Topic: 400F big bore question...

[dusterdude]

the best analogy of this is,like trying to build a 283 chevy to keep up with a small block 400.you`re behind when you start.

[mlinder]

I think you could still build a kick ass little bike, just choose the venue wisely when you want to run a Commando or Z1.  You shouldn't be able to look straight ahead and see the finish line.

Exactly. A course with little to no straight aways, you'd be golden.

[Tim2005]

A 300lb 55hp 400f would be a lot of fun, probably not impossible to build but very expensive (you could save yourself a lot of time & money & just go buy an Aprlia RS250, they're about that spec standard and are reliably tuneable to 70rwhp), but I'd definitely like a go on it if you get it built. 400f's need plenty of chassis mods to cope with the higher performance- braking and suspension first - and you do kinda lose something too as if you move to bigger tyres (which is an inevitable temptation) you lose a lot of the feel of the original bike and don't actually seem to gain anything by way of corner speed. Rearsets help, by improving the poor ground clearance, but can be pretty uncomfortable if you're tall like I am. Riding technique is a useful area to gain performance on a 400f... ride it like a 125 motocrosser... keep it revving all the time, above 6000rpm, run smooth wide lines on corners and keep a high corner speed (the stock brakes help there!). Fibreglass fenders, seat base and any non-stock exhaust all save useful weight... and you can sell the stock stuff off at a profit too!

[Pinhead]

Horsepower is all in your head. If you're willing to spend it, you could have your cylinder head welded to add some squish and raise compression, then get custom flat-top pistons. Or you could simply go with custom pistons to the tune of Larry Windmer... Porting/polishing would help, too. Then you'd have to worry about your crank/rods once you get into that kind of horsepower.

If someone wanted to spend the money (read BIG MONEY) they could contact Larry Windmer (www.theoldone.org) and see 1hp per cc of displacement...

http://theoldone.com/components/cylinderheads/Honda/Honda_Pricing_and_Menu.htm

[scunny]

"Riding technique is a useful area to gain performance on a 400f... ride it like a 125 motocrosser... keep it revving all the time, above 6000rpm, run smooth wide lines on corners and keep a high corner speed (the stock brakes help there!)"
had the privelage of doing that on my 500 on the local track, went round the outside of a very useful TZ350 rider on a nice fast sweeping bend. she was all hands on deck, sadly he passed me shortly after as I was left wandering how to clean my waste products from trousers during a race. I love stock brakes

[aptech77]

All is right GG. I dropped about 6K+ to do my 400F right. And still room to grow. 

[bwaller]

GG,
There's an MotorCyclist article I'll dig up & send to you. Mitch Boehm and some buddies built up a CB750 to go vintage racing. In 750 trim the engine produced 80 some rear wheel HP and was quite light also, a real nice package.

As I recall he tells the story of his first race on the thing doing well until out of nowhere being surprised and outbraked into a turn by a smaller bike which then gave him fits to keep up with and you quessed right it was a 400F racer!

Romantic stuff, but as a lot of guys here have said, not something you could have fun with on the street. These street based race bikes with a really narrow power band are all work to ride fast. Go ahead and "do up" your 400, but keep it streetable and enjoy it.

[GroovieGhoulie]

All is right GG. I dropped about 6K+ to do my 400F right. And still room to grow. 

My budget is 10K give or take a couple thou, so money shouldn't be a limiting factor.

Sort of like Yoshima back in the day, I want to do this because it is unique and there are VERY few hot-rod 400s around.  Also to prove that it can be done.

[ttr400]

Don't give up groovie, build that killer 400. In a race situation a worked 400 will most probably out run and out handle the Z1's just like Kaz used to do. But in a drag strip type race the the bigger bore bikes will outrun the little 400 four. I used to race a Honda RVF400 NC35 with about 68 rw HP, when not racing I used to practice on track days with a buddie on a 749R Ducati with a 855 kit motor, he had twice my HP, we had similar riding skills, on a track like Kyalami he could not shake me off his back wheel.  When I was leading I would leave him for dead through the corners and because I had higher corner speed and better drive out of the corner it would take him the whole length of the straight to catch me. the superbike crowd on the blades and R1's used to be pretty pissed when I used to pass entering a corner and they couldn't get it that I could blow there 150+hp bikes away. It was a great feeling to do that.

Kevin

[GroovieGhoulie]

Thanks for the encouragement.

And I sort of apologize for all the threads lately.  There's next to nothing to do around here and being able to use the forums to plan for what I want to do to my bikes when I get back is the closest I can get to motorcycling for right now.

This thread and my other hot-rod 400 threads have been a great source for "brain-food" and things to think about.  Thank you all.  I will keep everyone up to speed on my build, (if they care), and any SOHC'ers in the DFW area are welcome to stop by and check it out.

 

[Tim2005]

Yep, definitely keep us informed about the build. I'm already building a $10k 400f shopping list in my head. First thing is two $1000 400f's, one for the build and another to ride while it's underway!