Cams, Cams, Cams, What do you think
09-15-2008, 09:15 PM
#16
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I have nothin against scheids but I see them more as 12v p-pump guys, Not saying they dont make a good cam or a better cam, thats what the post is for... getting the info IJMO. Thanks for the info.
09-15-2008, 09:22 PM
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yeah I probably would of went with a Don M but all ready ordered the Scheid. I bet you'll drop your egts about 200 degress on the track. Also when my motor was torn apart the cam journals where all pretty well worn out so I went ahead and had my block lime bored so I wouldn't have a problem down the road. Not saying yours will need it but a good thing to look at.
09-16-2008, 06:31 PM
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i honestly dont drive my truck civil enough /often enough to tell about a true mpg increase.i did turn the smarty down on the last tank and with a 5000 turbo,dual stage ll pumps froom II and 66ml injects,and lowered compression motor i was able to get 19.7 mpg
09-16-2008, 11:01 PM
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billet cam requires you to get your block lime bored. the cam is more expensive also and lime boring is not cheap. Billet cams are overkill in a CR anyways. You mostly see them in a Big p-pumped truck turning big rpms.
09-16-2008, 11:24 PM
#23
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Their are several aspects to consider in a cam for a Diesel application. If valve to piston clearance is not an issue, then it opens the door to new possibilities.
There is not alot of room for much lift at TDC during overlap, 0.030-0.040" is about all that is available. To promote better spooling, we need as much as we can get without running the valves into the pistons, and still maintain some needed clearance. To accomplish this, the cam geometry gets compromised to make it all fit. The idea is to get the valve open quickly, hold it open as long as possible then close it quickly.
Since we have already dictated available lift at overlap, we must determine seat to seat events. Opening and closing events for the intake and exhaust valves, must allow for all the overlap we can stuff into the engine. This helps during low or no boost situations, after all until boost is present we have an N/A engine. Next in consideration is when the intake and exhaust valves open and close. If you keep the intake valve open well beyond BDC, you can lose some intake charge through reversion. When the exhaust opens, it must overcome the positive pressure already in the manifold. Obviously as the engine speed and load changes the dynamics change as well.
Custom cam development is here now. There are several options for cores, regrinds will not get you very far.
The most popular cam available has been around awhile, I think as choices have been very limited most go by what is available. The best cams are yet to come.
There is not alot of room for much lift at TDC during overlap, 0.030-0.040" is about all that is available. To promote better spooling, we need as much as we can get without running the valves into the pistons, and still maintain some needed clearance. To accomplish this, the cam geometry gets compromised to make it all fit. The idea is to get the valve open quickly, hold it open as long as possible then close it quickly.
Since we have already dictated available lift at overlap, we must determine seat to seat events. Opening and closing events for the intake and exhaust valves, must allow for all the overlap we can stuff into the engine. This helps during low or no boost situations, after all until boost is present we have an N/A engine. Next in consideration is when the intake and exhaust valves open and close. If you keep the intake valve open well beyond BDC, you can lose some intake charge through reversion. When the exhaust opens, it must overcome the positive pressure already in the manifold. Obviously as the engine speed and load changes the dynamics change as well.
Custom cam development is here now. There are several options for cores, regrinds will not get you very far.
The most popular cam available has been around awhile, I think as choices have been very limited most go by what is available. The best cams are yet to come.
It sounds like that the valve to piston clearance is the big issue. If I was building a motor it would be an automatic for me to cut the pistons. The idea that the cam ramps and valve train stress on these low rpm motors is a concern is nonsense. I cannot hardly believe how low a spring pressure is needed. My street gasser has 650+ lbs open pressure and 350 on the seat. 110 lbs is less than almost ALL stock gassers. The valve train is hardly working on our trucks. Lots and lots and lots of room to improve.
I see huge(0.7"+) exhaust lifts in the future.
Damon
09-17-2008, 12:17 PM
#25
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Damon, gasser tech doesn't always translate well to turbodiesels. For instance, at extreme lifts, flycutting pistons for valve relief can interfere with the bowl's contribution to stable ignition.
Even though the valvetrain has excellent lubrication features, it isn't exactly a high-RPM design.
If you've ever held a CTD bumpstick, you saw how much smaller the lobes are in terms of bearing surface compared to typical V8 thumpers... not to mention the mushroom tappets instead of roller lifters. The highest wearing area in the CTD is the tappet/lobe interface, and as Shane mentioned - seat pressure X 2...
Also, as I'm sure you know, lobe profiles on a forced-induction engine are vastly different than normally-aspirated versions... additionally there's important features distinct to turbo cams vs. blower cams.
However, I don't intend for any of this to be a wet blanket on innovation or testing - some day in the future we'll look back in amazement at the "junk" we're running now, and be glad for how far it took us... same as wondering how we ran the numbers decades ago with carburetors, points & no ECM.
Even though the valvetrain has excellent lubrication features, it isn't exactly a high-RPM design.
If you've ever held a CTD bumpstick, you saw how much smaller the lobes are in terms of bearing surface compared to typical V8 thumpers... not to mention the mushroom tappets instead of roller lifters. The highest wearing area in the CTD is the tappet/lobe interface, and as Shane mentioned - seat pressure X 2...
Also, as I'm sure you know, lobe profiles on a forced-induction engine are vastly different than normally-aspirated versions... additionally there's important features distinct to turbo cams vs. blower cams.
However, I don't intend for any of this to be a wet blanket on innovation or testing - some day in the future we'll look back in amazement at the "junk" we're running now, and be glad for how far it took us... same as wondering how we ran the numbers decades ago with carburetors, points & no ECM.
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