Want lumpy idle; where does adv. duration come in?

[Exit1965]

Hi all.

I have a 65 coronet with a 440 +30, 9:1, 452 heads, RPM intake and 750 Dp, 3000 10" converter, 3.91 rear end. The current cam is a Lunati bracket master (292 adv duration, 230@50, 109 lobe sep, .480 lift).

I would like to have a cam that has a bumpier idle, but my valve springs I don't think will handle over .500 lift, and the machinest who re-did the heads said they were all fine and would work good with the .480 lift cam I have in it now.

So I would like to just buy another cam and put it in place of the Lunati.

And I have noticed that cam manufacturers have cams that have the same Adv. duration, while the duration @ 50 is different. E.g there is the Mopar 292 which has like 246 or more, the Comp Cams 292 that has 244, my Lunati 292 that has 230, and a Mopar Perf 284 cam that has 240.

I have seen a cam by Erson in their catalog, rpm range 3000-6000, 306 adv. duration intake/exhaust, .470 lift, 235 @ 50, 108 separation.

How can this cam with less duration at 50 than a 284 Adv. duration cam have 306 advertised duration!?!?!?

Or putting it another way -- how do I get this thing to thump while taking advantage of my 3000 stall converter/gearing/etc. without changing my valvetrain??

Thanks all for any input!

[Zippo0007]

The difference with the duration is just due to the different manufactures. I know that with Mopars, calculated duration is different than with a Chevy, or others, due to the differences with lifter sizes. I've only heard good things about the MP 292/.509 cam, and I have just recently purchased one, along with a MP M1 intake (supposedly the best flowing intake for a chrysler available). I have the 440+.060 assembled and sitting in my 90' Dodge Dakota, but haven't fired it up yet. I still have body manufacturing to do..h.ahaha.

[Exit1965]

I have searched this site and it looks like the Mopar 284/484 cam is a good one for what im looking for, and people are running low 12s and high 11s with it.

I think our coronet will run a 12 now, so as long as it runs a 12 with the 484/284 thats cool.

I have heard a WAV file of a 292/509 and it sounds awesome, how similar/different is the 284/484?

[BB 70 Challenger]

I had that MP 284/484 cam in my Challenger last summer, and I´m definetely keeping it ;-)

I´ve changed some badly mismatch things last winter, ie. too low compression ratio and lousy exhaust system. The combination looks like this:
- 440 0.030"
- slightly ported #452 heads with small stock valves (flow benching will be done before the final assembly)
- 8.8:1 to 9:1 comp (heads are being milled right now today! I´ll measure the chambers once more when they´re done)
- RPM intake
- Holley 750 Vacuum
- Magnum cast iron exhaust manifolds
- 2,5" pipes with Hooker Aero Chamber mufflers

That MP 284/484 cam definetely has got a nice rumpy idle. All my friends thought it was just awesome ;-)

I had some kind of a stock replacement cam in there before, and the idle characteristics of these two cams are like night and day.

Hope You´ve got enough compression for those MP cams. The 284 likes at least 9:1 and the 292 needs more like 10:1. Just my 2 cents.

Also, these cams are designed to be installed in an engine equipped with headers, right? So thats the way to go, I suppose.

BY THE WAY: does anyone know the real @0.050 figures of these MP cams? Where should I look for?



[This message has been edited by BB 70 Challenger (edited May 12, 20

[Comp Chassis]

Advertised duration is the degrees in crankshaft rotation from the instant the valve leaves the seat until it touches it again. But, this is very misleading as no actual flow occurs until the valve is at least .050 off the seat.

So, depending on the opening and closing ramps of the cam, advertised duration and duration at .050 can be very different for 2 cams that look identical on paper.

And, lumpety idle is more related to valve overlap than it is to duration.

[Exit1965]

Well in the messages Ive scanned through this, PRO has calculated the cams to be @ 050:

284/484 = 235
292/484 = 246

He says to multiply the adv duration buy .83 and not .85.

Ok this leads me to another question; that Erson cam i mentioned before has 306 ADv duration but has 235 @ 50. Also the RPM range for that Erson is 3000-6000 and the MP 284 is I think (but not positive) like 2200-5800 or so. Both have 108 degrees of seperation.

Can someone explain where the difference comes in (ie between 284 and 306 and between 2200RPM and 3000 rpm)??

[ChristianCuda]

As Comp Chassis said below the Advertised Duration and Duration at .050 do not have anything to do with each other. Advertised duration is the degrees from when the lobe starts lifting to when the lobe stops lowering. Duration at .050 is the same thing but at .050 lift on lift and lowering. If a cam has a fast ramp rate it has a duration at .050 closer to adv duration. If a cam has a slow ramp rate it has a Duration @.050 lower than the advertised duration. All mopar purpleshaft cams are setup on a similar ramp rate. Other cams even between the same manufacturer can have different ramp rates. In case you dont know what a ramp rate is it is haw fast the cam gets to full lift. Roller cams have the fastest ramp rate of all cams this is due to the roller lifters. This is also part of the reason roller cams are so much better because it lifts the valve quicker and gets to full lift faster adn can stay at full lift longer. than a hydraulic or mechanical. Mechanicals have faster ramp rates than mot hydraulics but are usually slower than most rollers.

Hope this helps in your understanding of this.

Basically a faster ramp rate with a longer duration is wanted to get to more lift faster and stay there longer.

Christian

PS if i have anything wrong here please some that may know more than I do correct me.


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68 'Cuda 383 Working on adding EFI
69 'Cuda Race Parts Car
76 Duster 273 recent transplant
95 Neon 2.0 SOHC best of 16.96
84 Dodge Ram D50 transplanting 360

[440 Jim]

Remember, 0.050 is cam lift not valve lift.

Now some data from my Lunati 30306 cam. I picked this because I am running unported 452 heads, high flow big block cast iron exhaust manifolds, and full exhaust (dual 2.5"). I wanted more exhaust duration than intake.

Advertised duration: 285/295
Duration at 0.050: 235/245

When I degreed this cam, the 0.050 numbers matched exactly and assuming 0.004 for the advertised duration they matched within 1 degree of my measurements.

Here are the cam lift numbers at degrees of crank:

Degrees Intake Exhaust
20 BTC 0.156 0.027
15 BTC 0.136 0.040
10 BTC 0.119 0.055
05 BTC 0.101 0.070
00 TDC 0.086 0.087
05 ATC 0.070 0.103
10 ATC 0.054 0.119
15 ATC -.--- 0.137
20 ATC -.--- 0.154

I didn't measure 15-20 ATC for the intake since minimum valve to piston clearance occured at 7 degrees BTC for the intake. It was at 8 ATC for the exhaust.

Intake opens 11.5 BTC, closes 43.5 ABC
Exhaust opens 56.5 BBC, closes 8.5 ATC

Besides sharing data, the point I wanted to make was the fairly straight cam lift vs. degree position at this part of the cam, especially the exhaust from 0.027 to 0.154 cam lift (opening ex).

Rates seem about the same as MP hydraulic cams (good).


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440 Jim
E-Body Fish

[T748]

Advertised duration is self explanitory.It's a usless number used by the advertising department to lure the average joe into getting that companies cam.Works well with bigger is better.

[BB 70 Challenger]

Cool, 440 Jim!

You´ve got just that cam I should have picked, too! With stock Hipo cast exhaust manifolds I think the right way is to get more exhaust degrees on the cam, just like You´ve done.

Well, don´t ask why I picked a MP 284/484 cam, then ;-) You know, that MP284 is meant for headers, and I´m running those cast iron Magnum exhaust manifolds and 2,5" pipes, too :-(

How does the rest of Your combination look like? How much compression are You running? And how much does the cam need? What kinda vehicle? When should the whole thing be finished?

Keep up the good work