Thats what my understanding is as well! Although a wider LSA does not always mean less overlap (for instance increasing LSA and increasing lobe duration). LSA is the amount of camshaft (notice I said camshaft!) rotation in degrees from the peak of the Exhaust lobe to the Peak of the intake lobe.

 

ZO6Ted, everything I'm saying now and after this I'm saying with a smile on my face. I know sometimes it's hard to distinguish emotions over the net, so I just wanted to get all that out of the way so there's no misreading. Also know that I am by no means a camshaft guru, professional, installer or representative, nor consider myself any of those things. I'm replying based on my own personal experiences and understanding of this matter as an enthusiast like yourself.

ZO6Ted, the simple answer is: Valve events in an N/A motor are different than in a boosted motor and we can play with the those events to improve cylinder pressure. I'm positive you knew that, so read on.

One thing before I begin: ZO6Ted, take a quick look at ANY camshaft manufacturer/grinder (Texas Speed, Comp Cams, Lingenfelter, Thunder Racing). You might learn something cool just by looking at the cam specs of the wilder and more aggressive camshafts. Chances are, the standard will be 112 LSA, with a range typically from 109-113. It is interesting to see how in most cases durations go from 21x and 115-117 LSA's, to 22x durations and 112-116 LSA's and anything 23x+ is usually accompanied by 109-113 LSA's. I think it's neat to see the correlation, I think.

I think we will all agree that cylinder pressure is similar to the compression inside a motor; the more you have the more torque and horsepower you will make given the same combination of parts. Of course, too much of a good thing like cylinder pressure and compression and you start buying parts for a new motor. Rick_Vor's question asked if bringing the lobe separation angle down to 112 or 114 would help the XR265 high lift make more low end torque in his '95 full size 5.3L swap, which it will, here's why: A piston cannot compress the air and fuel mixture while the valves are open...right? If the valves were open the mixture would simply blow right out whichever valve is open. That's an over-exaggeration of what's being discussed here but I wanted to get you to start brainstorming. With that train of thought but in the context of getting more out of what we already have to work with, closing the valves earlier during the compression stroke will allow more of the air/fuel mix to stay in the cylinder, thus increasing the cylinder pressure while the mix is being burned. The valve of most importance here is the intake valve.

Picture the piston moving up the bore on the compression stroke, getting ready to compress and burn the mix with the heads. If the intake valve were open for a long period of time during this compression stroke, the mix would be shot back into the intake manifold and not compress until the valve is almost 100% closed. This is called reversion, and is not what we're after. Changing the ICL effects when the intake valve closes. Retarding the cam delays the intake closing and decreases the pressure. Advancing the cam causes the intake valve to close earlier which increases the pressure, which allows the piston to start compressing earlier and keep most of it's compression without bleeding it all off. This tampering of the valve events can be used to manipulate the torque peak up or down the rpm range as well, which is the crux of this thread and is the answer to Rick_Vor's question.

Time for examples: The XR265 high lift is a 265/271, 212/218, .558/.561 on a 115 LSA +0 (115 ICL). It has an intake closing event ABDC @ 67.5 degrees (Comp Cams rounds up if you're wondering why they list 68). Manipulate just the ICL and make the cam into a 115 LSA +1 (114 ICL) and you've successfully closed the intake valve 1 degree sooner than before, now at 66.5 degrees. That aint much. Bringing it down to a 112 LSA +2 like I suggested (110 ICL) closes the intake valve 5 degrees sooner, which is now starting to make a difference. The 112 LSA keeps overlap the same so it'll idle about the same too, but now the cylinders are making more pressure given the same cam specs for duration and lift. Cool huh?

To put this into perspective though, I still stand behind what I said that the off-the-shelf cam is going to feel very similar to the custom grind version with a lower LSA, because we're talking about a small change. How small is hard to describe as a feeling, but in perspective, even grinding it on a 112 LSA+2 would be the equivalent to milling the heads for 0.2-0.3:1 more compression. Can you feel that difference? Maybe a little bit, but like I said, money would have to be an afterthought if this gain were to be justified. At the very least though, I believe the theory is sound and if he wanted to pursue the idea, he's on the right track.

 

Thank you for the kind words and the very detailed explanation. You're right about the internet and I never want to be taken as aggressive, just curious. That's what I was looking for though. It was the 2nd sentence in paragraph 2 of post #3 that threw me. I took it out of context with the whole post and I couldn't wrap my little brain around it. It makes perfect sense now. I always enjoy reading your posts. Many thanks!

 

im with him

 

Thanks for all the good info/explanation SynergyV8. I think I will lean toward the 110 + 2 or the 112.

Thanks, Rick

 

A 110 LSA with 2 degrees of advance would be quite mean! I like it.

 

How much wud it be to put a H.P cam on a 2008 vortec max?

 

How much would it be to put a cam "on" a 2008? Well I guess if you bought the camshaft and set it on top of the Vortec Max engine covers, it would technically be "on" the motor.

If you want to put it "in" the motor, plan on $800-1000 when all is said and done after a tune. That big black 6.0L truck of yours would do very well with a camshaft like has been described here.

 

so what about doing a 114+4? so the valves would close like the 112+2 or am I wrong. would you net a better gain with a 114+4 or a 112+2? i have a tsp220 on a 114+4 and want a tr224 or comp xe 224 on a 114+4 or a 112+2 and am scratchin my head on which one to look for.

btw sorry for the thread jack..

 

It depends 100% on your system of parts and what you want the motor to do, but your train of thought is correct because a 114+4 and a 112+2 have the same 110 intake centerline. The 114+4 will have the least amount of valve overlap, which means it'll idle smoother and will be more directed towards a stock motor with a less-than-desirable exhaust system (stock headers, stock muffler, ect). In theory, the 112+2 will need a better exhaust system to help pull the intake charge in during the extra 4 degrees of overlap compared to the 114+4, but we're splitting hairs here with the small changes. The 112+2 will move peak torque lower and increase max torque, whereas the 114+4 will take the torque and stretch it out to broaden the curve, but make less of it. Unfortunately, the answer is clear as mud but like I said it depends on what job the cam has to fulfill within the vehicle.

I missed this earlier, when Rick_Vor said it's going into his Father in-law's truck....if he's an older gentleman and wanted an "Old Man cam", the 114+4 would be a great choice to keep the manifold vacuum the same and idle smooth. If he's an "all out" kind of fella, the 112+2 would surely let people know it's not a stock motor.