Javascript Disabled Detected

You currently have javascript disabled. Several functions may not work. Please re-enable javascript to access full functionality.

Rocker ratio on Holden 6

Started by _202 Corona_ , Oct 12 2018 11:26 AM

Please log in to reply

10 replies to this topic

#1 _202 Corona_

Guests

Posted 12 October 2018 - 11:26 AM

So I currently run a cam with 240 deg. Duration and 400 thou lift at the cam using 1.5:1 rocker arms. I sent away for cam recommendations now that it has triple Webers on it. The cams are all very similar in most aspects to mine, the major difference is more lift, which brings me to my questions,
1. Will changing the ratio of my rocker arm affect clearance/valve train geometry. (it is a strip only motor)
2. What ratios has anyone else ran before?

Back to top

#2 S pack

Scrivet Counter

Members
15,538 posts

Name:Dave
Location:Luggage Point
Car:73 LJ
Joined: 25-January 10

Posted 12 October 2018 - 06:12 PM

So I currently run a cam with 240 deg. Duration and 400 thou lift at the cam using 1.5:1 rocker arms. I sent away for cam recommendations now that it has triple Webers on it. The cams are all very similar in most aspects to mine, the major difference is more lift, which brings me to my questions,
1. Will changing the ratio of my rocker arm affect clearance/valve train geometry. (it is a strip only motor)
2. What ratios has anyone else ran before?

.400" lift at the cam or at the valve?

Back to top

#3 I'm a Red Motor fiend

Forum Fixture

Members
758 posts

Name:Adam
Location:Nairne SA
Car:LJ 4 door, LC GTR
Joined: 04-January 16

View Garage

Posted 13 October 2018 - 05:31 AM

Get your head finished first mate. Because its strip only aim for max compression. If you can run avgas aim for even more max compression! Get the head shaved to achieve this. Once its ported and flowed make a cam choice based on figures. You need more lift, more duration and tighter lobes.
I run SBC 1.6 rockers on my inlets 1.5 on the exhaust.
Cam has .540" lift with a 1.6 rocker, 262 deg duration and 105 deg LSA. Static comp is 11.6.
My head has .100" off it and the slugs are .010" above the deck everything clears with that lift.

Back to top

#4 _202 Corona_

Guests

Posted 13 October 2018 - 08:25 AM

Yeah at the valve S Pack

The motor had 11.8:1 compression before we touched it and was running AVGAS, so we will take it back to there.
My flat tops sit flush with the deck.
After seeing the head disassembled we are a little amazed it ran an good as it did!
Should be easy power there.

Back to top

#5 S pack

Scrivet Counter

Members
15,538 posts

Name:Dave
Location:Luggage Point
Car:73 LJ
Joined: 25-January 10

Posted 13 October 2018 - 09:09 AM

I agree with Adam, change the cam. .400" lift at the valve is only going to increase to .425" with 1.6:1 rockers or .438" with 1.65:1 rockers.

Back to top

#6 _202 Corona_

Guests

Posted 13 October 2018 - 09:41 AM

Sigh, was hoping the more flow/less cam might work. Oh well, back into the wallet I go 😅

Back to top

#7 LC-GTR-1969

Shed tinkerer

Members
1,162 posts

Location:New South Wales
Car:Which one?
Joined: 09-March 14

View Garage

Posted 13 October 2018 - 04:37 PM

You need to pick your cam based on the head flow specs. If the head flow peaks at .420 lift then the cam you have may be fine... but if you head flow peaks at .550 you should run a cam with more lift so that you match cam/ rocker lift with the peak flow with the head.

As others have said, if its a strip only car, irrespective of lift, your cam is pretty mild for a race only setup. Good drag racing cams are usually around 254-260@50 thou on about 106-107 LSA. The lift you should just match with the head. Some heads roll over at .450 lift so no point running much more than that if the head rolls over.

Back to top

#8 _202 Corona_

Guests

Posted 14 October 2018 - 12:10 PM

Sorry, by saying strip only probably eludes to some kind of weapon! In reality I run in street class, it is race modded is more what I should say, just trying to prevent the answers being related to drivability etc.
But yes thanks for pointing out what should have been obvious to me, will wait and see what the head ends up with.