YZ444 Questions

Hi Buzz64.
Try this.


http://209.197.247.209/Dyno_runs/SFO_index.htm

An unofficial before and after would be here...

http://209.197.247.209/Dyno_runs/baseline_yzf_+444.htm

thats not a bad answer for your first question!

Bill: you should write that up into a thesis and take it to your local University library!:)

Originally posted by bclapham
thats not a bad answer for your first question!

Bill: you should write that up into a thesis and take it to your local University library!:)

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It is all Riches doing.
He helped me each step of the way from doing the initial research on the yz-f build up to writing up the results.
I was just the willing hands to screw the thing together.

Originally posted by Buzz64



Rich, can you please expand on "but there is more there for the taking."

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I'll give it a try.
Riding a 53rwhp trail bike is a hand full.
I spent a lot of time in the trees when the thing would light up and catapult me into the brush. :scream:

I think more is there but it becomes somewhat esoteric. :think:
The immediateness of the power delivery is very exciting and tiring.
It is one thing to fire road it or run it through Baja, and yet another to just putt through the woods.
I think it really comes down to what YOU want.
Be carefull of what you ask for, Rich WILL deliver. :laugh:

Rich, are you saying that if someone would run a 97mm 13.5:1CR piston using the stock head area, that running a premium gas (93oct) would be an acceptable thing to do. The stock ignition would be used as well.

Originally posted by Rich Rohrich
...but there is more there for the taking ;)

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I don't know that I want any more. I have yet to hit the rev limiter...and I realise that is a rider thing, but it just seems that the power delivery is smoothe when you want and will punch hard as well. Seems very responsive even in a gear high. And all on pump swill! :)
( gotta give a shout out to James Dean as well! )

My woods trial of the bike was...well lets say I need to let another man critique the bike in the forest. But on the track, this thing is everything I thought I would want from a thumper. However, I have no seat time on KTM's. Just a 426 and XR's.

Bill, you and Mr Rohrich both rock. :thumb:

BTW....very nice first post, and welcome, Buzz!

Rich, you are soooo high test.
Build it and break it.
Thats my .02!
Pump gas ain't all that, I pour worse into my generator!

so, is that a yes it will work, or a no it won't work.
Hehehe(the evil laugh of a madman)

Damn thing wont let me add to my post, oh well.
Will the stock LC build more cyl. pressure than the LC that he is running?

Obviously there is more to building an engine than larger displacement. This engine is more powerful than the YZ 450 despite being slightly smaller.

How much of the extra power is due to the larger piston?

I would have loved to see you guys go through a stock displacement engine. Could you have made this much power with the stock bore?

I'm sure that you could get more power out of a 250f. The big question is, who will be man enough(or stupid enough) to be able to ride it. It would be like driving a funny car on a street course. What everyone wants is that huge flat torque curve that is easy to ride fast.

Welcome to DRN! I'll try to answer your questions in an abbreviated fashion because one could ellaborate on each question but that would require me not typing, mostly talking and a fresh supply of Foster's Bitter to lubricate my wit.

1) A high compression big bore raises the torque at a lower peak and that sort of answers question 5. From a riding standpoint its a blast, literally! But the top end goes flat sooner.

2) Go for the 13.5 to one, you're already going through the trouble and expense of doing a big bore, might as well go the full monty.

3) The composition of the fuel is "the 800 pound gorilla" or in your case "the 70 stone qualabear". With a short stroke and a giant bore you need a fuel that burns quick, Rich feel free to beat me over the head with your fuel can anytime here! But generally speaking if you don't change the cam timing you should be able to use a good grade of super unleaded premium petrol.

4) There is no need to modify the cylinder head to accomodate the bigger piston and head gasket because WISECO has already compensated with the crown profile. But there are gains to be had by changing the exit angle or "shrouding" in the combustion chamber to take advantage of the bigger bore.

5) 5-valve heads are inherently limited in peak flow based on valve area and scavenging patterns. The YZF head design is allegedly designed to produce a swirl scavenging pattern at low rpm and a tumble pattern at high rpm. Modern 4-valve heads are tumblers. Rich has fiddled around with larger center valves only and companies like Kibblewhite make oversize valve kits designed for big bores. Another limiting factor is the head pipe diameter, and companies like White Bros and Thumper make oversize header pipes for big bores.

6) Jetting baselines? Thats funny. Once I saw supermodel Elle MacPherson interviewed on an American talk show. The interviewer asked about her newest boyfriend and what pick-up line he used to win her affection. She said "hey bird, you fancy a shaggin?". Right after that I tried the American slang equivalent at the bars but all I got was a black eye! The moral of the story is there isn't a baseline for anything in life, everything is special!