LSA Crankshaft
I couldn't imagine why. Metallurgical speaking its a weak spot prone to cracking. The nice rolled radius like you see in the other crank makes more sense to me. Not to mention it is overall thinner and at an intersecting point at that.
I know the undercutting improves the strength, something to do with allowing the metal to shift, stress risers and what not. The equipment it takes to do it on a large scale is super expensive which is why the little guys don't do it. Do you have to use an LSA crank w/ an LSA block?
I know the undercutting improves the strength, something to do with allowing the metal to shift, stress risers and what not. The equipment it takes to do it on a large scale is super expensive which is why the little guys don't do it. Do you have to use an LSA crank w/ an LSA block?
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TECH Enthusiast
Joined: Jul 2008
Posts: 577
Likes: 1
From: League City, Tx
Correct me if I am wrong, but Compstar got a bad name when, a long time ago, for LS engines, they were using a non 4340 crank positioned where the compstar crank is currently.
It is a chinese forging just like Eagle or K1. All three good to support more than a stock crank can which we know will last above 1000hp for a while.
Dragonslayer and Magnum cranks are the same damn thing also, save some rounnding on the counter weights I believe.
Lunati Pro is another great crank option if spending the money.
I went with a K1. Heard their finishing machining was better than Eagle and low and behold they forgot to machine the step to allow the timing gear to slide on...
It is a chinese forging just like Eagle or K1. All three good to support more than a stock crank can which we know will last above 1000hp for a while.
Dragonslayer and Magnum cranks are the same damn thing also, save some rounnding on the counter weights I believe.
Lunati Pro is another great crank option if spending the money.
I went with a K1. Heard their finishing machining was better than Eagle and low and behold they forgot to machine the step to allow the timing gear to slide on...
DragonSlayers are forged at the Timken Foundry here in the USA, then fully machined, heat treated, balanced, in house at Callies.
Compstars are forged, machined and rough balanced in China. Final balancing and QC'd at Callies.
Eagle = Chinese junk...
K1= China, not sure of the quality, but you get what you pay for.
As I said, I'd trust anything GM over cheap china cranks.
None of the stockers gonna hold 1k rwhp for long.... They WILL flex... Especially on a blower car.
You are mistaken...
DragonSlayers are forged at the Timken Foundry here in the USA, then fully machined, heat treated, balanced, in house at Callies.
Compstars are forged, machined and rough balanced in China. Final balancing and QC'd at Callies.
Eagle = Chinese junk...
K1= China, not sure of the quality, but you get what you pay for.
As I said, I'd trust anything GM over cheap china cranks.
None of the stockers gonna hold 1k rwhp for long.... They WILL flex... Especially on a blower car.
DragonSlayers are forged at the Timken Foundry here in the USA, then fully machined, heat treated, balanced, in house at Callies.
Compstars are forged, machined and rough balanced in China. Final balancing and QC'd at Callies.
Eagle = Chinese junk...
K1= China, not sure of the quality, but you get what you pay for.
As I said, I'd trust anything GM over cheap china cranks.
None of the stockers gonna hold 1k rwhp for long.... They WILL flex... Especially on a blower car.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
It's the same with a lot of top level gear shafts and axles ( and only mentioning gears as had a pair of drop gears from Samsonas from a sequential Subaru transmission in my hand yesterday, and strangely for you'd think no good reason, they too have a groove machined in the shaft at points where diameter changes. Whereas the OEM Subaru gears do not ) just after the spline, or at key points there will be an undercut groove.
A friend was even telling me a few years ago, for his university studies he did lots of testing on axle bars on a live axle car for a small MG he used to race. And he found that a small undercut just after the splines on those shafts actually prevented shaft failure on a car where otherwise it ate shafts.
Same shafts, same materials etc
Presumably it's similar to why some head studs have a waisted shaft vs the thread diameter. It seems all wrong, but it actually gives a stronger stud.
I recall Vizard saying the undercut radius on Mini crankshafts was always preferable over those without too stating it can reduce the chances of fracture ( although it did reference to a more straight edge as opposed to a full radius edge )
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
You cant just assume that a straight shaft is always strongest at a thick diameter.
Even my axle shafts. I twisted several at the splines, yet strangely the only ones that never twisted where the 28 spline and smallest diameter shafts. Not the same thing, but still an oddity
The 28 spline large shafts, 31 spline large shafts all twisted the splines until I then sourced better 31 spline shafts from MW
But the small diameter 28 splines that I had used at the start, never twisted. I only changed them because I found out there were larger diameter options, thinking they would be stronger.
Clearly the thicker shaft move weak points or changed something allowing them all to twist at the splines.
Even a lot of OEM axle bars will have diameter changes at points for no apparent reason, when surely it would be easier just to make a straight bar ?
Although they generally fail where the retaining circlip resides, but that's almost always a sharp edged recess so not surprising. But often it isnt the smallest diameter of the shaft.
So on a similar line of thought, who would ever think the smaller shafts would have lasted longer or certainly appeared stronger ?
As said, it's also similar to proper head studs where some used a waisted stem. Seems silly to reduce the diameter, but it too actually reduces potential failure points because it moves stress loads to different locations in the stud without affecting it's ability to clamp.
Because it was a mechanical engineer who actually tested it with many designs and models in university with real shafts that told me ? I can only take his word over those who havent done such testing.
You cant just assume that a straight shaft is always strongest at a thick diameter.
Even my axle shafts. I twisted several at the splines, yet strangely the only ones that never twisted where the 28 spline and smallest diameter shafts. Not the same thing, but still an oddity
The 28 spline large shafts, 31 spline large shafts all twisted the splines until I then sourced better 31 spline shafts from MW
But the small diameter 28 splines that I had used at the start, never twisted. I only changed them because I found out there were larger diameter options, thinking they would be stronger.
Clearly the thicker shaft move weak points or changed something allowing them all to twist at the splines.
Even a lot of OEM axle bars will have diameter changes at points for no apparent reason, when surely it would be easier just to make a straight bar ?
Although they generally fail where the retaining circlip resides, but that's almost always a sharp edged recess so not surprising. But often it isnt the smallest diameter of the shaft.
So on a similar line of thought, who would ever think the smaller shafts would have lasted longer or certainly appeared stronger ?
As said, it's also similar to proper head studs where some used a waisted stem. Seems silly to reduce the diameter, but it too actually reduces potential failure points because it moves stress loads to different locations in the stud without affecting it's ability to clamp.
You cant just assume that a straight shaft is always strongest at a thick diameter.
Even my axle shafts. I twisted several at the splines, yet strangely the only ones that never twisted where the 28 spline and smallest diameter shafts. Not the same thing, but still an oddity
The 28 spline large shafts, 31 spline large shafts all twisted the splines until I then sourced better 31 spline shafts from MW
But the small diameter 28 splines that I had used at the start, never twisted. I only changed them because I found out there were larger diameter options, thinking they would be stronger.
Clearly the thicker shaft move weak points or changed something allowing them all to twist at the splines.
Even a lot of OEM axle bars will have diameter changes at points for no apparent reason, when surely it would be easier just to make a straight bar ?
Although they generally fail where the retaining circlip resides, but that's almost always a sharp edged recess so not surprising. But often it isnt the smallest diameter of the shaft.
So on a similar line of thought, who would ever think the smaller shafts would have lasted longer or certainly appeared stronger ?
As said, it's also similar to proper head studs where some used a waisted stem. Seems silly to reduce the diameter, but it too actually reduces potential failure points because it moves stress loads to different locations in the stud without affecting it's ability to clamp.
No but quite honestly I could care less what one engineer told you or what some head stud company does. They all have their opinions just like you and I. Not to mention you Guys are trying compare two completely different types of loads here. A head stud/Axle will in no way see similar loads to a crankshaft. The mechanical engineers I sit next to at work and all the major crankshaft manufacturers agreed that full radius is stronger, So that's what I'm going with.
Last edited by oscs; Apr 27, 2015 at 07:44 AM.
