[Skippy597]

I've always believed that a higher ratio rocker is better as it gives you extra lift and a hair more duration. However I see on this forum many times where a senior member much smarter than I am recommend a 1.5 rocker ratio. May I inquire as to why one would use a 1.5 vs a 1.65 rocker ratio. Thanks

[b-man]

Depends on the application.

You can’t simply swap 1.65 rockers onto heads that aren’t going to accept them without modification to the pushrod holes.

The 1.65 rockers move the pushrod closer to the rocker stud. On most heads the pushrod hole needs to be ground for pushrod clearance in order to use 1.65 rockers. Sometimes if adding 1.65 in combination with a low lift factory cam there will be enough clearance without doing any head mods, I’ve done it before with the 068 cam and RAIV stamped steel 1.65 rockers, however you still need to check.

The only factory heads that readily accept 1.65 are RAIV heads that were equipped as such from the factory. Surprisingly enough the Edelbrock aluminum heads that were pretty much patterned after the RAIV head still need the pushrod holes clearanced when using 1.65 rockers.

Of course there are other reasons besides the pushrod clearance issue but again application dependent.

[PunchT37]

If your heads can accept the extra flow at lift, then go for it. Mine can. But, I chose 1.5`s because of reliability. 1.5`s give me 600 lift. 1.65`s give me 660 lift. I chose not to run 660 lift on the street for a long time. My heads can handle it. But, power vs longevity is what one has to ponder.

[PunchT37]

I ran 1.65`s on my old 455. The heads flowed better at this lift of 575. So, I ran 1.65`s for many years with no problems.


Evaluate your situation.

[steve25]

A lot of you folks are bypass the fact that exh to intake ratios also change when swapping over to higher ratio rockers .
For example, a racing compression ratio in a 455 with it’s faster piston speed then a motor with a 3.750” stroke and running a duel pattern cam many times makes more power with just higher ratio rockers on the intake and does not need the much touted 75 % exh to intake ratio.

A 65 to 68% works better.
This is another case where the Butt meter can lead you wrong.

The only way to nail it down is making a swap during a dyno test or during a test & tune at the track.

[slowbird]

Always run 1.65 on intake side, always (assuming they fit). Exhaust side depends on some factors.

[77 TRASHCAN]

Originally Posted by b-man

Depends on the application.

You can’t simply swap 1.65 rockers onto heads that aren’t going to accept them without modification to the pushrod holes.

The 1.65 rockers move the pushrod closer to the rocker stud. On most heads the pushrod hole needs to be ground for pushrod clearance in order to use 1.65 rockers. Sometimes if adding 1.65 in combination with a low lift factory cam there will be enough clearance without doing any head mods, I’ve done it before with the 068 cam and RAIV stamped steel 1.65 rockers, however you still need to check.

The only factory heads that readily accept 1.65 are RAIV heads that were equipped as such from the factory. Surprisingly enough the Edelbrock aluminum heads that were pretty much patterned after the RAIV head still need the pushrod holes clearanced when using 1.65 rockers.

Of course there are other reasons besides the pushrod clearance issue but again application dependent.

I've read here that the Kauffman "D" port heads do NOT to be clearances for 1.65 rockers. I believe it was P-dude that said such, been a while...

Anybody?

[PAUL K]

Originally Posted by 77 TRASHCAN

I've read here that the Kauffman "D" port heads do NOT to be clearances for 1.65 rockers. I believe it was P-dude that said such, been a while...

Anybody?

That is going to vary with rocker arm brand and model.

[Stan Weiss]

What the engine wants / needs is a given valve lift curve for your combination of parts. Pontiac put 1.65:1 rockers on the RAIV, because with a .842"diameter flat tappet lifter you can produce a cam lobe that with 1.5:1 rockers can produce that valve lift curve.

Stan

[Lee]

Going from 1.5 to 1.65 is a 10% increase in lift.

Some heads will flow a lot more at that 10% additional lift - motors with those heads will see nice gains.

With unported D-port heads, you will probably see 3cfm or less with that additional 10%, so gains (if any) will not be significant.

[64speed]

I am running 1.7 BBC Chevy Rockers on mine. Seem to be doing ok. Made that 60919 Crower a little rowdier

[Don 79 TA]

I run the crower 1.7 and 1.65 on my setup
no issues
e-heads were clearance as part of the build
springs can handle it, geometry didn't change either
the 1.7s are a nice piece. not sure if they make them anymore or what they might cost now
pressed in studs might be more of a concern if your heads have them

[Half-Inch Stud]

Is good to start out with 1.5:1 on the Exhaust. Then go figure how it runs, and just maybe try 1.65:1 exhaust.

[chiefbigb]

If you drive the car on the street and don't race it this sounds like a wash to me. Aluminum head air flow potential is much greater than a iron head and a modern combustion chamber another positive draw. That's your most bang for the dollar. The speed master head's I used recently would work with a 1.65 but I had to modify to run 1.5 ratio. Everything needs checked everywhere. E heads I have used in the past were the opposite. I would change to round ports but that's just me.

[PAUL K]

More times than not the optimum pushrod length is going to be different for different ratio rockers even if they are from the same manufacture.... So if you plan to test at the track or on the dyno premeasure the pushrod lengths and swap them out with the corresponding rocker arms..... And let us know you're findings.

[Stan Weiss]

Originally Posted by Stan Weiss

What the engine wants / needs is a given valve lift curve for your combination of parts. Pontiac put 1.65:1 rockers on the RAIV, because with a .842"diameter flat tappet lifter you can NOT produce a cam lobe that with 1.5:1 rockers can produce that valve lift curve.

Stan

I should not post late at night. I have corrected my post.

The engine would need somewhere around a .940" diameter flat tappet lifter to be able to have a cam lobe that with a 1.5:1 rocker would produce the same valve lift curve as the RAIV with 1.65:1 rockers.

Stan

PS - Many cams are not designed close to the max. This shows the Intake valve lift for a Pontiac 068 cam and Sumit 2801 both with 1.5:1 rockers.

[chiefbigb]

My reply was to the guys stroker build but I hit the wrong post. Getting older sucks

[Skippy597]

Interesting. So does this tie back to a head with a good flow ratio doesn't need a dual pattern cam and so but using 1.65 on int and 1.5 on exh you kinda reverse a dual pattern back closer to a single pattern? Or does it have more to do with ramp rates and the exh liking a slower (smoother?) Rate?

[Skippy597]

I'll be running speedmasters but this was more so just poking at why I see them being recommended.

[android 211]

I put 1.6 ratio rockers on my '96' head 455. It has the 068 cam. I think it damaged the valve stem seal; it smoked and I had to pull the heads. What a pain. if you have headers then put the higher ratio rockers only on the intakes to balance the flow.