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Flat Plane Crankshaft by RilesOfSmiles
Started on: 07-14-2013 02:29 PM
Replies: 15 (982 views)
Last post by: fast40driver on 07-20-2013 01:29 AM
RilesOfSmiles
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Report this Post07-14-2013 02:29 PM Click Here to See the Profile for RilesOfSmilesClick Here to Email RilesOfSmilesSend a Private Message to RilesOfSmilesEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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trotterlg
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Report this Post07-14-2013 08:40 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
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
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crashyoung
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Report this Post07-14-2013 09:52 PM Click Here to See the Profile for crashyoungClick Here to Email crashyoungSend a Private Message to crashyoungEdit/Delete MessageReply w/QuoteDirect Link to This Post
Unless you change the cam and distributor so two cylinders fire at the same time, then you get higher torque.
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BV MotorSports
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Report this Post07-14-2013 09:56 PM Click Here to See the Profile for BV MotorSportsClick Here to Email BV MotorSportsSend a Private Message to BV MotorSportsEdit/Delete MessageReply w/QuoteDirect Link to This Post
Cool idea but cost prohibitive. There are other ways to get the sound though. I assume that is why you asked?

[This message has been edited by BV MotorSports (edited 07-14-2013).]

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trotterlg
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Report this Post07-14-2013 10:16 PM Click Here to See the Profile for trotterlgClick Here to Email trotterlgSend a Private Message to trotterlgEdit/Delete MessageReply w/QuoteDirect Link to This Post
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
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Marvin McInnis
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Report this Post07-15-2013 01:46 AM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post
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).]

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Will
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Report this Post07-15-2013 02:46 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Marvin McInnis:

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.
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Blacktree
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Report this Post07-15-2013 09:11 PM Click Here to See the Profile for BlacktreeClick Here to visit Blacktree's HomePageClick Here to Email BlacktreeSend a Private Message to BlacktreeEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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Will
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Report this Post07-16-2013 11:02 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Blacktree:

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).]

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RilesOfSmiles
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Report this Post07-16-2013 03:06 PM Click Here to See the Profile for RilesOfSmilesClick Here to Email RilesOfSmilesSend a Private Message to RilesOfSmilesEdit/Delete MessageReply w/QuoteDirect Link to This Post
Would be pretty cool to stick 2 2.8s together to make a 5.6 liter V12. Kind of like what aston martin does with ford mondeo engines
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sleevePAPA
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Report this Post07-16-2013 03:11 PM Click Here to See the Profile for sleevePAPASend a Private Message to sleevePAPAEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by RilesOfSmiles:

Would be pretty cool to stick 2 2.8s together to make a 5.6 liter V12. Kind of like what aston martin does with ford mondeo engines


GMC built the "twin-six" back in the day.

http://www.youtube.com/watch?v=QQVjOqTa44Q
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MarkS
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Report this Post07-16-2013 08:10 PM Click Here to See the Profile for MarkSClick Here to Email MarkSSend a Private Message to MarkSEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by sleevePAPA:


GMC built the "twin-six" back in the day.

http://www.youtube.com/watch?v=QQVjOqTa44Q


The GMC V6 of the mid sixties, now that's something you don't hear about much anymore; at least I don't. A truck engine after all.

The Buick V6 went even fire ~ 1978.

BR's,

Mark

------------------
86 SE V6 4 speed
86 SE V6 Auto
2008 G6 GT "Street" Coupe
2005 Buick 3.6 Rendezvous
2001 Olds Silhouette (AKA The Band Van)

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Will
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Report this Post07-17-2013 10:00 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by MarkS:


The GMC V6 of the mid sixties, now that's something you don't hear about much anymore; at least I don't. A truck engine after all.

The Buick V6 went even fire ~ 1978.

BR's,

Mark



I didn't think it was as late as the '80's... but wasn't very sure.
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Francis T
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Report this Post07-18-2013 12:13 AM Click Here to See the Profile for Francis TClick Here to visit Francis T's HomePageClick Here to Email Francis TSend a Private Message to Francis TEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.

http://superlitecars.com/superlite-coupe/

[This message has been edited by Francis T (edited 07-18-2013).]

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Will
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Report this Post07-18-2013 06:52 AM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
With twin-turbos, a flat crank will help them spool more quickly.

Who's making the crank? Cam?
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fast40driver
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Report this Post07-20-2013 01:29 AM Click Here to See the Profile for fast40driverClick Here to Email fast40driverSend a Private Message to fast40driverEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.

Mike
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