ASRoff
Club Member
As per Oldsstroker:
The "4/7" swap works with single plane (carb-type) manifolds, but not dual plane. I find it easier to visualize by drawing diagrams with 8 circles and arrows going from one cylider to the next in the firing order with firing degrees noted next to each cylinder. Connect the last back to the first for the complete picture.
You'll notice a few things:
you still get 2 adjacent cylinders on one bank firing 90 * apart.
(5-7 on SBC, 4-2 on "4/7 swap", and 3-1 on LS1. That should only affect 4-2-1 headers, not 4>1s)
you still have the center 4 cylinders firing consecutively and criss-crossing.
there are two extreme corner consecutive firings in the SBC and LS1 (1>8 & 7>2) although they occur at different times. 4/7 swap has only 1>8.
In the 4/7 swap, 4 goes from firing @ 180* to 540*, one revolution different. Same thing for 7 (540* to 180*) of course.
LS-1 doesn't have consecutive firing (and therefore induction) of 1 & 2, those nearest the plenum inlet, so perhaps they don't cause as much turbulance of incoming air which might disrupt the cylinders farther away. In fact, the LS1 has 7-8 at the end of the plenum consecutive. Maybe that might work on an LT-1 also.
I don't think you need a different crank, just different cam lobe orientation and timing and injector wiring swapping. AFAIK, cores for the LS1 firing order aren't readily available for SBC/LT1.
Part of the LS1 firing order was for less vibration for a smoother engine and therefore maybe a little more long term durability. My guess is the other reason was power. The 8100 big block has the LS1 order also.
As per our very own Hot Rod hawk:
LSM did this three years ago. Petty played with it and it stayed pretty tight liped till they started selling test dyno motors
I have a friend that has bought a couple of these test pieces from petty.
He put the sb2 cyl heads & intake on a 331 inch sbc ran 8.12 @172 at 3000 pounds. ThEn he switched the deal to the 4/7 swap and ran 7.91!
On a non related bit he just went 412 inches 4/7 sb2 and ran 9.23 on motor and with 32 jets in the fogger boggied out a 7.59 at 191 on ten inch tires at 2600 pounds testing at Bradington a month ago
By the way Jacko you have been living under a rock:laugh:
The cam has been out for years I heard that Reher-Morrison engineered it.
The "4/7" swap works with single plane (carb-type) manifolds, but not dual plane. I find it easier to visualize by drawing diagrams with 8 circles and arrows going from one cylider to the next in the firing order with firing degrees noted next to each cylinder. Connect the last back to the first for the complete picture.
You'll notice a few things:
you still get 2 adjacent cylinders on one bank firing 90 * apart.
(5-7 on SBC, 4-2 on "4/7 swap", and 3-1 on LS1. That should only affect 4-2-1 headers, not 4>1s)
you still have the center 4 cylinders firing consecutively and criss-crossing.
there are two extreme corner consecutive firings in the SBC and LS1 (1>8 & 7>2) although they occur at different times. 4/7 swap has only 1>8.
In the 4/7 swap, 4 goes from firing @ 180* to 540*, one revolution different. Same thing for 7 (540* to 180*) of course.
LS-1 doesn't have consecutive firing (and therefore induction) of 1 & 2, those nearest the plenum inlet, so perhaps they don't cause as much turbulance of incoming air which might disrupt the cylinders farther away. In fact, the LS1 has 7-8 at the end of the plenum consecutive. Maybe that might work on an LT-1 also.
I don't think you need a different crank, just different cam lobe orientation and timing and injector wiring swapping. AFAIK, cores for the LS1 firing order aren't readily available for SBC/LT1.
Part of the LS1 firing order was for less vibration for a smoother engine and therefore maybe a little more long term durability. My guess is the other reason was power. The 8100 big block has the LS1 order also.
As per our very own Hot Rod hawk:
LSM did this three years ago. Petty played with it and it stayed pretty tight liped till they started selling test dyno motors
I have a friend that has bought a couple of these test pieces from petty.
He put the sb2 cyl heads & intake on a 331 inch sbc ran 8.12 @172 at 3000 pounds. ThEn he switched the deal to the 4/7 swap and ran 7.91!
On a non related bit he just went 412 inches 4/7 sb2 and ran 9.23 on motor and with 32 jets in the fogger boggied out a 7.59 at 191 on ten inch tires at 2600 pounds testing at Bradington a month ago
By the way Jacko you have been living under a rock:laugh:
The cam has been out for years I heard that Reher-Morrison engineered it.
