rocker arm ratios

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dovercrossing

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I saw a article in Hot Rod several years back that said a higher lift rocker arm set was used on certain years of the slant 6 and I am interested in using them I think the standard is 5 to 1 and the ones in question were 6 to 1. Would it be worth the cost versus horsepower gained to use them I have oversize valves!
 
I've never heard this, but, if you can get a 1.6 rocker ratio for the engine, know that a higher ratio has a direct impact on HP output. Not much, but it is the extra lift that alows the head to breath in more and exhaust out more. The increased ratio also has a effect of giving the cam more intencity and a ever so tiny increase in duation.

Being that the cam is opening at the same time still and will allways will, it is the rockers increased ratio that lifts the valve (Ever so slightly) quicker and moving the valve off the seat (Ever so slightly quicker) that the duration @ 050 is increased.

Cost vs HP delivered worth it? Probably not, but then again, every little effort towards the goal is a good one and they do become a simple math equation of, item A + item B + item C = more power. Then add on D + E + F ='s more power.

Bang for the buck diminishs after certain add on's. But the effect ad's up. While thr rocker ratio change by itself is not alot on a stock engine, it becomes more of a power added as the engine is more and more modified.

On a stock engine, lets just say it is worth 5 HP. On a mild modified engine, it'll be worth 15 hp. On a very worked up engine, it'll be worth 30 hp and so on and so on. And now it is up to you.
 
dovercrossing said:
I saw a article in Hot Rod several years back that said a higher lift rocker arm set was used on certain years of the slant 6 and I am interested in using them I think the standard is 5 to 1 and the ones in question were 6 to 1. Would it be worth the cost versus horsepower gained to use them I have oversize valves!
Click to expand...

No, the OEM rocker arms are supposed to be 1.5:1, but they are in reality, more like 1.35:1, so higher-lift rocker arms are worthwhile... if you can find any.

AFAIK, no "high-lift" rockers ever came on a /6 from the factory.

Good luck.
 
yea dutra and mike jefferies have tested hundred of rockers and they range anywhere from 1.3 to 1.4 ratio...

just have to find places with big blanks to accommodate the extra lobe lift needed...
 
After searching through a fifteen year collection of Hot Rod Mags trying to find the article in question I came across my own answer! The rockers were listed in the Mopar Performance Six Cylinder Engines book ! Much to my dismay they were for the 3.9 V6 not the/6. I appreciate the info you all helped me with though. My car a 74 Duster has been a work in progress since 1996. I've gathered all the parts through the years and I'm finally going to complete it ( hopefully ) this summer!
 
Yes, the 3.9 is a "Magnum" engine which came with 1.6 rockers like the 318 and 360 Magnums.

One must also be careful with higher ratios, especially when using OEM springs, because a valve opening and closing faster usually requires a stiffer spring to be able to keep up with it and not float. Unfortunately, most of us have don't have a way to figure out the minimum spring pressures we need to use when swapping around cams and/or ratios. So we have to rely on the cam company's advice. They are in the business to sell parts, but it is usually good insurance to go stiffer with higher ratios.
 
Just an FYI. About 25 years ago I had a1963 VW Beetle. The engine had a big bore kit that increased it from 1200 cc to (IIRC) 1385 cc, and a header. The stock rocker arm ratio was 1 to 1. On later VW models they swtched to a 1.1 to 1 ratio. I bolted a set of the later 1.1 to 1 rockers onto my motor & could definitely feel the difference in the motor.
 
clifford now makes 1.6 rocker arms with the shaft..you have to order them..pretty expensive..(like everything clifford makes)..but you can get them..im thinking of putting them on my slant...71 scamp clifford torquemaster cam, intake, holley 450 carb, clifford headers, flowmaster mofflers
 
Clifford.....be careful of that name.
 
If you put the right cam in your slant there is NO reason to increase the rocker ratio. I see it as a fudge factor for a cam that didnt quite measure up.
Just my 02.
Frank
 
66aCUDA said:
If you put the right cam in your slant there is NO reason to increase the rocker ratio. I see it as a fudge factor for a cam that didnt quite measure up.
Just my 02.
Frank
Click to expand...

well as good as john was At erson he still gave my to small of a lobe... i was looking for .510 valve lift and told him that the rockers were 1.4 and he still only gave me a 340 lobe=.475 valve lift...

so i know where this idea comes from...
 
66aCUDA said:
If you put the right cam in your slant there is NO reason to increase the rocker ratio. I see it as a fudge factor for a cam that didnt quite measure up.
Just my 02.
Frank
Click to expand...

Exactly right.....and Erson is the DEAD WORST company about selling crappy camshaft grinds and then trying to push the higher ratio rockers on you. When Stoopid Shops had a store in Macon, that's all them boys could talk about was the higher ratio than stock rockers.....and if you looked through the Erson catalog, you saw why. All of their grinds were ridiculously low lift. Even when they got above 230* duration @.050" they still only had like .450 lift. It was stupid. It was like a big ploy to sell you a whole valve train of junk. I've never known anybody around here that had good luck with Erson anything.
 
StrokerScamp said:
Exactly right.....and Erson is the DEAD WORST company about selling crappy camshaft grinds and then trying to push the higher ratio rockers on you. When Stoopid Shops had a store in Macon, that's all them boys could talk about was the higher ratio than stock rockers.....and if you looked through the Erson catalog, you saw why. All of their grinds were ridiculously low lift. Even when they got above 230* duration @.050" they still only had like .450 lift. It was stupid. It was like a big ploy to sell you a whole valve train of junk. I've never known anybody around here that had good luck with Erson anything.
Click to expand...


I don't know about Erson cams, but I have tried tirelessly, to get a short-duration /6 turbocharger cam with over .510" lift and no matter which cam company I talk to, they all say the same thing: "sorry, but we can't give you a short-duration cam with over .484" lift. No "masters."

So, I was looking for some 1.6 arms, not being able to find a cam that had the kind of specs I needed.

Guess I'll do it with boost; that seems to be a lot cheaper than the "arm and a leg" they seem to want for these 1.6:1 arms....
 
What do you think about putting valve lash caps on the valves to increase lift.Just a thought.
TXDart
 
StrokerScamp said:
Exactly right.....and Erson is the DEAD WORST company about selling crappy camshaft grinds and then trying to push the higher ratio rockers on you. When Stoopid Shops had a store in Macon, that's all them boys could talk about was the higher ratio than stock rockers.....and if you looked through the Erson catalog, you saw why. All of their grinds were ridiculously low lift. Even when they got above 230* duration @.050" they still only had like .450 lift. It was stupid. It was like a big ploy to sell you a whole valve train of junk. I've never known anybody around here that had good luck with Erson anything.
Click to expand...


well me erson cam was supposed to be a .510 246@ .050 but valve lift ended up at .475...

once i build a all out race motor im having crower grind me a custom solid roller
 
805moparkid said:
once i build a all out race motor I'm having crower grind me a custom solid roller
Click to expand...

Well, get ready to pay $1,000.00 for a blank for them to grind it on... and to deal with the problems of finding rollers that can be made to work in the /6 block, and to deal with the worrisome problems of having no oil pump or distributor drive gear on the cam... alternative drive mechanisms will have to be created.

I looked into the roller idea and that is what I found.:sad9:
 
Everyone needs to remember that even with accurate 1.5 rockers, you WILL NOT get the advertised 1.5 cam lift in a small block Mopar. The main cause is the lifter/pushrod/rocker angles which are not "in line". I forgot the numbers, but I think it's at least .015-.020". Probably higher numbers with higher lift cams. Not sure how bad the big blocks are.
 
Locomotion said:
Everyone needs to remember that even with accurate 1.5 rockers, you WILL NOT get the advertised 1.5 cam lift in a small block Mopar. The main cause is the lifter/pushrod/rocker angles which are not "in line". I forgot the numbers, but I think it's at least .015-.020". Probably higher numbers with higher lift cams. Not sure how bad the big blocks are.
Click to expand...

This is a slant six discussion in the slant six section.
 
Locomotion said:
Everyone needs to remember that even with accurate 1.5 rockers, you WILL NOT get the advertised 1.5 cam lift in a small block Mopar. The main cause is the lifter/pushrod/rocker angles which are not "in line". I forgot the numbers, but I think it's at least .015-.020". Probably higher numbers with higher lift cams. Not sure how bad the big blocks are.
Click to expand...

.....or slant 6's. There can be smaller losses due to other factors also.
Is the /6 geometry inline or off to some degree?
 
Locomotion said:
Everyone needs to remember that even with accurate 1.5 rockers, you WILL NOT get the advertised 1.5 cam lift in a small block Mopar. The main cause is the lifter/pushrod/rocker angles which are not "in line". I forgot the numbers, but I think it's at least .015-.020". Probably higher numbers with higher lift cams. Not sure how bad the big blocks are.
Click to expand...

We're talkin slants

straight up and down go the lifter to push rod angle
 
Ok. I can't remember the last time that I looked inside a /6. Just putting out some possible reasons for lift loss.
 
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