ramairroughneck

iTrader: (35)

What are the benefits and drawbacks to higher ratio rockers? Gen 1s had 1.5s. Racers are now using 2.0s. Where does it end? Why did GM go from 1.8s on LS7s back to 1.7s on L92s and LS3s?

ramairroughneck

iTrader: (35)

If its beneficial to open the valves quicker how come none of the top shops use 1.8s?

KCFormula

iTrader: (4)

I have always heard the higher ratio the better, but never understood why. I think the benefits were more seen years ago with flat tappet lifters because they could run cam profiles that went easier on the lifters and could still gain a lot of lift. I could be wrong but that is my impression.
As far as a LS1 I think the main benefit would be seen at lift values above .650 or so

Old SStroker

Roller lifters have different problems from flat lifters with steep flank cams. Rollers have side loading problems flats don't.

Using higher ratio rockers you can get the lift the engine wants within the duration the engine wants without killing the lifters with side loads. You may have noticed the trend to lower mass (lighter) valves, springs, retainers which allow more lift at higher rpm, which may make more power.

Of course is the down side is that pushrod and normal (centeline) loads on the lifter are higher with higher ratio rocker arms. I think we'll see more high-end rockers in the 2.0 and up range in the near future. OK, some are above that now.

Perhaps the truck L92 and the LS3 production engines don't need/want the lift offered by the 1.8s. When choosing rockers you consider not only the lift the valve wants, but the loads in the valvetrain.

As RAR and rpm and cam agressiveness increase, sometimes simultaneosly, rocker arm stiffnes and moment of inertia become more critical. So we want a stiffer, lighter, lower inertia system. Sounds difficult to do...but not impossible, nor cheap!

Jon

Gregory

iTrader: (4)

Aren't there also physical size limits? A camshaft with too big of lift might have a lobe bigger than the journal diameters. Then, you couldn't get the camshaft inside the engine. Thus, the mechanical ratio of the rocker arm allows greater mechanical lift with a smaller physical size.

Old SStroker

Even better, you can use a larger base circle lobe with higher ratio rockers to more effectively use what diameter you have available. The larger the base circle the larger the core area between the lobes and the stronger the cam is in torsion. They do twist.

transaman98

iTrader: (16)

just chiming in here but I have a stock cubed LS1 with Comp 224/230 .581/.592 114LSA, with 1.85 Comp Rockers, Ported Heads, and Ported FAST 90/90. The car is a friggin dog. Could all of these modifications be a little too much for stock cubes??? I am just trying to figure out why the car has such a lack of power. I have a set of 1.7's chillin out waitin to go on the car do you guys think this will fix some power issues???

chriswtx

iTrader: (5)

Which heads and whats the intake port volume. Also whats your compression, which valve springs?...And what ICL is the cam installed at...Those rockers put your lift at .632 and .644 which is way to much if you didn't flycut the pistons...

ShiznityZ28

iTrader: (11)

FYI peak lift isn't where they hit. its how early or late they open and close . Thats where they are going to hit.

although the 1.85 rockets will have the valve open wider faster.

Sparetire

A fast 90 is a big intake for a 346. You will need to wind pretty high to use it.

And who ported your heads. Modern heads are pretty tricky, and just hogging them out does not help much.

coolmannso

now with the 90mm top you need a 175 hp nos kit too get it to suck air you got the cam kick it

dano73327

Yeah WORD!!! Dat ting is WACK yo! You best be suckin air for to go fast!

WEEEEEEEE!

dlove

iTrader: (23)

Does google have a translator for this? This must be jive.

transaman98

iTrader: (16)

haha jive. right. they are stock ported heads. I have a Nitrous Express Kit with all the fixins but i havent installed it on the car yet. how healthy of a shot you guys think would be safe on the stock shortblock???

ramairroughneck

iTrader: (35)

Hey thread ****, start your own. I'm trying to learn something.

mrr23

iTrader: (3)

some reading on using higher ratio rockers.
http://vincihighperformance.com/LS1%...HTML#quicklift

Old SStroker

You can adjust the geometry a number of ways. Here is another take on rocker geometry:

http://www.mid-lift.com/intro-mid-lift.htm

It's not a short read, and the author, like the Crane author, thinks his is the better method. Read all of the pages. Good food for thought.


Jon

mrr23

iTrader: (3)

everyone with an idea think theirs is better. it's how they can back it up is where it gets interesting.

Crane LS1 Gold Race Rockers “Too Powerful!” for Daytona!

crane cams newsletter mar 2006

Crane Gold Race® Rocker Arms Dominate Engine Masters Challenge

crane cams newsletter oct 2005

Chevy High-Performance Magazine LS1 Project Truck Gains Average 20 HP

Old SStroker

The Pontiac (LS6-based and destroked to 5.0L) Daytona Prototype (DP)engines that power the winners like Gainsco, Suntrust, etc. entries don't use Crane rockers. It's not because of excess hp or being banned by the same organization either. They have a 7100 rpm limit, as well as valve lift and duration rules, but they can use solid lifters. Perhaps lift and duration rules make aggressive lobes popular which can beat on the valvetrain, especially in a 24 hour race where the engine turns about 8 million revs in anger.

I really don't uderstand why they mandate stock rockers in some classes. Not to say the LS engine rockers are not quite good, but unless the class requires hydraulic lifters, it's tough to use the non-adjustable stockers on a solid. Possible, but not easy with stud mounts.