Can you guys help me out a bit with cam selection? I currently have an Isky 256, and want some more get up 'n' go. I really like the specs with with the Comp 260. I would go with that, and may still, if it sounded a bit meaner ... made that loved loping sound. That cam is bigger than its numbers! By that I mean it has more duration at .050" than some cams calling themselves 264. But for me I really want to hear that lope sound, that good ol' comforting lope of what I call a cam.

I would go with the Comp 268, but am concerned with mileage. Although it does impress me with the 110 lobe angle. If you don't have flowmaster 40's, that cam sounds tame, loping yes. But with 218 degrees duration @.050", that tells me performance will jump at the expense of mpg.

The other alternative is the Isky 262. With a LSA of 108 degrees, I know it will have that lobing sound. But it actually has less duration @ .050" than the comp 260! And the 108 LSA means less vacuum, a narrower power range, but greater low-mid range.

For me it always helps me make up my mind to hear other peoples experiences and opinions. BTW, I will be dropping back to the 1.6 rockers with the new cam. I am also concerned with what I have been reading about the Isky cam being 30+ year-old technology.

 

I don't know that the Comp cam uses any newer technology than Isky. Comp's 300 cam looks like it's just a mild Magnum style grind - and the Magnum line has been around as long as I can remember.

As far as LSA goes, when you're talking about <220 degrees duration it shouldn't make any appreciable difference in vacuum. Vacuum is related to overlap, so 208 @.050" w/108 LSA is no worries.

Here's an interesting article by David Vizard on cam selection.

Engine Camshaft Basics - Popular Hot Rodding Magazine



By his formula (cylinder c.i./intake valve diameter) a 300 with 1.94" valves wants the LSA between 102-104. Yikes!

 

What compression is your engine? stock converter? What RPM are you wanting your performance at?

 

Vizard "The Wizard" may have pulled those figures from an SBC although he has done work on a wide variety of engines. His books (volume 1 and volume 2) are an indispensable part of one's automotive library.

Remember Kevin, our engines are "30+ year-old technology" technology too...and so is Comp, Crane, Schneider, etc., when it comes to our engines.

 

Interesting, but technology has changed drastically in thirty years. Surely you don't believe that the cams available for our engine were all designed thirty years ago. Many of the programs used to design cams now--and I may be stepping into a gray area about which I know very little (but that won't stop me)--did not exist thirty years ago. Our engines are being retro-fitted with the aid of computers.

Or am I wrong?

 

BTW, I was browsing online and found some vids of cars and trucks with the 268 Comp cam. After seeing the vid on you tube of the bumpside with the loud flowmasters, I was surprised to hear an engine run with that cam in it and w/o the flowmasters. It really doesn't sound that radical.

 

I don't know if the 300 generates enough demand that cam manufacturers are updating their grinds with the newer lobe profiles.

Comp's XE cams are miles better than their old Magnum grinds, who knows if it trickles down to the 300. Maybe they would custom grind a 300 cam with the XE lobe patterns.

 

Narrowed it down to two choices: The Isky 262 for low/mid range power, or the Comp 260. With a LSA of 110, the 260 would idle smoother and has four more degrees duration, which I probably would not even notice. That is quite a bit of duration on that cam. But I would get the loping sound I want with the 262. And Isky is within driving distance!

From what I understand, with the LSA of 108 on the Isky, I would most likely get more low/mid range power than the Comp with the 110 LSA?

I thought I'd post a section of an article from Summit:

Lobe Separation Angle
Lobe Separation Angle, or LSA, is the number of degrees that separate the peak lift points of the cam’s intake and exhaust lobes. LSA helps determine the cam’s behavior; you can take a given set of lift and duration figures, change the LSA, and get cams with vastly different characteristics. Generally, a cam with wider LSA (112-116 degrees) offers less overlap between intake and exhaust opening and closing events. That translates into a wider rpm range, better idle quality, and higher engine vacuum, but at the cost of less torque at low and midrange rpm. A cam with a narrow LSA (104-108 degrees) offers greater low and midrange torque production, but with a narrower operating range, a choppy idle, and less engine vacuum.

For the street, you want a cam that offers a compromise--decent idle quality, respectable vacuum for operating power brakes and such, and good overall power production. separation. Again, much depends on the overall engine combination and intended use, but as a general rule, cams with a 110 to 112 degree LSA offer good power and decent street manners.

 

Those two cams have exactly the same overlap, my guess is you wouldn't notice a lick of difference between them.

I'd go with the Isky, never heard anything but good things about the company and their products. Besides, I'm looking at the same cam myself and would love to get some real world feedback form a reliable source.

 

[quote=BaronVonAutomatc;9776548]Those two cams have exactly the same overlap,

I'm curious. When you say 'overlap', do you mean LSA, which, if I understand it correctly, is the degrees of rotation between one valve closing, and another opening? Is that correct?

If it is, I believe the Comp cam has 110 degrees, and the Isky has 108. Or am I missing something?

 

Valve overlap, when the intake and exhaust valves are open a wee bit at the same time.

LSA is measured the peak of the lobes but the valve is opening/closing over 262 (and 260) degrees, 208 and 212 @ .050". The Isky cam has the same overlap with less total duration because of the tighter LSA.

It's the valve overlap that kills idle. But with big valve overlap you get over 100% VE at high rpm.

 

The funny thing is, and I'm kind of kicking myself for it, is that when I was building the engine, I was at Isky and they recommended the 262, but I opted for the 256! Why did I ask if I wasn't going to listen to them? ...live and learn.

 

Does anyone know if I would notice a difference between the Isky 256 and the 262? with 4 degrees narrower LSA, and 6 degrees more duration.

 

It should move your power peak up about 500 rpm; not a huge difference but probably noticeable. What gears are you running?

 

3.31's with a C6, but plan to be changing soon to a ZF! I think the 262 will be fine for me when I get the ridges removed, and the runners cleaned up, on my head. I've been dying to get these dang ridges removed from my chambers. I believe they are reducing the efficency of the engine/cam.