Displacement on demand RX8?
09-26-2018, 05:03 PM
#51
Smoking turbo yay
I think it'd be more accurate to say more RPM doesn't necessarily require more fuel. As RPM increases, pumping losses and/or volumetric efficiency may decrease (to a point), but parasitic losses will usually increase. That's why any engine gets its best fuel economy within a certain RPM band: high enough that it's breathing efficiently, but not so high that parasitic losses offset that.
So yeah, technically you need to have the lowest RPM with the highest load that isn't lugging your engine.
Some of the newer cars(like the 9th Gen Civic 5-speed I drove at the driving school) will show you live fuel economy and it will even tell you if your RPM is too low or too high for the best fuel economy.
Of course, on an 8, there is also carbon buildup we have to worry about, but 3~3.5k is a good ballpark.
10-01-2018, 02:52 AM
#52
While I admire the attempt to make rotaries more fuel efficient, the last thing I ever think of when driving my RX-8 is fuel economy. I actually get a little anxious if I haven’t diven it hard that day lol
10-01-2018, 01:20 PM
#53
Registered
I have a turbo REW and I get like 5 mpg. the trick to better gas mileage is to not drive it.
10-01-2018, 04:38 PM
#54
Registered
Thread Starter
10-01-2018, 06:31 PM
#55
Registered
Thread was over the minute it was suggested that removing half of the power on an engine that produces 150 lb/ft of torque was a possibility...
10-01-2018, 07:20 PM
#56
Registered
Thread Starter
Half of 150 is all you need when cruising. We are talking about 75 torques here. There are plenty of small displacement 4 bangers that weigh the same as the RX8 that run just fine. I'm not trying to be fast and economical. I'm trying to be economical or fast. Its totally doable with the correct setup as has been discussed. Its just not worth doing.
10-01-2018, 08:17 PM
#57
rev it up
My engine died at the drags. The rear apex seal got shattered so I had to drive the car out of the arena to get the car towed.
With one rotor it was a struggle to get it out of the compound. So I believe this idea will not work on the Rx8
With one rotor it was a struggle to get it out of the compound. So I believe this idea will not work on the Rx8
10-01-2018, 08:37 PM
#58
Smoking turbo yay
Half of 150 is all you need when cruising. We are talking about 75 torques here. There are plenty of small displacement 4 bangers that weigh the same as the RX8 that run just fine. I'm not trying to be fast and economical. I'm trying to be economical or fast. Its totally doable with the correct setup as has been discussed. Its just not worth doing.
I have driven a rental Jetta once when my RX-8 was in a body shop. The Jetta 1.4 TSI has 184 lbft of torque @ 1400 RPM. From a rolling start, it will probably pull away at an 8 until maybe 25 MPH or so. Of course, if you try to pass anyone on the highway, the 150 BHP will start to rear its ugly head, while I can pass people fairly easily in an RX-8.
I know small displacement cars are popular in Europe, but more and more of them are joining the smaller displacement turbo trend, which, again, focuses on low-end optimization. Same with diesel, good low-end torque with 4~5k RPM redline. And do I even need to start talking about hybrids and EVs with a good amount of torque available at 0 RPM?
Rotary just isn't built for that. It doesn't have that kind of low-end torque to do it.
10-02-2018, 07:16 AM
#59
Registered
Thread Starter
No **** have you not read any of the previous posts? We have gone over this. Without significant modification the disabled rotor acts as an air pump leaching loads of power and pumping fresh air over the o2 sensor making the car run even worse because it would run super rich.
10-02-2018, 07:19 AM
#60
Registered
Thread Starter
You can't just look at the peak torque. You have to look at how that torque is delivered as well.
I have driven a rental Jetta once when my RX-8 was in a body shop. The Jetta 1.4 TSI has 184 lbft of torque @ 1400 RPM. From a rolling start, it will probably pull away at an 8 until maybe 25 MPH or so. Of course, if you try to pass anyone on the highway, the 150 BHP will start to rear its ugly head, while I can pass people fairly easily in an RX-8.
I know small displacement cars are popular in Europe, but more and more of them are joining the smaller displacement turbo trend, which, again, focuses on low-end optimization. Same with diesel, good low-end torque with 4~5k RPM redline. And do I even need to start talking about hybrids and EVs with a good amount of torque available at 0 RPM?
Rotary just isn't built for that. It doesn't have that kind of low-end torque to do it.
I have driven a rental Jetta once when my RX-8 was in a body shop. The Jetta 1.4 TSI has 184 lbft of torque @ 1400 RPM. From a rolling start, it will probably pull away at an 8 until maybe 25 MPH or so. Of course, if you try to pass anyone on the highway, the 150 BHP will start to rear its ugly head, while I can pass people fairly easily in an RX-8.
I know small displacement cars are popular in Europe, but more and more of them are joining the smaller displacement turbo trend, which, again, focuses on low-end optimization. Same with diesel, good low-end torque with 4~5k RPM redline. And do I even need to start talking about hybrids and EVs with a good amount of torque available at 0 RPM?
Rotary just isn't built for that. It doesn't have that kind of low-end torque to do it.
I get what you and saying and I agree.
10-03-2018, 02:40 PM
#61
How much fuel is injected is a function of power demand, NOT rpm. I know it's weird, but more rpm doesn't require more fuel. To produce 30hp at 3000rpm requires X amount of throttle, where at 4000rpm the same 30hp is produced with less throttle, therefore less air and less fuel per revolution. Obviously it's not a perfect correlation, the actual efficiency of producing power varies with rpm, but there is no hard/fast rule about what rpm is optimal for a given engine and given speed.
The side port everyone is hating on is designed the way it is to improve fuel economy in low regimes, like city driving. ItsI a compromise for sure, but should be a net improvement in fuel economy for a city dweller over a peripheral. How was your FC's economy in the city?
The side port everyone is hating on is designed the way it is to improve fuel economy in low regimes, like city driving. ItsI a compromise for sure, but should be a net improvement in fuel economy for a city dweller over a peripheral. How was your FC's economy in the city?
Last edited by T-von; 10-03-2018 at 02:57 PM.
10-03-2018, 02:57 PM
#62
10-03-2018, 03:52 PM
#63
Not necessarily . If you are doing say 30mph in 2nd gear at 4000 and change to 3rd and rpm drops to 2500 you will also need to increase the throttle otherwise you will slow down. By doing that , more air and therefore more fuel goes through the engine PER REV! There are many other factors that determine whether it actually uses more or less fuel at the lower rpm. Rotaries being more efficient at higher rpm rpm could well be using more at 2500 than 4000.
Also to those of you worried about low rpm and carbon build up on rotays, that build-up mostly happens on a cold combustion chamber during warm up. I've done quite a bit of experimenting on my rotarys and found that the engines that were warmed up the fastest, produced less carbon buildup and were damn near impossible to flood. That's why I NEVER let my rotary idle to warm up because it takes too damn long for those 9lb hunks of cast iron rotors to heat up that way. Idling doesn't create enough heat in the combustion chamber. A cold fuel soaked wet rotor is a breeding ground for carbon build up, NOT a hot rotor that's up to temp in a hot combustion chamber.
10-03-2018, 04:21 PM
#64
But the video link I posted is the exact same video the other person linked from Engineering Explained showing fuel economy based on gear/load. Fast forward to about 3:30 and look how the fuel economy goes up as you increase load while running lower rpm's. Remember my 91NA very weighed te same as an Rx8 and got 26hwy mpg at 3krpms vs Rx8 getting 23mpg running over 4k. That is a HUGE difference.
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Also to those of you worried about low rpm and carbon build up on rotays, that build-up mostly happens on a cold combustion chamber during warm up. I've done quite a bit of experimenting on my rotarys and found that the engines that were warmed up the fastest, produced less carbon buildup and were damn near impossible to flood. That's why I NEVER let my rotary idle to warm up because it takes too damn long for those 9lb hunks of cast iron rotors to heat up that way. Idling doesn't create enough heat in the combustion chamber. A cold fuel soaked wet rotor is a breeding ground for carbon build up, NOT a hot rotor that's up to temp in a hot combustion chamber.
Last edited by Brettus; 10-03-2018 at 04:24 PM.
10-03-2018, 04:53 PM
#65
Registered
Thread Starter
But the video link I posted is the exact same video the other person linked from Engineering Explained showing fuel economy based on gear/load. Fast forward to about 3:30 and look how the fuel economy goes up as you increase load while running lower rpm's. Remember my 91NA very weighed te same as an Rx8 and got 26hwy mpg at 3krpms vs Rx8 getting 23mpg running over 4k. That is a HUGE difference.
Also to those of you worried about low rpm and carbon build up on rotays, that build-up mostly happens on a cold combustion chamber during warm up. I've done quite a bit of experimenting on my rotarys and found that the engines that were warmed up the fastest, produced less carbon buildup and were damn near impossible to flood. That's why I NEVER let my rotary idle to warm up because it takes too damn long for those 9lb hunks of cast iron rotors to heat up that way. Idling doesn't create enough heat in the combustion chamber. A cold fuel soaked wet rotor is a breeding ground for carbon build up, NOT a hot rotor that's up to temp in a hot combustion chamber.
Also to those of you worried about low rpm and carbon build up on rotays, that build-up mostly happens on a cold combustion chamber during warm up. I've done quite a bit of experimenting on my rotarys and found that the engines that were warmed up the fastest, produced less carbon buildup and were damn near impossible to flood. That's why I NEVER let my rotary idle to warm up because it takes too damn long for those 9lb hunks of cast iron rotors to heat up that way. Idling doesn't create enough heat in the combustion chamber. A cold fuel soaked wet rotor is a breeding ground for carbon build up, NOT a hot rotor that's up to temp in a hot combustion chamber.
The biggest issue with carbon buildup is the corner of the intake port, it collects carbon up into a big ol' chunk of coal. When it comes loose RIP apex seals and anything else in its way.
10-03-2018, 05:06 PM
#67
Registered
Thread Starter
Do the same with 2 stroke oil and there will be nothing, clean burn.
10-03-2018, 05:22 PM
#68
Smoking turbo yay
But the video link I posted is the exact same video the other person linked from Engineering Explained showing fuel economy based on gear/load. Fast forward to about 3:30 and look how the fuel economy goes up as you increase load while running lower rpm's. Remember my 91NA very weighed te same as an Rx8 and got 26hwy mpg at 3krpms vs Rx8 getting 23mpg running over 4k. That is a HUGE difference.
Also to those of you worried about low rpm and carbon build up on rotays , that build-up mostly happens on a cold combustion chamber during warm up. I've done quite a bit of experimenting on my rotarys and found that the engines that were warmed up the fastest, produced less carbon buildup and were damn near impossible to flood. That's why I NEVER let my rotary idle to warm up because it takes too damn long for those 9lb hunks of cast iron rotors to heat up that way. Idling doesn't create enough heat in the combustion chamber. A cold fuel soaked wet rotor is a breeding ground for carbon build up, NOT a hot rotor that's up to temp in a hot combustion chamber.
Also to those of you worried about low rpm and carbon build up on rotays , that build-up mostly happens on a cold combustion chamber during warm up. I've done quite a bit of experimenting on my rotarys and found that the engines that were warmed up the fastest, produced less carbon buildup and were damn near impossible to flood. That's why I NEVER let my rotary idle to warm up because it takes too damn long for those 9lb hunks of cast iron rotors to heat up that way. Idling doesn't create enough heat in the combustion chamber. A cold fuel soaked wet rotor is a breeding ground for carbon build up, NOT a hot rotor that's up to temp in a hot combustion chamber.
100% with you , but some people can't be convinced cuz their daddy that used to run carburetors told them to "always warm up yr engine son".
So maybe I should follow the Owner's Manual shift points for once?
And a rotary is still an ICE, so the idea from the video still carries over. Any ICE car is stupidly inefficient at lower RPM, and EE made sure to say that lugging will also be bad for fuel economy and the overall engine health. Bue even the Owner's Manual shift points made sure you stay above 2k RPM, which makes me wonder if that's enough to avoid lugging and carbon buildup.
I am asking because, well, if I can save a little bit of fuel, that helps. I have fun in it, but if I can keep the cruising RPM lower, I will, and I will just downshift when I need the power.
And yeah, "idling to warm up" should have died with carburators. About the only time I did that is when there is so much snow/ice on my windshield that I needed it to melt to start driving safely. Otherwise, 15 seconds are all I need.
The main cause for carbon buildup is not a hot or cold rotary. Its the dirty *** crank case oil being injected and not burning completely. Thats why running 2 stroke oil in a sohn adapter pretty much entirely fixes the carbon buildup problem.
The biggest issue with carbon buildup is the corner of the intake port, it collects carbon up into a big ol' chunk of coal. When it comes loose RIP apex seals and anything else in its way.
The biggest issue with carbon buildup is the corner of the intake port, it collects carbon up into a big ol' chunk of coal. When it comes loose RIP apex seals and anything else in its way.
Think about it: how much oil do you burn, anyway? It's insignificant compared to the amount of gasoline the car uses.
10-03-2018, 05:44 PM
#69
I am actually very curious about the optimal cruising RPM, as most people seem to suggest that 3~4k RPM is the sweet spot while 2~3k is generally considered too low.
So maybe I should follow the Owner's Manual shift points for once?
And a rotary is still an ICE, so the idea from the video still carries over. Any ICE car is stupidly inefficient at lower RPM, and EE made sure to say that lugging will also be bad for fuel economy and the overall engine health. Bue even the Owner's Manual shift points made sure you stay above 2k RPM, which makes me wonder if that's enough to avoid lugging and carbon buildup.
I am asking because, well, if I can save a little bit of fuel, that helps. I have fun in it, but if I can keep the cruising RPM lower, I will, and I will just downshift when I need the power.
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So maybe I should follow the Owner's Manual shift points for once?
And a rotary is still an ICE, so the idea from the video still carries over. Any ICE car is stupidly inefficient at lower RPM, and EE made sure to say that lugging will also be bad for fuel economy and the overall engine health. Bue even the Owner's Manual shift points made sure you stay above 2k RPM, which makes me wonder if that's enough to avoid lugging and carbon buildup.
I am asking because, well, if I can save a little bit of fuel, that helps. I have fun in it, but if I can keep the cruising RPM lower, I will, and I will just downshift when I need the power.
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Last edited by Brettus; 10-03-2018 at 05:56 PM.
10-03-2018, 05:49 PM
#70
I mean next time you do an oil change, throw some used oil into a metal dish and hit it with the blowtorch until it starts burning. I guarantee you there will be crap left behind. The only way to get that crap out the rotary is to rev high.
Do the same with 2 stroke oil and there will be nothing, clean burn.
Do the same with 2 stroke oil and there will be nothing, clean burn.
10-03-2018, 05:53 PM
#71
I mean next time you do an oil change, throw some used oil into a metal dish and hit it with the blowtorch until it starts burning. I guarantee you there will be crap left behind. The only way to get that crap out the rotary is to rev high.
Do the same with 2 stroke oil and there will be nothing, clean burn.
Do the same with 2 stroke oil and there will be nothing, clean burn.
A reasonably healthy Renesis will burn a quart of oil or less in 1000 miles. To burn a quart in 1000 miles, you need to be driving so that you get 12-15 mpg AFAIK. Let's assume 15 to be kind. So, at least 267 quarts of fuel for each quart of oil. Worth considering, no?
Plus, a blowtorch doesn't really simulate the conditions within a combustion chamber. There's a lot going on in there...
10-03-2018, 06:01 PM
#72
Smoking turbo yay
I actually have more than an opinion and theory on this .................I did some pretty extensive mileage testing as part of my patent application . I tested fuel consumption at highway speeds 100km/hr vs 80km/hr and also 80km/hr in both 4th and 5th gear (5 speed gearbox) . I was quite shocked at the terrible fuel consumption i got at 80kms/hr and 2400rpm ... way worse than at 100km/hr and 3000rpm . The difference between 4th and 5th gear at 80km/hr was not measurable.
I recall hooking up a Bluetooth OBD2 reader that has a live fuel consumption display. Not 100% sure how accurate it is, but I remember if I am going at about 65 km/h, it shows my car uses a bit less fuel at 5th(2600 RPM) versus 4th(3200 RPM). Might get a couple of screenshots later. Might be an interesting experiment for one tank of gas.
I have read one reason S1 folks tend to cruise at a higher RPM is that the oil injection injects too little oil on the stock tune when you are at a lower RPM, so you have to keep the RPM a little higher to force the ECU to inject a bit more oil.
10-03-2018, 07:35 PM
#74
Smoking turbo yay
And I wonder if there is a hole in the S2 map or they have fixed it. I am leaning towards the latter.