Okay, from memory so do your own research.
The obligatory TLDR avoidance version...
Stagger tuning an engine is nothing new. See Big Block Chevrolet Can Am tuning or XS John. (link provided below).
Long ago in a galaxy far , far away....
Actually it wasn't a Galaxy it was a Camero. So goes the tale of the 430 Can Am engine.
In their original form they were 4.440 in. bore and a 3.47" stroke. Original testing was done with the "short" 348/409 crankshaft followed by something a bit cleaner than a twisted forging loaded with internal tungsten weight.
On to the point of this mind vomit. The Big Block Chevrolet (other than the later spread port) head has two different sorts of ports. Due to the compromise all cylinder heads have to make between coolant passages, cylinder head bolt location and where to put push rods, the ports always suffer in some way. In the case of the Big Chev one port opens into the open cylinder and the other opens into the cylinder wall. So with 4 of each port what's a brother to do?
Actually it's simple if you put your mind to it . The port with the easier path to the chamber needed less ignition advance for complete combustion due to uninterrupted swirl in the combustion chamber. The weak sister opening into the cylinder wall suffered from a bit of fuel drop out in the chamber and needed a but more ignition advance.
But wait , that's not all!
Having a little extra fuel and needing a bit of port velocity the "weak" cylinder got a slightly longer intake path via either injector height or runner length. The "good" cylinder needed less help with velocity and got the shorter rummer length. The result was a V8 engine , running like two separate four cylinders in the same block. Remember this was Can Am and not a drag race. Road racing places a premium on bulk mid range HP and Torque. Put another way to go faster on a road course you need more area under the curve rather than peak output.
Various timing schemes were used to compliment the split tuned engine. The easiest was the fact that a spark jumps easier to a hot electrode. The weak port cylinder needed a hotter plug anyway so the good port got the cooler plug and as much as 4 degrees actual difference in spark timing. It's rumored that the original front distributor came about because of the need for a second timing source in these engines. I think it was to get closer to the timing chain and people getting tired of reaching to the rear, up against the firewall, across a hot engine, stock Chevrolet location.
So the reason for all this verbiage (mind vomit) is to let you know that what's new is old. It hasn't ALL been done before, but this has. In fact it has been done to the XS.
http://www.xs650.com/threads/a-collection-of-xsjohns-mods.2426/
Not everything John did was along the lines of good engineering (or oiling) but he was correct about the differences in right to left cylinder cooling and operation. John proposed running the XS650 as two separate single cylinders but not to the extent of different diameter and length of intake tract.
For my part I just overwhelm the original design rather than refine it. By the time I'm done I've rendered the original design into something closer to a grenade than a street tame daily driver. I do see the advantages in refining the original design however I don't see a single carburetor as an improvement. As far as aircleaner/airbox volume goes the stock battery box is not an insurmountable challenge. Today's batteries are much smaller and easier to relocate. Just do it.
As a secondary thought the vacuum diaphragm constant velocity carburetors are very good at covering up for the marginally too large ports of the 650. For the 750 the ports are about right with minor caveats. Straight or flat slide carburetors are a whole different animal and well covered by several members here.
bored yet ?
The obligatory TLDR avoidance version...
Stagger tuning an engine is nothing new. See Big Block Chevrolet Can Am tuning or XS John. (link provided below).
Long ago in a galaxy far , far away....
Actually it wasn't a Galaxy it was a Camero. So goes the tale of the 430 Can Am engine.
In their original form they were 4.440 in. bore and a 3.47" stroke. Original testing was done with the "short" 348/409 crankshaft followed by something a bit cleaner than a twisted forging loaded with internal tungsten weight.
On to the point of this mind vomit. The Big Block Chevrolet (other than the later spread port) head has two different sorts of ports. Due to the compromise all cylinder heads have to make between coolant passages, cylinder head bolt location and where to put push rods, the ports always suffer in some way. In the case of the Big Chev one port opens into the open cylinder and the other opens into the cylinder wall. So with 4 of each port what's a brother to do?
Actually it's simple if you put your mind to it . The port with the easier path to the chamber needed less ignition advance for complete combustion due to uninterrupted swirl in the combustion chamber. The weak sister opening into the cylinder wall suffered from a bit of fuel drop out in the chamber and needed a but more ignition advance.
But wait , that's not all!
Having a little extra fuel and needing a bit of port velocity the "weak" cylinder got a slightly longer intake path via either injector height or runner length. The "good" cylinder needed less help with velocity and got the shorter rummer length. The result was a V8 engine , running like two separate four cylinders in the same block. Remember this was Can Am and not a drag race. Road racing places a premium on bulk mid range HP and Torque. Put another way to go faster on a road course you need more area under the curve rather than peak output.
Various timing schemes were used to compliment the split tuned engine. The easiest was the fact that a spark jumps easier to a hot electrode. The weak port cylinder needed a hotter plug anyway so the good port got the cooler plug and as much as 4 degrees actual difference in spark timing. It's rumored that the original front distributor came about because of the need for a second timing source in these engines. I think it was to get closer to the timing chain and people getting tired of reaching to the rear, up against the firewall, across a hot engine, stock Chevrolet location.
So the reason for all this verbiage (mind vomit) is to let you know that what's new is old. It hasn't ALL been done before, but this has. In fact it has been done to the XS.
http://www.xs650.com/threads/a-collection-of-xsjohns-mods.2426/
Not everything John did was along the lines of good engineering (or oiling) but he was correct about the differences in right to left cylinder cooling and operation. John proposed running the XS650 as two separate single cylinders but not to the extent of different diameter and length of intake tract.
For my part I just overwhelm the original design rather than refine it. By the time I'm done I've rendered the original design into something closer to a grenade than a street tame daily driver. I do see the advantages in refining the original design however I don't see a single carburetor as an improvement. As far as aircleaner/airbox volume goes the stock battery box is not an insurmountable challenge. Today's batteries are much smaller and easier to relocate. Just do it.
As a secondary thought the vacuum diaphragm constant velocity carburetors are very good at covering up for the marginally too large ports of the 650. For the 750 the ports are about right with minor caveats. Straight or flat slide carburetors are a whole different animal and well covered by several members here.
bored yet ?
