Purdone

What would be the advantage of using a smaller lift cam, eg GM Hotcam (219/228 .525/.525 112) or Comp Cams XR227HR (224/228 .534/.537 112) and rockers

Rockers on a Hotcam: .555/.555
Rockers on a XR227: .565/.568

vs.

Just getting a cam with higher lift?

TR224: 224/224 .563/.563 112
XR275: 222/224 .566/.568 112

conan

iTrader: (5)

I'd get the higher lift cam your going to spend twice the money for the same outcome.

Purdone

That is what I was thinking, so I was wondering if there was some sort of advantage.

slt200mph

iTrader: (42)

No advantage

mrr23

iTrader: (3)

here's the real advantage vinci did this test in the PROJECT AFR 03 corvette auto

comp cams 220/224 .581/.581 115 LSA with 1.7 acclerated lift rockers vs the 055 cam 216/224 .551/.551 (1.7) 113 LSA with 1.8 accelerated lift rockers (brings total lift to .589/.589) smaller cam with larger ratio rockers makes more power than a larger cam with stock ratio rockers.there's a definite advantage.

mrr23

iTrader: (3)

and for kicks, here's the ACTUAL graph. no correction factor.

UnleashedBeast

iTrader: (2)

I think there was more to that then just lift differences in both the cams. There were other specs/factors about the lower lift cam combined with the better rockers that showed the increased gains. IMHO the rockers may have well amplified the duration as well as the lift. Also, look at how the cams meet up close to the same in the high rpm but the smaller cam has more low end TQ and HP. Did anyone ever think that this might be that way b/c the smaller cam has a tighter LSA. 113 vs. 115

My arguement is that you can chose a cam that is best suited to your demands and power curve needs and save the 350.00 rocker money for a mod that will make a difference. You can grind a cam to perform almost the same with stock rockers vs. the cam with rockers.

Tommy Tucker

IMO there is even more to this.
If you exagerate the situation to huge lift numbers (pick your own) to a point where the ramps are just too large for the cam to turn, you could still extract the same lift from a regular cam with high ratio rockers because it's a linear movement as opposed to a rotary one.
I think the overall forces on all components will be the same in each case although the forces on each end of the rocker will be different depending on the ratio.
However I am not sure why some cam manufacturers are saying you can't use high ratio rockers with fast ramps. I think it must have more to do with springs and PtV clearance.
A guy from Crane (I think) was talking about 1.9's with very fast ramps though.

mrr23

iTrader: (3)

2* of LSA just changes where the peak will be given the exact same specs. the comp cam had the same type accelerated lift rockers when tested. the motor only cares what happens at the valve. even though you can save money by doing it the cam way, here's my argument to counter yours. and the smaller cam was only smaller on the intake side.

when you do it the cam way, you are throwing the lifter, pushrod, rockers, and valve at the same speed. so, the valve spring has to control all those moving parts. now, by doign it the larger rocker way, you have slowed the lifter, pushrod, and rocker down to a more controlable speed. now, the valve spring only has to control the increased speed of the valve. people are trying to solve high rpm valve float isses and usually blame the valve spring as not being able to control the situation. the less stuff you have being tossed around at high speeds, the better the valve spring can handle it.

all the major motorsport, NHRA, NASCAR, ETC..., use higher ratio rockers for a reason. because it works. and these guys are turning upwards of 8000 rpms. and you can only imagine the ramp rates these guys use. some circle track motors are using 2.0:1 ratio rockers. it's not a new idea. just finally making it to the street level.

remember a smaller cam with larger ratio rockers did better than a larger cam with stock ratio rockers. i'm waiting to see it the other way around.

BADSZ28

iTrader: (39)

I have been throwing arround this for years. I am with you mrr23. Now if someone can make a huge duration cam with arround .550 lift.

BUYAMERICAN

I have some new (we just put on the motor for tuning, when it siezed(rear main)) Comp Cams Pro-Magnum 1.85 with studs, seats, harden pushrods. We had to pull the whole motor apart and are going to cut a much bigger (John Holmes) CAMMMMMM. So not needed anymore.

$515 for the kit
$140 for the hardened pushrods
$104 for the 1/2" valve cover spacers

I will take $700 shipped(650).

My guess this will get about 20 h.p./20 torque to tires. Tune will be necessary. Should give you an additional ten h.p.. You should be able to raise your rev limiter a couple hundred as well.

I also have some

#30 Delco's ($180)
& an
LS6 Manifold ($300) 10-12 h.p over an LS1
for sale unless it already got sold by my tuner.

All the parts would be pretty easy bolt-on setup for F-Boby or C5 corvette with minimal labor. Not interested in splitting the above group or below (just a waste of time).

BackinBlack02SS

iTrader: (7)

As minute as it may be, rotational weight/mass will be less with the smaller cam/larger ratio rocker than the bigger cam/smaller ratio rocker. Increasing the lift of the cam in turn means more metal and more weight. Increasing the ratio of the rocker doesn't change the weight at all. When you want the most, every last bit helps.

mrr23

iTrader: (3)

define huge. here's two from vinci's list of cams. they might be small to some. but, they do big things.

http://www.vincihighperformance.com/...%20LS1%202.htm

048 cam
DUR @ .004" 286*/ 290*
DUR @ .050" 224*/ 228*
LIFT .551/.551
OVERLAP 55*
LSA 116*

060 cam
DUR @ .004" 290*/ 294*
DUR @ .050" 228*/ 232*
LIFT .551 / .551
OVERLAP 68
LSA 112*

UnleashedBeast

iTrader: (2)

mrr23, you have made very valid points and after your post about mass/weight, etc. I see your side and now understand what is taking place. I agree with you now and see how higher ratio rockers can be the way to go. Now, I'm curious as to what the gains would have been on my 99 LS1 with the stock cam and 1.8 rockers instead of doing the TR224/227 .569/.572 114 LSA and keeping the stock rockers.

Hmmmm, could I add some yella terra 1.8 or harland sharp 1.8 rockers to gain more with my TR 224/227 cam? Well, I just remember reading where TR doesn't recommend the use of higher ratio rockers due to the fast ramp rate of my cam. What would happen if I did it anyway?

BADSZ28

iTrader: (39)

Dur. 240+ on both ends big.

BADSZ28

iTrader: (39)

Hmmm...the P/V clearance would be close but may work. You would be over .600 on both ends with another degree or two at .050. Also the valves would have faster ramp rates. I would expect 10-20hp gain.

UnleashedBeast

iTrader: (2)

What if I were to install a better 1.7 ratio rocker. I have read that the aftermarket 1.7s act differently than the stock 1.7 rockers and gain power over stock.

mrr23

iTrader: (3)

if piston to valve clearances or valve spring limitations are an issue, then go with the 1.7 vinci/crane accelerated lift rockers. they start off the seat at 1.79. then, by .250-.300 lift, they start reverting to 1.72. and on the way back down, they convert back to 1.79 at .300-.250 lift. no other rocker does this. that's the advantage of the vinci/crane over the others.

UnleashedBeast

iTrader: (2)

I think that for my daily driven street car I am just throwing money away by upgrading my stock rockers with only aftermarket 1.7 rockers. 500+ dollars for 5HP if I'm lucky is alot of money to throw away when I can gain more power with 500 in other parts.

Now, if I bought 1.8 rockers I think that would be worth the money, but would the stock 853 heads provide enough PTV clearance for .603/.606 lift?

m5guy

Quick question: does anyone know if the stock rockers in the 2001 LS6 engines are 1.7 ratio? I had read that 1.85 rockers required a valve cover spacer.

BTW, MMR23, thanks again for posting your dyno data. Saw it on the Z06 forums.

GW
2001 Z06