Why do buicks run 110 LSA cams?
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gnpoweredrail
Member
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- Mar 22, 2010
???
jimmymack87gn
Boost Junkie
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- Dec 21, 2011
To give the little v6 some bottom end. Kenny Dutweiller. used to run cams w/109.
Posted from the TurboBuick.Com mobile app
Posted from the TurboBuick.Com mobile app
Chris Hogeland
TWISTED 6 RACING
- Joined
- May 28, 2006
I don't.
That's a little overly simplistic. The LSA doesn't tell the entire story of how much overlap you have. Overlap is a function of lobe shape and lobe size.
A 110 LSA with huge fat lobes with a high ramp speed will have MUCH more overlap that a 110 LSA cam with skinny slow lobes.
As the lobes get widers, the LSA has to spread out to maintain the bottom end and not move the RPM curve into the stratosphere.
A 110 LSA with huge fat lobes with a high ramp speed will have MUCH more overlap that a 110 LSA cam with skinny slow lobes.
As the lobes get widers, the LSA has to spread out to maintain the bottom end and not move the RPM curve into the stratosphere.
When the lobes get tighter, the more time spend with both valves open. On a slow spinning supercharged engine, that means you're just shooting air/fuel right out the exhaust pipe. That's a double whammy with us... not only does it kill vacuum and gas mileage (and make the car lazy) but it means you'd be trying to drive the turbo with 20PSI or so instead of a nice hot exhaust burn. It also means that with pressurized exhaust and both valves open during the exhaust stroke it'll shove burnt gasses back into the intake (for the next piston in the firing order) to swallow
Overlap's job is to take a low pressure pulse (that we don't have) from the header collector and drag a fresh charge across the piston and 'suck' out all the burnt gasses.. With a turbo, that's not an option.
On a N/A engine you get that 'lope' everybody likes and it moves it RPM curve up. Often times, the curve gets moved up further than the engine will actually spin.
Overlap's job is to take a low pressure pulse (that we don't have) from the header collector and drag a fresh charge across the piston and 'suck' out all the burnt gasses.. With a turbo, that's not an option.
On a N/A engine you get that 'lope' everybody likes and it moves it RPM curve up. Often times, the curve gets moved up further than the engine will actually spin.
The LSA is determined after the valve timing events are analyzed for a pair of lobes. I don't spec based on a 110 LSA. Workout knowing proposed manifold pressure, back pressure, or power level intended LSA doesn't mean crap
No
All these cams from Cotton's are 110 LSA cams:
http://www.cottonsperformance.com/proddetail.asp?prod=EngHTC&cat=35
The first one has an advertised duration of 252 on both sides. That gives it 32 degrees of overlap, which doesn't sound like very much to me, but I'm more familiar with V8 applications.
The second has 40 degrees of overlap.
The third has 48.
The 91 Corvette in my signature had a cam with 56 degrees of overlap and drove pretty well.
The stock cam claims to have 38 degrees of overlap, but when you actually do the math on the numbers from gnttype it comes up as 46. Assuming the 107 is LSA and not ICL.
When turbo charging later model cars (LS cars, for example) the accepted theory basically is the opposite of everything the TR cams are. The wider LSA is something that has been the norm in that world (especially when turbocharging) for a decade or more. In those applications, typically a 114-115 LSA will drive better, be easier to tune, make more low end power, make more part throttle power, and just generally be a better choice for a turbo charged application.
Now, just because that's the way it's been done for the last 10 years or so doesn't make it the best way, or the only way, to get things done. Buick folks have been making it happen with turbo chargers much longer than the late model crowd - which drives me to look here for information, - which has shown me a fairly large disparity in the thought process of cam selection.
I'm wondering why the buick community seems to use cams, that by modern standards, could be considered inferior choices. I'd like to understand that choice. If it's rooted in the past, based on something ole' Kenny D. did back in 1994, that's fine, now I know. However, if there is more to it, I'd like to know that too.
Thanks for any clarification, and thanks for your time.
http://www.cottonsperformance.com/proddetail.asp?prod=EngHTC&cat=35
The first one has an advertised duration of 252 on both sides. That gives it 32 degrees of overlap, which doesn't sound like very much to me, but I'm more familiar with V8 applications.
The second has 40 degrees of overlap.
The third has 48.
The 91 Corvette in my signature had a cam with 56 degrees of overlap and drove pretty well.
The stock cam claims to have 38 degrees of overlap, but when you actually do the math on the numbers from gnttype it comes up as 46. Assuming the 107 is LSA and not ICL.
When turbo charging later model cars (LS cars, for example) the accepted theory basically is the opposite of everything the TR cams are. The wider LSA is something that has been the norm in that world (especially when turbocharging) for a decade or more. In those applications, typically a 114-115 LSA will drive better, be easier to tune, make more low end power, make more part throttle power, and just generally be a better choice for a turbo charged application.
Now, just because that's the way it's been done for the last 10 years or so doesn't make it the best way, or the only way, to get things done. Buick folks have been making it happen with turbo chargers much longer than the late model crowd - which drives me to look here for information, - which has shown me a fairly large disparity in the thought process of cam selection.
I'm wondering why the buick community seems to use cams, that by modern standards, could be considered inferior choices. I'd like to understand that choice. If it's rooted in the past, based on something ole' Kenny D. did back in 1994, that's fine, now I know. However, if there is more to it, I'd like to know that too.
Thanks for any clarification, and thanks for your time.
You posted complex stuff thinking it was overly simplistic. Therefore there is no simplistic answer. When it comes to cams, every "plus" change you make is a "negative" somewhere else.
The truth of the matter is that turbos are the great equalizer and they take a BUNCH of stuff off the table, ESP in the cam dept. There's a few rules when dealing with turbochargers... one is there's no low pressure pulse on the ex valve like a N/A, excessive overlap just wastes effort. There's no reason to leave the ex valve open much past TDC, and there's no reason to open the intake valve way before TDC.
It's not an 'old .vs. new' thing. minute changes in cam timing really aren't the place to find big power.
The truth of the matter is that turbos are the great equalizer and they take a BUNCH of stuff off the table, ESP in the cam dept. There's a few rules when dealing with turbochargers... one is there's no low pressure pulse on the ex valve like a N/A, excessive overlap just wastes effort. There's no reason to leave the ex valve open much past TDC, and there's no reason to open the intake valve way before TDC.
It's not an 'old .vs. new' thing. minute changes in cam timing really aren't the place to find big power.
750H.P.V6
Brutal 6 Racing
- Joined
- Sep 4, 2001
All other things being equal a wider LSA will broaden the torque curve and reduce overlap but peak H.P. will be less. 112-114 LSA seems to work well. On my last cam I would have liked to go wider but was limited by the cam blanks available. I know Allan and Brian have played around a lot with different lobe profiles and have quite a bit of first hand experience.
Neal
Neal
- Joined
- May 26, 2001
I do not remember the last time we used a turbo Buick cam with a 110 LSA?
We base cam selection upon each engine we build based upon the specific parts as well as the intended use of the final product the customer desires including his performance goals.
Since we have done many different engine builds over the years, this experience has given us actual results for many performance levels.
Cam selection for street or street/strip builds are not very critical as a rather wide range of cams is available to satisfy these simple requests.
It is when you get into competition engine builds where you need every available HP and still meet class rules to be a winner. We have had opportunities to build more than a few of these for customers over the duration of a few race seasons, and have changed cam profiles that would pick up 2-3 tenths and a few MPH each time.
Unless the build is for a sub-10 sec. GN, cam selection including LSA, is not that important as the stock cam can easily run into the 10's.
We base cam selection upon each engine we build based upon the specific parts as well as the intended use of the final product the customer desires including his performance goals.
Since we have done many different engine builds over the years, this experience has given us actual results for many performance levels.
Cam selection for street or street/strip builds are not very critical as a rather wide range of cams is available to satisfy these simple requests.
It is when you get into competition engine builds where you need every available HP and still meet class rules to be a winner. We have had opportunities to build more than a few of these for customers over the duration of a few race seasons, and have changed cam profiles that would pick up 2-3 tenths and a few MPH each time.
Unless the build is for a sub-10 sec. GN, cam selection including LSA, is not that important as the stock cam can easily run into the 10's.
It does look like most of the catalog type cams for our cars are 110 and 112 LSA.
Agreed. I really like the specs on that DLS cam that was for sale with the 114lsa. Sounds like a torquey beast which I like as I run a high boost but low rpm setup. Looking to continue this trend with 109 build 2.0 coming soon.
- Joined
- May 26, 2001
It does look like most of the catalog type cams for our cars are 110 and 112 LSA.
Comp can do larger LSA cams, there are not listed though.
TA usually has 112/114 LSA cams in stock.
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