Topic: 500 or 550 for bigbore race engine?

[Rod]

Hi - I have a couple of 500/4 engines one of which is race spec, I know very little about the 550. I want to build a full race bigbore engine, will it make any difference if I use a 500 rather than a 550 as the base unit? How big can I go?
Thanks
Rod

[Soos]

You might want to ask paulages....

He has a 550(500?)/650 hybrid in the neighborhood of 715cc's.


l8r

[Rod]

You might want to ask paulages....

He has a 550(500?)/650 hybrid in the neighborhood of 715cc's.


l8r

Thanks Soos - I've found the thread for paulages project and it looks like useful stuff.
Rod

[bwaller]

IF your plan is to roadrace, although you didn't really say that, you'll want to check with the race association to determine which class to run and what the rules will be with regards to engine displacment. Increasing bore will likely put you in a class with stuff that may outgun you, which will mean you'll have to shave even more weight, and bore even larger, and port even deeper, and..... you get the drift?

Otherwise bore away grasshopper!

[kayaker43]

In general terms the 550 had a better clutch. This was mostly due to a better release mechanism and different primary ratio that resulted in less torque through the gearbox and clutch. The 550 also had a better shift mechanism. Roadracing didn't beat up clutches like say drag racing, so either one was OK for a roadracer with moderate bore increase. I ran a 590 based on the 500 cases with no problems.

A cb650 engine is a way better starting point for a big bore, it already has more stroke, and a far better head than even a ported 550. It also has yet another increment of change to the primary ratio to spin the clutch and gearbox faster, again to reduce torque loading. Other small improvements too.

Of course a hybrid can be made too if you don't have to worry about racing rules. Try to use the 650 head no matter what else you do, but then you have to use a 650 header because the tubes are larger.

[hymodyne]

I'd go with a 550 lump if I had it to do over again. I had to sink a bit of $$ into the clutch actuating mechanism to get it back in working order. Plus, parts are easier to come by for that engine.

hym

[turboguzzi]

500's have serious gear forks problems, 550 has the oil pump for the gears = better.

if you are going for AHRMA's sportsman 550 class you cant really oversize.

On bigger classes people are running CB650 based 780cc motors which will outgun you indeed....

TG

[Ichiban 4]

Hi - I have a couple of 500/4 engines one of which is race spec, I know very little about the 550. I want to build a full race bigbore engine, will it make any difference if I use a 500 rather than a 550 as the base unit? How big can I go?
Thanks
Rod

When I've considered going to big bore on my 550..I came up with much the same answers as posted here previously.  Point seems to be..that if you're going to bore-out and/or stroke these mid sized engines..you still have a bigger mid-sized engine.

As much as I love the 550's for their handling and mainly for nostalgic reasons..I've got to agree that if it's HP and/or all out performance you want..then go up to a bigger engine like the 750 to begin with..seems to me anyway.

On other hand..if you just want the best all round, peppier performance from your 500/550..seems like their are many improvements..like hotter cam & ignition, perhaps blueprinting, balancing engine, porting, polishing, et al..that will result in marked increases.  That's what I've decided on for future..if I want to invest that much time, money into another 550 engine.

I have to occasionally remind myself that these are older bikes and engines (technology wise).  So we shouldn't be expecting to get out of them what the newer in-line 4's get..in terms of performance.  Having said that though..I've seen a few big-bore 750's>>850's>>900's that could give a modern crotch rocket a run for their money.

Ja,

Ichi

[Big Bob]

if you are going for AHRMA's sportsman 550 class you cant really oversize.

AHRMA doesn't have a Sportsman 550 class.  And even if it did it wouldn't do any good, Sportsman doesn't allow 4 cylinder machines.

The class for a hot-rodded 550 or 650 is Vintage Superbike Middleweight.  You could do pretty much anything you want to the engine short of nitrous or a turbo.  There's some bad-ass stuff in that class including a real fire breather of a CB 550.

There was a guy at Mid-Ohio last year with a CB 500 that he ran in Production Lightweight.  Against the rules, but nobody protested him.

[turboguzzi]

Hi Bob

Good catch! I meant Formula 500..... this is from AHRMA's rulebook

Cheers

TG

10.3.2 FORMULA 500: Two-strokes and certain four-strokes to 500cc. All motorcycles must be fully GP kitted. The cutoff date is December 31, 1972. Like-design models also are permitted. Among the eligible motorcycles are:

Bridgestone 350 Daytona GTR

Honda SOHC fours to 550cc, DOHC twins to 550cc

Kawasaki H1R, H1RA

Kawasaki 350 A7R, A7RA

JML (Kimtab 429) with wire wheels

Suzuki 500 Titan factory racer, GT380 and GT550

Yamaha RD350 and RD400 (air-cooled models only), TR2, TR3 and R5 based TR replicas

Yamaha TX500, TX500A

[Rod]

Thanks for the feedback guys. The bike is an TT F2 (600cc) 'special' raced in the late 70s and ran a 500 based big bore engine of some sort. When I acquired it in the early 80s it had been returned to a 500cc unit (full race), however it is now classic registered in the UK and because it is a 'special' i.e. non-standard frame it has to run in an up to 750cc group. I don't think there is any issue with me returning it to its original F2 spec (600cc). However, I will need to check eligibility for a larger engine but I assume that as the group is 750cc max this shouldn't be a problem provided I don't use units that weren't available before 1982. I don't know if the CB650 was on the UK market then, I'll need to check.

What that boils down to I think is, option 1) up to 600cc full race unit based on 500/4, or up to 750cc full race unit based on 550/4.

Having looked on the web there are clearly lots of race goodies for the 750, but all the after-market 500/550 stuff seems to have disappeared since I last raced (20 years ago). Therefore your expertise and suggestions are very much appreciated.
Rod

[Soos]

I believe the cb650 was available in '82.

I even think it was out in '79 in the UK, possibly '80... not to sure as I live in the US.
If you are stuck racing with up to 750cc bikes, a 650 mill with 65.5mm pistons gets it to 752cc's, 65mm pistons gets you to 740cc's.
The 65.5 pistons are available from Cycle-X, it's their 850 kit.
The 65mm pistons would be a 836 kit. Both meant for the 750 of course.
However you would need the pistons modified though....
Ask me how I know

A 650 motor *SHOULD* fit your "non-standard" frame, but don't quote me on that, as i cannot view your frame to judge whether or not it would fit.
I know a 550 frame will fit a 650 motor, and have heard rumors that the 500 frame uses the same mount points as the 550 and 650 as well...

Any way you do it, HAVE FUN!!

l8r