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Old 02-12-2021, 09:06 AM   #1
Jussi Alanko
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Default Turbolag smaller on e85? vs 98e ron.

So, you had to burn more e85 compared to 98e, does this mean that turbo wakes up earlier because of increased flow of exhaust gases?

This is an assumption that engine produces more exhaust gases because you had to burn more fuel, then you would think that engine produces more exhaust gases on given rpm. Is this true, and if it is, how much difference there is?

has anyone actually tested this thing?
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Old 02-12-2021, 11:25 AM   #2
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I can give you my experience. I running MS with header and gtx3076. The turbo is really to big for my application. I have ran my setup tuned on gas and E85. The E85 did help with the turbo lag but didnt fix the lag completely. Without a tach at this time, I can only guess that it helps lower the rpm by 200-300. Now If I can put more timing in it down low and little more fuel it might be more. Hope this helps you.
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Old 02-12-2021, 11:42 AM   #3
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...that's not really how it works, I believe.
Just because more E85 is required to acheive the same lambda doesn't mean you'll be making more exhaust gasses. The gasses will be different, but not more powerful. Adjusting the timing and fueling maps will have an affect on lag, and E85 will allow you to make those changes...but on it's own, it won't.
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Old 02-12-2021, 12:17 PM   #4
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there's more "stuff" coming out the pipe on e85 setups, which is why folks suddenly find themselves under-wastegated. eg, no boost creep on pump gas tune, swap to e85 and re-tune, suddenly boost creep. Seen this on my own stuff and other people's stuff. To be fair, the gate sizing was probably on the wire for pump gas at that point anyway, but still.

Pretty much every car that I've done flex or e85 on has spooled sooner than in it's pump gas form even when tuned out for both fuels. frequently it's several hundred rpms sooner, but that will depend on the overall setup. As far as specific testing back to back for that, I have not, although I could go pull datalogs from nick's 940 and see how it affected a tiny turbo setup, and I could probably do it on the blue car (3076r b23ft) if so inclined, but I'm sure other people elsewhere on the internets have done this.

incidentally, more in means more has to go out, I imagine exhaust volume and thus pressure, is higher with e85 than with pump gas, but I doubt it's a linear relationship with the additional volume of fuel required.
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Old 02-12-2021, 12:38 PM   #5
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there's more "stuff" coming out the pipe on e85 setups, which is why folks suddenly find themselves under-wastegated. eg, no boost creep on pump gas tune, swap to e85 and re-tune, suddenly boost creep. Seen this on my own stuff and other people's stuff. To be fair, the gate sizing was probably on the wire for pump gas at that point anyway, but still.

Pretty much every car that I've done flex or e85 on has spooled sooner than in it's pump gas form even when tuned out for both fuels. frequently it's several hundred rpms sooner, but that will depend on the overall setup. As far as specific testing back to back for that, I have not, although I could go pull datalogs from nick's 940 and see how it affected a tiny turbo setup, and I could probably do it on the blue car (3076r b23ft) if so inclined, but I'm sure other people elsewhere on the internets have done this.

incidentally, more in means more has to go out, I imagine exhaust volume and thus pressure, is higher with e85 than with pump gas, but I doubt it's a linear relationship with the additional volume of fuel required.
Very interesting. Do you think that the cooling effects of E85 would make it spool a bit slower?
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Old 02-12-2021, 01:32 PM   #6
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I have not noted that behavior, but the cooling affect can allow for moar bewst and contributes to the better overall performance.
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Old 02-12-2021, 01:51 PM   #7
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E85 has a stoichiometric ratio of around 9.8:1 compared to around 14.7:1 for non ethanol gasoline which reflects the fact that ethanol is an oxygen bearing fuel. So, per engine cycle an engine designed for 'gasoline' is getting 14.7/9.8 = 50% more O2 than it needs when running on E 85. To compensate for this you run a pulse width 50% longer (or use bigger injectors) to keep your AFR at the target value of 9.8. E85 has an energy content per gallon of fuel that is only about about 75% of gasoline so the energy released in burning 50% more fuel per engine cycle is only about 0.75 x 1.50= 12% more than with gasoline.

So, under the same operating conditions you should be releasing about 12% more energy on each engine cycle burning E85 compared to gasoline. The extra energy should elevate exhaust gas temperatures which should also increase the volume of exhaust gas (you heat air and it expands). That extra volume / higher temperature should be available to exhaust gas turbine causing a faster increase in turbine speed (compared to the same conditions burning gasoline).

As far as I know, the 75% guide for energy content in E85 purely reflects energy released on combustion. Clearly the E85 has a higher heat of evaporation which reduces the intake air temperature relative to gasoline. In a normally aspirated engine this should reduce the thermal efficiency meaning that you may not get the 12 % increase in energy release. On a turbo equipped car if you are already dealing with elevated intake air temperatures then then that cooling may not result in a material loss.

Its complicated!
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Old 02-12-2021, 02:05 PM   #8
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Oh well.

It is pressure of exhaust that runs the turbo. With Re85 you can run higher cylinder pressure than with gasoline, resulting higher pressure at the end of expansion stroke. -> more kick for turbo.
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Old 02-12-2021, 06:32 PM   #9
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The exhaust turbine is an expander. Both the temperature and the pressure of the gas drops as it expands through the turbine so the turbine extracts energy from both. That is why there is benefit to keeping the exhaust system between the exhaust port and the turbine as short as possible - less heat loss to the environment.

The higher compression ratio that you can run with E85 probably relates more to its resistance to detonation. The higher compression ratio creates a higher expansion ratio in the cylinder meaning the engine extracts more energy from the combustion process. It does not necessarily result in a higher pressure in the exhaust system once the exhaust valve opens. A higher expansion may drop the exhaust temperature slightly if it is effective at extracting more energy from the combustion process.

In my prior analysis I said that a gallon of E85 has only about 70% as much energy as a gallon of gasoline. I then went on to calculate the increased energy released in burning E85 to achieve a correct AFR. Thing is, stoichiometric targets are mass based, not volume based so my napkin math is slightly out; but, not by much. The specific gravity of E85 is around 0.78 and the specific gravity is around 0.74, so around a 5% error in the mass calculation which is perhaps lost in the grossness of my other simplifying assumptions.
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Old 02-12-2021, 06:39 PM   #10
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ok so tuned out on pump gas, nick's 16t 940 hit 207.9kpa at 3400rpms on pump gas
On e45 (because people get excited and put pump gas back in the tank along with e85 for... reasons...)
it hit 208.7 at 2960rpms

peak boost changed between the two fuels, but it hit a peak of 234kpa on e45 at 3760 and a peak of 223kpa on straight pump gas at 4035.

both runs were done in 4th gear, and both went WOT on the dyno within about 100rpms of each other (1693 for pump vs 1758 on e45). pump gas AFR was roughly 11.5 : 1, e85 was a little leaner in the same mid-range area, roughly 11.8 : 1
timing was actually higher on the pump gas map by about a degree there, but out the top we ran about 2 more degrees on the ethanol tune. part of that is stock bottom end love, no point in folding the factory rods out right off the bat, the car made solid... 20whp more on e45 than pump 93, but the numbers on 93 did exceed expectations.

AFRS were all measured on a pump gas scale for discussion. you can use lambda if you want, at that point scale doesn't matter because lambda doesn't change regardless of fuel.
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Old 02-15-2021, 12:39 AM   #11
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IMO it makes sense scientifically that all else equal, E85 will make the same pressure/flow earlier due to the higher energy of the exhaust gasses heading towards the turbine (if I've read everything above correctly).
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Old 02-15-2021, 01:03 AM   #12
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If you guys really want to get technical, it's momentum transfer from the high energy exhaust gas that spins the turbine.

Momentum is mass x velocity, mass is constant, so in other words the change in tangential velocity of the gas particles from a high speed at the blade tip to some lower speed is what drives the turbine wheel.

142 guy is right on though: exhaust gas temperature and pressure do drop as the gas expands across the turbine stage, and the increased knock resistance of E85 vs pump gasoline allows more aggressive timing and higher cylinder pressures without knock, hence higher power output from the engine. Cylinder pressure can be increased by increasing static CR, boost pressure, dynamic PR, or all of the above.

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e85 was a little leaner in the same mid-range area, roughly 11.8 : 1
11.8 would be extremely lean when running E85 (lambda 1.21). Do you mean lambda 0.80? That would be 7.84:1 with E85.
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Old 02-15-2021, 03:10 PM   #13
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Quote:
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If you guys really
11.8 would be extremely lean when running E85 (lambda 1.21). Do you mean lambda 0.80? That would be 7.84:1 with E85.
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AFRS were all measured on a pump gas scale for discussion.
So about lambda 0.80 if I didn't mess up the math.
On the street I can't say I've noticed big differences in spool speed between 98e/93 and e85. That's with a worn b230, Tractor cam and tiny 19T/7#. Full boost at roughly 3000rpm, but 1,4bar with e85 and only 1bar with 98e.
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