In last week’s discussion of the Boneville competition classes we covered what is referred to as the “frame “ classes, namely P-Production, M-Modified, A-Altered, and S- Streamliner. Today we’ll briefly cover the engine classes. Hopefully when we’re done here you’ll be able to look at the hieroglyphics pasted on the flanks of a competition bike at Bonneville and be able to make a bit of sense where it fits in the scheme of things. And maybe even guess how fast it’s likely to go. We’ll test your knowledge at the end.
The engine designations actually tell a fairly complete story of the nature of any particular powerplant. Knowledgeable fans can tell a lot about engine displacement, basic engine configuration, whether an engine is normally aspirated or supercharged, and what manner of fuel is feeding those horses simply looking at the class designation. Here’s a primer on how that works.
First of all, you’ll invariably notice that there is a number in the engine class designation. That relates to the engine displacement class, measured in ccs. There are lots of engine displacement classes, accommodating everything from 50cc tiddlers to 3000cc monsters, and in some classes even larger. Like unlimited! The breaks come at sizes that , to great degree, mimic engine sizes that are found in the marketplace. As an example, all the popular liter class sportbikes fall into the 1000cc class. Hayabusas land in the (up to) 1350cc class and so on. If you bore and/or stroke your Busa to a displacement larger than 1350cc then you’ll jump up to the next larger class which is limited to 1650cc. So, broadly speaking every engine class designation begins or ends with a number. Like this example of a 750 cc Production Class bike.
Once we know the displacement class, we can move on to the three other key “dimensions” to the classification scheme that can discerned from the class designation details. If you were a tech inspector, race official, another competitor, or even an especially knowledgeable fan then you might want to know if the bike fell into one of the pushrod engine classes or was it powered by an overhead cam unit. You might also be interested in whether it was normally aspirated or supercharged and last of all you’d probably want to know whether it was competing in one of the “gas” classes (i.e pump gasoline or something vaguely resembling pump gas) or rather a “fuel” class, powered by something more exotic (alcohol, nitromethane, nitrous oxide, ???) All of those details show up in the class label. Here’s how it works.
Let’s check out the “Fuel” vs “gas” angle first. It’s pretty simple – the “Gas” class bikes get a G in their class designator and the “Fuel” bikes get an F. Here’s an example of a bike with a simple class designation of 1000 M-G. It’s a bike competing in the 1000cc class with a modified frame (the “M”) and burning “Gas” (The “G”.) If this one were running on an exotic fuel like methanol then it would be designated M-F 1000.
Then let’s check out the normally aspirated vs. supercharged . This one’s also pretty simple – forced induction or “supercharged” units get a “B” in their designators, indicating “Blown”. Normally aspirated bikes get no additional designator. Here’s an example of a Modified (and Partially Streamlined) bike in the 1350cc Blown Fuel Class.
Then there is the “Pushrod” designation. This one has some historical roots. If you go back to the inception of the dry lakes and Bonneville racers in the late 40s and 50s just about everything was a “pushrod” motor – Brit bikes, Harleys, Indians. All of ’em. Today , of course, overhead cam engines are the standard by which all are judged but, giving a nod to history, the land speed racing sanctioning bodies maintain separate records for pushrod engine vehicles. While the class records are almost universally lower than the overhead cammers, the competition is every bit as intense. Pushrod motors get another “P” at the beginning of their designators. Here’s an example – 250 M-PG. It’s a 250cc class bike. Modified (but not Partially Streamlined) with a Pushrod engine running on Fuel. Get it?
There a a couple of exceptions to the engine class designations. First of all “Production” engines – the second “P” in that first picture above covers a lot of ground. If it’s “Production” it inherently is a “Gas” class so no fuel specific designation is required, neither “G” or “F.” Likewise , no normally aspirated or “Blown” designator is required – Production is “as delivered” whether supercharged or not. There is, however such a thing as “Pushrod” Production which would show a “PP” along with the engine displacement class. Simple as mud? There are also a variety of thinly subscribed classic and vintage classes that, in the interest of simplicity, we won’t try to detail here.
So let’s try out our newfound knowledge with a couple of test cases.
What have we got here? Like your teacher said, don’t read ahead for the answers!! 😉
This one should be easy. MPS means the Modified, Partially Streamlined Frame class. No? Sure looks like 650cc engine class and Blown Fuel to boot. How’d you do?
How about this one?
Let’s go with the Altered Frame Class, running on Gas. 1000cc class. There’s no PS designator in the frame class so it’s not partially streamlined, rather a “naked” bike and there’s no “B” in the engine designator so it’s normally aspirated. Just about as simple as they come.
Ready for another? How about this?
And here’s one last challenge for you.
This one should be easy too. “P” for Production Frame and a second “P” for Production engine, 1000cc class. Production is Always Gas, and Production is normally aspirated or supercharged according to the way the bike was delivered from the factory. No F/G nor “Blown” designator is required. Got it?
It’s all more than a little complicated and there are a plethora of classes, to be sure. Nonetheless, with just a small amount of study, you’ll be able to decipher the class designations in no time. Want to learn more? Go to the SCTA-BNI (Southern California Timing Association-Bonneville Nationals Inc) website at http://www.scta-bni.org/ and you can order a copy of their rules book and get the whole scoop. Winter’s coming soon and you may need some light reading for those snowy nights beside the fireplace!