Look up the specs for the Porsche 944, or the 2.7L 911s from the seventies. The 944 makes very similar power in NA and turbo forms with a 2.5L four cylinder from the same era. There are a number of NA piston engines that make over 100HP/L these days as well (S2000, Modena, M3, etc.), even with streetable exhausts. That is roughly in line with the most power you can make on an NA 13B rotary (270-300 HP), but the rotary will be very loud and weak on the low end. The 13B makes decent power for its 2.6L displacement, but it is by no means ahead of the best piston engines around the 2.6L mark.

-Max

 

I think a good way to summarize the rotary is like this:

Excellent power for its physical size
Very good power for its weight
So-so force per combustion event per individual chamber size
Poor fuel economy per power generated

 

The sway bar and the steering rack are in here are some pics...

 

and another

 

why

 

I've heard that when others have moved the rack, they have messed up the handling. What have you done to prevent this?

 

This is a good point but there could be many reasons for this. Maybe others have just worked out how to get more power from a small engine. I bet all of these 100HP/Litre engines have a smaller chamber volume, which makes a big difference to HP/Litre. Maybe the 13B is just horribly inefficient.

There are plenty of examples of where the 13B makes similar power to a 3.9L six in turbo form. It seams to me that any 2.6L that makes similar power to a rotary has just been taken more to the limit. I know from a friend who races that the rotaries dominate in the capacity class they are in.

Anyway, this sort of arguement is very debatable and won't prove anything, maybe the rotary an inefficient 3.9L motor. Just because its inefficient doesn't mean its a 2.6L.

I challenge you to look at the geared up 6 cylinder motor and find a fault in my logic, I don't think there is one. If you compare the 2 engines every chamber in the rotary is doing the exact same thing at the same time as each cylinder in the piston engine, every chamber is the same size, there are the same number of chambers.

The other way to look at it is to apply a gearing down of 1.5 times to the rotary. Then everything lines up with the 3.9L six, the thing is that all rotaries have this gearing down, its just in the diff.

 

The steering rack was 2 3/8" behind the ball joint on the steering knuckle, so all that i have done is move it 2 3/8" in front of the ball joint while maintaining the same hieght, so I'll see how that works....

Shaun

 

i must reply to this since i own a 240 and am putting in an sr20 this winter. i have only read the first page and have now skipped ahead to this so i hope im not resaying somthing. first of all the 6 speed tranny is ALOT weaker than the 5 speed. second 450 is very possible on stock internals but get a stainles steel headgasket. well that is all i will say for now if you want some good info go to freshalloy.com forums lots of good posts such as guys running 400+ power on stock head gasket and 550's and greasers thread about his 9:1 cr with hks gt3037 making i believe 454 hp?? somewhere around there. i know this is my first thread just in case your wondering my uncle has a rx-7 and now i have to fix it for him because i am the only one willing to take the time to figure it out, he is lazy and cheap, horrible at maintenance, it is a shame! i can't even get him to buy a boos gaugel :S

 

LOL! He certainly bought the wrong car, the rx7 is fairly maintenance intensive and quite expensive.

 

whats the latest on the conversion???

 

yea im dieing here

 

Let me start by saying I think this is a cool project, IMHO the magic of this car is in it's chassis, who cares what is twisting the crank. However...

I would be concerned with the changes in steering geometry based on your rack relocation. With the rack mounted behind the tie rod end (what I believe you're calling the ball joint) the rack translation to wheel angle ratio is increasing as you turn the wheel. Moved in front of the tie rod end it will decrease. With this decreasing ratio the steering effort may actually drop with increasing slip angle during high cornering loads. Your body uses a high point on the steering effort curve to determine when the front wheels are passing over their optimal level of slip. If your steering ratio is decreasing as more input is applied this peak will be "blurred" by mechanical advantage.

Less important, however still a factor, is the change in ackerman geometry (how much the inside wheel turns relative to the outside wheel). It's mostly a low speed issue but still may affect the car's behavior.

Good Luck, keep us posted.

Alex MacDonald

 

a 400hp SR20 will be slower that a 400hp 13b(where is your redline?)

once they get over 400hp they arent that much more dependable than a 13b.

alot of TIME and money for not much of anything.

In defence of the idea if you built it as a fairly stock 300hpish daily driver it would be ALOT more dependable and economical than a stock FD.

Buy a 240...

 

Shaun,
you should think about other options than using the S15 6 speed, I have read that the box it the same size as the 5 speed, whihc means that it will fit which is cool. but it also means that there is less gear mass per gear which means it is weaker. I will admit I don't have any first hand experience with the tranny. I just read on the nissam forums that people use the 5 speed in preference. Check it out, broken trannys suck

-Ben

 

just read the seconf page, where the 6 speed is addressed...... sorry


-Ben

 

Wana congrat you though, people get their panties in a bunch when people mess with what they think is the soul of the car. While the rotary engine is one is the coolest and mechanically interesting engines ever conceived it is not the most reliable. I love RX-7s, have since I first layed eyes and rode in one a few years back when I worked at a Mazda dealership washing cars. I don't want to rip on rotars, but their reliability issues have definately left room for people to wonder "what if I did something different" . I am also a big Nissan fan, so I find your swap all the more interesting . Pioneers like yourself and JimLab are always flamed for have different ideas. I say **** the flamers, your car is going to be awsome.


do what you like, don't sweat the chumps
-Ben

 

An RX-7 without a rotary is like dancing without music...

 

400hp is 400hp. If the car weighs the same with either engine they will be just as fast as each other.

 

You are both very wrong.

400 hp is not 400. It depends on the horsepower and torque curves. If both cars weigh the same, have identical gearing, and identical hp/tq at any given RPM, then yes...they will be just as fast as each other.

Let's say that two cars weigh the same, have the same gearing, and both make 400 hp and 400 lb-ft of torque at peak. One car makes this power through a V8, with the typical hp/tq curves of a V8, and the other makes the power through a turbo 13B, with the typical hp/tq curves of a turbo rotary. Which car do you think is faster?

 

faster or quicker ?

-Ben

 

That depends, if the gearing in both cars is the same does it suit the rotary or the V8?

Either way, the car with the flattest *power* curve will most likely be the quickest. The torque is not relevant.

 

Torque is absolutely relevant! And the above statement is completely wrong, or at least misleading. It all depends on where power band peak is, and what the power curve looks like in the engine's peak operating range, which depends on gearing. And of course power is the product of torque and rpm.

 

You are correct on the power band issue, I was over simplifying.

But torque is irrelevant. Torque is free, I can double my torque by running a reduction ratio. I can get 400 Nm of torque out of 1 watt electric motor if I gear it enough. A car with more torque *might* go faster but it is entirely possible for a car with less torque to also go faster, hence it is irrelevant.

 

Actually, I shouldn't say it is irrelevant. It is a factor but not the deciding factor.