I am wondering if anyone makes a 4/7 swap cam that is a solid roller in the .620 to .675 range. I can not seem to find one. Thanks

 

They're not worth the money unless you're building enough HP to run in ProStock. The tiny gains you may see won't justify the increased cost of a 4/7 swap cam. If they were the same price then using one would be a better option but they're just not worth it.

 

Contact Comp. They can custom grind the cam.

I would also suggest contacting Bullet and Cam Motion.

Later,
Bart

 

 

what is a 4/7 cam swap?

 

V8 engines have paired cylinders. What this means is that you can take the firing order 1-8-4-3-6-5-7-2 and split it down the middle.
So you have 1843 & 6572. Now take the first digit of each set and they are a pair. 1 and 6 they are paired cylinders. Then take the second digit of each set, which means 8 and 5 are paired cylinders and so on.

What this means is that when 1 is at TDC (top dead center or at the top of the bore) then 6 is in the same position. The difference is that that one is ending the compression stroke while the other is ending the exhaust stroke.

Now when you by 4/7 cam it swaps the two cylinders in the firing order. The reason for this is that the engine is supposed to run smoother. Also it is easier on the main bearings and the crank because the loads of the crank are more evenly distributed. It is supposed to also assist in flattening the torque curve.

 

I -need sleep. I can see what you are tyring to say but I can't picture it in my head or figure out how that could help out. oh well off to the wonderland in my bed.

 

Look at the firing order. 18436572.

Now look at a crankshaft. It has 4 journals, each with 2 rods on it. The 1 & 2 rods are on the same journal; likewise, 3 & 4, 5 & 6, and 7 & 8 are all "pairs" on journals.

1 fires immediately after 2; 3 immediately after 4; and 5 immediately after 6. That means, each of those 3 journals, gets 2 shots of power applied to it in rapid succession.

The 4-7 swap fixes ONE of those 3 instances of successive firing on the same rod journal. There are still 2 of them. Note that the 4-7 one is right between the other 2. Eliminating that one allows the crank to return to torsional "rest", so to speak, and helps keep from breaking.

The reason to swap that, is if you're running your motor at a specific RPM where the crank has harmonics, for an extended period of time. These vibration harmonics not only can break parts, but also reduce power output. But if the crank is not experiencing harmonics, then the swap accomplishes exactly nothing, because there's nothing to accomplish. In other words, for most people here, any money spent on doing that, is money wasted in accomplishing exactly nothing; it could be more usefully spent some other way.

 

however if your getting a custom grind done, it never hurts to ask them to have that done as well.

 

Is there any power to be gained from such a swap?

 

I don't think it's a substantial gain. More along the lines of smoother operation.

 

If you're not into the range of creating crank harmonics, there is NO POWER WHATSOEVER to be gained.

Same for "smoothness"; nothing there either.

It's like alot of things the "big name" type racers do, that get results in their business; but simply don't apply AT ALL to what we, as hobbyists, are doing.
In other words, for a street car, it's a waste of money. Could be alot of money, could be a little; doesn't matter, it's still a waste. If it costs a dollar extra, resist the temptation, and instead, take the dollar out of your pocket and set it on fire. You'll get just as much out of that; but at least then, you won't be fighting plug wire confusion someday on down the road.

I could build a house in Florida, and demand that it be braced against earthquakes, too. Might as well, right? ..... Would I get any benefit out of it? most likely, none at all. Should I really be spending my money on that? Ummm...... probably not. What I really need to be spending my "strengthen" money on if I'm in Florida, is HURRICANES. Same kind of a deal here. Spend your money on something that actually does something constructive FOR YOU, and not on just imitating what the guys with unlimited budgets and tight competition do .... SOMETIMES.

Because that's something else you have no way of knowing: it might make something else WORSE in your setup, such as fuel distribution for example. If you don't test it, you'll never know. Your extra money might just slow you down instead of speeding you up.

 

the only thing I Was thinking of would be along the lines of exhaust pulses or intake pulses.

 

hey if gm designed it into the ls1's then i think it has to help longevity somewhat. thats how i see it anyways.

 

And that would be relevant to a Gen 1 SBC .... how??Explain the logic (if any) that you're using to reach this conclusion.

But hey, it's your money, if you choose to spend it and get nothing in return, that's OK too. That's the kind of person I like to see in the other lane.

 

Hotrod did an article on it not too long ago and it actaully picked up about 7 horse under the power and then about 11 or so at peak versus the same cam except stock firing order.

 

I read that article myself, and while HOTROD did say they gained power, they also admitted that the increase wouldn't be as large as a purpose built race car. There are two important points here.

1. The 4/7 swap will make more power on even a street car.
2. A custom ground crank from Comp Cams is $249 with or without the 4/7 swap.

If you want every last horsepower you can squeeze out of your engine, then I think the swap is worth it. Plus eliminating one of the three impacts on your journals will happen no matter what, so from a longevity standpoint it's worth it. That's my opinion, and like I always say, "To each their own."

 

I was thinking of doing this on my next engine, does this swap change the engine sound? Will it sound like a Ford? Or like a ls1? And if it's such a good thing why hasn't GM and Mopar been doing it from day 1? There must be a reason they chose 1-8-4-3-6-5-7-2 over the other possible combinations.

 

Well I think testing it is something that Ford and GM did plenty of before they ever started puting cams like that into their engines.

And I agree with what iroczracer07 said. 7 hp is a decent amount to gain for something so small as that. And at no extra charge, why not?

Oh, really? No crank harmonics? Is that why every modern automaker puts this thing on the front of the crankshaft of every engine they make called a HARMONIC BALANCER?!?

If you didn't want to spend the money on a custom cam, I could see that. But if there is little or no difference in price for the 4/7 swap, I say go for it.

 

um not every engine has a harmonic balancer

 

Im yet to see a SBC without one...

 

he must be refering to hondas.

 

...which we couldn't care less about, hence the www.THIRDGEN.org

I was thinking of going with one, if I could get one for a reasonable price... But I didn't know it was only taking 1/3 of the damaging impacts and moving them... hmmm...

 

The reason GM used the old firing order is simple. The leaps in technology. They can measure more aspects of a motor than previously possible. Case in point, the fourth gen camaro suspension. It's the same set up as the 69 camaro, but do to suspension programs and sensors that can measure suspension travel in real time, they made some geometry adjustments to it and put it on the fourth gen.

 

Who said anything about hondas?

Sonix the quote I was refering to was
With the thirdgen.org maybe I was refering to a thirdgen nissan or something? It's still a thirdgen . A better comment would of been that is why this is a thirdgen f-body website

 

haha, ok, you got me there.
Are there any modern cars without harmonic balancers?

"crank harmonics" as sofa was talking about, is.... Different then why there is a harmonic balancer on cars. I won't waste my breath, as I don't fully understand it, let alone know enough to explain it to somebody else...

 

there are other methods of reducing or eliminating hoarmincs. some use counter rotating shafts. some just use extra weights. it's not the only method to remove the harmonics or at least reduce them

 

I see lots of the new powersports and utility engines nowadays use the seperate counter rotating shafts. kinda cool...

hmmm... what if we ran a counter rotating shaft in a SBC...

Maybe punch a hole in the lifter valley and run it off the timing chain

 

Its no secret that the 4.3 V6 was based on the 350, but did you know that some of the 4.3 engines actually use a balance shaft?

Also some people use hubs in place of harmonic balancers in order to reduce reciprocating mass. The hub is simply a piece of aluminum that has no ability to cancel negative harmonics. I personally think it is idiotic to do this. You gain no power and can make more power by reducing the torsional loads by using a dampener.

 

the only other thing I can think of by using a hub or just added weight is it might change the resonant point of the rotating assembly

 

I know I'm gonna catch a lot of flak for this, but the one piece rear main seal roller cam blocks are externally balanced. Not like a 400, the weight is the batwing on the flywheel vs. the inner hub of the balancer. If you don't believe me, check out John Lingenfelter's book on the sbc, or you could look in either the summit or jegs catalog for confirmation. I think that info is in there.

 

aye, my 1 peice stroker has the counterweight on the flexplate AND the harmonic balancer.

 

After hot rods tourqe convertor article they did when they said a 12inch convertor is better than the new 9.5's., i lost a lot of repsect and their credibilty. I think it's who's paying their bills is who they like that month.

 

Yeah, you're right. Mitsubishi had 2 "silent shafts" in the block to balance various vibrations in their 2.6 liter engine from the '80s. Also Chrysler had 2 balance shafts in the lower crankcase of their 2.5 liter engine. Neither of these engines have harmonic balancers. I was referring to engines in our cars when I made that comment, not DSMs or any other brand. Guess I should have noted that.

Speedfreaks101, that's really interesting. I didn't know GM made any counterbalanced engines. What cars or trucks were they in?

 

Well the 4.3 was in some 1/2 ton trucks , some s-10's and the marine engines. What is strange is that some of the trucks got the counterbalancend engine and some did not. The next thing is that the balance shaft is in the lifter valley above the cam.

Here is a link you might like,

AutoZine Technical School - Engine

 

Wow I just read that entire Autozine article...it was really good at explaining vibration and harmonics. I had no idea it was that complicated. I'm glad I read that. Thanks

 

From what I remember, that was another reason the 4-7 swap was thought up. The 5,7 fuel distribution was in succession of each other and the #5 cylinder supposedly robbed fuel atomization from the #7 cylinder on open plenum/single plane intake manifolds.

This never made sense to me. Looking at the two firing sequences, you've gone from the #5 cylinder robbing the #7 cylinder of fuel to the #4 supposedly doing the same to the #2 cylinder.

18436572
18736542

Your explanation makes much more sense.