10 replies to this topic

[drewpy]

I've a new head coming soon (thanks RCmad) and want to improve on what is there.

 

Will gas flowing /porting the head reap any rewards?

 

I can smooth out the inlets and polish the exhaust but wondered if someone has done a bit more than that?

 

I'll fit viton seals and check/lapp valves as a matter of course

 

thank you

[dandywarhol]

Yes - and chuck in a pair of Kent Yam9 cams at the same time. A mild porting job and cams transformed my 900 - should do the same for an 850

[TDrummer]

I would be interested in the results. 

I asked my machine shop who decked the head, replaced valves, springs, seals and exhaust guides if they would port the head also.

They advised that the porting on the stock Yamaha head is very good and should flow very well as is, no need to port.

 

this news did not sit well with me

I must port

I must

Except I didn't...

[drewpy]

I would be interested in the results. 

I asked my machine shop who decked the head, replaced valves, springs, seals and exhaust guides if they would port the head also.

They advised that the porting on the stock Yamaha head is very good and should flow very well as is, no need to port.

 

this news did not sit well with me

I must port

I must

Except I didn't...

 

I must agree to some extent, but I've seen the TRX guys, smooth the splitter in takes for a smoother flow.
 

I'm thinking either sharpen up those in take webs or smooth them down, still to decide when I have more info 

[howardsmed]

if you relieve the area around the inlet valve seats, and get a really good valve seat job done ( Serdi or Newan single point machine) the head will flow the best it can,

 

if you are fitting Kent 09 cams, you will need to lift the compression up a little, as the Kent cams have later closing inlet timing. if you don't the bottom end power will be abit lacklustre 

 

I angle milled my TDM850 head and ran around 11.2:1 on 95 octane fuel for many years it was ever nice too ride with lots of bottom end power

 

Howard

[drewpy]

Thanks Howard, really useful

[howardsmed]

The Kent Yam09 cams are only a tiny bit more wild than the stock 850 inlet cam. the 850 cam will fit the 900. the exhaust is a similar casting, BUT has a cam position sensor on the left hand end. I will fit an 850 inlet and probably regrind the 900 exhaust too 850 inlet spec

 

when Kent regrind the stock cams, whether its for an 850 or 900 the base circle is reduced a fair bit which requires much thicker shims, not a problem relay a think some Honda ones fit.

 

The Kent inlet cam is not really much that wilder than the stock 850 inlet, they quote their cam figures at either seat to seat which is 300 degrees OR at 1mm lift where it is 240 degrees, the stock 850 inlet is 236 degrees at 1mm.

 

What you are paying for is a quite a bit wilder ex cam profile. I have dynoed an 850 with Kent cams and it picked up 3hp ( just under 5%) at the top end, this is what one would expect as the " under the curve" area is 5% more than the 850 inlet

 

my 900 has had the ecu re-flashed, it runs very well, I dynoed it with stock cans with the CAT removed and got 77.5hp rear wheel. I changed to set of Scorpion slip ons mainly to narrow the back end of the bike, the power has dropped by 0.6hp at 7000rpm ( different day acceptable dyno error) however the one thing that the de-catted stock pipes and all properly set up slip ons bring to the party, is vastly improved throttle response.

 

this year will bring 850 spec cams, re-cut valve seats, and squish properly set up.

 

my 850 which I built 7 years ago is still running with a 0.030''/0.75mm squish and has done 20,000 miles, the man who it is on the TRX 750 forum.

 

getting a 900 to where Yamaha designed it ( what people call blueprinting, but as all design is done on a very complex engine simulation and design program, maybe it should be called CAD-printing now) is relatively easy to accomplish, will yield benefits in fuel economy, part throttle response, and torque.  

 

H

[drewpy]

I've finished the head, just started to strip the bike as taking the engine out for a repaint too, seeing as I have more time.
got the head skimmed smoothed the exhaust and opened/blended the inlets.

had the seats recut and  fitted Viton valve seals

[howardsmed]

The BEST value for money will come from a really good valve seat cut, by which I mean a head shop machine, whether it be a Serdi or a Rottler or the best which is a Newan contour BB. These machines are upwards of £50K to buy

 

you can have the best ports in the whole world, BUT if the co-efficient of discharge ( seat and valve flow) is bad you will gain nothing. ALL the flow gains are within 1/2 inch of the seat upstream and downstream.

 

I build racing XS650 engines and I cannot over emphasis the importance of tight valve to valve guide clearances, and repeatable high quality valve seat cuts. I am achieving 102hp per litre out of 2 valve air cooled twins

 

I use a 5/6/7 angle inlet cut. and a full radius for the exhaust.

 

I can give you list of people who do good work with these machines

 

and ignore the salesman with their smoke and mirrors talk about porting, it only works at WOT anyway.  

 

Howard

Edited by howardsmed, 26 April 2020 - 07:25 pm.

[drewpy]

aye, my machinist is a former motorbike racer and knows his stuff.

 

Thanks for the offer though   

[wicklamulla]

The BEST value for money will come from a really good valve seat cut, by which I mean a head shop machine, whether it be a Serdi or a Rottler or the best which is a Newan contour BB. These machines are upwards of £50K to buy

 

you can have the best ports in the whole world, BUT if the co-efficient of discharge ( seat and valve flow) is bad you will gain nothing. ALL the flow gains are within 1/2 inch of the seat upstream and downstream.

 

I build racing XS650 engines and I cannot over emphasis the importance of tight valve to valve guide clearances, and repeatable high quality valve seat cuts. I am achieving 102hp per litre out of 2 valve air cooled twins

 

I use a 5/6/7 angle inlet cut. and a full radius for the exhaust.

 

I can give you list of people who do good work with these machines

 

and ignore the salesman with their smoke and mirrors talk about porting, it only works at WOT anyway.  

 

Howard

 

 

very interesting reading H.  Do you remember Halco Tuning on the south coast that used to fettle XS 650's with big bore kits and all manner of goodies?  Can we see some pics of your bikes and handy work please? W