Big Block 284/484 Mopar Performance Purple Shaft - Why all the hate?

[SlinktRR]

I run the MP 484 in an 8:1 engine with 20 degrees initial timing. It gives up 40-50 ftlbs compared to the stock cam and is really soft on the bottom, idle quality is not so great. The compression doesnt help. But the power is sweet at high RPM, I like it anywhere from 3000+ and is a blast 5000-6200. It does well with the right combination of parts. My next build will have a modern solid flat.

 

[Sonny Black]

my problem with the 484/(413cid), 355rear, is what carb to use???....BTW; headers helped a lot!

it pulls well @ 3,000 to 4,800rpm....then fades...

...no problems starting, nor street driving...

 

[Cranky]

I've used the old 284 cams in both low compression and higher compression engines and actually got pretty good results with the low compression engine. A customer with the higher compression engine asked for that cam so he got it and it too ended up running pretty good but I never drove that one. It was a 440 powered 69 Charger with 3.55 gears, 4 speed and 275-60's on the rear. He was happy with it at least. The engine was mild build with the valve pockets done on 906 heads and stock exhaust manifolds. From experience with that cam and others, compression has a lot to do with how much timing the engine likes.....and I generally go for a bit of advanced cam timing with that one too. Those were the last two engines I built using the 284 cam (90's) and both checked out ok when they were checked.

 

[SlinktRR]

mine is a 383ci with mopar M1, hooker comps 1 7/8" and 2.5" TTI exhaust with dynomax mufflers and an 800cfm AVS tuned for power. When I had a 650 AVS on the same engine it was a slug over 5000 rpm, carb definitely a restriction. The 800 really opened things up and I can run all the way to 6500. Gas mileage sucks with the 800 compared to the 650. I used to get 17 with the 650 and its tiny primaries, now I'm lucky to get 12 with the 800. More fuel/air...more gas money...more fun. That's the trade off, if I were to take this on a long trip I would put the 650 back on but the 800 is like running uncorked.

 

[lewtot184]

mine is a 383ci with mopar M1, hooker comps 1 7/8" and 2.5" TTI exhaust with dynomax mufflers and an 800cfm AVS tuned for power. When I had a 650 AVS on the same engine it was a slug over 5000 rpm, carb definitely a restriction. The 800 really opened things up and I can run all the way to 6500. Gas mileage sucks with the 800 compared to the 650. I used to get 17 with the 650 and its tiny primaries, now I'm lucky to get 12 with the 800. More fuel/air...more gas money...more fun. That's the trade off, if I were to take this on a long trip I would put the 650 back on but the 800 is like running uncorked.

my experience with the 750 and 800 edelbrocks is that out of the box they're way too rich. a 750 might make a nice compromise in your build. i used to race a 383 back in the day in a '68 road runner and really liked the holley 780vs, but a factory 440hp avs ran identical times.

 

[lewtot184]

my problem with the 484/(413cid), 355rear, is what carb to use???....BTW; headers helped a lot!

it pulls well @ 3,000 to 4,800rpm....then fades...

...no problems starting, nor street driving...

what carb are you using now? i think a quick fuel 780vs would make a very nice street carb. a 750 edelbrock would work too, with some jetting changes.

 

[SlinktRR]

its hard to compare carbs just based on cfm too. For example if I look at the 650 thunder avs vs the 800 thunder avs they are externally identical. But if you look at the 650's primary throttle bores they are much smaller than on the 800. I think the thermoquads and the new street demons have the small primaries too. This makes them nice and responsive, easier on gas, but at least on the 650 avs they give up the top end to some degree. I dynod this engine with the 650 and the horsepower completely stopped climbing at 4900 rpm. This was with the 650, stock intake and shop headers. Now with the m1 and 800 it pulls cleanly past 6000 no issues.

 

[Sonny Black]

what carb are you using now? i think a quick fuel 780vs would make a very nice street carb. a 750 edelbrock would work too, with some jetting changes.

I think I am "under-carbed" with a 600carter (weber).............Edelbrock 1407 Performer - Carburetor 750 CFM???

 

[lewtot184]

I think I am "under-carbed" with a 600carter (weber).............Edelbrock 1407 Performer - Carburetor 750 CFM???

600's too small. actually the 600 is the same size as one street hemi carb. the 1407 would work fine, but i'd down size the jets. the 1407 is virtually a '67 375hp 440 carb with a larger air horn.

 

[383man]

I ran one in a mild 383 and loved it. It was the old MP .484 can with 284 advertised duration. Most people that dont like it dont run it in the proper combo. A guy with a 440 kept saying how bad a cam it is and he ran a summit cam I believe in his 440. But his 440 Coronet ran 12.90's and my stock bore and piston 383 Dart with iron 452 heads and the MP .484 cam on a 104 ICL ran 12.30's and would smoke that 440 every day. I milled the 452 heads a little to get a true 9.5 comp in my 383. That guy hated the MP .484 cam even when he knew how much better a mild 383 with the .484 cam ran then his car did. Myself I loved it in that combo as it had an idle I loved and with 3.91 gears and a tight 10" converter it hit 12.31 @ 110 mph. Another guy ran in the 10's with that cam in a 440 Duster. Like many cams it can work fine in the right combo and it can work like crap if the person using it does not understand how to use it in the right combo. Ron

 

[ykf7b0]

I never said they don't work. They do. When made with some semblance of quality, matched with the right parts and machining, and in the rpm range they old manuals say they do. Some things, like torque convertors, have also advanced light years ahead and a modern convertor can certainly help with the issues the MP designs can exasperate. But- there are reasons why a modern performance rebuilt engine makes as much power as it does. A big one of them is modern camshaft design.

You have got me thinking. Now which cam in the same ballpark would be superior to the MP 284/484?

 

[hunt2elk]

i ran an ssh44 for a short period of time; i believe it to be the basis for the 292-.509.

What did you think of the ssh44? I have one in a 451 and am having a hard time getting it to run the way I think it should. Seems to be really lazy under 3000rpm.

 

[lewtot184]

What did you think of the ssh44? I have one in a 451 and am having a hard time getting it to run the way I think it should. Seems to be really lazy under 3000rpm.

it's just the big hydraulic cam headache scenario. they have a lot of duration and overlap that isn't real happy with mufflers and not enough timing. in my opinion, anything past the 284-.484 hydraulic i'd just move into a mechanical. i do think you can make the ssh44 run in 450 cubes but you'll need some good tuning expertise.

 

[hunt2elk]

i do think you can make the ssh44 run in 450 cubes but you'll need some good tuning expertise.

I sure hope so. Jim at Racer Brown said it would be no problem getting my combo to run, but so far that is not true. Been playing around with it for a year now. Trying to get some more idle timing to help the laziness.

 

[lewtot184]

I sure hope so. Jim at Racer Brown said it would be no problem getting my combo to run, but so far that is not true. Been playing around with it for a year now. Trying to get some more idle timing to help the laziness.

it has been many years ago that i ran the ssh44. i used a very aggressive timing curve.