TIMSPEED

In a given engine, which would be better to have a camshaft with a little more duration, or one with a little more lift.
I'm trying to build a pretty decent 350cid for my 75 Chevy Truck. I've already decided that I'm going to go with the Vortec Heads with Modified Valve Springs to accept up to .525" lift. I just can't decide on which camshaft I want to use. Now, I know that the Vortec's are pretty well maxed out right at .500" lift. I know I'm going to have about 9.75:1 Compression with a 2500rpm stall converter backed with 3.73 gears.
I'm torn between:
Comp XE274
Duration @ .050 = 230/236
Lift @ .050 = 487/490

Lunati VooDoo 60103
Duration @ .050 = 227/233
Lift @ .050 = 489/503

CFI-EFI

I only look at the lift as an after thought. It is the duration, lobe separation and the resulting overlap that will dictate the demeanor of a given size engine. Depending on the weight, gearing, and usage, of that truck, both those cams look too big to me. Just as with everything else, the biggest number at the end of the curve that you use the least, doesn't necessarily make the best choice.

RACE ON!!!

SWCDuke

You're splitting hairs. Assuming those two cams have about the same centerlines they will not likely produce significantly different torque curves. If the centerlines are quite different the torque curves could be quite different

Cam selection starts with specifying where you want the 80 percent torque bandwidth to start. Then you need to match the cam to the flow characteristics of the engine. This includes head flow on both sides, inlet system type and relative restriction, and exhaust system type (headers or manifolds) and exhaust system back pressure.

Then you use a good simulation program like Engine Analyser and try various valve timing schemes until you find one that yields a torque curve that is closest to what are looking for.

Anything less is just guessing!

Duke

TIMSPEED

Yes, their LSA and ICL/ECL is exactly the same. I think I'm going to go with the comp, because it's $10 cheaper, and I think the little extra duration will do me good
BTW: The truck only weighs 3600lbs with a full tank of gas and me in it. The goal is to make a 300rwhp smallblock.

71coupe

I would go one step down on both. I have an XE268 in my car & it has a good powerband with a nice idle. Anything bigger would just bleed off compression with a power loss under 5000 rpm.

cardo0

I think ur trying to compare lift to duration and thats just not how i choose a cam. I look for the most overlap i can live with my application and the duration is limited by that. Most cam companies can provide u with custom lobe sep angle (LSA) cam and 108* is what i would use for the 350" Chevy with stock heads for max torque - but 110 maybe OK/good enough with better heads. BTW Isky sells thier MEGA cams off the shelf with 108* LSA.
Since stock Chevy heads are vlv limited in breathing u can't get enough lift out of the vlvs (less than .6"). For cams <270* full duration, 1.6 rockers all the way around is the ticket.
Tim i wouldn't worry 'bout hp for a truck - i would want max torque.
If u want to talk overlap just ask but for now i'll shut up.
cardo0

TIMSPEED

Well, I think it was CarCraft or HotRod that built this Vortec 350, and it made 440bhp on the dyno. The Comp cam has more duration to it, therefore it'll have more overlap. In this truck, I can live with a LOT of overlap, because this'll not even be a weekend driver, only a toy. I want a cam that'll have a nice pop to it.

cv67

It should run good with the 274, IMO the 268 will be a better choice. You'll still be able to hear it

mike 1985

the one difference in those 2 cams is the voodoo is a more aggresive ramp, therefor it should make more power.

the XE 274 is 274 advertised with 230@.050


the voodoo is 268 advertised with 227 @ .050..their supposed to set the valves down slower and create less noise. Me personally i would use the voodoo cam. Actually i would like to put that exact cam in my car...try it out for me and let us know how it works.

Mike

REDC4CORVETTE

In my Experience Small blocks like alot of lift and very little duriation .

Cory1970

The Comp cam is a great choice. I personaly run the xe274 and I love it. I have 70 double hump heads, Airgap RPM manifold, Hooker sidepipes, and a 650 Speed Demon carb. My set up is great!. People told me I should have chosen a smaller cam, but i took the risk and got the 274. I am so glad I didn't go smaller. As far as duration goes, it is much more important than lift. You can always make up lift with bigger rocker arms. I have out run cars with similar set ups and much nicer heads. I have 373's out back which help out with the lack of low end torq. Go with the comp cam, you will never look back.

Mike 1985 is correct the voodoo has a more agressive ramp, but that can cause some problems in a flat tappet set up. If the ramp is too agressive, the lifter will bounce off the cam at high RPM's. As far as the comp cam goes, I can rev my motor to 6k with no problem. I can even break the tires loose when I floor it at 2500 RPM with out even dumping the clutch.

I am currently getting my heads and intake ported. Heck now I wish I had a bigger cam. Also If you end up liking the cam, comp makes one with the same durration and centerline, more lift, but it is a roller.....