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Highest Compression Ratio for E85 2
- Thread starter PhdDave
- Start date
Crystal1clear, and your point is? By definition at 100 octane you can run 12.5 : 1 and not detonatein a variable compression engine test stand, so auto iginition doesn't hold water. Try your numbers out on nitro-methane and methanol too.
After many years of study, catapillar engines and waukesha engines use a modified octane calculations for fuel mixtures, all emperical and not related to autoignition.
spracer2, I'd like to read that article too, I run the same 2zzge engine myself. The engine is a 11.5 :1, Over in England they can run higher net CR (as adjusted for turbos/superchargers) than in the US, just look up a misubishi FQ400.
Phdave, the 2zzge engine has a high HP ouput to weight ratio at 100HP/liter and the FQ400 is 400HP for 2 liters with a highly tuned and fuel cooled engine, so a turbocharged 900 cc engine could get you 100 HP.
After many years of study, catapillar engines and waukesha engines use a modified octane calculations for fuel mixtures, all emperical and not related to autoignition.
spracer2, I'd like to read that article too, I run the same 2zzge engine myself. The engine is a 11.5 :1, Over in England they can run higher net CR (as adjusted for turbos/superchargers) than in the US, just look up a misubishi FQ400.
Phdave, the 2zzge engine has a high HP ouput to weight ratio at 100HP/liter and the FQ400 is 400HP for 2 liters with a highly tuned and fuel cooled engine, so a turbocharged 900 cc engine could get you 100 HP.
patprimmer
New member
pipehead
The two engines you mention are diesel so they are hardly relevant to this discussion.
crystal1clear's calculations work reasonably well for gaseous fuels, but get fairly well out of whack with liquid fuels due to latent heat of evaporation and variations in burn rate (and therefore rate of pressure rise) due to fuel particle size. As already mentioned, they also obviously ignore a number of other factors which generally only have a moderate to minimal effect.
I should have posted this link a lot earlier as it contains good data to answer the OP and to dispel a lot of myth and garbage that has been presented in this thread to date.
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The two engines you mention are diesel so they are hardly relevant to this discussion.
crystal1clear's calculations work reasonably well for gaseous fuels, but get fairly well out of whack with liquid fuels due to latent heat of evaporation and variations in burn rate (and therefore rate of pressure rise) due to fuel particle size. As already mentioned, they also obviously ignore a number of other factors which generally only have a moderate to minimal effect.
I should have posted this link a lot earlier as it contains good data to answer the OP and to dispel a lot of myth and garbage that has been presented in this thread to date.
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WHAT PATPRIMMER? the 2 liter mitsubishi engine sold in the EVO and the 1.8 liter toyota sold in the celica, vibe, matrix, corolla, elise are gasoline.... These along with the 2.5 liter subi and 2.3 liter ford/mazada are top contenders for HP/CI ratio engines.
Good generalized link for the consumer. It doesn't eplain 400 HP from 2 liters on 95 RON (oh, ineurope they do not post ron + mon / 2 like here only RON)). How, do dragsters work based on all the info. It's a bigger picture once you step outside the typical consumer stuff. Don't you remember all the word fights in the 70's, whats better a 454 vette or a 3 liter (190 ci) porche. Man a VVTL-i ot DI engine changes all the common rules.
Good generalized link for the consumer. It doesn't eplain 400 HP from 2 liters on 95 RON (oh, ineurope they do not post ron + mon / 2 like here only RON)). How, do dragsters work based on all the info. It's a bigger picture once you step outside the typical consumer stuff. Don't you remember all the word fights in the 70's, whats better a 454 vette or a 3 liter (190 ci) porche. Man a VVTL-i ot DI engine changes all the common rules.
patprimmer
New member
Umm
These are the diesels you refer to
This guy asked a pretty general question in the OP
Can we respect the forum rules and stay on that topic and be constructive rather running off on tangents.
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These are the diesels you refer to
This guy asked a pretty general question in the OP
Can we respect the forum rules and stay on that topic and be constructive rather running off on tangents.
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look up this link to the cat spark engines.
The OP wanted to know the maximum compression ratio and people started talking about ignition temps that dictate it which is wrong. The term of octane number is the best way to calculate maximum compression ratio. Put the octane value has to be found emperically from the lab, not by ignition temperature. To make things even more difficult, there is no set rule for what E85 is othan 85% ethanol, heck, the other other 15% could be jet fuel. So to make a point that ignition temperature is not a corerelation, I pointed out all kinds of other engines and fuels that do not follow the trend trying to be laid out.
The OP wanted to know the maximum compression ratio and people started talking about ignition temps that dictate it which is wrong. The term of octane number is the best way to calculate maximum compression ratio. Put the octane value has to be found emperically from the lab, not by ignition temperature. To make things even more difficult, there is no set rule for what E85 is othan 85% ethanol, heck, the other other 15% could be jet fuel. So to make a point that ignition temperature is not a corerelation, I pointed out all kinds of other engines and fuels that do not follow the trend trying to be laid out.
bentwings1
Mechanical
- Mar 8, 2006
- 48
- 0
- 0
Hi,
I just came from a streetrod event Sat. There was guy who was selling carbs modified for E-85. His 2 demo cars were a 6-71 blown small block Chev in a Nova..quite a large one 427 cu in. This one had a dyno sheet that showed well over 500 hp and 600+ ft lbs torque. It ran about 7 pounds of boost. He said that while it is really a hot rod it actually was pretty mild mannered. He said it could make a lot more power just by upping the boost and changing carb jets. His other car was a tamer Camaro with a 383 cu in SBC. This one was much more of a "driver". Both cars are driven to the local streetrod events and on numerous rod runs and are not trailer queens.
To answer the question the blown one had 12.7:1 and the unblown one had 13.7:1 compression ratios.
E-85 is readily available here in Minn so it is an alternative. It takes high compression to make it work and you probably won't get the greatest MPG as it simply takes more fuel to burn properly. It does work however.
99 Dodge CTD dually.
I just came from a streetrod event Sat. There was guy who was selling carbs modified for E-85. His 2 demo cars were a 6-71 blown small block Chev in a Nova..quite a large one 427 cu in. This one had a dyno sheet that showed well over 500 hp and 600+ ft lbs torque. It ran about 7 pounds of boost. He said that while it is really a hot rod it actually was pretty mild mannered. He said it could make a lot more power just by upping the boost and changing carb jets. His other car was a tamer Camaro with a 383 cu in SBC. This one was much more of a "driver". Both cars are driven to the local streetrod events and on numerous rod runs and are not trailer queens.
To answer the question the blown one had 12.7:1 and the unblown one had 13.7:1 compression ratios.
E-85 is readily available here in Minn so it is an alternative. It takes high compression to make it work and you probably won't get the greatest MPG as it simply takes more fuel to burn properly. It does work however.
99 Dodge CTD dually.
Found this on e85 octane. This article states e85 will be 100 to 105 octane, but there is specification like we have for gasolines RON + MON being at least 85 octane minimum (83 at high altitude). Right now the flex fuel vehicles are tuned and have a CR such that you can use 85 octane. The CR will be from 8.8 to 10.0 to 1 based on other engine and tuning factors. As soon as blenders get it fiquired out, they will reduce octane on E85.
patprimmer
New member
pipehead
Thank you for the link.
That is all you need to do to avoid controversy when you throw in comments from left field.
Re your comments to crystal1clear.
Auto ignition point is just one of many factors to consider. That does not mean it is wrong to consider it in detail.
The point that there are many factors involved was already mentioned. See quotes below.
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Thank you for the link.
That is all you need to do to avoid controversy when you throw in comments from left field.
Re your comments to crystal1clear.
Auto ignition point is just one of many factors to consider. That does not mean it is wrong to consider it in detail.
The point that there are many factors involved was already mentioned. See quotes below.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
crysta1c1ear
Automotive
Ok, here are some more thoughts about ethanol.
Firstly, if octane rating is about ability to resist autoignition, then I think it is just as valid to think about autoignition temperatures as it is to think about octane ratings, since the main subject is neither. The thread is about compression ratios.
Now, does it actually make sense to talk about an octane rating for ethanol? What is on my mind is that evaporation can cause such huge differences in behaviour, depending on whether evaporation occurs in the cylinder and depending on concentrations (ie AFR), that what we'd like to think of as a single property - octane rating - is not going to be something that fixed in practice.
(Of course octane ratings will be defined under precise conditions so in a sense is fixed. But if the conditions in our engines are different from the reference engine, the figure somebody gives us as an octane rating for ethanol are then likely to be meaningless to us.)
Note the quote above about ethanol evaoration being able to push octane ratings of gasoline ethanol mixtures to 130.
Here's why I think ethanol evaporation is so important.
Autoignition temperatures (kelvin)
n-heptane 560
iso-octane 690
There is a 130 kelvin difference between the two fuels, thus causing n-heptane and iso-octane to have very different octane ratings.
Now I'm going to calculate later that evaporation of ethanol can cause an even bigger 140 kelvin temperature drop (or potentially even more in a rich mixture).
With gasoline, the temperature change caused by evaporation
will be very significantly less. So changes in AFR shouldn't affect knock so much, and maybe using an octane rating makes more sense.
[highlight]If you design a high compression ratio ethanol engine with evaporation in the cylinder, then I would think very carefully about what might happen if it runs a bit leaner,[/highlight] doesn't get the temperature drop from evaporation, and so maybe starts to knock.
The references above give octane ratings of 85 for gasoline and 100 for E85, and yet of 130 for some mixtures. Maybe that sort of variation is a partial cause of the question of compression ratio for E85, or lack of a clear answer. And now I am suspecting that evaporation is the main reason why.
In the next post I'll calculate 140 kelvin or so as a potential temperature drop due to evaporation.
Oh, and how does all this affect compression ratio? Well, as you compress the mixture in the cylinder the temperature rises. As the fuel evaporates the temperature drops. If the temperature rise from some of the cylinder compression and the temperature fall from evaporation cancel each other out, then that bit of compression is in a sense free and hardly contributing to the end gases autoigniting, ie knocking.
crysta1c1ear
Automotive
Here are my calculations for the possible cooling effect of ethanol (143 kelvin) and gasoline (33 kelvin) in a stoichiometric mixture, together with sources for my data.
My procedure is quite simple. Take the heat required to evaporate a kilo of fuel.
Divide by the AFR to work out the heat taken out of a kilo of air (as the fuel evaporates at constant temperature).
Divide that by the specific heat of air to see how much that kilo of air would cool down.
Heats of vapourization
Ethanol 920 * kJ/kg
Gasoline 350 * kJ/kg
AFRs
Ethanol 9
Gasoline 14.7
Specific heat of air
715 * J/(kg*kelvin)
Calculations to paste into a windows calculator
920000/9/715=
350000/14.7/715=
results
ethanol 143
gasoline 33
My procedure is quite simple. Take the heat required to evaporate a kilo of fuel.
Divide by the AFR to work out the heat taken out of a kilo of air (as the fuel evaporates at constant temperature).
Divide that by the specific heat of air to see how much that kilo of air would cool down.
Heats of vapourization
Ethanol 920 * kJ/kg
Gasoline 350 * kJ/kg
AFRs
Ethanol 9
Gasoline 14.7
Specific heat of air
715 * J/(kg*kelvin)
Calculations to paste into a windows calculator
920000/9/715=
350000/14.7/715=
results
ethanol 143
gasoline 33
I just talked witha large gasoline blending and here are some insider things taking place in ethanol.
The gasoline blenders are testing ethanol movements in pipelines with extreme caution, it may take a year or more for the results. A early error occurred in the Alanta market where a small amount of water from the ethanol got into the the tanks at a few gas stations. The water caused consumer engine problems and over 100 gas stations were shutdown in the area for a week or so. This cause the other stations to pick up the slack with extra fuel brought in and lines at the stations.
They have also set up a very low octane grade of gasoline to be used as ethanol blending stock. This low octane, low vapour pressure blend mix can only be used with high (E85) type blends. It will allow the ethanol blend to be low octane.
The blenders are scrambling to find ways to get the ethanol to other markets, from the midwest. The southeast will be the next area to place ethanol fuels.
The gasoline blenders are testing ethanol movements in pipelines with extreme caution, it may take a year or more for the results. A early error occurred in the Alanta market where a small amount of water from the ethanol got into the the tanks at a few gas stations. The water caused consumer engine problems and over 100 gas stations were shutdown in the area for a week or so. This cause the other stations to pick up the slack with extra fuel brought in and lines at the stations.
They have also set up a very low octane grade of gasoline to be used as ethanol blending stock. This low octane, low vapour pressure blend mix can only be used with high (E85) type blends. It will allow the ethanol blend to be low octane.
The blenders are scrambling to find ways to get the ethanol to other markets, from the midwest. The southeast will be the next area to place ethanol fuels.
crysta1c1ear, the information you provided on heat of vaporization is very interesting. If I remember correctly, H vap. is the result of IMF's (intermolecular forces) between the hydrocarbon molecules found in both fuels. Ethanol is a much smaller molecule with less powerful dispersion forces (attractive) between molecules but its polar nature (the hydroxide group "O-H") of the molecule results in much stronger IMF's then the larger but non-polar Octane. This accounts for an increased capacity for cooling during the phase change from liquid to gas as the fuel enters the engine. This however, has nothing to do with the amount of energy contained within the fuel. A greater cooling capacity will fundamentally have greater knock resistance but it is the CHEMICAL reaction with O2 that results in combustion and the powerful explosion caused by ignition. I'm sure that any chemists here can explain that better than I can.
The fuel that I run in my 60 Chevy Hot Rod and in the plane I fly is a 100 octane low lead gasoline. The increased octane is the result of lead increasing the cooling capacity of water (I believe the principle is similar to adding salt to water to raise it's boiling temp.). This was how so many muscle cars where able to benefit from running both gasoline and high compression. FYI most lycoming all aluminum, air coolled engines run on 100LL and have very high compression ratios (ie. 13-15 range I believe) and these little engines have a VERY high power to weight ratio, although at a much lower RPM than most car engines (they red line under 3K) and they have much different torque requirements because of the systems that they are driving. I hope this is helpful.
The fuel that I run in my 60 Chevy Hot Rod and in the plane I fly is a 100 octane low lead gasoline. The increased octane is the result of lead increasing the cooling capacity of water (I believe the principle is similar to adding salt to water to raise it's boiling temp.). This was how so many muscle cars where able to benefit from running both gasoline and high compression. FYI most lycoming all aluminum, air coolled engines run on 100LL and have very high compression ratios (ie. 13-15 range I believe) and these little engines have a VERY high power to weight ratio, although at a much lower RPM than most car engines (they red line under 3K) and they have much different torque requirements because of the systems that they are driving. I hope this is helpful.
crysta1c1ear, the information you provided on heat of vaporization is very interesting. If I remember correctly, H vap. is the result of IMF's (intermolecular forces) between the hydrocarbon molecules found in both fuels. Ethanol is a much smaller molecule with less powerful dispersion forces (attractive) between molecules but its polar nature (the hydroxide group "O-H") of the molecule results in much stronger IMF's then the larger but non-polar Octane. This accounts for an increased capacity for cooling during the phase change from liquid to gas as the fuel enters the engine. This however, has nothing to do with the amount of energy contained within the fuel. A greater cooling capacity will fundamentally have greater knock resistance but it is the CHEMICAL reaction with O2 that results in combustion and the powerful explosion caused by ignition. I'm sure that any chemists here can explain that better than I can.
The fuel that I run in my 60 Chevy Hot Rod and in the plane I fly is a 100 octane low lead gasoline. The increased octane is the result of lead increasing the cooling capacity of water (I believe the principle is similar to adding salt to water to raise it's boiling temp.). This was how so many muscle cars where able to benefit from running both gasoline and high compression. FYI most lycoming all aluminum, air coolled engines run on 100LL and have very high compression ratios (ie. 13-15 range I believe) and these little engines have a VERY high power to weight ratio, although at a much lower RPM than most car engines (they red line under 3K) and they have much different torque requirements because of the systems that they are driving. I hope this is helpful.
The fuel that I run in my 60 Chevy Hot Rod and in the plane I fly is a 100 octane low lead gasoline. The increased octane is the result of lead increasing the cooling capacity of water (I believe the principle is similar to adding salt to water to raise it's boiling temp.). This was how so many muscle cars where able to benefit from running both gasoline and high compression. FYI most lycoming all aluminum, air coolled engines run on 100LL and have very high compression ratios (ie. 13-15 range I believe) and these little engines have a VERY high power to weight ratio, although at a much lower RPM than most car engines (they red line under 3K) and they have much different torque requirements because of the systems that they are driving. I hope this is helpful.
Here's a great history and some more info on octane. I can noit seam to get Crysta1clear off the auto ignition as a reason for octane number. Nor the heat of vaporization. He's even proved my point earlier. n octane has a low compression ratio about 4 before detonation and has a low auto ignition 650 degrees, iso octane at 100, has a 12 to 1 compression ration and an autoignition higher than n-octane, but he cannot explain that pure methane has the same 100 octane rating and can go to 12 to 1 compression, but it's auto ignition temp is way above that of iso octane.. get it no connection here.
Then the heat of vaporization, pure methane as fuel has no heat of vaporization, get it again, it has nothing to do with it. What you do get with the heat of vaporization is more dense air and fuel, more pounds in the cylinder, more explosion, more power. SEE also CAI, CO@ Chiller, NOs dry injection systems.
I don't think the lead changes chemistry or temperatures, it interfeers with the combustion process and inhibits detonation.
Interesting thread, hope you guys don't mind a newbe commenting on this.
I have a carbureted 68 Camaro that I recently converted to E85 and thought I would offer some comment from the "practical experience side" of this discussion.
My engine is a 410" small block Chevy and has a static compression ratio of 11.49:1. The intake valve closes at 68* after bottom dead center (during compression stroke). Prior to switching to E85 I ran 93 octane in the engine and under certain circumstances (hot coolant temp, hot ambient air temp) it would show early signs of detonation. Cranking compression on this engine averages 225 psi.
When I switched to E85 I started with a carburetor calibrated for E85 but due to differences in fuel blends (as stated above) and engine characteristics I needed to do a LOT of tuning to get it right. During the course of tuning I ran the engine too lean (near stoichiometric) while it was too hot with too much ignition advance. I even ran nitrous oxide too lean (a MAJOR no-no with gasoline) and never once had any sign of detonation.
The octane rating of the E85 that I use is 105 however, I believe that the cooling effect mentioned above is a significant factor in this fuels apparent effectiveness in preventing detonation. That would be disappointing if the suppliers find a way to reduce the octane rating because IMO that is the major advantage to this fuel.
Incidentally, my engine picked up power on the E85 fuel (runs 10.9's in the quarter mile). I do use a lot more of it than gasoline (approx 25% more at cruise and 35-40% more at WOT) but it seems to be a good alternative for me at this point (it runs 50 cents cheaper per gallon than pump premium gasoline octane and is $2 cheaper than race gasoline).
As an aside, re: the comment on water contamination in the Atlanta area. ethanol is known to be less corrosive than methanol which is beneficial for the use of aluminum parts, however, I have read that ethanol forms acids when mixed with >1% water and becomes much more corrosive. Any comments on this?
I have a carbureted 68 Camaro that I recently converted to E85 and thought I would offer some comment from the "practical experience side" of this discussion.
My engine is a 410" small block Chevy and has a static compression ratio of 11.49:1. The intake valve closes at 68* after bottom dead center (during compression stroke). Prior to switching to E85 I ran 93 octane in the engine and under certain circumstances (hot coolant temp, hot ambient air temp) it would show early signs of detonation. Cranking compression on this engine averages 225 psi.
When I switched to E85 I started with a carburetor calibrated for E85 but due to differences in fuel blends (as stated above) and engine characteristics I needed to do a LOT of tuning to get it right. During the course of tuning I ran the engine too lean (near stoichiometric) while it was too hot with too much ignition advance. I even ran nitrous oxide too lean (a MAJOR no-no with gasoline) and never once had any sign of detonation.
The octane rating of the E85 that I use is 105 however, I believe that the cooling effect mentioned above is a significant factor in this fuels apparent effectiveness in preventing detonation. That would be disappointing if the suppliers find a way to reduce the octane rating because IMO that is the major advantage to this fuel.
Incidentally, my engine picked up power on the E85 fuel (runs 10.9's in the quarter mile). I do use a lot more of it than gasoline (approx 25% more at cruise and 35-40% more at WOT) but it seems to be a good alternative for me at this point (it runs 50 cents cheaper per gallon than pump premium gasoline octane and is $2 cheaper than race gasoline).
As an aside, re: the comment on water contamination in the Atlanta area. ethanol is known to be less corrosive than methanol which is beneficial for the use of aluminum parts, however, I have read that ethanol forms acids when mixed with >1% water and becomes much more corrosive. Any comments on this?
Your experience matches what I've set out in my posts.
Your opinion is that E85's major advantage is its high octane. All the E85 cars sold today have nothing done to them to take advantage of the octane and until SAE or someone sets an absolute octane number on E85, they will not. About the onlything I can see they need to do is change out the fuel system, put in bigger injectors, and do something with the ECU mapping.
Auto manufacturers will not take advantage of higher octane because they have warranties on their engines whereas your 410 CI has none. In Europe they modified an engine to 400 HP from its 290 Hp generated in the US because the average temperature across the island in way lower than in Las Vegas and there top gasoline has about 3 more octane than here in the US. (BTW it is a 121 CI engine 11.9 1/4 mile stock)
Your opinion is that E85's major advantage is its high octane. All the E85 cars sold today have nothing done to them to take advantage of the octane and until SAE or someone sets an absolute octane number on E85, they will not. About the onlything I can see they need to do is change out the fuel system, put in bigger injectors, and do something with the ECU mapping.
Auto manufacturers will not take advantage of higher octane because they have warranties on their engines whereas your 410 CI has none. In Europe they modified an engine to 400 HP from its 290 Hp generated in the US because the average temperature across the island in way lower than in Las Vegas and there top gasoline has about 3 more octane than here in the US. (BTW it is a 121 CI engine 11.9 1/4 mile stock)
GregLocock
Automotive
"All the E85 cars sold today have nothing done to them to take advantage of the octane "
really? None of them? not even the ones with adaptive spark? I find that curious.
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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
really? None of them? not even the ones with adaptive spark? I find that curious.
Cheers
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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
I think maybe maybe dcasto was referring to compression ratio ??
In my opinion increasing compression ratio is the most important way to take advantage of ethanol as a fuel and would have way more effect on efficiency then spark management (unless you are pulling timing out for gasoline so it doesn't knock?). By the way, in my engine E85 likes less total timing than gasoline so advancing timing past what gasoline likes would not make more power. Although, at part throttle maybe more timing would help with E85 (sorry not used to thinking about part throttle
)
Here's a thought
Now what if you could make an engine that was capable of altering cylinder pressure (dynamic compression) to take advantage of high octane fuels when available and back off the cylinder pressure when a lower octane fuel is used. I believe this would be possible with true variable valve timing -- something that would not be limited by a cam lobe (ie: hydraulic or pnuematic operated valves.) You could build the engine to be capable of 12:1 static compression and in effect reduce volumetric efficiency and/or cylinder pressure for lower octane fuels.
Maybe I'm just dreaming . . .
In my opinion increasing compression ratio is the most important way to take advantage of ethanol as a fuel and would have way more effect on efficiency then spark management (unless you are pulling timing out for gasoline so it doesn't knock?). By the way, in my engine E85 likes less total timing than gasoline so advancing timing past what gasoline likes would not make more power. Although, at part throttle maybe more timing would help with E85 (sorry not used to thinking about part throttle
) Here's a thought
Now what if you could make an engine that was capable of altering cylinder pressure (dynamic compression) to take advantage of high octane fuels when available and back off the cylinder pressure when a lower octane fuel is used. I believe this would be possible with true variable valve timing -- something that would not be limited by a cam lobe (ie: hydraulic or pnuematic operated valves.) You could build the engine to be capable of 12:1 static compression and in effect reduce volumetric efficiency and/or cylinder pressure for lower octane fuels.
Maybe I'm just dreaming . . .
patprimmer
New member
It's easy, just screw the waste gate down a bit. More boost means more total compression.
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patprimmer
New member
Or if not already turbocharged, install a turbo and have adjustable waste gate, set at different boost settings for each fuel.
If you wanted to be real tricky, develop a device so that a knock sensor adjusts the waste gate rather than adjusting timing.
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If you wanted to be real tricky, develop a device so that a knock sensor adjusts the waste gate rather than adjusting timing.
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