340 Heads Recommendations- Aluminum vs Cast J
Need advice on where to go with my head situation in the Duster,
My advice/experience;
I ran OOTB Eddys with my 292/292/108 cam at 11.3Scr for a CCP of near 180psi. I ran this with the 2.66low 4-speed, and 3.55s, at 3650 me in it.
This combo never liked the 3.55s.
First gear went to 60=7050, and 30mph was 3500.
With a manual trans, and idling at 750, the slowest driveable speed was 6.4mph. So parading was out. Furthermore, trying to drive at 750 rpm with typical ignition timing, is only possible until the engine starts bucking thru the drivetrain due to the very strong power pulses. Parading was impossible.
I had to back off the timing to 5* to reduce the idle-power very significantly; which allowed the in-gear idle to drop to 550
[email protected] mph, still not parading, if people are walking in the parade.
I swapped that cam out PDQ.
Now, if this means nothing to you, then ignore the rest of this post.
--------------------------------
I first replaced that 292 with a 270/276/110 cam(223/230/110) that I very much enjoyed for about 4 years, Then
When it dropped lobes, I installed a 276/286/110 cam(230/237/110). I liked the smaller one better, it had great street manners.
This last cam is a fair match to yours, idles down to 500rpm at 5* advance, and with my new Commando low gear (3.09) she will pull herself at 3.7mph, still with the 3.55s. So parading, for a while, became a thing.
Ok, I noticed that your 284cam is advertised at .004 tappet rise, whereas all my cams were .008 tappet rise.
There is no way to directly compare a .004 cam to a .008 cam.
however, I can guess.
In keeping with your .050 numbers of 228*, my guess is that the Crane will be closer to a
[email protected], give or take a lil.
Lets look at all the events of these two cams; mine first
276/286/61/115 compression/105 extraction/ Ica of 65*,in at +2
274/274/50/116 compression/106 extraction/ Ica of 64*,in at +5
That's a pretty good match, but Ima guessing at the .008 numbers.
As you can see, the extra intake/exhaust durations of the 276 cam, mostly come from the overlap, so I get that the my cam may idle a tad lumpier.
Here's another thing.
To make power with your cam, yur gonna have to pump up the cylinder pressure, and Iron heads stop at about 160/165psi, due to detonation on pumpgas. Whereas alloy heads will tickle 200psi on best gas, without detomation.
Since 1999, my 367 has run on 87E10, and up to 192psi.
So the bottom line is this,
pressure is heat is power, so yur combo is sorta committed to running hi-pressure which points to alloy heads. Iron heads at 9:1 Scr are NOT gonna cut it.
At my fudged numbers;
that Crane cam in your engine with open-chamber iron heads, wants at least 10.0 for 161psi to run on best gas.
and with closed-chambers, a tight-Q, and alloy heads, she will like 11.1 for 184psi to run on cheap-gas
These results are taken from the estimated Ica of 64*, after fudging your .004 numbers to .008. You gotta actually install that cam and measure the .008 tappet numbers to know the truth. That will tell you where to go and/or what to expect.
