Alternative engines
 

Wankel engines. far superior to a reciprocating piston engine. i'd just like to see a debate about it. and desmodromic valving too. and just mechanical oddities in general. And i think it would be cool if someone made DOHC 4V heads for a 302. im sure it could be done. a little difficult, but possible.

------------------
If it ain't broke, make it go faster

I dont think dohc could ever work on a 302 block.

------------------
95GT B303 cam, 1.7 rockers, 65mm TB, 73mm MAF, milled heads, 355's K&N, off road pipes, pulleys, msd coil, 9mm wires, Tremec 3550, Pro5.0 shifter,10.5 Motorsport clutch, FMS aluminum driveshaft, weld in subframe connectors

Rotory engines are large externally, and while they can make very high power levels per ci, they need turbocharging to really be strong because of the very small displacement of the engine. I do not feel the rotory engine is superior, they are very inefficient as far as fuel usage for displacement, they are short lived (especially when turbocharged), they have difficulty passing emissions, and due to externally large size they are impractical in many cases.

The Mazda RX-7 was the most successful rotory powered car in history, the later versions making 255hp from a small 80ci engine (2x 40ci engines together). With twin turbocharging the car was very quick in a 2800lb chassis, but once you begin putting on poundage, the results would have been less than stellar. Very poor torque production would seriously hamper acceleration of a large mass car.

The RX-7 managed a terminal velocity at the end of the 1/4 mile significantly below that of the Mustang Cobra approx 101 vs 104, and slightly slower times as well. With a 600lb weight advantage you'd expect a 255hp car to perform better, but lack of low end power, and little reciprocating mass hurts the engines performance.

Dispite having a high top speed, the RX-7 was not an impressive performer in my personal experiance between 80-120mph. Only after 120 does the RX-7 have the edge due to aerodynamics when compared to the average stock 5.0. While it can reach a terminal velocity higher than the 5.0, it's slow getting there. I have walked more than one Gen III RX-7 TT from 80-120mph in a stock Mustang 5.0. The times posted for the car from Motor Trend is 0-60 5.2sec 1/4mile 14.1@101mph. I'm not normally one to say Motor Trend does a good job driving cars at the track, the 0-60 time is evident of a very good launch. While a tremendous 0-60 performer, you can see as the speeds begin to rise, the RX-7 slouches off. The only thing that allows the car to attain such an impressive top speed is it's very good drag coefficient.

Speaking with many RX-7 owners you may find that the performance of the car drops dramatically with increasing mileage, most TT RX-7's are well on their way to rebuild stage by the time they accrue 80,000 mi. The very nature of the RX-7's engine requires it to be under boosted conditions much more than a standard piston engine, which is one of the reasons the wankel has longevity problems. The overall maintenance record of the powerplant is problematic as well. The RX-7 is not a reliable car, this may well have to do with the complexity of the design. Maintenance costs are also exceedingly high due to limited production runs and parts availibility.

I used to be a tremendous fan of the rotory design, but now that I've looked deeply into the complications around it, I've come to the conclusion that while the engine may have extreme performance potential for it's size, it's fallbacks outweigh it's advantages at this point.

All in all you could bet that if Mazda thought they could make a superior product with a different kind of engine, they would have marketed the rotory in other cars as well.

There is a set of 4v heads availible for the 302. Or at least there was. The heads used the existing OHV design, simply adding more valves. They were/are called the Dominion 32v heads. They make a ton of high rpm power with tremendous breathing capability. Due to the extreme stress on the cam, I doubt they are too reliable.

As far as desmodromic valving are you talking of the design used on Ducati motorcycles that uses a valve closing part to control valve floating at high rpms?

What's more impressive in head design is a technology pioneered by Mercedes Benz back in the 60's. Electronic valving. Using an electronic system to open and close valves instead of a mechanical system.

The potential for this type of technology is huge! Can you imagine the benefits of having a computer open and close the valves without any mechanical drivetrain? Huge low end torque, coupled with extreme high rpm horsepower? A computer controlled valve system would make a mockery of VTECH and the current 4.6 DOHC motors varible systems. The drawback? Reliability.

Are u sure there isn't dohc or ohv style heads for 5.0. I have seen tested heads for Chevrolet in the past for the regular small block. http://www.mustangworks.com/msgboard/cool.gif

I remember seeing a spherical valve engine setup for the 302 that was (in a way) similar to DOHC engines. It used two shafts with these half-sphere shaped chambers instead of valves and springs. I can't remember for the life of me exactly how it worked, but I can remember that it blew my mind to read about it. The whole setup for a 302 was like $20,000 or something. It also used a redesigned block due to the lack of a camshaft.

I've never thought rotary engines were all that and a bag of chips. They've been sold on their efficiency for decades and, while their horsepower-to-size ratio is impressive, they've just never done anything that really wowed me. And like Unit said, they need to turbos to make big power...and thus cutting their lifespan.

Those dominion heads were really impressive (if not enoumously expensive). The four valves made big power up top and the fact that the valves themselves were relatively small allowed for decent low end torque. Not a bad combination if they didn't rip your cam apart in the process.

------------------
1984 1/2 GT350 (#842 Hatchback w/ T-tops), 302HO, Comp cams Xtreme Energy cam, Carter 625cfm carb, Weiand Stealth intake, MSD distributor, MSD coil, FMS 9mm wires, 1 5/8" MAC unequal shorties, 2 1/2" MAC Prochamber H-pipe, Flowmaster 2 chambers, KYBs, 16"x8" 4 lug Cobra Rs, Falken 245/45ZR16s

Check out http://www.coatesengine.com/Body.htm for some more info on the spherical valve engine.

------------------
1984 1/2 GT350 (#842 Hatchback w/ T-tops), 302HO, Comp cams Xtreme Energy cam, Carter 625cfm carb, Weiand Stealth intake, MSD distributor, MSD coil, FMS 9mm wires, 1 5/8" MAC unequal shorties, 2 1/2" MAC Prochamber H-pipe, Flowmaster 2 chambers, KYBs, 16"x8" 4 lug Cobra Rs, Falken 245/45ZR16s

Oh, PGkelly I actually forgot to note, do you know what the maintenance on a Ducati is like? Ouch. Something like every 3,000mi the valves need to be checked because of their unique valve closing properties. Although it's rare to see them out of adjustment at that point, it's been seen before.

While I personally think it's a really cool system in theory and to talk about, I don't really think it's practical in high mileage engines you find in cars. They would need to come up with a much less variable system before it could work. Actually Ducati's are on the wee bit side of finicky too. Like actually on the way bit side of finicky when it comes to adjustments in their valvetrains. The maintenance costs with the current system exclude this technology when the current systems in place already perform adaquately, if not good.

I am not really a fan of rotary engines myself, but check out the new Mazda RX8. It is an NA rotary that puts out around 250hp...

oh, yeah. Duc's are horribly unreliable, and the top-of-the-line superbike needs adjustments every 2,500 miles. Rotary engines are large when compared to engines of similar displacement, but they make much more power for their size. and since they have significantly fewer moving parts, there is less maintenance to do. But don't forget, the reciprocating piston engine has had the benefits of a century of technological advancements from hundreds of different companies. the rotary engine was invented in the fifties, and so far has been used by Mazda, NSU, and Norton (motorcycles). And it doesn't need a turbo (or forced induction) to get power. naturally aspirated rotary engines killed so much on racetracks that it had an engine speed limit placed on it, and a 50kg weight penalty (in the form of lead weights). it's simple design, however, does not lend itself to tuning. most of the engine modifications you can do involve auxiliary bridge ports (intake), exhaust tuning, and porting/polishing the intake tract. you can't really bore it out, and to increase compression you get a rotor with smalled "dimples ". It also runs a lot smoother than a reciprocating engine.

------------------
If it ain't broke, make it go faster

I wouldn't say they are unreliable, just that they have much higher maintenance schedules.

My friends shop has had 4 Ducati's in at a time for scheduled maintenence. As long as they are kept up, I haven't heard of them having many problems.

Well, you can get power out of a rotory engine without turbocharging, but not enough to really impress me for it's external size. As far as the piston type engine design being around for so much longer and getting the benefit of increased R&D efforts, I'll agree, but the rotory engine is also an internal combustion engine which can benefit from some of the idea's that have been implemented into piston engines.

What do you think a N/A RX-7 could make for hp? 180? Nice, but even at 180 it wouldn't be 14 sec car. The older N/A RX-7's made what, 140? I don't think a 2x 40ci engine like in the RX-7 could make more than 200hp without the addition of forced induction. Sure, you could spin the **** out of it to get some more power, the RX-7 redlines at 7,000 under boosted applications, but like I pointed out earlier, their torque production sucks.

They just don't make much torque, which is very important in larger mass vehicles. Look at the Gen III RX-7. It makes a piddly 217lb/ft@5000rpm. That's under forced induction!!! Many forced induction motors will make as much torque as hp, if not more, and they'll make it well below 5000rpm, usually 3500 or below. Even small displacement engines such as the 2.0L Mitsubishi Eclipse made 210hp@6000rpm and 214lb/ft@3000rpm. As many people will attest that engine has huge performance potential, although it's pretty unreliable under those conditions. Let's do a comparo between a few production engines.

Aston Martin DB7
335hp@5750rpm
361lb/ft@3000rpm
3.2L I-6 DOHC 24v? Supercharged.
105hp/liter

Ferrari F360 Modena
400hp@8500rpm
275lb/ft@4750rpm
3.6L DOHC 40v V-8 Naturally Aspirated.
111hp/liter

Ford Escort Cosworth RS
276hp@6250rpm
221lb/ft@3500rpm
2.0L DOHC 16v I-4 Turbocharged.
138hp/liter

Honda S2000
240hp@8300rpm
153lb/ft@7500rpm
2.0L DOHC 16v I-4 VVT Naturally Aspirated.
120hp/liter

Lotus Esprit Turbo
264hp@6500rpm
261lb/ft@3900rpm
2.2L DOHC 16v I-4 Turbocharged.
120hp/liter

Mazda RX-7 TT
255hp@6500rpm
217lb/ft@5000rpm
1.3L (2x40ci) Rotory Turbocharged.
196hp/liter

Mitsubishi Eclipse GS-T
210hp@6000rpm
214lb/ft@3000rpm
2.0L DOHC 16v I-4 Turbocharged.
105hp/liter

Porsche 911 Turbo ('96)
400hp@5750rpm
400lb/ft@4500rpm
3.6L DOHC F-6 Turbocharged.
111hp/liter

After looking at some of those car's you can see that the rotory engine faces some stiff competition. Both the S2000 and the F360 Modena have well over 100hp/liter N/A, the Ferrari also maintains an impressive torque output to boot. Turbocharging enables the gap between potential performance between the rotory and piston engines to increase, but lets be honest. Pound for pound, inch for inch externally, I don't think the rotory is all that hot **** it's been trumped up to be.

Great! The rotory can make gobs of hp/liter, but it takes up about the same amount of room as a small V-8 that's making the same hp with more torque and a better powerband. It's performance can be eclipsed (no pun intended) by a small displacement turbo I-4 taking up less or equal space.


[This message has been edited by Unit 5302 (edited 03-13-2001).]

granted, the rotary doesn't make very much torque at low rpm's. But i like the idea of pure rotary motion, and i think it should be pursued. I also think that with increased development, the rotary could really improve by leaps and bounds. also, when you think about it, one rotor does the work of three pistons. And I've read reviews for Ducati's that have said their electrics are rather unreliable, and FI systems on some of the bikes would take more than a minute to warm up. but they sound good, and look good, and have a whole lot of torque, and handle well, and go fast. BTW, a little while ago i read something about a turbine-powered motorcycle that makes 415 ft-lbs of torque, which is constant through the rev range. it had a maximum engine speed of 50,000rpm's and its transmission had one forward gear and neutral. but back to the RX-7, it is one of the winningest cars in GT history. which says a lot. and you seem to be ignoring the obvious, that the RX-7 is 1.3L. you can't get very much torque out of 1.3L. in the 70's Mazda made an engine called the 21A, that was built to go into a 'vette/jag competitor. it had a single chamber displacement of 1050cc, giving it a total displacement of 2.1L. preliminary tests showed 180hp, but a production version could have had 200+ production N/A. they also toyed with 3 and 4 rotor designs, but ran into problems with the eccentric shaft. Like they say, there is no replacement for displacement (except money). Both of these engines were killed by the oil sheiks during the oil crisis. as for the oil problem, older rotaries (L10A, L10B) had a carburetor that mixed oil with gas a-la 2 stroke. this was to lubricate the trochoid housing. the issue of decreasd performance in high-mileage engines comes from the apex seals. they are made of (at least in gen. 2 rex's) cast iron and are 2mm thick. they wear, sometimes as much as 1mm over 80,000 miles. all you need to do to repair performance is replace the seals. relatively simple, the apex seals are the same as the piston ring seals in a recipro engine.

p.s. my RX-7 will spin trochoids around your mustang

p.p.s. i don't really have an RX-7

------------------
If it ain't broke, make it go faster

[This message has been edited by PGkelly (edited 03-14-2001).]

btw, for some very interesting articles on Ducati technica, go to http://www.ducati.com/bikes/techcafe.jhtml
very interesting stuff.

------------------
If it ain't broke, make it go faster

"The big book of everything you need to know about cars" -- Brought to you by Unit 5302 http://www.mustangworks.com/msgboard/smile.gif.

Hehehe, I wish! I know a little about a lot. Plenty more room to learn considering I'm only 23 years old. http://www.mustangworks.com/msgboard/wink.gif

This is my first time cross posting from another forum, and though I came in with a suspicion of slander, I was pleasantly surprised to see that there was dialog between gentlemen taking place.

I would love to defend the power to weight ratio, to reliability, but there's not much to contest. Yes, the third generation RX-7 is prone to malfunctions at unpredictable times. There is no denying that it suffers from an overburdening of under hood temperatures, the primary cause of component failure, and that the parts are in limited availability.

There is however, a dramatic and distinct difference that one experiences while driving an RX-7 that I'm not sure one could experience from a car under $35K (Or higher for that mater) There is a sense of balance and responsiveness that connects directly to your synapses, and back again to the controls. Not only will you car react as you think it to, it will surprise you that it did it better than you willed it to. RX-7s are not Ferraris by far, but the sure allow you to feel like there one.

I'm not saying that performance to longevity isn't important, believe me it is, but there is a valid argument that performance comes at a price. I don't believe that the price is too high. There are ways to prevent damaging the car and maintaining a reliable machine. I think that many current 7 owners understand the complexities, and the no no's of owning a high performance machine.

A final note before I step off my soapbox. I would not underestimate a third gen RX-7 when met on the road. The sevens have had plenty of time to be refined by their succeeding owners, and though it may look stock, or even sound stock, you may be in for a hell of a race.

If you want to talk power to weight ratio, check out the Dodge Omni GHLs. A fellow 7 owner reminded me that even the ugliest sheep could be a visious wolf in disguise.

Later, and feel free to visit the RX7Forum anytime, as long as you are nice and polite.


Take care, and drive safe!