Cam question for 5.7 Vortec tuners

**Busted Knuckles** · 12-13-2006, 05:54 AM

I'm rebuilding the 5.7L engine for my '99 'burb. Flat top 4VR pistons, zero decked block, torque plate hone, yada yada. I don't want a lopey idle and don't care to mess with tuning, etc. I plan to keep lift at .450 or so, heads have had bowls blended and cleaned up but I'm sticking with stock studs, self-guiding rockers, etc. What's the biggest duration I can go with and not have to mess with aftermarket chip/tuning, etc.? I realize that LSA has a lot to do with it since part of what the computer is reading is engine vacuum. I'll be having the cam custom cut in the next week or so. Thanks in advance for your help!

**diadora516** · 12-13-2006, 08:43 AM

you would want to reprogram anyways to get the most out of the cam...

**Busted Knuckles** · 12-13-2006, 08:55 AM

As I understand it, with only a small bump in duration/lift, the computer can "re-learn" the new combo - is this right or am I misinformed?

**diadora516** · 12-13-2006, 10:14 AM

maybe that is the case...i figure if you are going through a cam swap might as get the most from it

**Pauly** · 12-13-2006, 11:07 AM

The Vortec engines come from teh factory with dished pistins, 64cc heads and a 9.4:1 CR.

Flattops will boost the static CR up a certain amount.

CPM tuning WILL be needed to bring the combo together. The PCM can learn teh crusie fueling, but cannot do anything with WOT fueling.

Building an engine and NOT tuning the PCM, is like building a nice 350 and throwing an old unrebuilt carb on top of it.

peace
PAuly

**Busted Knuckles** · 12-13-2006, 03:46 PM

This is a family burb, WOT will rarely if ever happen. I'm more after efficiency than anything else, just wanted to optimize the slightly warmed over rebuild. I have an '81 Corvette that's getting a 3.75 x 4.600 solid roller big block and a '94 crewcab dually that'll have a hydraulic roller cammed 565 inch tire shredder, I can get all the WOT thrills I need from both of those

**Jake Wade** · 12-13-2006, 08:03 PM

I am with pauly on the CR. A zero deck and -6cc flat tops is going to bump you up to around 10.3...go with a -12cc dish piston.

**diadora516** · 12-14-2006, 12:47 AM

for effiency you will want a tune. yes you will also have more power but without proper tuning you will never see optimal power/effiency. with my old engine i had the cat gutted, magnaflow muffler 3" in dual 2.5" out, k&n air filter, the air box silencer and that crap removed and a custom chip and i could knock down 14mpg in the city and 19.8 on the highway. this was with 275/60/15 tires and 3.42 gears with 165,000 on the truck. not bad for a 16 year old truck

**Busted Knuckles** · 12-14-2006, 07:35 AM

At 3500 feet, we have a lot of flat top Vortec combos running around with no problems on low test pump gas. Since reliability is my main concern, I may just drop the stock cam back in with some 1.6 rockers, should still clear the valve guides. I'll be using a set of ZZ4 springs, since I won't be spinning it past 4500, I think the combo should be fine. Thanks for all your help!

**TexasSmoker** · 12-16-2006, 06:34 AM

i am in the process of doin the same, an by the sounds of it pretty dam close to yours, i am running a forged crank, forged rods, forged flat top pistons, i kept my L-31 heads and had them ported an polished, 5 angle grind. i called crane to find out what would be the best set up for my stock injection system.
crane recomended using part # 104225, wich i got from summit for 325$

438 lift on the intake with a 264 duration
452 lift on the exhaust with a 270 duration
rpm range 1400 -5400

good luck with your build!!!