help BIG BLOCK MOPAR

[lucien440]

I have a 383 with big cam all kinds of upgrades.i did not build the engine.the valve train makes noise.stock rocker shafts.pops through carb.sounds like bad lobe.did some research.if you use stock valve train.you must use different length pushrods.i dont want to go to roller rockers,etc.what duration and lift and centerline,can i use to just use stock components,with no modifications.i can not find specs for original camshafts.now i know why they call it mopar madness.would appreciate any suggestions

 

[Garage Doctor]

Run a quick compression test to see what the cylinder pressure is. Valve duration may be to long with that larger cam and stock valve train. 130+PSI your ok, 85 PSI or lower that’s not good.
You can also run a cylinder leak down test.

 

[lucien440]

really got some problems with it just need to know what lift i can use and duration cam,with stock rocker shafts and pushrods.i will take a compression check on it and see what cylinder it is just makes funny noise like a sewing machine in valley pan for lifters.and it pops through carb on high revs.im sure its got a bad intake valve lobr on cam.what do you recommend high 200 for duration and 450 465 list is that too much.im a chevy guy.this is a new animal for me.id appreciate any input

 

[pushrod]

I run a comp. .510 lift 248-248 duration on stock valve train with no problem

 

[74Satellite]

to bad comp cams went out of business....

 

[daredevil]

popping at high rpm may be from stock springs on high lift cam. weak springs cant close valve fast enough. check to see if pushrods will spin free when the rocker is up,if not thepushrods are too long. a cheap fix is to bend 3/4 washers in a half moon and bolt between shafts and pedestals. then check to see if contact patch on rocker is on tip of valve. try this and post and we,ll go from there.

 

[Patrick]

The only way for the push rods would be to long is a .60 cut on the heads. Carb pop back is an open intake valve, valve would stay closed with a flat cam lobe. Could be as simple as a crossed plug wire, or the engine wired clock wise B, RB and 426 HEMI wire counter clock wise. Or the timing could be to high. Check, the firing order, Check timing at 2,400 RPM. If thats ok run the comp test. Comp cams are still in business it was Crane that sold out. Also a weak coil or to little dwell will [points] will cause one to break up at high rpm.
Now if you turned the rocker shafts upside down the rockers and valves can't oil causing sticky valves to the point of not closing and the noise you here. The oil holes in the rocker shafts turn down facing the head you will have to abc everything to locate the problem. And if you don't have a big block mopar book get one.

 

[pushrod]

I believe it was Crane Cams that went under.

 

[69 Runner]

You forgot about the possibility of an exhaust lobe being wiped out. Valve stays closed. Exhaust exits through intake.

Correct on the pushrod length shouldn't be a problem unless heads and/or block were cut. That would make them to long. Don't know of a single lifter that isn't stock length.

Big cam should have big springs to close the valves as someone else already said. It sounds to me like you really need to start from square one with your top end, cause it doesn't sound like you really have a clue as to what you're running.

 

[lucien440]

you are correct not a clue i traded the car for a truck i had, it was supposed to be a 440,well tuned out to be a 383 or 400 because of the distributor shaft is shorter.im on a learning curve,on these high dollar builds.i want to thank all the guys out here with the imput.ill buy the book and run with it.as the t shirt says.mopar are the only men? anyone remember that one at the drags.

 

[daredevil]

is that because little boys wear bow ties

 

[69 Runner]

The pad under the distributor will tell you if it's a 383 or a 400. Popping your heads off for a checkup is a good idea, especially if a cam and spring change are in order (although you don't actually need to pull the heads to do either. it's possible to change the cam on a big block Mopar without even pulling the intake)

Popping the heads will also let you check your pistons and deck height (that combined with knowing the chamber cc and which gasket you're running can calculate your compression ratio)

It isn't necessary to run really big cams to get really good power from a big block Mopar. K.I.S.S. applies here