Gas-Flowing Head - .: XT660.com

richardsracingmad · # 1 22-08-10, 08:38

I am considering a gas flowed head, and would like to hear of any success/failures done in the UK.

Any recommended machine shops? (Flow bench set up).

Thank you...Richard

Kev · # 2 22-08-10, 09:11

Off The Road is the only one I know off in that neck of the woods.

richardsracingmad · # 3 22-08-10, 09:31

Kev, there are a few engineering co.'s in the UK with flow benches...I will try and avoid OTR, but thank you for your input mate.

Kev, why did you sell your head and big bore kit? You didn't like it??? I know you are probably more of the sort that likes projects, but surely that was a "keeper"?

dazmatic · # 4 22-08-10, 10:21

I believe Kev had his big bore on his old XTX and sold the big bore seperately when he sold his bike.

Not to mention it also pathes the way for a 2009 XTX big bore.

richardsracingmad · # 5 22-08-10, 10:45

So, its a possibility for Daz's bike too?

I think if you're doing a big bore, you might as well flow the Head....

I would like 12:1 or under compression, not a mega bore, just 700-ish, flat top type piston if that is possible,, and keep standard valves.

dazmatic · # 6 22-08-10, 11:17

I'm a long way off before I start engine mods im afraid.

Quite simply don't have the funds. I do know of a company locally to me though that can machine out the cylinder and possibly plate it so its all possible.
I have other projects I need to attend to first.

I believe a 700 system on these is a 102mm piston? So that would require a 102mm head gasket and if possible, blending of the head to the cylinder.
Thats if you stick to the standard cylinder and bore it out.

If you do like kev and fit a cylinder of a raptor 700, there are a few extra mods you need to do, including fitting a different base gasket.

I'm not sure if its possible to bore the standard 100mm to 102mm without removing to much material, remember, if you start removing material reliability would be degraded but it would make for an easier job unless you swap the liner for a 2mm larger one.

Flat top piston with this style of engine is hard to come by.
The reason a piston would have groves in it is to make room the for the valves. Some cylinder heads are designed so that the valves sit proud of the machined base of the head. Because they sit proud, they enter the top of the cylinder, only by a few MM mind when closed. As the piston rises during its Cycle, it'll come very very close to the top of the cylinder, if it was a flat top, it'd likely collide with the valves, even when closed!
With the grooves it allows for the piston to come ever closer to the valves during the compression cycle, the deeper the grooves the closer it can get increasing the compression ratio.

There are of course other factors to take into account of compression ratio such as the height of the pistion, centre of the gudgeon pin, crank height, con rod length, even the thickness of the valves.

There is a resonable amount of power that can be had from decent head work. I used to have a VW Polo, little 1.3 where the head gasket had gone and struggled to start because of water getting into the cylinder.
I removed the head, took it to work and skimmed off an unknown amount (cowboy, yeehaw!) to remove some pitting, new stem seals and relapped the valves into the seats.
No gas flow, or port and polish. Just a small skim and lapped valve seats!
After refitting the head I took the car for a drive and there was so much more go in it. It picked up speed quicker and red lined in every gear whereas before, it struggled, was like a little go-kart!

Kev · # 7 22-08-10, 12:09

If you are after torque velocity porting shows big torque gains, if you want to build a monster you will need to fit an ignition module as well to over come the 7200 rev limiter.

You can safely bore & re-plate a standard 100mm XT660 cylinder to 103mm, been done already.

I have done the big bore & want more, I have now worked out where & how to get a stroker crank made, it's just the cost of doing it that has put me off, around $1000.00 to get it made + the money to install it. My thoughts are for a stroker crank, 103mm cylinder, ported head with +1mm valves. +3mm throttle body & a 5050 Raptor cam, ignition module, producing a 70+hp XT.

GSR2010 · # 8 22-08-10, 12:12

holeshot racing in northern ireland gas flow heads??,thats who im getting to build my engine when i get the monies together should be the job

richardsracingmad · # 9 22-08-10, 12:34

thank you GSR...I wouldn't mind going to Sligo anyways....lovely part of the world!

GSR2010 · # 10 22-08-10, 12:48

Quote:

Originally Posted by richardsracingmad

thank you GSR...I wouldn't mind going to Sligo anyways....lovely part of the world!

http://www.holeshot-racing.co.uk/ go into engine tuning then motorcross/atv think there in belfast in northern ireland,were ya in sligo before?some nice roads for xt fun wel ya know if your ever passing trough let a man know and we can do damage on them roads i mentioned

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