I was reading a thread about shaft rockers on www.pro-touring.com recently and one gentleman in the thread made an interesting comment. Here's the quote:

"Most shaft systems will allow you to run any ratio you want and have the ability to change the ratio on the spot. In the past we did some development and found that we made more power with 1.35's on the four corners and 1.5's on the inners."
http://www.pro-touring.com/forum/showthread.php?t=18904

What's the rationale behind this? Does it have something to do with the "load" that the ends of a camshaft sees in regards to the timing chain sprocket and distributor/oil pump drive? Also, wouldn't a setup like this require that the "inner" cam lobes be ground with less lobe lift to equal out the valve lift over all cylinders?

 

He is referring to a carb intake where the 4 corners runners are longer and takes more time to get the fuel/air charge to the plug.
If ya slow down the valve action the valve will stay open longer giving the charge the time to fully load the cyl.

That trick has been around since the '50's. and works to varying degree's on different set ups.
Not worth buying several ratios to try IMO.

 

I'm curious how much of a power gain the author of the quote found from doing that. Might be something for the guys doing single plane conversions to try. (After they've tweaked everything else to death.)

Old 50's Hot Rod trick: haha that's cool as hell.

 

To carry that to the extreme, Nextel Cup engine builders treat the V8 as eight single cylinder engines on a common crank. Each cylinder may get different valve timing, spark timing, intake and exhaust tuning lengths/diameters as well as different flowing ports. Remember those guys would sell their girlfriend for a couple of lb-ft.

It's not unusual to treat a single carbed V8 as two V-fours with the inner 4 being one and the outer four being the other. I'm not so sure too many folks were varying the valve events in the 50s but Smokey might have.

 

Depends on the motor that he is talking about. It's not about loads but it's about what the different cylinders need. The rocker arm change also changes the lobe area and the valve duration. (just not seated duration)

In that instance the cam to match the inner cylinders needed more duration and more lobe area than the outer cylinders.

FWIW, you have to know what your doing but "require that the "inner" cam lobes be ground with less lobe lift to equal out the valve lift over all cylinders?" your going in the right direction here. You don't have to have equal lift, which I dont think he was talking about in that situation but if the cam is done correctly you don't need more lift on some cylinders vs. others. The constraints that characterize lift are still the same cylinder to cylinder.

Bret

 

Larry,

How you gonna get the valve open longer with slower valve action and the same cam lobes....

That's why you get a cam that does it for you ;-)

Bret

 

The valve is slower to get to the max lift point with 1.3 vs 1.8. So the valve is open longer and not as much.

Back then ya run what they had.

I have found some gain(small) by going to higher ratios on the four corner intakes,never tried lower than 1.5's.

 

Larry,

How can when you decrease the valve area and keep the seated duration the same the valve be open longer? Especially if you have less lift with the lower ratio rocker and same lobe. They take the same amount of time to get from seated to max lift, it's just that the valve doesn't move as far.

Throw that in EA Pro and look at the valve area calculations in the output AND look at it graphically. Just take a motor and run it once then go back in and change nothing but the rocker arm ratio down a few notches and notice the difference.

You gotta be havin a brain fart here.

Bret

 

Summary:

Higher ratio rocker arms open the valve faster, higher, and hold it open for a much greater total period of time as compared to lower ratio units. Does this cause more stress on the valve train? There will be more pressure on the cam lobes due to the friction and pressure caused by the higher lift and resultant greater spring load. However, as compared to providing the same higher lift and effective longer duration with a more radical cam and even stiffer springs, the higher ratio rockers may create less total valve train stress. And such a cam lobe would be very aggressive and would require much heavier springs to keep the lifter from flying off the lobe. Very radical lobes will also add more side stress on the lifters/bores and could possibly cause lifter bore failure. The added pressure on the studs from either higher ratio rockers, or more radical lobe, will be well within the capabilities of modern after market studs.

If a 1.8 is faster and higher,then a 1.3 MUST be lower and slower.

 

Don't know where you read that, but it is wrong.

Opening and closing points will be the same no matter what ratio you choose, the cam determines this...the ratio will effect "area under the curve" and max lift. You could make that statement true by saying higher ratio rockers hold the valve open longer above a certain lift value, with a 1.6 rocker compared to a 1.5. say at .400", the 1.6 will reach .400" faster than the 1.5 due to its higher multiplier and then close it later, and hense hold it above that point for longer period of time. But the simple fact is the valve will be unseated for the same amount of time no matter what rocker you choose.

Think about it for a second, like Bret said - must be a brain fart, happens to me all the time

 

http://www.pontiacstreetperformance....ockerArms.html





Ya are correct that the starting and ending point won't change but in relation to crank degrees the 1.3 is much lower and slower. The valve is OPEN but not as much.


MAKES YOUR CAM BIGGER, TOO!
An increase in rocker-arm ratio nets more than additional lift. It will also change the cam’s duration characteristics. Because the increased ratio effectively speeds up valve movement, that means the valve will reach any opening height sooner than it would with a lower ratio rocker arm. Higher ratios open the valves quicker and close the valves a little later. Since the increase is symmetrical on either side of the cam lobe, centerline a higher ratio will lengthen the overall valve timing making your cam act bigger. The higher ratio causes valve timing to increase proportionally as the valve opens further (see chart).

http://www.popularhotrodding.com/eng...0511phr_ratio/

 

Perfect chart!

I knew you were using those crazy rockers on the kids motor for a reason!

Bret

 

From that article in the PopularHotRodding link 1racerdude posted:

http://www.hotrocker.com/

This has to be the coolest thing I've ever seen.

 

When ya got the cam to do it,THEN add the rockers one of two things gonna happen--- It's gonna make plenty HP or it's gonna come apart before it gets out the driveway. Heeee Hee

There is a secret to that too(the coming apart thing that is)

Ya know now, why the Schubeck lifters too

 

Man that would be a nightmare to have all that monkey motion's get out of time. Ya would be running 1.8 on #6E and 1.5 on the rest and 1.6 on 3 intakes and the rest running 1.8.
Try troubleshooting that!!!!!! Maybe scratching ya *** 'cause it's down on power. Don't EVEN want to think about it.