brillo

I know the Renesis uses the same alternating aluminum/iron sandwich design that goes back quite a ways. I would think that since both these metals have different heat properties that could cause some issues in terms of expansion.

Is there some logic to this? I've seen aftermarket parts for the FD's engine that are all aluminum and look like parts of a engine rebuild,, is this just for weight?

I guess I'm trying to understand the deisgn theory here.

ProtoConVert

also... arent there differences in electric potential between iron and aluminum... like dont components rust because of this?

RX-8 friend

Yes, it becomes somewhat of a battery. That's why it's important to change the coolant frequently. At least once every two years. Lots of RX-7 owners change it every year. Keeps the anti-corrosion compounds topped up. I use 50/50 distilled water and glycol coolant in my 3rd gen. RX-7 even though I don't drive it in the winter, as my garage isn't heated. This mixture gives better corrosion protection than weaker mixtures.

The rods that bolt the stack together are torqued to a spec. that when the housings expand and contract the rods act like springs, keeping the stack under tension. Also the coolant seals between the housings had to be "O" rings, as the engineers knew they couldn't rely on good tension between the housings.

The side plates are cast iron and the wear surfaces are treated with nitride coatings, so they last under the high wear from the side and corner seals. The replacement aluminum parts don't last as long, but are lighter. They are for racing. The rotor housings are chromium plated on the wear surfaces. In previous engines the higher the power output, the more extreme their heating/cooling cycle was. This meant the chromium bonding failed sooner on the higher power engines. The extreme example of this is the 3rd gen RX-7, where the heating is so great the coolant boils just the other side of the combustion part of the housing (bottom). This caused tiny bubbles to form in the coolant, which lowered its' effectiveness, so an "air separator tank" was added to remove those tiny bubbles. Champaign coolant?

The Renesis may experience very long rotor housing life, as the apex seals don't "bounce" over an exhaust port. We have yet to see how long the side seals last, as they pass over more and larger ports now.

brillo

interesting info, but I'm still not clear why the engine isn't just all aluminum or all cast iron for the "block"

RX-8 friend

As I said, the aluminum doesn't last very long with the side and corner seals running on it. I suspect they tried chrome plating it like the rotor housing but I guess it didn't last there either (probably peeled off). There may also be a strength issue. The stationary bearings are in those end and centre housings. It may be to get the needed strength the housings would have to be too thick.

GTRay

another area of contention is the twisting effect of high power rotaries...

this is why early Turbo second gens are prone to cracking at the dowels near the oil filter. this area has since been strengthened and reinforced. i don't suspect an aluminum housing would last long when under that kind of twisting force.

Ray

RX-8 friend

The coolest thing I saw was the honeycomb stiffener Mazda had to use at the "oilpan flange" in the four rotor Lemans winning 767. The dowel pins couldn't cut it with over 700 HP.

I put oilpan flange in quotes because there was no oil pan - it was a dry sump engine.

rotarygod

They had that honeycomb stiffener on the top and bottom of the engine.

I would like to see all aluminum housings with an insert for the sliding surfaces. Here's a diagram I found elsewhere on the net of the idea.

http://home.earthlink.net/~rotaryeng...-end-house.jpg

Japan8

I see... kinda like in a piston engine... cylinder liners. Cool idea that could shave some serious weight...

wakeech

yeah, but how much more would it cost?? remember that these are already hand built motors, and the castings have changed next to nothing for almost 20 years on the 13B block. i'm not sure that Mazda would be able to make a profit on those fancier side housings on a production size scale.

but yeah, they would do better taking the stress on the oil pan and housing bolts and make the engine a few pounds lighter.

i have a question that's been buggin' me for a while now: couldn't the whole block be studded and girdled somethin' awful instead, once the whole dealy was aluminum??? does anyone know if this has ever been tried?? i'm aware that to girdle the studs you'd certainly have to modify/cast a new end housing... and i'm not even sure how the bell housing would fit with that either... hmmmmmmmmmmmmmmmmmmmmmmmmmmmmm......

brillo

I'd like to see what a all aluminum rotary engine would weigh, well almost all aluminum, as pointed out above, the inner lining might have to be iron/steel.

I understand the point of using what you know works, it keeps the costs down and is proven. That said, Mazda is making quite a bit of money now on the 8's, if it wants to continue to push the sports car envelope, they need to advance the rotary engine structure design as well.

wakeech

meh, it's not really a big deal for production cars. it's not a matter of a few hundred pounds, but a few tens of pounds. the cost simply outweighs the benefit by a LOT. if you were racing, however, then yes i'm sure that Mazda will in the nearish future dream up a better solution than alternating block materials.

Mr M

Why make the rotary engine lighter? It is already 25% or more lighter than any all-alloy reciprocal engine producing the same power! When a better material than cast iron comes along Mazda will probably consider it, but they won't bend over backwards to make an inferior material (for this application) like alloy work. It doesn't make sense.

rotarygod

It may be hard to believe but the LS-1 V-8 is nearly the same weight.

Racer Rick

I once had an opportunity to discuss this with the man who originally set up Mazda's competition department. His comment at that time was that the development and tooling costs were thought to be too expensive for Mazda to bear. This was just after the 1st gen RX7 became very popular. Mazda was still wary of sinking more development $$ into the engine on this front. Remember that they had worked very hard to solve the side housing wear issues, apex seal issues, water o-ring failure issues on the early 12a engines. Jump forward to today and Mazda has already made a substantial reinvestment in rotary technology with the Renisis side-port development. Arguably, this is a major gamble given the commercial failure of the 3rd gen RX7 (as fine a car as it was)!! Hopefully, the RX8 will be a huge commercial success and Mazda will be motivated to forge ahead to pursue ideas like this. Personally, I would love to see Mazda develop a higher eccentricity engine giving a more balanced output of torque and Hp.

CERAMICSEAL

Piston engines are making so much headway on rotaries in the areas that the rotary still has advantages. It's sad. Mazda is such a comparatively small company. As RG pointed out there are more powerful engines that are almost as light. When the talk and rumors of the renesis first began to circulate I thought they would have a much more considerable weight difference over their predecessors. Even the rotors have only lost 100 grams or so.
For those who aren't aware the 10A used in the '67 Cosmo 110S
had all aluminum housings. I had the pleasure of driving one of these about a decade ago and it still had the original, untouched motor in it.

rotarygod

Just to put engine weight into perspective here, rotor weight has gone from 11.5 pounds before 1986 to the current 8 pounds or so. Obviously the counterweights need to lose a little weight too. The eccentric shafts stayed the same weight untile the lighter Renesis shaft came out. It isn't much lighter though. Guru Racing makes an eccentric shaft that weighs about 2 lbs less than the current ones and is stronger. Go figure. The aluminum end housings that Racing Beat used to sell weighed about half of what the cast ones weigh. The front end housings and the intermediate housings are about 25 lbs apiece and the Racing Beat housings were about 12 lbs apiece. The rear housing is about 30 lbs and the Racing Beat one was about 15 lbs. These numbers may not be 100% correct but they are close enough. Just by using lighter components alone, a rotary engine can shave at least 50 lbs of weight off and probably more. The problem is that the current design works good and meets the needs of the industry. A redesign out of aluminum would be very expensive and from a business standpoint not worth it. V-8's are getting lighter from the use of aluminum yet the rotary hasn't. One day it will. You have to remember that piston engines have evolved more in the past decade than the rotary has in the past half century. Regardless look at how good it is. One day, we'll have a lighter, more powerful, more economic rotary engine. We just need to wait for spending to catch up with technology.

wakeech

not all of them, and remember that the LS-1 is only the absolute best example of the V8. Ford's DOHC motors are retardedly huge and heavy, and i'm quite sure the Hemi is a whole lot worse *not a dodge guy*.

as it stands, the 13BMSP is still a helluvan engine (won it's second consecutive International Engine of the Year Award).

rotarygod

I was actually basing my statement from the standpoint that SOME engines are done this way, namely the LS1. Never the less they still have them. I am a fan of the LS1 so typically when I make comments about V-8's, they are directed at these engines. I think Ford's V-8's are pathetic.

I just love it when a Dodge Hemi gets up next to me and the guy is dumb enough to believe the commercials! Wake up call.

Racer Rick

Another idea MAzda should pursue is gasoline direct injection. As Audi have shown on their LeMans winning prototypes GDI can offer some significant benefits in terms of fuel consumption per Hp produced. The rotary has a distinct advantage here in that the injectors don't need to be exposed to the combustion gases. That should make GDI much easier to do in the rotary.

rotarygod

Mazda has tried direct injection. In the late '80's and early '90's they had an experimental engine designation known as DISC which stood for Direct Injection Stratified Charge. They would inject fuel into a small chamber where it would then fire into the engine from between the spark plugs. Another version of the engine fired the fuel into the engine from just before the plugs. One of the engines even had a supercharger attached to it. I don't know what the current state of the experiment is but it has been tried.

babylou

The Renesis weighs 303 lbs and the LS1 V8 weighs 458 lbs in automatic guise and 497 lbs in manny tranny form. The new 6.0 liter LS2 V8 weighs 482 lbs in manual tranny guise. All weights are fully dressed. The new LS7 in the 2006 Chevy Z06 weighs...well I can't tell you that one but the horsepower is...ah I gotta go.:D

wakeech

:p shaddap you damn braggart.

i'm guessing on the plus side of 440bhp.

babylou

Umm...higher.:D

1stRX8

There is a company designing a certified rotary for aviation. I believe it is all aluminum. Obviously weight AND durablity are extremely important in a certified aircraft. Over the years there have been experiments with Mazda rotaries modified for experimental aircraft with varying results. This will be a certified engine specifically for aircraft.

b/c propellers like to turn at about 2500 rpm, a reduction system must be used with the Mazdas.

The new engines will produce 190, 220, and 320hp, AND be light. I look forward to see what configurations are chosen to deal with:

1. low RPM peak HP - Mazda has never done that
2. durability with alluminum housings.
3. Cooling