4/7 Swap Cam

[LateModel B23]

Selling some parts to a guy. He does not want the cam I have included he wants a 4/7 swap cam. I have never used one but he is telling me smoother running, easier on the rotating assy. and in some cases more power.

Well, is it true or just more crap???

[speedbuggy]

Under ideal circumstances, you MIGHT see 3-4 hp increase in a 500+ hp motor. Not worth worrying about. I have run stock and 4/7 motors and there is no discernible difference. If I was buying a new cam, I might consider getting either a 4/7 or 4/7-2/3 swap cam(LS1 firing order), but wouldn't be trashing a stock order cam just because it wasn't a 4/7. He should be more concerned about the lift, duration, and LSA meeting his needs.

Having one tire a pound off on air pressure would cost you more in a race than not having a 4/7 cam.

[perfconn]

Where MIGHT that 3 or 4 come from?

[speedbuggy]

Where MIGHT that 3 or 4 come from?

All I've ever heard and read about it is that it changes the pulses in the intake such that the cylinders fill a little more evenly/efficiently. I've never personally seen an engine dyno'ed back-to-back with only the cam change swapped. Any of the articles I've read about it either say zero or little-if-any gain. 3-4 hp would probably be a best-case scenario in a dyno room.

The point I was trying to make is that, IMO, whether a motor has a 4/7 cam or not wouldn't be a factor in me making a decision to buy a motor.

[perfconn]

I understand where your coming from.I have used 4/7 swap cams and there is no difference in anything.Not smoother,no more hp,no more torque.Its strickly a sales gimmick used by engine builders to justify their bill when you pickup your motor.
Same c.i.,same rockers,same cam profile,same compression,same pistons,same rods,same crank,same intake,same carburetor,don't ever keep doing the same thing and expect different results.

[DaveBauerSS6]

My guess was that Cup cars running 9500 peak rpm on the big tracks and 7600 sustained on the long tracks would see a longevity gain. The aftermarket then sold the idea to the Saturday nite racers looking for the trick of the week. Never interested in one.

[let-r-eat]

Marketing!

[Ruhlman Race Cars]

the reasoning behind 4-7 swap cam is to get rid of a lean mixture issue in the intake manifold. The left side of the intake is leaner than the right due to lateral cornering force putting more of the fuel towards the right side runners. The issue is magnified on cylinders 5 and 7 since they draw one after the other and the two ports are siamesed which causes both cylinders to try to steal fuel from each other. In a 4-7 swap, the two siamesed cylinders that fire sequentially are 2 and 4 which are on the right side of the engine so there is extra fuel on that side of the manifold so the lean condition of paired cylinders is counteracted by the excess fuel that is present on the right side of the manifold.
The double swap cam 4-7-2-3 or LS firing order is for better crankshaft harmonics. With that firing order, the 4 outer cylinders are fired then the center 4 cylinders are fired. This results in less crankshaft harmonics and a smoother, quieter running engine. In a double swap, the paired firing cylinders are 1 and 3 which are back on the left side of the engine so it would be a great choice for a drag engine or street car, but not desireable from a mixture point of view on a circle track engine.
The 4-7 swap firing order can make more power since the overall mixture can be run leaner and more timing can be run since cylinders 5 and 7 are not the limiting factor on jetting and timing.
Hopefully this info was helpful.
Brian

[perfconn]

Firing order swaps are not legal in Nascar Cup cars

[DANNY]

http://www.4m.net/showthread.php?247048-4-7-swap-cam&highlight=firing+order