284/484 for stock 383

NV64sportfury · Sep 7, 2019

Hi all, looking for input...i have a bone stock 66 383 that's all rebuilt. 10.1 to 1.. 4bbl auto 355 SG. Im looking for more performance and a nice bump in my idle etc.... I dont race my car it's a cruiser. I've heard the mopar purple shaft 284/484 is the way to go? Thoughts / recommendations? Thanks a bunch.

Lefty71 · Sep 7, 2019

You'll like it. You'd like a .509 too. I would'nt go much further than that if you stick to the street tho. HTH, Lefty71

Dajkzo · Sep 7, 2019

There's nothing wrong with the 484 purple cam. They just seem to be overpriced and the popular/current trend is an asymmetrical profile.
I think you would be happier with something like a Hughes or Comp Xtreme Energy. If you have 10.5:1 static CR, you'll need duration to compensate or wind up with too much cylinder pressure for pump gas.

Don Frelier · Sep 7, 2019

I have a 66 383 with the 484 cam in it. It runs well and does have a nice sound at idle. But unless you get performance heads I would suggest something more like the mopar .455 / 272 or the roadrunner cam.

old guys rule · Sep 7, 2019

The 272 is a better bet I think. Especially if the engine is stock and run on the street

Bee1971 · Sep 7, 2019

Everyone forgets they have two versions

108 LSA
https://www.summitracing.com/parts/dcc-p4120235ae

114 LSA
https://www.summitracing.com/parts/dcc-p5007697ae

BSB67 · Sep 7, 2019

1) it is very unlikely you have 10.5:1. Tell us how the 10.5:1 was determined.

2) depending on the actual compression ratio, the MP 280, .471" works well in a 383 with decent cylinder pressure (180 psi)

1 Wild R/T · Sep 7, 2019

BSB67 said:
1) it is very unlikely you have 10.5:1. Tell us how the 10.5:1 was determined.

2) depending on the actual compression ratio, the MP 280, .471" works well in a 383 with decent cylinder pressure (180 psi)

Yup... He does have the advantage of 516 heads with closed chambers.. But even with that 10-1 is hard to achieve, never mind 10.5-1...

Steel shim head gaskets, mill the heads about .060 & use the tallest flat top piston with no notches you can find... You might touch 10.5-1 but now the valves are gonna hit the piston...
Unless you use a tiny camshaft... And then it's gonna ping from to much cylinder pressure...

NV64sportfury · Sep 7, 2019

BSB67 said:
1) it is very unlikely you have 10.5:1. Tell us how the 10.5:1 was determined.

2) depending on the actual compression ratio, the MP 280, .471" works well in a 383 with decent cylinder pressure (180 psi)

NV64sportfury · Sep 7, 2019

BSB67 said:
1) it is very unlikely you have 10.5:1. Tell us how the 10.5:1 was determined.

2) depending on the actual compression ratio, the MP 280, .471" works well in a 383 with decent cylinder pressure (180 psi)

Sorry my bad its 10:1

NV64sportfury · Sep 7, 2019

1 Wild R/T said:
Yup... He does have the advantage of 516 heads with closed chambers.. But even with that 10-1 is hard to achieve, never mind 10.5-1...

Steel shim head gaskets, mill the heads about .060 & use the tallest flat top piston with no notches you can find... You might touch 10.5-1 but now the valves are gonna hit the piston...
Unless you use a tiny camshaft... And then it's gonna ping from to much cylinder pressure...

Yes its 10:1 not 10.5 my bad...

BSB67 · Sep 7, 2019

NV64sportfury said:
Yes its 10:1 not 10.5 my bad...

But how? The details are very important. You say that the motor has been rebuilt. Because replacement pistons have not been available for about 40 years, almost any 383 that has been "rebuilt" since then is actually much lower in CR.

You need to know piston part numbers, cylinder head casting numbers and chamber cc's before truly knowing actual compression ratio.

Not to be negative Nancy, but 99% of 383s that have been "rebuilt" in the last 40 years have an 8:1 compression ratio.

Curiousyellow71 · Sep 7, 2019

Nearly 30 years ago...we use to have a 383 with the .484 cam. I liked how it ran with headers and decent heads and 4.10 gears. But that was a long, long, time ago when cam selection was limited. Cams have improved in the last 20 years.

My concern for the .484 in a 1966 383 is the 516 heads if they are stock... they aren't going to respond to that much cam.

We ported a set of 516s...we enlarged the 1.6 exhaust valves to 1.74 and spent hours and hours on a flow bench trying to get the 516 to run with 346 or 906 heads. We gave up and put them on the car.... It still ran ok but it took considerable work too even get them to match up with a stock 906.

As for compression if you don't know what you have exactly....checking the static compression would be helpful for the forum members to help you.

Kern Dog · Sep 7, 2019

I think what I am gathering here is that a cam with the profile of the Mopar Performance 284/484 NEEDS more compression, MORE gear, MORE converter or it will be a pig. I can see the logic in that.
This cam does deliver a choppy idle. I had one in a 440 with 2266 TRW Six Pack pistons with a calculated 9.6 to 1 CR. The car had 3.91 gears and an 11" converter. It was okay at midrange and fair at the top end but did NOT have the snappy throttle response that my previous engine did. I had a reringed 440 with milled heads and a 280/474. That car felt strong at all points. The smaller cam didn't sound as aggressive but it performed well.
I had a 292/509 in my 440/493. It ran great but had low idle vacuum.
The conundrum always is.....IF you have a low compression ratio and try to use a lumpy cam, you have to spin the engine at higher RPMs to get any power out of it...BUT if the heads are iron and not ported, they don't flow well at the higher rpms to let the cam make any power.

Lefty71 · Sep 8, 2019

Curiousyellow71 said:
My concern for the .484 in a 1966 383 is the 516 heads if they are stock... they aren't going to respond to that much cam.

Kern Dog said:
The conundrum always is.....IF you have a low compression ratio and try to use a lumpy cam, you have to spin the engine at higher RPMs to get any power out of it...BUT if the heads are iron and not ported, they don't flow well at the higher rpms to let the cam make any power.

BUT, the cam hes asking about is hardly any huge upgrade from what the factory would use in a 426 street wedge engine of his vintage, and the 383 will like revving a little more anyway. We are'nt exactly talking bracket race cams here. I think he'll do just fine, and the only additional consideration would be go to a 3.90 rear to make the car flex a little muscle, if he's not hunting awesome gas mileage ( which I always think is silly anyway). HTH, Lefty71

Bee1971 · Sep 8, 2019

When I rebuilt my 1971 383 Magnum back in the early 90s

I went with Speed Pro Forged 2315 Pistons Flat Tops

When I ripped it apart a few years ago they where only .015 in the hole when I measured so decent compression was definitely available with those pistons

Problem was the 1971 88 cc heads
Yes I cut them - Don’t remember the specs

I ran the 284-484 cam for almost 25 years with zero issues

Timing , intake , 3:91 Gears solved a lot of issues down low
Didn’t have the option of two 284/484 available cams back then

Advance it 4 degrees was another option

Right up until I installed the 75 cc E Street Heads with larger valves and kissed those flat tops running almost 6000 Rpms on the highway

Bee1971 · Sep 8, 2019

BSB67 said:
But how? The details are very important. You say that the motor has been rebuilt. Because replacement pistons have not been available to about 40 years, almost any 383 that has been "rebuilt" since then is actually much lower in CR.

You needs to know piston part numbers and cylinder head casting numbers and chamber cc's before actually knowing actual compression ratio.

Not to be negative Nancy, but 99% of 383s that have been "rebuilt" in the last 40 years have an 8:1 compression ratio.

Speed Pro 2315 Forged Flat Tops
1.920” Compression Height

BSB67 · Sep 8, 2019

Certainly the 2315 piston and 516 head could put some decent cylinder pressure in a 383.

We are doing a lot of speculation, and the OP has not really made clear what the motor really is.

At the end of the day, if a lumpy idle is the goal, he's good to go with the 284.

Then we can go round two when he comes back after the install because it won't idle in gear, it burns his eyes at idle, and a turd below 3500 rpm, and its all done at 5000.

Then we'll tell him that he needs more gear, a different converter, and different cylinder heads.

BSB67 · Sep 8, 2019

Bee1971 said:
Speed Pro 2315 Forged Flat Tops
1.920” Compression Height

of course. If you've read any of my previous posts regarding the 383, you'll know that I'm well versed in the piston selections for it. But the question was not to you. Like me, you don't know what pistons he has

Lefty71 · Sep 8, 2019

BSB67 said:
Then we can go round two when he comes back after the install because it won't idle in gear, it burns his eyes at idle, and a turd below 3500 rpm, and its all done at 5000.

Then we'll tell him that he needs more gear, a different converter, and different cylinder heads.

Easy now, he joined yesterday. We dont want to scare him off.

284/484 for stock 383

Member

Well-Known Member

FBBO Gold Member

FBBO Gold Member

FBBO Gold Member

Well-Known Member

Well-Known Member

FBBO Gold Member

Member

Member

Member

Well-Known Member

FBBO Gold Member

Life is full of turns. Build your car to handle.

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Well-Known Member

Similar threads