Big Inlet and Exhaust Valves (+1mm)

[Killerwhale]

My mech RG engineering has done it before and on our enjuns he reckons the gains will be 1-3HP
I´ll pass

[sanddune51]

My mech RG engineering has done it before and on our enjuns he reckons the gains will be 1-3HP
I´ll pass

Killer,
Thanks for your input. I would be most interested to see his results,pictures of the head and the full specification of the engine before and after the big valves were fitted. I am espesially keen to know of the changes to the point of maximum torque due to the bigger valves alone,perhaps I could see the Dyno sheets.When you say our engines,were there more than one and was it/they your engine or his or someone else's entirely?

Oh, and one final thing, if your mechanic has done it before,perhaps you would be good enough to ask him who manufactured/supplied the valves that I can enquire if these are a stock item or made to order. If your mechanic is correct you might have solved all my problems......or not.

Mark.

[Tarwetijger]

Now lets see if I get this right.
Bigger valves mean more oomph, I get that.
But besides the valves itself the cilinderhead needs some serious work;
bigger valve holes (10 times!) and new, bigger valve seats (10x).
Isn't this head work far more expensive than the (now reasonable priced, indeed) valves itself??

[Killerwhale]

Well, i had to wait for 2 weeks for an answer on this. I know his top fuel season just finished and now he travels the last motoGP races.
He will be getting in next seasons race bikes in nov-dec, i know him to well....he will not spill one minute taking out info for an online forum.
But i trust him more than any mech i´ve met and that´s good for me.
I know he made the valves himself, he has all tools and gadjets in his shop.
http://www.rg-engineering.com/

[dandywarhol]

Now lets see if I get this right.
Bigger valves mean more oomph, I get that.
But besides the valves itself the cilinderhead needs some serious work;
bigger valve holes (10 times!) and new, bigger valve seats (10x).
Isn't this head work far more expensive than the (now reasonable priced, indeed) valves itself??

My understanding is that the standard valve seats have enough metal on them to allow a 0.5mm opening each side.

Bigger valves does mean reporting the throats to make use of their size and that's what it's about. Look at it from the other direction - you want more performance and you open up the ports to get more gas in - but you can only get so much gas past the valve - put in bigger valves and you've gone the next step towards better performance. The real skill is getting the modified porting correct - and that's where experience of what to do comes in - the bigger valves are just part of the package.

[sanddune51]

The 3 posts above are great. Thoughtful, insightful and well informed. This thread is becoming a very interesting discussion of the subject.

Bigger valves, especially inlet, do (up to a limit) mean better cylinder filling and thus more power. Bigger exhaust valves can increase exhaust flow and improve cylinder scavenging. This scavenging whilst the ehaust valve is open, not only rids the cylinder of burnt combustion gases but creates a depression (low pressure in the cylinder) that plays a very important part in encouraging the fresh charge to start flowing into the cylinder much sooner than the depression created by the descending piston alone.

The valves in our Trx's and Tdm's were designed and originally intended for the 750cc XTZ Yamahas. Our 850's are now 100cc's bigger(13%), big bore 878cc are 17% bigger and Tdm 900's have 20% more capacity but all use the same sized valves from the old 750 engine. When we modify them by fitting bigger carbs (Fcr's), port the cylinders and fit free'er flowing pipes and silencers all we are in effect doing is encouraging the engine to pass more air (with fuel) through it more quickly. None of that is at all cheap , many hundreds of pounds running into thousands.
This increased air mass still needs to pass though those same sized valves from that old 750 from 1989. Our ports (and indeed the rest of the inlect and exhaust tract) can now easily flow far more air than our valves. The valves are now the pinch point, the weakest link in the chain.

There is no requirement to fit bigger valve seats for +1mm valves. This is why I have chosen this size of valve. The inisde diameter of the valve seat is enlarged concentrically to the sizes I mentioned in a previous post. New multi-angle seats are then cut. The seat cutting I will have done professionally, This is the crucial task but won't break the bank.

As for cost effectiveness, I have done all the work on my cylinder head myself. The main reason is because it interests me it is absolutely cost effective and is engrossing and satisfying. It is not difficult.
To pay someone who will tell you it is a highly skilled job requiring very expensive and specialised equipment will not come at all cheaply.You will be paying his wages and for the overheads for his business and his profits. What are garage/workshop rates these days? perhaps £50 per hour. It can all get horribly expensive.
I believe that an enthusiast who has the skill level to remove his cylinder head strip it, clean it and then rebuild it and refit it, EASILY has the skills to port it fitting bigger valves. I agree though, he may not have the experience in modifying his head. There are no short cuts in gaining experience, just patience, enthusiasm and care.
Until 2 years ago I had never hung wallpaper, but I have often seen the awful aftermath of other peoples attempts. The difference was that I took the time to see how the experts did it. I'm actually thrilled with the results I achieved. The internet has all the knowledge, you just need sort the wheat from the chaff.

I would encourage anyone with the skill to build an engine to have a go especially if you happen to have a spare head in the workshop.
If you are still not convinced this is a DIY proposition bring your bare head down to me and I will be more than happy to spend a day showing you how to do it and the inexpensive tools used. I think we could get the best part of the job done. I won't charge a penny and I'll make the tea/coffee. How about that? I'm in sunny South Kent,postcde TN28.

Mark.

[Mincehead]

I 100% AGREE with Mark on this folks, the valves used by Yamaha are considered undersized by many tuners for the 850cc varients (likely Yamaha simply wanted to use up stocks and keep their parts numbers down which in turn saves money all round in production) and yes, there`s nothing too difficult in prepping a cylinder head to the stage Mark is talking about.
I may well do my own INSIDE my flat, you can never have too much dust and stour in your house!
He`s already very concisely described how he has done his own in previous posts on this thread.
That said I also agree with Mark that the seat cutting should be untrusted to someone with the experience and correct type of equipment and tooling to do it properly.
Valve seats are incredible hard (or they should be), they must be ground using the correct grades of bonded grit type tools, not only to remove the correct amount of material to the correct depth and angles / dimensions, but also to ensure the correct surface finish is achieved too. Blimey having just read that back I used correct correctly 3 times!

You know Mark, I might just make a trip down from not so sunny Scotland to Kent just to have a blether (chat) and get that free tea pal. I would of course expect a biscuit or two as well

[HansJ]

I might also be interested. For starters, i assume these valves will be lasting longer than the Yamaha ones. I also re-call my tuner talking about bigger valves, but i will have to double-check with him if he can do something with my already tuned head before i order some. Completely un-expected, i bought a house last week, with a big in-house garage. The positive about this is obvious, but since it was un-planned, i haven't really discovered yet what all expenses will be in the near future. I'd rather wait until spring, by then i assume i will have full control again...

What are the plans for delivery of the valves and when would you like to have the money?

[Mincehead]

These valves are of a MUCH higher spec metallurgically speaking than the Yamaha originals Hans.

[alextrx850]

the Husqvarna Nuda is an interesting comparison to what is being contemplated here,...while the Nuda is a 4 valver..,not a fiver on the TRX, the origional 798 BMW motor with claimed 86 horses was taken out to 103 horses by raising the compression to 13.2.1....100cc capacity extra ..revised cam profile and 1 mm bigger valves....33mm inlet and 28.5 exhaust, oh and a 46mm throttle body.
I dont know how the 315 degree crank differs to the 270 on the rex, however, the emphasis was on the cam profile..compression and the 1mm bigger valves.

[Mincehead]

Interesting Alex, cheers.
315 degree crank eh? Obvious compromise I would say. It IS a cracking bit of kit for sure:

http://www.totalmotorcycle.com/motorcyc ... da900R.htm

Here folks a good wee read:

http://www.ashonbikes.com/cross-plane_crank

And another for the technophile of internal combustion engines (like me)

http://www.epi-eng.com/piston_engine_te ... issues.htm

Slight thread hijack but hey, it`s all good stuff. Ok let`s get back on track with BIIIIIG valves :

BigValves-A.jpg

I know this shows `simple` two valve heads from V8 car engines but the pictures give those with less understanding some insight into what the thread`s about:

http://www.britishv8.org/articles/insta ... valves.htm

[Mincehead]

Just to keep some balance in views surrounding porting, the pro`s and cons etc, I will add this:

High velocity porting is another method to extract more power, this OFTEN involves building up intake ports and reshaping / profiling them.

To support this view:

http://mototuneusa.com/think_fast_intake_porting.htm

http://www.max-boost.co.uk/max-boost/in ... mework.htm

I`m still choosing the bigger valves approach for all the reasons already spoken of on this thread.

[redkiwi]

I'll put my name in the hat for set. Located downunder, just wondering what the go is on payment? Paypal?

[Mincehead]

I'll put my name in the hat for set. Located downunder, just wondering what the go is on payment? Paypal?

Pm Mark (sanddune 51)

[Tarwetijger]

Okay, first: I'm interested in a set too.

Then: If the valves remained the same over some models, these bigger-valves-set can also be used on TDM850 and TDM900's?
If yes, then the market is just getting bigger Sanddune51!