Stock high compression 340-Max cam lift?

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71duster06

71duster06

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I have a 1970 340 with the stock 10.5-1 compression pistons. Who all has this same motor and what is the maximum lift cam that can be used before valve-to-piston cleaence becomes and issue?

Im by no means looking at going with a radical cam but I would like to know what range I need to stay within. Any inight will be great!
 
The lift is not your concern. It's the duration you need to be worried about. It's not how much the valves are open, but when.
 
..as SS says but also which heads you have.
..i don't know but have heard stock heads stall around .490 lift
 
We used to run the old Direct Connection 509/292 cam with the stock 10.25 pistons. You could actually still run this with stock rockers(borderline) if you didnt mind shoving a pushrod through a rocker once in a while!
 
hemichuck said:
We used to run the old Direct Connection 509/292 cam with the stock 10.25 pistons. You could actually still run this with stock rockers(borderline) if you didnt mind shoving a pushrod through a rocker once in a while!
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X2 i never broke a rocker arm though and put 60000 on it
 
StrokerScamp said:
The lift is not your concern. It's the duration you need to be worried about. It's not how much the valves are open, but when.
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x2 if your gonna cam it find some stock 273 adjustable gear and go solid lifters and cam . helps free up some extra ponies for cheap jmo
 
If the block is being blueprinted, you will want to stay below .520 advertised lift. You lose about .019" because of the pushrod angle of the block. Normally the "10.5:1" pistons actually are closer to 9.5:1 and nowhere near the valves. But you will want to be careful if you're using a modern high-rate-of-lift cam. IMO, you'd do better to get a better and lighter piston with deeper valve pockets if this is a full rebuild.
 
moper said:
If the block is being blueprinted, you will want to stay below .520 advertised lift. You lose about .019" because of the pushrod angle of the block. Normally the "10.5:1" pistons actually are closer to 9.5:1 and nowhere near the valves. But you will want to be careful if you're using a modern high-rate-of-lift cam. IMO, you'd do better to get a better and lighter piston with deeper valve pockets if this is a full rebuild.
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Correct. So would the Lunati 60404 be too much cam? Also what lift is the stock 340 spring good for?
 
71duster06 said:
Correct. So would the Lunati 60404 be too much cam? Also what lift is the stock 340 spring good for?
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The stock springs WILL NOT work. Not enough seat pressure for a 60404, even if they weren't 40 years old. Lunati also recommends dual springs on all of their cams. That said, I found a set of single springs with a damper that meet the seat pressure needs. You'll also have to pay attention to coil bind when selecting the springs for the 60404.

I have a '68 340 that I rebuilt with 308 heads, 2.02/1.60 valves, KB 243 pistons (.060 over), and a Lunati 60404. Although I haven't fired it yet (one of these days it will be in my Challenger), I didn't have any valve to piston issues. Pistons are .018" over the deck, just like Ma mopar actually spec'd (most probably aren't quite so far out). But, the valve pockets on the 243's are quite a bit deeper than on a stock 340 piston.

If you're taking the heads off and having them ported, measure the pistons to the deck and find out what you're dealing with. And it'd be a good idea to measure the valve to piston clearance with some clay to be sure its right. With a smaller cam you might get away with using some stock components, but with a 60404 you're going to need new springs, and I'd recommend an adjustable rocker set up as well. Its a lot of pressure and lift for the stock stamped rockers to deal with. Also, is your car an automatic? If it is, you'll need a higher stall converter too. Lunati recommends at least 3.73 gears as well.
 
So by the sounds of it I should probably start looking at the 268XE type cam then? Looks like that is going to be the most aggressive cam with stock valve trance components. I am installing 273 rockers as well. Does this cam or a comparable cam sound a little more realistic?
 
I ran a 70 340 in my bracket racer with 296/557 MP solid with ported J heads milled to 63cc chambers. Ran that combo for years with no problems.
 
darndart said:
I ran a 70 340 in my bracket racer with 296/557 MP solid with ported J heads milled to 63cc chambers. Ran that combo for years with no problems.
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How well did it run? I've been pondering that cam myself in a similar combo.
 
moper said:
Yup. More so in the hydraulic roller engines (shorter pushrods = more angle).
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Interesting....next question, is it any worse (or better) with a 48* block? Just kinda wondering......
 
inkjunkie said:
Interesting....next question, is it any worse (or better) with a 48* block? Just kinda wondering......
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That's the reason there is a 48° block, and it's why the heads dont interchange easilly between the two. The angles cause lift loss, but more important ona race engine is the harmonics the pushrods can develop beign pushed sideways at rpms.
 
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