premix increase in MPG?

Place for discussions about the RX-8
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

hmm mines an r3 so no recall

interestingly its only over night. poss battery ? but just got back from 100 mile drive so id doubt it
graemeS83
Former Member
Former Member
Posts: 96
Joined: Thu Jun 21, 2018 9:41 pm
RX-8: R3
Colour: Sunlight Silver
Location: Cheshire
Has thanked: 1 time
Been thanked: 10 times

Re: premix increase in MPG?

Post by graemeS83 »

Just to chime in on this, this has happened to me recently, also an R3. Parked up for a couple days after a long drive, on just under a 1/4 tank, when I next went to drive it it had jumped up almost another 1/4 and remained artificially high until I next filled it. Parked on a downward slope which could be having an effect. Only happened the once.

Sent from my TA-1012 using Tapatalk

User avatar
warpc0il
Spin Doctor
Spin Doctor
Posts: 32537
Joined: Sat Sep 06, 2008 10:56 pm
RX-8: 231
Colour: Lightning Yellow
Location: Groomsport, Co Down, NI
Has thanked: 444 times
Been thanked: 2080 times

Re: premix increase in MPG?

Post by warpc0il »

That makes sense. If you're using fuel rapidly, driving such that the fuel level has little chance to settle, and then park on a slope, the PCM calculation can get thrown off.

My fuel level once went up by 1/4 tank after a 15 minute track session that was red flagged - no cool down lap.

A couple of gentle miles on the flat would then give a more accurate result.

Sent from my SM-G800F using Tapatalk

Dave
The Spin Doctor ™
uǝǝɹɔs ɹnoʎ ʇɹǝʌuı ǝsɐǝld :ɹoɹɹǝ
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

OK so 150 miles into my journey and I've only used half a tank. Or so it says going to top it up.
BTW my drive is a 1:4 slope....
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

28.3l to 152 miles
PeteH
Former Member
Former Member
Posts: 5849
Joined: Mon Apr 11, 2016 1:26 pm
RX-8: 231
Colour: Custom
Location: West Sussex
Has thanked: 54 times
Been thanked: 367 times

Re: premix increase in MPG?

Post by PeteH »

24.4mpg, having used 43.5% of your fuel. All seems correct to me...
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

Yup will go for a couple hundred tomorrow
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

Well topped over 250 so far so significantly more than I've had before.

Will see how the next tank goes next week. Impressive tho
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

finally got 288 to the tank. at least 88 miles increased on a "run" will see what around town is.
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

Ok so been keeping track of this.

Bearing in mind that im not really getting to the 65l before i fill up. more like 55 ish. Ive kept the reciepts and marked on the mileage and fuel type.

I dont seem to be getting any difference in mileage between vpower and normal shell. Note im only using shell.

with no premix i seem to be getting around the 145miles on average to a tank. this is about 11mpg.

with 200ml of shell premix im getting around 170 on average so about 14mpg ish.

no difference in anything else.

I know that some suggested that it might have freed something off. well i went back to no premix (3 tanks) and it dropped again and then back to premix and its gone back up.

Note that the majority of my drives are about 2 miles each way so it hardly gets warm. Tire pressures are monitored weekly during this. (i have noticed that going from 29psi to 32 psi increased mpg by approx 1-2mpg)

If i go on a longer run on the motorway i can see mpg increase to 22 -25 ish with premix. about 18 without.

Im not sure what, if anything this means.
User avatar
warpc0il
Spin Doctor
Spin Doctor
Posts: 32537
Joined: Sat Sep 06, 2008 10:56 pm
RX-8: 231
Colour: Lightning Yellow
Location: Groomsport, Co Down, NI
Has thanked: 444 times
Been thanked: 2080 times

Re: premix increase in MPG?

Post by warpc0il »

Less friction inside the engine?

Sent from my SM-G800F using Tapatalk

Dave
The Spin Doctor ™
uǝǝɹɔs ɹnoʎ ʇɹǝʌuı ǝsɐǝld :ɹoɹɹǝ
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

possibly. although i would have expected this to be covered by the oil injected when running?

maybe its helping to seal? if so again why doesnt the normal oil do this?
PeteH
Former Member
Former Member
Posts: 5849
Joined: Mon Apr 11, 2016 1:26 pm
RX-8: 231
Colour: Custom
Location: West Sussex
Has thanked: 54 times
Been thanked: 367 times

Re: premix increase in MPG?

Post by PeteH »

warpc0il wrote:
Tue Jan 15, 2019 12:11 pm
Less friction inside the engine?
It seems like a sensible suggestion, but the calcs make it somewhat implausible. If we assume that the car is averaging 30mph during the 2 mile journey then the difference in consumed power between 11mpg and 14mpg is 32bhp :shock: That means, when you stop premixing, the drag of your engine increases by the equivalent of 32bhp (or 25kW, if you want it in 'electrical' units). 25kW of extra friction would melt almost everything in your engine. According to the many dyno printouts we see on the forum, 25kW is the sum total of all the drag forces on the entire car when at peak revs, which includes all the engine, ancilliaries, cooling system, gearbox, diff, driveshafts, tyres, etc. etc.). Put all of that energy directly into your apex seals and they will vaporise..... Engine friction can only ever be a tiny proportion of that power level. It's just not feasible for it to be a reduction in engine friction.

If it's real (sorry to be sceptical), then I think the only feasible way for this to happen is if the pre-mix is somehow fooling the ECU into running 25% leaner. I don't really see how, since the stoichiometric ratio will not change much with the pre-mix, but maybe the pre-mix has some unidentified and peculiar affect on the sensors :-k . And, if it is true, it's rather worrying in itself....

More likely. 11mpg is a huge amount of fuel, and is indicative of very short runs in low gears, and with the "choke" on (I'm old....). These conditions are very transient and variable, and very small differences in 'test' conditions will have a radical influence on the results.

I applaud your application of science to the issue, Andy, but I don't believe we have the answer yet. :(
I still think this will only get answered if someone is prepared to fill up with pre-mix, then join a long motorway and set the cruise control to 70mph for 5 hours in the middle of the night (no traffic), then repeat on the same roads after refilling without pre-mix. If someone does that then I'll believe the result.
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

I agree that the majority if not all of my journey will be on the choke. If that's the case it's almost fixed isn't it.?
RenesisRaceBuggy
Former Member
Former Member
Posts: 1191
Joined: Sun Mar 11, 2012 11:58 pm
Colour: Custom
Has thanked: 30 times
Been thanked: 92 times

Re: premix increase in MPG?

Post by RenesisRaceBuggy »

Some friction reduction (2 stroke oils will lubricate to much higher temps than normal engine oil), but mainly better sealing, - you see the same on 2 strokes, going from 100:1 right up to silly ratios like 10:1 still increases power, and only after that do you start to struggling from oil fouling and replacing so much of the fuel.
I've mentioned elsewhere, but when we were testing premix ratio's the car made more and more power the richer we went, and I think we stopped testing at either 30:1 or 20:1 just because the plugs kept fouling up and it'd slowly loose power and eventually start to misfire - ended up running all the time on about 50:1

One note - don't use dyno figures to approximate engine friction - dyno's only do a wheel/flywheel friction test on coastdown to check drivetrain drag - that doesn't give any indication of the frictional drag in the engine under load - you could easily be loosing 30bhp just into the oil through the main bearings at full RPM/load for example. A rotary motor already rejects a significant amount of power through friction and heat - a Renny wastes something in the order of 250bhp in friction through the bearings, gearset, seals and waste heat through those huge combustion chambers at full chat - not even including what's going out of the exhaust.
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

so were kind of agreeing that its sealing then (which is what i thought)

sooooo. could this be a good way of keeping older rx8's on the road? would you see it as a compression increase on a comp test?
User avatar
delta0
Former Member
Former Member
Posts: 901
Joined: Sat Dec 19, 2015 6:08 pm
Location: London
Has thanked: 66 times
Been thanked: 45 times

Re: premix increase in MPG?

Post by delta0 »

For a compression test the chambers should have no fluids present so premix won’t show a difference there. I expect it does aid compression slightly during normal use.

It would be interesting to understand what it does to the flame front propagation and if there are any benefits there.
RX8 R3 Aurora Blue Mica

BHR coils+MSD leads, Stage 1 ecu tune, HKS Hybrid oil filter, Idemitsu 10w30, BHR engine mounts, RB oil cooler lines, Essex Rotary undertray, RB Revi Intake+Ram Air, Milltek/Pettit cat+catback, braided brake lines, SuperPro bushes, RB flywheel, Exedy stage 1 clutch, Pettit Ti flywheel nut, powder coated and fully resealed everything underneath
User avatar
AndyBrad
Former Member
Former Member
Posts: 606
Joined: Wed Mar 09, 2016 4:28 pm
RX-8: R3
Colour: Aurora Blue Mica
Location: Huddersfield
Has thanked: 5 times
Been thanked: 28 times

Re: premix increase in MPG?

Post by AndyBrad »

probably nothing i would expect?
User avatar
warpc0il
Spin Doctor
Spin Doctor
Posts: 32537
Joined: Sat Sep 06, 2008 10:56 pm
RX-8: 231
Colour: Lightning Yellow
Location: Groomsport, Co Down, NI
Has thanked: 444 times
Been thanked: 2080 times

Re: premix increase in MPG?

Post by warpc0il »

In another thread it was proven that measured compression results could be improved by a squirt to oil into the chambers, which is hardly surprising.

This does however mean that an unscrutable seller could produce a printout that indicated much better numbers than would be otherwise obtained.
That said, it's already too easy just to make up results or copy reports from another car.

Mazda also recognise this phenomena, which is why the later PCM firmware loads give the OMP a kick to squirt oil into the chamber when you switch the ignition off, so there's a coating left to help start-up compression.
Dave
The Spin Doctor ™
uǝǝɹɔs ɹnoʎ ʇɹǝʌuı ǝsɐǝld :ɹoɹɹǝ