cheeto

Now i have been doing a quite a bit of reading on tuning and various things, and one things that i thought of that could be applied to the renny, is maybe a new intake manifold design. Long, narrow intake runners make good low end torque, and short wide runners make good power up top. my question is that do you think that the design of our intake manifold is good to support both of these things?

i know that our intake opens suceeding runners as the rpms go up to allow better air to flow into the combustion chamber for better VE. but how long and narrow are the initial runners that supply the air for the lower rpms?

im thinking that mazda mainly focused on the top end of the renny's rev band because rotaries love high rpms, and they didnt really put a lot of thought into the lower rpm intake runners. I may be wrong, but if they did do that, and we redesigned the runners to accommodate longer narrower runners for the low end torque to increase, while having the same, or better short wide runners for high rpms, that that would increase the power for the renny on both ends of the spectrum. And also implementing succeeding butterfly valves to open and close to keep the midrange also good. Am i right, or did mazda do a really good job designing the intake manifold?

Charles R. Hill

iTrader: (7)

Mazda did a great job. Take a look at the torque curve.

zoom44

the upper could be just a smidge longer. if it was just a liiiittttle bit longer from the lower to the bend for the TB(working from the block out)

cheeto

so in other words, it wouldn't be worth redesigning the whole thing?

Nemesis8

iTrader: (3)

Not for NA but maybe for FI

cheeto

got it.

The Underdog

iTrader: (2)

What you gotta do is make one that is infinitely variable that adjusts on the fly for maximum power at every point on the rev and load range.

cheeto

that would require a LOT of R&D. and the N/A design would be different than the FI.

zoom44

not really all someone needs is windshield wiper motors and some tubing

cheeto

and some butterflies.

rotarygod

Actually they are 2nd gen RX-7 retractable headlight motors. I have a couple of them and some tubing lying around!

TeamRX8

iTrader: (25)

and some duct tape ...

rotarygod

Of course! How could I forget the duct tape!

The Underdog

iTrader: (2)

Heh, I was kidding but then I read somewhere that BMW actually did this. Apparently they made an intake manifold with some kind of rotating center section that can steplessly vary the length of the intake. I don't know if it varies the plenum lengty or the runner length or what though. I couldn't find much in the way of technical info on it. It would be interesting to see what they did just for curiosity's sake. I'm sure the effort required to reproduce it on the RX8 would put you in the mental hospital.

cheeto

well from what i have read the rotary isnt that much different than a piston in N/A terms as the engine creates a vacuum and draws the air in. now its the different amounts of air that is drawn in at different rpms that is the issue. i initially opened this thread to see if the intake manifold on the renesis was properly designed for proper air flow at mostly all rpms, with long narrow runners at low rpms to fill the chamber with as much air/fuel as possible to provide low end torque and short wide runners to provide high airflow at high rpms. now i was thinking that the lack of torque on the rotary on the low end was the cause of the intake manifold not being long and narrow enough to fill the chambers as much as possible at low rpms.

as you can see, people have posted that overall the intake was designed pretty good. im just looking to see if the intake can be further looked into and improved on for those who want to get the most out of their engines whether it be N/A or FI. if you would care to read more about the bmw intake manifold redesign and come back here and share that would be great.

rotarygod

The Renesis intake is very well optimized to account for tuning and airflow requirements at various rpms. That's why there are so many valves that open at different times. It will be extremely hard to improve on it. Nothing is impossible although fitting an improvement under the hood might be pretty close to it. It's not saying it can't be improved of course.

BMW's system was basically a big rotating valve inside the plenum and it's degree of rotation changed the total runner length. Here's a diagram of it:

http://www.histomobile.com/histomob/...hniqu/73-3.jpg

cheeto

thanks rg. thats what i thought

i have never seen anything like that bmw manifold. weird.

The Underdog

iTrader: (2)

The reason the rotary has no low end torque regardless of what intake manifold you use is that it has a very short lever arm with which to turn the crankshaft. A crankshaft is just a lever. If you've ever seen a piston engine's crankshaft even once you'll realize that the average one has about twice the distance from the center of the crank to the center of the journals that a rotary does. So for the same compression and cylinder pressure you're just going to get less torque from a rotary by design. It's like turning a bolt with your fingers rather than a wrench. Fingers can't break it loose, but wrench would take forever if you used it to take the bolt all the way out.

Soo... That being said, someone needs to invent the impact engine. Torque AND speed. But possibly not very smooth. lol

The Underdog

iTrader: (2)

Oh, and that BMW diagram was pretty cool. With that intake manifold and their variable valve timing and lift system, just the act of getting air into cylinders has become quite an endeavor. I wonder what rotaries will be like when they've got a hundred years of refinement to them.

cheeto

i knew a little about that but thanks for the explanation. well improving the rotor face could also help to increase torque like in the 16x.

CERAMICSEAL

Mazda spent a lot of development time on the intake manifold and it's effect on low end torque. They did a remarkable job. If the car were as light as a Miata or first gen Rx7 people wouldn't be talking about it's lack of torque. Nobody's going to do a redesign that superior in every way for the NA renesis than Mazda did. It is TRICK.

The 16X or whatever it will be called will truly improve things with it's increased 'stroke'.

Seal.

rotarygod

Actually torque is dictated by total displacement and the rotary doesn't have much of it. The "stroke" of the engine just dictates where the peak will be. A longer stroke will produce more torque down lower in the rpm range and a shorter stroke will place it higher but the total torque generated by the engine is limited by displacement.

The Underdog

iTrader: (2)

That's an interesting factoid there rotorygod... I don't mean this to sound snide or anything but if you read that somewhere I would seriously like to read the same book. If it's just something you figured out I want to eat the same breakfast as you. Good job.

rotarygod

I don't eat breakfast very often so start starving in the morning!