Not a single puff or hint of smoke over multiple 20+ minute sessions. To me that says compression rings. If I can find a bad cylinder, maybe I just re-ring it and call it good.
Compression Testing technique?
I'm not a fan of the current cam in it anyway, so 2 birds with 1 stone.
