bren5279

iTrader: (15)

Ive got an 05 r8 auto 4spd, and I dont mind having the auto since it has the manual overide, but the difference in hp does quite bug me.

The difference is about 50hp, so my question is what mods that would be under $500 that would add up to that kinda gain short of a turbo, or is there any? I already have the knn air cyclone intake, but i have no idea what kind of hp it adds, anyone know?


Like how much hp would an exhaust add?

And how much help would getting it dyno'd do?

dozer

iTrader: (3)

RIWWP

iTrader: (2)

Since HP is a function of torque, and the AT makes about the same amount of torque as the MT (faintly more actually), all you have to do is increase the rev limit on your AT to 9,000 RPM (and have maps capable of mapping the additional data) and BAM, you have almost all of the difference made up.

Not quite all, because an AT loses more power from drivetrain losses than MT, having to churn a mass of fluids and all.


Course, the lower rev limit was largely in place BECAUSE of the transmission, so do it at your own risk.



Increasing "power" is actually increasing torque. RPM then takes that torque and uses it over time to produce horsepower.

People forget that this is how the whole thing works.

MazdaManiac

iTrader: (3)

Unfortunately, though the 4-port's peak torque is a bit higher than the 6-port, that peak happens at a significantly lower RPM.

The assumption above only works if torque were constant over the rev band, which it is not.
Raising the RPM limit increases the area under the curve, but not the HP peak - at least not in a significant way.

Apples to apples, the 4-port is typically 75 HP or more under the 6-port in dyno tests. The most cost effective way I've seen to bring the peak power up to the level of the 6-port, bar none, is FI.
And it just barely accomplishes this.

Sorry - the real world is significantly more disappointing than the world on the bench.

ShinkaEvo

iTrader: (3)

Wondering where does that 75hp or more comes from, just curious....

MazdaManiac

iTrader: (3)

From countless hours I've spent on the dyno with hundreds of RX-8s.
4-port, 4-speeds make 125 to 145 at the wheels typically and 6-port, 6-speeds make 175 to 205 HP.
The lowest NA 4-port I've seen is 117 HP and the highest NA 6-port was close to 230 HP.
For FI, the 4-port can do up to almost 300, though the numbers are typically right around 200.
The FI 6-port will do 240 typically, up to about 400 HP.

ShinkaEvo

iTrader: (3)

Thanks for the info, MM~ appreciated.
There are just too many factors would affect whp....

To OP:
For $500 you really can't do much....maybe get cobb AP to start with.

MazdaManiac

iTrader: (3)

I figure the 4-ports make between 140 and 185 HP at the crank.

They are almost ALL horribly tuned right from the factory - much worse than the 6-port, which probably says something about Mazda's confidence in the 4-speed autotragic tranny.

FWIW, the 6-port, 6-speed autos make about the same power as the 6-port manuals.

RIWWP

iTrader: (2)

Agreed

This is why I made an attempt to point out what most seem to not realize....v

Revolutions per Minute.


Ignoring MazdaManiac's real world corrections for a minute, just to get your mind wrapped around theory:



Yes, this isn't an actual dyno, I made a chart after some plugged in values in a spreadsheet. But it serves to explain this.

See how the AT might be making a bit more torque (the flat line), but since Horsepower = RPM * TQ / 5252, as RPMs increase, you get more Horsepower out of the same torque.

Being unable to get 1,500 RPM farther down the chart prevents this example AT from reaching the MT horsepower. If the this example AT were to suddenly be able to get 9,000rpm, then they would surpass the MT, as it has more torque at the same RPM.


Again, all examples to illustrate a point. Once you add in real world considerations, such as the actual torque curve (which increases and/or decreases across the RPM range), powertrain losses, airflow limitations, fuel flow limitations, etc... this isn't something you can just call with a single reason.

But, the limitation of RPM puts you behind, and it's something that is VERY hard to overcome. Typically, if a vehicle has similar HP and TQ ratings, it means that the peaks are closer to 5,252 RPM. If they have much higher torque ratings than horsepower ratings, then they have RPM peaks less than 5,252 (like diesel engines, heavy machinery, etc...). If they have might higher HP ratings than TQ ratings, then they usually have peaks higher than 5,252 (like 800hp 300tq formula 1 cars, 16,000+ revs)


It's just how the math works.




Again MM, I get that real world is a massive monkey wrench in this....

MazdaManiac

iTrader: (3)

Here, let me help you with that:

RIWWP

iTrader: (2)

.

ShinkaEvo

iTrader: (3)

Thanks guys, definitely lesson learned.

bren5279

iTrader: (15)

Wow thank you for all that info, wish more people would respond more like that!

So how badly would force injecting it drop the fuel mileage...

So all in all are you saying that if the manual reved at the same as the auto, they would both have close to the same pull?

bren5279

iTrader: (15)

Can anyone explain why the numbers are so low compared to the mazda numbers?

I feel like with all the numbers and gas consumption that mazda should have just put something like a v6 in it.......



Anyone out there actually have a dyno sheet comparing the 05 at 4port vs however many port the 04 mt is?

RIWWP

iTrader: (2)

FI = Forced Induction, I.E., turbocharger or supercharger.

As mentioned above, just increasing the rev limit doesn't eliminate a host of other reasons for being a lower horsepower. But it does help.

The auto actually has more "pull" sensation than the MT, being higher torque. The MT just can hold it longer/later.

All of these numbers are wheel horsepower numbers. Meaning the engine is being dyno'ed AFTER drivetrain losses. Mazda's numbers are at the crank, so the motor doesn't have anything extra to rotate. Unless you pull the engine out and have it dyno'ed separately, you won't get those numbers on a stock engine/8. Some debate if you still will or not. There is no point to that however, as that isn't real world. What is put to the ground is what matters, and when the engine has to turn the transmission gearing, the fluids, the diff, the driveshaft, the axles, the wheels, tires, etc... the soak power, as some of the effort of the engine is being used to just turn these, not move the car.

Powertrain losses increase as RPMs increase, so our drivetrain loss % at peak RPM are higher than other cars with much lower peak power points.

bren5279

iTrader: (15)

Wow, that all explains a lot. So basically if they both revved the same then the mt would actually feel like it was pulling harder?


So what kinds of things short of a full on turbo would give the best effect for raising the torque if at all possible?

and would getting a turbo even be worth it?


lastly would getting the ecu remapped aka tunin it on a dyno help at all?

RIWWP

iTrader: (2)

No. If they both rev'ed the same, the AT would still feel like it pulls harder, because it has more torque (although lower on the RPM), however, AT's lose more power to drivetrain than MTs, because of all the fluid they have to spin around, so the torque drops off faster, and the resulting HP at the same RPM is similar at best, or lower. All else being equal. Which they never are.

The 4 port has 2 fewer intake ports than the 6 port, so naturally aspirated, it simply can not pull as much air through the ports, less surface area of the openings to put it another way.

Horsepower is all about air flow. Volume, not pressure.

Nothing really. Mazda milked this engine for basically all it could get right out of the factory. The only 2 easy increases are removing the naturally restrictive CAT that they have to have on there for federal emissions, and to tune the ECU to match your specific car and remove conservative tune that is designed for the average consumer. Combined, they give a MT 8 about 15hp, 20 tops depending on how bad the tune was before. All other bolt on mods put together MIGHT give a MT another 5-10hp. Maybe. Most aftermarket bolt ons are inferior to factory (intake, cat back, etc...), so the only reason to do them is to change the sound of your 8 or reduce weight (the factory exhaust IS heavy).

Depends on what your priorities in life are. If you can't afford to budget $10,000 for forced induction, then don't even start trying. If you can afford it, then yes or no depends on how valuable it is for you.

Yes. Covered above.

mdw1000

If they'd put a V-6 in it, then I wouldn't have been able to gain on an F430 in the carousel at Road America with only 5 psi of boost. The car would be too nose heavy to have the balance that it does.

Don't forget gearing as a factor in acceleration in all this. Those of us with the 4AT have a huge gearing disadvantage to the other three transmissions.

09Factor

So let me get this straight. Adding a form of FI would over come the lack of HP/TQ compared to a 6 port Renesis?

alnielsen

iTrader: (4)

We had a local dyno day this spring. MDW1000 (post above), with his supercharger, dyno'ed 10hp higher than my stock MT.

RIWWP

iTrader: (2)

This is like asking "if I get money, will I make up the deficit between what I have and what Bill Gates has?"

There is a critical qualification in there of HOW MUCH that allows us to answer yes or no.



Is it possible to go FI on a 4port AT and get to the 6 port MT rated power? Yes. It is also possible to surpass it. It is also possible to not get there at all. Hell, it's even possible to not get an improvement over where you are at now.

The other qualification is "for how long". I bet there are FI methods that will top 500hp....for maybe a mile. If that. IS that a stretch? Ok. Would you rather take 260hp for 80,000 miles or 330hp for 20,000 miles. (Just throwing numbers out there. There are tons of variables in how far you will get, considering you can also take 160hp for 5 miles). But, the more power you go for, the more stress you have on your engine, and the shorter it will last. So finding out how much is enough is something alot of people don't think about.


That being said, if your goal is "power like a MT", then you can spend $10,000 or so putting FI on your auto.

Or, you can take that $10,000, add it to your trade in value of your 8, and buy a 6 port MT. You still have the warranty, a newer car, you don't have the headaches, the down time, the troubles, the hassles, or the pending failures.



If you want to do it, sure, go ahead. But there isn't a simple or easy black and white answer to this.

mdw1000

And I was only running 3 psi that day. And I am non-intercooled.

ShinkaEvo

iTrader: (3)

Any don't forget skills effects performance...

There is always better and faster car out there.
At the end the only thing matter is, do you enjoy your ride or not.

Rud'X8

hi guys after reading all the info on these RX 8 , this is my actual first Rx8 AT previous owner of a 93 RX-7 MT, my question is < i haven't seen any mods or app as far as flywheel for the automatic , has anyone changed the flywheel to a lighter one ? , all im finding will fit Std trans, or is the flywheel on the AT different ?

mdw1000

Automatics don't have a flywheel.