Firing order swap on 4&7 and 2&3.

[d72hemi]

I know in the race world there has been a lot of talk and experimental use of cams that implement a 4/7 swap (18736542), and 4/7-2/3 swap (18726543). I would like know if anyone has tried any of these (or other trick cams) for their street or strip motors. As for Mopar related information on these cams I have not been able to find out much information. Most of the information that I have found on the web is mainly SBC and BBC ( http://speedtalk.com/forum/viewtopic.php?t=130&postdays=0&postorder=asc&start=0&sid=6a8ba7804b59f3954113965860410aa8 ). At this time I do not have a cam swap in my 440 install budget, but this is something that I am looking forward to in about a year. So at this time I am looking for information. If you know anything on this topic please let all of us know.

Ian

[Ghoste]

It seems to be mainly popular with the Chevy guys as you have already noticed and even they seem to have a lot of disagreement over it's worth.  But, truthfully, I don't know a lot more about it.

[is_it_EVER_done?]

Unless you are trying to coax the absolute last couple of horsepower out of a class spec engine at 9000 RPM, It would be the most worthless modification per dollar spent that you could possible do. For the most part, it has fallen out of favor, and whatever the next "magic" mod (whatever that might be this week) is the new "secret".

In other words, stick to the "4-C's" basics of - cam/carb/cubes/compression- for worthwhile modifications.

[TylerCharger69]

I know that Ford  uses a few different firing orders for the 302s    depending on particular engines.....but i dunno about Mopars

[d72hemi]

It seems to be mainly popular with the Chevy guys as you have already noticed and even they seem to have a lot of disagreement over it's worth.  But, truthfully, I don't know a lot more about it.

You are right about the Chevy guys. My father is running a 4/7 cam in his friends 562 BBC injected alcohal dragster that is ran out out Denver. The last time I was out there it sounded awsome with that cam running at Bandimier. I know a few T/F and prostock guys are running these. Not to mention my dad and a few other guys in the 70's and 80's played with 180* cranks in T/F . With the way Dad described the way they sounded on fuel, I wish I could have been around for that. not to mention the ease of teardown between rounds. Pull out 4 pistons, turn to crank 180*, then pull out the other 4.

I mainly started this thread to see what information is out there concerning Mopar. The odds of me ever doing this to a street/strip car is slim, but I still would like to know.

Thanks for your input.

Ian

[andyf]

Running the Ford (or new Chevy SB) firing order seems to decrease crankshaft harmonics and that helps to make a little power.  You can buy off the shelf cams for SB and BB Chevy with the revised firing order but you can't buy a Mopar cam that way without doing a special order roller cam.

I have a 52mm roller bearing cam in my 400 block so I can change the firing order if I want since it is a full custom cam anyway.  (made from an unground lobe blank).  I'll probably change the firing order to the Ford style next time I get a cam for that motor.  Not because it will make anymore power but just becuase is sounds like something different to do.

[max]

i seem to recall reading that the fellows running hemis in the F.A.S.T class racing change the firing order to help the engine sound more "stock" with the huge cams that they are running but i don't remember just what they changed the firing order to.

[deputycrawford]

I was also going to mention the Ford thing. A Fords firing order is just a Chevy with the 4/7 swap. Ford just numbers the cylinders differently. Crankshaft harmonics are most of the reason for the firing order change.  Go for it, for something different to do, but leave it if you aren't looking for the last possible points to earn in a racing program.