Land Speed Racing

[SlowerThanYou]

How often do you drag race guys need to replace the pistons and rings and cranks

 

On methanol, we had to replace the pistons & rings at the end of the season around 200 runs. The crank (cast) would last about 400 runs before needing freshened.

 

On race gas, piston & rings replaced around 600 runs. We ran a billet crank, it had over 600 runs & was still going strong after I sold it. 

 

[registered user]

Yes, 250 singles will go 10000 but they have been designed as a 250-- crank life would not be like a MXer.  Remember a banshee engine was designed

I think its irrelevant what they were designed for as the banshee is based on 35yo ideas. most likely it wasn't designed to go much above 9k or so, atleast that's what the engineers probly had in mind at the time. that's not far off from what a modern stock 250 is designed for. it might be closer to the low 8000 but still not far off

 

the point to my previous statement was only to say that the piston speeds generated at 10k by a 68mm stroke are still below the mechanical limits of the crankshaft assembly, atleast for short to medium periods, assuming you have good parts. whether or not your particular engine will have the ability to run up that high or sustain those engine speeds for miles and miles is hard to say. if you have experience with other Yamaha twins like you say, then you should have no trouble sorting it all out

[Deadbeat]

 see how fast you go with 4mm first, one cost of a big stroke billet crank can pay for multiple Hot Rod cranks, it might blow first outing then yur fucked big exotic pile of scrap.. you could of had 2 spare motors ready to go.

 

4mm on meth should be getting 120hp depending on what cyls its got

[trickedcarbine]

Elephant in the room:

14mil stroke in OEM cases. Yeah you can epoxy the waffle ribbing on the bottom of the cases and trench them to take the 68mm crank, but the vibration is known to rattle cases apart on 300' machines. This thing needs to be able to roll in real easy and then be flogged wide open for say a full minute.

 

There is gonna have to be ample testing done to make sure the domes and pipes allow the motor to rev that high. Most big stroke banshee based motors are barely getting over 9,500. Drag guys kill shit with extreme load and shutter, the land speed stuff kicks the bucket over harsh harmonics. Speak with Crankworks or Falicon about balancing the rotating assembly.

 

Gearing, might need to call Robinson for a custom ratio trans. With everything on the market right now your probably gonna end up getting an RZ based trans, putting 2.08 primaries on, and 17-18 front sprocket up front with a rear sprocket barely bigger then the rear hub.

[sleeper06]

I suggested sleeving because of another convo me n the op had at another time about him maybe dropping cc class

[sleeper06]

Tricked is correct, Robinson can make custom trans , as long as it geared correctly , pipes/domes are configured to let it pull gear after peak power, fuel pump supply plenty of fuel, it should last more than one meeting

[m671054]

the point to my previous statement was only to say that the piston speeds generated at 10k by a 68mm stroke are still below the mechanical limits of the crankshaft assembly, at least for short to medium periods, assuming you have good parts. engine will have the ability to run up that high or sustain those engine speeds for miles and miles is hard to say.

what rod ratio do those 250 have? Pretty positve with the 125.3 rod recomended on a 68 cub your max safe rpm is not 10k. Probably 9 to 9.5

 

As far as trickeds comment of them shaking apart thats a bunch of bullshit. Maybe in a spaghetti frame with a bunch of flex they are popping epoxy. But mine ran 3 years of dune racing before i had to rebuild it and not due to case epoxy problems.

 

I would try and contact brandon from what was wildcard racing. He has real world experience on the salt, he lives in utah, and was an engine builder. Hes not really doing it anymore but its worth a shot.

 

What size tire you run? I want to run it through my calc to get primary,secondary and trans ideas.

Edited January 4, 2016 by m671054

[trickedcarbine]

Meh, the asphalt guys I know shake epoxy cases apart over 10mm stroke. I'm not saying they can't live, but it's gonna be hard to keep alive for the duration of land speed racing.

[m671054]

I agree that much stroke probably wont last at that rpm for that duration.i would think a 7mil super cub might work better

[Bones25]

Thanks every one..

  It looks like there will be  huge amount of development and then it may not make the required HP.

I was trying not to do so much development to not get the reliability and power needed.

 

I will go with the TZ250 which I have which I know.

 

Again --- Thanks for your help        Bones

[Deadbeat]

what sort of power will you expect out of a TZ motor

[Bones25]

I have heard that a TZ 250 A -- 1990. The last reverse cylinder, parallel twin will make 90HP. @ 12k

 

But I think these are Japanese HP. Probably measured at the crank-- no water pump-- no oil pump.

I recon 80 would be more realistic  Maybe make a little more with different pipes.

They make more than the next model, a V twin, but are not as rideable.

I think the last of the Aprillia 250 GP bikes were making 100hp. 

 

cheers   Bones

[m671054]

If your only chasing 80-90 hp you dont need a real big motor like you were asking about. You can get that from a 4mil no problem.

[registered user]

these threads are gay. anyone with competance in chassis fabrication and engines wouldnt be on here asking for advice or help

[lil Doobie420]

lol