4/7 swap

[PAPA]

I was just wondering if anyone is doing this? From what (very)little research I have done on this it seems to have better harmonics over 7 grand and the idle is a little better also. Some say that a 3-5 HP gain can be seen also. The harmonics is the most important from what I've been reading. I would think that would help in making the motor live a little longer. I'm not an engine builder by any means but was just wondering if its something someone is doing.

[txtom]

Don't know about the current classes, but it was common in ROMCO.

The 4/7 Swap reduces crankshaft torsional vibration for smoother dampening.

 

It also has slight HP gains. It is widely believed that NHRA Pro Stock racer Steve Schmidt was the first to develop and have success with this swap.

[racer61]

All of my motors since ROMCO (and there has been several) have had a 4/7 swap cam. Im not sure I can "feel" a difference but its been working great so if its not broke dont fix it.

[jwmbishop]

We used it in our NDirt outlaw 87-89. It was amazing how much smoother the engine sounded and felt. the engine was a complete Lunati kit - very high HP and CID so don't know how much the swap contributed by itself - but it sounded like it was turning 6K when it was hitting 9. And even with 40 cars on the track you could always hear ours (not louder so much as very different - in fact ours was one of the quietest).

 

Couple things to keep in mind. First SFOs only presents gains at higher RPM. And you will see gains generally only in open plenum (or very low floor dual plane) manifolds. what the swap accomplishes is smoothing out the intake reversionary pulses and thus giving better fuel atomization. Cams are avail that swap 4-7, 1-6, 2-3, or 5-8. the 4-7 has the best gains in harmonics and as that is imediately noticeable even to a rookie ear - it is by far the most common..IMO.

 

As far as Schmidt being credited with developing this I would seriously doubt it. He may lead the way in VOLUME of builds using it (which I have heard a few times). But (unless he prototyped and brought to fruition a modelling when he was 11 years old) Bruce Crower and Dave Schneider were both selling SFOs - even before crower/schneider split to their own respective companies in 61. Schmidt gives his birth year as 50. In the early to mid 70's - my Dad and I were working out of catalogs and grind sheets from the late 60's! (hey it took time to "inherit" old catalogs - the 'net has truly spoiled us all).

 

I believe the factory tried all different orders possible back with the 348 (which hit production in 58) - the current order was the smoothest from idle to 4500 - the usable range for a daily driver. But the data they obtained hit the field in the late 50's.