[JLMounce]

I'd like to get everyone's opinion on this. As I'm looking at different cams for my engine build, I've already been given some various opinions on this. I don't know enough about what this does to valve motion, side loading of the lifter, and valvetrain stability to say for myself.

I already have 1.5:1 HS roller rockers. In order to get to the near .6" lift that my redone heads are going to want, that would require a .4" lobe lift.

Alternatively, I could run a cam with lob lift closer to .36 and a 1.65 rocker (I would go with the HS) which gets me very close to .6" of theoretical gross valve lift.

Does the smaller lobe aid in valvetrain stability and reduction in noise because the cam side events are softer? What about the effect of the higher ratio rocker transferring more force back to the lifter?

The lower ratio rocker on a higher lift lobe would seem to benefit from less force on the lifter and the lobe, but the trade-off may be noise and valvetrain stability.

The higher ratio rocker, cam size being equal may make the engine see a slightly larger cam.

I'd love to hear everyone's thought on this subject. My goal is to get the gross valve lift up near that .6" area to take advantage of the porting I'll have done on my KRE D-ports. At the same time, I haven't enjoyed having a loud valvetrain the last 8 years or so. I'm constantly embarrassed by it rolling through parking lots. So keeping the valvetrain as quiet as reasonably possible for a hydraulic roller cam is my aim. Even if it means giving up some maximum performance.

Thanks in advance!

[Dragncar]

I have always had the opinion that as far as valve train stress you are better off getting lift with the cam and not the rocker arms.
Its cheaper too if you already have the 1.5 rockers and not the cam that you need to buy anyway.
Never given a thought to the effects on valve train noise.
I like the noise.

[ta man]

If your heads flow well at .600 lift or higher run a lobe in the 390 to 400 range with 1.65 rockers. My cam has a .391/.400 lobe lift with 1.65 HS rockers..zero issues.

[b-man]

Well the big boys are using something like 2:1 rockers now.

Modern passenger car engines are using 1.7:1 and 1.8:1 rockers.

Myself I prefer less lifter travel and getting the job done with rocker ratio.

Just because you already own a set of 1.5:1 rockers doesn’t mean you’re married to them.

[tom s]

I prefer lobe lift,if you have 1.5s the whole world is open too you for more valve lift.Tom

[steve25]

How much HP are you looking to make that you need to run .600” lift ?
I ask because your posting in the street section.

[JLMounce]

Originally Posted by steve25

How much HP are you looking to make that you need to run .600” lift ?
I ask because your posting in the street section.

I'd love to be in the 560-580 range. Most of the money is going to have to be spent to rebuild my engine anyhow.

Block is going to be machined with upgrades in the rotating assembly. Heads are going to be rebuilt anyway, it's not that much more to do port work at the same time. I need a new cam and lifters anyway.

This has turned into a might as well project. I've got to spend the money, might as well get the most out of the combination that I can.

My fuel system will support a bit over 600hp. My drivetrain should be capable of 600 at the tire.

So my goal is to maximize the combination for a performance street application. Talking with Jeff Kauffman, at or around the 310cfm port on the heads and porting my current tii manifold, he wants lifts in the .580 to .6" range.

The cam I was running ran a .3620 lobe for .543" with the 1.5's. That was setup for the as cast heads.

[steve25]

What rear gears will the / does the car have?
It should only take 290 cfm to make 75 Hp per cylinder.

What CID is your motor?

[JLMounce]

Originally Posted by steve25

What rear gears will the / does the car have?
It should only take 290 cfm to make 75 Hp per cylinder.

What CID is your motor?

Drive train is a 4l80e with a TSP converter that stalled at 3200rpm behind my current engine. Triple disc clutch that gets full throttle lockup in 2nd through 4th gear. Rear gears are a 3.31 with a 26" tire.

Currently +0.030 455. The rebuild will go to +0.040. The current plan is to reuse the factory 4.21" crank if it's salvageable. If not, I'll go to a 4.25" crank.

[Steve C.]

With the mention of Harland Sharp 1.65 rocker arms my post #7 in this thread could be relevant.....

https://forums.maxperformanceinc.com...ighlight=1.684

Note- The link within the post no longer works but it really wasn't necessary. In addition further info within the thread might be of interest as well.


.

[steve25]

Is your cam a duel pattern?
A 455 with the stock rod to stroke ratio might make less power when you move up to 1.65s on the exh side.

[JLMounce]

Originally Posted by Steve C.

With the mention of Harland Sharp 1.65 rocker arms my post #7 in this thread could be relevant.....

https://forums.maxperformanceinc.com...ighlight=1.684

Note- The link within the post no longer works but it really wasn't necessary. In addition further info within the thread might be of interest as well.


.

Thank you. Yes I’m aware that the HS rockers tend to come in with slightly more ratio, likely to combat deflection of the aluminum body. As a result a package that doesn’t run as much spring pressure may see more than advertised ratio.

Originally Posted by steve25

Is your cam a duel pattern?
A 455 with the stock rod to stroke ratio might make less power when you move up to 1.65s on the exh side.

The current cam the Jeff K spec’d is a 232/236 112 with 4 degrees of advance ground in. My heads still use a 2.11/1.66 valve. I don’t foresee that changing with the head rebuild.

I’m targeting a 242@.050 intake lobe and whatever I need on the exhaust.

Estimated compression is going to come in at 10.36:1

[PAUL K]

I'm going out on a whim here and will say with complete confidence.... It depends on the combination.

Personally I like to look at the entire combination, especially the flow characteristics of the heads, the design of the chamber, piston, rod length, etc. etc.

But in short if the owner of the engine is on a budget (which 99% of us are) and already has a good set of rocker arms, most likely you could accomplish the goal of the task on hand finding
lobe that will work with the existing rocker arm ratio.

The "ratio" affects the acceleration of the valve and also the deceleration, along with controlling the total amount of space the valve will have between the seat throughout the lift cycle.

One can get that valve moving real fast with an aggressive lobe and a high ratio rocker arm which is very desirable for some applications. One could also open a valve a tad bit slower, use a taller lobe and create the same amount of space between the seat and valve.

In this particular build the OP has 1.5 rockers that are useable, knows they fit the head and with a little luck might be able to reuse the current pushrods.

To switch rocker ratio; one needs to buy new rocker arms, possibly clearance the pushrods and most likely need different length pushrods.

There are many lobes available that will get you the lift you want. Generally Pontiacs use heavy valves, long pushrods and are plagued with lifter noise.... All those issue will be helped with a slower acting rocker arm.

[Jay S]

Are you shooting for 560 to 580 HP at your altitude? That would figure out to be an equivalent of around 640 to 660 HP for me a state east of you. I think that is going to need the big .4”ish lobe and the big ratio rockers for that, and more than .6” lift.

If that 560HP to 580HP is a sea level equivalent and you want to be about .6” lift it makes sense to stick with 1.5s HS rockers and a .38” to .40” lift lobe.

[JLMounce]

Originally Posted by PAUL K

I'm going out on a whim here and will say with complete confidence.... It depends on the combination.

Personally I like to look at the entire combination, especially the flow characteristics of the heads, the design of the chamber, piston, rod length, etc. etc.

But in short if the owner of the engine is on a budget (which 99% of us are) and already has a good set of rocker arms, most likely you could accomplish the goal of the task on hand finding
lobe that will work with the existing rocker arm ratio.

The "ratio" affects the acceleration of the valve and also the deceleration, along with controlling the total amount of space the valve will have between the seat throughout the lift cycle.

One can get that valve moving real fast with an aggressive lobe and a high ratio rocker arm which is very desirable for some applications. One could also open a valve a tad bit slower, use a taller lobe and create the same amount of space between the seat and valve.

In this particular build the OP has 1.5 rockers that are useable, knows they fit the head and with a little luck might be able to reuse the current pushrods.

To switch rocker ratio; one needs to buy new rocker arms, possibly clearance the pushrods and most likely need different length pushrods.

There are many lobes available that will get you the lift you want. Generally Pontiacs use heavy valves, long pushrods and are plagued with lifter noise.... All those issue will be helped with a slower acting rocker arm.

Thanks Paul for the information. I am planning on needing to change the pushrods. I'm moving to a different manufacturer lifter, so that will probably necessitate that change. Saving a bit by reusing my current rockers would definitely be helpful.

Originally Posted by Jay S

Are you shooting for 560 to 580 HP at your altitude? That would figure out to be an equivalent of around 640 to 660 HP for me a state east of you. I think that is going to need the big .4”ish lobe and the big ratio rockers for that, and more than .6” lift.

If that 560HP to 580HP is a sea level equivalent and you want to be about .6” lift it makes sense to stick with 1.5s HS rockers and a .38” to .40” lift lobe.

I should have clarified that this would be a sea level corrected number. I'm not expecting to make that kind of power up at my altitude.

[Jay S]

Originally Posted by JLMounce

I should have clarified that this would be a sea level corrected number. I'm not expecting to make that kind of power up at my altitude.

HAH! I wondered about that. I was thinking man he is going for it!

I have a .4” Howard’s HR cam with 243*@.050” in
an engine with 1.6 rockers on it. I think for the most part, for HR street cams, if your having to use a .4” lobe it is actually a little too big of a lobe for HR cam profiles designed for most std cam tunnels. Much above .38” and most of the HR grinds start too have nose bounce from the extra negative acceleration over the peak. Too much negative duration in to narrow of an area, and are harder on valve terrain parts from the harsher harmonics. My .3823 lift Bullet cam with 245* @ .050” with 1.65s will run more RPMs with less spring pressure than the 4” lift Howard’s cam with 1.6’s past 6000 rpm. Both have SR lifters on them now, I think if you put HR lifters in them it would be even more difference because the Howard’s also quite a bit more acceleration off the seat. The Howard’s is decent, I would put it up against a high lift .4” Compcams magnum like a SDP Road paver cam runs. There are a couple Marine grinds that Compcams has that are really good also, close to equal to that Bullet grind. I have a Bullet .3823” set up for 1.8 rocker arms in a Pontiac.

If I were you I would open up the pushrod clearance so you could run bigger rockers than 1.5s if you wanted, but for now keep in that .38’ ish range with the 1.5 HS rockers for longevity. If you want more lift than that I would move up to a bigger ratio rocker.

[65 Lamnas]

If I wanted to keep down the stresses in the lifter valley area, I'd probably choose a higher ratio rocker or more lobe lift, so I guess there's that to consider. Lobe lift becomes an issue at some point or mega braces wouldn't have been invented. But maybe that's a moot point if you're only talking .600 lift.

[Formulajones]

I usually leave decisions like that up to the cam manufacture and engine shop when the whole combo is sitting in front of them. And looking at a certain HP goal

Lately the last few engines I've done using bullet cams and Paul C have leaned towards putting more rocker arm on them. The previous Pontiac build was the same way. The current 327 I'm doing they wanted a 1.6 rocker and picked a lobe to give me .613 lift in that little engine.

It's always worked out really nice so far on these pump gas street engines, lots of miles logged and no issues. I trust their judgement.

[Steve C.]

Interesting article.....

https://www.motortrend.com/how-to/hp...-phase-tuning/


Keep in mind it can also be beneficial in some instances to have a lower rocker arm ratio on the exhaust than on the intake side.
There is lots of information regarding this specific subject available.
That's not the specific topic in the article here, but it touches base on the subject.


.

[Jay S]

SR cams are quite a bit different on this topic compared the HR’s. It is much easier to make up for a rocker ratio with a different profile on the SR.