KevinK2

I don't think SAE has a standard for displacement, but the rule is the swept volume of all the cylinders. The 2 cycle engine's true displacement has "factoring" involved, and is about 2/3 of that value as the stroke is interrupted by the intake and exhaust events. Each face of the rotor is equivalent to the top of a piston, and for the 2 rotor engines that's 6 faces. To fire them all on a 13B would be 6 x .65L = 3.9L in 3 revs of the crankshaft. It's better to just consider 4 firings in 2 rotations, for 2.6L . Piston 4 stroke engines take 2 revs to fire all pistons.

Kevin

KevinK2

"I also found the Rx8 was rated at 2.6L for a current pro race. Just can't find where I saw it. "

Well I found the source, in the 2019 SCCA ratings for GT3:

"GT3 1. #26028 (Armen Megregian) Request for RX7 Turbo/Follow up to letter #25695
Thank you for your request. The 13B rotary has a displacement of 2.6l and is beyond the 2.0l limit for turbo consideration for a GT3 engine ...."

also found a list of 8 Mazda rotaries, including 13B and Rx8 versions:

Engine Family, Engine Type, Disp. (cc)

13B Streetport 2616
13B Bridgeport 2616
13B Peripheral Port 2616
Ren. Street Port 2616
Renesis Bridgeport 2616
Renesis Peripheral Port 2616
13B Bridgeport 2616

Thanks for all of your input. When the 787b won in 1991, displacement did not matter since cars were fuel limited.
Kevin
Admins, please close this thread.

EFINI_RX-7_RZ

The 787B won against faster machines: the much lighter F1-aping 3.5L V10 Peugeot 905 (both entries leading from the start of the race until they retired due to engine problems), the ballast-handicapped 5.0L twin-turbo V8 Mercedes-Benz C11 (all 3 entries taking the lead after the Peugeots retired and only surrendering it after they, too, succumbed to engine problems, the same basic engine previously won the 1989 Le Mans), the winner of the previous year's Le Mans: the ballast-handicapped 7.0L normally aspirated V12 Jaguar XJR-12 (finished 2-3-4), and the already very old but still competitive albeit also ballast-handicapped 3.2L twin-turbo liquid-cooled flat 6 Porsche 962 (best finishing 7th overall, right behind the 2nd 787B). Mazda had only managed a best place overall of 7th in 1989 and 20th overall in 1990 with the 13J, while the other brands (except for newcomers Peugeot) had either won or were runner-ups (Porsche), so I believe it was fair on the FIA's part to rule not to impose a handicap ballast on the Mazdas, especially since Wankel engines were to be completely outlawed from the next year on. You could argue that Mazda's win was mostly thanks to bad luck besieging the Mercedes and Peugeots cars as the Mazdas didn't hold any weight, power, aerodynamics, or reliability advantages against their competitors. Mazda's only advantage was in fuel consumption, begging to question why Mazda didn't use the R26B's second trailing spark plug on subsequent production rotary engines. At the end of the day, Mazda won the 1991 Le Mans fair and square.

EFINI_RX-7_RZ

In 1991, the C2 class in which the 787B competed grouped all the "obsolete" C class cars from the previous years, which included the 7.0L normally aspirated V12 Jaguar XJR-12 and the 5.0 twin-turbo V8 Mercedes-Benz C11. So no, even if you count the R26B as a 5.2L normally aspirated engine it would have fit within specs, although all piston-engined C2 cars were handicapped at 1000 kg while the Wankels were allowed to run at their 830 kb weight. If you do the math, the 787B still had a heavier weight-to-displacement ratio than the XJR-12 even if you use the 5.2L displacement calculation for the R26B. The C1 class were the newer specs cars, basically closed bodied F1 cars running similar to F1 3.5L engines, with no allocation within the rules for Wankel engines. Mazda didn't sneak the R26B in. In fact, Mazda had already been racing the "2.6L" 4 rotor 13J the previous 2 years and no competitor lodged any protests or complaints against them, AFAIK.

cloud9

iTrader: (4)

I'm basically repeating myself but..

"better" is a generous word. It's only considered 'appropriate' to think about the calculation this way with respect to comparing the rotary engine to a piston engine. On it's own, without the existence of any consideration for comparing this engine type against another, it would make no sense to consider a calculation for rotary engine displacement that way. It would be totally arbitrary to pick 4 firings in 2 rotations when thinking about the rotary engine architecture by itself.

That said, I do understand why people do it within the context of comparing it to a piston engine.

From my perspective, the technical debate is whether it's a 1.3L or 3.9L. My opinion is that is makes more sense to consider the rotor housing as the chamber as opposed to the rotor face. Mazda seems to have agreed with that interpretation for 50+ years and that's good enough for me.

KevinK2

Edit: I was later convinced that displacement was not a major consideration at that event, as the cars were mostly limited on the fuel load. But mazda did argue about the added weight they were to carry, getting it reduced a 40 pounds. Displacement may have come up in this regard.

Note: This just corrects the weight reduction Mazda argued for at Le Mans, 1991.

j9fd3s

iTrader: (3)

in a race like Lemans that is competitive (and the last one you car would be legal for), you would argue you case about as much as you can. anything you can do to increase you chances of winning.

Sgtblue

iTrader: (16)

What does SAE say. What were the existing rules. Trying to argue anything else sour grapes.

gmonsen

Really a tiresome subject. Of course Mazda won honestly. Losers complained. We've discussed this on and off for years. Some people really like the 2.6L comparison. Who said it is in any way meaningful to compare piston engines with rotaries based on anything? Displacement is the major thing? Why? You can do it, but is the comparison in any way really relevant to anything? I don't think so, but of course its okay if others think it is. Next we'll see people trying to compare the "displacement" of electric-engined cars to piston-engined cars and so on.

KevinK2

Sgtblue
As I already said, there is no SAE std for measuring displacement. The method is repeated in prior posts.

KevinK2

Nice to hear from one of the original posters, perhaps from the "Big List" days. Back when I argued with some expert who called himself "Mr Wankel", or something like that.

Very simply, Dr Wankel effectively decided to rate his new 4 stroke engine displacement for one crank revolution, while the billion 4 stroke piston engines out there are rated based on 2 revs. If I had a NA 1.8L piston engined car and were auto-crossing against a 13B rotary, I would make sure it was rated at 2.6L, as all racing series do.

There is also the various ratings for comparison, like "power density" , = HP/Displacement

Kevin

Zepticon

iTrader: (1)

There is no such thing as "fair" and "honestly". Unless they broke any rule, they won. That is the whole idea.

1 - Give a set of rules.
2 - Watch the different teams bend, circumvent, overcome and sidestep as many of them as possible with creative and ingenious solutions.
3 - It something is "too good" they ban it the next season.

That is how you force innovation. A competitive environment where any and every idea that can improve your time is worth testing.

GoodfellaFD3S

iTrader: (213)

No need to close the thread....... in the classifieds users in the past have requested to have FS or WTB threads closed once the parts were sold or found. But in this case, this is a community discussion thread. Let the people discuss to their heart's content

KevinK2

Another heavy hitter from the past, Thanks

Sgtblue

iTrader: (16)

OK, since no rules were violated, just sour grapes then.

j9fd3s

iTrader: (3)

i was thinking about comparing piston vs rotary based on chamber size, 654cc chamber is a 5.2L V8, or a 4L v6, so possible, you'd just find out that piston engines are lazy though. most of the time they are not doing any work!

Sgtblue

iTrader: (16)

So was it decided if Mazda cheated 30 years ago at Le Mans with the rotary engine? Do we have Critical Rotary Theory (CRT) settled? Can we move on to something REALLY important …like synthetic oil vs mineral oil. And did MAZDA cheat if it was used in the 26b? Should this Brandon guy go by himself or should we go with him?

TeamRX8

iTrader: (2)

the unfair advantage and racing pretty much go hand in hand …

j9fd3s

iTrader: (3)

there is even a book!
and a film,

ptrhahn

iTrader: (9)

Yeah, I think achieving a "perfect" equivalency formula is sort of a fool's errand. It's just not solvable empirically. So no, it wasn't "cheating" but there's a reason that it was given a bad equivalency formula or outright banned.

No different that trying to figure out the exact equivalency for a turbine engine or 4-wheel drive. The precise amount it would provide advantage would literally be a constantly changing, circuit by circuit, day by day, weather-dependent formula of impossible complexity.

It's in part why racing is going more and more spec as time goes on, and the cars themselves less interesting.

j9fd3s

iTrader: (3)

when we ran PTD and PTE we were allowed a certain weight, and hp (2360lbs, and 136hp) and they would dyno us at important races. the fun part was that the dyno was notoriously um random. so we had a dyno session to be able to tune the hp +/-10 hp, so when we dyno high, we could dial it back. luckily at the nationals, we dynoed low so we dialed in more hp.

there was a corvette at the nationals and they dynoed +10 hp every run for like 12 runs in a row. so it put down like 150hp, 160hp, 170hp, etc. then they put it on the other dyno and it was rinse an repeat

KevinK2

I used to watch SCCA Trans AM races at Summit Point Raceway in the late 80's, and saw the arrival and domination of the Audi AWDs driven by Hurley Haywood and Hans Stuck. The current cars were tube framed V8 race cars, while the Audis were reinforced production sedans. The 2.1L Turbo Audis were a bit slower than the V8's, putting out 500 hp at 44 psi boost, but they could pick any line through the corners, and started winning every race.

KevinK2

As DaveW said "The rules at the time were dictated by fuel consumption, so displacement was kind of moot."

It was only earlier races where the Wankel was misrepresented as being 1/2 it's true displacement. Examples include:

1968-73 Sedans run in endurance racing, .982L Mazda's R100 Small Sedans 10A engine

1968 Mazda wins 84 hr endurance race with "1L" Cosmo 10A engine: Mazda Cosmo wins 1968 endurance race

1990 IMSA GTO Race, the rules put the car in the "over 2.5L" class: 2nd gen Mazda allowed 4 rotor 13J engine
So in this class, they allowed 2.6L, based on 4 x .65 = 2.6L, so they were thinking that the 13B was 1.3L

The 1973 RX3 ran at the mount panorama circuit Australia, and the rotary was rated at twice the Mazda RX3 racing in Australia
rating of the 1.2L engine, from 1.146L to 2.292L, They finally had it right at 2X !

j9fd3s

iTrader: (3)

you need to dig deeper with your IMSA example. the IMSA GTU cars were all 12A's, because the 13B was more than 2.5L....

KevinK2

It was tough enough to cover the examples I did. I gave plenty of examples, not ALL of the examples. In my 1990 GTO example, the engine rating was based on Mazda's low values, with no racing multiplier. Your GTU/GTO examples included the 2X correction used in later races, what year did you look up?