Quote from morpha :

The only reason why it doesn't produce as much boost in lower gears as in the higher ones is that the gears are to short to give the turbo enough time to spool up.

Yachtzee!

This is why Man invented anti-lag.

Bit of an old topic, but I think the turbo is very well simulated.

Turbo spins trough energy in exhaust and depends on these factors:

Amount of exhaust gas (RPM and Throtlleposition)
Temperature of exhaust gas (hotter = more energy, hot gas expands and creates more volume to spin turbo)
Load of engine (well, more torque gives more push in exhaust)

These three combined will not get very linear turbolag.

I think the lag is very good, when off-throttle, you need about half a sec to spin back the turbo. I am experiencing it very well with the XRR on Westhill. The first lefthand corner, you need to brake a tiny bit and step on it again. When you do that with one foot, you have a turbolag. When doing a left-foot brake and applying full-throttle to keep turbo spinning, you accelerate out of the corner much quicker.

This experience is very realistic to me TBH. (Oh, i drive a Renault 5 GTT, so i know turbo LAG )

The reason you don;t get full pressure in 1st gear is that the the amount of time is too short, when hitting rev-limiter the torque drops massively, so no turbopressure there.





But, I found this topic to report a bug in the game, and don't know where to put it:

When out of fuel, applying throttle still spins the turbo (testen when rolling) That's impossible.

If you are standing dead still in first with clutch engaged (XRR), the turbo will reach full boost after 3-4 seconds, then you will have full boost right through 1st gear if u dump the clutch, but if you put it in first and accelerate normally, not dumping the clutch and then accelerating hard you will reach 1.1 - 1.2 bar boost before changing to second gear, simply because there isn't a long enough duration in first to full spool the larger turbo that the XRR has. If you do the same with the XRT you will reach full boost (0.8 bar) in 1st gear because number one the boost is set lower and I am sure that the turbo is smaller.

Quote from morpha :

That can't be, the turbo is driven by the exhaust gas which should be solely rpm-dependend. However, I think the turbo inlet valve is now somehow connected to the throttle, I don't get any turbo pressure at all if I don't floor it

lol real turbos are NOT RPM based
a comment miss conception is that its the exhaust gas that spools the turbo but its really the Heat from the gas that makes a turbo spool harder and faster. A turbo charger has to rely on the gas being hot so it can travel extreamly fast to hit the rear housing fins more heat ='s faster expanding gas = more load on the engine = more heat and in turn ='s more boost.
allso most turbo cars u can hold them flat to the floor in nutrel and it wont go over 0psi exept on its way up to redline. allso the AR's of the intake and exhaust wheels have ALOT to do with how a turbo will react on the car allso engine displacement and ALOT of other things come into affect ie tuned lenght extractors and even the placement of a external gate can alter how the car spools.

but as this is a racing sim forum i wont go into much more depth :P
the turbo's are wrong but Not as bad as they used to be.


oh and AjRose stupid me calling it a dump :P its just what it looks like to me as thats the only pipe im going to dump into the air :P

I thought that the boost that a turbocharger produces is related to the RPM, displacement, volumetric efficiency, and the density of the air entering the engine. Volumetric efficiency, and air density, are altered by load and RPM, as far as I know. I have no idea if I am correct or not, but that's just what I think is the case.

To react on MAD"s first line, more RPS is more air, for so far you were wrong

It IS the exhaust gas, the heat makes it expand so more volume. It all comes together. SO you are right in a way but not explaining it properly

Quote from Riel :

To react on MAD"s first line, more RPS is more air, for so far you were wrong

It IS the exhaust gas, the heat makes it expand so more volume. It all comes together. SO you are right in a way but not explaining it properly

well yer i know what you mean but their is so many things that come into play i cant explain them for the life of me

example
in a road car i drive if i put it foot flat from 1000 rpm it dose this
1st gear wheel spin and 11 psi at 2200 rpm and drops off at 4000 rpm to 4 psi
2nd gear 14 psi at 2400ish rpm wheel spin and drops off to 12 at about 5000rpm
3rd gear no wheel spin 15psi and drops off to 14 psi at 6000 rpm
4th same as 3rd
5th would be the same but cant get the car to 6000 rpm cause thats like 270kph :P

as u can see when rpm's are higher and load on the engine is lower it makes less boost

but the main reason the car lose's boost at higher RPM is the turbo ar's and size is wrong for the engine displacement

Yes, I wanted to mention but I read your last line

For my 1.4 GTT (renault 5) and hybrid turbo the boost just climbs
It's in there at 2000rpm (well, current turbo's are way better then they were in the 80's).

Well, it's very hard to say how a turbo would react, tbh

But, that bug, is it reported anywere? Think it is stupid to spin turbo while out of gas

I'm not sure if this is what MAD3.0L explained, but if your boost drops off at certain rpm's without any reason, it's not working properly. Probably wastegate opening in wrong situations and not able to keep the desired boost.

When turbo works as it should, it first wakes up and then keeps to boost as where it is adjusted for, as long as you keep your foot down.

Quote from BigPeBe :

I'm not sure if this is what MAD3.0L explained, but if your boost drops off at certain rpm's without any reason, it's not working properly. Probably wastegate opening in wrong situations and not able to keep the desired boost.

When turbo works as it should, it first wakes up and then keeps to boost as where it is adjusted for, as long as you keep your foot down.

As big engine tend to suck in a lot of air at high RPM it is good possible the (small) turbo can't blow that amount of air. So it gets sucked a bit, dropping boost. A turbo can spin a certain amount of RPM (somewhere between 110.000 and 170.000) and for each turbo the efficiency is, just as with engines, at a certain RPM.

So when you 1) push your turbo above a certain RPM (like with old air-filters (the "i hold my hand on the vacuum cleaner hose"-effect) ) 2) Make TOO much boost, it drops performance, and another thing is that the outgoing air will be too heated by the bad performing turbo, dropping Power drastically.

( My GTT for example, will have 200nm torque at 3000rpm, and its HP will be at 140hp at 5500 RPM, running on 14psi of pressure.

When I, with my small turbo, run on 20psi, I measure 220nm torque at 3000RPM (good, increase), but 135hp at 5500 RPM! Performancedrop coz turbo got out of range.

yer more or less my issue with this turbo is it cant flow enough air at higher RPM for to hold the boost at higher RPM im only talking about 3rd gear up.the issue with the lower gears is wheel spin limits load yer . i cant explain what i mean :P but if anyone wants to learn more about it go to allmost any decent car forum and you shall be enlightened

their is 2 ways i should go about fixing this

1 is change the exhaust wheel from a .73 ar to a .86 or 1.06 rear ar

or get a bigger turbo with both .86 ar's like a GT35/82 that i will be buying





Riel

i dont have a hot air issue 600x330x90 intercooler dose the job well rated at around 700hp :P
btw im only making 290 HP at 5500 at the wheels and about 450 NM of tq at 4000 :P
got about 7k to spend to get 400+

Ah, nice cooler
But when the air is cooler when it goes inside the cooler, you always win more. 3% more air at 10 degrees temperature drop (Celcius).

The wheeldiameter can be a solution for sure, but it'll take spooltime. Twin-setup maybe?

Anyway, it's really not easy, and maybe it even isn't theoreticcally explanable for the sake of normality Mostly it's a combination of knowing what you do and experience.

Good luck with your setup, got a story running somewhere on the net?

But, well, the XRR drives quite predictive in terms of boost. So not that bad.

Quote from Riel :

Ah, nice cooler
But when the air is cooler when it goes inside the cooler, you always win more. 3% more air at 10 degrees temperature drop (Celcius).

The wheeldiameter can be a solution for sure, but it'll take spooltime. Twin-setup maybe?

Anyway, it's really not easy, and maybe it even isn't theoreticcally explanable for the sake of normality Mostly it's a combination of knowing what you do and experience.

Good luck with your setup, got a story running somewhere on the net?

But, well, the XRR drives quite predictive in terms of boost. So not that bad.

na no story mate i been slowly modding the car for 2 years now owned it 8 years done all the work my self
list of mods

custom cold air intake
3inch mandrel bent exhaust (paid for this to be done)
boost controler set from 6psi to 15
converted from auto to 5spd manual
put lsd in live axel removed broken lsd (1 week) installed mini spool
re did the hole suspension with custom kingsprings ie the lb progressive rates
swaped out so many differnt size tyres and rims its not funny looking for traction
removed rear swaybar to help with the locker on the track

repaced the clutch twice

and other various things but my current step is waiting on my tyres
Falken Azenis Sport - RT-215
235x40x17's
and after that im geting a custom 35mm front swaybar ebc redstuff pad's and then on to more power

Quote from Riel :

As big engine tend to suck in a lot of air at high RPM it is good possible the (small) turbo can't blow that amount of air. So it gets sucked a bit, dropping boost. A turbo can spin a certain amount of RPM (somewhere between 110.000 and 170.000) and for each turbo the efficiency is, just as with engines, at a certain RPM.

So when you 1) push your turbo above a certain RPM (like with old air-filters (the "i hold my hand on the vacuum cleaner hose"-effect) ) 2) Make TOO much boost, it drops performance, and another thing is that the outgoing air will be too heated by the bad performing turbo, dropping Power drastically.

( My GTT for example, will have 200nm torque at 3000rpm, and its HP will be at 140hp at 5500 RPM, running on 14psi of pressure.

When I, with my small turbo, run on 20psi, I measure 220nm torque at 3000RPM (good, increase), but 135hp at 5500 RPM! Performancedrop coz turbo got out of range.

Yea well ok I'm actually quite aware of that, but I just didn't put into consideration that a turbo car would have a turbo what is so too tiny for the engine.
But now reading MAD3.0LT's post I notice that his car is very far from stock, so it is just a bad choose of turbo.

I would replace to better turbo immediately, because something what drops at 4000 rpm just sounds horrible to me. In my car the engine is starting to just live there! Not a turbo tho.

I'm also more of a "two-litre" man, so cars what are usual in my hobby, it is very rare that someone haves a turbo what actually isn't able to keep the boost, of course on bigger engines that is more likely to happen.

BTW I browse many very decent car forums.

hehe i did other things to the car like the cooler and better intake piping for more air flow but the turbo is what the RB30ET came standed with

That just sounds weird to me that a stock car would have a turbo what isn't able to keep the boost up. I see that's possible then too.

Tho when stock the effect might not been that high, because the stock boost was only 6psi, with the higher boost it is just not able to keep it up. But of course you already know this, so get a bigger turbo man.

Quote from BigPeBe :

That just sounds weird to me that a stock car would have a turbo what isn't able to keep the boost up.

It's because they use a turbocharger that is most efficient at that specific boost level with no modifications whatsoever to the engine. So when you "tune" a stock turbocharged car (or any car for that matter), it is likely that you will make it less reliable then it was from the factory.

Quote from wheel4hummer :

It's because they use a turbocharger that is most efficient at that specific boost level with no modifications whatsoever to the engine. So when you "tune" a stock turbocharged car (or any car for that matter), it is likely that you will make it less reliable then it was from the factory.

Yes. But as like I said, that's not usual with the cars I'm interested about, of course with these bigger engines the "boost drop" is easier to produce.
But ie. with Cossie engines with the original turbo it is possible to get even +100bhp extra out of the engine without even opening it, quite reliable too, without having problems with keeping up the boost.

Tho this "boost drop" doesn't have a much to do with reliability. But raising boost can lower the reliability, depends of the engine and how much.

The thing what I actually meant with that what you quoted, was that it sounds weird that a stock engine would have a "boost drop". When I originally started about the boost drop thing I assumed the engine was running with stock boost.
As a stock it runs 6psi and it may have a little drop to 4psi, but that isn't that noticeable I think.

When it comes to turbos with me, for my budget now it is more something like "get all-stock in decent condition Ford Pinto 2.0i engine + some turbo and a manifold and downpipe + few k-jet injectors for extra fuel supply + maybe a intercooler + do some piping from the turbo to the intake and then just launch the engine, have some boost and give right foot to the engine, it's ready! There's no many turbos what would have problems keeping the boost up in build like this.

Quote from BigPeBe :

As a stock it runs 6psi and it may have a little drop to 4psi, but that isn't that noticeable I think.

Maybe that is some sort of exhaust leak? The exhaust pressure gets higher with more load on the engine, and then a leaky gasket ends up blowing apart because of the pressure?

lol the boost drop im talking about in 1st and 2nd gears isent cause the turbo is to small it cause their is no load on the engine cause the wheels spin so easly and thats in the dry :P in the wet the most boost i can make is 12psi in 5th gear at 110 kph befor it spins :P

and yer im going o up grade my turbo but injectors ECU and exhast manafold and new plenum will be needed befor the turbo

allso got a 255L PH fuel pump and sard reg siting here to go in

but in stock form no car should lose boost at higher rpm

Quote from Riel :

To react on MAD"s first line, more RPS is more air, for so far you were wrong

It IS the exhaust gas, the heat makes it expand so more volume. It all comes together. SO you are right in a way but not explaining it properly

ever taken a look at a compressor map?
considered pressure ratios?

Quote from Ball Bearing Turbo :

This is precisely why turbocharged vehicles benfit from larger exhaust systems since the pressure drop is greater and therefore spool times are shorter. This is also why the positive feed back effect you correctly mentioned happens - but not directly because of the increased flow as cylinder pressure rises; what rises with cylinder pressure? OH right, the EGT skyrockets - often causing the turbine housing to actually glow.

i know this thread is a couple months old but i thought i'd add my obervations since i have been daily driving, and tracking turbocharged cars since i got my driving license.

i wanted to add that the first sentence in the above post is not always true. it is true for probably 90% of all turbo applications since most people aim for larger power over stock or n/a. for many factory turbo setups where a car is equipped with a fairly small turbo, i have found that the exhaust size can be used to shift the power band around. the larger the exhaust, the higher the power band till you maximize the pressure differential.

for example i have a fairly small turbo on my car. it was designed to be a very livable-daily around town setup. the turbo spikes at 18-20 psi early and tapers to 12-14psi around optimal shift points for best acceleration.

from a 2" to 2.5" spool was much quicker, mid range was strongest of the exhaust systems i have tried. 2500-4000 was quite a bit stronger than the 2" exhaust. 235ft-lbs and 195hp to 250ft-lbs and 205hp at the wheels was obtained. boost pressure seemed to taper off quicker than the 3"

from a 2.5" to 3" spool was slightly slower than the 2.5", but i had more top end. with the 3" on the motor in my car some people have experienced over spinning and damaging their turbine. when the turbo sppols, it spools quicker, but slighty later compared to the 2.5" or 2". 2000-3500 was slightly weaker than the 2.5" as the turbo didn't spool quite as fast, but 3500-6000 was a lot stronger. 240 ft-lbs and 215hp at the wheels. it makes pretty much the same amount of torque past 4000 rpm's, but is shift up in the powerband, netting slightly higher HP figures.

i attribute this to the way the exhaust gasses flow through the turbine at faster velocities where the flow may not be as efficient as if there was some back pressure on the turbo form the 2.5" vs the 3".

i have always used engine load to explain how boost is built, and how fast from my observations. with a 24 pound flywheel my car generates more boost in neutral than a 12 pound. but the 12 pound accelerates quicker as there is less rotational mass.

EGT's reach in the low thousands of degrees C. without going into positive pressure my EGT's are around 300-400C depending on around town cruising or highway cruising. which is the efficiency range of a catalytic converter for emmissions purposes. when i really get on it over and over again they are in upwards of 1000-1200C, and my turbo starts to glow orange. this is why some people install turbo timers on street cars. the engine must run to allow the oil and/or water to cool the turbo so coking does not occur in the oil lines and houseing of the turbo where the oil flows. so if you have a turbo charged car, don't beat on it, then shut it off without idleing the engine for a few seconds (15-60 depending on how hot your EGT's are), or driving a short, low-load distance.

Very nice post, glad to have you here!

Indeed, that wasn't the whole story as you very nicely expanded on, generalities are not invaribale truths

lol many months later and this thread is still a intresting read

nice post erfrag though i dont fully agree with some of ur post most of it would make sense depending on the setup/conditions/ lots of things

one question erfrag what kind of boost controler are you useing on this car or is it actuator controled?

if its controled is whats the setings of the controler