Ok, it is a 79 L-48 with THM-350 and 3:55 rear end(i think), Vortec heads, Edlebrock Perfomer Vortec manifold, dual exhaust, stock exhaust manifolds(plan on changing later). I am rebuilding the engine so I want to replace the cam to match everything that I have put in. The heads are the weak spring versions that are said to be good for .450in of lift(Scogin Dickey says I might be able to get away with a cam of .460 I think). I saw springs good for .490in in a Jegs catalogue so I'd replace them if I have too. I want a lot of low end torque. So what's everyone's recomendations?

 

For some torque I say something along the lines of the Comp Cam 262 or 268 cam. I ran the 268 in my 327 and really liked it. It had a great sounding idle, and had a good bottom end decent midrange.

:cheers:

 

http://www.compcams.com/information/...62H-10_001.asp

This is the cam I put in my car. It has the biggest torque numbers of any of the XE cams. http://www.compcams.com/information/...ts/DynoSheets/

This is the link for the rest of the XE dyno sheets. Give them a look.


[Modified by Eddie 70, 5:55 PM 4/10/2003]

 

I am thinking of a Comp Cams XE250H-10. Comp Cams dynoed it and it reached 412ft lbs. torque, so it doesn't seem that bad. Also anyone know how the GM Hi-Perf would be? When it comes to cams I'm kinda lost.

 

The XE-250 falls about mid way between your stock L48 cam and the L82 cam. You should be able to go a couple notches higher than the 250 without giving up too much low end. For your combination, I like the 268H, the XE256 or XE262, and the factory L82 cam. There are bunch of other cam grinders besides Comp that make cams that would also be good choices. I'd definitely heed the valve spring advice. If needed, the extra expense and effort will be well worth it.

 

When I looked into cams I went to http://www.compcams.com/information/...on/default.asp and they sent me an email with the recommendation that a Magnum 270H would be perfect.

I went ahead and did another thorough analysis between a 268H, XE262H, and a Magnum 270H. Here's the spreadsheet: http://67.116.80.82/Vette/Files/Cam Comparison.xls

Basically, the 268H has the same grind for it's intake and exhaust lobes, the 270H is the same way. The XE262H however has an exhaust lobe grind that is very close to the 270H lobes. In my opinion anyone getting an XE262H is just wasting their effort at upgrading their valve train to support the exhaust lift while allowing the lower intake lift to choke their intake. A Magnum 270H has a very similar grind for BOTH intake and exhaust as does the exhaust lobe on the XE262H.

 

:iagree: XE262 :smash: :thumbs:

 

Comp Cams 268H should be good :cheers:

 

I agree that the 270H is a nice cam but I don't agree that an XE-262 would be a "wasted effort". I don't see how using any cam that has significantly more intake duration and lift than stock would "choke their intake". When low end torque is a consideration (as 79corvette said), less intake duration is better than more. At the same time, more exhaust duration can decrease low end torque also but proportionately less. The logic behind split duration cams is twofold. One purpose is to compensate for the differences in intake port flow vs exhaust port flow. The other purpose is reduce pumping losses that result in less power to the flywheel. Keep in mind that while one cylinder is producing power on it's downstroke, another cylinder is absorbing some of that power on it's upstroke while pushing the exhaust gasses out. The same benefit can occur by increasing intake duration but the negative effects on low end torque and overall efficiency are greater. In most applications, the intake duration will have a greater effect on the engine's power range (good or bad) than the exhaust duration.

Cam grinds are a compromise. If not so, there wouldn't be any need for the thousands of choices out there. One guy has low gears and a stick or a high stall converter auto, another has tall gears and an auto. One guy cruises around town, another wants the lowest et's and at any cost to drivability. Personally, I'm very happy with a larger cam in my 327 than is being discussed here (XE-274) but it suits me and my car.

 

Point well taken. I didn't intend to say that upgrading from stock by just installing a XE262H was a wasted effort. What I meant was that the XE262H really requires stiffer springs, pushrods, and roller rockers to compensate for the exhaust lift and duration to keep from breaking something on an old set that may have been in there for 30 years...and that expense would be the same for a Magnum 270H, so I just feel that not getting the higher lift out of the intake would be a waste of effort to upgrade the intake. So, basically...the XE262H just needs the exhaust hardware upgraded while the intake side can stay stock...I'm not sure how this would effect balance, but it seems to me that having the same lift on each valve would be a better balance, and upgrading the intake valvetrain for an XE262H would not be as efficient as going ahead and getting the 270H.

Anyway...we all know that even a 256H would be much better than what was put in the L48's! :thumbs:

 

With the stock vortec heads and 1.5 lifters, you are limited to the following cams with less than .470 lift (that's pushing it):
GMPP (used in 350HO with Vortec heads): 212/222@.050; .435/.460 lift
Comp 265 Dual Energy, 211/221@.050, .442/.465 lift;
Comp XE262, 218/224@.050, .462/.469 lift;
Crane PowerMax H-266-2, 210/216@.050, .440/.454 lift;
Isky and Edlebrock cams are all low lift for the duration, you have to add 1.6 self aligning rocker$$$.

From what I read, the springs are not the problem, it's the retainer to seal clearance that limits total lift.

Joe




[Modified by joe73vette, 10:21 PM 4/14/2003]