Forcefed86

iTrader: (4)

Say I was looking at putting a cam in an SBE 4.8.

Ones a 212/218 @ 112 .600 lift. The other is the exact same but .550 lift.

Any real benefit going with the higher lift on a factory 706 casting? At what point do they choke?

wannafbody

iTrader: (2)

Wouldn't lower lift springs need to be changed less frequently? I remember in the past guys using high lift cams had to replace springs at 30K, that might not be true now with different cam profiles. I'm not sure.

JoeNova

Think of it as a shift point.
Is it better to shift as soon as you hit peak power, or better to Rev it out if power doesn't fall off?

You won't gain more flow going over .550, but the valve will spend more time at the heads peak flow.

KCS

iTrader: (20)

The .600" lift cam will probably open the valve quicker, which is pretty important to make power.

kinglt-1

iTrader: (26)

There is about 10-12hp difference between the .550 lift and .600 lift cam. I am basing this off of TSP engine dynos between their high lift and low lift truck cams. Basically the low lift is designed to run stock ls6 springs and push rods making it more budget friendly. The high lift needs springs and push rods, so you just added 250-300.00 to the cost of the cam swap.

truckdoug

iTrader: (25)

are the valve events exactly the same otherwise?

i assume you're boosting right?

Forcefed86

iTrader: (4)

I’ve got a 4.8 I’d like to squeeze the most out of cam wise while maintaining lowish duration/overlap to keep it turbo friendly. If I can get an extra 5-10hp by bumping the lift up I might as well do it. But If It’s just going to cause added wear and tear with no real benefits…

So assuming I kept the duration under say 220 and LSA around 110-112… Roughly what’s the lift cutoff point on an untouched flattop 4.8? Will also have the .051 HG thickness so extra cushion there. Could I get away with .625” or so? Would I even want to? Do they even make a lobes with lowish duration and lift that high? This is a toy and will never see 30k so I’m not concerned about spring life.

The Texas Speed dyno’d a “stock” 5.3 with their Stg2 “high lift” and Stg2 “low lift” cams. One was at .550 and the other .600 with the same duration and LSA grinds. Larger lift lobe appears to make more peak power across the board. Just not sure how much I can get away with…

KCS

iTrader: (20)

Comp makes a QXI lobe with 219 duration @ .050" and .377" lobe lift that they describe as having "excellent stability", but I don't know that I would recommend that much on a stock rocker arm. I have .64x" on a stock rocker and it looks sketchy. A roller tipped rocker would be fine though.

JakeFusion

iTrader: (7)

I think Brian Tooley has used the QXI or maybe the QNX lobes on some of his cams. So they are stable. However, anything over .630" lift with a stock rocker is iffy for longevity due to the increased wear.

I'd also look at the HUC lobes as they are designed based off Marine profiles but have added lift ~ .619" but only go down to 219 degrees. The HLO go down to 213 but the lift starts at .659"...

kinglt-1

iTrader: (26)

If running stock rockers I would keep the lift at or less then .600 lift.

Forcefed86

iTrader: (4)

Anyone use these Procomp 1.8 roller tip rockers for $112? Then I could use a milder 600 lift lobe and be around 635?

http://r.ebay.com/3L4w9c

A.R. Shale Targa

iTrader: (2)

Even if the @ .050" and @ .200 were the same; the higher lift requires a smaller base circle as the lifter needs to travel a greater distance
So the flank speed/jerk (rise over the run) WILL BE FASTER
harder on push rods, rockers, and springs
I would not go more than .600" with a stock rocker as the tip simply begins to "scrub" and trash the valve tip
I've seen a TSP .624" continually trash the rocker and valve tips on an LS3 app

JoeNova

I have the speedmaster shaft mounted LS rockers, never used them on anything though. They look OK. Been sitting in storage for a year.

The problem with low duration and high lift is ramp rates. Valvetrain weight starts to become a factor when you're trying to move things that fast.

Howards has a 218/218 113 LSA .604/.604, and a 218/224 112 with the same lift.

Forcefed86

iTrader: (4)

Originally planned on this 216/222 @111 .56X lift deal. Claims it takes the power out to 6800rpm which I figure is about all the LS6 intake is good for. And the tight LSA would help with the gutless 4.8 get into boost down low. But I didn’t want to leave 10-15 free NA HP on the table. Since those numbers will likely double or triple in boost. It’s a 1.32 T6 S480, so it should breath ok with relatively low back pressure.

https://m.summitracing.com/parts/cca...make/chevrolet


I’m kinda torn now. The guys running the numbers these days on small bore SBE stuff are revving them to the moon. With the 4.8’s shorter stroke that makes me think I should really be pushing 7500 or more. So I don’t want to beat the valve train up any more than I have to with huge lift.

Capizzi was shifting his SBE 5.3 @ 8100 rpm on the factory valve train with a 23X duration and .600 lift BEI cam. No idea what lobe they used but I’d think it would have to be really lazy to keep everything stabile. He was on factory rockers/lifters as well.

A.R. Shale Targa

iTrader: (2)

The S400 series turbos "work" but the hot side is huge at 96mm
My 1.32ar/475 was a SMIDGE lazy on a 218/218 385" gen I but my
Converter was tight.
Boost does seem to add about a thousand RPMs to what a given stick
Would feed an NA combo. My shift point was 6500 with hollow valve
Fast burn heads on blow thru carb.
I think you're right on to keep the intake lobe small with only 293 inches
And the short 3.268" arm
IMO the GT2-3 would be cool in that set up
Short intake at 207 but the 220 exhaust and wide LS would carry out to
7-7200 nicely with some PSI maxlifes.

truckdoug

iTrader: (25)

hey those pro comp rockers---stay very far away from them.

thunderstruck507

iTrader: (18)

I'm currently running .637/.620" lift with no issues to valves tips on stock rockers.

Previous cam was a .620"/.602" and there were no issues with it either.

Must be other variables.

wannafbody

iTrader: (2)

How many miles? I've heard of guys trashing valves in 10,000 miles on a LS7. Mamo doesn't recommend the stock rocker arms due to valve guide wear issues on aggressive cams.

thunderstruck507

iTrader: (18)

I'd say 6500-7000 miles on the previous .620/.602 cam and the same or so on the new one. I'd have to look up records.

I have been keeping a close eye on the valve stems since I've been checking lash anyway and also we ground my valve stems to get them all the same height so I feared the tips might not be as hardened as untouched valves.

Kip did say he was speccing my LLSR to be the max comfortable lift with stock rockers. And it very well could be causing guide wear, I have no way to check that easily other than by feel when the rockers are off.

JakeFusion

iTrader: (7)

Hot side at 96mm is still too small for the 80mm and 84mm billet wheels being fitted to them. The 1.32AR is too small for anything over a 370. Backpressure is insane. But on a 4.8L or a street driven 5.3L... I'd probably do a 75/92 combo with a 1.10 AR and it'd be plenty streetable.

I wonder what my cam 227/244 115 would do with something like that. It would probably send backpressure through the roof? I was looking at doing a 76/96 1.25 AR T4 on my 346 with a 3600 stall. But I don't feel like ripping out my cam. lol

/sorry to hijack

I'd do the Stage II 4.8 Turbo cam from LJMS: 218/223 .598/.571 112+3