What is the advantage to7-4 and 5-3 cam swap

Trying to see if the 7-4 and 5-3 cam swap on a BBC would be advantagous. If so what gain would I see.

 

You mean a 7-4 & 2-3 swap. Known as "C" fire. You must make sure that you have the correct headers first or it will cost you power.

 

Blown Hemi...ZERO difference on the Dyno...just "sounded" different

 

When Steve at LSM ground my cam he did it as a double swap, he mentioned it makes for a smoother running engine which helps the bottom end(bearings etc). He had a cam core in stock so it didn't cost much more (75 bucks I think) so I took his advice. In a blown application I doubt it would get you any more power.

 

Swap, double swap, triple swap, put the mag in at six and you have the quadruple swap.

 

If you swap it enough times won't you come back to the beginning? Like two wrongs don't make a right but 3 rights make a left?

 

Exacttly

 

You see the camshaft grinder "gain" some of your money.

Blessings........Ron

 

My long time understanding is it originally developed out of the Pro Stock intake plenum designs at the time they started appearing.
That's along the lines of Mike's comment.

Blessings......Ron Clevenger

 

I found out that you don't want to use a 4-7 swap cam in a BBC with a high helix and a BDS manifold. Some weird distribution problems. 30 jet sizes different in the ports front to back.
I think the biggest benefit to the 4-7 swap is it's easier on the main brgs because of the angle of the rods in relation to the main caps.via rotation.

-Dale

 

I too experienced about 30 different on jet sizes with my BDS but I have normal cams.

 

You mention the BDS manifold specifically, any idea on others? Or is it a trial and error thing? I have an Indy manifold.

Corey

 

I don't think that's very accurate at all . I had a 526 Chevy with a lsm 4-7 swap cam . It had an m5 on it at 20 over and made 2400 hp on Dmpe dyno . Never seen any dist problems at all. Most of the cylinders were within 10 of each other . That motor ran flawless up to 10000 rpms. Maybe blower outlet into manifold placement is where I'd start looking.

 

Our conventional headed BBC Indy manifolds are very close to equal nozzle jet sizes. We have high helix SSI 8's on top of them.

I don't recall exactly but I'd guess they are from 40 to 50 stock and I work on the insides to get them closer.

 

I also have a BDS manifold on a BBC with the 7-4 swap. Im not running a hi helix, just a standard 14-71 with a couple mods done. Around 30-32 lbs boost. I also have a 28 spread between front to rear port nozzles. Interesting?!?!?

 

Would the size of your hat nozzles cause a larger spread in you ports nozzles, like if you had 60-70% of your fuel in the hat as opposed to say a 50/50 fuel split? Less fuel coming out of the bottom of the blower would not cool the cylinders as much?

Just learning all this, thinking out loud.

Corey

 

Yes, it did on mine. More of my hat fuel ended up in the front cylinders. So if you made the hat nozzles smaller the front cylinders leaned more than the rear ones did.

 

You mention the BDS manifold specifically, any idea on others? Or is it a trial and error thing? I have an Indy manifold.

Corey

I think it has something to do with the peaked section in the manifold floor. We had a Indy manifold with a large plenum-with a 4-7 swap cam on a similar engine and it only had 4 jet sizes different front to back. The difference in jet sizes in the BDS manifold tells me that the rear cylinders are not getting their share of air, and are down on power.
I think the BDS would work good with a conventional blower with the total bottom being open so that the air goes mostly straight down- top to bottom.

-Dale

 

dont forget with a hi helix the charge goes straghter down than a regular helix. Think of a nut on a bolt; fine vs corse thread.