r0tor

iTrader: (1)

thank you

r0tor

iTrader: (1)

this is how racing beat runs their engine stands - increasing the rpms very gradually. Their dyno actually will take 70 seconds to go from 2000rpms to 9000 rpms, which is longer then a 5th gear pull would take by a long shot (which also means "more resistance" on the engine to some people here it seems)


https://www.racingbeat.com/testprocedures.htm

"We undertake all dyno testing in sweeps, starting below 2000 rpm then accelerating by 100 rpm increments per second, and the dyno makes dyno inertia corrections that arise while the engine is accelerating. Data is logged during these test sweeps and reviewed at the completion of each run."

dmp

:tup: :D


as a side note, my PGT had nearly 20 more HP in 4th, than in 3rd gear - on the dyno (after boost).

I'd like to dyno a boosted RX8 in 5th...in fact, when I dyno my stock RX8, chances are it'll be a 5th gear run. I've seen cars to WOT, top speed runs on dynos w/ little worry about things I'm reading on this site. Naturally, I have no idea if those cars are still running, or not. :D

PoLaK

iTrader: (1)

Ummmmm no.
Although the engine creates a vacuum effect and naturally suctions air in as a function of throttle position and RPM, airflow is just as much dependant on the volume and speed of the air entering the intake.
Your post is in complete ignorance, if airflow through the engine was a fixed value there would be no need for a Mass AirFlow Sensor, inaddition to that why do you think they have special dynos with GIANT wind tunnels in front of them designed to blow HUGE amounts of air at cars being dynoed, RAM air....

..... Your talking apples and oranges, its an engine dyno they closely monitor engine temps down to a tenth of a degree, I'm willing to hinder a guess that they also cool the engine differently and more efficiently.
___________
Simply put, Higher the gear the greater the load the greater the chance for ping, the greater the chance for overheating, both due to the lack of airflow; made worse by doing more then 1 run a session.

I wouldn't do more then one without a cool down period.

MazdaManiac

iTrader: (3)

Ram air effect is negligible if there is no ducting to take advantage of the effect.
The RX-8 has no such ducting.

What ever amount of air goes past the MAF goes into the engine. It is "fixed" in that whatever is metered, goes into the motor while it is under load.

On a dyno, the absolute load remains the same for a given amount of airflow regardless of gearing.

The issue with gearing is simply a function of load over time. You are putting the engine in a loaded situation for a longer period of time in higher gears and, therefore, generating wasted energy (heat) for a longer period of time. However, the cooling capacity of the system remains the same so the stress goes up.

rotarygod

Actually pr0ber and PoLaK are BOTH right when it comes to airflow. At least in how we can control the fuel delivery to the engine that is. I know you guys are both talking about the physical amount of air entering the engine but I'll explain how this translates into fuel requirement. There are more forms of control than what I am going to mention so I will just stay with the two basic comments made. More specifically I am going to address the comment about the need for a mass air flow system.

pr0ber stated that "airflow through the engine is a function of throttle position and rpm". PoLaK's reply included the sentence " if airflow through the engine was a fixed value there would be no need for a Mass AirFlow Sensor".

Yes and No. The RX-8 uses several factors to determine the proper way to meter fuel to the amount of air entering the engine. Among them is the amount of calculated airflow into the engine, engine rpm, air intake temperature, and throttle position. All of these can be in nearly infinite combinations. The ecu takes all of these signals and based on preset values determines the proper way to meter fuel for the most power, emissions, drivability, and/or economy. Each aspect may take precedence over the others based on how the car is being driven at that point. This is but only 1 way to calculate the air/fuel requirements.

Another popular way ONLY takes into account the throttle position and rpm. This method is called Alpha-N. Most race cars use this method and it works very good in terms of making full power. Holley has an aftermarket efi system that replaces carbs called the Pro-jection that uses Alpha-N. It is a system that is more common on high overlap engines such as those in race cars. This is because Alpha-N does not require a strong vacuum signal to function properly as some other systems do. Most standalone efi systems also have the ability to run Alpha-N. The disadvantage in Alpha-N is that it is not the best for fuel economy or emissions. It can not vary the air/fuel ratio depending on load as a map type of system can. Alpha-N can also have a very touchy feel to it. This is because the throttlebody is typically sized for max flow at max rpm. This means that at lower rpm's, the throttle body doesn't necessarily need to be opened all the way in order to provide the engine with all the air it needs. Any throttle position above this is worthless in terms of making more power. Alpha-N is setup to provide fuel based on the engine's requirement. At 4000 rpm it may be injecting just as much fuel at 50% throttle as it would at 100% since the engine may be getting all the air it needs. There is alot less fine tuning with Alpha-N. Alpha-N makes it very clear that just because you are at a higher throttle at a particular rpm, it doesn't mean that any more air is entering the engine.

Now for the real answer. The reason why the pressure changes with increased throttle is because the throttle plate is opened farther. It doesn't mean that the engine wasn't ingesting all it could at a higher vacuum level. This really depends on rpm and size of the throttle plate. If this is the case, the vacuum level will change with throttle position but the amount of air ingested won't. This phenomenon will also vary with rpm as at lower rpm's you can be at max airlfow potential at a low throttle level whereas at max rpm you need to be at max throttle. This is all independent of intake manifold design. That has it's own effect.

FWIW: In order for a fan to provide "ram air", it would have to be blowing somewhere over 100 mph and even then it's only ram air if the intake is designed for it. A 100 mph wind blowing on an air filter is not necessarily a ram air system nor is it necessarily ramming any more air in than no wind at all. Most likely not. Not even the "Ram Air" Trans Ams have a "ram air" system. It's bad marketing bother there and the aftermarket that is confusing people. Those large fans are there soley to keep the car from overheating. That's it. At high engine loads and speeds, the stock fans are not adequate to remove heat from the oil coolers and radiator.

shaolin

A bit off topic, but RG are you an engineer? Or have you just been playing with rotaries for a long time?

RX3+5

Our engines have allot less mass to absorb heat before they go critical. That's not a bad thing at all, just something to be aware of.

Vince

XeRo

fellas...just found out i'll be travelling to Newark tomorrow - Fri...if Jon/Jeff are near or will be near that area let me know...i wanna check out your cars...

dmp

Did I miss somewhere in this thread about where the RX7 guys dyno? Is it comparible to say if 'they' dyno in a 1:1 gear, our cars should have little trouble doing likewise?

Apples:Apples there?

RX3+5

I think you should try it and prove it to yourself!!!


Vince

Nemesis8

iTrader: (3)

Jon, I found this:

"Commanded Equivalence Ratio – fuel systems that use conventional oxygen sensor displays the commanded open loop equivalence ratio while the system is in open loop. Should report 100% when in closed loop fuel. To obtain the actual air/fuel ratio being commanded, multiply the stoichiometric A/F ratio by the equivalence ratio. For example, gasoline, stoichiometric is 14.64:1 ratio. If the fuel control system was command an equivalence ratio of 0.95, the commanded A/F ratio to the engine would be 14.64 * 0.95 = 13.9 A/F."

So I guess the answer is yes.

I agree, I want a sCANanlyser also, but I could buy this product today. Time is money...

beachdog

If the rx8 does not have ram air wouldn't the engineers locate the intake in an area of positive pressure? Wouldn't the big fans help intake by creating an area of positive pressure?

Lschiavo

More videos pleaseeee!!! Thanks for your great contribution philodox and everyboy in this thread.
:D

davefzr

Maybe this will finally make it feel more like your race car Are you going to purchase the GReddy kit, or do you have your eye on possibly another choice?

rotarygod

There are areas of the car that exibit different pressures. The nose of the car and the base of the windshield are higher pressure zones. The middle of the hood is a lower pressure zone. You obviously want to place the intake in the higher pressure zones. The RX-8 intake is behind the front bumper where the air passing this area is higher pressure. However, just because it is higher pressure than other areas does not make it "ram air". The big fans used at dynos aren't blowing terribly fast. Definitely not over 100 mph. The speed they are blowing at isn't even enough to give you positive intake pressure at off idle rpms. As the engine rpm's rise, the effect the fans have on intake pressure gets lower and lower. The whole point is that while airspeed past the car makes a difference at speed, fans at dynos don't do enough to be significant. They are adequate to help remove heat from the cooling system though and that is their purpose.

"Ram air" is a subject that many people don't understand. GM and many aftermarket companies have really created a false image of how it works. By simply placing an air filter in the airstream, you do not have ram air. It is a "cold air" system. You aren't ramming anything anywhere. Even if you aimed the tube straight into the airstream so air flows directly into it, you still don't have "ram air". The reason is that as you are trying to force more air into the pipe, you are trying to increase it's velocity. As airspeed increases, density decreases. You've gone backwards. What actually happens is that the pipe resistance just becomes too great and much of this air goes around while what does enter the intake is at a lower pressure. Also not that this can happen even if the filter is in the high pressure regions of the car.

"In order to "ram air" into the engine, you need to find a medium that can do it for you. A turbo or a supercharger "ram air" into the engine. The question is how do we do this without the help of a turbo or a supercharger? One method that is built into every engine is the intake manifold design. This uses the airs inertia to help cram inn a little more right before the port closes. It's effect and rpm range is based on intake runner diameter and length. We've already got that though and want to know how to make the intake itself a "ram air" setup. In order to "ram air" into the engine, we need to compress it. In order to compress air, you need to make it slow down, not speed up. This is what a turbo or a supercharger do. If you could measure the airspeed before and after these units, you'd see that the air is faster on the inlet side.

To design an intake box that does this we need to do more than just place the air filter in the airstream. You need to have an intake tube in the airstream that then feeds a larger expansion (or more appropriately and compression) chamber. A way to do this would be to take a 6" pipe and feed it directly into the oncoming air. This pipe then feeds into a "box" where the area expands many times over the area of the inlet pipe. This box can contain the filter and then go on to the engine. When the air flows through this large pipe from the forward speed of the vehicle, it enters this chamber and the expansion in area slows it down. When it slows down, it compresses a little. This compressed air is what the engine is actually breathing. This is "ram air". How much of an effect this has is based on 2 things. The most important is vehicle speed but the next one is engine rpm. Obviously at 100 mph at 5000 rpm, the engine needs less air than it does at 100 mph at 9000 rpm. The amount of "ram air" available would be greater at 5000. Postive pressure is positive pressure though and a gain is a gain. For everyday driving though, you won't benefit at all. You might, maybe, possibly, on a cold day, see a slight amount of positive pressure at speeds as low as 75 mph but it probably won't be enough to feel. At speeds up over 150 mph though you might get a couple psi of "boost". In 1979, Racing Beat found that on their nonturbo 13B Bonneville Land Speed record RX-7, a "ram air" setup done in this fashion added 3 mph to the cars top speed. It hit 183 mph. Without "ram air" it would do 180 mph. Remember that the effect is much greater at high speeds. How much of a benefit does a properly setup "ram air" system really have on the street? I'd say little to none. At least not at legal speeds.

rotarygod

Real Estate agent.

I just study all the info on rotaries and cars in general that I can find. None of it is a secret. An anonimous forum member even went out of his way in an insult attempt to let me know that I know nothing that anyone else can't learn. That's true!

philodox

Well guys, I couldn't resist and put on my Mazdaspeed Front Bumper. Now the Intercooler is REALLY noticable. Unfortunately, the pics are at night. I'll take some daytime pics tomorrow. How do you guys think that Intercooler looks?

Kel Rx8

ure the man jon
i guess i should of been a pilot or water that money tree some more.
great job buddy

Moostafa29

respect!

PoLaK

iTrader: (1)

Salt sux on titgrey eh? Thank god i shloped on my winter coat of zaino b4 it started

philodox

Yeah.. and I've washed my car twice in the last 5 days to get the salt off.. it's a daily battle.. hehe

RotorManiac

Looks mean... I just wonder how air is reaching the radiator now. It looks like there is no gap left
By the way Jon, how many miles how you done with the turbo?

MazdaManiac

iTrader: (3)

I wish I could do that.

Mine is staying in the garage because every source of water around here is frozen solid. Even the self-washes are rock solid.

philodox

There's plenty of airflow. Those pics don't really show it all. I'll take some better daytime ones tomorrow. Also, you must realize that the air going through the intercooler still continues through to the radiator and A/C grills.

Oh yeah, it's been about 500 miles now. Averaging 15mpg. 17mpg on my road trip down to Jeff's place for the dyno. Which is very strange considering that I was getting 10mpg before the turbo. Mazda really has the stock maps running tooooooo rich.