TechGeek

Yeah... I don't get to login and post as often as I'd like.

The article was from April 1, 2008... no? Either way not real yet.

Wurmfist

I hate to be a correcter correcterson and I may get flamed but as an engineer there is a large mistake that has been commented on here several times.

Oxygen is not flammable. The properties of oxygen is that it is an oxidizer that promotes rapid combustion. But if there is no other fuel source the oxygen itself would not detonate or combust. It needs to be treated very carefully (I.E. Read about the apollo 1 crew disaster) because it supports combustion but again, it is not flammable.

Nitrous Oxide is an oxidizing agent, when it's in the presence of combustion it releases oxygen, but it is much safer than pure oxygen.

Sorry, but I had to clear that up.

Kane

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New more advanced information available on my blog under General Performance - www.ppo2performance.com

Updating as I get some free time.

dansy

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Oxygen yap your right.....but I believe they are talking about LOX Liquid Oxygen and in that case it will literally burst in flame with contact with fuel or grease...I do follow a long list of precautions when I fill-up the plane with it.... and everybody knows that aircrew like shortcut......but I like to stay unburn

And before you say only ground crew does that....I'm a Flight Engineer and I can do and sign for any jobs on the plane.

wcs

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Great read Kane, thanks for all the work, and to all who contributed.

FazdaRX_8

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I get frustrated with the superchargers parasitic loss which will result in a torqe hit witch the Renisis is already lacking

Pittit racing dyno shows 300hp and 195tq,
turbo 300hp and 245tq

on nearly the same boost pressure

that's 50lbft. often hear the expression hp sells cars and touqe wins races?

as far as superchargers being more reliable, hence you hear less engine failures. this comes from the driver/tuner. you can't just raise boost with a supercharger, you got to get another pully and install it.

with a turbo, you have some guy with turbo kit designed for 5-7 psi, but he has a boost controller and sets if for 10, cuz, he can? result = boom

so turbo failures are due to boost controllers and ignorant people

Kane

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That is true - and I had that in my original post...


However I will say; ultimately it is the POWER that makes a car fast, torque does no work.

FazdaRX_8

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power as a form of measurement? as what values?

Kane

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Power is measured in force over time.... torque is just measuring force.

cliffkemp

tq is force. work is force x the distance and hp is work done over time. they are all apart of a physics equation. Its a matter of where the power is when usable. I see so many cars with dynos showing 600hp or more but it peaks at 7k rpms and from 2k to 5k there is little power comparatively speaking. Great for tall gearing but not for us. The whole sc vs turbo is a matter of where you want the power and how much. We have more rpms to play with so a turbo would be better but, as someone mentioned, you cannot just boost it and think everything is going to be ok. With either system, it comes down to the same thing, usable power. Both are good but, the real question is, how are going to cool the thing with all that power. So many focus on power and not the cooling and lose the engine.

Second, taller gearing will help in mpg whether in town or highway. Anytime you can decrease the rpms, you decrease fuel used at a given speed. The trick is to use your dynos and figure out when you have enough tq to maintain a speed at a given rpm. If you cannot maintain the speed and are having to downshift, you need a shorter gear for that speed. The 8, even at 45mph at 2250 rpms is maintaining that speed on a 6% grade so there is room for improvement. Its really comes down to what you want and how you want to go about it.

mysql101

Even if you don't down shift - if you have to increase load (more throttle) to maintain the speed, you may end up using more fuel in the higher gear than you would have in a lower one (higher rpm, lower load).

cliffkemp

To an extent. There is only so much air/fuel available even at low rpms hense the power available at that rpm. If you are at lower rpms, you dont use as much fuel cause you dont have the power available as you are not burning as much fuel. Hope you got that. I can try to explain it a different way if you didnt get that. You have a higher load, yes. At a given rpm, you only have a certain amout of fuel that can be burned. This is simple physics. Have any questions, feel free to ask.

Point is, you are better off at lower rpms provided you can maintain the speed, too low and you will lose speed. The 8 is geared too low for highway speed but, for a reason. Some mags stress passing ability in top gear and mazda fell for the 30-50 test and the 50-70 test and made the gearing too short to achieve better fuel economy at highway speeds although the tq is there to keep the same speed at lower rpms. My 8 can maintain a 6% graded hill at 45mph. I am sure where it is flatter, the 8 can be geared so that it would have more like my neon and get 27mph/1000 rpms instead of about 20. I am not sure what the 'happy median' would be as I have not had time to test that. For those that dont like to change gears as much to accel, I am sure you are happy with the current gearing as 6th pulls well at 80mph.

cliffkemp

You are very correct on this and with many that I talk to on other sites, they do not seem to get this and claim to be engineers and such. Due to design, the rotary doesnt do much with tq at first but, it does a lot more work. Part of the reason for this is that it has a handicap at low rpms due to leverage of the eccentric shaft.

The gearing I stated later on this discussion is similar. You stated, and other, that if you used taller gearing, you would use more gas as you would want to press the accelerator more. This is true to a certain extent. With taller gearing, you can get better mpg. The best gearing mazda could have put in the 8 is leaving the first 5 pretty much the same and using a much taller 6th. I believe that mpg could be close to 30 if we had closer to 26 or so mph/1000 rpms for 6th.

I have done this with my neon. I used to have a sport trans with a 3.94 and 5th was a .81. Now it is a 3.55 with a 5th of .72 which changed the leverage in each gear. I get 9 mpg more with the taller transmission and results will vary based on how people drive. The main difference was 21 to 27 mph/1000 rpms. It doesnt pull like it used to but, its the power available at the rpm is what makes a difference in mpg as well. This is why I said to use your dyno if you want to take the gearing thing further.

Brettus

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Normally (with a piston engine) you would be correct - however with a rotary engine your volumetric efficiency at low rpm is way less than at higher rpm . So yes , it is possible to get better fuel economy at a higher rpm .

cliffkemp

That would hold true as long as you just have one set of fuel injectors working as you do in a piston engine. We have 6. I hear the new 09 has just 4 now though. My point is, if you are under identical situations and one car has lower gearing, the other has taller gearing, you will get better mpg in the taller gear as you will be going faster with the same fuel used. The rotary is no exception to this. Fuel burned at a given rpm tells power available. I have tested this time and time again and if I drive at lower rpms but stay less than 3000 rpms, I get better mpg. The part that I will agree with all of you to certain extent is load depending on speed and %grade of the hill. It is a fine line.

My point is that if you keep the rpms low, you will use less gas just as a piston would. Engine load is a variable that is hard to pin down cause you will never be constantly going up hill for a full tank of gas and if you go down a long hill and use engine braking, you mpg will not be true cause there will be no load and no fuel will be injected until you either get slow enough that you hit idle speed or you hit the 'gas' yourself. Engine load has little impact in most circumstances. I have gone up and down the appalachain mts and tested this going 35-40mph with cruise on and got better than average mpg both up and down the mountain.

Verify for me if you will, I have heard that at idle, the rotary runs somewhat rich. Assuming this is true, you are better off engine braking than pushing the clutch due to this. There are many variables that can take into account. It may seem like you get better milage on the interstate at speed but with a taller gear (to an extent) it can be much better. I try to draft behind trucks many times but, careful to do so as wind resistance means less air to the radiators as well.

mysql101

At idle I am at 15 AFR range. But obviously engine braking uses zero fuel, so it would be more fuel efficient.

Anyway, back to the point - I watch the live fuel usage on the scangauge II as my comparison basis. If I am in 6th and need to apply throttle to maintain speed up a hill, I have found shifting into 5th and driving with a higher rpm uses less fuel. This seems counter intuitive, but there is less load on the engine with the lower gear.

Brettus

iTrader: (2)

when I said it was possible I din't mean it was necessarily true - just possible . Did you know that rotaries can actually be more fuel efficient than piston motors with similar power in competitive circuit racing ?

As far as engine braking goes - yes in most situations better to engine brake than push the clutch . Not only for fuel conservation but for control of the car as well .

mysql101

one of the reasons why they won le mans.

cliffkemp

I agree with you to an extent. Sometimes it is more efficient to go to a lower gear. This is why I said there are certain circumstances. I do agree with you. We all know that there are many factors that can influence this.

BTS89

i have a ZEX nitrous system in my car (it came on it when i bought it and im a noob when it comes to nitrous) i was woundering what i would have to do to put a bottle in and run it. any engine mods gauges or any of that sort?

JinDesu

iTrader: (2)

Might want to explain what you mean by "having" the ZEX nitrous system. Pics could help, along with quickly learning how nitrous works.

Viich

I'll admit that it's not a 13B-MSP, and that the side exhaust ports could make a big difference, but my 12A gets significantly better fuel economy in 4th gear at highway speed than in 5th - 20% or more difference. Overlap could be a factor, but there isn't that much overlap in a stock 12A. Best fuel economy observed was keeping the tach between 4000 and 5500, and that's the highest I've tested. On a 28 year old engine with 200K on it, I don't want to push the revs any higher.

cavemancan

Another...Not sure if this should go in this thread but I hope I can get some direction.

So...I've been reading...thinking...planning...deciding...My head hurst. My current situation is this...Buy a new car for $40k + (I hate payments) or keep the Rx8 and restore her to an even better state then it's original condition. Keeping the Rx8 would mean I could save a significant amount of money by modifying the car over buying a new one ($25K).

My point: I am keeping the Rx8 and my engine is on the verge of death at 94k miles (low compression). I am going to Mazda to see if I can get it replaced under warrantee. Either way I need MORE POWER! I think I decided on what I should do...Greddy Turbo with MM upgrade but I need more guidance to make sure I am making an informed decission. I reviewed several threads discussing all the other Turbo options and compared them with my wants. I even considered a v8 swap due to easy reliable power but I don't want to risk loosing that "OMG this thing handles like a dream" feeling I get when driving her!

This is what I want:

- Track level reliability (emphasis on cooling...road course and autocross for more then 20 minutes of racing)
- relative ease of maintenance (can be fixed with hand tools and a little know how)
- Daily driver
- Torque...I heard Chicken and Brettus were making awesome numbers
- No OMG moments due to inconsistant boost (@Brettus...Dyno thread with Greddy Boost controller)
- CONSISTANT
- About 300 to 340 wHP (start low and build up as I become more comfortable with the car at that power level).
- Cobb friendly (I might buy it early in NA form to keep me busy till I take the plunge and go MM Greddy)

Based on this I figured...The greddy setup is the most widely used kit and therefore should have the most reliable setup per HP ratio? My brain is not always utilized correctly so please feel free to correct me.

Things I should get on top of the Greddy kit:

- BHR rad
- Mazsport water pump and thermastat
- BHR coils (got um already)
- BHR fuel pump
- BHR midpipe (already installed and made of the AWESOME! )
- Bigger 2nd injectors (just in case)
- Greddy oil pan?
- Sohn? (I remember reading about this but I forget about the benefits)
- External wastegate (I keep reading about issues with an internal wastegate re: greddy kit...Can someone explain and how hard would it be to convert to external?)
- What else?

Finally...Can it be done for $10k to $15k...and no I can not do the work...I can help but I only know enough to be dangerous. I am guessing, based on some research, I can get all the parts for about $8k +...Then add installation, tuning, and any other "OMG I need this" moments and I am guessing I will be in the $12k neighborhood?

I think I might get the Greddy MM kit plus the BHR rad and clutch/flywheel first...then work on everything else as I go along.

I will delete this post if it is not appropriate for this thread...Thanks!

Chris

Kane

iTrader: (1)

The biggest problem you have is availability. I am not sure the MM can be had anymore, you could go BNR or the SFR kit. Look up wanted two's FI thread, he has a really good dream sheet shopping list. With a motor that old, a d you HP goals, I'd be looking at new motor and turbo at the same time, what you sound on parts you will save on labor of paying to do each project seperatly.

As for low vs top mount etc, I've installed and tuned both, and I don't really see a HUGE differenceesp at our low boost street driven power levels.

cavemancan

Thanks for the advice...I'll check that thread out.

Also...about the engine...my sig says it all...pending warrantee. If Mazda covers it I am going FI.