Are cylinder pressure and boost pressure inextricably linked

[Flynn]

Since the last topic was locked I decided to start a new one. The question is above, in addition to which I would like to ask the following question:

Does a larger charger flow more air and;

Is it better to have more air flow at less psi or less airflow at more psi

Dave did a writeup on theywhoshallnotbenamed but I am still banned from there so can't read it.

Thanks.

[Dan!]

Less psi is better, flow is what you really want, but thats hard to measure unlike boost pressure. If you put a large restriction in your pipe from the turbo -> TMIC (I.e a load of wire wool or similar, not recomended, thats just an example) then you would probably get a few more psi, but performance would still be down as the air flow is restricted.

Also worth remembering, smaller turbos flow less and they also produce a hotter charge, whereas bigger turbos will flow more at a lower charge temp (because they are spinning slower) Which is why a TD04 at 25psi will be fairly reliable and produce ~160hp with the fuelling to match, and a GT15 at 25psi will be spinning it tits off, producing a very hot charge and only about 130hp.

[Flynn]

Well done Dan! for providing a good answer without going off on one. By the way you look like Ed's twin brother in your avatar! Haha! Now would someone tell me whether boost pressure and cylinder pressures are linked because I thought they where but mark_airy seemed to imply that they were not. Not to be funny or anything, but these things are kind of important to know :roll: Just incase certain people think I am getting a power trip from asking reasonable questions :? Not saying they would because that would be really paranoid of them, but just incase 8-)

[Toms306]

This is a bit off topic but flynn probably mind....Dan, where do you learn so much about deisels and turbos and stuff? Do you go college or just have an epic brain that knows everything lol? I've been wondering for a while after seeing the pump mods and stuff that you do...

[Dan!]

Well done Dan! for providing a good answer without going off on one. By the way you look like Ed's twin brother in your avatar! Haha! Now would someone tell me whether boost pressure and cylinder pressures are linked because I thought they where but mark_airey seemed to imply that they were not. Not to be funny or anything, but these things are kind of important to know :roll: Just incase certain people think I am getting a power trip from asking reasonable questions :? Not saying they would because that would be really paranoid of them, but just incase 8-)

Thanks for the patronising, its just what I wanted! Funnily enough I dont just go 'off on one' for the fun of it, its only when you act like a lady garden that I turn into the hulk.

This is a bit off topic but flynn probably mind....Dan, where do you learn so much about deisels and turbos and stuff? Do you go college or just have an epic brain that knows everything lol? I've been wondering for a while after seeing the pump mods and stuff that you do...

I actually put something about this in my CV Itspurely from reading up on the internet and getting stuck in tbh, I enjoy doing it/learning about it and thats why I spend most of my free time (and paid time reading about stuff....) Iv never actually been 'taught' mechanics in my life.

[darrenjlobb]

I think its important to note here, that the whole "more flow as less psi" thing is kinda missleading, and people dont really understand...

For as long as you dont change anything on your engine (cam / head / ports etc) then there is only so much air you can flow at a set pressure, changing the turbo wont change this....(it will due to exhaust back pressure etc, but ignore that for now)....the reason people make more power is more due to the fact the turbo is making its pressure higher in the rev range, hence making more horsepower....its only now, because your doing MORE rpms, that your flowing MORE air at the same psi, and making more power, not just the same setup / same rpms somehow making more power and more flow even though the pressure is the same....

And yes, boost effects cylinder pressures massively...as does compression ratio and injection timing / quantity....

[Flynn]

But is it like if for example 450psi cylinder pressure as standard and you run 20 psi does that make the cylinder pressure 470psi?

[darrenjlobb]

No...

Your adding 20psi to the pressure at intake, you need to figure out the new pressure under compression taking into account the current compression ratio / etc.....

[ginge191]

Which is why a TD04 at 25psi will be fairly reliable and produce ~160hp with the fuelling to match, and a GT15 at 25psi will be spinning it tits off, producing a very hot charge and only about 130hp.

On this note - in terms of torque and A/R ratios - this is what im primarily trying to understand at the moment.

using your exmaples, would the GT15 have a greater low end torque due to a quicker small time? or would it mean both turbos create the same torque, but through a prolonged period?

What im trying to achieve is the best possible low end torque and through reading, understanding that the larger turbo's have a greater a/r as apposed to smaller turbos creating a larger bhp? but not necessarily a decent low end boost?

clarification or am i getting this confused?
appreciate the patience

[Toms306]

This is a bit off topic but flynn probably won't mind....Dan, where do you learn so much about deisels and turbos and stuff? Do you go college or just have an epic brain that knows everything lol? I've been wondering for a while after seeing the pump mods and stuff that you do...

I actually put something about this in my CV Itspurely from reading up on the internet and getting stuck in tbh, I enjoy doing it/learning about it and thats why I spend most of my free time (and paid time reading about stuff....) Iv never actually been 'taught' mechanics in my life.

Ah cool, wish I could pick stuff up as quick as you seem to! College is good and I have learned a hell of a lot from there, but its really still only basics and a lot of the stuff we're taught is old now and barely used on 'modern' cars. I'm trying to learn more about diesels and yeah I might take the piss and say I don't like them but actually find it really interesting how everything works, especially when I got the g*lf, started looking up how PD engines are different and what a VNT turbo does for example......but I just seem to get to a point where I hit a wall reading something that, for example, Darren/Ruan/Bryn has written and I'm just like :?

That said, I'm really enjoying working at Ford on work experience atm. I'm in the commercial workshop which is mainly vans and trucks and given the choice I would've chosen the car side.....but am really enjoying it and learning loads in the commercial side, and haven't worked on a petrol all week lol!! And now I can see the stuff while fixing different things (obviously with supervision, they havent let me loose on stuff alone yet lol) it all seems to just click and I think 'ah, so thats why that happens' or 'thats what that does'...........I just don't seem to have the right mind to read stuff and take it all in, but if I physically do/see something I can work it out. This is really why I'd love a project car if I could afford to......would have bought JJs DT if I had the money!

[mark_airey]

Well done Dan! for providing a good answer without going off on one. By the way you look like Ed's twin brother in your avatar! Haha! Now would someone tell me whether boost pressure and cylinder pressures are linked because I thought they where but mark_airy seemed to imply that they were not. Not to be funny or anything, but these things are kind of important to know :roll: Just incase certain people think I am getting a power trip from asking reasonable questions :? Not saying they would because that would be really paranoid of them, but just incase 8-)

Care to point out where I said this instead of slandering my name (sort of, but since there is nobody on here with the user name you mention I guess you mean me)

[mark_airey]

Sorry for the double post, on my phone so its more of a faff to reply

Which is why a TD04 at 25psi will be fairly reliable and produce ~160hp with the fuelling to match, and a GT15 at 25psi will be spinning it tits off, producing a very hot charge and only about 130hp.

On this note - in terms of torque and A/R ratios - this is what im primarily trying to understand at the moment.

using your exmaples, would the GT15 have a greater low end torque due to a quicker small time? or would it mean both turbos create the same torque, but through a prolonged period?

What im trying to achieve is the best possible low end torque and through reading, understanding that the larger turbo's have a greater a/r as apposed to smaller turbos creating a larger bhp? but not necessarily a decent low end boost?

clarification or am i getting this confused?
appreciate the patience

As far as I understand it ginge the smaller turbo will spool up sooner in the revs thus giving you more boost sooner in the revs so providing you can supply the fuel to burn you would get more power sooner in the revs which would tail off qicker than with a larger turbo due to the smaller turbo going outside its efficiency range sooner if that makes sense?!

[Flynn]

Well done Dan! for providing a good answer without going off on one. By the way you look like Ed's twin brother in your avatar! Haha! Now would someone tell me whether boost pressure and cylinder pressures are linked because I thought they where but mark_airy seemed to imply that they were not. Not to be funny or anything, but these things are kind of important to know :roll: Just incase certain people think I am getting a power trip from asking reasonable questions :? Not saying they would because that would be really paranoid of them, but just incase 8-)

Care to point out where I said this instead of slandering my name (sort of, but since there is nobody on here with the user name you mention I guess you mean me)

more to the point, you didn't say anything, therefore leaving me to rely on my best guess as to what you were getting at so don't you dare have a go at me for 'slandering' your name :evil: Read the following posts for 'evidence:

At those PSIs I would be more worried about blowing the gasket or chucking a rod rather than the turbo blowing, which is a relatively small thing in comparison to either of those events.

Ignore this.........

People run 40+psi on TMIC's no problem and although performance wont quite be as good as a FMIC, it wont be far off. The problem comes with long term power, if you are driving hard for more than a few minutes the power will drop considerably and you will also need to keep your eye on engine temps as they will climb much faster on TMIC.

IMO a VERY safe boost to run on TMIC, worry free would be ~18/19psi. Any higher and you will just need to be sensible and have some mechanical sympathy.

Listen to this

Okay then smart guy what causes headgaskets to blow and rods to chuck then? Obviously raising the psi does because that makes the overall compression ratio higher which strains those components more. I really want to smack you sometimes :x

Lol, you have no idea at all do you

Yeah I know it was Dan! but he is your cohort and you did say to ignore my airing-on-the-side-of-caution advice.

[mark_airey]

more to the point, you didn't say anything, therefore leaving me to rely on my best guess as to what you were getting at so don't you dare have a go at me for 'slandering' your name :evil: Read the following posts for 'evidence'

Yeah I know it was Dan! but he is your cohort and you did say to ignore my airing-on-the-side-of-caution advice.

18/19PSI is never going to be a problem unless there is an underlying problem such as damaged rods or seriously fatigued rods (which would go by themselves in time in a standard setup), hence my disregard of your comment!

I'm still waiting for you to answer my original question since your comment was pretty much, that I had said that boot pressure and cylinder pressure were not linked which clearly they are since the boosted air goes into the cylinder..............

also I think Dan will have something to say about the last comment but, since he isn't a companion or an associate I fail to see what you are trying to imply by that statement?!

Instead of targeting me because you don't like me due to whatever stupid reason you have created in your head you should maybe concentrate on not being a troll and starting arguments/personal attacks on people trying to help for no real reason at all!

[ginge191]

As far as I understand it ginge the smaller turbo will spool up sooner in the revs thus giving you more boost sooner in the revs so providing you can supply the fuel to burn you would get more power sooner in the revs which would tail off qicker than with a larger turbo due to the smaller turbo going outside its efficiency range sooner if that makes sense?!

So would this have any impact on torque levels at all??

I'm trying to get my head around a way of getting a decent low end boost from a derv without resorting to massive changes in the engine. I'm already running a bosch setup a small KKK turbo at 18psi, runs recently nicely and has a nice boost low end - trying to get a bit more - getting an FMIC sorted soon.

[mark_airey]

So would this have any impact on torque levels at all??

I'm trying to get my head around a way of getting a decent low end boost from a derv without resorting to massive changes in the engine. I'm already running a bosch setup a small KKK turbo at 18psi, runs recently nicely and has a nice boost low end - trying to get a bit more - getting an FMIC sorted soon.

In theory if you have the same amount of air and fuel going in then you have the same size of explosion during the combustion cycle (same amount of force pushing piston down-turning force on crank) as you would if you reached the same level of boost higher up the revs so you should reach peak torque sooner in the revs as the extra air will be available sooner, clear as mud?!

Also in theory FMIC wont make all that much difference as long as your not staying on full boost for prolonged periods of time (as if you do the TMIC will struggle to cool the increase in charge temps) and worth considering is that the longer the pipework the more space you have to fill with boosted air before it reaches the engine resulting in (marginally) more lag so distance from turbo-inlet should be as short as possible.

[Seb_Ryan]

Trolls getting fat with all this food chucked at him :clap:

[ginge191]

In theory if you have the same amount of air and fuel going in then you have the same size of explosion during the combustion cycle (same amount of force pushing piston down-turning force on crank) as you would if you reached the same level of boost higher up the revs so you should reach peak torque sooner in the revs as the extra air will be available sooner, clear as mud?!

Also in theory FMIC wont make all that much difference as long as your not staying on full boost for prolonged periods of time (as if you do the TMIC will struggle to cool the increase in charge temps) and worth considering is that the longer the pipework the more space you have to fill with boosted air before it reaches the engine resulting in (marginally) more lag so distance from turbo-inlet should be as short as possible.

i see where your coming from, but again, the current standard pipework is farily restrictive behind the TMIC it seems very narrow, taking that into account, would and FMIC be a better option.

As said before, im trying to get the best amount of low end possible but dont want to spend money on a front mount if its going to be pointless - some say its worth it, others say not..



And wheres the troll :geek: ??

[mark_airey]

I see where your coming from, but again, the current standard pipework is farily restrictive behind the TMIC it seems very narrow, taking that into account, would and FMIC be a better option.

As said before, im trying to get the best amount of low end possible but dont want to spend money on a front mount if its going to be pointless - some say its worth it, others say not..



And wheres the troll :geek: ??

I guess you mean from the filter to the turbo where it kinks round the inlet manifold? if so I would try and re-do the intake pipe in something less restrictive, as this will allow the turbo to spool up quicker (due to having less restriction on the air it can have) if you think that the top mount is still being restrictive (which I personally don't think it will be in your application but may be wrong) then carry on to fit a FMIC install, this way you would spend no more money than you have to

[ginge191]

I guess you mean from the filter to the turbo where it kinks round the inlet manifold? if so I would try and re-do the intake pipe in something less restrictive, as this will allow the turbo to spool up quicker (due to having less restriction on the air it can have) if you think that the top mount is still being restrictive (which I personally don't think it will be in your application but may be wrong) then carry on to fit a FMIC install, this way you would spend no more money than you have to

yeh thats where i mean..
yeh i may attempt to relocate the inlet for the turbo, see whats happening... just see where the pipe goes ino an '0' shape is a lot worse than a straigt ' O ' shape if that makes sense...

would you see a fmic as being pointless then and creating more of a burden for the turbo spool?
http://rusubaru.com/intercooler-efficiency/ < -- interesting stuff there, i know its for scooby's but its the same concept

[mark_airey]

yeh thats where i mean..
yeh i may attempt to relocate the inlet for the turbo, see whats happening... just see where the pipe goes ino an '0' shape is a lot worse than a straigt ' O ' shape if that makes sense...

would you see a fmic as being pointless then and creating more of a burden for the turbo spool?
http://rusubaru.com/intercooler-efficiency/ < -- interesting stuff there, i know its for scooby's but its the same concept

I know exactly where you mean I would re route it with a 180* bend off the turbo and back along the back of the bay to the stock location in 2" or bigger pipe, as it will do away with all the restrictive intake piping and for what you are trying to achieve I can't see a front mount being any help, if you find the car getting hot then you haven't lost anything and could continue to fit and FMIC.

Same concept and exactly what I'm trying to say (although I did skim read ) is that scooby article, nice find

[ginge191]

hmm ok, think it would be hard to find piping to get from the turbo to continue to the stock location???

a U bend perhaps, but would be quite tight no?

found this http://www.ebay.co.uk/itm/Intercooler-U ... 35b2204b84

[Ruan]

It's all to do with efficiency in relation to the shaft speed.

That's where the compressor map comes in.

A GT1546 compressor will put out enough air to maintain 26psi at 5000rpm on an XUD9, but the problem lies with the shaft speed, to produce that pressure with the airflow required at 5000rpm, you'd spin the compressor WAY past it's design max, theoretical max and you'd be down to something like 30% efficiency. Turning it into a hairdryer.

A T2 is a "bigger" turbocharger, but is of an older design, so it'll put out a bit more air when comparing compressor maps to a GT15 at it's design max, BUT it'll be even further down on efficiency, putting out even hotter air. When you actually work out how much power you'll get, that's why the T2 and GT15 are surprisingly similar - BUT - BIG MASSIVE BUTT (Just like your mum...) this DOESN'T take into account the hotside.

The hotside of the turbo also makes a big difference to whether you can get the air out of the engine - this is down to the "size" in cm^2 and it's A/R. I could go heavily into what A/R is and it's relations to other dimensions, but basically it's how "tight" the housing is, how small the gap is for the gasses to get into the turbine wheel, which affects the velocity of the expanding gasses. The smaller the A/R the tighter the housing is, i.e. the gas will be moving faster, which makes the turbine wheel spin up quickly... The bigger the A/R the slower the gasses will be going into the turbine, therefore spinning up slowly, BUT it's to do with backpressure - a small A/R will give high backpressure and not let much gas out, strangling the engine, giving high exhaust mani pressures and affecting inlet pressures, a larger A/R will spool slower, but allow more gas through.

That's where a VNT turbo comes in, you've got a VARIABLE A/R which means that at low engine speeds and lower volumes of exhaust gas, the vanes are up close, you have a small A/R the turbine will still speed up quick, but when the engine gets quicker, more hot gasses, the vanes open up, giving a really big A/R - loads of gas out, improves flow out of the engine MUCH better, but the turbo is spooled up, so it doesn't matter about spooling it up...

[Poodle]

Ginge, if you want to boost low-end torque (heh heh), you want a quick-spooling turbo with minimum lag. VNT is ideal, but expensive and complex to do right. Low-tech version is the twin-scroll... No where near as good as vnt, but a decent improvement over standard.

Really it all depends what your end-goal is, am I right in thinking you want a combination of easy power and good economy? If so, a quicker spool will keep revs down as you won't need to rev for the power, it'll also keep the power easily accessible without having to shift down all the time. The main downside is back-pressure at motorway speeds, but on the island you won't really see those. I'd keep the top mount for now, more efficient turbo will make up for no fmic if you're not revving it.

[Flynn]

But low end torque is dangerous for the conrods and more boring than high revs.

[THE_Liam]

But low end torque is dangerous for the conrods and more boring than high revs.

If you prefer high revs to low-down torque you really want a petrol...

[Flynn]

Try telling anyone with a gov mod that

[mark_airey]

Try telling anyone with a gov mod that

6k isn't high revs though...........

[Flynn]

Well I clearly meant it in relation to diesels now go back under your little bridge...

[Poodle]

Will you give it a f*cking rest! Haven't you heard - it's good to do something different once in a while, just leave it.