13 replies to this topic

[B(Kuch)Kucera45]

I was wondering what the difference in lap times between an open diff and an LSD or torsion diff if any ?

[James York]

I was wondering what the difference in lap times between an open diff and an LSD or torsion diff if any ?

 

That would be very track dependent on corners types.

 

But I once remember driving someone's 1.6 a long time ago with an open diff (the viscous thing) in an enduro (just funnin aroung) and compared to my mazdacomp LSD equipped 1.6, it was a dog out of every slow, tight corner.  I had to adapt to take corners at right angles in order to get the car straight ASAP in order to get the power down.  At that one particular track it was at least 1 second, maybe 1.5 slower.  (2 mile course, 14 turns)

[B(Kuch)Kucera45]

Thanks James,that's the kind of info I'm looking for.

[James York]

One of the corners where it was getting hurt badly led onto a long straight, so not being able to launch out of the corner well hurt times.  The car I was driving didn't have any data, so its not conclusive, but just a comparison of lap times, feel and competitiveness. 

[Brandon]

There also has been unpublished data noting a loss in HP to the wheels when using a Torsen vs. Mazdacomp.  It could be considered marginal and/or possibly within the 'noise variance' with most dynos but the apparent loss combined with the additional weight of the larger diff (on the 1.6L specifically) a lot of guys have tended to stick with the smaller one.

[B(Kuch)Kucera45]

So how much HP/TQ do you think you would lose going from an open to a torsion ?

I couldn't see it being that much,but even with a little lose of hp/TQ wouldn't the benefits of a torsion out weight the difference of an open diff ?

[SaulSpeedwell]

Hey Bob, at "our" tracks we know an open diff will light up the inside tires, and the Comp LSD has proven faster than the Torsen with multiple cars and drivers ... the 1.8 Torsen definitely has more inertia, but it is (almost) purely an open diff when going down the straightaway so *in theory* it should be faster on slightly bending straightaways (e.g. Mid O backstraight) versus having to overcome the "X" ft-lbs of preload in the Comp LSD.

 

Just like trying to push a straight axle go-cart with the wheels turned, a clutch LSD like the MazdaComp takes torque from the motor to overcome the breakaway torque.  That's why anyone running a Comp LSD should be running the LEAST breakaway torque they can.

 

I've only built a couple Cuscos so far, but they really *should* be the best of both worlds - open on coast, clutched on drive, and completely tuneable. 

[B(Kuch)Kucera45]

Hey Bob, at "our" tracks we know an open diff will light up the inside tires, and the Comp LSD has proven faster than the Torsen with multiple cars and drivers ... the 1.8 Torsen definitely has more inertia, but it is (almost) purely an open diff when going down the straightaway so *in theory* it should be faster on slightly bending straightaways (e.g. Mid O backstraight) versus having to overcome the "X" ft-lbs of preload in the Comp LSD.
 
Just like trying to push a straight axle go-cart with the wheels turned, a clutch LSD like the MazdaComp takes torque from the motor to overcome the breakaway torque.  That's why anyone running a Comp LSD should be running the LEAST breakaway torque they can.
 
I've only built a couple Cuscos so far, but they really *should* be the best of both worlds - open on coast, clutched on drive, and completely tuneable.

So your thought,how much estimated time a lap do you think you would lose with an open diff. On our tracks ?

[SaulSpeedwell]

Not sure if this is what you want to hear, but converting to a LSD from open never gives as much laptime as you would hope   Murdick was the last to convert, his videos had what seemed like 2 seconds of "one wheel peel" coming out of Keyhole, but moving him to an LSD only seemed to drop a few tenths.

 

You gotta do it, just don't get your hopes up TOO much.  It will be worth half what you are hoping for

[B(Kuch)Kucera45]

Not sure if this is what you want to hear, but converting to a LSD from open never gives as much laptime as you would hope   Murdick was the last to convert, his videos had what seemed like 2 seconds of "one wheel peel" coming out of Keyhole, but moving him to an LSD only seemed to drop a few tenths.
 
You gotta do it, just don't get your hopes up TOO much.  It will be worth half what you are hoping for

You know I still have the open diff in my car,but I don't have an LSD I have a torsion and didn't know if I should waist my time putting it in ?

[Ron Alan]

I think only those at the very front can truly feel the difference between the Mazdacomp and the Torsen. Obviously the 1.6 car is the only car allowed to run either...the 1.8 is stuck with the Torsen as the only LSD option( why is that?). The main reason most 1.6 owners convert is reliability...not grip. The 7" diff if just much stronger than the 6" diff in the 1.6. The Mazdacomp rarely is the failure issue in the 1.6...usually ring and pinion or bearing failure. But for those who do change...note that you are going to add about 17lbs of nice low weight over the rear wheels. But also adding more rotating mass!

To your question Kuch...the guy at the back will see no difference in lap times from any open to an LSD. The guy at the front will see 1sec I would think(again track dependent). Slow right handers are the worst.

[Bad Rusty]

If you ever want to enjoy racing in the rain, you'll want a lsd in there

[ECOBRAP]

I converted from Mazdacomp to Torsen this year, and did not notice a difference in lap time whatsoever. I raced my 1.6 w/Torsen against a similarly prepped 1.6 w/Mazdacomp, and would say the difference is no more than 2/10ths at a 2 minute track like Sonoma.

 

You would also expect it to be a very different driving experience, but there is so little torque in our cars and so much grip, that it doesn't feel very different under racing conditions. The main place I notice a difference is when hopping apex curbs, but that's about it. Unless you're on two wheels for longer than James Bond, it doesn't make much difference!

[FTodaro]

Running an open diff can take the push out of the car, in some corners but that is because, your rear end is tighter , or less lose. I ran an open diff for awhile at mid O at first, it was slow as I had to feed the gas much slower coming out of the keyhole.