Mark Johnson

iTrader: (1)

Hey guys- as most of you know I'm piece- mealing a cam together refining the specs as I decide on displacement and components. The BIG question is about overlap; is it measured from the seat or at .050? When does ovelap begin to affect vacuum? Trying to stay on the conservative side at these higher elevations..................

joelster

What duration are you looking at? If you want a small cam with around 220/230, you could grind it on a 104 and still have plenty of vacuum.

Vortec350ss

iTrader: (20)

with a 5.3 even as little as -10 of overlap you will notice a choppy idle. You will have plenty of vacuum, but the idle will chop pretty good.

Overlap is measured at .050.

Mark Johnson

iTrader: (1)

oh no- very short durations, like around 198* @ .050. Not looking for chop, just trying keep what precious little vacuum here at 7,200 ft..............

Vortec350ss

iTrader: (20)

Oh man you will be fine...

a mild cam in that truck that would work well for you would be something along the lines of a 212/218 low lift. Its a 114 LSA with 2* advance I believe. Vinci offers some small cams that would work well also. Be careful with a cam that has a lot of advance if you dont plan to run headers as it can disrupt your intake flow opening the valve too soon.

Mark Johnson

iTrader: (1)

Cool-
this is for a 4.8 project I'm cooking up down the road. DD, maybe/ probably a little added zing. TB torque converter fer sure..........

Fast355

Overlap can be measured seat to seat as well, usually .004 or .006 depending on whose specs you are looking at. With a 23* head 10-40* works well for towing, 30-60* for a mild street cam and up to about 50-75* for hot street setups. Anything beyond that is Strip/Race territory. Keep in mind the better the head the wider the LSA it will want for a given duration.

Daily driven, mild LS engines seem to respond well cams in the 112-116* range for LSA when running modest durations. High altitude is going to naturally reduce cylinder pressure and idle vacuum.

OP, I would probably do a set of milled/ported LS6 243 style heads first to get the compression ratio up then make a cam change. I would likely run something around 212/218 @ .050 on a 112* LSA and advanced 4*.

Then again you could always do as I have done and swap the junk vacuum booster for a hydroboost setup and run the lumpy cam of your choice.

Fast355

Yank SS3600 converter, 4.10 gears, Hydroboost, milled/ported 243s, long tubes, a 220/228ish cam on as tight of a LSA as you dare and spin that 4.8 a little.

Mark Johnson

iTrader: (1)

Holy mother f*** I'm not bracket racing. I purposely sought out a truck with the T engine(*706 heads) for their small valves in the quest for gas mileage. Just lookin' for a little more zing, I have no business in the stoplight to stoplight drag race scene............

Fast355

I think we all assumed you were interested in performance without a massive driveability sacrifice. For a stock truck, the best fuel economy is likely with a stock cam considering about the smallest off the shelf cam I can think of is a 206/212 comp on a 115* LSA and even Comp advertises it as making midrange and top-end gains. Then again I had a Comp XFI grind in my 5.7 Hemi Ram and it got better MPG than it did with the stock cam. It was 212/212 @ .050 on a 114* LSA and 110* ICL. With 4.56 gears, APS 2,800 rpm converter, heavy 32" P305/50R20 tires, long tube headers, the Comp Cam and SCT tuning I frequently saw 18-20 MPG on the highway.