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Shift point for stock FD engine with single turbo?
I dynoed my car the other day and got a corrected value just under 350 hp (flywheel, I assume) and I think it peaked basically where the pull ended, which I think was at 8,000 rpms.
Since power peaks at around 8,000 should I shift there, even if the rev counter seems to suggest shifting sooner?
Can you shift any higher than that with a stock FD engine, or is that too high for the rotating assembly, regardless of the power band?
I think my P-FC's rev limiter may have been set for 8,100 or so.
A stock FD makes peak power at 6500. So shifting at 7500 is fine. Even though power falls off, due to gearing it still makes sense to shift that high.
In your case, you should be good to 8500 with stock rotating assembly. A series 5 non turbo red lined at 8k. It made peak power at 7000. I would set limiter to 8600. The SAE paper lists the REW as having a max engine speed of 8000.
What you do is make up an Excel spread sheet to calculate torque at the wheels referenced by vehicle speed and run it for each gear. Use your dyno plotted torque for 4th gear. Then graph each gear so you can see the overlaps.
Or you can just log acceleration values for each gear if you have a logger.
Basically, you are going to find why you rev 1st and 2nd to the limiter and then short shift 3rd, 4th and 5th at ever more progressively lower rpms- the human body works pretty well as an accelerometer.
I will give you examples of wheel torque from my single turbo FC spread sheet so you can see what I am talking about.
If I just look at wheel torque at peak torque rpm (4,305rpm) and redline (7,777rpm) and vehicle speed at each of those rpms per gear you will get the picture.
Why would you change your redline due to a turbocharger change?
It should be near stock, period. Realistically, the motors can take more, so go up to where you stop making power +300 RPM and that's usually a great stopping point.
You guys might find this interesting. Buried in the brochure for the 93 FD is a chart (kind of grainy and low resolution once you blow it up) of engine speed, wheel torque, and vehicle speed.
I labeled each axis to make it easier to read. The curved lines are the wheel torque, the straight lines are rpm and vehicle speed for individual gears. There are also curved isolines but I'm not sure what they represent, maybe wheel power. See below:
Besides the turbo and the completely different power curve...
So you're saying that if I throw a GT55 on my 1.8L Integra and it continues making power beyond it's 7200 RPM fuel cut that I should just bypass it and rev it out to 9500 RPM where the turbo wants to be?
The mechanical/balancing aspects of the factory 13b of the OP's motor is untouched, so the influence a power adder has shouldn't be the driving factor over common sense. If the motor is relatively well balanced from the factory (which it is), then MAYBE, at most, maybe 750 RPM over the factory redline of 7000 RPM.
Yes, the elimination of the twin turbos helped with breathing on the top end and it WILL continue to make more power up there than it used to, but the MECHANICAL side things should dictate where you place your powerband, not your bolt ons.
If he instead talked about dynamic balancing of every part of the rotating assembly, then the factory turbos being balanced and everything hand ported, I'd say rev it out to the moon. 9500 RPM? No problem!
Sounded like a good idea. Everyone thought it would be oK.
It was ok for a while and then the rotor contacted the side housing and stuck a single side seal in so now I have low compression on one rotor face.
I have no idea what my engine is (original? rebuilt? reman? replacement?). I do know with poly engine mounts it really buzzed way more than my FCs engine with solid engine mounting and with AC on it was unbearable.
I suspect the rotors were at least 2 letter weights apart. This imbalance would flex the e-shaft more which would throw the rotor into the side housing.
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What you should do if you want to rev to 9,000rpm.
Use new FD rotors that are already side cut from Mazda or have your existing rotors side cut.
Have rotating assembly dynamic balanced.
Use stock 2mm seals (no 3mm steel, 3mm ceramic ok).
Use the largest rotor bearings available.
Use RX-8 stat gears/bearings.
Now you have an engine that like the 13B-MSP Mazda would be willing to rev to 9,000rpm with warranty.
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If you want to rev higher than 9,000rpm or even more reliably you can get into some of the other old school NA rotary mods including full oil system upgrades with loop line, clearancing and such. That is a big topic.
If you want to rev higher than 9,000rpm you should use ceramic or carbon/aluminum apex seals.
Sounded like a good idea. Everyone thought it would be oK.
It was ok for a while and then the rotor contacted the side housing and stuck a single side seal in so now I have low compression on one rotor face.
I have no idea what my engine is (original? rebuilt? reman? replacement?). I do know with poly engine mounts it really buzzed way more than my FCs engine with solid engine mounting and with AC on it was unbearable.
I suspect the rotors were at least 2 letter weights apart. This imbalance would flex the e-shaft more which would throw the rotor into the side housing.
------------
What you should do if you want to rev to 9,000rpm.
Use new FD rotors that are already side cut from Mazda or have your existing rotors side cut.
Have rotating assembly dynamic balanced.
Use stock 2mm seals (no 3mm steel, 3mm ceramic ok).
Use the largest rotor bearings available.
Use RX-8 stat gears/bearings.
Now you have an engine that like the 13B-MSP Mazda would be willing to rev to 9,000rpm with warranty.
-------------
If you want to rev higher than 9,000rpm or even more reliably you can get into some of the other old school NA rotary mods including full oil system upgrades with loop line, clearancing and such. That is a big topic.
If you want to rev higher than 9,000rpm you should use ceramic or carbon/aluminum apex seals.
So you're saying that if I throw a GT55 on my 1.8L Integra and it continues making power beyond it's 7200 RPM fuel cut that I should just bypass it and rev it out to 9500 RPM where the turbo wants to be?
The mechanical/balancing aspects of the factory 13b of the OP's motor is untouched, so the influence a power adder has shouldn't be the driving factor over common sense. If the motor is relatively well balanced from the factory (which it is), then MAYBE, at most, maybe 750 RPM over the factory redline of 7000 RPM.
Yes, the elimination of the twin turbos helped with breathing on the top end and it WILL continue to make more power up there than it used to, but the MECHANICAL side things should dictate where you place your powerband, not your bolt ons.
If he instead talked about dynamic balancing of every part of the rotating assembly, then the factory turbos being balanced and everything hand ported, I'd say rev it out to the moon. 9500 RPM? No problem!
If you had read my post, you would have realized I was talking about where to shift given the limitations of the stock rotating assembly and the power band of the engine.
*No one* said anything about shifting at 9,500 rpms just because the engine could theoretically make power there (it wouldn't, as my dyno chart shows).
*No one* said anything about shifting at 9,500 rpms just because the engine could theoretically make power there (it wouldn't, as my dyno chart shows).
But it was really interesting to me how hard the stock turbo, stock engine (around 300rwhp) pulled up to 9,000rpm in 1st and 2nd.
If you take your dyno pull and input this data into your torque at the wheels equation the answer is there.
Torque multiplication through gearing in the low gears means you are making more torque at the wheels not shifting even though torque is dropping off at the flywheel.
The stock turbos with full bolt-ons are actually pretty good for not dropping torque in the high rpm power compared to a small 300-400rwhp single turbo since they have two 51mm exhaust wheels in big 1.20AR combined (0.60AR each) exhaust housings.
So you're saying that if I throw a GT55 on my 1.8L Integra and it continues making power beyond it's 7200 RPM fuel cut that I should just bypass it and rev it out to 9500 RPM where the turbo wants to be?
The mechanical/balancing aspects of the factory 13b of the OP's motor is untouched, so the influence a power adder has shouldn't be the driving factor over common sense. If the motor is relatively well balanced from the factory (which it is), then MAYBE, at most, maybe 750 RPM over the factory redline of 7000 RPM.
Yes, the elimination of the twin turbos helped with breathing on the top end and it WILL continue to make more power up there than it used to, but the MECHANICAL side things should dictate where you place your powerband, not your bolt ons.
If he instead talked about dynamic balancing of every part of the rotating assembly, then the factory turbos being balanced and everything hand ported, I'd say rev it out to the moon. 9500 RPM? No problem!
the rotary is way different than a honda. the IMSA GTU guys in the 80's were running 24 hour races, shifting at 8500-9k with engines that were basically built to the same specs as a stock FD.
the honda will explode completely if you rev it to 7201rpm (in fact seriously keep it under 7k). they drop valves, throw rods, etc. major damage, its not pretty. the KA engines are even worse, in an endurance race the factory teams can't even keep them together.
or maybe the rotary is to the honda if the honda came with a fuel cut at 5000rpm from the factory.
the rotary is way different than a honda. the IMSA GTU guys in the 80's were running 24 hour races, shifting at 8500-9k with engines that were basically built to the same specs as a stock FD.
the honda will explode completely if you rev it to 7201rpm (in fact seriously keep it under 7k). they drop valves, throw rods, etc. major damage, its not pretty. the KA engines are even worse, in an endurance race the factory teams can't even keep them together.
or maybe the rotary is to the honda if the honda came with a fuel cut at 5000rpm from the factory.
I didn't expect this from you of all people. No, it has nothing to do with rotary vs. reciprocating engine. All I'm saying is that mechanical (dynamic) balance is the primary determining factor for setting redline on ANY motor.
Sometimes redline is set artificially low because the way decibel limits are tested are by revving the engine to a percentage of redline and measuring.
Sometimes redline is set artificially low because the motor is dropping torque so hard before that point that revving the engine any higher just results in more wear without an increase in acceleration.
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The rev-limiter (when existing, ie on modern efi cars) is the hard limit the manufacturer decides to put on rpms to limit their financial liability.
I think this is what you are referring to.
Note- the early rotaries did not have a rev-limiter (and many other old carb'ed cars).
In the production car rotary racing the redline buzzer was used in reverse, when the engine came down off the buzzer the drivers downshifted to get the rpms back above redline buzzer.
So there is a red mark at 7500rpm on an FD tach, and a solid red mark at 8000, for manual trans vehicles. based on your charts, and the chart from Mazda I posted above, that's still a pretty good guideline. Shift between 7500 and 8000rpm. The limitation is either the stock turbos (too much backpressure for one thing) or the stock ports (intake port closing timing especially).
Without bigger turbo(s) and street port shifting over 8000rpm probably doesn't benefit you.
Actually, you can see from Tom's dyno chart that the stock twins are less restrictive on the exhaust side than a single turbo with similar output potential.
Makes sense, two 51mm turbine with combined 1.20AR versus a single 70mm turbine in a 1.05AR exhaust housing.
That is probably why his stock twins make slightly better high rpm torque (both our compressor are maxed out on these dynos).
I am doing this research because I am developing my FD the racing class below what my TII was in that requires stock turbos and stock engine internals (just balanced).
Looks like the stock twins have great potential, but I won't be able to be in the right gear all the time in auto-x.
To cover for that I plan to put the stock twins compressors into series compounding boost during spool up and below 225rwhp and then switch to parallel above that.
That way I can run 30psi fading to 17psi - hmmn, just like on the EFR single turbo. Dyno chart will probably look very similar to the EFRs.
06-11-17, 09:26 PM
