High lift cam vs High ratio rockers

[Jerryl]

Lets assume you are looking for 0.500 valve lift. Which listed option would you go with, and why?

A - High lift cam, low ratio rockers
B - Low lift cam, high ratio rockers.

 

[gunzandgearz]

Lets assume you are looking for 0.500 valve lift. Which listed option would you go with, and why?

A - High lift cam, low ratio rockers
B - Low lift cam, high ratio rockers.

Flow your cylinder heads and spec the cam for the heads and cubic inch combo,you can always play with the longer ratios if you think your motor would like a little faster valve action, but it might not like it, best thing is just to get the proper cam ground for your combination

 

[turbobitt]

Lets assume you are looking for 0.500 valve lift. Which listed option would you go with, and why?

A - High lift cam, low ratio rockers
B - Low lift cam, high ratio rockers.

The cam I selected on my latest refresh had such a high lift, short duration aggressive lobe that i had to back down on the ratio that I normally ran. So for me it was all about running a particular lobe family.
AG


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[gunzandgearz]

The cam I selected on my latest refresh had such a high lift, short duration aggressive lobe that i had to back down on the ratio that I normally ran. So for me it was all about running a particular lobe family.
AG


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Yeah the lobe selections have gotten pretty good in the last 5 years The Rocker ratio chasing it's kind of an old-school thing of the past because of all the different lobes you can get these days, honestly if the rocker arm ratios change your stuff you don't have the proper cam for the combination

 

[hensleyt]

As fast as the new roller cam ramps the valve open and close I prefer the low ratio .
But the new spring and retainer combo is lighter .
Lots of people running that combo and you don’t hear people talking about valve float .
To me it’s a personal thing no real science

 

[earlbrown]

Damn. I have no idea how to ask for specifics on this one.


I'll start with this one though... What's so special about .500 lift?

 

[earlbrown]

Note: I did enjoy all the 'set in stone' advice, yet none of us know if the cam is flat or roller, solid or hydraulic......


'cause, you know..... there's a difference.

 

[Jerryl]

Damn. I have no idea how to ask for specifics on this one.


I'll start with this one though... What's so special about .500 lift?

It was a hypothetical question and didn't want to introduce the increased lift variable.

 

[bison]

Aggressive cams have more lift because they need time to decelerate the lifter from the aggressive ramp. Increasing rocker ratio increases duration at higher lifts where cylinder fill mostly occurs. Increased rocker ratio might help if you have a non restricted setup that can use the additional lift. These turbo engines cover up a lot of sins with cams unless you’re cheap and buy the cheapest stuff available just because it was cheap. You still need to spring these properly. Most of these never get a fighting chance because of cheap inadequate valvetrain parts. Some people use the same cams over and over because they failed when they tried to use something more aggressive with their cheap springs.


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[gunzandgearz]

Aggressive cams have more lift because they need time to decelerate the lifter from the aggressive ramp. Increasing rocker ratio increases duration at higher lifts where cylinder fill mostly occurs. Increased rocker ratio might help if you have a non restricted setup that can use the additional lift. These turbo engines cover up a lot of sins with cams unless you’re cheap and buy the cheapest stuff available just because it was cheap. You still need to spring these properly. Most of these never get a fighting chance because of cheap inadequate valvetrain parts. Some people use the same cams over and over because they failed when they tried to use something more aggressive with their cheap springs.


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I agree,I do have a little different viewpoint on the duration part of that but no sense in rehashing that discussion I will say this the longer ratio will get the valve off of the seat faster which will help low lift flow but one thing that people need to understand is the upper lift Flow doesn't really matter when it comes to The Rocker ratios because once the valve curtain area gets larger than the throat area the valve is no longer the restriction the throat area is so the upper lift flow is now being determined by your cylinder head throat area,not the valve

 

[Jerryl]

Thanks for replying gents.
I was thinking that the final decision "depends" and as usual, there never is a "one size fits all".

It would be interesting to see if the aftermarket would create a custom rocker with a ratio to maximize / ensure curtain area for a specific setup.

 

[earlbrown]

It would be interesting to see if the aftermarket would create a custom rocker with a ratio to maximize / ensure curtain area for a specific setup.

Already done. I'm a Harland Sharp dealer, and they will make me any ratio I want for free on any of their rockers.

I did that a few months ago with a Ford 400 I'm building. The only roller cam I could get was more lift than I wanted so I lowered the rocker ratio so I didn't have to spring the hell out of it, then have to buy very expensive lifters (and I have an engine that's way overcammed)

 

[Jerryl]

Already done. I'm a Harland Sharp dealer, and they will make me any ratio I want for free on any of their rockers.

Awesome and a great option.

 

[No disintegrations]

Already done. I'm a Harland Sharp dealer, and they will make me any ratio I want for free on any of their rockers.

I did that a few months ago with a Ford 400 I'm building. The only roller cam I could get was more lift than I wanted so I lowered the rocker ratio so I didn't have to spring the hell out of it, then have to buy very expensive lifters (and I have an engine that's way overcammed)

Speaking of Ford's. Did you ever find a way to remember or have a cheat sheet as to what bell housing bolt pattern each engine uses?

 

[Jerryl]

What are currently the main differences between HS and T&D?

 

[earlbrown]

Speaking of Ford's. Did you ever find a way to remember or have a cheat sheet as to what bell housing bolt pattern each engine uses?

351M, 400, and 460 use the same bolt pattern. Modulars have their own bolt pattern so I can't use a new transmission on any of my 460s (I have an extra TR3650 now so I can measure and investigate what it'll take to make an adapter. I still haven't checked to see if my 3V will fit between the frame rails on my NECKCAR). I was at TTA308s house last night and was about to see, but a freak rainstorm showed up at just the right time.

 

[earlbrown]

What are currently the main differences between HS and T&D?

Color.



(and Harland Sharps are cheaper though me because I pass on the savings for being a WD dealer)

 

[bison]

What are currently the main differences between HS and T&D?

I’ve had to modify the spacers a couple times on HS. Also they kick you in the nuts for replacement hardware like replacement adjusters. Other than that they are gtg. Most of what’s been said here matters little as far as lift. The overlap is what’s going to make the most difference if you’re pushing it and running out of turbo. You can only fill the cylinder so much. Having a bunch of inert gas trapped in the clearance volume will hurt engine efficiency. The camshaft itself will matter more than the rocker ratio. Can’t correct a problem with cam overlap with a different set of rocker arms


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