Thread: Top end cam duration

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I am trying to choose a cam that will increase my CR but also has a duration for hi-rpm.If the motor I am building has hi-rpm capability,and I don't care a rats butt about low rpm performance,shouldn't I go with a hi/long duration cam? The majority of recomendations as far as cam selection take into account drivability,well I am not concerned about that.If I want only top-end performance wouldn't more duration and a wider LSA be the way to go? At low rpm, opening and closing rates are slower and a 110LSA would be desirable for good cylinder filling and smooth operation.But at anything over 4000 rpm wouldn't the VE suffer and a 112 or 114 LSA with 300+ duration work much better? Better flow and filling characteristics are desirable for hi-rpm,so why cut the flow short with 110 LSA and a street duration?

106 to 110 work good for tq and auto trans cars. with a stick trans you can use more lsa and what you said this holds true. the howards soild cam 11206-06 is 520/520@.050 240/250 is what i use in my friends 383 and had the lsa moved on it to 112

Thanks Pat. Yes 106-110 is good.Keeps compression up at low to mid rpm and with the 'built-in' torque caracteristics of a 383,it probably screams.Did that cam help the mid-upper rpm? Sounds like a pretty good one for a 383,but I'd guess what ever cylinder flow he has would determine that better.

yes it was low on cr. but that cam comes 106 but he wanted to do hiway hi speed runs and wanted it all it hase a set of dart pro 215 heads with a cool can intake it should run built the dam thing over 3 years ago. i would like to hear it run

i havent read my books lately but i thought that LSA of 108 and up was for autos cause the torque curve was wider. and a LSA of 108 and down was for manuals cause the peak torque faster?

383 chev,there are 'many' people on here that could better answer that,I don't know alot,thus the thread.But a 108 and lower would 'usually' have quicker open/close rates and probably be better for auto's because of the ability to efficiently charge the cylinder(for smoother low speed performance).But some of these new cam designs I don't understand well.Whether 108 or what,I think it would depend on how much duration is put in the lobe??? But again,it depends on whether we are talking daily driver,3/4 race,full race,etc.,,

read iskyracing cams book on cams the 5 cycle long duration cams for more over lap for better scavenge of the combusbustion in effect making a 5 cycle on a 4 cycle engine but the way i see it is bigger duration and more overlap with no cr is not good but sometimes a bigger engine like a bit more duration on it and if you go to lets say a cam with 104 they come on fast and pull very hard and peak fast and a cam with 112 will may not pull as hard as fast but will be broader i have been working on a new cam for my pump gas engines that like s 115 to 117 lsa it is a big engine and with a cam like this i hope to get a round 900 hp and 800+ tq and if you look it some big block cam that run 800 lift and@.050 298 they will run them at112 cars with a 106 to110 your stall in your trans will work better this was told to me from art carr over 10 years ago

Wide LSA cams broaden the torque range with a flatter torque curve for a longer period where narrow LSA produce more power but in a on/off torque band. Duration determines the operating range of a cam and ICL determines more of the CR the cam will give.

300 adv. duration 260 @.050 106 LSA Installed 106 will have close to the same effective compression as a 300 adv. duration 260 @.050 112 LSA intalled 106 intake centerline. The 106 will make more power but the 112 will have a broader power curve. The wider LSA will idle better but will be down on hp/torque. As Pat pointed out, when cams get really big the LSA has to widen because of overlap. Blowers and Nitrous applications need the wide LSA to blow the cylinder down. On a wide LSA cam, the exhaust opens sooner. This can hurt a N/A engine by allowing usable cylinder pressure to bleed off too soon. By using a large cam with a low CR, you don't really gain much performance, but it will push the power band way up into the rpm range. Best performance comes by matching the cam to the CR.

Here is a calculator you can use to see the effective cr with a given cam and Intake centerline. www.zonk.com/crcalc.htm