Topic: CB500/4 Yoshi Specification Data

[kos]

I am looking for pictures, but have had no luck...the guy who had control over the bike and engine is getting ready for daytona so he has no time to look for his photos. Post Daytona we would have some . The valves sizes we ran were 28.5 mm Intake and 24mm Exhaust, Ignition timing was 31 degrees before TDC and we used Elf Pro Moto, fast burning fuel with 2% Oxygen.

Sorry I could not get more info...


KOS

[turboguzzi]

thanks, it's all pretty interesting,

my own little 3D CAD geomtry check shows that with the 500's very compact CC, the pistons would actually need to be slightly dished to keep CR under 13:1.... sort of negative dome, do yo recall if that was the case?

Cheers

TG

[kos]

Let my call and ask my teammate, as he was more involved it the head on this one and I stayed with 750's,. shoot, we ran 5 different bikes at one time back then. I wonder how we did it all, as now I can't remember the difference between a four and a twin!


KOS


PS: I don't like that much compression myself, as it leaves you with serious change in jetting situations, more problems with heat in the engine and more chance of detonation, if carb and ignition settings are not dealt with at each event, each day due to temp, humidity changing. He has the dyno numbers also.

[kos]

thanks, it's all pretty interesting,

my own little 3D CAD geomtry check shows that with the 500's very compact CC, the pistons would actually need to be slightly dished to keep CR under 13:1.... sort of negative dome, do yo recall if that was the case?

Cheers

TG

Got some more details with conversation with my Teammate:

The first and most raced engine was tested on a very conservative dyno, here are the results:
56.8 RWHP@ 10,500 RPM
31.2 foot pounds torque @8250

We did timing sweeps at 36,38, 40, 42 & 44 degrees
Found most power at 40 degrees at TDC

Compression with bathtub head and 4th over OEM Honda pistons was 11 1/2 to 1

We did another head where we  reshaped and made intake track smaller by adding epoxy, but never tested it on Dyno...no time, we were racing, BUT it was much faster.

KOS

NOTE: we found that the more we rev-ed it, the more power we could get, but stopped at 10,500 RPM in the interest of safety... as we had stock rods on stock, non lightened crank. This bike always ran hot and we did not have an oil cooler. Fuel was Elf Pro Moto. Specs: research Octane 106, Motor 91 & R+M/2 98, Oxygen % 1.5, final 115. Lead, g/l 1.0

[turboguzzi]

good to hear some numbers kos,

with 11.5:1 I wouldnt indeed expect too high hp's,

Mine is running at 12.5:1 and makes 61 on a dynojet dyno.

Overall, I think that fin area on the 500/550 was not really meant for racing duties, guess thats part of the reason they tend to run hot.

the two thing that i dont get:

What do you mean by timing sweep? ignition? i thought you run that motor close to 31 degs BTDC @ full advance not 40....

Did those pistons had any squish against the flat areas of the 'tub'?



 

[kos]

good to hear some numbers kos,

with 11.5:1 I wouldn't indeed expect too high hp's,

Mine is running at 12.5:1 and makes 61 on a dynojet dyno.

Overall, I think that fin area on the 500/550 was not really meant for racing duties, guess thats part of the reason they tend to run hot.

the two thing that i dont get:

What do you mean by timing sweep? ignition? i thought you run that motor close to 31 degs BTDC @ full advance not 40....

Did those pistons had any squish against the flat areas of the 'tub'?



 

Yes, to the squish area on side of tub, did direct coming charge up towards spark plug.  And the CR750 ran 28-29 but this engine in it's first form ran timing a bit more. Second motor with faster (smaller)  ports, was less advance but I will have to wait to get those details.

Timing sweeps are the timing adjusted by a few degrees and checked over and over... until you have run the entire range of chosen degrees on each dyno pull.

KOS

[Rod]

Peter - would a 400/4 base be the way to go? I dont know if that head can be made to breath any better than the 500, but I do remember racing against a very quick yoshi/4 in clubmans F2 races (1980s) cant remember if it was 460 or 498.

It ran at the front with the quickest of the 2strokes (mainly RD350s with TZ internals), the rider was clearly talented as well but the bike flew. I particularly remember a race at Mallory in which the yoshi guy and Dennis Trollope (also on a 4 stroke) cleared the field of strokers to take a comfortable 1st and 2nd - that isn't the main reason I remember the race, its burned into my memory because I came last having been lapped by the bastards.

[turboguzzi]

peter, the 400 vs 500 is a question that's been discussed here a few times

Regardles of race potential, first there's the issue of cut off dates, there are 5 years between the 400 and the 500 so depends on the racing body.

there's also the issue of size, tried once the 400 based of a friend and at 6'4" I could hardly fit, 

said guy, (very quick , 2nd in championship) used in some races his 400 based '500' instead of his usual 500-4 and ended going back to the 500 four. bike was fast on slow twisty circuits, could not match the 500-4 on faster ones.

bike was also fragile, after two major blow ups (rods) it was getting on his nerve.....

seemingly, it cant be made ot last unless you go with carillos

[Howell]

For sale in belgium Yoshimura based Cb400:
http://www.kapaza.be/Motoren/Oldtimers/22454100/Honda_Four_Yoshimura_466_cc_racer.html
Specs:
Honda CB 466 cc Four Yoshimura racer.

6 gear, 134 kg , 53 hp abw .
Yoshimura pistons 54.5 mm and 10.5:1
CRS 26mm Keihin's
Cat Cams 245° and 6.5 mm lift
Electronic ignition Kawasaki ZZR 1100 .

[HondaFreak]

Just an update on the 'forgotten 500/4 project'

The attached picture is of the 500/4 being developed by DaviesMotorsport for next years CRMC series and Manx GP. The rolling chassis is complete, using a Reynolds 631 replica road frame weighing less than 8kg. The engine is under development, so I will post some figures once we have run it on a dyno. The complete bike will weigh approximately 125kg when finished and run 4 open megas for The Manx. The only area to be sorted are the carbs as we are waiting on a decision from the CRMC.

The bike will be at Stafford this weekend in the rearmost hall.

Pete

[turboguzzi]

hei pete

thanks for the update, looking good!

frame is replica of what?

125kg? gee, that's like a 500 gp paton.... wow

now they need to milk out of it +70hp and they're set

Keep the info and pics coming

TG

[Sam Green Racing]

Just an update on the 'forgotten 500/4 project'

The attached picture is of the 500/4 being developed by DaviesMotorsport for next years CRMC series and Manx GP. The rolling chassis is complete, using a Reynolds 631 replica road frame weighing less than 8kg. The engine is under development, so I will post some figures once we have run it on a dyno. The complete bike will weigh approximately 125kg when finished and run 4 open megas for The Manx. The only area to be sorted are the carbs as we are waiting on a decision from the CRMC.

The bike will be at Stafford this weekend in the rearmost hall.

Pete

See ya Saturday then.

If I come through the main doors, is it the narrow hall straight across the main one or the back one of the halls over to the left of the main hall?

Sam.

[Howell]

Just an update on the 'forgotten 500/4 project'

The attached picture is of the 500/4 being developed by DaviesMotorsport for next years CRMC series and Manx GP. The rolling chassis is complete, using a Reynolds 631 replica road frame weighing less than 8kg. The engine is under development, so I will post some figures once we have run it on a dyno. The complete bike will weigh approximately 125kg when finished and run 4 open megas for The Manx. The only area to be sorted are the carbs as we are waiting on a decision from the CRMC.

The bike will be at Stafford this weekend in the rearmost hall.

Pete

Look here: http://forums.sohc4.net/index.php?topic=63228.msg874659#msg874659

[CR750]

I'll make an educated guess....

around, eeeehm, let's say... £1850 ?!


 

http://www.daviesmotorsport.com/framekits.html