Lo all, just wanting to pose a question about the 88 GTU and GXL models. I noticed, as I'm sure have others, that the GTU has a higher redline than the GXL, by about 1000 RPM. Its also heavier then the GXL but around a hundred Kilos.

I was just wondering why the GTU has a higher redline, what mechanical differences are there that allow this? What would I have to do to achieve a similar 'redline'?

 

Those two cars have the same engine. They have the same redline. Are you sure the car with the "higher" redline did not have its cluster or at least its tachometer swapped at some point?

 

i know the series five cars have a higher redline. my 88 gxl redlines at 7k.

 

The factory gave 89-92 non-turbo engines a slightly higher redline due to lighter rotors and an advanced intake system. You can read about the details in SAE 900036.

The important thing to understand is that the intake system has been reconfigured such that the engine makes its peak power at a higher rpm, and therefore the rotating system was modified to allow for a higher operating rpm. If you just use the gas pedal to increase the rpms with the stock engine then you will make less power at higher rpms and you will chew up the engine.

You can make your own high-rpm rotary engine that gets even more horsepower, but it will require "porting" to flow more air at that rpm, as well as modifications to the engine that will allow it to function at a higher rpm. This is something that should be performed by a professional, but you can learn more about porting here:
http://mazdarotary.net/porting.htm
http://www.mazdatrix.com/faq/porting.htm
http://www.mazdatrix.com/engmain.htm

 

To sum it up: All 2nd gens have a 7k redline, except for S5 NAs, which had an 8k redline.

 

No, mine has 8k Redline -> 1986 S4 NA all stock. Buzzer at about 7k.
Speedo goes to 240 Km/h max

 

Redline is where the red STARTS on the tach, not where it ends. The buzzer goes off directly before redline (about 6800 RPM). No S4 redlines at 8k. I have the SAE paper Evil Aviator mentioned; PM me your email if you would like to read it.

 

Sorry, my bad. Thanks for pointing that out.

 

Don't s5 auto N/As redline at 7500?

 

My cars an S5 that was swapped from an automatic and still has the auto cluster.

Redline is 7K.

 

A little off topic, my 87 n/a, doesn't have a buzzer. Never heard it.. What would cause it to not work?

 

you're not driving fast enough

 

LOL, well I do hit 7500 weekly for carbon build-up and there is def. no buzzer...

 

it could be disconnected or broken, or the redline setting misadjusted (I've heard there's a screw, I think on the back of the cluster, that let's you adjust what RPM to start the buzzer).

 

NO. i read a procedure for changing the rpm in which it goes off, and you have to solder in a diffrent resistor... i think, this was like 3+ years ago....

 

thats true... i swapped to manual and i dont hear a buzzer for redline....even the needle bounces but nothing.....

 

Regardless of it being auto or manual it WILL have a buzzer from the factory [S4 NA auto->5sp conversion, buzzer works perfectly]

 

hmm cheap..i got ripped off .. i know the buzzer works for sure but nt at redline..

 

Mine don't work, well I won't go very far from start of redline. Sry I meant 6500-6800 in first post.

 

Can you expand on this a little? I ported my engine some when I rebuilt it. TII center plate, mild port on the secondaries, and big porting on the auxiliaries. S5 rotating assembly, but all S4 manifolds though. Obviously S5 manifolds will help significantly, but what else is necessary? Ignition?

Thanks

 

race clearancing is a big issue. all the gaps between the seals to the rotors will be larger, the rotor should be narrower, there may be end play concerns and rotating assembly balancing is probably a must.

control over fuel and spark would also be important. no stock FC allows the motor to rev to 10k, I think the highest stock limit cuts fuel at 8000RPM??

 

Common high-rpm modifications include lightened rotors, balancing, clearancing, lightweight hi-rpm flywheel, upgraded bearings, hardened stationary gears, locked rotors, oil system modifications (e-shaft plug, oil jets, upgraded/shimmed regulator, etc.), underdrive pulleys, and carbon apex seals. The exact modifications depend on the rpm range dictated by the porting, and on how an individual race shop builds their engines.

 

the redline is just a baseline for just past peak power, meaning there really isn't much reason to bury the needle to the peg. the engines can still breathe beyond 8/9k even in stock form but the ECU just isn't mapped beyond that so it hits a soft rev cut.

 

Does that mean I should be shifting my race car at 9K? Dipping below 6K seriously sucks on a road course, shifting 2 --> 3 on stock ratios (modified tranny gears not allowed). (car goes from "some" torque to imperceptible torque, until it winds up to 6500 or so.....)

 

use the RPM range which best suits the powerband of the engine, so holding off til later in the RPM range is probably better than shifting earlier and losing a chunk of torque/acceleration versus losing just a little by pushing beyond the peak power range.

with a lightweight flywheel you should be able to wind the engine up to 10k, if the ECU was capable of it. it won't really hurt the engine much(the bearings will wear slightly faster and apex seals will chatter if not premixing).

the main thing i believe that is holding your engine back from higher RPM peak power is the exhaust inserts since that was one of the very first n/a builds i did about 9 years ago and didn't modify anything after the second owner paid for a basic rebuild after the overheat session. the "wings" get yanked on every n/a port job now.