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Unread 01-22-2013, 11:41 PM   #1
carlege
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Default Agressive cam and leakdown test

will an aggressive cam make a leak down test harder to perform?
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Unread 01-23-2013, 12:42 AM   #2
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Nope. TDC is still TDC and easy to find. The valves may ramp open more drastically than a lesser cam, but that has no effect on TDC with the valves closed - where the leak down is taken.

I should also add that camshaft overlap has an effect on a compression test, but not on a leak down.
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Unread 01-23-2013, 09:40 AM   #3
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Nope. TDC is still TDC and easy to find. The valves may ramp open more drastically than a lesser cam, but that has no effect on TDC with the valves closed - where the leak down is taken.

I should also add that camshaft overlap has an effect on a compression test, but not on a leak down.
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Unread 01-23-2013, 08:49 PM   #4
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No problem. Your best bet for a question like that is a general google search. Not that people here are knowledgeable enough, however, you'll find an immediate answer in the form of a technical article, etc. You may find more information that what you're looking for. Some of the best articles I've found were from random searches. Even though there is a lot of junk out there, there is quite a bit of great stuff as well.
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Unread 01-23-2013, 09:22 PM   #5
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Have a friend with a lindsay built 3.0 but he is having "28% blow by on all cylinders" in his leak down test. He has been running things in his head and that was one that stuck.

But not burning oil and 450-500 hp on the engine he cant make sense of it. either way he cant sell it because the ppi shows that problem
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Unread 01-24-2013, 04:35 PM   #6
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Ok I can help but I need more information than that. If the car is not using oil and has 450-500 hp it doesn't have 28 % leak down. Are you saying it had 450 hp and is now down on power? What symptoms is it having? If it's Lindsey built, did he go to them first?

If there is blow by in all cylinders that is equal, that's most likely a ring sealing issue. If it's just one cylinder and doesn't use oil, could be a burnt valve.

Give me as much detail and history as possible and I'll help you figure it out.
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Unread 01-24-2013, 06:13 PM   #7
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Ok I can help but I need more information than that. If the car is not using oil and has 450-500 hp it doesn't have 28 % leak down. Are you saying it had 450 hp and is now down on power? What symptoms is it having? If it's Lindsey built, did he go to them first?

If there is blow by in all cylinders that is equal, that's most likely a ring sealing issue. If it's just one cylinder and doesn't use oil, could be a burnt valve.

Give me as much detail and history as possible and I'll help you figure it out.
Ill direct him towards this thread.
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Unread 01-24-2013, 06:29 PM   #8
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I'm the owner of said car. A bit of background. I had a 39,000 mile 951 with a cracked block. I had Lindsey racing build me a 3 liter engine with Wosner Pistons and Pauter rods. 89 944S2 block, 951 head that was sent to LR for their stage 2 head work package, webcam etc. LR attached the head to the block and shipped it to my mechanic for install.

The car was broken in correctly and never run more than 17 psi. I had an interested buyer who I took it to a German Car place for a PPI, they didn't know the extent of the mods and kept the timing the same. The leakdown numbers were like 60%. Obviously the PPI was done wrong.

I took the car to my mechanic and he adjusted timing to TDC and got 28% on all 4 cylinders. The engine has 2000 miles on it and after dyno tuning at 500 miles the leakdown was 4% across the board. The car dyno'd 410 rwhp at 17psi about 10 months ago. It runs super strong with no problem. I have the M-Tune, LR Super 65 turbo, full 3 inch fabspeed exhaust, stock intake that is honed.

Why a year later is leakdown now at 28%. Did the rings lose tension and if so, why? The engine was scoped, no detonation on the pistons, no scaring on the cylinder walls.

I'm at a loss. The car doesn't burn oil, or have smoke on decelleration. I have a custom catch can and there is a bit of oil in that and some smoke from it when the car idles. Can the rings just lose tension, especially on all 4 pistons? Something doesn't add up and before I have the engine torn down I want to make sure its not an issue with the leakdown test. My mechanic has been in the 944 game for a very long time and I trust his work.

Lindsey is suggesting I run Shell Rotella T for 100 miles, swap to Joe Gibbs BR Oil, run that for 100 miles then do another leakdown test. It's a process of elimination.

Any ideas?

Thanks.

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Unread 01-25-2013, 03:16 PM   #9
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First off, take a deep breathe and understand that this kind of stuff happens more often than most people would ever like to admit. Unfortunately, this is the nature of modifying a car, problems come up if you’re not extremely experienced with the specific car/engine. Even then, things will still surprise you.

Now with the therapy out of the way, let’s continue with the problem. I’d like to start with having you describe a few more things. You mentioned that originally and even now, the car shows no problematic symptoms. The only reason you had a leak down done was for a PPI for a potential buyer. You also mentioned the car runs super strong, does this mean it pulls as hard as it always has (at least as much as you can tell)? Your mechanic has done many leak down tests before, correct? You think he’s capable?

Have you done a compression test? It’s not as useful as a leak down but a compression test is easier to perform and a correctly performed compression test is more useful than an incorrectly performed leak down.

The fact that you have M tune is comforting. Josh at Rogue does it right, that makes me feel better about your situation. However, in the effort of being exhaustive, do you have a wideband so you can view and ensure the correct A/F? It’s possible to have something fuel related fail and cause issues.

The engine, can you give more info about it? If it’s Wossner pistons, that means it’s on honed Alusil bores, correct? Also, don’t waste your money on changing the oil, that will accomplish nothing but lighten you wallet. What oil have you been running? Do you have an aftermarket or additional oil cooler to increase your cooling?
If we assume the leak down to be accurate and you are down 28% on all cylinders, that points to a few potential things. The first is that it’s all cylinders. That would mean that it’s most likely not detonation because that would happen to one or a couple cylinders, in most cases not all. And if it were all cylinders, they would have different leak down numbers. If the rings have lost tension, which can happen, this is due to an overheating. Overheating of the rings can happen due to inefficient cooling. 944s pushing higher horsepower figures are very susceptible to high oil temperatures due to their large frictional surfaces and small stock oil cooler. The sheer size of bore, crank/rod journals, etc, especially on a 3.0 is incredible. There is a lot of moving surface area that produces friction and therefore requires oil and produces heat. Then add the heat of boost and you’ll need a large oil cooler.

Describe your catch can setup, please. Does it recirculate back to the intake? Describe the smoke at idle also. Are you saying smoke out of the exhaust at idle? How much oil do you find in the catch can after about an hour of driving hard? Do you have the stock AOS in?

If I were to speculate, and if you really do have 28% leak down, I would guess somehow there was heat damage to the rings. That would explain the even 28% across the board and the lack of scoring in the cylinders. However, with 28% leak down you’re looking at a substantial difference in power. You should
I should mention that a burnt valve could cause a bad leak down. It’s highly unlikely, though, that all 4 exhaust valves would have burnt. Make sure you take everything I say as only a possibility because as of right now there are too many questions. Don’t go tearing that thing apart until a few other possibilities are exhausted. If it comes down to the fact that it is the rings and you solve the issue that caused them to fail, you can just toss new rings in the engine and it’ll seal really well. I realize technically you should hone, etc. before you re-ring, however, I’ve re-ringed an engine in the past even with slight scoring and it sealed so well no one would ever know I re-ringed it. Leak down and compression test numbers were as if it were honed and new. And if that’s all you have to do, with all you’ve done to get to this point, it’s gravy baby.

Lastly, a 3 liter at 17 psi should make far beyond 415 whp. There is a lot more power to be had out of that thing. One thing at a time, obviously, but just be aware there is much more power on the table with that engine. I would start by throwing that webcam in the garbage. Just saying.

Where are you located?


Take care.

EDIT: I forgot to mention that as your first step going forward from here, your mechanic, when performing the leak down, needs to verify that the leakage is coming out of the crank case and not out of the head. In other words, if it's leaking down 28%, find where the pressure is being relieved out of. If it's coming out of the AOS or catch can, it's the rings, if it's coming out of the exhaust/intake, it's valves, or if it's out of the headgasket, it's, well, you get it. The leak down should be performed on a warm engine, and only on the compression stroke. The only way a camshaft's overlap will become an issue is if you're attempting a leak down on the exhaust/intake stroke, which, if the camshaft has overlap, will allow leakage into the exhaust and intake.
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Last edited by DDP; 01-25-2013 at 03:40 PM.
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Unread 01-25-2013, 04:21 PM   #10
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Hi Derek, Thanks for all your help on this. I live in Atlanta, GA and my mechanic is Motorwerks Racing. Matthew Forte is a good mechanic for these cars. He's done a ton of work to 951's. He isn't a source of concern at all for me.

This car pulls as hard as it has from the day I got it back from having the work done. The 410 wrhp was done with the Lindsey Quad MAF I originally bought before the M-Tune was made. I made the switch less than a year ago.

The PPI had a compression test and it was 130/130/140/125. I do have the Zeitronix A/F kit installed and the A/F ratios are within range 12.0-12.2 full boost.

As for overheating, I seriously doubt that has happened as this is a street car that I don't beat on. I'd say 95% of driving is minimal boost. I have the stock oil cooler that I had sonic cleaned along with all the hoses. It's in great shape and since its a "sunday driver" type car and not a DE or track car it wasn't something I needed to address. I also have a LR Stage 2 intercooler.

It is Wosner pistons in an 89 S2 block, that's all I know about it. Lindsey recommends The Joe Gibbs Break in oil and then Joe Gibbs XP4 until about 3000 miles on the motor.

The catch can is something my mechanic made and it sits in the front of the engine. It's basically a PS resevoir with a hole cut out in the top. It's open on the top. There is a small sponge in there to absorb the oil. It's not heavy, filled with a lot of oil. I get no heavy oil smoke out of the exhaust that would happen with high leakdown numbers. I believe the car has the stock AOS in it.

I know I'm leaving power on the table and with the M-tune, it should make more power. Not that I need it

What's wrong with the webcam? What cam do you recommend?

Thanks,
Chris
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Unread 01-25-2013, 10:19 PM   #11
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I'd also try and speak to LR's builder as I don't believe they do their own engines in house. Not sure who is doing them or whether they'll tell you (which they should) but it would be nice to speak to the guy that put it together and get his opinions too.
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Unread 01-26-2013, 07:43 AM   #12
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Chris,
Tuning-in...
If the Web-cam has much overlap, then it a leak-down test needs to be done at the compression -> combustion TDC point. Doing a leak-down at the exhaust -> intake TDC will report incorrectly.

Derek touched on this, but it is an easy mistake to make - so I feel the point needs to be re-iterated.
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Unread 01-26-2013, 01:49 PM   #13
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Agreed, Josh.

Chris, when I say overheated rings, I don't necessarily mean the engine overheated. If timing is really far off, or combustion is pre-igniting, etc. This can cause excessive combustion heat without raising coolant temperatures; although I don't believe that has happened to you. However, if the engine is really 28% down on all four, smoked rings is highly likely. After thinking about it for some time, I really think that your mechanic did the leak down with the first timing mark at TDC, which would be the intake/exhaust stroke. I think I've even done that in the past when I wasn't thinking clearly, got some funky leak down values and realized what I had done. It's easy to do. Discuss this with him and let us know.
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Unread 02-01-2013, 11:09 PM   #14
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Hey there guys. Thanks for stating this point Derek. That was what I was trying to mention to Chris when he e-mailed me about his car....since his is similar to mine. I just didn't know how to word what I was talking about. I hope this is the case with the engine.

The first timing mark possibility thing. I understand it but didn't know how to explain it.
So this is the cam spec on mine I was trying to relate things to the above and the valve overlap...if I am using the concept correctly.

Solid Lifter Cam
Web - 457/274 grind:
Intake lift - .495"
Intake duration - 246 degrees
Exhaust lift - .480"
Exhaust Duration - 234 degrees
Lobe center - 112 degree lobe center - 16 degrees overlap

I hope things are working out for you Chris

Good luck
Jason

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Agreed, Josh.

Chris, when I say overheated rings, I don't necessarily mean the engine overheated. If timing is really far off, or combustion is pre-igniting, etc. This can cause excessive combustion heat without raising coolant temperatures; although I don't believe that has happened to you. However, if the engine is really 28% down on all four, smoked rings is highly likely. After thinking about it for some time, I really think that your mechanic did the leak down with the first timing mark at TDC, which would be the intake/exhaust stroke. I think I've even done that in the past when I wasn't thinking clearly, got some funky leak down values and realized what I had done. It's easy to do. Discuss this with him and let us know.
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Unread 02-13-2013, 03:14 PM   #15
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I just saw this in a post on Rennlist about modifying a 944 Turbo.

This is regarding the webcam: Webcam offers off the shelf cams for the 951 but you need to shim the exhaust valves like the intake valves to accommodate the extra lift the cam offers.

Not sure any valves were shimmed. Could this be a contributor to the high leakdown numbers?
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