Can someone explain to me the difference between an even fire engine and a flat plane crankshaft? Is there a difference? I've been toying with the idea of modifying the 2.8 to be a flat plane engine if its even possible. I know its not the best bang for the buck but I'm just thinking of doing something unique. I don't care about keeping the engine looking stock this is just one of those "because I can" projects.
I don't think a flat plane crank is suited to a 60 degree V6. On a V8 it puts two piston on each side up at the same time and two down at the same time. On them it is commonly done with even current production engines. Not really sure what you would gain or quite how you would do it. Larry
I think with a flat plane crank the cylinders fire one on each side not two together, but I think it only works with engines with an even number of cylinders on each side or inline. Larry
Discussing a flat-plane vs. cross-plane crankshaft is essentially meaningless in any context other than a 90-degree V8 engine. (Of course, it's a given that virtually all 4-cylinder in-line engine designs use flat-plane crankshafts.) It is unsuitable for a V6. Putting a flat-plane crankshaft into a 60-degree V6 would 1) destroy the inherently perfect first and second order balance of the configuration, and 2) disrupt the inherently even alternate-bank cylinder firing intervals.
What follows assumes a 90-degree V8:
Advantages: A flat-plane crankshaft will yield a cylinder firing order that alternates between cylinder banks, which simplifies optimized intake and exhaust system design. A flat-plane crankshaft also has lower rotating mass and lower moment of inertia vs. a cross-plane crankshaft, which translates to slightly more usable power.
Disadvantages: A 90-degree cross-plane crankshaft, through the use of integral counterweights, can achieve perfect first-order and second-order balance. A flat-plane crankshaft has no counterweights and cannot be properly balanced without the use of separate balance shafts.
[This message has been edited by Marvin McInnis (edited 07-15-2013).]
Advantages: A flat-plane crankshaft also has lower rotating mass and lower moment of inertia vs. a cross-plane crankshaft, which translates to slightly more usable power.
Disadvantages:A flat-plane crankshaft has no counterweights and cannot be properly balanced without the use of separate balance shafts.
This applies to low RPM applications only. (Who builds a single plane V8 for low RPM applications?)
For high RPM applications, both types need to be "fully counterweighted" meaning that each throw has its own pair of counterweights. There ends up not being any difference between the two in terms of crankshaft weight or MOI.
The balance in the cross-plane V8 isn't so much a function of the counterweights as it is a function of piston order.
To make a long story short, a flat-plane crankshaft will completely screw up a V6 engine.
On a flat-plane crankshaft, all the crankshaft throws are on the same plane (i.e. 180 degrees apart). So a single plane could intersect all the crankshaft throws and the centerline of the crankshaft. This works on 4 and 8 cylinder engines, because the 180-degree separation between crankshaft throws coincides with the firing sequence. But a 6-cylinder engine needs to have a split-plane crankshaft, because it fires cylinders at 120 degree intervals.
The difference between even-fire and odd-fire engines is in the firing sequence. As the name suggests, an even-fire engine has the cylinders firing at even intervals. For example, the 60 degree V6 has one cylinder fire on the left head, then one on the right head, then the next one on the left head, etc, which makes it an even-fire engine. But on most American V8's, this is not the case. Their firing order will have two cylinders fire one after the other on one cylinder head, then a pause while cylinders are fired on the other cylinder head. That oddly spaced firing order is what gives the American V8 its distinctive burble.
To make a long story short, a flat-plane crankshaft will completely screw up a V6 engine.
On a flat-plane crankshaft, all the crankshaft throws are on the same plane (i.e. 180 degrees apart). So a single plane could intersect all the crankshaft throws and the centerline of the crankshaft. This works on 4 and 8 cylinder engines, because the 180-degree separation between crankshaft throws coincides with the firing sequence. But a 6-cylinder engine needs to have a split-plane crankshaft, because it fires cylinders at 120 degree intervals.
The difference between even-fire and odd-fire engines is in the firing sequence. As the name suggests, an even-fire engine has the cylinders firing at even intervals. For example, the 60 degree V6 has one cylinder fire on the left head, then one on the right head, then the next one on the left head, etc, which makes it an even-fire engine. But on most American V8's, this is not the case. Their firing order will have two cylinders fire one after the other on one cylinder head, then a pause while cylinders are fired on the other cylinder head. That oddly spaced firing order is what gives the American V8 its distinctive burble.
You need to distinguish between even-fire engines and even-fire banks. Cross-plane V8's are even fire engines with odd-fire banks. Single-plane V8's are even fire engines with even fire banks. Even fire means that the firing intervals in degrees are the same at all points in the firing sequence.
The early versions of both the Chevy 4.3 V6 and the Buick 3.8 V6 were odd fire engines due to either unsplit rod journals or insufficiently split rod journals. Some time in the '80's, both went to 30 degree split journals to make then even-fire. The 60 degree engines have 60 degree split journals to make them even-fire
Yes, a single plane crank in a 6 cylinder is a ridiculous idea.
[This message has been edited by Will (edited 07-16-2013).]
My son is building an SLC and putting a modified vet engine: twin turbo, flat crank, etc, etc, etc. I think he's going the flat crank route more for the sound than anything else. Lol, like twin turbo in SLC won't be quick enough.
I still work on Detroit Diesels, 92 series blocks come in 6V and 8V - two V6's make a 12V, two 8V's, a 16V, three 8V's, a 24V. In all cases, the blocks are bolted together, multi-part cranks are used, also bolted together. 149 series stop at a 20V - one 8V block, and two 6V blocks. The old V12 gas engines used a one piece block and crank, just two heads on each bank, and two intake manifolds, distributor heads, etc.
