It does seem obvious if not spelled out, that punching the jug and stroking the crank would in most cases grossly exceed the limit “intended” in the rules. If the intent of the racer/builder is to exceed the intent of the rules, they will do so regardless, and who the hell will know in any case. Is there a pot of gold at the finish line? Paul.
Where “displacement” is specified it does tie the bore and stroke together. If you increase the stroke you can’t bore so much without exceeding the displacement limit. Stroker cranks are harder to come by then bigger pistons, so I don’t think we will see any strokers. Could add “Stock stroke required” to eliminate all doubt. Only problem I see with “Cylinders may be overbored to give a displacement of 5% over the class limit” is that the “class” doesn’t have a single limit. Possibly “specified limit” and the example of 750=787.5 would work. Anyway, it seems the Yamaha is to be treated like any other 750.
Please post it here if you come up with different wording. Our meeting of the rules committee is mid January. It would be nice if we could agree on the same wording and that the wording removed all doubt from what is meant.
As far as the cheating is concerned, I think there are many out there that want to take advantage of the rules without breaking them. 5% more power on that long uphill straight at Mosport would be great, especially if it is just enough to keep you even with the guy that used to pull away from you there.
Bruce Richmond USCRA #66
While Bob Coy and Paul Whittaker(who"s son Al raced with me) make some good points about class equilibrium ,I respectfully say you are killing the shade tree guy aka Rudi Kurth,Jock Taylor,the Renick Konig etc , C’mon guys you didn’t invent the sidecar,s This shit was and is excitibg,the 70’s were a period of amazing guys and innovators ,someday it won’t be all overbored 650 twins Btw I’m retired and as such have no vested interest in this class,tho I do have some period 3 trophy’s for a class that no longer seems to exist,I’ll send anybody a picture of Rudi Kurth"s machine from 1974 if they will post it…Respectably Gord
Hi Gord, P3 does exist in VRRA and I assume would be allowed to run with SRA? should they turn up. However people writing the rules cannot make racers built/buy bikes, get them to the track. In the years since VRRA’s P3 rules were written by a member/s? of the SRA, only one P3 had been out up until this year when Clark was joined by Pierre on a Rotax powered rig, for one race. Clark and the GT750 has been to several events over those years. The old adage of use it or loose it is still true today and that was the start of this thread.
By the way what makes you retired? I consider a racer retired when they are in a box. Paul.
Speaking from a professionnal point of view : you don’t need to look for the underlying “intent” of the rules if they are clear. A clear solution would be to just speak in terms of maximum displacement allowed instead just speaking of bore. If we want to allow overboring just so people could make their engines live longer, then we should just allow overboring and disallow stroking. As simple as that.
This stuff is more important that it may seem to some, but believe me, when you work hard all lap to pass someone and then he just flies by you on the Andretti Straight (cause he’s got a better engine and/or because he’s not a 210 pound windjammer like myself), it can get pretty frustrating…
That makes sense to me…I told with certain engines in P4 it’s exceptionally easy to mix parts, change the stroke and get way larger displacement…I also argree with what Stan said, the 5% overbore over class displacement makes sense.
Hi Francois, Wouldn’t it be nice if everything was as clear as that. Unfortunatly writing technical rules that everyone will interpret the same way, especially when as racers and tuners we are looking for some legal advantage, is very difficult. That is why I believe the intents of the rules need to be published with all of the rules. Some of our rules seem odd when read 25 years after the fact. The oral intent fades with time with some of this stuff as members leave or pass on.
The overbore rule as written now allows any engine to be bored to the class displacemen limit plus 5%. Lots of people have taken advantage of this rule to increase performance and they are completely legal as the rule is written. As far as stroking goes you are allowed any internal modifcation (except P1 CB350s) that makes your bike go faster. The trouble with the way the rule is stated right now is that if you were protested, found to be at 5% oversize in displacement with a stock size bore and longer stroke the bike would probably be deemed illegal by the inspector. The language around this rule needs cleaning up to prevent misinterpretation. Rick and his crew should be easily able to take care of that.
You have raised valid points in this discussion and I agree with you and your solution. It sounds good to me.(especially the windjammer bit-I understand)
Hoping for clear rules is like hoping the Leafs will win the Stanley Cup.
Merry Christmas eh!
Paul
I have a question which my not directly relate to side cars, sorry.
With the rule
Should “class limit for engine configuration” be worked into that statement? I ask this because most classes have mixed engine configurations and each configuration is allowed a different displacement. So P3 light for instance allows V twins to 650cc but 4 cylinders to 550 cc. I do not think we want to allow the 550s to be 5% over the class limit 682cc. If the intent is to allow 5% over the class limit of 650cc then I need some bigger pistons. Can any one clear this up?
Cheers,
OMG!!!
Firstly, this comment has nothing to do with Sidecars. I like them, if the funds, time, knowledge etc. were available, I (we) would have one.
My point, given the (a) speed differential in classes and (b) utter confusion over the rules, clarifications and our recent vote. Is someone truly going to tear down my motor and break out the internal micrometers and depth gauges to enquire if I have spent too much in a machine shop?
If anyone truly feels they need to spend thousands of dollars on their motor to build it to their “interpretation” off the rules in order to claim a $25 trophy, good on them.
I voted with the best intentions off my knowledge to help keep / get bikes on the track, apparently I was wrong in most cases. Now we are going to do battle over what crank / piston combination we can run? Will this ever end I ask myself?
If it’s on the track, leave it alone. If it’s in someone’s shop, let’s work together to get it out on the track. Let’s stop whining over a chunk off aluminium that I could have machined as an apprentice over twenty years ago, where someone wants too stick there pipe! Or what size hoops you wear on your ride. Last time I checked they were all round with black sticky bits on the outside.
If anyone needs to know, my ZX7 is completely stock except for the pipe and shock as far as I or the previous owner are aware. In fact, looking at what is exposed of the gaskets, I don’t think anyone has been inside the motor.
Then again, why would you need to? It’s a Kawi!!!
Let the protests fall where they may. Ride it and beg for forgiveness.
Back to the Eggnog!
Regarding stroke & bore…
This is how it is addressed in the AHRMA rulebook
9.7 MECHANICAL REQUIREMENTS FOR VINTAGE CLASSES
Rule 9.7.2 ENGINES
c) Allowable overbore is a class’s maximum displacement plus the following limits, or
the specific machine displacement, as in the performance-indexed classes (such as 200 Grand Prix and Classic Sixties 650): Cylinders may be bored to a maximum of .080”, singles; .060”, twins; .040”, triples; and .020”, fours.
To determine displacement limits, .080”, .060”, .040” and .020”, as appropriate, shall be subtracted from the actual
bore prior to calculation.
Note: These limits do not apply to Class C and Pre-’40 classes, which have a maximum overbore of .080”.
d) The formula for calculating engine displacement in any class is:
Bore x bore x .7854 x stroke x number of cylinders.