I am finishing up my 65 327/350 and ran across a set of factory stamped steel roller rockers off a later engine I had saved and am considering using them om the 65. I don`t remember exactly the year but think early to mid seventies. I assume they are stock ratio but thought I would ask the board if someone else has tried them with stock alum covers? Any input would be appreciated. Thanks
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Re: C2 Rocker Arms
GM never built any Gen I SBs with roller tip rockers, so I doubt if they are OE. They did use either roller tip or full roller rockers on the LT4 in the nineties.
I never recommend anything other than OE rockers. Those roller tip abominations are HEAVY and will reduce valvetrain limiting speed. If they are higher than OE ratio they will further limit valvetrain speed further because they increase valve dynamic forces at any given speed.
With massaged heads a L-79 will produce usable power to at least 6500, and the OE valvetrain will get there with the '67-up OE 068 springs and proper attention to installed height.
If you didn't massage the heads you left a good 30 HP and 500 useable revs on the table and no whiz-bang rocker arm will get it back.
One of my 327 LT-1 "customers" installed a set of name brand 1.5 roller tip rockers. I tried to talk him out of it, but they were "free". So other than being a PIA to adjust lash because you need a thin wall socket to get on the nut, the valvetrain showed signs of false motion at least 200 revs before we expected it, so I had to tell him to limit revs until he fixes the problem.
As soon as he finishes his house project the OE rockers are going back on.
Duke -
Re: C2 Rocker Arms
Thanks Duke. Exactly what I wanted to know. I`ll put a set of stock rockers on her. Shes just to cruise in and I`ll race with my 07 thats got a warrenty. MikeComment
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Re: C2 Rocker Arms
Mike----
As Duke mentioned, GM never used any stamped steel type roller rockers (i.e. roller tip) on ANY PRODUCTION or, for that matter, any SERVICE engine. This includes all Gen I, Gen II, Gen III and Gen IV small blocks as well as all Mark IV, V, and VII big blocks.
The ONLY use of roller rocker arms was, as Duke mentioned, 1996 Gen II LT4 used in Corvette-only. These were fully rollerized, aluminum rocker arms manufactured by Crane.
Gen III and Gen IV small blocks use cast steel rockers with roller fulcrums. These are in no way adaptable to any other series engine.In Appreciation of John HinckleyComment
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Re: C2 Rocker Arms
Thanks Joe. These came on an old corvette engine that I knew no history of. They are steel roller tip only. Probably changed sometime in its lifetime. I appreciate the info. MikeComment
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Re: C2 Rocker Arms
These stamped, roller tip rockers are another example of an aftermarket solution to a problem that doesn't exist, and it's amazing how many guys shell out the $150-200 a set that they cost.
People also seem to be willing to pay more for a bottle of water than a bottle of beer. I guess that proves the power of marketing and advertising.
Back in the late sixties/early seventies Trans Am cars had to use production valvetrain components, and I don't recall that the OE type rockers caused problems at the 7500-8000 peak revs that those engines ran.
Needle bearing trunnion rockers do reduce friction, especially in a very high rev applications, so they were typically used in F5000 engines of the same era where they were legal, and the current OE use of roller trunnions is motivated by a slight reduction in internal engine friction, which combines with other internal friction reduction changes to increase the numbers in the CAFE game.
But for vintage engines that will only see high revs for brief periods of time they are just fine, and I have no qualms about reusing them (and pushrods) if they pass a thorough visual inspection and show no signs of obvious wear or galling on mating surfaces. When an engine is disassembled, the pushrod, rocker, ball, and nut should be bagged together and tagged so they go back on together and in the same location if they are resued.
I don't buy the arguments of "reduced valve guide wear from less side force". The OE rocker tips have an arc, so they "roll" rather than slide across the top of the valve stem. If your rocker geometry is within reason of design intent the center of the rocker tip arc should be in contact with the center of the valve stem at mid lift.
Engines that have significantly shaved decks and/or heads and monster lift aftermarket cams might have a problem, which is solved with different length pushrods or custom length pushrods as required, but if your engine is fairly close to OE machining and uses a cam within reasonable range of OE lift, the rocker geometry should be okay.
DukeComment
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i bet a lot of corvette owners do not know
that these stamped steel rocker arms were developed by pontiac not chevy at GM. back in the good old days with some modifications we use pontiac super duty 1.65 rocker arms on chevy enginesComment
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Re: i bet a lot of corvette owners do not know
That's always been my understanding. The Pontiac OHV V-8 was in development at the same time as the SBC and when Chevy saw the Pontiac stamped rocker arm design they adapted it to the the SB. They turned out to be what I call an "elegant design" - simple, reliable, light, inexpensive, and gets the job done! Good engineering is all about doing more with less.
So what was the original SBC design - shaft mounted rocker arms?
DukeComment
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Re: i bet a lot of corvette owners do not know
there was a company back then that tried to market a shaft mounted rocker arm setup for the SBC. i guess it do not sell very well.Comment
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Re: i bet a lot of corvette owners do not know
As Duke noted, the only part of a rocker arm that benefits from rollerizing in terms of friction reduction is the fulcrum; roller tips have essentially zero impact on friction reduction (or on valve guide wear), which is why the OEM's don't use them. If you look at the OEM roller rocker arms on the Viper V-10 and the Corvette LS-7, only the fulcrum has rollers - the valve stem end is plain, and the rocker arms on both of those engines, developed independently, are almost identical. Viper shown in the photo below (with stock "beehive" valve springs, which were NOT invented by Comp Cams, in spite of their marketing hype - they were introduced on the Viper V-10 in 2002). The plate on the pushrod side in the photo is an assembly aid - photo was taken on the Viper engine assembly line at the Viper assembly plant.
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Re: i bet a lot of corvette owners do not know
the beehive valve springs first showed up on the LS-1 corvette engines in 1997Comment
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Re: i bet a lot of corvette owners do not know
I'll bite, What's the benefit of the beehive design?
I'd speculate that since the coils change size that they compress into a more compact stack. This would mean that you could get greater valve lift out of spring with a shorter non-compressed height. But that's my un-edumacated guess.
Am I close?Comment
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Re: i bet a lot of corvette owners do not know
The L79 with a set of ported head and flow matched manifolds are worth more than 30 but almost 50 HP. I did the head porting acording to "Smokey" back in 1969 - god rest his sole. It turned out great. The rest of engine is stock. It has the TI and FI springs in the distributor. The rocker arms are the Z-28's with the chrome tips and an O over the top. I don't have the exact part number but these were the race parts back then.
38 years later - the test results.
The test result is that the little 350 HP 327 made 20 more HP at the rear wheels than a 66 390 Hp 427. and only 20 less lb ft of torque. The HP at the rear wheels was the same as a 2007 4.7 L double over head cam Mustang.
Even with the bias ply tires on my 66 consuming a lot of HP more than radials.
It was intersing to see the car run at 126 MPH red line in high gear. The air filter was removed, base left and we picked up 5 more HP at the rear wheels. You could also see the standing wave of fuel on top of the Holly. Remember this is a chassis dyno. and everything was working.
Thes runs were made at the end of July 2007. We are planning to publish some intersing dyno runs in the Vette-Gazette our chapter news letter, in the near future. Look for it "www.ncrs.or/mvc".Comment
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Re: i bet a lot of corvette owners do not know
Because of the varying OD, these "beehive" valve springs have variable, not constant rate. Variable rate can also be achieved by varying coil spacing as on '64 to '67 front suspension coil springs.
Variable rate means that the spring does not have one fixed natural resonant frequency - it varies depending on spring compression, so the spring is more resistant to "spring surge".
Surge can be seen in high speed photography of a working spring and is essentially a superimposed compression wave that bounces back and forth. The combination of normal spring compression and a surge wave can cause coil bind and easily break a spring if it gets into serious surge.
They are a great idea and probably cost little or nothing in additional manufacturing cost.
The flat wire dampers inside vintage OE single springs accomplish a similar purpose. The friction generated by their impingement against the spring wire provides a damping effect that damps out surge, and this works well, but a spring design that naturally resists surge and doesn't need a damper is an even better idea.
DukeComment
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Re: i bet a lot of corvette owners do not know
So can you provide the 80 percent torque bandwidth, peak torque and power at their respective engine speeds, peak test speed, and what if any type of data correction was used?
Any other pertinent details like headers or open exhaust?
DukeComment
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