Topic: CB500/4 Yoshi Specification Data

[HondaFreak]

Does anyone have access to the original Yoshimura tuning data / specs for the Honda CB500/4 K1? My friends and I are looking to race one in 2011 but it would be useful to have a baseline spec to work from. Have seen some data suggesting they put out about 75bhp, but I don't have anything on hard copy. Can anyone help? Any info would be useful....

Many Thanks,

Peter

[Sam Green Racing]

Several members are building 500 race bikes at present Peter, just look at some of the threads.
Where abouts are you in the UK ?
Welcome to the forum mate.

Sam.

[HondaFreak]

Thanks Sam. which threads would you recommend? to save me trudging through?

I am in the East Midlands. It is only a project in mind at the moment until we can establish that you can safely get 75+bhp from that engine.

Cheers,

Peter

[Rod]

Generally figures seem to be around 65 - 70 at the rear wheel, but there is more to be found depending on your wallet.

[HondaFreak]

Wallet is decent size if we can sort out the potential of the engine

[Sam Green Racing]

Check out this thread Peter, Honda only managed 80bhp from the SOHC and that was bored to 650cc.

http://forums.sohc4.net/index.php?topic=37074.msg382765#msg382765

Sam.

[Bill/BentON Racing]

Welcome aboard mate,you will be pushed to get that out of CB500 Yoshi spec engine.I know,I built one or two over the years.My CB590 Yoshi spec motor,Pop's ported the head,all kind of goodies,crank about only stock item produced 60 RWHP.You also said reliable,thats the real challenge.Check my posts on CB590 Yosh kitted race bike.Good luck and keep us posted.If class limit is 500cc,I don't know? Turboguzzi,Paulage,Mike?What do you guys think?,Bill......Paulage has 718cc CB500/550.

[HondaFreak]

Thanks for all the feedback. I am curious that out of a 4 cylinder 500 there is only 60hp at the wheel. We run a 500 twin (500T) at the moment and get reliably get 60 bhp at the rear wheel from that. By 'The Laws of Honda' the mutlicylinder should be capable of producing more; what is the limiting factor with the 500/4? i.e. is weak spot.

[bwaller]

The limiting factor is the 500's cylinder head. That compromised chamber doesn't allow for larger valves easily (1mm at most) so ultimately breathing is the biggest restriction. Some Yoshimura racers of the day used 31mm carbs which seem huge for that head. I would like to see a dyno readout for that engine.

Guys lean towards a 650 head for a better chamber, larger valves and bigger ports as well as the potential increased bore of the cylinder, but this all depends on what class you race and what the rules allow.

[Bill/BentON Racing]

Cycle Guide Dec.'75 CB550F RWHP 35.8 @ 8500 rpm.

[Bill/BentON Racing]

Cycle Guide July '75 CB750F 53.8 RWHP.

[Rod]

Thanks for all the feedback. I am curious that out of a 4 cylinder 500 there is only 60hp at the wheel. We run a 500 twin (500T) at the moment and get reliably get 60 bhp at the rear wheel from that. By 'The Laws of Honda' the mutlicylinder should be capable of producing more; what is the limiting factor with the 500/4? i.e. is weak spot.

Peter - It does seem counter intuitive, but when you look at the CRMC races/lap times there are plenty of Hailwood replicas going round but none of the very quickly. What class are you looking to run i?

[HondaFreak]

Potentially looking at the CRMC 500 class, that new series over 4 rounds. Only potentially. Lots of stuff is counter intuitive about the Honda bikes - like my mate has done the headwork on my 350 twin engine, filled the inlet ports and exhaust ports, as opposed to make them bigger and we are making more power with 30mm carbs than 32mm carbs and with less duration on the cams. Idea on the 500/4 is to weld up the chamber and completely reprofile it to raise the compression whilst staying with a flat top piston - or flat ish. Personally I was hoping to use more lift and skinny valve stems to get the flow into the cylinder and improve in-cylinder filling with porting and high inlet gas speed. I also design exhaust systems and wont be running a 'replica' open mega 4 pipe replica of the Hailwood type - it would be a 4-2-1 with balance pipes to extract the gasses as efficiently as possible - certainly the Honda twins are very sensitive to this and there are big gains to me made simply by fettling the intake and exhaust systems....comments please

[Rod]

Peter as you will have guessed, you're in the right place on this forum - if its been done before, someone on here will have done it or know about it. If you're running in the 500cc aircooled class I see why you feel you need 80 bhp - bloody stinkwheels.

[turboguzzi]

hei freak,

You shouldnt be surprised about the 500t beating the fours, Todd Henning beat even MV's with his crazy 500 twins. But you cant get that kind of horsepower witout plenty of $$$, heavy mods and switching to coil valve springs. getting 60-65 from a four is 'relatively' easy and cheap, managed to do that in my small and not very well equiped garage. 75 rwhp from a 500c.c. CB500 four ? Would love to see the dyno print or just send us a link to the data you saw. Some very smart people here are not getting that kind of number even with 600cc+ motors, so dont believe the all hype you hear / read.

Weak spot in the 500-4 is like some said, the small IN valves, motor can safely rev to 13K but stops breathing well at 10K or so. Solving that would involve fitting new seats at a different included angle, not a cheap excersize in a four pot motor, but it has been done by big Honda in their little known CB500R (a 650 actually). Got the time and money to go into that? The 650 head looks like a interesting option even if not quite vintage legal. It will need special high dome pistons too if you wan to stay 500cc's

Cant see why you would want to redo the CC in the 500 head. Its very compact as it is and you can get 13:1 with a pretty low piston.

Regarding useful threads, too many to list, check some of mine under "racer developement" and "10 degrees downdraft" "small block pride", + posts by howell, TTR, bwaller, benton, mrieck, CB500four



C'mmon, dont be lazy.....  

TG

[HondaFreak]

Thanks for all your help; much appreciated. I will take note about the limits on the inlet valve for certain. My mate has done a lot of work even on current 600's with combustion chamber shaping - I will post the link to a forum thread about the Integra R engine he built with totally reshaped chambers. Looks 'mint' when it is complete and made significant torque increases esp off v-tec - The idea would be to make more of a bathtub shaped head like the USA guys use in their 2v V8 heads, with significant squish and get pistons made to match.

Who is making the best 'off the shelf' kit for racing the 500/4's? Any one offer a good package or is it a cam from here and valves from there? etc etc.

[Sam Green Racing]

Try this out Peter.  http://www.dynoman.net/bikepages/cb550/index.html

Don't forget the import duty though.

Sam.

[kos]

hei freak,

You shouldnt be surprised about the 500t beating the fours, Todd Henning beat even MV's with his crazy 500 twins. But you cant get that kind of horsepower witout plenty of $$$, heavy mods and switching to coil valve springs. getting 60-65 from a four is 'relatively' easy and cheap, managed to do that in my small and not very well equiped garage. 75 rwhp from a 500c.c. CB500 four ? Would love to see the dyno print or just send us a link to the data you saw. Some very smart people here are not getting that kind of number even with 600cc+ motors, so dont believe the all hype you hear / read.

Weak spot in the 500-4 is like some said, the small IN valves, motor can safely rev to 13K but stops breathing well at 10K or so. Solving that would involve fitting new seats at a different included angle, not a cheap excersize in a four pot motor, but it has been done by big Honda in their little known CB500R (a 650 actually). Got the time and money to go into that? The 650 head looks like a interesting option even if not quite vintage legal. It will need special high dome pistons too if you wan to stay 500cc's

Cant see why you would want to redo the CC in the 500 head. Its very compact as it is and you can get 13:1 with a pretty low piston.

Regarding useful threads, too many to list, check some of mine under "racer developement" and "10 degrees downdraft" "small block pride", + posts by howell, TTR, bwaller, benton, mrieck, CB500four



C'mmon, dont be lazy.....  

TG

Todd might have spent a small fortune to have others build him cylinder heads like Kenny Augasteen and Kevin Carmeron for his bikes, but he did not beat factory M's... closest he got was Daytona 1999 where he finished a distant second to Franco Bonera on the factory 3 cylinder MV, and our M3 CR450 replica finished third. But, we all did BEAT all of those british single cylinder replica G50's & BSA's that cost a minimum of 50K! We felt good.

KOS

[Sam Green Racing]

Plus Manx Nortons. 

[kos]

Plus Manx Nortons. 

Yes, that day was up and down, as we had just debuted out F2 big valve head, max compression CR750 with disastrous results. Our primary drive issue rared it's ugly head. built three engines in two days only to have it all right again in final last chance race of AHRMA Daytona event when out rider Adam, came in running on three cylinders, All that taking of the tank on and off due to engine rebuilds andinstallations ..we had knocked a spark plug wire off the dyna coils. Shoot, Adam was so good at not hurting the bike or engine he decided to come in...but he was still a half a lap ahead of, one Todd Henning and could have won the event on three!

But, then later in 500 Prem we beat all those British 500's including Cronshaw and Mooney!

KOS

[Sam Green Racing]

I didn't know John was still riding, he must be about 110 now fast Goldie though if you can call it one.

Sam.

[turboguzzi]

I didn't know John was still riding, he must be about 110 now fast Goldie though if you can call it one.

Sam.

Sam, you are worse than me, that was 1999....

That said, John came to Italy last years and got spanked too  (so he still rides)

Lea Gourlay on the other hand, gave everybody a 2 sec a lap lesson on the 500 paton... some rider

My own memory must be playing tricks, thought I rembered todd beating an MV once or twice, but I am old and senile by now  (and i wanst even there.).

Back to the subject, I am tempted to give the 500-4 the title of "easiest vintage  4stroke to get 65 hp from"

Freak, nice idea about the bathtub thing, but I dont think its very relevant to a 57mm bore. with a thin 7mm sqush ring spark timing can be already very late' like 30 degs or less. I tend to think that a Bathtub approack is much more relevant to 400cc + pots, with bores more than 80-90mm where fast burning is critical. my 0.02

[kos]

I didn't know John was still riding, he must be about 110 now fast Goldie though if you can call it one.

Sam.

Sam, you are worse than me, that was 1999....

That said, John came to Italy last years and got spanked too  (so he still rides)

Lea Gourlay on the other hand, gave everybody a 2 sec a lap lesson on the 500 paton... some rider

My own memory must be playing tricks, thought I rembered todd beating an MV once or twice, but I am old and senile by now  (and i wanst even there.).

Back to the subject, I am tempted to give the 500-4 the title of "easiest vintage  4stroke to get 65 hp from"

Freak, nice idea about the bathtub thing, but I dont think its very relevant to a 57mm bore. with a thin 7mm sqush ring spark timing can be already very late' like 30 degs or less. I tend to think that a Bathtub approack is much more relevant to 400cc + pots, with bores more than 80-90mm where fast burning is critical. my 0.02

A few things to cover here... First Patton used today are not even close to their original design as they made them up now with 4 valves per cylinder and they never raced in the day... that way. I am not sure why the British, and Europeans have to change history in that way. They still are mad that Honda came over and kicked their arsses!...I suppose.

Secondly...bathtub chambers work on any size chambers..we had great success with "tub-ing"our M3 CB500 based racer from 1997-2000 in AHRMA but we could not beat the Yamy RD350 derived two strokes on the big tracks. Just too much port area and a lot lighter, but occasional they would do "the two stroke thing" and blowup sometimes moving us up two places to get on the box at Daytona!

Also, Robert Yates of Yates Racing Engines, the developers of the latest NASCAR Ford two valve V8's has lead most builders down the road of almost flat pistons tops, small bathtub chambers, smaller than normal valves and not that large of ports to be the HP king in that group of BIG engines. He gets very early late ignition timing numbers, as there is NO dome to have to climb over with your intake charge.

Note: probably the WORST bore stroke multi valve combination ever made?  Yamaha 5 valve. That engine need almost 47 degrees of spark lead just to get it lit off in time to make any power. Have you noticed they never used 5 valve tech in Moto GP, new YZ450 motocross bike and even Ferrari quit trying to make it work. When Mr Gotto came over from Honda GP car team and joined Ferrari, after Honda quit at end of V12 & V10 era...the first thing he did was to s**t can that idea.


KOS

[HondaFreak]

I have attached pics of my mates work, which he couples with small ports an reshaping. Probably try it on the 350 first, valve angles permitting. Good to hear of the CB500 sucess with bathtub head. The other thing Ineed to consider is a spec if we were to run it at the Manx. There it would be very hard work against the GSXR Paton and the 125K MV....but we all love a challenge
Thanks for the links to US site too; very useful to see what is around. Of the cams, are most based round the Yoshi spec profile? Is anyone making a 'high lift cam'?

[turboguzzi]

kos, we are still waiting for a pic of those bathtub 500 heads!

my current pistons hardly have any dome, so its hard to believe the little there is is getting in the way of the flame path.

got the feeling on the other hand that the closer proximity of the re-shaped "tub" surface to the perimeter of the valve's head does something good to the flow.

what size valves were you running on those "tub" 500? ignition advnace?

have some 3D files here from the time a vintage racer asked me to re-design a G50's head to bath tub config, so maybe I can just scale down the dimensions...

BTW, they did use the 5-valve in the first generation of the 990 motogp, they went back to four valves (and cross plane crank) only when Valentino arrived to the team. Guess that Jeremmy Burgees told them to get rid of the stupid head ASAP,