Why didn't Rotary ever catch on?

Paul Makarucha · Posted: Tue Oct 30, 2012 9:40 am Post subject:

If not on the rotor than the apex seals go on the wall/liner or on hmm, i guess we'll call them the ports. The rotor in such a case is typically not a triangle but more of a "8" shape.

In this case there are two versions of this rotary which do not require apex seals on the rotor itself.

I haven't seen an Aixro myself yet. I've heard one on track but was too busy to go check it out.
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Chris Hurst · Posted: Tue Oct 30, 2012 12:11 pm Post subject:

Paul Makarucha · Posted: Tue Oct 30, 2012 3:23 pm Post subject:

Yeah I'm rather fond of rotaries. I did a quick search but couldn't find any pictures to show what I'm talking about. There are few really awesome designs out there. The one with the seals on the ''ports," The ports are connected to cams that lift off of the rotor to control intake/exhaust timing. With this setup you effectively can have a variable cam timed rotary... awesome possibilities there.

Not rotaries but check out this link:

http://www.popularmechanics.com/cars/news/fuel-economy/6-prototype-engines-to-get-your-brain-firing#slide-1
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Brian G. Wilson · Posted: Tue Oct 30, 2012 3:37 pm Post subject:

Higher rpm's will kill this engine, they have a rev limiter but suggest you never hit the limiter. If you keep it just below the limiter, they suggest a rebuild every 100 hours to replace the ceramic apex seals and the main bearing at 300 hours. They warn if you disable the rev limiter or go above the recommended max rpm's, the engine will produce flying shrapnel.

As far as 298 hours between a rebuild, I guess if the engine was driven easy and well below max rpm's all the time, it would be possible, but not ideal.
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Chris Hurst · Posted: Tue Oct 30, 2012 10:04 pm Post subject:

Paul- Thanks for the link to the article. I'm reading it now, some really interesting engines.

Brian- That is actually pretty incredible and if you think about it the initial hit of $6000 for an aixro would easily make itself up when you think about the rebuild costs on some of the higher end shifter / TaG motors if you were to drive those 300 hours.

Other than the up front cost of the motor I don't see why this hasn't caught on in the US. They seem like a great way to go fast without having to do the maintenance. I've heard they generate a TON of heat, but it's not as if thats the be all end all of why these haven't caught on.

Brian Degulis · Posted: Wed Oct 31, 2012 4:57 am Post subject:

Part of the problem might be that from a cost perspective they are often compared to a TAG engine package I guess because they're single speed and self starting. They should be compared to the cost of a shifter.

Brian

Justin Martin · Joined: 27 Mar 2012 Posts: 331

Exactly! an ICC is $5,500! There are many people that seem to be jut fine buying an ICC and then paying for rebuild costs constantly

Benn Herr · Joined: 18 Jul 2001 Posts: 1584

The problem is three parts.

First, the power band is "wrong" for karting. It has a reasonable bottom end, good mid-range, strong peak power, and nothing past that. You can get away with that on an oval if you pay attention to your gearing. They really don’t like to be over revved. Damage comes quickly (and expensively) if you do that. Some of the UAS guys use them with great success. The big bore 450 single four strokes have the same issue.

Second, they don’t like long runs at full power. That limits their use on the bigger Road Race tracks. Gear the kart so you don’t over-rev and you’ll be on the clutch for a long time. If you can find a clutch that will deal with that kind of abuse. At least the big four strokes come with a gearbox if you’re going to do that.

Third, they make a lot of heat. As in burning through the standard mufflers. And a muffler you will need. Open pipe rotaries are ear piercingly loud.

Then there is the usual marketing hype that is used to sell so many new things to karters. They used it on all the Rotax, TAG, Clone, ICC/KZ, etc.. engines. It lasts forever! Hundreds of hours between rebuilds! It will always have competitive power! Yeh, right. It’s an engine and you’re going to race it. That means you will use it as hard as you can. And that means it will break and somebody (you) will have to pay to fix it.

I suppose you could all agree to run a conservative gear and don’t mess with the tuning. But that’s not really racing is it?
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Justin Martin · Joined: 27 Mar 2012 Posts: 331

Benn, while I agree with what you are saying on some of your points, if you run an ICC past its rev limiter to say 19k or 20K you will surely blow it up too. So how is that even close to a reasonable answer?

Benn Herr · Joined: 18 Jul 2001 Posts: 1584

Justin, While I don't know if an ICC will even go that high, you can spin it well past it's power peak and not experience rapid engine destruction. At that time you pull the lever and catch another gear. The Italians are very good at making engines that can do that.

The big four strokes and the rotary don't tolerate the same kind of abuse. Float the valves a little bit once in a while and it's no big deal. Do it for the last couple of seconds of the straight every lap at your local Sprint track and be ready for a parts bill. Same goes for the rotary.

There is also the problem of having too much power. You can easily fry the tires coming off a corner and that can be a little overwhelming for the non-expert(what a problem to have!).

I like the way it fits on karts and the amount of power it makes for how hard it's stressed. But that's not how we treat kart engines. We always ask for everything engine will give us, and that's the weak point in the system. It's too easy to go from running fast and fine to hard and hurting it.
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TJ Koyen · Joined: 03 Oct 2004 Posts: 1458

If we were running this engine at a national level, we would rev it as high as we needed to go fastest. Benn is right, any engine that is used in a serious racing format will be abused, and all the figures of "100 hours between rebuilds" will come tumbling down. Even if it doesn't need rebuilding, there are people who will spend money to rebuild it, just to make sure it's completely fresh every time they go out.

That's why these karts work so well for trackday type events, and part of the reason it isn't being raced competitively.
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Chris Hurst · Posted: Wed Oct 31, 2012 6:28 pm Post subject:

joseph hollinger · Posted: Wed Oct 31, 2012 9:22 pm Post subject:

Brian Degulis · Posted: Thu Nov 01, 2012 5:15 am Post subject:

Jim McMahon · Posted: Thu Nov 01, 2012 7:22 am Post subject: