4-7 Firing Order Swap

[Lloyd Barnes]

I'm taking my car to a rolling road sometime this month hopefully which has got me thinking again about my engine build as I'm wondering what to expect. Particularly as I had a bit of a mare with the cam (Comp Cams cam arrived from the states oversized and seized up in the bearings) so ended up with a slightly different one to the one I originally specced.

I remember seeing cams that changed the firing order, swapping 4 & 7. Never really understood why you would want to do that? Anyone know what the benefits are?

[stevey]

Lloyd
it is all to do with different torque and power curves that can be obtained in the States in Pro stock Warren Johnson made major advances when he debuted a flat plane cranked engine which effectively had a different firing order (made it sound like a V6 IMHO) it is a black art and best left alone if you want more power just fit this!

[Lloyd Barnes]

Originally Posted by stevey

Lloyd
it is all to do with different torque and power curves that can be obtained in the States in Pro stock Warren Johnson made major advances when he debuted a flat plane cranked engine which effectively had a different firing order (made it sound like a V6 IMHO) it is a black art and best left alone if you want more power just fit this!

Now thats almost worth spoiling my nice new paint job for!!! I've no idea what power the engine currently produces, especially as the exhausts are welded almost shut to get through SVA, although it should be pretty decent. However I may take it apart over winter if I get bored/its not enough!

When I built it I toyed with using a roller cam. I didn't go for it in the end as had already ruined the budget with the heads Just exploring ideas at the moment for winter projects

[Nobby]

Dave Vizard did a lot of research on the 4 - 7 firing orderswap in a couple of his V8 tuning books. Seems there are some benefits and a small power increase if done right. May be worth it for a few BHP though?

Hot Rod did some tests to see if it really did make a difference.

Testing Lunati Cams - Intake Manifold - Results Of the Dyno - Hot Rod Magazine

This article is based on Lunati cams and was published a while ago but it's worth a read

[Clarkson]

I have a roller 4/7 swap in my chevy, and it goes really well.

The idea behind it is better fuel distubtion in the intake manifold. Google it.

[Lloyd Barnes]

Originally Posted by Clarkson

I have a roller 4/7 swap in my chevy, and it goes really well.

The idea behind it is better fuel distubtion in the intake manifold. Google it.

I did and confused myself more!! Seems like opinions is really split as to whether they work or not.

Where did you get yours from Dave and what spec is it? Seem to remember you're running AFR195 heads as well.

[Clarkson]

Originally Posted by Lloyd Barnes

I did and confused myself more!! Seems like opinions is really split as to whether they work or not.

Where did you get yours from Dave and what spec is it? Seem to remember you're running AFR195 heads as well.

Mine was custom ground by Lazer cams which are out of business now Tim Adams sorted it out for me.

It was a 230/236 at .50 on a 110LCA with .510 lift. Yes I'm using AFR heads made 420hp at 6100rpm and 415lbft at 4,600rpm not bad for a mere 350ci on std bores. Might not be every one's idea of a nice street motor, but was really quick once you have wound it up!! If you have a 383 with the same cam it would be really nice maybe peaking 500rpm earlier.

Of the shelf cam, the 270xe roller is my faviorte profile for strokers.

Anything over 230 and your loosing good street manners for little gains above 5000rpm.