Changing firing order
 

Besides the cam change, the only other thing I would imagine would be changing the orientation of the plug wires. Is there anything else I'm overlooking, or any drawbacks to the swap?
Thanks,
Bill

I don't think that there's any draw backs to the 4/7 swap. You might want to shoot Langer or Bruce Maichle a PM or e-mail. I know that they both have a decent amount of experience with the 4/7 swap.

-Brian

Bill,

Chevys have been using this "swap" for many years. It helps "even out" the torque curve...

No other changes. The only drawback is that some may revert and put the wires on the "old" way, causing issues... It actually helps reduce the load on the crankshaft (the main purpose) and improves harmonics.

Jim

I'm not too familar with this, why isn't everyone doing it though?

Not everyone can just throw away their conventional Ch!T and buy new. LOL

Some of us have had 1-8-4-3-6-5-7-2 playing in the background of our brains too long- couldn't deal with a change!

They did this on "Horsepower TV" in september with a sbc. It gained around 30hp from what I recall. I would say that is a fair amount for the cost difference, I know I will be doing it on my next combo :)

On Marty's Turbo Engine we looked at doing a Ford 351 firing order as that took the double firing hit (Number 2 and then Number 1) off the front main. This was a durability fix that Ford has used for years. The Ford 302 firing order is EXACTLY the same as the GM numbering EXCEPT that Ford numbers the cylinders differently vs GM.

Reher/Morrison did a lot of testing with the different firing orders and found that doing the 4/7 swap eliminated some of the heat in the back of the block from the 5/7 firing deal. The 4/7 deal still has the two front passenger side cylinders firing next to each other 4 then 2 and you still have the 2 then 1 front main double hit BUT the water pump discharge is much closer to the 2 and 4 cylinders so the double hit is cooled much better with the 4/7 swap.

Making power is based on looking at the whole system and trying to find the best compromised for best durability and power.

With a Belt Driven Supercharger there might be increased gain in durability of the crank with doing the 351 Ford firing order. With a NA engine the best combo might be the 4/7 swap. For a typical street strip deal the cost of the parts might not warrant the change. (Specially ground camshaft).

Everyones unique decision.

Tom V.

maybe they could have swapped 3 more pairs and gained 30hp for each?

The oddball cam blanks are a little pricey but then if you are swapping you are probably using expensive valve train parts anyway.
I think Indian Adventures or BOP (maybe others) sell swap blanks then you send them out to be ground.

BOP is the only Pontiac company to actually have "round cams"
produced. You can buy the round cam from Butler, Spotts, Pontiac Dude, and others but it will come from Wade at BOP.

Wade really helped the Ram Air V guys and the overall pontiac community when he and Mark H. stepped up to having the cores made. JMO

Tom V.

For "high end" rollers, Comp uses the swap for Pontiacs. They have their own cores. We were told when we got the cam for the blown/alcohol project, that was the ONLY 50 mm cam core they have for Pontiac.

Jim

I've been thinking of doing this with the 505 I have going together. Does anyone have actual dyno results before/after the swap?

I'm stuck running a Eagle crank in my engine so I'm interested in taking all the load I can off of the crank. --- Is it really that big of a difference?

It did not help
 

The Timing change in one of my Super stock Motors did nothing for me

I've bought round-lobe Pontiac cams from both Lunati and Crower, and could also have bought from Crane. Are you saying that these three companies all get them from BOP?

Jack,

If you notice Tom said "Pontiac Company" However we have sold to most of the companies you listed. The deal is that we keep these cam cores on the shelf for customers so they have them when they need them. Most cam companies do not stock round lobe cores for Pontiacs. They often say they do but then call us.

Agree!

Tom V.

So, I have to machine my block (IAII) to do the cam swap??

The "round cam" allows camshaft people to put a given intake or exhaust lobe anywhere in the 720 degree firing order. It also allows them to but what ever lobe separation they want and what intake centerline they feel is best.

You will not have to machine your block to use the cam if the correct cam is ordered for what you are trying to do.

BOP offers round cam blanks that work with factory block bearings as well as race applications.

Tom V.

Thanks, Wade, for setting me straight. Do you stock both cast iron and steel blanks?