The ZX1R story

**Skunk** · 5th August 2008, 22:27

Originally Posted by speedpro

A rev limiter is not neccessary if the motor is built properly. Have a listen to the ones Gaz and Karl are riding. They have John Connor big cams as well and are out to 140-150cc.

How do they stop the collet ring from snapping off and dropping the valve on over rev?

**speedpro** · 5th August 2008, 22:31

Originally Posted by Skunk

Hmm, yeah. Anyone know the ignition on these very well?
I'm thinking there's a waste spark... the points are triggered every rev rather than every second aren't they?...

Exactly - FZR is a typical 4 cylinder with 1&4 and 2&3 paired. ????? - or do you mean the standard points system? Either way you get a waste spark I sold Olly the FZR ignition for his CB125T. With no changes apart from fitting the ignition and doing back to back runs there was an immediate horsepower increase of a couple of horses. We ran the bike up on the dyno, fitted the ignition, and then ran it again. The bike didn't even come off the dyno. It also got a lot easier to start when cold and was a lot less cold blooded. It's one of the best things you can do to a 125T.

**speedpro** · 5th August 2008, 22:43

Originally Posted by Skunk

How do they stop the collet ring from snapping off and dropping the valve on over rev?

Don't know, but have a listen in this vid.

http://www.youtube.com/watch?v=JsJxaA4tLLQ

I don't think the sound is well synced to the vid but you can hear the twins. They rev hard and last well.

**Skunk** · 5th August 2008, 22:54

Hmm, yeah. Might see if I can track down this John Connor.

**koba** · 5th August 2008, 23:03

Originally Posted by Skunk

Hmm, yeah. Might see if I can track down this John Connor.

Arnies been looking for him for ages now and has met with little success...

**Slingshot** · 6th August 2008, 19:40

Originally Posted by Skunk

Hmm, yeah. Might see if I can track down this John Connor.

You'll find him in the post-apocalyptic future leading the human rebel group, Tech-Com.

Sorry, had to.

**Buckets4Me** · 6th August 2008, 19:54

or on amcc.co.nz

or at Mt Wellington

**Skunk** · 6th August 2008, 20:01

Thank you. I can never remember the address.
The chances of me getting to Mt Wellington - nil.
And a search of the site failed to find him... EDIT: Found!

**SHELRACING** · 7th August 2008, 19:08

Originally Posted by Skunk

I think it was Speedpro who was telling me about that engine. I would be very interested in any info you can come up with.
I'll be up to the Taumarunui Races October 11th and 12th. Staying at the Hilton.

I'm working on a rev limiter that cuts one cylinder too.

Hey Skunk K14 has asked for some info on the FZR setup as well. I'm going to do some pics, so you can have them if you like.

As I said to K14, have a meeting this weekend and Auckland the week after. With some major repairs on my own bike I'm a bit busy at the moment. As soon as I can find the gear I'll do the pics.

You're right there is a wasted spark on the system not that it appears to be an issue with the running of the bike. Although a common problem is a missfire, cough and splutter around 9000rpm which is annoying especially coming out of a corner.

Not sure (with all due respect) I agree with Speedpro's comment
'A rev limiter is not neccessary if the motor is built properly'

It is very easy to take the rev counter off the clock, and you can hear the valve bounce very clearly. Worse, if you use a reverse gear pattern and forget. Biga da boom. I have the pistons and valves to proove it.

I found on a track like Taupo over revving not an issue as you have so much time and room to think. But on a tight kart type track caution is required.

Anyway at the end of the day the twin is a great motor. Put the motor into a decent frame, Hmmm hard to beat.

Sorry by the way. We probably wont be at the Taumarunui meeting. I'm running near top of the 'B' points table so will probably be going to Auckland. Pity the Taumarunui track is about 2km down the road from us.

**speedpro** · 7th August 2008, 19:31

Originally Posted by SHELRACING

Not sure (with all due respect) I agree with Speedpro's comment
'A rev limiter is not neccessary if the motor is built properly'

It is very easy to take the rev counter off the clock, and you can hear the valve bounce very clearly. Worse, if you use a reverse gear pattern and forget. Biga da boom. I have the pistons and valves to proove it.

If the valves are bouncing the motor needs better valve springs. If the motor is already revving hard and you shift the wrong way a rev limiter is not going to help.

**gav** · 7th August 2008, 21:41

Tell that K14 nothing, he's already fast enough!!

**Skunk** · 7th August 2008, 21:48

One of the issues we have is the collet groove breaking and the valve simply dropping.

**speedpro** · 7th August 2008, 22:35

Originally Posted by Skunk

One of the issues we have is the collet groove breaking and the valve simply dropping.

Classic failure caused by valve float. The valve is moving so fast it ends up not following the cam profile and the valves are allowed to freefall back onto their seats and the shock breaks the valve. With heavier valve springs the valve has more force making it follow the cam profile and the closing ramp lowers it in a controlled manner onto the seat. If a motor has been left lying for years with a couple of valves open those springs are bound to have sagged out a bit. Springs also get hot in use. If the engine has an issue where things got or get hot up top that isn't going to help the springs either. They need a good supply of oil to dissipate heat.

Once you get into really high lift and/or speed you also need to start looking at resonant frequencies of the valve train. In this case just the valve spring really. It needs to be comfortably above where the engine operates or you can get a nice little harmonic thing happening and for instance end up with the spring doing nothing more useful than a slinky spring right where you need it most. Big drag race motors for instance could have titanium valve springs with only 3 turns and a new set every run. That is for 9000+rpm and around 1"(USA) lift.