Valve Overlap Limits For Daily Driver
Valve Overlap Limits For Daily Driver I have been searching for some valve overlap guidelines, and haven't found what I'm looking for. Important issues, are maintaining manifold vacuum for power brakes, using a full exhaust, etc. I have been playing with cam designs with 6 to 12 degrees of overlap at .050" lift, and up to about 60 degrees total. Please, share any experience or theory.
TECH Fanatic
Joined: Jun 2002
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From: Upstate NY
Originally Posted by NoMoreFWD
I have been searching for some valve overlap guidelines, and haven't found what I'm looking for. Important issues, are maintaining manifold vacuum for power brakes, using a full exhaust, etc. I have been playing with cam designs with 6 to 12 degrees of overlap at .050" lift, and up to about 60 degrees total. Please, share any experience or theory.
I suggest you get some good professional cam design help to achieve as many of your goals as possible. OEM cams do what you mentioned, but you are probably looking for more torque/power. Everything is a compromise in cam design, and every engine combination is unique.
FWIW, I've seen cams with negative overlap @ .050 make tons of torque and power. It's the entire combination that matters.
TECH Fanatic
Joined: Jun 2002
Posts: 1,979
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From: Upstate NY
Originally Posted by NoMoreFWD
I hear what your saying. There are a lot of variables. I'm looking at a cam only LS2 with a M6. I'm trying to educate myself as much as possible and then work with a cam designer.
He may share some cam spec information with you...perhaps not. Folks who have preconceived notions (lots of them garnered from poor info on the internet) about what cam specs should be often try to second guess the cam guy's specs. You are buying performance, not specs!
Be prepared to tell your cam guy everything abnout your ride: engine and vehicle mods, gears, emission needs, driveablility desires, performance desires, etc. Be realistic: your DD cam-only isn't going to be a 9 second car for $400.
If your cam guy changes his specs for your custom cam because you didn't like his choice, try another guy, or just "design" your own and get it made. Then you will only have yourself to blame... or congratulate for the performance of your engine.
My $.02
Originally Posted by Old SStroker
Tell your cam designer where you want to go, not how to get there.
He may share some cam spec information with you...perhaps not. Folks who have preconceived notions (lots of them garnered from poor info on the internet) about what cam specs should be often try to second guess the cam guy's specs. You are buying performance, not specs!
Be prepared to tell your cam guy everything abnout your ride: engine and vehicle mods, gears, emission needs, driveablility desires, performance desires, etc. Be realistic: your DD cam-only isn't going to be a 9 second car for $400.
If your cam guy changes his specs for your custom cam because you didn't like his choice, try another guy, or just "design" your own and get it made. Then you will only have yourself to blame... or congratulate for the performance of your engine.
My $.02
He may share some cam spec information with you...perhaps not. Folks who have preconceived notions (lots of them garnered from poor info on the internet) about what cam specs should be often try to second guess the cam guy's specs. You are buying performance, not specs!
Be prepared to tell your cam guy everything abnout your ride: engine and vehicle mods, gears, emission needs, driveablility desires, performance desires, etc. Be realistic: your DD cam-only isn't going to be a 9 second car for $400.
If your cam guy changes his specs for your custom cam because you didn't like his choice, try another guy, or just "design" your own and get it made. Then you will only have yourself to blame... or congratulate for the performance of your engine.
My $.02
I am in the same boat as him, just trying to learn more, however I am letting my designer do what he thinks is the best. I just want to try and understand why he is doing what he is doing!!
Old SStroker, thanks for the advice. I think the worst thing that I could do is the common over-camming. I think I will let someone run with it, and in the end, hopefully our ideas will be somewhat aligned.
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From: Metairie, LA
There are some of us, like me, who are buying specs just as much as buying performance. I, personally, want to know the specs of my cam and know why it works well, or does not, with my specific setup. Those who don't give out cam specs, like it's some big secret, will just not get my business.
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I think you'll find people driving around with more than 20* at .05 if you look at the biggest cams from TSP or TR (Without looking them up, I don't exact overlap figures). Your definition of a full exhaust, usable rpm range, and acceptable idle speed all influence your decision.
I don't know if LS1's react different to overlap than LT1's, but I have ** degrees at .050 and I have to keep it above 2k in 1-5th or it bucks like crazy, and this is with a dyno/street tune too.
Last edited by speed_demon24; Feb 2, 2007 at 05:33 PM.
I used DynoSim Pro Tools to design the cam that I've been using for a couple of years now and I am very pleased. With a program like DynoSim, you can look at what happens when you change valve events like IVO, ICL, etc. and get a sense of what will happen to the torque and power curves. The program doesn't have perfect fidelity as would be expected. However, it can be a great help in learning about the dynamics of cam design, the influence of improved heads, and a host of other variables.
Steve
Steve
Originally Posted by speed_demon24
I don't know if LS1's react different to overlap than LT1's, but I have 13 degrees at .050 and I have to keep it above 2k in 1-5th or it bucks like crazy, and this is with a dyno/street tune too.
My current cam for my 454 LS2 has 27.5*.
LS1's differ a bunch from LT1's in terms of overlap and a lot of that changes with the heads and VJ's you are running. Some stuff can take overlap well and other stuff just can't. Race motors compared to street motors are a different thing all together, even if they are in the same RPM range as what we run on the street.
Actually the amount of TQ the motor produces at part throttle is as important as anything else, not just the overlap numbers. Plus if you have more gear, or a higher overdrive (like a 4L60 vs a M6) then you can stand more overlap in driving situations.
Add: I had a customer with a 400 cube LS motor and wanted more drivability, he didn't like the cookie cutter 242/248 deal but I swapped him over to a smaller cam with virtually the same overlap and he picked up TQ all the way to 5500rpm with the same HP level and drivability improved. The TQ improvement was 15-20rwhp from idle to TQ peak with the same peak HP numbers...
Bret
Actually the amount of TQ the motor produces at part throttle is as important as anything else, not just the overlap numbers. Plus if you have more gear, or a higher overdrive (like a 4L60 vs a M6) then you can stand more overlap in driving situations.
Add: I had a customer with a 400 cube LS motor and wanted more drivability, he didn't like the cookie cutter 242/248 deal but I swapped him over to a smaller cam with virtually the same overlap and he picked up TQ all the way to 5500rpm with the same HP level and drivability improved. The TQ improvement was 15-20rwhp from idle to TQ peak with the same peak HP numbers...
Bret
Last edited by SStrokerAce; Feb 2, 2007 at 08:04 PM.
