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sudso wrote:
More torque equals more power but how come deisels have more torque but less power than a petrol engine with say a less amount of torque? Rpm difference?
I'd say it's also the higher energy produced by the "high compression bang" and slower burning? of a deisel but at much lower revs.
A petrol engine doesn't produce as much energy with each "bang" because of it's much lower compression (blow up a balloon until it pops and it releases a lot more energy than a balloon with half the air pressure) and needs the revs to keep momentum up (or make power).
my 2c of dribble
think that's more to do with the octane (petrol/LPG) and cetine (Diesel)
Diesel engines are a lot more suited to making torque than power, Diesel fuel is only 50 Cetine BP/49 Cetine for Shell, also the air/diesel mix would be far more in favour of air(oxygen) than diesel, diesel requires a high temp before it burns up.
So the extra amount of air(oxygen) would only help to produce more torque, The trade off in diesel engines is the fact they are using the heat from compressed air to allow the diesel to burn.
You need long stroke to first stuck in enough air then you have to allow a certain amount of time to compress it, the burning part would be the quickest part of all.
Petrol has an Octane of 91 to 110 and LPG has an octane of 114+
Onctane is basicly the amount of time it takes before it burns up.
So if you have a highly modded petrol engine you need to use a higher octane fuel to stop pre/post-detation, which can cause damage to engine parts.
The trade off with this, is that petrol burns up easy at a low heat, so you can't be messing around for a long time because your mixing the air/fuel at the same time inside the cyclinder, compressing air produces heat.
I always thought of the Diesels having more torque and less power due to the size of the cylinders. Due to the larger size it cannot rev as hard (more weight going up and down rapidly), although each combustion cycle creates quite a bit of energy due to the size of the chamber.
In comparison, there aren't too many petrol 4 cylinder 2.8L engines around.
The magna was close however with the 2.6L 4 cylinder... they weren't overly great though.
A good comparison is the new Holden Astra range, showing how the diesel revs lower to create its power and torque compared to the petrol engines.
The Diesel has more power and torque than the n/a ECOTEC (110kw vs 90kw), however it falls short of the outright power of the 2.0 Turbo SRi (110kw vs 147kw). The diesel creates bucketloads of torque though (320nm vs 262nm).
Goes to show you the newer diesels are narrowing the gap... slowly
HotFourOk wrote:I always thought of the Diesels having more torque and less power due to the size of the cylinders. Due to the larger size it cannot rev as hard (more weight going up and down rapidly), although each combustion cycle creates quite a bit of energy due to the size of the chamber.
In comparison, there aren't too many petrol 4 cylinder 2.8L engines around.
The magna was close however with the 2.6L 4 cylinder... they weren't overly great though.
A good comparison is the new Holden Astra range, showing how the diesel revs lower to create its power and torque compared to the petrol engines.
The Diesel has more power and torque than the n/a ECOTEC (110kw vs 90kw), however it falls short of the outright power of the 2.0 Turbo SRi (110kw vs 147kw). The diesel creates bucketloads of torque though (320nm vs 262nm).
Goes to show you the newer diesels are narrowing the gap... slowly
I think Gary nailed it with this:
DAMKIA wrote:The slow reving nature of diesels is related to the lower volitility and slower flame propagation of diesel compared with the higher volatility of petrol and higher flame propagation.
Slow burning fuel means they won't rev, so maximise the low rpm torque. Since they won't rev, larger reciprocating mass isn't as much of an issue, so use larger cylinders/pistons.
I guess the higher compression means they can achieve higher BMEP, so they can get large downforce without needing large piston area, so again the long stroke/small bore compromise for swept volume.
I wonder if improved atomisation from CRD improvements will allow higher revs?
It's also a good point that we traditionally compare a turbo-charged diesel with a naturally aspirated petrol engine. A turbocharged petrol is still a clear winner for power.
Don't worry - I understand it all, and have done for a long while. It's your awkward explanations which give me a headache - trying to work out if you really understand what you're typing.
zagan wrote:Because you need extra heat to burn up diesel you need to spend a little bit more time on the up / down part of the stroke.
Petrol doesn't have the time to be waiting, so need to be moving quicker
Zagan wrote: You need long stroke to first stuck in enough air then you have to allow a certain amount of time to compress it, the burning part would be the quickest part of all
Doesn't understand the difference between compression ratio, and oversquare ("longstroke") and undersquare cylinders.
Not being picky Zagan, but it would help everyone if you got your facts straight. Try not to source and base your knowledge on the various "Ricer" forums information. They are not exactly known for being factual....
George Carlin, an American Comedian said; "Think of how stupid the average person is, and realise that half of them are stupider than that".
DAMKIA wrote:Doesn't understand the difference between compression ratio, and oversquare ("longstroke") and undersquare cylinders.
On this subject, I prefer to use "long stroke" and "short stroke" because I've seen "over-square" and "under-square" definitions change from one site to the next - i.e. what you and I call "short stroke" I've seen one author define as "over-square" while another author defines it as "under-square."
Who would expect that you can't trust everything you read?
Diesels also have a longer fuel burn , thus producing a longer power stroke (more toqure). There is a heap of info on this in a mag called Diesel Power, Banks power has a lot to say on it too.
Back to topic,
I run a Gt25 .70 a/r ( big blingy 4"snout) and ?? exhaust, I think...... it doesnt come on till around 2000prm and boost is at 22psi at the moment.
Mi2c
DanielS wrote:Back to topic,
I run a Gt25 .70 a/r ( big blingy 4"snout) and ?? exhaust, I think...... it doesnt come on till around 2000prm and boost is at 22psi at the moment.
Mi2c
Daniels
glad to see we are back on the topic.
the 0.70 a/r is that comp or turbine, do you know the full specs.
The .7ar is for the compressor side, best thing you can do is go to the website turbobygarret.com
This has compressor maps of all ball bearing turbos, from there you can decide what is suitable for you.
Reading this thread I think you are asking a little too much to have a turbo on full boost by 1400rpm and expect to hold out until 3-4000 rpm. Even if you dont drive in that range, when you need to one day the turbo will be too restrictive. Unfortunately its all a compromise on what you want.
You need to decide on what you want the vehicle to do and match a turbo to that range.
DanielS wrote:Diesels also have a longer fuel burn , thus producing a longer power stroke (more toqure). There is a heap of info on this in a mag called Diesel Power, Banks power has a lot to say on it too.
Back to topic,
I run a Gt25 .70 a/r ( big blingy 4"snout) and ?? exhaust, I think...... it doesnt come on till around 2000prm and boost is at 22psi at the moment.
Mi2c
Daniels
Daniel is that a GT28RS?
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Dzltec wrote:
Reading this thread I think you are asking a little too much to have a turbo on full boost by 1400rpm and expect to hold out until 3-4000 rpm. Even if you dont drive in that range, when you need to one day the turbo will be too restrictive. Unfortunately its all a compromise on what you want.
i am aware it would run out of breath at the top end but it doesnt get driven all the time at 3500-4500 rpm. majority of driving is up to 3000 even in the bush and only gets pushed when needed so would be better to have the boost in the range driven most often.
DanielS wrote:Diesels also have a longer fuel burn , thus producing a longer power stroke (more toqure). There is a heap of info on this in a mag called Diesel Power, Banks power has a lot to say on it too.
Back to topic,
I run a Gt25 .70 a/r ( big blingy 4"snout) and ?? exhaust, I think...... it doesnt come on till around 2000prm and boost is at 22psi at the moment.
Mi2c
