Outer Limits 4x4 Board

I have heard a lot of people talking of high boost figures such as 15 and 18+ on turbo diesels (patrols & cruisers).
I have a bit of background in Turbo Petrols but not the Diesel.

What mods are done to safely run the motors at higher boost?
Can you drop the compression by alternative head gasket or is that not an option on the diesel?
What are the risks?

I havn't heard of too many smaller capacity diesels running high boost, is there any reason for that? in particular I have a 2.8 Hilux with mechanical injection and the standard surf turbo and skyline intercooler topmounted.

Also Looking at running smaller turbos than the standard turbo to gain boost earlier in the rev range to try to widen my useable revs as at the moment i really only have 800 revs to play with before she bogs down or runs out of puff.

Hope people don't say this should be in toyota as there are more modded patrols out there than toyotas so hoping to hear some of there experiences.

Thanks for any help, I love the diesel and would rather squeeze a bit more out of her before conceeding to go the v8.

Cheers
Banga

Some diesels already run high boost. Land Rover 300Tdi and TD5 (2.5L 4cyl and 5cyl, respectively) engines run around 17psi stock. Many bigger diesels in trucks run about 30psi stock.

Indirect injection diesels don't show much benefit when the boost is increased too much. But direct injection diesels are different, and these are often the engines that are built to run high boost from the factory.

There is not a lot you can do to build a diesel to take more boost, as it comes down to things like the strength of the crank and durability of the main and big-end bearings. But a lot of turbo diesels are over-engineered, so they can be tweaked a bit without problems.

EDIT:
You do not want to decrease compression, that will likely make the engine hard to start when cold. Turbo diesels aren't like turbo petrols in that respect.

The most important thing in a diesel is to keep the EGT (Exhaust Gas Temperature) low - about 500-550°C max. Before you start tweaking, buy and fit an EGT, then adjust the fuelling according to the EGT. Diesels run cooler when lean (unlike a petrol).

In the interests of longevity, oringing the block will help the head gasket seal under higher boost. A very good i/c is needed to keep inlet temps down and also a pyro to monitor exhaust temps is critical.

Higher boosts may require a boost compensater to be fitted to allow for adjusting of fuel under boost and not off idle.

Hope this helps

i'll disagree with a few things

i suspect quite a lot run high boost but do not run the fuel to match ie they don't run max fuel.

all motors have max pressure limits, which is generated by burning fuel simialr to petrol motors. this is why some motors reduce the fuel as the boost goes up...they try to limit max pressure to save the motor when it overboosts. the big limit on deisels is the static compression. to run big boost with the fuel to match means you have to lower the compression, just like you do with a petrol. however older deisels burn fuel very poorly at low compression hence poor starts etc.

the advantage of upping the boost is it increases the compression which helps fuel burn, which is why 2.8 hilux run so well with turbo's even tho they ave no extra fuel being added. just the increase in compression and the extra air means the existing fuel burns better.

the newer comman rail deisels run low compression (15:1 @ 20+ psi boost), the key thing here is they have head design and injectors setup that allows them to burn fuel well at low compression, which means they can run big boost and large amount of fuel without exceeding max pressures.

leehamescort wrote: I have a 2.8 Hilux with mechanical injection and the standard surf turbo and skyline intercooler topmounted.

Also Looking at running smaller turbos than the standard turbo to gain boost earlier in the rev range to try to widen my useable revs as at the moment i really only have 800 revs to play with before she bogs down or runs out of puff.


Cheers
Banga

personally i think the surf turbo (2lt ??) is a bit to small. i'm sure you have seen plenty of comments of people high flowing them and finding more power, lees heat and earlier spin up.

not sure what you mean by only have 800revs to play with. you should have 2000-4000 rpm band to play with.

do you run a boost compensator ?

ISUZUROVER wrote:Some diesels already run high boost. Land Rover 300Tdi and TD5 (2.5L 4cyl and 5cyl, respectively) engines run around 17psi stock. Many bigger diesels in trucks run about 30psi stock.

Indirect injection diesels don't show much benefit when the boost is increased too much. But direct injection diesels are different, and these are often the engines that are built to run high boost from the factory.

There is not a lot you can do to build a diesel to take more boost, as it comes down to things like the strength of the crank and durability of the main and big-end bearings. But a lot of turbo diesels are over-engineered, so they can be tweaked a bit without problems.

EDIT:
You do not want to decrease compression, that will likely make the engine hard to start when cold. Turbo diesels aren't like turbo petrols in that respect.

The most important thing in a diesel is to keep the EGT (Exhaust Gas Temperature) low - about 500-550°C max. Before you start tweaking, buy and fit an EGT, then adjust the fuelling according to the EGT. Diesels run cooler when lean (unlike a petrol).

X2.Well said Ben.

Also, have you tried tweaking the pump yet? You will actually get a bit more go by adjusting the boost fuelling and main fuel, and shortening the wastegate actuator.( Only has an aneroid adjustment if a factory turbo engine...2LT or 3LT)I have made the Tdi's pull a whole lot better by doing similar mods.
DON'T DO ANY OF THIS WITHOUT A BOOST GUAGE AND PYRO.

JC

justinC wrote: DON'T DO ANY OF THIS WITHOUT A BOOST GUAGE AND PYRO.

JC

As Justin said - if you don't have them fitted, first install a boost guage (to the inlet manifold, not just after the turbo), and a PYRO/EGT guage. That way you know what boost you are getting at the inlet manifold, and what your EGTs are like.

If the EGT is low, begin by simply tweaking the fuelling as Justin suggests. Then look at increasing boost on the turbo you have (shortening wastegate actuator), and fuelling with it.

PM Dumbdunce or search through previous posts from him for engine-specific stuff for your engine. Like max safe boost levels, etc.

Say it with me ............................................... V8


It's time we can have it done by VicWinch

HG wrote:Say it with me ............................................... V8


It's time we can have it done by VicWinch

I pulled my 4.7 V8 in favour of a 3.9 turbo intercooled diesel Isuzu, it has more torque and uses half the fuel. With the intake whistle and the awesome bottom end, I more than happy!! Go Diesel but go cubes and forced induction.

JC

Thanks for the help, How do i go about installing a Pyro? Is there somewhere on the manifold that i can scew one into on a the standard manifold or do i need to get something made up.

Seems to be a bit of argument on putting it before or after turbo, seems like there is no real difference other than making sure you account for temp according to location of sensor.

I already have a boost gauge and it runs at about 9psi, i have done nothing to up boost.

Correct me if i'm wrong but as i understand:
So the killer is really the exhaust temps, I can run whatever boost i can get away with before the exhaust temps get too high. The only real way to reduce exhaust temp is to have the exhaust side flow better so the gasses are not building up heat
- high flow turbo/different turbo/s
- improve manifold design for better flow
- bigger exhaust (but only will have effect if turbo is better)
Intercooler to reduce temps pre combustion thus reducing temps(hence put an intercooler on and up the boost) I have an intercooler but have not upped the boot yet.
- so the more effective the intercooler the greater possible gains in boost. (turbo being a limiting factor still)

The bottom end is also a restricting factor but i'm more likely to kill the motor with high exhaust temps before i reach the bottom ends limits.

Once i have the Pyro, i can then start adjusting boost up. as I adjust boost up I can add fuel in small increments to gain further power but if I ad too much fuel exhaust temps will increase.

If i adjust the boost without additional fuel I will be only getting partial gains from the boost until additional fuel is adjusted, but no potential damage.
- except if i up the boost beyond the turbos working range i will get higher exhaust temps.
- opposite to a petrol car if i have higher boost it is safer to have less fuel, if i over fuel it it will get hot.

Tuning (in small increments of boost and fuel)
- Raise the boost only, checking exhaust temp change.
- if minimal additional heat add more fuel until exhaust temp begins to raise then back fuel off slightly.
- Will the additional fuel at lower revs be a problem as the engine is off boost so not under high load??
- Repeat the above preocess until raising boost results in raised exhaust temp as efficency of turbo system has been exceeded.


Sorry for the long post and all the questions, I could take it and get it tuned by a turbo place but i like to know how things work and always prefer to do something myself.

Please correct me where i am wrong, this is my interpretation of what i have read.

Thanks for any help

Regards
Leeham

PS.
HG - what was that.....a river crossing.....better get your CRC out!!

from what i have read here its better to put one in the manifold instead of after the turbo. your trying to measure combustion temps. there is a fair bit of temp drop after the turbo which will vary depending on turbo, so before turbo is really the only way getting actual temps.

one thing i would like to know is whats the diesel ver of knock etc caused by to high compression? there must be a reason the comp ratio is only ~22:1. the must be a limit of the fuel....like octane rating of petrol.

- Will the additional fuel at lower revs be a problem as the engine is off boost so not under high load??

yes, fit a compensator.

leehamescort wrote:Thanks for the help, How do i go about installing a Pyro? Is there somewhere on the manifold that i can scew one into on a the standard manifold or do i need to get something made up.

Seems to be a bit of argument on putting it before or after turbo, seems like there is no real difference other than making sure you account for temp according to location of sensor.

I already have a boost gauge and it runs at about 9psi, i have done nothing to up boost.

Correct me if i'm wrong but as i understand:
So the killer is really the exhaust temps, I can run whatever boost i can get away with before the exhaust temps get too high. The only real way to reduce exhaust temp is to have the exhaust side flow better so the gasses are not building up heat
- high flow turbo/different turbo/s
- improve manifold design for better flow
- bigger exhaust (but only will have effect if turbo is better)
Intercooler to reduce temps pre combustion thus reducing temps(hence put an intercooler on and up the boost) I have an intercooler but have not upped the boot yet.
- so the more effective the intercooler the greater possible gains in boost. (turbo being a limiting factor still)

The bottom end is also a restricting factor but i'm more likely to kill the motor with high exhaust temps before i reach the bottom ends limits.

Once i have the Pyro, i can then start adjusting boost up. as I adjust boost up I can add fuel in small increments to gain further power but if I ad too much fuel exhaust temps will increase.

If i adjust the boost without additional fuel I will be only getting partial gains from the boost until additional fuel is adjusted, but no potential damage.
- except if i up the boost beyond the turbos working range i will get higher exhaust temps.
- opposite to a petrol car if i have higher boost it is safer to have less fuel, if i over fuel it it will get hot.

Tuning (in small increments of boost and fuel)
- Raise the boost only, checking exhaust temp change.
- if minimal additional heat add more fuel until exhaust temp begins to raise then back fuel off slightly.
- Will the additional fuel at lower revs be a problem as the engine is off boost so not under high load??
- Repeat the above preocess until raising boost results in raised exhaust temp as efficency of turbo system has been exceeded.


Sorry for the long post and all the questions, I could take it and get it tuned by a turbo place but i like to know how things work and always prefer to do something myself.

Please correct me where i am wrong, this is my interpretation of what i have read.

Thanks for any help

Regards
Leeham

PS.
HG - what was that.....a river crossing.....better get your CRC out!!

All sounds good but a few points,
1) Boost is to a certain extent fuelling dependent, more fuel equals earlier / more boost/ power, up to when the wategate opens, and sometimes smokey only until boost comes in strongly.
2)at 9 psi, an intercooler is not really needed, and may cause a lag problem due to air flow interuption. If running a water to air top mount or similar, it will work better at low boost.(below 10 psi)
3)Are you certain your 2L/ 3L is up to it? I have had told to me that 7 to 9 psi is max for engine life. I would check on this with a few Toyota experts before going too wild with boost and fuel etc. Reliability with a turbo instalation is pretty important if you are in remote areas...

Good luck and PM / Phone if you need help.

JC

Thanks for posting this up leehamescort. I was pondering posting similar.

I am in the middle of swapping my pos switzer turbo for a garret T03 which I beleive is a touch too big though will definately be a better choice than the switzer that has shit itself three times.

I posted similar in the exhaust tech thread last night, a post I read in there suggested that higher boosting was mechanically fine with some exhaust mods?

I too am under the impression that you don't run any toyota diesel over 10psi, I have always ran mine on 7psi only.

I wouldnt mind boosting my new turbo up further than 10psi but only if I had some peace of mind about it. Being that it is basically a completely new set-up I am in the position to totally change the exhaust size and positioning etc so am keen for replies.

I was already going to buy a boost gauge for myself and my oldman(setting his up at the same time) but I will now look at pyrometers as well.

Personally I am not keen on an intercooler, seems like a lot of trouble to stop an engine going pop when a little commonsense while setting it up should be all that is nescessary without band-aids.

Before I put a V8 in my Surf I ran a 2.4 turbo diesel with a heap of mods done (Leeham knows my car well) and I ran an adjustable boost that maxed out at 15lbs, mine had the electronic fuel pump with a modded computer as well, 3" exhaust, hi-flowed turbo etc.
I put 120,000 kays on it with all these mods and it is in a mates Surf now going strong as, so if it's built & maintained right then the little diesels go well with these mods.
Leeham's Surf has a boost guage, 3" exhaust & intercooler installed now and it goes well, so I guess he needs to install the Pyro and up the fuel pump then the boost to get more go .


I tarp up before hitting the water