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What are everyones thoughts on doing the 4/7 swap and when to do it. I have noticed that a lot of engine builders don't really agree on why this does or doesn't help a particular engine, but the facts are that it sometimes does. I have also never heard of anyone doing it with a blown/forced induction motor, why, is it not as effective on a forced induction deal? I would just like to get a little chat going about this and see what everyones thoughts are on the subject. Thanks!
4-7 swap cam is to help with 5 and 7 competing for an intake charge. No competition when using a supercharger.
If you look at firing orders as a continuous event. All GM firing orders have two adjacent cylinders competing for an intake charge at some point. I guess intake manifold design is more forgiving to some adjacent cylinders than others.
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What are everyones thoughts on doing the 4/7 swap and when to do it. I have noticed that a lot of engine builders don't really agree on why this does or doesn't help a particular engine, but the facts are that it sometimes does. I have also never heard of anyone doing it with a blown/forced induction motor, why, is it not as effective on a forced induction deal? I would just like to get a little chat going about this and see what everyones thoughts are on the subject. Thanks!
Talked to LSM---suppposed cam gurus about my blower motor and they gave me cam specs that included not only the 4-7 swap but also 3 and 2. Mentioned a little horse power gain but mostly lowered harmonics, a better balance --thus longevity. Word has it,these number swaps may be in the new 500 hp vette engine. anyway go figure....Steve
Never heard of such a thing .... but I'm watching to see what I learn now. :smile:
Infomaniac put what I know about 4-7 swaps in a nutshell. I've heard that results vary. From my experience, most engines are suffering from worse HP robbing mistakes and/or oversights than what the swap will gain you. It makes sense on paper.
I asked Dave Reher of Reher Morrison Race Engines about this and he mentioned the intake charge thing but he said in his opinion the reason it helped the most was because of harmonics. I asked Steve Schmidt about it also and he said,"Man, I don't know why it works, but it does." Now, I don't believe for one minute that Steve Schmidt doesn't have a pretty good idea why it works, he just might not be able or willing to take the time to put it into words.
Infomaniac put what I know about 4-7 swaps in a nutshell. I've heard that results vary. From my experience, most engines are suffering from worse HP robbing mistakes and/or oversights than what the swap will gain you. It makes sense on paper.
I agree, the 4-7 swap is usually found on a max effort engine. Plus when you are revving to a high RPM you want the least amount of vibration. I never heard of the intake deal but I can see that playing a part, makes sense you don't need it with a blower motor.
perhaps Info or Steel can put a little lite on this swap...back in the 60's when every1 was looking for a little more HP...there was a T/F team that tried a 180* cam that fired like 2 seperate 4 cyl engs...they ran pretty gd...made alot of HP...of course...they were blown on nitro...i dont know if they stuck with it or not...also...there was a co. called WH Ducoil who made a dual coil distributor for Fords (thats what i had..427ci FE) that u wired like a 4 cyl useing the stock cam pattern (no lobe swap)...it worked great for me...i think there is alot to this 4/7 swap...cause of the intake chg & certain cyl's running lean...especially on the BBC...look at Info's schematic & u will see that the new GM fireing order has the swap!...i think this swap (i could be wrong) comes in the 502's....Info..Steel...shed some lite on this :)
Ron (fastrat)
i think this swap (i could be wrong) comes in the 502's....Info..Steel...shed some lite on this :)
Ron (fastrat)
I don't know about the 502s, but I'm pretty sure that the 8.1 liter big block has a revised firing order; I would assume the small blocks have the firing order revised as well.
Brian
I have done a few of the 4/7 swaps. Unless it is a max effort engine for competition the gain is only slight. As someone said you can find more power in other areas then what this will gain you. You take a 2 barrel Nascar latemodel engine, a gain of 3 or 4 HP is huge in this competitive field. For a boat guy you will never feel the gain. Now for the OEM headed BBC engines you can grind an intake lobe for the good runners and the bad runners. This can be a 50HP or so gain but the cost is expensive, around $800 for one of these cams.
The new Ls1 is a symetrical port and is a totally different animal. It is more like a Windsor Ford then the SBC of years past.
Chris