340 hp rocker arms

[Robert K.]

I thought I'd ask what the current thinking is on the best rocker arms for a stock 327/340. I do plan to run Duke's recommendation of the LT1 cam. The rockers must fit under the stock valve covers. Back in the day I collapsed a GM triangle rocker arms and was told to get the Oval rockers. I did and they worked. I don't see oval rockers for sale any more. So what now? Are roller tipped any better/stronger? Do I have an option for 1.6 instead of 1.5? Do I need long slot with the LT1 cam? What are your ideas?

Bob

[Joe L.]

Re: 340 hp rocker arms

I thought I'd ask what the current thinking is on the best rocker arms for a stock 327/340. I do plan to run Duke's recommendation of the LT1 cam. The rockers must fit under the stock valve covers. Back in the day I collapsed a GM triangle rocker arms and was told to get the Oval rockers. I did and they worked. I don't see oval rockers for sale any more. So what now? Are roller tipped any better/stronger? Do I have an option for 1.6 instead of 1.5? Do I need long slot with the LT1 cam? What are your ideas?

Bob

Bob------


Conventional, non-guided small block rocker arms have not been available from GM in years. They were replaced by the guided style rocker arms but these would not be a good choice for a mechanical lifter engine.

The best conventional, stamped steel rocker arms on the market are the Crane Nitro-Carb rockers. However, I do not know if these are available from Crane since their "death and resurrection".

I recommend only a stock 1.5:1 rocker arm ratio for small blocks.

addendum:

The Crane Nitro Carb rocker arms are still available as follows:

http://www.summitracing.com/parts/CRN-11801C-16/

[John H.]

Re: 340 hp rocker arms

I thought I'd ask what the current thinking is on the best rocker arms for a stock 327/340. I do plan to run Duke's recommendation of the LT1 cam. The rockers must fit under the stock valve covers. Back in the day I collapsed a GM triangle rocker arms and was told to get the Oval rockers. I did and they worked. I don't see oval rockers for sale any more. So what now? Are roller tipped any better/stronger? Do I have an option for 1.6 instead of 1.5? Do I need long slot with the LT1 cam? What are your ideas?

Bob

Bob -

With the stock valvetrain, stock rockers will work just fine; the ones with the "o" stamp have better heat-treating, if you can find them. You don't need long-slot rockers, and 1.6 rockers are a complete waste of money (and require head modifications). The OEM stuff is essentially bulletproof for normal operation, proven in millions of engines.

[Duke W.]

Re: 340 hp rocker arms

What John said and the OE 340 HP rocker arms and pushrods are fine.

When you disassemble the engine bag the pushrod, rocker, ball, and nut and mark their position. Either at disassembly or sometime later, carefully inspect the wear surfaces for galling or unusual wear. If they merely appear "burnished", they are fine to reuse.

I've never seen a rocker arm nut break-away torque spec, but any nut that is less than about 15-20 lb-ft should be replaced with one that makes at least that breakaway torque.

Install new OE equivalent '67-up valve springs, which are Sealed Power VS677 - about a buck apiece, and as long as the engine has no history of pulling the pressed in studs, they do NOT need to be pinned or replaced with threaded studs. The LT-1 cam actually places less load on the stud than the Duntov cam!

With properly massaged heads, the LT-1 cam, and proper valve spring installed height it will make power to 7000+, so don't forget to replace the OE rods with something like the SIR5700.

Email me if you want my engine restoration paper, which has a lot more details.

Duke

[Robert K.]

Re: 340 hp rocker arms

Thanks guys

[Clem Z.]

Re: 340 hp rocker arms

no matter whose rocker arms you use check the finish of the sides of the stud slot as this slot is punched and sometime these sides are rough and need smoothed up with a small diameter stone in a die grinder. these rough areas can cut into the rocker arm studs

[Robert K.]

Re: 340 hp rocker arms

Duke, what are the Sealed Power VS-739R springs.

[Clem Z.]

Re: 340 hp rocker arms

Duke, what are the Sealed Power VS-739R springs.

good spring for a small block chevy with a cam lift up to .480

[Timothy B.]

Re: 340 hp rocker arms

Does Sealed Power make 1.5 original replacement rocker arms and what's wrong with them if you can't find the GM parts.

[Clem Z.]

Re: 340 hp rocker arms

i have no idea who makes these aftermarket SBC rocker arms but when we were having trouble about 10 ears ago with them failing i called a contact at GM to see what was the problem. he said it was cased by the fact the manufacturer had cut down on the number of steps used the stamp them out and in his opinion that was the problem causing the failures.

[Clem Z.]

Re: 340 hp rocker arms

Does Sealed Power make 1.5 original replacement rocker arms and what's wrong with them if you can't find the GM parts.

F/M part # is R865R

[Duke W.]

Re: 340 hp rocker arms

Duke, what are the Sealed Power VS-739R springs.

I dont' know. I recommend VS677, which is equivalent to the '67-up OE spring. With proper installed height these will go to 7200 with a LT-1 cam and 6500+ with a hydraulic cam.

Of course, to get usable power to these levels, you need well massaged OE heads and better than OE rods to assure bottom end durability.

Duke

[Duke W.]

Re: 340 hp rocker arms

"Does Sealed Power make 1.5 original replacement rocker arms and what's wrong with them if you can't find the GM parts."

What GM sells is most likely made by F-M, so it's the same part - just a different box.

But these rockers are of the later "slotted" type can cannot be used with mechanical lifter cams.

Whatever you buy in a "GM" box for these vintage engines, nowadays, is almost always made by and outside supplier like F-M or Dana unless it's been sitting in the warehouse for over 20 years.

Duke

[Joe L.]

Re: 340 hp rocker arms

Does Sealed Power make 1.5 original replacement rocker arms and what's wrong with them if you can't find the GM parts.

Tim-----


The F/M are probably OK. However, if it were me, I'd be using the Crane Nitro Carb.