What factors limit the max rpms on an engine?

[RemyCanad]

Originally posted by: earthman
What's the point of all this? Engines that rev really really fast tend not to last all that long, regardless of how advanced they are...how long do you think racing engines last? One race, if they are lucky. My old van can't rev over 4800 probably, but its run for 300,000 miles. In the real world, you need to balance performance with longevity.

I would also like the proof of that. Racing engines in no way can be compared to a normal engine. Your not running pump gas in them. They run for many miles at high RPM..........

 

[earthman]

Every real race car I've ever seen or heard of gets a new/rebuilt engine every race. And how many cars drop out of a race with engine problems? How many dragsters blow the engine 2 seconds into a race? I rest my case.

 

[RemyCanad]

Originally posted by: earthman
Every real race car I've ever seen or heard of gets a new/rebuilt engine every race. And how many cars drop out of a race with engine problems? How many dragsters blow the engine 2 seconds into a race? I rest my case.

What case are you resting? A racing engine is not the same as a normal car engine.... Secondly look at Le Mans. Hmm the Audi car (don't know if theres a name for it) runs 24 hours straight at extreme speeds and puts tons of strain on the engine. It redlines at 10,000 and up. That seems like pretty good reliablity to me.

Secondly I wan't to know of a car engine. Racing engines are totaly different and you cannot use them as examples.

Also you van was not ran near redline that whole time.

Finally how can you in any way compare a dragster? First off are you talking about top fuel? Hmm they make 6000+ HP. They use extreme supercharging. I wonder why they blow up.

 

[Audiofight]

Hahaha

Someone mentioned my good ol' Rotary engine before I could.

There is a good point with bringing it up:

The rotary engine came stock in the mid-80s to early-90s with a 7k or 8k rpm redline (86-88 = 7k, 89-91 = 8k rpm). With a rotary engine, there aren't any valve train limitation factors, plus the rotors spin in circles, thus not putting the strain on the internal components the way a piston engine does (up and down constantly). This allows for a linear power curve. The higher the rpm = the higher the hp rating. Simple as that.

The rotary engine has intake and exhaust ports (like a 2-stroke engine). This allows for higher rpms to be achieved without drastic measures to be taken. With racing rotors (perfectly balanced weight wise), 10k-15k rpm redlines can be achieved with no long term damaging effects to the rest of the block, unlike a piston engine that will see a constant wear on components when trying to achieve 10k rpm redlines.

My rotary engine is 1.3L, 80 cu. in.

It is producing 140 hp right now at bone stock. I know many people with turbo-charged engines in their cars pushing from 200-500 hp in a street driven car, all from the same 80 cu.in. engine. Mine is only F.I.

Where else can you find a 1.3L engine that is capable of pushing up to 800 hp. It has been done, not a streetable motor by any means, open header with a turbo that rivals the size of the entire engine pushing upwards of 40 psi of boost, but it is possible.

The only big downfall of the rotary engine, the EPA was constantly pushing emissions controls down Mazda's throats and forcing more "junk" to be added to the drivetrain to lower emissions and also weigh the car down on top of bottle-necking power as well. Hell, my RX-7 originally had 3 catalytic convertors in line. Now, I am down to one and that one will be replaced this spring with a straight pipe. Gotta love MI's lack of emission controls.

1988 Mazda RX-7 SE
Re-painted 94 GM Torch Red as of 3/02

 

[RemyCanad]

I would so love to have a 1993 RX-7. But they are really hard to find. Let alone get the money for one. (Would get a WRX before anyways)

 

[Peter]

Originally posted by: audiofight

The rotary engine came stock in the mid-80s to early-90s with a 7k or 8k rpm redline (86-88 = 7k, 89-91 = 8k rpm).

Just to put the history record straight, the rotary engine first appeared in production cars in the mid-60s, in NSU models Ro80 and Wankel Spider (NSU to be absorbed by Audi soon after). Citroen joined in 1973 with GS Birotor. These companies had a joint venture motor fabrication. Mazda's own had its debut in 1967.

Excellent site:

http://www.monito.com/wankel/wankel.html

regards, Peter

 

[earthman]

One of the previous posters implied that race engines "ran a long time" at high RPM. Well, I guess, if you call a few hours a long time. The fact is no engine running at high speeds all the time will last very long. Certainly not the normal lifespan of a car.
As for rotaries, this may piss people off, but they are a technical dead end. Rotor tip friction is a serious problem and they just don't hold up well, although Mazda did a great job with them. And I have driven one of the last RX7 Turbo IIs - a great car. Rotary engines in the early days were terrible and in fact put NSU out of business and almost did in Mazda as well. They just wore out very fast. They also got very poor fuel economy. An early Z car would get twice the mileage of an early RX-7. The later ones were pretty bad, too, rated at like 16-17 mpg. Come on, there are 1 ton trucks that do better than that now. And emission controls are there for a reason. We need to breathe someday. Piston engines easily exceed the strictest requirements now, if rotaries are so great, why don't they? And who said taking your cat off gives you all that much more power? It may do the opposite, usually kills your torque.

 

[Mr.IncrediblyBored]

The rotor tips are called apex seals, and yes they broke often on the FD (third-gen) RX-7's. This was in part due to the added heat by the turbos. You can order ceramic seals that hold up leaps and bounds better than the OEM seals - of course, the downside being cost.

high compression + old, crusty oil = extremely hot running temp = broken apex seals


By the way, the Le Mans Audi is called the R8, and I believe there are 3 teams racing with Audi's, and they kicked ass all year.

 

[RemyCanad]

I wish I had one of thoughs audis.

Lets just all drive electric powered cars. (That are charged by some huge solor power thing that I will some day invent. )

 

[TOOCOOL]

Did anyone else ride a rotary engined motor bike that was a trip almost zero vibration

 

[BillGates]

If an engine was made by Harley Davidson, running limits the max RPM of the engine. That is, anytime it is brought above 0 rpm (that is, started), it will careen toward unavoidable failure coupled with poor performance along the way.


* Wait a minute, I thought this was the Lowly Technical forum, sorry guys! *

 

[monckywrench]

You must have been traumatised by the iron-cylindered engines H-D built long ago. Anything from the Evo motors on up is boringly reliable by motorcycle standards. I had over 80,000 abusive miles on my '88 FXR before I bothered to do a valve job on it, and this is typical.
I'm a multi-brand motorcycle mechanic and not a fanboy of any make, BTW.
I do agree they are slow, but they were never intended as sportbikes.

 

[dkozloski]

According to Consumers Report, the Mazda RX-7 rotary engine in its final form before it was discontinued was the most reliable engine ever put in a car. One tenth of one percent of all owners reported engine trouble of any kind, including running out of gas, and the average milage reported when the trouble occurred was 168,000 miles. The president of Mazda loved rotaries and demanded that the troubles be fixed. Early rotaries were plagued by seal failures, phasing gear breakage, and water leakage between the sections. All these troubles were fixed. In retrospect, the biggest cause of seal failures and scored housings was fuel system problems that leaned out the engine. The engine generated high emissions due to the inherent poor combustion chamber shape but could develope 500H.P, plus from 1300cc's. Puerto Rico is the hotbed of RX-7 developement and street legal cars that do the quarter mile in 8sec. have been reported. Technical expertise on Mazda turbo rotaries is limited in the western United States, I found only two businesses that could answer my questions when I had my '87 RX-7 turbo, one in Long Beach, California, and the other in Texas. I know of two brands of rotary motorcycles. Norton built many for the police in England and I think NSU built a small one in Germany. Evinrude built a rotary snow machine. Garrett AirResearch did some experimental work on turbocharged Mazda rotaries and was astounded at the power and durability. They built a streetable RX-7 that they drove at 230MPH on the salt flats in Utah and then drove it to New Jersey and ran the quarter mile in the low 11's in 1988. It was the only car at Bonneville that was driven there from home, back and forth to the motel every night, and that ran over 200MPH. I know a fellow that used to race rotary sports cars. He said he lost all the water out of one during a race aand it continued to run fine and lead with just cooling from the oversized oil-cooler. He finally had to quit, however, when the smoke inside the car got so bad he couldn't see where he was going.

 

[Howard]

Earthman, there's a mantra oft repeated in F1 circles: "If it doesn't break, it's probably too hefty." Racing engines are built so they last a race, not forever. Otherwise, acceleration/cornering/braking/possibly top speed would be affected. Extra weight isn't something you can shrug off so casually.