SIPSOIL

Some food for thought...

A new 350ci/260HP Engine is $1500 here: Chevrolet Performance 10067353 GM Goodwrench 350ci/260HP Engine & Packages

A new RENESIS engine is $6000 and I believe that for that amount of money even a small group of twenty buyers can have a s***load of parts made for a dozen engines - each.

Car manufacturers do not have the objective to build disposable engines that have to be replaced after a few 100 hours of operation, however the advantage of Wankel engines is that they are simple and should in principle be dirt cheap to make, especially if they haven't been designed to last as long as piston engines.

Operating cost at $4/gallon of gas and 20MPG is $0.20 per mile, so an engine core that lasts 10000 miles and costs $500 adds only $0.05 per mile driven.

Suggested reading:

foxed.ca/rx7manual/manuals/REbyKenichiYamamoto-1971.pdf‎
foxed.ca/rx7manual/manuals/REbyKenichiYamamoto-1981.pdf‎

Dear mods: Maybe we could have a separate section discussing everything Wankel engines. I know there are (many) other places, but I suppose most people who own a car with a Wankel engine will own an RX-8.

Flame away!

RIWWP

iTrader: (2)

no flaming permitted here, but many may disagree. The new price you quoted is misleading as there are no 'new' Renesis engines left. Remans have a list price of $2,001.

I believe that the cost of making your own internals is going to be far higher than you think. Tooling costs...

Posted From RX8Club.com Android App

bladeiai

iTrader: (1)

I'm not sure I understand the point of this post? You are suggesting we get together and make our own internals?
We should put cheap Chevy engines in our cars? I am not trying to flame you, I'm just not entirely sure what you are getting at...

alnielsen

iTrader: (4)

This isn't a project for a new owner. So, I'm moving it to the appropriate forum.

The Chevy engine may be cheaper, but the total cost will end up being much more. Plus, you will be without the use of the car for a couple of months.

RIWWP

iTrader: (2)

Al, I think he is talking about building rotary engines, not the Chevy engine.

alnielsen

iTrader: (4)

I guess his intentions are unclear.

RIWWP

iTrader: (2)

I can agree with that.

SIPSOIL

You're absolutely right if one were going to make the engines the way manufacturers like Mazda do it. Tooling costs per unit drop rapidly when one makes thousands of parts. However, manufacturers also want to keep cycle times as short as possible. For example, if the goal is to make 100.000 units a year, even a 24/7 production only allows cycle times of 5 minutes and a labor-intensive meticulous tweaking process that takes several hours doesn't fit the "one part flow" philosophy.

Peripheral porting allows very large ratios of bore to stoke with wide housings and rotors. The chamber could be made from elastic sheet metal with frames spaced every 15mm or so. Cooling would necessarily be circumferential, which has the benefit that we can directly pass coolant from hotter to colder areas. The wider the rotor, the less important is sealing the sides and corners.

In theory, mechanical pressure (e.g. with bolts) to certain points of the frames should make the spring steel sheet behave like a cubic surface spline.

The error of a cubic spline is smaller than 5/384 * h^4 * f'''' and an epitrochoid with moderately low eccentricity is already very smooth (f'''' is small). For illustration: squashing an elastic at two equidistant points, i.e. opposite sides, already gives us a figure-8 and the error decreases 16-fold when we double the number of points), so an 8-point spline gives us 1/256th of this (already low) error.

The rotor could be constructed using similar techniques, the framing could be offset, forming a screw which moves oil through the core, possibly replacing the oil pump.

The e-shaft could be constructed from two pipes with 6 bearings (two for the rotor, two for the shaft itself and two to keep the sides of the combustion chamber in place) . For balancing, the inner pipe could be weighted on the inside, opposite the rotor.

P.S. In case my intentions were unclear clear: if we can get a 500lbs engine with block, crankshaft, 8 pistons, 8 connecting rods, 12 bearings, 2 cams, 16 valves, carburetors, etc. for $1500, then we should be able to get a 200lbs rotary engine with 1 rotor, 1 housing and 1 eccentric shaft for much less than that.

RIWWP

iTrader: (2)

I don't think I can adequately convey the number of problems I see with your idea.

Strength of materials, heat cycling, Mazda's proven results with various aspects of various iterations, the width of the Renesis rotors/housings already being too wide, peripheral ports can't meet emission requirements, lubrication needs still exist, etc...


Math is great, but real world results shouldn't be discarded. Don't forget the thermal dynamics, chemistry, etc... of the rest of what happens with multiple fluids, temperatures of condensation and boiling, heat saturation, flame fronts, heat cycling, etc...

Carbon8

iTrader: (4)

Supply and demand, you can't compare the price of a GM V8 to a rotary engine no matter how hard you want to.

If you don't understand that, I suggest opening up an introductory to economics text book.

SIPSOIL

It's been a long time since I opened up an introductory to economics text book. I gradated Dipl. Volkswirt in 1999.

If you don't understand that marginal unit production costs do not equal retail prices, I suggest you work on your functional literacy. If the goal is to make your own engine (hint: thread title!), would you attempt to make a single rotor Wankel engine or a V8?

P.S. If one wants to have a couple thousand units made to spec, alibaba.com and kickstarter.com are your friends.

bladeiai

iTrader: (1)

You do know we have 2 rotors right? Also do you have any idea what it cost to R/D an engine? Especially a rotary engine? Carbon is right about the economics involved, you are comparing apples to snozberries.

SIPSOIL

difficult =/= impossible

Practically all of which is addressed in Kenichi Yamamoto's book (which you have read or at least have skimmed through, I hope). However, today we have almost unlimited access to E85 and significantly more capable electronics. For example, optimal A/F ratio and injector timing can be determined by knowledge of the shaft rotation gradient.

Sound like fun!

bladeiai

iTrader: (1)

This is true, with a few hundred thousands of dollars (and possibly millions after reading your posts) I'm sure you could build yourself a very nice engine that would work as well as a well build $10,000 Renesis engine.

Carbon8

iTrader: (4)

He's not getting it, subbed for the amusement I guess.

RIWWP

iTrader: (2)

I think it's more that he just finds the challenges trival.

I wish him the best. Maybe he will make it onto Mazda's rotor development team and we will have figure 8s instead of doritoes.

SIPSOIL

I have no idea, I have never R/D'd an engine before. But neither have you or Carbon8.

However, I did spend a day researching papers on epitrochoids. It appears that even this very limited amount of knowledge makes me the expert among the three of us.

So far the total cost is $0 + the cost of figuring out who's going to be on my ignore list, which is approximately 30 seconds/ignoranus.

RIWWP

iTrader: (2)

Sorry if our skepticism shows a bit when you talk about making a rotary out of sheet metal.

FazdaRX_8

iTrader: (1)

you want to get the people who make the parts together

aluminum rotors and titanium rotors have been done, aluminum side housings are being sold today. E-shafts have been machined custom too. some folks/companies have worked on the rotor housings. the problem is all these company's are small and secretive.

the high prices of stuff and scattered locations of shops have led to a lot of DIY and figure it out yourself mentality in the rotary community.

if some rich person purchased all the shops and had them work together there would be a "crate rotary engine" but for now I can't see it happening.

as far as new motors you can sign up for mazdaspeed racing or something and get engine parts with a hefty discount. still a reman at 2k with a 1k core exchange is hard to beat

Carbon8

iTrader: (4)

Since when does theoretical knowledge ever directly transpire to real word results

Spout your derived theory all you want, without the real world results its just banter

Under derived theory the rotary engine was perfect 40+ years ago, thats been proven to be quite false to todays standards.

Apparently your 1 day research unearthed some knowledge that eluded Mazda's top engineer's for over 40 years

bladeiai

iTrader: (1)

Unfortunately some of us are burdened with living in the real world where we read your idea for building an engine and wish to steer you away from wasting your time and money.

I you want to talk about the idea or theory of such an engine being designed/constructed that is fine, but that is not what your title lends to your intention. "So, you want to build your own engine..." It bludgeons through the vision of a mad scientist in is garage/basement/methlab constructions some ridiculous monstrosity that he thinks is both ingenious and world changing just before he cranks it up and blows himself to pieces.

In your self-discovery of the incredible genius that is you, did you ever stop to ask "did anyone ever consider my stupid idea before me?".
The perception of genius without humility is worthless.

SIPSOIL

Yup! All you need to do is draw the right conclusions from what you just wrote.

Mazda's top engineers have put in a lot of effort over the last 40 years, yet no Mazda Wankel is currently in production. Do you think the engineers are incompetent? Do you think they enjoyed wasting their time?

Or do you think that Mazda management might have demanded that they solve the wrong problem?

I think they might as well have told them to make a large gasoline engine to compete with a marine diesel.

So, instead of wasting a lot of resources on marginal improvements to the shortcomings of Wankel engines, let's look at what we can do to improve the strengths of Wankel engines.

1. Wankel engines are less complicated than reciprocation engines. This makes them cheaper to manufacture.
2. Awesome power to weight ratio.

However, a fully tuned ZX-14 engine generates 200rwhp and weighs 50lbs less than the RENESIS engine and a Mazda reman engine costs $500 more than a brand new V8.

I think it's possible to easily beat both of those, if we cheat a bit and declare E85 to be standard "pump gas" and design the engine to run on 115 octane.

So, the real questions are:

1. Can we make a Wankel that we can carry a spare in the trunk or even the engine bay?
2. Can we design so that we can swap in the spare in the same time it takes to change a tire?
3. Can we design to make rebuilding the spare cheap in parts and labor?

9krpmrx8

iTrader: (46)

The real question is, why run a rotary when there are butt loads of Isuzu Rodeo V-6's out there?

Carbon8

iTrader: (4)

You sir should have stopped while you where ahead, I can't seriously construct a retort to what I hope is a sarcastic response.

Starting to think we are getting trolled

Nobody can be this dense.

RIWWP

iTrader: (2)

In this case, you aren't really thinking about the circumstances of history and development correctly. The rotary has by no means "failed" just because they aren't in production at the moment. Simply the economics of being able to produce a rotary powered car meeting the very unscientific regulations on emissions is more than one of the smallest car manufacturers is able to handle at the moment.

The latest interation is also only the ... 8th? production iteration of the wankle. Hardly a huge backbone of development to lean on. It's a pretty tiny team in a very small manufacturer that has collectively done all the work.

It didn't help that Ford was largely running Mazda during the R+D of the wankle.

Actually #1 would only be true if produced in the volume of piston engines. Since they aren't, the cost to produce isn't comparable. Wankles are mechanically efficient, but are thermodynamically horrific. The weight can easily come down even further with lighter metals (the end plates and center plate aren't called 'irons' for nothing), however the thermodynamics of the engine just get worse and worse, and an increasing proportion of power is lost to waste heat. Having to meet emissions regulations is also a very non-trival problem. Most of our engine flaws are simply the long term side effect of having to meet those emissions regulations.


You don't need to assume E85 as the base gasoline. All E85 does is allow higher compression. Mazda is achieving higher compression on 87 octane through a lot of really creative and ingenious methods. Are you ignoring those methods and benefits? Most of them can be applied to the rotary, and indeed, Mazda has officially noted that there is a "Sky-R" within the company.

1) Why? Are you going to also carry all of the fluids you would need to drain out of the engine to change it on the side of the road? How about hazardous material disposal for the coolant and oil? Also going to carry all the tools? You are at a minimum doubling the "weight of the engine". No one is going to accept a 200lb engine if you are carrying a 2nd 200lb engine around too. Kinda kills that "power to weight" benefit doesn't it?

2) Yes, but the cost to do so is significant. The Freedom Autosport Grand-Am team has their 2.0L engines installed and prepped in such a way as to be able to do an engine replacement in about an hour. It sure isn't cheap to do.

3) You have mentioned a "10,000 mile engine" before. You can get that for around $200-$300 now with the Renesis. Pull it apart, replace some seals, put it back together, and you can expect it to last 10,000 miles at most. I don't see what you are gaining?