Roller Rockers

C

cometguy

Well-known member
OK, the best gift this year may be from the IHRA tech department. I just received the 2007 rule book and they have approved roller rockers for use in Stock Eliminator.

Apart from the obvious benefits, can any of you share any substantiated hp improvement numbers with me? I'm counting on some upper rpm reliability as well.

Just to provide some background, this is a 200 based dragrace engine with OEM adjustable rockers.

Thanks guys.
 
The main one is that the rocker ratio will be right on the limit from the factory. Second, there are no side loadings on the exhast valve guide, allowing you to redcuce blow by to next to nothing. You may have to k-line the guides, but its doable.

Third, the oiling system can be reworked to eliminate oil feed to the rockers. You can supply more oil to the rest of the system, with a stock oil pump. Just some spray at the top is all thats needed. According to Ford engineer Lee Morse, who redesigned some of the wildest Ford small blocks on the 60's and 70's, the oil temperature is critical to long term valve life, but if eliminated, just replace the springs more frequently. Old TransAm guys blocked off supply to there 302 Boss engines cylinder heads, just ensuring the normal oil smatered 5 to 10 cfm blowby you get at 7500 rpm did the oiling. They just replaced springs all the time as a result.

Forthly, there is a need to recalibrate the contact point the roller rocker makes with the valve. You can get 1.6:1 if you use the right rocker arm geometry, or valve length. You can bush the rocker arm like the Mini and A-series SCCA Austin Healy Sprite guys did in the 70's. There are a lot of very good tricks from David Vizards books on it.


Fifthly, there is no gain in power with roller rockers, but after 1000 miles, the reduction in valve guide wear was significant enogh to reduce blowby and.


Sixth, roller rockers still do brake. They are practically indestructable, but always keep a few spares around.


Cheers


Dean
 
Hey CometGuy, do you have to stick with the stock rocker arm ratio or can you run the 1.65:1 rollers rockers offered at classicinlines? I imagine that would help your valve lift nicely if you could.
 
xctasy":1una4yhv said:
Fifthly, there is no gain in power with roller rockers, but after 1000 miles, the reduction in valve guide wear was significant enogh to reduce blowby and.

Dean
Click to expand...

I think there is a definat gain in power. The oil temp is greatly reduced at the pivots of the rockers. This heat has to be generated from somewhere. To make this heat it take energy and energy is power.
The amount of power is defintly mearsureable and on some engines it is noticable and mearsureable .
 
But.....is it enough gain to really count? Switching to rollers for a 1/3 hp gain wouldn't be very worthwhile.
 
There is not a schread of evidence, anywhere, that there is any more than 2% power increase on an apples meat apples basis.

The info I have from Yella Terra, Crane, BRC, SVO, none of it defines the gain scientifically.

The are real subsidary benefits attributable to the being able to optimize the combination because of roller rockers (side clearance reduction, blowby reduction, no galling on the exhast valve when you have roller rockers, the ability to run practically no valve guide into the intake becasue of no side loadings, being able to get a season out of a 320 Isky cam in a Pinto 2000, rather than six races, yadda yadda yadda).

The three engine I am familar with that benefit most from roller rockers are A-series Minis, Ford SOHC Pinto and SOHC Limas, and the heaviest valve gear engine ever, the 351M, 400 and 351C '335" series engines. All have terriable durability problems with big cams when that have no roller rockers. There is a potential for a 25% boost when roller rockers are used and the package is built around them, but they are a catalyst, not a source of power.

There are funadamentally five gains I have read about.
1)The difference in sled fulcrum frictions verses needle bearing friction and (specific to some ohv pushrod engines)
2) reduction in side loading friction in each valve.
3)The side wipe from the machined face of the rocker against the OHC cam lobe on some Lima/Pinto/Romeo engines and,
4) on all engines, the almost total reduction in side wipe against the valve tip.
5) The reduction in required valve seat pressure (averting spot weld valve seat loads and overloading the pushrods and reduction of critical loads on all parts of the system). This is a huge gain in long distance endurance events. The first use of roller rockers (illegally) at Bathurst by Alan Moffat in the seventies capitalised on this facet.

These five items are the only both only machanical benefits. All friction is manifested as heat out, so the gains are related only to these to factors.

No disrespect to any maker of roller rockers, but there benifits are very small 2 percenters on street engines at the time of dyno testing. At 50 000 miles, I sure there could be a 10% difference. A roller rocker is a 'catalyst' or 'portal' to optimizing the rest of the engine, not an absolute source of power in themselves.

I'd never used them on an engine unless there engine was built around them to capitalise on there strenghths.
 
roller rockers are pretty cool looking, but the real advantage is in strength and stability, not friction reduction. At higher spring pressure and rpm, stock stamped or cast rockers can deform and deflect.

Stock rockers are also not known for consistency. A nominal 1.5 stock rocker might be 1.45 or 1.55, depending on the quality of that days machining run.

For consistency alone, this would be a worthwhile swap for a racing engine.
 
Wouldnt you gain HP by the increase in lift? Stock is 1.5 ratio, FSPP rockers are 1.6 ratio and the Yella Terra are 1.65 ratio.

Doug
 
Sure, but if there are 1.6 conventional rockers out there too, IIRC. Probably not much gain compared to those.
 
The rulebook dictates that the cam lift, which is not to exceed stock spec, is to be measured at the valve using a solid lifter. The rocker ratio is not specified.
 
cometguy":hbe0461d said:
The rulebook dictates that the cam lift, which is not to exceed stock spec, is to be measured at the valve using a solid lifter. The rocker ratio is not specified.
Click to expand...

Cool! Then you could pick up some extra valve lift using the yella terra roller rockers without breaking the rules.
 
So cam lift can't exceed stock, but rocker ratio can - and they want to measure cam lift downstream of the rocker arm?

That's bizarre!
crazy.gif
 
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