I'm not sure if I'll get the time and money to do this or not, but I've been thinking very hard about doing a cam swap in the bird this winter. First of all I want to convert to a roller cam, second I want to go with something a bit less aggressive because I really don't have the compression ratio for the cam I'm running now, and I think I can get better economy and maybe even more power out of something a bit milder, and finally, I'm working on prepping for my eventual forced induction system, which, if all goes according to plan, will be twin turbos, probably somewhere in the 15psi range on the street.

That being said, I'm running a Lunati cam right now, which came with my Holley SysteMax topend kit (heads, cam, and intake) when I first built my engine. I'm still using the Holley aluminum heads but now I've got a Stealth Ram and Commander 950 rather than a 4 bbl and dual plane intake.

Current cam specs:
Duration (I/E): 235/240 @.050" (Advertised 290/297)
Lift: .490/.490 (with my 1.5 full roller rockers)
Lobe Separation: 112

Now, I'm only running about 9-9.3:1 compression and I've put down (on my best pull) 295 HP and 310 TQ at the rear wheels on the dyno running 87 octane fuel. My most recent run was 282 HP and 305 TQ.

My plan is to drop back on the duration, maybe somewhere in the 218-220ish range, and go big on the lift, possibly also swapping to 1.6 rockers, but try to get myself somewhere around .570" lift or so. My heads are supposed to be ok up to .600" lift, but I figure it's wise to give some margin on that. My hope is to end up about the same HP wise, probably gain torque down low where it's fun to play with, and have a good breathing setup to move air once I get the snails in place.

I've been doing a good deal of reading on cam selection for turbocharged applications and my head is kind of spinning right now. I've also been playing with Desktop Dyno and Comp Cams Cam Quest software, both of which I take with a large grain of salt when it comes to HP numbers! LOL Razz I'd love to hear some real world experience and advice on all of this. Am I on the right track, or should I head back to the drawing board? Any and all discussion is MORE than welcome, I'm working to understand cam selection and I know I'm just beginning to scratch the surface!!

Thanks in advance!

-Paul

 

anybody?

 

How did you end up with a non-roller motor in a '92? From your '84 possibly?
I think you're on the right track going with a milder cam, whether or not you end up turbo-ing it. Just make sure you get some very stout valvetrain components to go with the aggressive lobes you're talking about. .570 lift with only 220 degrees @ .050 is serious valve motion even with a roller cam.

 

I'm not the most experienced, but If this was my project, here's what I'd do:
COMP has those new XFI HR lobes, and as a for-example, if you wanted a 214/224 cam, for peak HP at 5500 rpm, the lift with 1.6:1 rockers would be about 565/555. I don't have the exact numbers on hand. Harland Sharp offers 1.65:1s.
When new to turbos, it's easier if one avoids any overlap "at 50", so I'd consider the GM "HOT" cam as the largest, though lift with 1.6s is just 525/525. It's best under 6200 rpm.
That's my 2 cents worth.

 

Those Comp XFI lobes are exactly the kind I was warning about in my post above. People that are running them hard (which you would do if you wanted to utilize their potential) are quickly discovering they are valvetrain wreckers. The Comp XE lobes (3300 series) are the most aggressive I would run in a street application.
The LT4 Hotcam is not a good choice for a turbo application. Despite it's modest .050 duration numbers, it has lazy ramps that result in way too much seat-to-seat overlap. It IS easy on the valvetrain though, which was exactly why GM developed it - for roadracing in Vettes and F-bodies.

 

the duration on it is 279/287. Not so big. You need lazy ramps to keep the rate of acceleration of the lifter reasonable to keep from collapsing the lifter at too low of rpm. Those XFI lobes will get you 6500 rpm, but you absolutely must use beehive springs and stiff pushrods, as they will and do kill stock parts.
For my own turbo setup, I'd go way smaller on the cam than the HOT, but I'd also be using AFR 180 heads.
Also, AFR's hydra-rev kit seems like a good idea with XFI lobes, but I'd go solid roller.
Thing is, you can't use a big nasty cam and avoid overlap at 50. So solid roller is out.

 

Thanks for the advice guys, good food for thought, keep it coming!

The block is actually a '78 truck block with 4 bolt mains. I ran it in my '84 and then swapped it to the '92 when I built it after the '84 got wrecked.

Several of the COMP Cams kits I've been looking at come with new valve springs and all that good stuff. Holley claims my heads are OK for .600" lift right out of the box, and I haven't done any work to them, at least not yet, aside from attach the 1.5 roller rockers to them.

I'm pretty sure I want to keep a 113-114 LSA to go with the turbo idea, but I also don't want to have a totally gutless powerplant when the boost isn't there. I probably can't have the best of both worlds, but I can dream, right? LOL

Keep the ideas coming, it's much appreciated!!

-Paul