HEMI -4-7 SWAP

[daytonalo]

DOES ANYONE MAKE A 426 HEMI 4-7 SWAP CAM , FOR THOSE WHO ARE SCRATCHING THERE HEAD . THIS IS A CAM WHERE YOU SWAP THE FIRING ORDER BETWEEN 4 AND 7 AND IT MAKES 30 H.P

[resq302]

I think I just saw something on that on Horsepower TV yesterday.  Don't know how it would work or how it would get extra horsepower just by changing the firing order.

[daytonalo]

The engine breaths better and runs smother ! I race a offshore boat and a few guys have gone this direction

[Blown70]

The engine breaths better and runs smother ! I race a offshore boat and a few guys have gone this direction

I have seen this first hand,  THOSE motors run smooooooth!! I was very surprised.

ALSO, I would think any custom grid shop should be able to do this?

[Rolling_Thunder]

The engine breaths better and runs smother ! I race a offshore boat and a few guys have gone this direction

I have seen this first hand,  THOSE motors run smooooooth!! I was very surprised.

ALSO, I would think any custom grid shop should be able to do this?

yep - any cam place should be able to make a cam for this....     just tell them what you are doing...   

[daytonalo]

blown 70 , can you tell more about your experience?

[andyf]

Crane can grind you a 4-7 swap for a Hemi.  Comp Cams can probably do it also.  I think you have to use an unground lobe cam which is more expensive.  I'm not so sure it makes any more power or runs smoother.  After all, a lot of Ford engines came from the factory with that firing order and nobody ever said they made a lot of power or ran smoother than a Chevy or Mopar.

[Rolling_Thunder]

After all, a lot of Ford engines came from the factory with that firing order and nobody ever said they made a lot of power or ran smoother than a Chevy or Mopar.

yeah...     that is a good point

[daytonalo]

I just saw the dyno sheet , only after 4-7 swap , increase of 30 hp .......................................

[Blown70]

blown 70 , can you tell more about your experience?

U have a PM

[andyf]

If a motor picked up 30 hp after changing to a 4-7 lobe then something else was wrong that got fixed at the same time.  The average engine is not going to pick up 30 hp just by changing the firing order unless something is way out of whack.

There is nothing new about the 4-7 firing order change.  As posted before, a lot of Ford engines came from the factory with that firing order and they didn't make an extra 30 hp.

The new Chevy SB engines have changed to this firing order and they didn't pick up 30 hp.  The engineers did change the firing order because it seemed to reduce engine vibration a bit.  Evidently moving the firing pair from the rear of the engine to the front of the engine reduces some crankshaft harmonics.  I'm not sure why, maybe because the front of the crank is less lightly loaded than the rear?  Anyway, I've never seen a detailed engineering explanation for why the 4-7 swap works but it does seem to make the motors a little smoother for some reason.

But it doesn't add 30 hp.

[daytonalo]

I have been on the phone all day about this to a few offshore race teams , and this is common practice and when you lake it on paper it just makes sense . I'm sorry I missed on what type of engineerering back ground you have , but dyno sheets don't lie . all that is involved is a custom cam and a firing order change , they also inform my besides less vibration it inherently breathes better because of better engine intake pulses .

[andyf]

Actually it is pretty easy to make dyno sheets lie!  A 4-7 swap might pick up a little power on an engine and it might not.  But there is zero chance that it is going to automatically add 30 hp to the average engine.  Whoever is telling you that is just yanking your chain hoping you'll buy some expensive parts.

[daytonalo]

ask around , then get back to me

[firefighter3931]

If a motor picked up 30 hp after changing to a 4-7 lobe then something else was wrong that got fixed at the same time.  The average engine is not going to pick up 30 hp just by changing the firing order unless something is way out of whack.

If the engine in question picked up 30hp....then the profile was altered. You won't see a 30hp increase with identical lift/duration/lsa specs and a simple 4-7 swap. Dynos measure under a constant load so even engines that rev faster/smoother won't show any increase in measured power (on the dyno).


Ron

[Challenger340]

If a motor picked up 30 hp after changing to a 4-7 lobe then something else was wrong that got fixed at the same time.  The average engine is not going to pick up 30 hp just by changing the firing order unless something is way out of whack.

If the engine in question picked up 30hp....then the profile was altered. You won't see a 30hp increase with identical lift/duration/lsa specs and a simple 4-7 swap. Dynos measure under a constant load so even engines that rev faster/smoother won't show any increase in measured power (on the dyno).


Ron

I agree too !  Just can't see it.
2 ways to increase power,(among others), are to increase Volumetric Efficiency, or to decrease Parasitic forces internal of the engine.

I had thought the 4/7 swap deals, were a development targeting the BB Chevies "good port/bad port" head design, to even out the carb pulses, really intake problems, which manifest as both Volumetric, AND Parasitic torsional.

Just proves,  I KNOW NOTHING !   LOL ! 

But I still Pluck at the 30 h.p. unless something else was "FIXED", like Ron says.

[daytonalo]

The results were on horsepower TV, on a 572 , Chevy ramjet

[Lightning]

hmm....could this work on the small block mopars as well?  (even without gaining HP, it'd be nice to have it run smoother)  I've seen an ad in the stock car racing mags advertising such a swap on the SB Chevys for years....

[resq302]

One thing to remember too when you are on a dyno with the motor out of the car, it is usually in a controlled environment and they usually run it with the air cleaner housing off.  That alone will give you extra horsepower due to no restriction of the air filter or the air filter housing.  I doubt it will give you the extra 30 horsepower but it will certainly help the numbers.