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Author Topic: Maximum Revs?  (Read 3742 times)

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Offline Rod

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Maximum Revs?
« on: July 26, 2007, 02:33:50 am »
I have a road race CB500/4 that was originally built for the I.O.M. in 1978. Its about to go back on the track as a classic after 25 years but I dont know what would be a safe maximum rev limit to use for short circuit racing. It runs lightened pistons (11.5:1), stock lightened and polished rods and a stock crank that has been balanced. At 11,000 it is still pulling strongly and aspiration is no problem, it runs 29mm smooth bores and a Yoshi cam. Clearly I dont want to destroy a good engine, but equally it would be nice to race it to its potential. I've heard and read about some racing CB400s pulling really high revs, but cant find anything on the 500 unit. Any advice would be greatly appreciated.
Thanks

Offline crazypj

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Re: Maximum Revs?
« Reply #1 on: July 26, 2007, 02:39:06 am »
Don't know if this is going to be any help but I have a CB550 with modified and lightened CB750 pistons thats been up to 13,500rpm.
 Stock rods and crank.
PJ
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Offline Rod

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Re: Maximum Revs?
« Reply #2 on: July 26, 2007, 02:50:41 am »
Don't know if this is going to be any help but I have a CB550 with modified and lightened CB750 pistons thats been up to 13,500rpm.
 Stock rods and crank.
PJ

Thanks PJ, that sounds promising. I'm interested to know more about your rig as my bike in I.O.M. spec originally ran a 550 engine bored out but not sure of final capacity. I have considered going this route as the racing class I'll be competing in is up to 750cc. Do you need special liners to use the 750 pistons?
Thanks again.
Rod

Offline Rod

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Re: Maximum Revs?
« Reply #3 on: July 26, 2007, 02:22:20 pm »
Forgot to add that the valve train is also stock but lightened.
Rod

Offline Hockers Choppers

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Re: Maximum Revs?
« Reply #4 on: July 26, 2007, 02:45:28 pm »
I'd say about 500 rpm before it comes apart ;D ;D ;D!!!
The thing about common sense is that, it's not that common.

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Offline crazypj

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Re: Maximum Revs?
« Reply #5 on: July 26, 2007, 10:24:54 pm »
I used a Piper Cam (they don't list it for 500/550 any longer and didn't reply to my queries couple of years back, seem only interested in new inline 4's and automotive stuff) with an S&S race exhaust, about a 20" reverse cone on 4into 1 (not the American company) I think they got bought out by JAMA? from Holland
 You can use standard liners with stock CB750 pistons (they need some turning on tops) If your going further oversize a set of CB650 cylinders would probably be a good idea or maybe just shorten CB650/750 liners and bore 550 block (don't remember how much clearance there is to allow 750 liners) the Honda pistons are way lighter than Wiseco's and seem to hold up pretty good ( although the ring wear is pretty bad, never could get much more than 8,000 miles and changed them at 10,000 (did 70,000+ miles with 591cc 'kit') I think if you fit a CB650 crank and 'kit' its pretty close to 700 cc?
 I remember seeing a stupidly fast CB500/550 at Pembrey. It was almost as quick as Yamaha Genesis 1000 which was new on the market at the time (86~87?)
PJ
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Offline Rod

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Re: Maximum Revs?
« Reply #6 on: July 27, 2007, 01:43:49 pm »
PJ - thanks for some great info. I'll be racing the bike with the 500 unit toward the end of the season and have a dyno session booked next month. That will show if there is any thing to gain in running much higher revs, judging how well it still pulls at 11k I'm sure there is more to be had. A winter build of a 591 unit is definitely on the cards now based on the info you've been able to provide. However the next hurdle will be the transmission, I run an HRC close ratio cluster which is great, but clutch plates dont seem to last long before slippage sets in. I've tried Barnetts but they were worse than OEM in taking the power. Any ideas?
Thanks again.
Rod

Offline ChevelleSSLS6

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Re: Maximum Revs?
« Reply #7 on: July 27, 2007, 06:11:30 pm »
isn't the 500 and the 550 the same engine, with a 2mm bore increase for the extra 50 ccs?
also if I read right somewhere once the 550 has a smoother shifting mechanism than the 500s... is this true for your race bike as well, or did they use 'special' stuff.... or do I just not understand since I'm a sorta-newb? ???

Kids these days... all they do is ask questions and think they know it all... :P
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Offline HondaMan

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Re: Maximum Revs?
« Reply #8 on: July 27, 2007, 07:31:10 pm »
However the next hurdle will be the transmission, I run an HRC close ratio cluster which is great, but clutch plates dont seem to last long before slippage sets in. I've tried Barnetts but they were worse than OEM in taking the power. Any ideas?
Thanks again.
Rod

The Barnett units require some special attention, if they are to be used. The springs must be Barnetts or stronger, the oil delivery holes in the clutch hub modified, and the plates cleaned of the "Barnett fuzz" that they always seem to generate early on.

The CB750 plates with square block corks, or the Yosh version of the same thing, should hold up well: worked in my 750 and 500 roadracers for long periods with no issues. Don't use the ones with the slanted (rhombic-shaped) cork blocks, as they will slip after release until the oil slithers out, unless you install them backward, at which point they won't engage at all, trapping the oil rather effectively in the plates.
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Offline crazypj

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Re: Maximum Revs?
« Reply #9 on: July 28, 2007, 08:17:38 am »
I forgot to mention heavy duty clutch springs, use the heaviest you can without getting blisters or distorting clutch cover. My '550' has done about 105,000 with original plates.
 The 550 moor is better than the 500 in my opinion as it has slightly stronger mainshafts and a dedicated oil pump for transmission, its built into bearing on output shaft behind clutch, not mentioned anywhere you just have to know its there (its why 550 has small oil line connected to pick up in sump)
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Offline malcolmgb

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Re: Maximum Revs?
« Reply #10 on: July 28, 2007, 09:20:19 am »
any pictures of it Rod and where are you planning on racing it?
Malcolm

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Offline Rod

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Re: Maximum Revs?
« Reply #11 on: July 28, 2007, 11:54:16 am »
Hi Chevelle – I’m not too sure about the subtle differences between the 500 and 550 either, I’m on a learning curve. Thanks PJ and HondaMan for the gen on clutches, do the 750 plates drop straight into the 500/550 basket or are mods required? HM I’d also be interested to know what rev ceiling you used for your racing 500. Malcolm, I hope to have the bike ready for the CRMC meet at Snetterton in Sept. I’m waiting for a set of 29mm Keihins to arrive in replacement for some 28mm Dellortos which I cant get to work, wide open is fine but getting the progression settings for partial throttle has me beaten. Once the Keihins are on I can get a new set of pipes, it still has an open 4 to 1 exhaust which is sheer music. Not sure yet whether to go 2 into 2 or 4 into 1, the former should give better mid range, the later for top end. The CRMC post-classic race group is up to 750cc so one argument is push for top end power to close the bhp gap, the other is concentrate on drive out of corners and acceleration as it should stop and turn better than the bigger machines – guys I’d be interested to know which way you would go? Thanks for the advice and interest, I’ll dig out a pic to post.
Rod

Offline Rod

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Re: Maximum Revs?
« Reply #12 on: July 30, 2007, 03:10:27 am »
Malcolm - pic as promised

Offline malcolmgb

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Re: Maximum Revs?
« Reply #13 on: July 30, 2007, 10:13:03 am »
hmm could have done with a bigger picture, my eyes are poor too much ........, anyway it looks a real racer, is that an old TZ750 seat I see?
Malcolm

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Offline turboguzzi

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Re: Maximum Revs?
« Reply #14 on: July 30, 2007, 02:40:47 pm »
hei rod

I am racing a quite heavily modified CB500 in the Italian classic bike championship.

for last race I had at last an electric rev counter fitted and can tell you at last something about revs. the previous mechanical rev counter was all over the place....

I upshift at around 12-12.5 K revs and engine climbs up to that speed very very eagerly.
Stretched it a few times to 13,000 but with my current setup I can feel the power starting to taper off.

there's a lot of work in that engine, look for my threads but in a nutshell:
lightened +050mm stock pistons with a squish band machined around the edge on stock rods.
i run in the 500 class so cant go to 550..... only +050 is allowed
stock valves with s&W springs, stock retainers.
lightened rockers
12620 megacycle cam 25-54 / 54-25
CR 12.5:1 by machining block
28 mm smoothbore mikunis
custom downdaft manifold.
ex-GSXR750 electronic ignition
some really heavy porting

Hope it helps, let me know if you have other questions
+there's a UK forum member racing a cb500, peterc

TG
« Last Edit: July 31, 2007, 02:43:29 am by turboguzzi »

Offline Sam Green Racing

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Re: Maximum Revs?
« Reply #15 on: July 30, 2007, 02:52:21 pm »
PJ - thanks for some great info. I'll be racing the bike with the 500 unit toward the end of the season and have a dyno session booked next month. That will show if there is any thing to gain in running much higher revs, judging how well it still pulls at 11k I'm sure there is more to be had. A winter build of a 591 unit is definitely on the cards now based on the info you've been able to provide. However the next hurdle will be the transmission, I run an HRC close ratio cluster which is great, but clutch plates don't seem to last long before slippage sets in. I've tried Barnetts but they were worse than OEM in taking the power. Any ideas?
Thanks again.
Rod

Welcome to the forum Rod.

Once it's been set up on the dyno you'll know when to change gear. It's no use reving a motor for revings sake.
When you get the read out from your dyno man, look for the point that it flatens out or the power drops off, it's no use reving it beyond that point.

The gear cluster that's in it is probably RSC (pre HRC) and if the person that fitted it could afford a box like that, I am sure the work he's had done to the rods should stand you in good stead to push the revs wherever you need to.

Regarding the clutch slip, have a word with peter c, he's been running one for a while now and should be able to point you in the right direction.

Sam. ;)
« Last Edit: July 30, 2007, 02:58:26 pm by SamCR750 »
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Offline Rod

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Re: Maximum Revs?
« Reply #16 on: July 31, 2007, 09:49:48 am »
hmm could have done with a bigger picture, my eyes are poor too much ........, anyway it looks a real racer, is that an old TZ750 seat I see?

Well spotted Malcolm, its actually TZ350 - the engine is mounted as a semi-stressed member in a TZe frame, with a modified swing arm in order to take a short de Carbon monoshock which is mounted under the seat. In the pic it still has the high capacity I.O.M. fuel tank which I will replace for Snetterton. I'll try and find a better pic to post.
Rod

Offline Rod

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Re: Maximum Revs?
« Reply #17 on: August 01, 2007, 04:42:21 am »
Thanks TG and Sam for some great advice, Sam re:gear cluster, could you tell me who/what RSC is? Also re: previous posts in thread from PJ and HondaMan - do 750 clutch plates fit into a 500/550 basket? Thanks guys for some really valuable knowledge and insight.
Rod

Offline Sam Green Racing

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Re: Maximum Revs?
« Reply #18 on: August 01, 2007, 12:29:12 pm »
Hi Rod, RSC was the forerunner to HRC and stood for Racing Service Club.

I have no experience with the 500s so can not comment about the clutch plates.

Sam. ;)
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Offline turboguzzi

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Re: Maximum Revs?
« Reply #19 on: August 02, 2007, 03:30:46 pm »
Hi Rod

I am currently running stock plates with stock springs preloaded by an extra 1/16" and every thing holds fine even if power should be now above 65 hp (havent dyno it yet)

Fast guys here run barnett kevlar plates.

TG

Offline Rod

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Re: Maximum Revs?
« Reply #20 on: August 03, 2007, 08:13:16 am »
Hi Rod
I am currently running stock plates with stock springs preloaded by an extra 1/16" and every thing holds fine even if power should be now above 65 hp (havent dyno it yet)
Fast guys here run barnett kevlar plates. TG

Thanks TG - as no one else seems to have clutch-slip problems on performance engines, I think I'd better check my steel plates for warping!

Offline Bill/BentON Racing

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Re: Maximum Revs?
« Reply #21 on: September 24, 2009, 04:53:13 pm »
Cool another 500/550 racer,I used a Action Fours 9 plate clutch kit and springs in my Yoshi kitted CB590cc,would and did spin up to 13,000+ all race long,looked down one time thought I broke it and tach(popped out of gear)shifter dragged on track hit false nuetral,didn't see needle,then it came from under tape,tape started @ 14,000 rpm,I think it hit 15,000,Yosh recommended shift pt was 11,500.Had a yosh TT cam and Pop's head,titanium retainers,Yoshima pipe,wt was 372 lbs w/fluids.Going to post some old race pics I found last week. Oh yeah Welcome aboard! ;D ;D,.Bill
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