4/7 swap
11-18-2003, 08:56 PM
#1
Registered
Thread Starter
Join Date: Oct 2000
Location: On the river
Posts: 3,372
Likes: 0
Received 0 Likes
on
0 Posts
4/7 swap
I am in the market for a new solid roller cam. I see the new trend is changing the firing order on the small block chevy from 1-8-4-3-6-5-7-2 to 1-8-7-3-6-5-4-2. meaning they are swapping 4 and 7 around. Are there any drawbacks to use this sort of setup?. i am trying to ring every hp outta this 383..
Thanks in advance...
Travis
Thanks in advance...
Travis
11-19-2003, 10:10 PM
#4
MarineKinetics
Platinum Member
Traviss,
Years ago we did development on 180 flat cranks and revised firing order engines and the results were expensive, incremental and difficult to obtain. When you consider that 8-10 hp in a pro stock engine(as sited below) is less than a 1% increase, your dollar per hp ratio is better spent in other areas in this application.
A typical Chevy firing order is 1-8-4-3-6-5-7-2. For the vast majority of applications, this firing order works nicely and there’s probably no need to change it. But in a race application, there are various firing orders that can effectively improve power and reliability in an engine. Typically, there are seven other firing order arrangements which can be used without changing the crankshaft layout on a Chevrolet V8. These firing orders include the following:
1-8-4-2-6-5-7-3
1-8-7-2-6-5-4-3
1-8-7-3-6-5-4-2
1-5-4-3-6-8-7-2
1-5-7-3-6-8-4-2
1-5-7-2-6-8-4-3
1-5-4-2-6-8-7-3
Reher-Morrison has tested the various combinations and found some interesting results. When the firing order is revised to 1-8-7-3-6-5-4-2, you’ll find some power and reliability. Now, if you race a Pro Stock car, this is no secret since the revised order has been in vogue for some time. With the revised firing order, fuel distribution dilemmas are resolved. The engine tends to run cooler, and perhaps just as important, the engine is actually smoother. How much extra power is there? Anywhere between 8 to 10 measurable horsepower. There was once a caveat here though: The average enthusiast couldn’t easily get a cam with the revised lobe positions, but not so today. Reher-Morrison sells such a package (called Big Stick Cams) for Chevy big block/Big Chief head combinations.
Courtesy Hot Rod
Hope this helps,
Bob
Years ago we did development on 180 flat cranks and revised firing order engines and the results were expensive, incremental and difficult to obtain. When you consider that 8-10 hp in a pro stock engine(as sited below) is less than a 1% increase, your dollar per hp ratio is better spent in other areas in this application.
A typical Chevy firing order is 1-8-4-3-6-5-7-2. For the vast majority of applications, this firing order works nicely and there’s probably no need to change it. But in a race application, there are various firing orders that can effectively improve power and reliability in an engine. Typically, there are seven other firing order arrangements which can be used without changing the crankshaft layout on a Chevrolet V8. These firing orders include the following:
1-8-4-2-6-5-7-3
1-8-7-2-6-5-4-3
1-8-7-3-6-5-4-2
1-5-4-3-6-8-7-2
1-5-7-3-6-8-4-2
1-5-7-2-6-8-4-3
1-5-4-2-6-8-7-3
Reher-Morrison has tested the various combinations and found some interesting results. When the firing order is revised to 1-8-7-3-6-5-4-2, you’ll find some power and reliability. Now, if you race a Pro Stock car, this is no secret since the revised order has been in vogue for some time. With the revised firing order, fuel distribution dilemmas are resolved. The engine tends to run cooler, and perhaps just as important, the engine is actually smoother. How much extra power is there? Anywhere between 8 to 10 measurable horsepower. There was once a caveat here though: The average enthusiast couldn’t easily get a cam with the revised lobe positions, but not so today. Reher-Morrison sells such a package (called Big Stick Cams) for Chevy big block/Big Chief head combinations.
Courtesy Hot Rod
Hope this helps,
Bob
Last edited by rmbuilder; 11-19-2003 at 10:12 PM.
11-20-2003, 08:11 AM
#5
Registered
4/7 SWAP.
Hey Travis,
Basically the 4/7 swap is another one of those things us boat guys cannot take full advantage of because of the low RPM's we turn. At 6000 or less RPM you would probably see 5 HP at best. At 7000 or 8000 RPM there may be 10-15 HP. I don't know of any drawbacks to using the racing firing order besides a few extra bucks and then having a "nonstandard" cam. If it were me I would save the $20 bucks, get a standard cam grind and have a little extra beer money!!
You can't go wrong either way and the 4/7 swap probably won't provide any noticeable gains.
Basically the 4/7 swap is another one of those things us boat guys cannot take full advantage of because of the low RPM's we turn. At 6000 or less RPM you would probably see 5 HP at best. At 7000 or 8000 RPM there may be 10-15 HP. I don't know of any drawbacks to using the racing firing order besides a few extra bucks and then having a "nonstandard" cam. If it were me I would save the $20 bucks, get a standard cam grind and have a little extra beer money!!
You can't go wrong either way and the 4/7 swap probably won't provide any noticeable gains.
Last edited by WETTE VETTE; 11-20-2003 at 08:13 AM.
11-20-2003, 10:52 AM
#7
Registered
Join Date: Oct 2002
Location: New Orleans,La.
Posts: 983
Likes: 0
Received 0 Likes
on
0 Posts
I've heard they do the 4/7 swap on circle track cars because the left side runs leaner then the right and they want stop 7 firing behind 5.Causes a lean condition.That puts 2 behind 4 on the right but that side runs richer.I agree with WETTE VETTE.Less headaches more beer money.BOB
11-20-2003, 12:21 PM
#8
MarineKinetics
Platinum Member
Traviss,
Some new information. Harold Brookshire (Ultradyne) is now the head cam designer for Lunati. They just introduced a new line of 4/7 solid rollers for sbc and bbc engines available at a reasonable price without any other modifications so it might be a cost effective modification. Not sure if they have a grind that will work in a marine application yet as Harold was out at the time, but it might be worth a conversation. He is very approachable and informative. His direct line is 1-901-365-0950 x135.
Here is the press release.
http://www.holley.com/hioctn/NewsInfo/NewsRels/l-36.htm
Hope this helps,
Bob
Some new information. Harold Brookshire (Ultradyne) is now the head cam designer for Lunati. They just introduced a new line of 4/7 solid rollers for sbc and bbc engines available at a reasonable price without any other modifications so it might be a cost effective modification. Not sure if they have a grind that will work in a marine application yet as Harold was out at the time, but it might be worth a conversation. He is very approachable and informative. His direct line is 1-901-365-0950 x135.
Here is the press release.
http://www.holley.com/hioctn/NewsInfo/NewsRels/l-36.htm
Hope this helps,
Bob
11-20-2003, 06:35 PM
#9
Registered
Thread Starter
Join Date: Oct 2000
Location: On the river
Posts: 3,372
Likes: 0
Received 0 Likes
on
0 Posts
thanks boys... i will probably go with it cause i am trying to squeeze everything outta this motor. I have to buy a new cam anyways so why not do it. Crane has a "SFO" option which they will machine any of there roller cams for the 4/7 swap.
I apprecaite the info on everything
I apprecaite the info on everything
11-21-2003, 06:16 PM
#10
Registered
Join Date: Jan 2003
Location: Broken Arrow, OK
Posts: 311
Likes: 0
Received 0 Likes
on
0 Posts
4 - 7 swap was intended to minimize the lean condition of 5&7 competing for a fuel charge.
As it turns out 4 - 7 swap also causes less twisting of the crank. Fires the end cyls then the middle.
The new GM firing order is supposed to transfer the stress of successive firing impulses on the same main journal to the rear of the engine that is oiled first.
I made this chart a while back for a visual representation of what is happening. Big difference when you look at it as a continuation of firing instead of just 8 firing.
As it turns out 4 - 7 swap also causes less twisting of the crank. Fires the end cyls then the middle.
The new GM firing order is supposed to transfer the stress of successive firing impulses on the same main journal to the rear of the engine that is oiled first.
I made this chart a while back for a visual representation of what is happening. Big difference when you look at it as a continuation of firing instead of just 8 firing.
Last edited by Infomaniac; 11-21-2003 at 06:22 PM.
