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Hey there. I am doing a mild engine upgrade on my 1976 l48. It has 3.08 gears. I have installed a Lunati 262 grind cam and Edelbrock e-street heads 5089. My question is what rocker arm gear ratio should I go with to get the best low end performance out of the car. The research I have been doing is very confusing. Some sources say that a 1.6 ratio will make the low end suffer and I won't feel the gains until 4500 rpm. Other sources are saying that the 1.6 gear ratio will make it better all the way around. Yet another source said that 1.52 is definitely what I want. I am looking for some input here. Thanks guys.
What kind of performance you looking for? Going to 1.6 will effectively up the duration a little. Make it slightly slower off the line but extend the top end slightly.
What kind of performance you looking for? Going to 1.6 will effectively up the duration a little. Make it slightly slower off the line but extend the top end slightly.
That pretty much answers my question. I am looking for more low end performance. I am still researching and I am leaning towards 1.5 ration rocker arms at this point.
Opening and closing timing is affected only by the cam. Nothing else.
The increase in rocker arm ratio will increase the lift. But has zero effect on timing.
So I respectfully disagree with the earlier statement that it would or could change duration.
The slightly larger ratio just opens the doors wider. But when they open and close is controlled only by the grind of the cam lobe and the manner in which it is timed.
No matter what, that rear end gear is going to be a dog off the line...
Switch it out for a 3.55 or 3.70...
Mouse motors don't come into their power until higher RPMs...
I had a 70 LT-1 with 4.11's and it would burn the tires off in all four gears....
Actually, changing from a 1.5 to a 1.6 does change the duration ever so slightly. Duration is the time the valve is open. If the ratio is changed the amount of time to close the valve is a fraction longer. But lets not get into all that nonsense.
Let's look at the mechanical side of your question. Even though some rocker arms claim 25+ H.P. gains, let's be realistic.
Instead of adding valve lift through a rocker, why not order the cam lift you want to begin with? So, in layman's terms, those 1.6 rockers are cheating the design of the valvetrain. But with repercussions.
Here are some of the drawbacks with 1.6.
The new ratio stresses the valve stem. It puts a side load on stem, sometimes the retainer and sometimes the spring and guide.
You may or may not run into interference issues with the bottom of the retainer and the top of the guide.
You may add unneeded stress to the rocker studs.
You may or may not run into interference issues with the spring binding.
In my opinion, installing 1.6 for a few more horse is not worth the damage that could occur. What I am getting at is, some heads can not, should not handle that ratio.
Again, in my opinion, a better choice would be Comp Cams 1.52 rocker. A little more flow without added stress to the valvetrain.
Opening and closing timing is affected only by the cam. Nothing else.
The increase in rocker arm ratio will increase the lift. But has zero effect on timing.
So I respectfully disagree with the earlier statement that it would or could change duration.
The slightly larger ratio just opens the doors wider. But when they open and close is controlled only by the grind of the cam lobe and the manner in which it is timed.
You may be only looking at the max opening of the valve, even there this would not be correct however. For EVERY degree of cam rotation the valve is open farther at 1.6 rr vs it's 1.5 rr counterpart. Which equates being at the equivalent 1.5 rocker ratio opening sooner. Ergo it DOES have the affect of greater duration.
Think about it as the max opening if you want. When does the 1.5 rr reach let's say .450" if that is the max lift? At the max lift of the cam lobe, right?
When does the 1.6 rr reach .450" lift? Sooner or later? Sooner of course, then it goes on to lift it to .480". So was the valve at a level of .450" longer? yes, and it lifted higher then had to come back down to .450" it's TIME spent @ .450", or greater, was longer or as we like to say of a greater DURATION of time.
this happens all along the rotation of the cam however and not just when max lift is achieved.
No you cannot change the cam and it's duration or timing, but the cam is just the tool we use to get the desire valve action. So it's effect on the valves can be changed through the use of different ratio rockers EFFECTIVELY changing the duration. And the valve action is what we're trying to effect through a cam change or RR change. That's what ultimately matters.
sorry for all the caps it's just easier on a phone to use that than try to italicize the words.
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Wow. Lots of big brains arguing over common sense stuff....coooool!!!
How about you use your 1.5 ratio lifters, then throw in some 1.6 and see what it does....i bet you might notice a tiny bit more power at the top but if you are just taking off from street lights and its a dog you are going to have to learn to bring it up higher in the rpm range before you let out the clutch. A pouch car needs torque multipliers to get the tires spinning. Different first gear ratios. Different rear end ratios....Torque is what you are looking for, small blocks dont necessarily have that with small cam, small compression motors.
3.08 was good for a big block with 400 ftlbs at 3000 rpm. Either get deep into your motor or go get a 3.70 or 4.11 rear. If you get someone to build yours up look for a 3.90 gear.....if you have a 4 speed set it up as a M20, lower first gear than the M21. If you have an auto, do as commented above, put in a shift kit to tighten it up and a higher stall convertor
Cam timing, Duration is from the time the valve just starts to lift. Until the time it is closed. This is NOT affected in any measurable way by a slight increase in rocker arm ratio. No way! Not a chance.
yes the valve will reach the lift of the lower ratio slightly sooner, but it also reaches out further. So your point is mute.
cam timing affects the power band much more so than total lift. True. But more lift, opening the valve further allows more mixture to be pulled in and compressed. If the engine, combustion chamber design will allow the extra suction to make it all work.
1.6 rockers in a small block will add more lift to the cam. But does not and can not affect Duration or cam timing.
I see someone runs a roller cam in a L48 block. The roller cam opens and closes the valves quicker than a flat tappet cam. And thus roller cams make more power, by having the valve open longer. But this still doesn't change the Duration!
Again, I respectfully disagree.
Lobe lift on the 262 Lunati is .307/.321.......with a 1.6 that comes out to .491/.514..@ 1.52 it is .468/.489....the 5089 Edelbrock head stalls at 249cfm @ .600 but it is 248cfm@ .500 so very little gained from .500 to .600......so .bumping the lift .025 is beneficial.....the Eddy head picks up 12% from .400 to .500...and like .5% after that.....the lift will help fill the cylinder.......I would do it. Always try to match lift with the capability of the cylinder head......it costs nothing extra at this point of the build. All of your LS stuff is short duration super high lift because LS heads flow very well.....take a page from this book.
Break it in with some shitty 1.5 stamped rockers for added insurance........make sure your lifters spin freely in the bore when you drop them in......moly on the heel and oil on the side......
4-vettes,
Use Bing or Google search engine. It will explain better than I.
But the correct answer is YES, swapping from a 1.5 rocker to a 1.6 rocker DOES affect duration.
According to web sites, it's as small as one degree to as many as 8 degrees.
But the ratio difference still changes the duration. Its advanced geometry.
No, cam timing, and Duration are from when the heal of the cam starts to move the pushrod, until the other side of the lobes heal of the cam let's off. No change in rocker arm ratio can change that.
Changing from the 1.5, going to 1.6 ratio, will not change the actual point in which the valvetrain begins in-motion (that as say at the lifter), as this is dictated by the camshaft lobe to lifter interface; but, it will change that which is often voiced as the "effective" duration. This as stated previously at each observed lift point (e.g. .050", .100", .200", .300" etc.) will be both earlier and later, at or above such for a greater period of time in the event of valve lift to crankshaft rotational positioning.
Me..........I'd put the 1.6 ratio rocker arms on, Edelbrock heads will accept such just fine, the guide wear issue is real but still insignificant here, the possible trade-off of low-end performance is small vs. the mid-range and upper-end gains realized, and also as mentioned previously, as the cam is just too short and not going to allow one to reap possible performance benefits in the swap to the Edelbrock heads anyway.
And I also agree, in that it being a priority: change out that 3.08 ratio rear-end gear! At least to say something of 3.50 ratio!
No, cam timing, and Duration are from when the heal of the cam starts to move the pushrod, until the other side of the lobes heal of the cam let's off. No change in rocker arm ratio can change that.
you are correct in that we cannot change the CAM timing or duration through rocker ratio.
Would you agree however that the VALVE duration will change through different RR?
And isn't that what it's all about. VALVE action?
If physics allowed we'd use 3:1 rr or 10:1 rr wouldn't we?
The goal being to get the valve opened and closed ASAP. Unfortunately mechanical limitations get in the way.
Cam companies measure advertised duration beginning @.006" of lift of the VALVE not the pushrod, and not zero lift.
the key word is "effective" having the effect of greater cam duration.
Simulation seems to support extending the top a little. More hp through RPM and slightly higher tq around 4000 to 4500.
interesting it does not show any loss down low really (1 lbft @1000) and benefits start around 2000 rpm.
Not to send this thread sideways, but do your research when buying rockers. There are YouTube videos out there showing how inaccurate manufacturers claimed ratios are. Such as the stated ratio was 1.6, however when measured was 1.4x or 1.5x.
Rocker arm ratio
