I'm having my engine builder rebuild my stock 350 with the goal of low end torque for cruising and mpg. He recommends a custom roller cam that swaps the firing order of the #7 and #4 cylinders. He said it improves the idle quality, efficiency and sounds better. Does anyone have any experience with this style of cam and what to expect? Duration is ~ 218, 226 with .480 lift.

The rest of the rebuild is typical, new pistons, turn the crank, but going with longer, undercut valves, and springs to match the roller hyd cam. Also going one size larger on the intake valve but stock exhaust on the #47 heads, but longer duration on the cam to compensate.

The rest of the drivetrain is 200-4r overdrive with lockup, and 2.56 posi

Thoughts?
Thanks

That sounds interesting. I've never heard of that. It would be fun for future owners of your car to figure out the firing order.

I've only heard of the 4-7 swap cam for Chevy engines, supposedly increases and smooths out the torque curve for those running 1/4 mile shots. Don't know if there is any benefit on the street.

Just as an aside, 2.56 seems like a pretty tall gear for an 200-4R overdrive. I have 3.55 in mine with 245-60 15 rear tires, and run around 2200 rpm at 70 mph.

I thought the same thing, or when I forget... It will be documented in the folder I keep with the car, that will go with the car, when it goes to a new owner. Hopefully many, many years from now.

The 2.56 will probably get swapped out next year if it doesn't work well with the 200-4r. The swap from the TH400 is happening when I put the engine back in next month.

1 thing leads to another, what started as a rebuild and trans swap now included a complete exhaust system, engine bay detailing, A/C system, etc...

Do you have a 2.56 POS?

Is it just me, or does an engine builder working on a Ponitac block make you nervous when he suggests a "trick" that that is Chebby motor related and is only beneficial for drag racing?

Check out the PY forum. This has been discussed there...

Went looking, could not find it...

I heard of a trick where you orient the cam gear 180 deg off and change the firing order to 6-5-7-2-1-8-4-3

Well you asked for thoughts.
Mine is:
If you have a bunch of money and you are playing with three or four engines just for fun, then why not try it and see what it's like;
If you have one car and want a good reliable engine with lots of torque and sound great, build it the way Pontiac did.
Just my thoughts, I've been wrong more than once.

4-7 swap is a custom grind used on alot of serious race engines.
If the cost is no more then a standard roller, i'd be interested.

I recall in one post on the PY site that the only improvement with the 4/7 cam in terms of HP was in the upper RPMs. No gain in lower RPMs. I had the choice to doing that with my roller cam and decided not to in the end.

The smallest roller cam that I have seen recommended on the PY site was a 220/224 grind that one guy was using in his 400. He liked it a lot. He said it made the motor feel bigger.

I have the same motor goal, a cruiser with the torq down low. I have both a 350 and a 400 to chose from. I was reading a ton in the PY archives I could find no evidence that anyone was getting better millage with the 350 over the 400. This build is for my 326 tempest with 2:56. I just love cruising with it but it has nothing for torq and it currently gets around 20mpg on the highway. It just smooth and comfortable down the road.

PY's GeeTeeOhGuy has a 400 with small valve #15 heads and a 068 cam that he consistently gets around 21mpg and enough torq to spin his posi 2:56 rear. So I'm planning an a very similar build. I have the #15 head already. The small valves gives plenty of intake velocity and about 9.3:1 compression on a 400. The 068 has a wide LSA that make it idle smooth and gives a wide flatter torq curve and plenty of vacuum.

Another archive post a guy had compared several cams and posted .10 better in the 1/4 with the 068 with 1.6 rockers over the summit 2801. He also said the Lunati super cam was his all time favorite cam. It has shorter duration number like the 067 but higher lift like the 2801 and a tighter LSA. He said it was like an electric motor off the line and could spin his 2:56 gears with ease and claimed MPG around 22 with that combo. I have been really considering it but the 068 is tried and true. Remember the lower the duration the lower the peak torq will be in the RPM.

The cam you mentioned in the first post sounds like it would work. I'm sure other might be able to comment more if you provided more detail on it.

Having considered the roller cam my self I just cant justify it. The roller shines when you want high lift and shorter duration numbers beyond that they are just an expensive PITA. Have yet to see good Pontiac hydraulic roller lifters. The flip side is HFT cams going flat. But sounds like if you go with Johnson lifters and use the right additive and break in lube you shouldn't have any issues.

So I don't know what the priority is for you but just some food for thought.

The only reason I went to roller was I didn't want to take it apart again due to a flat tappet cam going, well, flat. I have too many friends who got almost no miles before their flat tappet cam was toast and they did a thorough break in. And yes I did have to take out the Competition Cams lifters and replace them.

I still don't know if I believe Comp's claims that it was the oil that caused the failures, most of the guys I know used break in oil.

The only reason I went to roller was I didn't want to take it apart again due to a flat tappet cam going, well, flat. I have too many friends who got almost no miles before their flat tappet cam was toast and they did a thorough break in. And yes I did have to take out the Competition Cams lifters and replace them.

I still don't know if I believe Comp's claims that it was the oil that caused the failures, most of the guys I know used break in oil.

Thanks so much for the input, everyone.

Gus68, yes it is a 2.56 posi. Kind of a crazy gear set but great on the open road.

The idea of using a 7-4 swap never crossed my mind until suggested, and explained that by not firing #7 & #5 cylinders back-to-back it should smooth it out. I guess it allows a little more time between firing to cool, and also more time to empty the exhaust manifold. But I may be wrong.

Rohrt, i agree that a 7-4 swap may not help in low rpms but I thought I'd give it a shot. I've never read anything that said the 350 is better on mpg than the 400, plus the decision to give up the cid for less HP and for more money was tough but I only have the 350 plus it's original so I thought I'd do something different. I was considering the Butler 383 stroker kit if I needed a new crank, but mine was OK.

The Lunati cam sounds like a great street cam, low duration, high lift. That gives me some comfort knowing mine is close to that. The decision to go roller was made when I tore the block down for the rebuild. Prior to this, If the car had sat for more then 10 days, when it would start it sounded like a rod bearing was knocking. It was a lifter (4 actually) that had mushroomed and the bottoms were scored. This bothered me because I take pride in maintaining my cars with good oil & filters frequently, and I never ran this engine hard, it's a cruiser. It had 152,xxx miles on it and the rest of the engine was normal. I don't want to take a chance that a cam would go flat. If I have to go through this engine again I'm probably won't be any younger, so do it once...

I did the swap and have no complaints.

Ultradyne roller 284/288
Lobe separation 112 degrees
Duration at .050 Intake 230 exhaust 234
Lift – intake .3533” exhaust .3533”

Dude, where have you been? Busy or what? You should check in more often.

Sounds like an interesting build, I wish you luck with it. A lot of guys want race everything and are disappointed when their street car doesn't run well at low RPM and in traffic. Seems like you thought things out with the intended use in mind.
This firing order thing has me screwed up.
The stock firing order is 18436572, cylinders five and seven are adjacent and fire back to back. If you swap the four and the seven you get
18736542, four and two are adjacent and fire back to back. If you swap the cylinder that fires fourth in line [three] and the cylinder that fires seventh in line [seven] you get 18476532 five and three are adjacent and fire back to back.
What exactly is the firing order of your proposed cam? If it's 18476532 is the advantage the two adjacent back to back cylinders are the inner two and not the outer?

Well it has to be 18736542 the piston would not be at top dead center with 18476532.
My problem is I don't know enough about too many things, the older I get the less I seem to know.
I've checked everywhere and read a few hundred different opinions on what is the advantage or disadvantage of the swap and why. Intake, exhaust, smoothness, lope, everyone has an opinion and none the same. I finally found a Dec. 11th, 2006 article from Hot Rod magazine. Lunati gave them a 7-4 swapped cam to try on a big block. They have a bit of info that satisfied some of my curiosity about the switch.

Seems the early Fords have the same firing order as our Pontiacs and Chevs, if you renumber the cylinders with #1 on the left instead of the right. The later 351s and 5.0L Fords and the Chevy gen III and IV LS engines have the 18736542 firing order.

According to the crank and valve train guys at GM the swap beginning with the gen III was not made for smoothness or power gain or any of the other reasons tossed around but to even out main bearing load. Seems they had no problem with the earlier cranks but with the new engines the # four main had significantly higher peak firing loads than number two main. They swapped the firing order to even them out.

It's an interesting article with input from a lot of top race and engine people.

We started seeing mostly #2 main and some #2 rod bearing issues on my old buddys NA 700 HP sprayed to 1100 HP.
Did the 4-7 swap last year, and claims it helped.
He moved to INDY few yrs ago, so I don't do the disassembly/reassembly any more.. Have to take his word on it for now....

hmmmm, #2 is supposed to have less load before the swap not after. When I tore down my 428 the front bearings were worse than the rear, I put that down to oiling. But you'd think the further from the flywheel the more the crank flex when under heavy launch load.

This thread got me looking more into the archives on the 7/4 swap.

One guy thought it was only an advantage if using a single plane intake and thought he lost power on a dual plane.

Another guy in the race section said he gained 15hp on a 700 hp build.

Cliff R said he has chosen not to try them because from all the Pontiac builders that have dyno'd them for street motors they found no benefit.

I think it was Tom Voight however was more open to them since he is a ford guy it is more of a ford firing order for the Windsor more (I think).

The two benefits that were highly debated was how the firing order effected the main bearings and how the firing order distributed the intake charge. I guess that would also effect the exhaust pulses as well.

I think someone said that Crane wanted an extra $100 for a 4/7 cam while some of the other like Lunati would do it for nothing.

Anyway you can read up on it by searching "4/7" in the archives.