Okay Camshaft Gurus..Let's talk about the 4/7 swap

[DeputyDawg]

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!

[Infomaniac]

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.
http://marineassault.net/2113-med.jpg

[steve d]

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

[SmokinLowriderSS]

Never heard of such a thing .... but I'm watching to see what I learn now. :smile:

[steelcomp]

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.

[DeputyDawg]

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.

[LUVNLIFE]

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.

[FASTRAT]

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)

[PC Rat]

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

[cstraub]

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

[BUSBY]

wow ... stumbled across this thread ... old school right here boys!
4/7 swap IMO not worth it. Tried it w/ my uncle (NHRA 1970's & 80's) from time to time.
George Striegel (Clay Smith Cams) was one of the originators of the idea. From what I was told by him it was born from the Ford Windsor deals ... using the firing order for the Windsor from the 289/302 engines I believe. (I'm sure there are some Ford guru's here that can chime in on that, but I think those who are running small Ford hard swap the cams around).
Info is primarialy right on here ... but it never really worked in any great HP gains ... acutally we ended up spending too much money chasing it 2 or 3 different times.
IMO ... spend your money on your heads on getting them done right ... that is where the tricks are kept!

[flat broke]

I can't say what the GM revised firing order is good for on my motor compared to a traditional firing order engine of the same build, but I will offer this up for deliberation. There has been a string of pump gas sub-500ci 4.25 stroke BBCs to come out of DNE in the past few years, and for the most part, each motor has seen better hp than it's comparable predecessor. One of the changes that was made between my incarnation and earlier builds is the addition of the revised firing order on the cam grind.
As Chris mentioned, perhaps it is only good for 3-4 HP, but when a custom ground cam costs $XXX, you might as well choose the grind that will give you the most hp for your $. People always talk smack about the "little things" that the big name builders do, and how they are are great for competition, but you wont see the gains in every day performance applications. As I look at the attention to detail spent on my motor, I can tell you that when you add enough of those "stupid little things" together, you get a measurable increase in peformance.
Will the revised firing order make your boat faster than your buddy's? By itself no, but if the same attention to efficiency is applied throughout the entire build, you will end up with a sizeable difference.
Just my $.02
Chris

[steelcomp]

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 remember the TF motor you're talking about, but don't remember who. If I'm not mistaken, they ran what's called a flat crank. All the rod journals were directly opposed. I also remember the Ducoli...my dad had a 55 "Bird that had a stroked 406FE (462ci) and it had a Ducoil in it. Also had one on the motor in our boat...a J2 Olds.
I really can't shed much light on the 4/7 swap thing. Just haven't had that much experience with it.

[steelcomp]

I can't say what the GM revised firing order is good for on my motor compared to a traditional firing order engine of the same build, but I will offer this up for deliberation. There has been a string of pump gas sub-500ci 4.25 stroke BBCs to come out of DNE in the past few years, and for the most part, each motor has seen better hp than it's comparable predecessor. One of the changes that was made between my incarnation and earlier builds is the addition of the revised firing order on the cam grind.
As Chris mentioned, perhaps it is only good for 3-4 HP, but when a custom ground cam costs $XXX, you might as well choose the grind that will give you the most hp for your $. People always talk smack about the "little things" that the big name builders do, and how they are are great for competition, but you wont see the gains in every day performance applications. As I look at the attention to detail spent on my motor, I can tell you that when you add enough of those "stupid little things" together, you get a measurable increase in peformance.
Will the revised firing order make your boat faster than your buddy's? By itself no, but if the same attention to efficiency is applied throughout the entire build, you will end up with a sizeable difference.
Just my $.02
Chris
Good post Chris. This is exactly what my point was before. For the guy buying parts from Smmit and trying to bolt them together, the 4/7 is a waste of money. For a guy like Dave, or when you are capable of addressing every detail as best as possible, or as a customer's budget will allow, then it seems to makes sense to take advantage of what the swap has to offer. Even then, though, the gains are minimal. But at that point, a gain is a gain, and they all count. I doubt it's worth it in a jet boat, though, unless you're running a reduction, or some ungodly small impeller, and can really zing the motor. I doubt there's much to be gained at the 6500 rpm level, but I could be wrong.

[FASTRAT]

I remember the TF motor you're talking about, but don't remember who. If I'm not mistaken, they ran what's called a flat crank. All the rod journals were directly opposed. I also remember the Ducoli...my dad had a 55 "Bird that had a stroked 406FE (462ci) and it had a Ducoil in it. Also had one on the motor in our boat...a J2 Olds.
I really can't shed much light on the 4/7 swap thing. Just haven't had that much experience with it.
hey steel...
im loseing it here lol...ur rite...it was a 180* crank...not the cam...i was doughin' lol...anyways...do u think it would work in a BBC?
glad to hear that someone else besides me had tried the Ducoil...i wish i still had mine
Ron (fastrat)

[steelcomp]

hey steel...
im loseing it here lol...ur rite...it was a 180* crank...not the cam...i was doughin' lol...anyways...do u think it would work in a BBC?
glad to hear that someone else besides me had tried the Ducoil...i wish i still had mine
Ron (fastrat)
Crank's a crank, block's a block, rods and pistons don't know what they're hooked to.
It's all about the harmonic phases when it comes to balancing. V8's balance better than most any configuration. Next are 60 deg v12's and 6's. Flat fours and 6's like Porsches and VW's and Lycoming's and others are on the bottom of the list, just above a 90 deg v6 or v12. If the flat crank would work in the v8 better than what we have now, it'd be in every one. Falconer took two SB Chevys and made a 90 deg v12, somewhere in the neighborhood of 600ci. It's a bitchen motor, but they have a bad rep for breaking cranks. V12's (and 6's) need to balance at 60 deg, not 90.
I'm hoping someone else will chime in here, because I really am not sure the 180 deg. v8 had a flat crank in it...but I think it did. I think they discovered that flat opposed cranks need opposing or in line cylinders to work correctly. I haven't talked about this stuff for so long I've forgotten all the terminology. There's basically two frequencies of balancing when a motor is running. and the different configurations effects these two frequencies differently.
Ouch...my brain hurts. Might be a good topic for a new thread.

[ttmott]

Historically, if I remember correctly, the greatest gains, firing order wise, was to balance the exhaust pulses in the headers (non zoomie). In all GM firing orders there exist two pulses on each side next to each other in the order causing ineffeciencies in cylinder scavenging and intake charge. There existed what they called 180 degree headers that crosses over the conflicting two exhaust tubes to the other side collector balancing the pulse timing. Some short track cars still use the 180 deg systems. The piping for the exhaust is a bundle of snakes. It would be interesting to see what DNE has to say about this.
Tom

[72 Hondo]

I could be WRONG but, I heard the 4/7 swap had something to do with triing to run the Chevy small block? in a reverse rotation.

[steve d]

I remember the TF motor you're talking about, but don't remember who. If I'm not mistaken, they ran what's called a flat crank. All the rod journals were directly opposed. I also remember the Ducoli...my dad had a 55 "Bird that had a stroked 406FE (462ci) and it had a Ducoil in it. Also had one on the motor in our boat...a J2 Olds.
I really can't shed much light on the 4/7 swap thing. Just haven't had that much experience with it.
Back in the 70's there was a Sprint Car #111, in CRA at Ascot that ran a Keith Black motor---They had a name for the motor--damn can't remember-anyway this motor fired two cylinders at a time. Shot like hell comin out. Ran for a few years--nothing much came of it. Is this what you would call a flat crank? Seems like it would vibrate like an old Triumph V.T.---Steve

[UBFJ #454]

It's my opinion, in terms of gaining Hp, that unless someone is going to build, as Chris says "A (Truly) Competition Motor" (a naturally aspirated motor) and go the route of using and integrating such things as a Tuned Intake Manifold (Built & Tuned To The Specific Heads Your Using); High Flow Heads w/Appropriate Chamber Size, Valves, and Push Rod Geometry; Special Ground Larger Diameter Roller Cam(s); Tuned Step Headers; Etc. ... Your not going to gain much by doing the 4/7 Swap ... The dampening of Harmonics, especially with a smaller dia. stock cam and its valve train, is something one should consider though.
$800 for a 4/7 Swap cam seems a bit Pricey to me ... Our Special Grind 55 mm 4/7 Swap LSM Roller Cam wasn't even close to that.

[SUICYCOLE DIMARCO]

They Called Them 180 Motors For The Crank Design.then They Had A Custom Cam Designed For The Crank Design.i Dont Much About Details..i Have Run The 4/7 Cam Didnt See Much Diff,but Id Imagine On The Dyno You Would See Something..

[cstraub]

Bear,
My reference to $800 cam was not clear. That cost was not for a 4/7 swap that was for grinding 3 different lobes on 1 cam; 2 intakes and 1 exhaust. This was old PS technology from the late 70's to the early 80's when the GM heads were asymetrical ports. I still do a few of these cams where class rules limit the engine to OEM cylinder heads.
Chris

[steelcomp]

Bear,
My reference to $800 cam was not clear. That cost was not for a 4/7 swap that was for grinding 3 different lobes on 1 cam; 2 intakes and 1 exhaust. This was old PS technology from the late 70's to the early 80's when the GM heads were asymetrical ports. I still do a few of these cams where class rules limit the engine to OEM cylinder heads.
Chris
Chris, how did they correct for differences between the two different intake ports? Just a lift adjustment, or would the duration change as well? Or just duration?? Seems to me the duration would want to stay the same, since duration has more to do with the rpm range, and that wouldn't change between ports. Are the ports different enough in length to warrant a different duration between the two?
Oh man, I just thought of a ton of questions about this...but I'll settle for those for now. :D

[cstraub]

Chris, how did they correct for differences between the two different intake ports? Just a lift adjustment, or would the duration change as well? Or just duration?? Seems to me the duration would want to stay the same, since duration has more to do with the rpm range, and that wouldn't change between ports. Are the ports different enough in length to warrant a different duration between the two?
Oh man, I just thought of a ton of questions about this...but I'll settle for those for now. :D
Scott, its all relative. Lift, duration and valve events can all be different. We have computers that now will adjust timing for individual cylinders on say a v-8 engine, so putting different cam timing in each cylinder with a different lobe is no different. In the 80's some PS teams were running cams with multiple lobes. Port length does play a part. When tuning for the intake pulse to find that last bit of HP, yes it plays a part.
Duration yes sustains the power at a given rpm, but the ability of the port to flow A/F to sustain the power is based on how well the port flows. If the port is not good then the cam will have to "crutch" the port. If the port is exceptional, then the cam doesn't have to help as much.
Chris

[steelcomp]

Makes sense. Thanks. :D