Jeep Strokers

Does anyone know the duration @.050 for the mopar performance 30AB cam? (Lucky enough to find 2) Also any advantage to running a split lift/duration cam?

Good score. I have no idea on the lift @ .050 ABDC.

My best guess is between 214* to 216* @.050" This is Assuming, that the lifter ramp rate is the same as the small block LA (non roller) Eng......................


Flash

dwg86 wrote:Does anyone know the duration @.050 for the mopar performance 30AB cam? (Lucky enough to find 2) Also any advantage to running a split lift/duration cam?

Advertised duration is 256 degrees. My guess is that the 0.050" duration is about 200 degrees.
The stock 4.0 head has relatively poor exhaust port flow compared to the intake ports so the engine responds well to a dual pattern cam with longer exhaust valve opening duration and higher exhaust valve lift.

Cheromaniac wrote:

dwg86 wrote:Does anyone know the duration @.050 for the mopar performance 30AB cam? (Lucky enough to find 2) Also any advantage to running a split lift/duration cam?

Advertised duration is 256 degrees. My guess is that the 0.050" duration is about 200 degrees.
The stock 4.0 head has relatively poor exhaust port flow compared to the intake ports so the engine responds well to a dual pattern cam with longer exhaust valve opening duration and higher exhaust valve lift.

So do you think running 1.7 rockers on the exhaust side would benefit?

Could you even put 1.7 rockers on ONLY the exhaust side?

Yes. I have emailed Yella Terra and Harland Sharp. They both said they could be ordered as a mixed set. The lift would go to 478 with 1.7 rockers. I'm not sure how that would effect the performance of the 30ab cam, I aso don't know what the lobe seperation is. From what info I can find on the web, it says 108 centerline. Now if thats intake centerline, and it is to be installed that way with 4 deg advance, the lobe seperation would be 112. Also in the mopar performance book, it says to take advertised duration and multiply by .850 to get duration at .050. That would make the 30ab duration 217.6 @.050.
I have 2 of these cams and I'm trying to figure out if the specs are what I want. I have thought about having the cams reground to a different lift/duration. I like the wider cam lobes' but not sure if the specs are good for my application.

I don't think you should grind one/them without trying it out. Put one in and see if you like it. Port the head if you want the exhaust to flow better. If you don't like it, I'm sure you can sell one for a lot more than you paid for it to someone who is searching, and then you can use that money to get a custom ground cam w/ wide lobes.

dwg86 wrote:So do you think running 1.7 rockers on the exhaust side would benefit?

The 30AB cam already has 0.450" of valve lift with 1.6 ratio rockers so the answer is no. If you add 1.7 ratio rockers, valve lift will increase to 0.478" and you'll need heavier springs to close the valves quickly enough. The port flow of the stock 4.0 head levels off above 0.450" of valve lift so you'd need to port it to see any performance benefit from a valve lift higher than that.

He's already gonna have to buy the heavier P5249464 springs(or equivalent) to use the 30ab cam anyways and they are good for .4-.525" lift, so why wouldn't they work with the 1.7s?

Velocity, velocity, velocity. That the spring is not fully compressed at that height lift does not mean it is the correct spring for that cam/rocker ratio.
John

John wrote:Velocity, velocity, velocity. That the spring is not fully compressed at that height lift does not mean it is the correct spring for that cam/rocker ratio.
John

I can't see the cam(valve) floating with the heavier P5249464 springs.............I mean, after all, we can only spin these eng in the 5,000 esh rpm range any ways.

I do however understand your comment (velocity) as the speed of the valve, opening......and closing, will be increased.....could be harder on the valve seats.......which could cause it to bounce of the seat.... ...........

Yeah, i know, can't decide which side of the descustion, i want to be on

Well here's another thought. the alu rocker arms are lighter, right! less rotating weight of the rocker arm could allow more speed and lift with out bounce................????? is the alu rocker arm lighter then the a factory stamped steel one!!!!!!


Flash

Now for those wanting to run a stock cam/know they can trust it thus use it, aren't the 1.7s a good upgrade?

Oh, I have stainless, undercut, swirl polished 1.94/1.50 sbc valves that I will be using. I like the mopar valve springs or lunati 73084(270lbs/in), haven't decided yet. I have a 7120 head that I will be cleaning up the runners (no major porting). I have already opened up and polished the combustion chambers to 61.4cc's. I will do a final measure after the new valves are installed and the head is milled flat. Hopefully it will only take a few thousands.
Is opening and closing the valves fast a bad thing? Wouldn't that be more like a roller?

Yes it is the valve seat at rpm that I was talking about, aluminum rocker arms are lighter, but that doesn't change the mass of the valve, spring and keeper. Also consider that if it is bouncing, some of that will impact the cam as well. You are going to have to change out more than rockers. Balanced system working together. If I change item A what do I have to do to item B and C. Now we are back to the camshaft, when the rocker ratios increases on the intake, the cam LCA needs to be spread about a degree, and as the exhaust is less sensitive to valve acceleration but is more sensitive to duration,the rocker ratio for the exhaust is usually kept at or lower than the intake ratio.
Going to refer you to this article http://www.popularhotrodding.com/tech/0 ... ction.html And when we are done have we optimized for RPM's likely above our needs?
John