Trying to decide on a cam for the wifes '40 chevy pickup (std. 350,650 holley, weiand stealth, camel hump heads, stock dist. w/ pertronix, unknown compression - need to buy pistons still - stock T350 w/ stock stall, 9" with unknown gears but I am sure they are probably pretty high) This will be a daily grocery getter but it has to have a good lope and be able to get out of its own way (per her request). I've always been under the ***umption that .500/300 degrees was pretty much the threshhold for a street cam (.500 causing valve bind/ valve interferance with stock components and 300 duration no idle and no bottom end) I think I am looking at something in the .480 and 280-90 range. What I have no clue about is the lobe seperation - I see them with everything from like 105-112???
LSA is an insteresting thing because the larger #'s, like 112-114 are for modern computer controlled performance cars, or forced induction motors. The wider angle reduces valve overlap given the same duration #'s. It also makes for a broad torque curve, but kills that crispy idle lope everyone loves. 110 is about average for a street performance cams. comp cams pretty much uses it across the board. 108 is old school- and moving towards a "circle track" sort of torque profile. It will yield a more "peaky" torque curve and give you a nasty idle. Just an opinion- If you are running something like 9:1, with 1.94 valve heads, there's simply no need to go big for a street cam. Magazine dyno tests seem to love the 262xe and 274xe cams from Comp Cams, and that's a best bet for your combination i would guess. As far as duration numbers for a stock type motor- like you said large duration cams bleed away cylinder pressure (i.e. compression) in the lower RPM ranges, only to come alive right when the stock type heads are running out of breath. To me- big duration cams really only sound hot when there is alot of compression to make them real crisp anyway. Otherwise they sound a bit like you have a burnt valve-lOl
With a stock stall converter and unknown gears I would tend to agree with 58Fridge100 and point you to a smaller cam that will help get that thing moving. I would definitely get to checking on the gear ratio as that can have a large effect on the overall performance of the truck and what cam choices make sense for you. I would also recommend calling one of the cam manufacturers tech lines and see what they recommend for your application.
Look at Lunati's Voodoo cams. Their 268 #60103 version has a great sound (type in 'lunati 60103' in youtube and you can hear it in a few cars) and would work well with your combo. It's like .489 lift and .227/.233 dur.@ .050. Lobe center is 110 (which means you still have lots of vacuum for accessories) and lower, say 106-108 and it's way too much for a streetable (i.e. huge converter, big carb, good heads, low gears, etc.) combo. Do your math and get it between 9.5-10:1 in the compression department (deck height, chamber size, pistons, head gasket thickness, etc.) You may want to get a little more converter than stock (around 2200) pretty much with any stepped up cam. Check it out...
stock convertor ...keep the advertised duration 270 or less. just from personal experience. for a driver , i like the old 268 high energy comp. seemed like it was always in the sweet spot when driving day to day. smaller torque cams will leave you with a smile , a big cam on the street usually will get ya a ticket.
Actually: 108 LSA would increase cylinder pressure compared to a 112 Vac***e would be worse with a 108 LSA and better with the 112 108 LSA cam would increase peak TQ to more of a peak and 112 would flatten and lower peak TQ a little 108 LSA the RPM's fall off after a certain point where a 112 LSA cam would hold on to the RPM"s longer
If you want a nice lopy idle go with Isky 270 mega cam If you want a more of a smooth idle and great power Comp XE262 or XE268. These cams will all give you a ballpark RPM range of around 1800-5800
fiveohnick, It is confusing- I wanna go back through this to make sure I got it correct: Narrow LSA (106-108): More valve overlap, less cylinder pressure in lower RPM range. Overall: allows you to run higher static compression ratio on the street, but provides weaker vacuum signal. lopey idle. Peaky torque curve with higher torque numbers. Wide LSA (112-114) Less valve overlap, more cylinder pressure and vacuum in lower RPM range. Allows you to run higher duration numbers on the street, but yields a more "stock" sounding idle. Broad, flat torque curve. Do I have it right now?
Talk to cam manufactures, tell them your combination, they will give you what you need. They pay engineers to figure this out.
If this is your wifes truck, does she want it to lope? Take awhile to warm up and then run good? Stand on the brakes to sit at a light? You need to be more specific. Altho a 268* .470 on a 110 is a good cam for a stockish setup.
similiar to what im running. im running a 350 with 461 camel humps, edelbrock intake, stock bottom end. im running a comp 268EX cam, i have no complaints, love it. my rear end is a 3.08 10 bolt posi, its just enough rearend to keep the tires from spinning everytime you punch it. I have it idling around 800 rpms in gear,my vac*** gauge reads around 8hg's at idle. Ive seen the gauge up to about 22hg's when cruisin and down to about 5 or so when i punch it......i like the 268EX it will get up and go Edit: i should add, my heads are 1.94, roller rockers and the stock 3/8 press in rocker studs......over 5,000 miles and no problems.....good luck
if she wants a cam with a nice rough idle, tell her she's gotta cough up the $$$ for a converter and rearend gears, plus the extra gas it will burn
I wouldn't get over 270 advertised duration and stay with 110 lobe separation. Thats what it sounds like you're wanting. Should run and sound good. Comp Xtreme Energy 268 duration or Magnum 270 duration or Crane, Lunati, etc. equivalent. Good luck
I would suggest a Summit K1103 or K1104. These are $89 with lifters. If you plan to run air conditioning, stay a bit smaller on the cam. Both of these get good reviews for idle quality and 'lope'. Without port work, compression, and high stall convertor, it is very easy to go with a cam too big. That 650 Holley may be a bit too big, especially with tall gears. From the school of hard knocks, I would bet that .480 is too much for your application and definately too much for stock springs. Maybe too much for Z28 springs. Definately don't cheat and go with springs that cam manufacturer recommends.
Absolutely correct. Narrow LSA has more overlap (and therefore more lope) but also MORE cylinder pressure because the intake valve closes sooner. Dan -- here's a cam that will give you a decent lope w/o killing cylinder pressure or low speed performance: CompCams 268H. I also like the Isky 270 Mega cam suggested above.
I've studied camshaft catalogs to try to make educated decisions about camshaft choices. LSA? Computer friendly cams, torque cams, and stock type cams have a tendency to have a LSA between 111 degrees and 116 degrees. High winding dirt car and drag car cams are between 104 degrees and 107 degrees. Summary on LSA, higher number equals reality street with a close to stock engine. Duration? All the cam makers agree that if your running a stock converter, the duration at .050" valve lift shouldn't exceed 225 degrees on intake or exhaust. Sometimes less than that is better. Lift? Hydraulic flat tappet lift dimensions will match how much duration. Hydraulic rollers can have more lift because of how the components work together compared to a flat tappet cam. I enjoyed the fire out of a .040 over 350 with a K1103 Summit cam package in it. Had a nice bump, good drivability. 112 degrees LSA for vacuum capabilities. K1103 I-214/E-224 degrees duration at .050/ I-.442/ E-.465 lift to be friendly with stock stamped steel Chevy rocker arms. The price is right too.
The Jalopy Journal
