I'm in the final stages of machining on my procharged 406 SBC short block. I'm considering a cam ground with the 4/7 swap. I have not yet compared pricing as I'm waiting to here back from comp, However my builder stated the price difference is minimal due to the cam being a custom grind anyway. The HP gain he has seen is from 5-15hp. in addition to reduced crank flexing and harmonics.

Anyone have any hands on experience, whether it be track or dyno experience? lets here it.

No hands on, but there have been a lot of reviews and tests both here and in the magazines and most say it is a waste of money and almost no gain!? Good Luck!

the things i have read about it lately claim that you actually lose some power in some cases, unless you have an intake specifically designed to run with the 4/7 swap. personally i think it was just a fad a couple years ago and there's not much to it. as far as harmonics, i never knew sbc's had bad harmonics when you have them properly balanced anyway.

We did alot of testing using 4/7 swap cams a few years ago and found that it was not worth doing and if it made the gains as advertised in the magazines I would be running them to day in the engines we build and if your doning a flat tappet cam the core comes from Turkey and the material used is not quality as it seems to soft.

Now instead of 5 and 7 firing next to each other now you have 4 and 2 firing next to each other what is really the differance here?????????

Carl, have you guys done any testing of the LS1 firing order on the SBC?

1-8-7-2-6-5-4-3

Basically a 4/7 and 2/3 swap together.

Its also the equivalent of the newer Ford firing order (since the 5.0HO EFI days began) if you number the cylinders Chevy-style.

we have tested both and our findings were very very minimal to non on the dyno.

I dont think the cylinder firing next to each other is the real reason, its the spread of firing order to even out cylinders, As quoted its about 30 bucks more to grind a 4/7. Carl have you had any testing with NOS,blowers, turbos? not only dyno but a racing season of info?

I have heard that N/A its not worth anything but forced air and nitrous its commonly used. Anyone here run 4/7 with NOS or forced air?

I'm not really considering it for the 5hp its more to help any torsional vibration. Big inch motors with bad rod ratios are known for short life span/ or necessary maintenace. Its only a 3.750 5.7 406 but still not the rod ratio endurance motors are known to run.

The main advantage seems to be in smoothing out torque impulses. I only recommend the 4/7 swap for dirt-track cars---EVERYBODY seems to love it on the dirt---or for high-NO2 engines, where it smooths out the power pulses to the rear wheels. It's only good for about 1% power gains, which can only be measured in 1000+ engines(10 HP!).

UDHarold

Thanks Harold, how about adding the 2/3 swap. Same theory smooths out the torque impulses?

The 4/7 swap takes the 5-7 firing and moves it to 4-2 , this in turn moves the typical hot spot near 5 and 7 towards the water pump. Remember the old "how to hot rod your small block Chevy " book? There was a picture in the book of a restrictor on the passenger side water pump opening to heat up cylinder number 2. I think there was mention of it in Grumps book too.
I can totally see the benefit in a dirt track car which might get really hot during a race, or in a heavy Nitrous application.
To get better pulses you need to go with the LS-1 firing order. (Both 2/3 and 4/7 are swapped).
FWIW, Most of the Pro stock truck cams had the LS-1 firing order.