Which pushrods to use?

[mrbill426]

I am sure this has been asked and answered somehow before but I am looking for advice on what pushrods to use.  I am rebuilding a (early) '72 340 but want to take the internals back a few years with earlier higher compression forged pistons a wee bit stronger HYD cam, and a LD340 intake.  I have and want to use iron adjustable (273) rockers but am not sure what pushrods will work with that combination.  I know they should be ball/cup but I don't know the correct length or how it is measured on the rod.     Years ago I installed ISKY iron rockers with a HYD cam in a 383, and it was a snap; loved them.  But I cannot seem to find a definitive answer to this 340 setup.

Appreciate any info here; brand and part number would be a bonus.

Thanks!

[Chryco Psycho]

You have to buy or make a pushrod checking tool & measure the rods , if the block has been decked or the heads milled & even the thickness of the gasket will alter the length needed . you can use threaded rod & a coupling nut to check length with just round off the bottom of the rod .

[mrbill426]

Thank you Chryco for the response. 

Not to be argumentative at all, but is the valve train geometry that different between the small and big blocks?  I admit I am new to the small block and am learning.  As I mentioned I was able to convert a 383 with Hyd cam and stamped rockers over to iron adjustable rockers with off-the-shelf components; no issues at all.  Course that was 37 years ago, maybe parts have changed a bit  I would think the adjustability of the rockers would compensate for any milling or gasket choice.

Maybe I am trying to over-kill this engine anyway, but I was told once that the 340 had a weak valve train    so I am trying to beef it up a bit.  It WON'T be a race car, it will be a street driven occasional show car but I just want it to be "healthier" than it was in '72.  I'm even still using the stock exhaust manifolds.

 

[Chryco Psycho]

The Adjuster will allow for varience , but there is a best length , personally I want to be as accurate as possible & always order pushrods to the exact length I need

[mrbill426]

Gotcha, and thanks 

I was wondering, any opinions on even messing with the conversion for street use or is the "weak valve train" a myth?  Are there heavy duty stamped rockers for the 340?  I was eyeing a Lunati #60402 cam and appropriate springs as a choice.
Or maybe you are more of a big block guy and don't have an opinion there? 

The Adjuster will allow for varience , but there is a best length , personally I want to be as accurate as possible & always order pushrods to the exact length I need

[72bluNblu]

I wouldn't use stamped steel rockers for anything, including a stock build. I pulled a couple that had cracks in the cups off of my '71 GT, and the lack of adjustability just bugs me, no allowance for wear, slight variations in the rocker, pushrod, lifter cam etc. If you can track down a set of stock adjustable rockers off a 273 they'd be plenty strong enough for a Lunati 60402.

As far as the pushrods go, I'm with CP. You might be able to run stock length push rods for a 340, or stock length for an adjustable rocker set up. Or not! My '68 340, which has the stock deck height, 308 heads (just trued up, no major milling), Lunati 60404 and Lunati lifters, and Harland Sharp 1.5 ratio adjustable rockers uses 7.00" pushrods. That's over half an inch shorter than stock pushrods for a stock adjustable set up, which are 7.59". I thought it was the roller rockers until I bolted up a set of stock adjustable rockers, they need the same length.

I don't see where I got that big of a change, but there it is. No point in buying a set of pushrods without checking the length, might just be wasting money.

[mrbill426]

Appreciate that info too 72bluNblu 

I do have the 273 rockers (a few sets actually), new shafts, and the MOPAR Performance aluminum hold-downs .  I noticed some of the iron rockers have different casting numbers and I am trying to sort that out..., maybe they are mixed with some other small block adjustable? 

I wouldn't use stamped steel rockers for anything, including a stock build. I pulled a couple that had cracks in the cups off of my '71 GT, and the lack of adjustability just bugs me, no allowance for wear, slight variations in the rocker, pushrod, lifter cam etc. If you can track down a set of stock adjustable rockers off a 273 they'd be plenty strong enough for a Lunati 60402.

As far as the pushrods go, I'm with CP. You might be able to run stock length rockers for a 340, or stock length for an adjustable rocker set up. Or not! My '68 340, which has the stock deck height, 308 heads (just trued up, no major milling), Lunati 60404 and Lunati lifters, and Harland Sharp 1.5 ratio adjustable rockers uses 7.00" pushrods. That's over half an inch shorter than stock pushrods for a stock adjustable set up, which are 7.59". I thought it was the roller rockers until I bolted up a set of stock adjustable rockers, they need the same length.

I don't see where I got that big of a change, but there it is. No point in buying a set of pushrods without checking the length, might just be wasting money.

[Chryco Psycho]

the only factory iron rockers are the 273 & the 340 T/A , the exhaust rockers will interchange , the intake will not