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While I agree with others, especially that the LS2 intake manifold is restrictive and a swap to aftermarket would add almost as much as a mild cam with a lot less work, if you want a cam for stock converter car with good manners and is easy to tune, keep the overlap to no between 0 and -4. 224/230 115 with 2 or 3 degrees of advance would meet that requirement. For a little more grunt off the line at the expense of the top end, 220/228 113 +2 would do ok.
I spent most of my last drive in the twisties for hours in 3rd. I would like to see more higher up I guess?
Where did this idea come from that a cam can have "negative overlap"? If it's negative, then there's no overlap in the first place. On top of this, ALL cams have overlap, some just have less than others - but it's in the range of 50 degrees and up.
Most people on the LSx forums with larger memberships quote the cam specs at .05 lift. At .05, overlap can be negative and still a much bigger cam than stock. If you are looking the specs measured at .006, then you would see much more overlap and the quoted duration is much larger also. A cam with a 224* or 230* lobe at .006 would be a very small cam, smaller than the stock cam.
I spent most of my last drive in the twisties for hours in 3rd. I would like to see more higher up I guess?
I would opt for something like a 224/230 115 +2 if most of your spirited driving is above 3000 rpm.
You really should take a look at the intake manifold. I remember years ago when the FAST 90 came out, the LS2 cars were showing +20 ft-lbs or more in the midrange and gains on the top end. Even porting the LS2 intake for a couple hundred bucks was producing at least 10 ft-lb and 10 HP gains. It would really complement a cam to do something there and have the tune incorporate both changes.
Thanks for jumping in here, drag racing is not what I have the car for, it is for mountain carving (it is where 80% of the 188,000km is from). I just got back from a brilliant 8hr mountain run yesterday, it was amazing ripping through the tight corners. Nevertheless, I have only been down the strip once in this car, broke into the high 12's after my 1st pass, but, once again, not looking to run 11's.
So you really want torque rather than HP and that's a whole different problem. You might as well disregard all the previous suggestions, since they apply to HP from the 5000 to 6500 rpm range and acceleration on flat land. I'm guessing you live more in the 3500 to 5500 range with constant elevation changes.
To really get the most benefit from any changes, a scanned record, especially with video, of one of your typical mountain runs will help determine beneficial mods more than any other thing. Without that, you're just guessing.
Most people on the LSx forums with larger memberships quote the cam specs at .05 lift. At .05, overlap can be negative and still a much bigger cam than stock. If you are looking the specs measured at .006, then you would see much more overlap and the quoted duration is much larger also. A cam with a 224* or 230* lobe at .006 would be a very small cam, smaller than the stock cam.
What are "larger memberships" and what does that have to do with how a cam is ground? Get any cam card that shows opening and closing events and you'll have your overlap numbers. Again - by definition there is no such thing as negative overlap. If two or more things don't overlap, they simply don't. Negative overlap (if it existed) would mean that there is no period where both intake and exhaust valves are open at the same time. That doesn't happen, partially due to the pumping losses that would be created and the sharp drop in cylinder filling (less mixture into the cylinder means less power) from the negative pressure created by the exhaust leaving the cylinder and pulling the intake charge in to fill the void.
Did you read the entire section on cam lobes in the link I supplied?
What are "larger memberships" and what does that have to do with how a cam is ground? Get any cam card that shows opening and closing events and you'll have your overlap numbers. Again - by definition there is no such thing as negative overlap. If two or more things don't overlap, they simply don't. Negative overlap (if it existed) would mean that there is no period where both intake and exhaust valves are open at the same time. That doesn't happen, partially due to the pumping losses that would be created and the sharp drop in cylinder filling (less mixture into the cylinder means less power) from the negative pressure created by the exhaust leaving the cylinder and pulling the intake charge in to fill the void.
Did you read the entire section on cam lobes in the link I supplied?
Examples of larger membership forums are this forum and LS1 Tech. I cite that because a common language is used in the LSX community, including vendors, for discussing cam specs. I've purchased a number of cams for LSx motors and helped others select cams. In discussing various options, it's rare for anyone in this community to quote a cam based on upon the .006 lift specs. Take a search through the C6 and C5 tech sections at cam posts and you'll see that. I look at the .006 specs (and at the other lifts) as the change in duration from .006 to .05 helps in evaluating how aggressive the lobe profile is.
A cam card typically has .006 and .05 specs. If you do the math for overlap using the duration at .05, you can get negative overlap on smaller cams, even if there is overlap at .006. Everyone knows it is not truly negative, if that is the concern. Overlap at .05 is often used as a proxy for drivability and power potential, and the negative number has meaning in that context. Obviously there is more to the selection of a cam than that, but that it is a good data point to consider.
Yes, I've read that link and other materials on cams.
07-06-2018, 12:27 AM
