ARI stage 2 with 1.6 versus stage 3 or Crane 272

[Kreb]

My custom intake for the 3.4 should be arriving soon, and I'm starting to think about porting and the cam.

I don't really have a strong technical grasp on cam dynamics. My goal is to get close to 200 WHP and pull reasonably strong to 6500 RPM (Hell, 180 would be a big improvement from my current 138!) The stage 3 has similar specs to the 272, although the 272 has a bit more duration. I've been told that I'll have to go back to 1.52 rockers to accomodate the hotter cams and avoid piston interference.

So the question is whether the 272 or stage 3 will be worth the expense and time, or will my current setup be "close enough"?

I've got headers and a Holley 390 on there. The intake will be the Camaro SFI with a custom upper. Here's the comparison chart for the various cams:

http://www.engine-parts.com/GMV6/GM28cams.html

edit: I'd be up for a hotter cam possibility, but I want to stay with hydraulic lifters.

Thanks, guys

Berk

[geoffinbc]

The 272 cam will work fine. 1.6 rockers wont make it hit the pistons. However I cannot say anything about the lift causing valve guide interferance or coil bind.

TurboZ24 is running over 285 duration a .6 lift on the intake and exhaust without hitting the pistons.

[TurboZ24]

But I also have 8.0:1 dished pistons.

[Syn]

i am running the crane 272 with 1.6 rockers, ls6 valve springs. but praying the valves don't hit

[Kreb]

Thanks for the feedback guys.

I don't have the cojones (or budget) to risk interfierence. I suppose that the ideal situation would be to use different pistons or mill reliefs into the current pistons to allow the 272/1.6 combo, but that may be more than I want to bite off right now.

I guess my question boils down to this: My old setup - headers, offy, Holley 390, ARI stage 2, 1.6 rockers, MSD, dyno'd about 140 HP/180 TQ at the wheels in a mediocre state of tune, with power falling off over 4200. With freeer flowing heads and intake I should be able to hit higher peak values at a higher RPM. So [i]how much will the current cam/rockers hold me back? IF I didn't want to modify the pistons to accept 1.6, would the difference between the 272 and my current setup be negligable or worthwhile? And are there any hotter cams available than the 272 while remaining hydraulic?

[geoffinbc]

Here is a list of 60* flat tappet cams. It is all the cams I could find fromt he major vendors

http://members.shaw.ca/betterthanyoutoo/camshaft_guide.htm

With the 272 and 1.6 rockers your only going to have .512 lift on the exhaust . I know there are people running a hell of alot more.

[Kreb]

That's great. Way to come through with the tech! So what I'm inclined to do is buy the 272 or stage 3, dry fit it and put some modeling clay on the piston. Crank it by hand to check for spring bind or piston contact, and use the clay for a reference as to clearance. If there is an issue I can either pull the pistons and tap-'em with a grinder as necessary (wieghing them afterwards for uniformity), or I can throw the stock rockers back in there. Does that sound about right? Will I weaken the pistons considerably by adding a few mm of relief?