rb70383

Would a flat tappet cam and a roller cam or comparable/equal size produce the same idle quality?

For instance if one was to replace a 5.9 magnum in a ZJ with an LA 360, could an la style cam with similar magnum specs be used to keep the computer happy? I know about it needing a crank sensor, and the need for conversion to
Magnum heads.

During a discussion this topic came up. So I started wondering how flat tappet and roller cams compare in regards to idle or mainly map signal in this case, regarding the sizing between the two.

RacerHog

Basically no to answer the direct question.

Now with that said You could build both cams for Idle quality, But that is not what the intention of those type cam profiles are for.

But Idle quality is different...

Just my 2 cents

440roadrunner

As I understand it, roller cams allow "more aggressive" valve opening rates without pounding the valve gear to death. With modern oils (no zinc additives) this is a problem for flat tappet cams

I've heard guys expound on Rhoads (spelling?) lifters to improve idle quality and vacuum on a "big" cam. I would guess what this amounts to is that they are "soft" or "leaky" at low RPM

rb70383

Ok figured so.
So maybe another way, would a flat tappet cam need to be one step bigger to equal a roller cam? Generically speaking.
I am thinking of installing a cam similar to the mopar RT cam into an LA 360 to swap I to our jeep. I want to keep the computer happy yet gain a little more area under the curve.

rb70383

I missed your response 440RR. Makes sense as well. A steeper ramp is easier for the roller tappet. So within realistic reason a step bigger flat tappet could be close to one size smaller roller.

I have a 9k mile la 360 and our 98 zj needs a new motor. Trying to see about using the la in place

Some one said the computer won't work since it's a roller cam vs flat tappet.

RacerHog

I think I understand where you are going..... You can run ether or cam... The problem lies in the ECU your trying use. "And you are correct" in trying to stay in the ECU's working Spec's and keeping the Emission for your build from keeping the Check engine light from coming on.

The ECU Working Spec's are only so wide....

There are a few cams out there that i'm sure work, But i'm not sure as to what those would be ..

Coronet 500

My understanding of this issue is based on what my Ford Dealership Mechanic son tells me and Bob is correct. Even though the newer computers have more inputs and peramiters they are less forgiving as they are so finely tuned to that specific engine/chassis combination.

He says they have had vehicles in with aftermarket cold air kits and improved exhaust that have changed the air fuel mixture so much that it is out of the "learning" range of the computer and engine damage has occurred.

I think the key thing to do is maintain intake pressure and air fuel percentages as close to OEM with a cam change. Now this goes against my Hot Rod brain's thinking of make it better, faster for the time and money spent.

I would probably search around some of the truck or turbo forums to see if any are having success without a reprogram or "flash".

I did go the other way on our '92 truck with carb and basically used the computer for dash lights, gauges and not much else.

rb70383

As I thought. Lol. Looking a ecu friendly builds and the mopar rt cam works. The 360 I'm using is from my 85 crewcab and idled really smooth. Shouldn't be an issue as but, as said, the hotrod in me says make it faster. Lol. Why the concern about trying to match cam types yet go bigger within limits. I should Dutch the computer and go standalone. Lol

RacerHog

85 ,,,,I Dont even know anyone that could reprogrammed those 1985 units. as far as I now, it was back to Chrysler For a new board... And that was it...
I think the only one back in those days was Motech and another you could use witch I cant remember the name of. and you have to map it yourself.....

Now back to what your up too....
Are you looking for a specific rpm range to work in? And are need of power?

rb70383

Well it falls on its face at around 4500. Wants to extend the power band maybe another 500 rpm. It's going in a jeep that we take camping so I want the torque. Just a little extra top end power. Like I said I dont want to have to start running piggy backs to keep the ECM happy.

RacerHog

Look into a lower rpm Thumper Cam Or a VooDoo... Those would be my choices..
My top pick... VooDoo ...

rb70383

I was looking at lunati cams actually. The Voodoo line seem like something that would work. I think I might try this one as it is the second cam and a power band of 1000 to 5500.
From what I found it's very close to old mopar performance RT cam. Now I wonder if this is with 1.5 or 1.6 rockers? Lunati says lift with factory rockers. Lol. Magnum or la? I'm planning on them using the 1.5 and will check clearance with 1.6 lift which puts the exh at .503 iirc. This one here :

Part Number: 10200701LK
https://www.lunatipower.com/Product....d=2341&gid=287

RacerHog

Always good to check.... But Most of the stocker pistons are down in the hole a-ways. So you should be ok with ether or Rocker Ratio.... But always check twice...
Just my 2 cents

mikerp76

where do you live at? if your not in cali and the emission laws aren't that strict i would ditch the computer and run a carb.

rb70383

Too much to ditch the computer. It also controls the transmission. Plus I like the mpfi. Just needs a new engine and I happen to have a 9k mile 360 la shortblock. Starting to think of piggy backing a megasquirt on it. It will allow more options for performance. Gears are turning. :-/



Yes I will double check clearances at least twice! Lol. Like I said if I do the piggyback ecu I can run either cam without the factory electrons getting pissy. :-)