Flat crank shaft for LS1?
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FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
A flat crank is a crank with two of the rod journals in the middle in one plane and the other two rod journals are at the ends and are also in the same plane but 180 degrees on the opposite side.
This turns a V8 into two four cylinders basically with even firing intervals to the header collectors but with irregular firing intervals in the manifold. It sounds different but makes less power. IRL cars are required to run these cranks so they sound like they do but otherwise they would not in this day and age most probably.
180 degree headers as someone was mentioning make the headers work like they would on a four cylinder by connecting cylinder groups that fire every 180 degrees just like a 4 cylinder would. This is also why equal length headers on a regular V8 don't help that much.
This turns a V8 into two four cylinders basically with even firing intervals to the header collectors but with irregular firing intervals in the manifold. It sounds different but makes less power. IRL cars are required to run these cranks so they sound like they do but otherwise they would not in this day and age most probably.
180 degree headers as someone was mentioning make the headers work like they would on a four cylinder by connecting cylinder groups that fire every 180 degrees just like a 4 cylinder would. This is also why equal length headers on a regular V8 don't help that much.
Teching In
Joined: Jun 2002
Posts: 16
Likes: 0
Here is a good link describing different crankshaft characteristics.
http://www.e31.net/navmisc_e.html
FWIW, Ferarri is still using the a flat crank in thier V8's, but I think an LS1's rotational mass is far too heavy to be able utilize a flat crank design. Ive contemplated trying to build a flat crank 4.0L DOHC Cobra and spinning it to 8000rpms. I just have no clue what car to stick it in.
http://www.e31.net/navmisc_e.html
FWIW, Ferarri is still using the a flat crank in thier V8's, but I think an LS1's rotational mass is far too heavy to be able utilize a flat crank design. Ive contemplated trying to build a flat crank 4.0L DOHC Cobra and spinning it to 8000rpms. I just have no clue what car to stick it in.
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
You can use flat plane cranks in most american race series but no one does because of the power losses. They even tried back in Pro Stock but basically gave up because they are slower. They are lighter though as that article says which is the reason that everyone tried them.
Teching In
Joined: Jul 2004
Posts: 3
Likes: 0
From: Highlands Ranch, CO
well that is not entirely true. Flat cranks can actually make more power than a 90 degree crank and that is why the IRL uses them. The only problem with using one on an LS1 (which i would also like to try) is that they make their power with higher revs which a stock pushrod engine can barely get to but if you upgrade the valvetrain to make it lighter and use stiffer springs, then you could raise the rev limiter quite a bit and you would be more able to tap into the extra power you get from the flat crank.
I am not too sure how good they would be on the street with stop and go driving but on the track they would kick butt! That is why the IRL uses them. also because they are more balanced then a 90 degree crank that also helps them rev higher.
I am not too sure how good they would be on the street with stop and go driving but on the track they would kick butt! That is why the IRL uses them. also because they are more balanced then a 90 degree crank that also helps them rev higher.
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
Originally Posted by t_newnes
well that is not entirely true. Flat cranks can actually make more power than a 90 degree crank and that is why the IRL uses them. The only problem with using one on an LS1 (which i would also like to try) is that they make their power with higher revs which a stock pushrod engine can barely get to but if you upgrade the valvetrain to make it lighter and use stiffer springs, then you could raise the rev limiter quite a bit and you would be more able to tap into the extra power you get from the flat crank.
I am not too sure how good they would be on the street with stop and go driving but on the track they would kick butt! That is why the IRL uses them. also because they are more balanced then a 90 degree crank that also helps them rev higher.
I am not too sure how good they would be on the street with stop and go driving but on the track they would kick butt! That is why the IRL uses them. also because they are more balanced then a 90 degree crank that also helps them rev higher.
Flat crank I have a custom Crower billet Ferrari flat crank here for a special project I am working on. I thought it would help you folks visualize what Erik was talking about.
The flat or 180 degree crankshaft for a V-8 looks identical to a four cylinder inline crankshaft. The 180 degree crankshaft is balanced independently of the rods and pistons, etc. just like an inline four or six (no bobweights).
As Erik said, these cranks offer no improvement over a conventional 90 degree crankshaft in most applications. They do seem to work better with individual intake runners and only because the exhaust pulse tuning is better with even firing cycles per bank. Intake manifolds for the LS1 and most other V-8 engines were designed for a 90 degree crankshaft. Unless you have a lot of time and money to come up with an intake manifold that will work effectively with a 180 degree crankshaft you will loose power.
Another problem area is the secondary imbalance with these cranks. Other than using a pair of balance shafts there is no easy way to get rid of the imbalance.
Ferrari guys love the sound of the flat crank. Also, the only cams made are for a flat crank so I have no choice in the matter. I am taming down the secondary imbalance by using titanium rods and very light pistons in these engines.
Steve Demirjian
Race Engine Development
Sponsor
The flat or 180 degree crankshaft for a V-8 looks identical to a four cylinder inline crankshaft. The 180 degree crankshaft is balanced independently of the rods and pistons, etc. just like an inline four or six (no bobweights).
As Erik said, these cranks offer no improvement over a conventional 90 degree crankshaft in most applications. They do seem to work better with individual intake runners and only because the exhaust pulse tuning is better with even firing cycles per bank. Intake manifolds for the LS1 and most other V-8 engines were designed for a 90 degree crankshaft. Unless you have a lot of time and money to come up with an intake manifold that will work effectively with a 180 degree crankshaft you will loose power.
Another problem area is the secondary imbalance with these cranks. Other than using a pair of balance shafts there is no easy way to get rid of the imbalance.
Ferrari guys love the sound of the flat crank. Also, the only cams made are for a flat crank so I have no choice in the matter. I am taming down the secondary imbalance by using titanium rods and very light pistons in these engines.
Steve Demirjian
Race Engine Development
Sponsor
