4/7 Cam...Advantages...Disadvantages

6T5RUSH · 02-10-2007, 12:05 AM

Hello,

I've tried doing an advanced search on 4/7 Cam and keep coming up with nothing specific to cams where the firing order is changed from 18436572 to 18736542.

Can anyone give me or point me to the archived threads that explain in laymen's terms the benefits of running cams that swap the firing order of the #4 and #7? Is there an advantage for a street driven motor to do this?

Appreciate any and all responses on this.

Thanks in advance!

Regards,

Jim

cardo0 · 02-10-2007, 09:17 AM

Isky says the 4/7 swap reduces crank tortional vibs- http://www.iskycams.com/swapcams.php.

Crane says the swap enhances fuel distribution - http://www.cranecams.com/?show=newsLetters&no=28. But i assume that would be limited to carbureted engs.

Comp wants u to call them.

Well i think i read something in the Chevy Pwr Manual or maybe D. Vizards "How to Build HP part I" on this swap but don't have those books right now. This 4/7 swap is catching on as all the major cam mfrs are selling them. Haven't read of any "before then after" results testing though.

Let us know what u find and any result u get.

cardo0

6T5RUSH · 02-10-2007, 10:03 AM

cardo0,

Thanks for the response. Guess there's a lot more questions then answers that pop up regarding this swap. Would like to get real world experience/feedback from those out here who may have done this. Kind'a think this swap is more for the full race sector and not a street application.

Thanks again and I've got to do some more reading up.

Regards,

Jim

Deakins · 02-10-2007, 11:36 AM

Well it started in the full race sector and has not come on like everyone though it would. The main reason is that they do not show much of an increase in hp on an engine dyno so most street guys don't see the point of changing over. The main reason we run them in our fast street cars and race cars is that they do seem to have a much better idle and run overall much smoother. So we feel that they do really help longevity and street manners; but the power is limited to the grind like on all other cams.

gkull · 02-11-2007, 11:58 AM

I purchased the 4-7 swap custom billet roller for my 427 SB. I'm always ready to try new things like that. I also use thermal coatings for the pistons and chambers. Every little edge can make a great difference.

Surfer69 · 02-12-2007, 10:39 AM

The show Horsepower TV just did a dyno swap only changing cams and showed 30 HP increase with just the 7/4 change.

Curveit · 02-12-2007, 06:21 PM

I saw the show...On another forum I visit; with some well respected engine builders, don't buy the results showed on the program. I've read it's only a few HP more. I personally don't know.

gkull · 02-12-2007, 07:12 PM

I had heard/read about 7-15 HP depending on the combo.

I have run single plane exclusivly(SP?) since the 80's in my Vette. On many tear downs, you can see the inequality of fuel distribution/heat per cylinder. After talking to ....................... I even tried staggerd jetting in the primaries............

I came to the conclusion that without sequential FI with 8 tube monitering you are never going to get it right. FAST electronics for $3500 and Sheet metal intakes are the closest we can come to perfect. Your never going to compete with altered cam timing for the outer 4 cylinders like NASCAR has done.

I don't have the resources for dyno time on any little mod

zo6vetteman2003 · 02-15-2007, 10:56 PM

There was an article in CHP on this. They did the swap on the same motor and dynoed it. The result was that the current firing order actually made slightly more power. I'm talking so slight, they were almost identical in comparison on the dyno sheet. This all originated as a engine building secret among NASCAR teams, doing a 4/7 swap would add more power.

maxrpm69 · 02-23-2007, 04:06 PM

One of the other benefits besides slight icrease in hp of the 4/7 swap comes into play with bigger stroke combo's. With standard firing order 18436572 you have 3 hits in order over the #4 main being 657, with the 4/7 18736542 its more evenly distibuted and easier on the mains.

Slalom4me · 02-25-2007, 07:01 PM

For their part, Hot Rod has this to say on the subject of firing
order

From: Which Firing Orders Improve Performance?

With the revised firing order, fuel distribution dilemmas are resolved.
The engine tends to run cooler, and perhaps just as important, the
engine is actually smoother. How much extra power is there? Anywhere
between 8 to 10 measurable horsepower.

C4 Tech had some entertainment from the topic in a couple of threads

Not much came out of this one unless you count picturing guys
sitting at PCs making rumpity-rump-rump-rump noises.

- Can i program my LT4 to fire in sequence?? 12345678

Midway down, this thread had some diagrams illustrating how switching
4 & 7 might reduce one cylinder influencing the charge of another.

- Idea for StealthRam Custom Plenum and better air flow dist.

.