wrankin

Exactly. DamonB made the comment earlier that:

And while I see his point, there is also the old adage that "In order to finish first, you must first finish" .

Clearly nobody races to lose. But on the other hand there are a lot of people who race because they enjoy the sport and the competition. If you are a pro, well that's one thing. But if you are club racing then you are out there it enjoy the sport. Winning a pro race means big bucks for all involved. Winning a club race means you get a piece of wood.

Budget is a huge concern for the amateur. Unlike F1 teams, I can't afford to replace my engine every other race. The less I have to spend on rebuilding engines means the more I have to spend on tires, brakes, fluids and fees (and tow vehicle, and safety equipment, ad. nauseum ).

Experience as well as second hand evidence from others all indicates that a properly cared for 13B will last (and stay competitive) longer than corresponding piston engines. A good example of this is from the old (very compeptive) Formula Mazda series. These guys were running open wheel cars with factory sealed 13B's rev limited to 6500 rpm. They suposedly could get 3 good seasons out of an engine without having to replace it, while their piston-powered brethern in other similar series had to replace engines much more often. I heard mentioned on multiple occasions that this reliability made the series very attractive for the budget minded.

Now in the land of club racing you will always have those people will the cubic-dollars to spend to make sure that they have a front running car. C.Ludwig pointed out the BMW examples from ITS. The Spec Miata guys are paying $5k plus the cost of a fresh crate engine for a Sunbelt motor.

But for those who are on a budget, the rotary represents a good reliable platform that is fairly easy to maintain.

See my earlier post. Chris Ludwig or one of the other ITS guys can speak better as to what people are actually running on the track. The class includes Acura Integras, Datsun 240-280Zs, the FC, Porsche 944 and the BMW 3 series to name a few. Go to the SCCA website and download the General Competition Rules (GCR) for the full lists for all the classes.

Good luck,

-b

Nihilanthic

wranklin - what about under boost? :p

I know street 13bs tend to go 50K generally before compression starts to take a decline and need a rebuild, but in race situations its totally different than street stuff - youre on boost almost all the time, making mucho torque, and thus loading the motor a lot more. How long do 13BTs last in racing? I know over boosting = seal goes pop, but assuming you dont knock I mean.

How do most race piston motors fair under turbo conditions? Id imagine the higher cyl pressures would beat up on the cyl rings and the pistons if not oil cooled would get rather toasted up, but you wouldnt need high revs or a wild cam (or wild ramp rates) to get plenty of power with a turbo so the valve train would be happier, as well as your rotating assembly as far as tensile loads anyway (rod bolts).

RotaryDrift

no disrespect, but your a mod and cant even spell rotary right? something isnt right here.

Nihilanthic

can we please not flame here...

C. Ludwig

iTrader: (27)

With respect to piston engines and boost...for a given amount of power the boosted engine will generally be less stressed than the NA engine that needs lots of additional revs to achieve the same power. The inertial loading of the rods and bearings from higher revs is much greater than that of additional cylinder pressure at lower revs. There's a reason so many of the ultra-successful endurance cars have been turbo charged. The NA engines that last at those revs have over-square bores with very short strokes to limit piston speed and thus inertial loading. Those engines, while developing a nice peak HP number, aren't generally going to have the sweet torque spread of a turbo engine of the same peak Hp rating.

The first problem to deal with a rotary is the amount of heat that needs to be rejected. There's that thermal inefficiency again. Listened in on a great conversation Rick Engman was having about the 792 at the Mitty. What little info is out there says the car was plagued with cooling problems from the start. 14 years later Rick is still making modifications to the car to keep it cool for historic events. And that's all NA stuff. Cooling, cooling, cooling. Now throw boost on top of an already troubled situation and the problem is compounded. The total heat load of a 600hp NA 4-rotor will be somewhat similar to that of a 600hp forced-induction 2-rotor. However there is the additional need to cool the intake charge and the turbo is heating the engine oil as well. All those coolers have to fit somewhere. This site is littered with threads on cooling problems and most of the street cars that have issues only see short WOT bursts. Building a FI car to take a 20 minute sprint race, let alone long endurance tests, would be enough to keep the thermal engineers up at night.

Nihilanthic

Nice 1000th post

Also, just thinking about things, I came to a conclusion, and Id like input on if its true or not:
<flamesuit>
The reliability of NA rotaries in race situations is due to their inherantly low compression (9.4:1 max, apparently) and lower BMEP due to thermodynamic inefficiency - they dont produce as high of a pressure and thus dont strain the seals as hard as if they were very well insulated and at higher compression.
</flamesuit>

C. Ludwig

iTrader: (27)

The low compression is certainly part of it. If a rotary could make use of 14:1 compression we'd be doing it and we'd see more common seal failures and heat related problems as a result.

Another piece of the puzzle is that the rotors are only spinning at 1/3 crank speed. Combined with a short stroke even the heavy rotors, relative to a piston rod combo, don't produce noticeable bearing wear. I just got back from my machinists and had a long conversation with him about what I wanted done with an e-shaft that I'll be using in a j-bridge engine that will see constant use at near 10k rpm. A week ago I dropped it off and said I wanted it cut down x number of 1000ths. Today I showed up and he said he knew I'd made a mistake and only cut about 2/3 of what I'd asked for. I told him I was looking for total clearance of y and I already z so I needed x cut down. "But the bearing will wear to give you the total number you're looking for." No... The bearing doesn't wear. Still not sure if he believes me when I tell him I can tear down a 100k+ mile street engine and measure bearing clearance that is the same as the day it left the factory.

Alpine

if rotaries are so great, don't you think more teams would be developing it?? Imo, the best road racing engine is a Honda in terms of reliability to power ratio

C. Ludwig

iTrader: (27)

The development happens because the manufacturers have a vested interest in seeing their product perform and thus become a marketing icon. Audi went diesel with the R10 to showcase their capability in that area. Mazda is the only manufacturer in the world producing a rotary engine so the development falls completely on them. It's hard to make a business case for dumping large sums of money into a program when the net return is so small (read RX-8 sales). It's true that factory backed rotary development effectively stopped in the early 90s and the last 10 years have seen an explosion in terms of piston engine development in terms of power but more importantly reliability. One needs look no further than the marque endurance events that have turned into round the clock sprint races.

I don't think any of us are saying the rotary is the end all engine. It's not. But the original poster asked for it's advantages and in so many words asked those that are tempted to troll to not. Some of us have pointed out the advantages and you choose to troll.

We'll get to see next year how the Honda (Acura) engine stands up to the Porsche in the LMP2 class. Don't forget to check back here next year to confirm that I was right when I say that Porsche will firmly trounce the Acura through the ALMS season next year. Further Honda hasn't exactly set the world on fire with the F1 engines over the last several seasons. Troll, troll, troll....

GtoRx7

iTrader: (5)

One thing that recently has me more interested in further rotary development, is cermet coatings. The 787B had cermet coated rotor housings and side plates. A problem with any rotary is the amount of heat it wastes, and if building a rotary with cermet coated rotors, side plates, and rotor housings, the heat would be no longer transfer as much to the engine, putting less stress on cooling systems. A additional benefit is less drag on the side seals and apex seals, producing more power. And the last gain, is virtually zero wear to side seals and apex seals as well. JHB performs this service, and its not overly expensive, since its proven a race rotary is MUCH cheaper, it could be used to make a turbo rotary with better gas mileage, and less heat, less wear, and more power. Total cost increase would be about $1,500 to do a whole engine. Might be worth its weight in gold to me.
Side note- the aluminum side housings from racing beat are cermat coated, so the wear is next to zero.

carbon man

Yes with most piston engines the out put is lower but in every car that I have measured the centre of gravity the Mazda RX7 FD was lower. When I compare it to a V8 the centre of gravity of the Mazda was a lot lower, and even when compaired to a Porsche the FD was lower. The other luxury most rotories have is with having less weight overhanging the front axle

Nihilanthic

You do realize a lot of that is due to the design of the car itself, right? I mean, how else do the other engines that people put into RX7s still have the same balance?

V8Mongrel

Thanks. I remember this coming up when people ask why there were so few rotary Miata swaps. Lower CofG than a Porsche flat six is pretty impressive. Visually, most 911 engines seem to be at or below knee level!

V8Mongrel

You are correct. BMW has managed to have 50/50 weight balance using looooong straight six engines which are very difficult to get behind the front axle centerline. I think the point is, however, that one can do it with a rotary in a more compact vehicle package than perhaps certain piston engine designs.

I would be interested to see the physical dimensions of a 13B versus some of the more modern 60° V6 engines. I just did an engine swap in a friend's Contour SVT (now a 3.0) and that engine, even with big DOHC heads is a really small, sqaure package. Comparison versus rotary cars is difficult, as most of the 60° V6 engines are installed transversely, a role for which they are particularly well suited.

C. Ludwig

iTrader: (27)

There is a big difference between balance and polar moment of inertia and center of gravity. You can hang and 1000lb iron head V12 over the front axle and have a 50/50 front-rear balance by stacking the same amount of weight over the rear axle. The builder jumps up and down to say it's perfectly balanced but it still won't turn as well as a vehicle of the same weight where the mass is concentrated at the center of the vehicle. The first example has a high polar moment and it's more difficult for it to change direction.

Nihilanthic

I understand what PMOI is exactly. Ive also heard the bowling ball vs barbell (both of same mass...) arguement

But that in and of itself is also to do with the chassis. All swapped motors Ive seen are behind the front axis centerline, either mostly or entirely, in the RX7s I've seen them swapped into. The RX7's design with the front wheels forward and the engine back against the firewall is to thank for that, and the fact that it remains the same with completely different motors in it is a testament to the flexible and effective design of them.

Alpine

I was referring to club level racing, most of us can't afford to race at lemans.

carbon man

the engine on a Porsche is a flat enging bit it is mounted reasonably high in the car chasis and behind the rear axle

peejay

Exactly. Move the axle centerlines around and you automatically change weight distribution. Look at old F/X cars, they went from 60/40 or somesuch to 46/54 mainly by sliding the front axles 5" or so forward, and the rears 15". Or how Porsche lengthened the 911 by a few inches (just in front of the rear axle) in '67 or '68 or thereabouts, partially for a longer, more stable wheelbase, and partially for the increased frontal weight.

Of course, the rear axle's position is more or less dictated by how much interior room you want to have, and the front suspension needs to mesh with the packaging of all the other stuff ahead of the firewall.

For a more contemporary perspective, Ford's FR500 "package" for the SN95 Mustang moved the front axle centerline a few inches forward, necessitating new fenders and etc. but it drastically affected weight bias.

Of course, in the Real World, a car is much more than one or two specifications figures, it is a sum total of a whole matrix of characteristics. Which is why Porsche 911s, with one of the *worst* layouts possible for handling, had dominated racing for so long. The initial layout sucks but hardcore engineering put to that basic problem resulted in good performance. (In not so many words, the 911 is a good car despite, not because of, being rear-engine) Likewise, Subarus, some of the sweetest-handling cars around, have the entirety of the engine in front of the front axle, but the suspension geometry and tuning overcome the basic flaws.

aussiesmg

iTrader: (1)

Road racing rotaries in Australia include:

2 X Australian Touring Car Championships
5 X James Hardie 12 Hour Bathurst wins (in fact every event held)

Then add in the multitude of amatuer racers, rotaries are arguably the most successful cars run in Australia. And this despite CAMS (Austs SCCA) ruling that the capacity be multiplied by 1.7 liters when being classed, add a turbo and multiply by another 1.8.

I raced my 13B BP for 5 years almost every weekend for 5 years without ever opening the engine, just minor tuning and oil. I won two state hillclimb titles and ran in many autocrosses, hillclimbs, HPDE and even a couple of rallycrosses.

Boostmaniac

Dammit dammit dammit, I read the entire thread and you beat me to this.

Just wanted to make sure it was here before I added my tidbit, i knew SOMEONE had to post that.

^Truth, a very important truth.

But basically, what you need to do is go buy an RX7 first and see if you think it would be good for your type of racing. Regardless of the trolling and flaming that has happened here, you have to realize that you came to a rotary based forum and asked if our engines were good for racing. The answer is most likely going to be yes from many of the members.

A good N/A build will last you and make you competitive in your class.

A turbo will last a while if it is well tuned, but will most likely not last near as long as the N/A.

Would I build one to race with? Absolutely. I'd also tear it down and do a soft seal rebuild every year when I was done, and also check my hard seals to see if they need to be replaced, but that is just me and I am **** about things like that.

My advice, try it, i think you'll be pleased.

peejay

You're not **** until you have every piece of your suspension Magnafluxed once or twice a year.

Hmm, that's actually not a bad idea either.

Boostmaniac

That really isn't a bad idea, but I am not completely certain of what magnaflux does. Isn't it just a way to clean the parts? Or does it make them stronger?

tims

Magnafluxing checks for cracks in ferrous materials.

V8Mongrel

Which is why he uses the process to check his suspension members. If the picture next to his name is indeed his car, I can assure you that are no non-ferrous suspension parts on that car from the factory.