Camshaft grinds for turbo

mschilling · Post by **mschilling** » Wed Dec 20, 2006 10:51 am

I realize that the topic is cams in turbos, but how about cam in fuel injected turbos compared with cams in carburated turbos. I was told that efi does not tolerate the overlap of the old school cams in the same way that carbs would. What is the difference? I've heard people comment that since it's efi, the tuning should be easier, but in reality it isn't.

turbo_bob · Post by **turbo_bob** » Wed Dec 20, 2006 12:22 pm

Matt Davis wrote: Not the 2 engines I help out with. MUCH larger than that. I have the ones cam card in front of me. He asked me not to display it, but it isn't close to 236 @ .050

The duration numbers I was refering to was his Buick Grand National V-6 turboed engines.

MinamiKotaro · Post by **MinamiKotaro** » Wed Dec 20, 2006 1:54 pm

mschilling wrote:I was told that efi does not tolerate the overlap of the old school cams in the same way that carbs would. What is the difference? I've heard people comment that since it's efi, the tuning should be easier, but in reality it isn't.

It depends on the type of fuel injection system you have. The only real problem with a radical cam and fuel injection would be the idle on a MAP system. If you have a MAP-based efi system, it won't like to idle a radical cam because the vacuum signal will be unstable. There are ways to work around this. A MAF system shouldn't much care about anything but what the air meter says.

The sky should be the limit with cams and efi.

EDIT: What kind of EFI system are you using?

mschilling · Post by **mschilling** » Thu Dec 21, 2006 6:55 am

I've got a Tec3r which has all the features like MAP blend, etc., but I'm not sure why you would intentionally choose a cam that needs that workaround to get good response at the lower end. Wouldn't it be easier to just get a more appropriate cam?

BoostedBug · Post by **BoostedBug** » Fri Dec 22, 2006 2:37 pm

Custom grind here but somewhat close to a FK8

Nitrous Bandit 2 · Post by **Nitrous Bandit 2** » Sun Dec 24, 2006 12:14 pm

"Turbolag: The few seconds when the other guy thinks he has a chance"

Phil

Marty · Post by **Marty** » Sun Dec 24, 2006 12:19 pm

Nitrous Bandit 2 wrote:"Turbolag: The few seconds when the other guy thinks he has a chance"
Phil

Aint THAT the truth!

MinamiKotaro · Post by **MinamiKotaro** » Sun Dec 24, 2006 2:01 pm

mschilling wrote:Wouldn't it be easier to just get a more appropriate cam?

Of course.

Some people just can't live without that lope-a-lope-a-lope idle, though.

bugsterkafer · Post by **bugsterkafer** » Sun Dec 24, 2006 5:03 pm

Marty wrote:
Nitrous Bandit 2 wrote:"Turbolag: The few seconds when the other guy thinks he has a chance"
Phil
Aint THAT the truth!

I love this sentence too

scott the viking · Post by **scott the viking** » Sun Dec 24, 2006 5:07 pm

Agreed...that cracked me up

BoostedBug · Post by **BoostedBug** » Mon Dec 25, 2006 4:45 am

That line was in my signature for my Turbo Hayabusa. It made 491rwhp and weighed 500lbs...

Man that bike was fun.. So I thought it fit here also...

Matt Davis · Post by **Matt Davis** » Tue Dec 26, 2006 2:12 pm

turbo_bob wrote:
Matt Davis wrote: Not the 2 engines I help out with. MUCH larger than that. I have the ones cam card in front of me. He asked me not to display it, but it isn't close to 236 @ .050
The duration numbers I was refering to was his Buick Grand National V-6 turboed engines.

I gotcha Bob! The 2 I help out with are 388+ci twin turbo.

mschilling · Post by **mschilling** » Wed Dec 27, 2006 8:46 pm

What do you guys think of having NO overlap? Good or bad for turbos?

turbo_bob · Post by **turbo_bob** » Wed Dec 27, 2006 10:51 pm

mschilling wrote:What do you guys think of having NO overlap? Good or bad for turbos?

http://www.wallaceracing.com/cambasics.htm
The lobe separation angle is basically the measurement in degrees of the angle between the intake and exhaust lobes, and is generally between 104 and 118 degrees. This measurement may also be denoted as the lobe displacement angle. Intake and exhaust duration along with the lobe separation angle and camshaft lift combine to determine the amount of overlap, which is the amount of time in which both valves are open. Excess overlap can hurt low rpm performance, and will cause an engine to idle poorly. However, in some engines large amounts of overlap can help high rpm performance by scavenging the cylinders and improving volumetric efficiency. Assuming the lobe separation angle remains the same, the more lift and duration a camshaft has the more overlap it will have. A greater lobe displacement will decrease the amount of overlap, lift and duration being the same. Generally, smaller lobe separation angles cause an engine to produce more midrange torque and high rpm power, and be more responsive, while larger lobe separation angles result in broader torque, improved idle characteristics, and more peak horsepower.

Overlap and Compression- A very common idea, although for the most part incorrect, is that overlap bleeds off compression. Overlap, by itself, does not bleed off compression. Overlap is the angle between the exhaust closing and intake opening and is used to tune the exhaust's ability draw in additional intake charge as well as tuning idle vacuum and controlling power band width. Cylinder pressure is generated during the compression cycle, after the intake valve has closed and before the exhaust opens. Within practical limits, an early intake closing and late exhaust opening will maintain the highest cylinder pressure. By narrowing the Lobe Seperation Angle 'LSA' for a given lobe duration, the overlap increases, but the cylinder pressure can be increased as well. Thus cylinder pressure/compression can actually increase in this scenario, by the earlier intake closing and later exhaust opening. By increasing duration for a given LSA, the overlap will increase, the intake closing will be delayed, and the exhaust opening will occur earlier. This will decrease cylinder pressure, but the decrease/bleed-off of compression is not due to the overlap, it is due to the intake closing and exhaust opening events.

Excessive low RPM cylinder pressure will split your cylinders, detination.
Some overlap and wide LSA in turbo cams are the way to go.

scott the viking · Post by **scott the viking** » Thu Dec 28, 2006 6:19 am

mschilling wrote:What do you guys think of having NO overlap? Good or bad for turbos?

Ive experimented with it a little. It's one of those things that works "in some circumstances". It's best to have a little on an engine that is not a constant experiment. I know that they are all that to some degree. As far as good or bad goes....I'll have to say good...but then I'll have to say 'Not for most".