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340 cam question

HP2

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Got myself a 71 Duster a couple of years ago, seller had no clue of engine internals or nothing else but I got a good deal and bought it. Haven't had time for it until now.
340", Eddie heads, Torker intake, expensive red dp carb, newer crap MP distributor, Hooker Comp headers... that's what you can see.

Fiber glass hood and bumpers, subframe connectors, full interior, drag radials... Will see mostly short trips and some visits to the 1/8-mile. Stalls around 3,000. Would guess 3.91 gearing. Manual valve body.

Started it and it run. Drove it home, 7 miles. No noises but run like a pig.
Did a compression test: 150-154 psi except for cyl 1 with zero. Stamped steel rockers. Exhaust pushrod stamped its own hole in a rocker, his brother intake had an s-shape so I pulled the engine and then the head. Looks all good otherwise. No damage on head, cyl walls look good. Pistons all the way up to deck.
Single springs seems a little strange with that high lift cam. Will check pressure open and closed.
Got a set of 273" ductile iron rockers from a friend yesterday. Will check lift and duration on cam tonight. Will also pull pan and see if there's something there I don't want to see there.

Fiber glass hood and bumpers, subframe connectors, full interior, drag radials... Will see mostly short trips and some visits to the 1/8-mile. Stalls around 3,000. Would guess 3.91 gearing. Manual valve body.

Have no experience of 340's so looking for advice. I guess to much lift and high revs for OEM rockers and 273" rockers will do?
What duration, lift and LS would work best with the combo above?

Thanks!
 
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How do u know how much lift the cam has. Many back I the day used the factory 340 single spring with a dampner. The street Hemi grind Mopar cam for 1. Even the next size up which is referred to as the 284/484 cam. Pull the front cover a bd timing chain. Their may be some clues there. And yes many were run with the stamped rockers. If u go to the 273 rockers u will need new pushrods. Kim
 
How do u know how much lift the cam has. Many back I the day used the factory 340 single spring with a dampner. The street Hemi grind Mopar cam for 1. Even the next size up which is referred to as the 284/484 cam. Pull the front cover a bd timing chain. Their may be some clues there. And yes many were run with the stamped rockers. If u go to the 273 rockers u will need new pushrods. Kim
I measured both lift and duration with a dial indicator directly on the lifter
 
I measured both lift and duration with a dial indicator directly on the lifter

And? What numbers did you come up with? Stamped rocker with a hole punched through it I've seen many times... The pushrod next door being a pretzel probably was some kind of contact with pushrod number one...

No signs of piston/valve contact? Might want to check lift on all sixteen lobes just to be safe... Less then .385 lobe lift should be Okay with the Edelbrock springs if you trust Edelbrock... To be safe .350 would be .525 @ the valve assuming true 1.5 ratio.... Which isn't likely...

Edelbrock claims their springs are good for .575 lift... 273 rockers & proper length pushrods will probably solve it...
 
How do u know how much lift the cam has. Many back I the day used the factory 340 single spring with a dampner. The street Hemi grind Mopar cam for 1. Even the next size up which is referred to as the 284/484 cam. Pull the front cover a bd timing chain. Their may be some clues there. And yes many were run with the stamped rockers. If u go to the 273 rockers u will need new pushrods. Kim
Flip the numbers probly a .484 lift and 284 duration I run a .509 lift and 292 duration on stock rockers with no problems other than lopy idel at 1100 rpm. But when they wake up its fun you can do a different ratio rocker and push rods and all the fun stuff if you dont the old scoolers that built them. Lobe seperation is also a thing to look at I run 112 degrees. Cam choices are always interesting for sure all depends what you want it to do .
 
And? What numbers did you come up with? Stamped rocker with a hole punched through it I've seen many times... The pushrod next door being a pretzel probably was some kind of contact with pushrod number one...

No signs of piston/valve contact? Might want to check lift on all sixteen lobes just to be safe... Less then .385 lobe lift should be Okay with the Edelbrock springs if you trust Edelbrock... To be safe .350 would be .525 @ the valve assuming true 1.5 ratio.... Which isn't likely...

Edelbrock claims their springs are good for .575 lift... 273 rockers & proper length pushrods will probably solve it...
Never assume that would make an *** out of you and me lol.
 
Flip the numbers probly a .484 lift and 284 duration I run a .509 lift and 292 duration on stock rockers with no problems other than lopy idel at 1100 rpm. But when they wake up its fun you can do a different ratio rocker and push rods and all the fun stuff if you dont the old scoolers that built them. Lobe seperation is also a thing to look at I run 112 degrees. Cam choices are always interesting for sure all depends what you want it to do .
That’s what I said. 284 D. 484 L
 
I'm so sorry gentlemen, I beg your pardon! My post didn't come up by some reason and I have been busy on not been able to check my laptop...

Here is what I came up with:
217° @ .050 and .507" on intake. Way to small.

A buddy has an old purple shaft, 292° (248° @ .050) and .508 but it might be to much?
 
And? What numbers did you come up with? Stamped rocker with a hole punched through it I've seen many times... The pushrod next door being a pretzel probably was some kind of contact with pushrod number one...

No signs of piston/valve contact? Might want to check lift on all sixteen lobes just to be safe... Less then .385 lobe lift should be Okay with the Edelbrock springs if you trust Edelbrock... To be safe .350 would be .525 @ the valve assuming true 1.5 ratio.... Which isn't likely...

Edelbrock claims their springs are good for .575 lift... 273 rockers & proper length pushrods will probably solve it...

217° @ .050 and .507" on intake.
I agree on your guess. That or just over rev.

No signs at all. Pistons look new. I will need another cam.
 
If you don't know what the springs are and you want to know what cam you can run.... measure the coil diameter, number of coils and the installed height. Usually you can figure out what they are and then get a cam. Also measure how far your pistons are down the deck if it's apart, cc the heads and use a online calculator like summits to figure your compression. If you know what piston are in it...usually the mfg lists the valve relief volume on there site.
[email protected] w .507 lift is a bit odd for a hydr cam????.
 
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What duration do you get @ .002 or .006 lift?
That might help steer you in the direction of what that cam is.
Check for shitty lobes.
I would have slipped a couple rockers on there and some pushrods, to see if 8 cyls pulled the "runs like a pig" out of it.
 
Very odd indeed. I suspect there is something wrong in the measurements.
You are perfectly right. I must have been drunk or something. Now I got my good indicator back so did it all over yesterday. Sorry again
All @ .050
Intake opens 14 deg BTDC
Closes 55 deg ABDC
249 deg duration
Lift .505
Take the numbers with a pinch of salt, as you already have figured out I’m not an expert of taking measurements but this time it should be pretty close!
 
Sounds like you have a mp 292.
.050 figures Mp uses 298×.85=248.2 @.050
Personally I would use the 273 adj rockers, buy better pushrods and do a solid cam.
I would not do a mp cam. They are expensive and there is better options. The mp cams do use some aggressive profiles with lift suitable for stamped steel rockers. Just depends on your springs and rocker capabilities.
We have old forged Federal Mogul trw pistons in our 340. The block has been decked and they pop up past the deck now. It's also in a 71 duster.
 
Sounds like you have a mp 292.
.050 figures Mp uses 298×.85=248.2 @.050
Personally I would use the 273 adj rockers, buy better pushrods and do a solid cam.
I would not do a mp cam. They are expensive and there is better options. The mp cams do use some aggressive profiles with lift suitable for stamped steel rockers. Just depends on your springs and rocker capabilities.
We have old forged Federal Mogul trw pistons in our 340. The block has been decked and they pop up past the deck now. It's also in a 71 duster.

I think you are correct about cam, .501 is pretty close to my measurements and when I tried to check advertised or full duration I got 295 degrees. Cam and lifters look all good so I decided to stick with the current stick. The only parts I will need is a set of pushrods.
One other weird thing I noticed today is that the pistons is higher on one side than the other. They also pop up past the deck, but .010 on the left side and .035 on the right. Hard to explain, I'll try to upload a pic from my phone. Never seen anything like it, must be an error from manufacturer. Don't know what brand but thinking of taking them out and do a simple honing so then I might be able to find some info on the underside. Anyway, if everything looks good with the pistons I will put them back, even if it's not optimal. 150-154 psi is still good. Fel Pro .039 compressed gaskets.
 
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B5047A9F-5351-4FFB-B9BF-A417024C447A.jpeg
 
Pistons look like the old TRW L2316 forged piston. If I remember correctly they were positive deck height, about .013” and the stock 340 pistons for ‘68 were the same.

Different deck height, that’s worth having a closer look at, .035” is way to much and could cause an issue with the edelbrock heads, I don’t believe they are an open chamber head and the piston could contact the quench area with the wrong gaskets.

As for the 273” arms. They are pretty good but not bushed and require the correct rocker shafts with the “banana “ cuts in them for proper lube. Also don’t forget to swap out the stock non locking adjusters for a new set.

Good luck,
Cliff Ramsdell
 
Pistons look like the old TRW L2316 forged piston. If I remember correctly they were positive deck height, about .013” and the stock 340 pistons for ‘68 were the same.

Different deck height, that’s worth having a closer look at, .035” is way to much and could cause an issue with the edelbrock heads, I don’t believe they are an open chamber head and the piston could contact the quench area with the wrong gaskets.

As for the 273” arms. They are pretty good but not bushed and require the correct rocker shafts with the “banana “ cuts in them for proper lube. Also don’t forget to swap out the stock non locking adjusters for a new set.

Good luck,
Cliff Ramsdell

Engine has been run with this combo and no signs of piston/valve contact so all good about that. Now I have found that cam is 4 deg retarded and I want to change that to 0 deg so will have to check clearance again after that. Anyway, how can pistons be "leaned" to the left?

Good point about the banana cuts, will look for them! The non locking OEM has already been changed, but thanks!
 
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