Octane vs. Engine Temp
#31
10-22-2017, 10:41 PM
#32
10-22-2017, 11:36 PM
An atmospheric engine (non turbo or non supercharged) will have more compression = (power) at lower altitude compared to higher altitude due to loss of compression at higher elevation, that's why airplane piston engines that are non supercharged have 13 to 1 or even higher compression ratio's, to make up the loss as they climb up, and what do they do to not blow the engine when they are at ground level,? They use aviation fuel, which is 105 to 110 octane,, (& most racers try to use same fuel for their very high compression engines if they can get their hands on),,
compression ratio is independent of local atmospheric pressure. I think you are confusing compression with mass.
airplane fuel is a whole different subject. It has to have a very small deviation from nominal vapor pressure for flight safety.
as far as 87 RON rated fuel being different from 93 RON rated fuel look at the yellow sticker on the pump. minimum RON rating. 93 meets all lower minimum RON specs. If you want to direct me to some data that shows different energy densities for petroleum based fuel with different RON ratings I'd love to see them, but I already know they don't exist. Now when you get into composition fuels like e10 sure the energy density drops due to the ethanol content while the octane rating rises, but I don't think that's what you are claiming.
#33
10-22-2017, 11:46 PM
higher octane rating is just the measured resistance to pinging in a test engine. The energy density is much lower than petroleum based fuel so per mass it burns cooler. The stoich ratio requires more ethanol than petroleum for the same mass of air. I don't know off the top of my head if that counters the lower energy density, but by gut feeling is no, it burns cooler. Only benefit is for race cars that run much higher dynamic compression ratios than petroleum would allow, and that it subsidizes the corn market.
#34
10-22-2017, 11:52 PM
The factory rover heads have a very flat port angle. Poor flow characteristics. As well as the inline valves. The redesigned heads bring the intake and exhaust ports to a steeper angle and I believe they rotate the valves as well. They've got an open chamber as well I believe. Point being that they are a much more modern design, closer to that of an LS or aftermarket SBF head.
My point about the hot vapor engine was that engine sophistication isnt everything. Smokey built a hot air engine out of a fiero piece of crap. It made like 250hp and got 45+mpg. On a super lean, super hot burn.
My point about the hot vapor engine was that engine sophistication isnt everything. Smokey built a hot air engine out of a fiero piece of crap. It made like 250hp and got 45+mpg. On a super lean, super hot burn.
Direct injection does allow lean burn with cooler cylinder temps thanks to the atomization of the fuel in the compressed air and that prevents the high temps required for NOx formation and from my understanding many of the newer vehicles on the road are running higher than 14.7:1 at cruise with no increase in NOx output.
That fiero piece of crap also weighs half what todays cobalt piece of crap weighs.
Last edited by robertf; 10-22-2017 at 11:54 PM.
#35
10-23-2017, 04:09 AM
Baja
You are absolutely wrong!
87 octane fuel of reputable brand makes more calories per unit when burned compared to 91 or 93 octane of same brand,
perhaps you should do a little research b4 making such a claim,
Lower octain is more combustible under same pressure than higher octane,
Higher octane isn't a cleaner or better fuel if that's what you think,
Higher octane is for engines that will have a pre ignition detonation if they use a lower octane fuel, back in 60's most normal engines had (7.5 -8 to 1 ) compression ratio and anything 9 to 1 ratio or higher was considered high compression and needed higher octane to work properly & not have a pre detonation due to limitations in combustion chamber designs in most engines, (and yes there were high performance engines with even higher compression ratios 10 to 1,,, even 11 to 1, in some road cars and all had to use high octane fuel to avoid detonation,, Rover V8 is an old design combustion chamber, so 9.35 to 1 is high compression for this engine,, (As a rule of thumb in most cases a larger diameter piston is more likely to have pre detonation at same compression ratio compared to a smaller diameter piston, even when both have the same displacement , )
Today's newer design combustion chambers are so much better than even with 9.5 or 10 to 1 ratio they can run on 87 octane with no problem,,
-----
An atmospheric engine (non turbo or non supercharged) will have more compression = (power) at lower altitude compared to higher altitude due to loss of compression at higher elevation, that's why airplane piston engines that are non supercharged have 13 to 1 or even higher compression ratio's, to make up the loss as they climb up, and what do they do to not blow the engine when they are at ground level,? They use aviation fuel, which is 105 to 110 octane,, (& most racers try to use same fuel for their very high compression engines if they can get their hands on),,
Higher octane fuels are more expensive not because they are cleaner or burn better (as oil companies advertise) but because it's more difficult to produce a gasoline that does not want to catch fire as quickly under pressure & heat as a regular gas,
(Higher octane gas makes less calories per unit, but when you have higher compression ratio, you will be able to make more power from same displacement & will make up for loss of calories in fuel & then some,)
And yes it is safer to use higher octane fuel in lower compression engine rather than using lower octane ina high compression engine, first one will only cause the engine to underperform , but second will cause predestination & commonly called ping.
87 octane fuel of reputable brand makes more calories per unit when burned compared to 91 or 93 octane of same brand,
perhaps you should do a little research b4 making such a claim,
Lower octain is more combustible under same pressure than higher octane,
Higher octane isn't a cleaner or better fuel if that's what you think,
Higher octane is for engines that will have a pre ignition detonation if they use a lower octane fuel, back in 60's most normal engines had (7.5 -8 to 1 ) compression ratio and anything 9 to 1 ratio or higher was considered high compression and needed higher octane to work properly & not have a pre detonation due to limitations in combustion chamber designs in most engines, (and yes there were high performance engines with even higher compression ratios 10 to 1,,, even 11 to 1, in some road cars and all had to use high octane fuel to avoid detonation,, Rover V8 is an old design combustion chamber, so 9.35 to 1 is high compression for this engine,, (As a rule of thumb in most cases a larger diameter piston is more likely to have pre detonation at same compression ratio compared to a smaller diameter piston, even when both have the same displacement , )
Today's newer design combustion chambers are so much better than even with 9.5 or 10 to 1 ratio they can run on 87 octane with no problem,,
-----
An atmospheric engine (non turbo or non supercharged) will have more compression = (power) at lower altitude compared to higher altitude due to loss of compression at higher elevation, that's why airplane piston engines that are non supercharged have 13 to 1 or even higher compression ratio's, to make up the loss as they climb up, and what do they do to not blow the engine when they are at ground level,? They use aviation fuel, which is 105 to 110 octane,, (& most racers try to use same fuel for their very high compression engines if they can get their hands on),,
Higher octane fuels are more expensive not because they are cleaner or burn better (as oil companies advertise) but because it's more difficult to produce a gasoline that does not want to catch fire as quickly under pressure & heat as a regular gas,
(Higher octane gas makes less calories per unit, but when you have higher compression ratio, you will be able to make more power from same displacement & will make up for loss of calories in fuel & then some,)
And yes it is safer to use higher octane fuel in lower compression engine rather than using lower octane ina high compression engine, first one will only cause the engine to underperform , but second will cause predestination & commonly called ping.
Bom2oo2 is on the correct wavelength. Think Ford Cosworth DFV of the 1960's and 1970's
https://www.google.fr/search?q=photo...CaaCYSkIodRDM:
This was the mega engine of it's era.
Last edited by OffroadFrance; 10-23-2017 at 04:15 AM.
#36
10-23-2017, 04:32 AM
Baja
Ward's 10 Best Engines | News & Analysis content from WardsAuto
High compression ratio causes early engine failure, mixture compression requires stronger and more resilient engines and that is why more manufacturers target the mass market requirements and emission requirements where the vast majority, repeat, the vast majority of engines are between 9 and 10:1 compression ratio, of course there will be exceptions, there always are.
High compression ratio causes early engine failure, mixture compression requires stronger and more resilient engines and that is why more manufacturers target the mass market requirements and emission requirements where the vast majority, repeat, the vast majority of engines are between 9 and 10:1 compression ratio, of course there will be exceptions, there always are.
#37
10-23-2017, 04:53 AM
Baja
In truth, take a long hard look at earlier N/A F1 engine, admittedly, they are designed to last just a few hours not years. They have 'special' petrol formulated within regulations along with low friction engines, gearboxes and drivetrains.
Today's turbo engines are the 'cheap' way to extract max: power from far smaller engines but also meet emissions B/S requirements, BUT, these engines require far more servicing and aren't truly designed for old ladies to poodle around in due to cat regen: needs.
Another problem is, fuel quality and RON varies drastically from country to country and continent to continent and the manufacturers vary the fuelling accordingly but therein lies the inherent problem when buying vehicles designed for other countries/continents whereas most manufacturers take the 'mean average' requirements for 'all' types of drivers it's impossible to cater for everyone.
Today's turbo engines are the 'cheap' way to extract max: power from far smaller engines but also meet emissions B/S requirements, BUT, these engines require far more servicing and aren't truly designed for old ladies to poodle around in due to cat regen: needs.
Another problem is, fuel quality and RON varies drastically from country to country and continent to continent and the manufacturers vary the fuelling accordingly but therein lies the inherent problem when buying vehicles designed for other countries/continents whereas most manufacturers take the 'mean average' requirements for 'all' types of drivers it's impossible to cater for everyone.
Thread
Thread Starter
Forum
Replies
Last Post
twilightcall
Discovery II
14
03-04-2018 06:55 PM
rrbc
General Range Rover Discussion - Archived
3
11-13-2009 04:59 PM