2edybrd

I am just sitting here thinking about what I want to do to my car this summer. I have pretty much decided on headers and a cam for now, then heads during the winter.

My internal debate revolves around getting a high lift cam or going with a lower lift cam with tons of duration and higher ratio rockers.

It seems to me that the main point of debate for the high lift cam is the strain it puts on the rest of the valvetrain. I guess a high lift cam (say .600, just for the argument) with long duration would, by it's very nature have a very fast ramp rate.

This would mean that a much stronger spring, or dual springs, and new or stronger lifters would be needed. Even with these pieces, at least the springs would have to replaced fairley regularly.

Now, for the low lift cam with say 300* duration, let's use the ASA cam. With .525 lift and 236 intake, 300 exhaust, if tuned correctly, seems to make surprising power.

O.K. combine this cam with, say 1.85 ratio rockers. To my way of thinking there would be much less strain on the rest of the valvetrain compared to using a high lift cam. Here's my reasoning. Even though the ASA cam with 1.85 rockers now has around .600 lift, it is till a very easy ramp rate, so the springs aren't slammed on, the lifters aren't mashed from the need for a higher spring rate.

Now that I think of it, would the springs even be compressed as far as they would with a high lift cam alone? I mean when the ratio is changed to 1.85 does the back side of the rocker that compresses the springs change as well? I'm certain the springs are compressed more than stock, but is it as much as a high lift cam?

Hell, you could even spin the ASA cam to a higher RPM more safely.

What do you guys think?

MyLS1Hauls

iTrader: (2)

High lift is high lift, regardless of how you get it. High ratio rocker arms are actually harder on the valvetrain. High ratio rocker arms put more strain on the already delicate stock lifters, and the change in geometry can also cause problems. Stock ratio with an XE-R lobe based cam is the best setup really. If you use good springs, an aggressive cam will be just fine. High ratio rocker arms increase valve lift and the effective ramp rate of a cam. For 1.85 ratio rocker arms, take any advertised valve lift for an LS1 cam and multiply it by 1.15 and that will be the new lift. Also, the ASA cam doesnt have 300* of exhaust duration at .050" I'm not sure of the exact specs, but its nowhere near that big.

someday

Asa: 226/236-.525/.525-110

WAHUSKER

iTrader: (4)

What Brad said is true, hi lift = hi lift no matter how you get there. As for the higher ratio rockers putting more stress on parts, I dunno...seems the same to me. One thing you will get by going with hi ratio rockers & a smaller cam is BETTER rocker arms. The stock ones are weak, to put it mildly. I installed 1.8 HS rockers & am now installing a Hot Cam under them. So I end up with the equivilant of a Lingenfelter GT1 (or 2?) cam, with more a durable valve train. (~220/230 @.050, .560/560, 112LSA) But to each his own.....

Mark

MyLS1Hauls

iTrader: (2)

The 1.85 ratio over the 1.7s do put more strain on the lifters. The 1.85s put 15% more load on the lifters...yah that might be splitting hairs, but it does. Another problem with using 1.8s is that if you ever want to change cams, you'll have to specifically use lower lift cam lobes to keep lift reasonable.

Nasty N8

iTrader: (33)

Yes always build the lift a dur into the cam and not with ratio. The added ratio adds to the strain on the valvetrain conciderably. 1.8 is for those that DO NOT want to change the cam out but want the added benefits.

Nate

J-Rod

There are about a million factors that go into determining what ratio rocker to use. It also depends on the lobe and how fast the ramp rate is on it. This is referred to as "jerk". In other words how many thousandth of lift you get per degree. Another issues is how fast the lift from .006 to about .020 takes place.

So, depending on your lobe, with a 1.7 and a 1.8 rocker you might see the same stresses on your valvetrain depending on the lobe.

Also, if they are roller tip rockers, there is 0 sideloading, so that isn't an issue. With the stock arms, there are some sideloading issues to be aware of.

I think you may see some folks begin to mix ratios on the intake and exhaust side in the not so distant future.

Also, look at some of the posts discussing cam design. Some folks who are much smarter than me felt that many of the cams are rather excessive in their lift, and, since we are not limited by duration or lift rules on the street, you might be able to get a cam that is much more reasonable than you think that will make good power...

I think there are better cams than the ASA open to you...

nuzee

iTrader: (2)

Typically, higher duration allows higher lift. Lower duration lobes are lift-limited because you have less “lobe” to smoothly open/peak/close the valve.

High ratio rockers are attractive to guys that don’t want to significantly increase duration over a stock cam which will move the power band into a higher rpm range, but want to add lift which, theoretically, should increase torque/power across the board from a small lift-limited cam.

I still may get a set of SLP 1.85s to experiment running them in combination with the stock arms on a stock cam. I might then do the same experiment on a slightly larger cam. That should keep me busy (without spending more money) for a good long while, lol!

panic

To calculate the lift when going from a 1.7 rocker arm ratio to 1.85, multiply by 108.8%, not 115%.
This also increases the spring load on the pushrod and tappet by 108.8%.

speedtigger

iTrader: (16)

This may be a record. You revived an 11 year old thread. I am thinking they have completed this build by now. LOL

KCS

iTrader: (20)

Good lord