OzVMX Forum

Marque Remarks => Yamaha => Topic started by: pancho on March 12, 2009, 12:51:30 pm

Title: 35mm?
Post by: pancho on March 12, 2009, 12:51:30 pm

the inlet port diameter on my XT slider head measures 35 mm. is the inlet port on the SL500 the same or bigger? the carby i'm using is 38mm and i was thinking about opening the port to the same dia. in an effort to improve top end performance but i'm concerned i may lose bottom end torque which currently is my only claim to fame.[hole shots] cheers wally.

Title: Re: 35mm?
Post by: jimg1au on March 12, 2009, 01:25:23 pm

wally
just put a sr500 big fin head on thats what i have.you wont lose any bottom end.when my brither raced this bike he used to beat eveything off the line including modern mx bikes as most other clubs mix sliders with mx bikes
the valve size on the sr is 47mm inlet you should have 45mm inlet
jim
hagon tt500

Title: Re: 35mm?
Post by: mick25 on March 12, 2009, 03:54:13 pm

Later model TT 500 have same inlet value as SR 500 same part nos but SR heads have bigger fin heads

Title: Re: 35mm?
Post by: Marc.com on March 13, 2009, 03:41:13 am

(http://i245.photobucket.com/albums/gg71/marcFX_photo/iwataco-img600x450-1213856187yi80lm.jpg)

38mm seems a good size, try and leave the floor of the port as is and work upward.

Title: Re: 35mm?
Post by: jimg1au on March 13, 2009, 06:43:26 am

would it not be better to start with the 47mm inlet than the std 45mm
cheers
jim

Title: Re: 35mm?
Post by: Colin Jay on March 13, 2009, 08:46:05 am

Be carefull if you are going to open up the inlet port on any 500 Yamie head, one of my SR500 head had been ported and I found that there was an air leak through a section of the casting (on the outside of the port into the air passage between the inlet port and the camchain tunnel) that was a bit pourous. When we tried to TIG weld it, there was not enough metal to get a good weld and it kept "pin holing". The problem was eventually solved using an epoxy instant metal. That head has been painted black and now resides on one of my XTs so the repair is not really noticable.

CJ

Title: Re: 35mm?
Post by: Marc.com on March 13, 2009, 04:19:47 pm

exactly, it is better to try and lift the inlet port, SR500 inlet valve is mandatory and then also don't forget the exhaust port.

Title: Re: 35mm?
Post by: pancho on March 13, 2009, 10:16:36 pm

thanks for the info cheers.

Title: Re: 35mm?
Post by: Marc.com on March 16, 2009, 04:47:54 pm

the Daytone head is 38mm and is D port with the floor of the inlet port being flat.

I am using 38mm Keihin magnesium body CR carb, tight fit to the frame, cam is megacycle MX cam. Megacycle is good because it is not reground cam so has better ramp angles/