max boost b4 Detonation?

[triniVr4]

question...what is teh maximum boost the VR4 (2.5L) can handel before you look to change up your internals?

i'm getting a boost controller and i'm looking at an Emanage as wel lto do some tuning.

any help would be great....

[Kieran]

This seems to differ from car to car.... And is much debated!!!

I would suggest the following as guidelines.

Standard boost........ 0.6-0.7 Bar

'Safe' raised limit.... 0.9Bar (Might get away with 1bar if lucky!

Maximum boost limit on standard internals hasn't been totally established yet. In the UK, at least one member is pushing 1.2Bar, with uprated injectors, intercooler and fuel pressure regulator, etc. I'm not sure if they are running upgraded internals or not.

In my experience on here, with standard fuelling and internals, 1 Bar is about as high as it goes without causing problems.

[zentac]

You wont get detination if you do it correctly and set your fueling up, fit a catch can and only run super unleader. Im running 1.1 bar without a problem.

The standard turbos wont hold any higher boost that 1.1bar. You can get it to peak higher but not consistantly hold it.

[triniVr4]

ok..now 1 bar equates to what in PSI?.....

[Kenneth]

14.7 i think (PSI)

[Quail]

Would a large FMIC allow you to run more boost safely? Ie, would 1bar be safely achievable with a decent quality IC?

[Nick Mann]

I don't think boost is the problem. The internals will take 350ish reliably if the fueling is right for the boost. There are several people on here running that kind of power plus 100 bhp ish of NOS. They are running standard internals.

As Richard said, turbos run out of puff before internals can't take the power. Just make sure the fuelling is right for the extra boost.

[triniVr4]

^^^^ ahh....so we're saying that is possible to go up to 16/17lbs of boost once we have proper fuel delivery. Am i also to understand that you can run 350BHP and still have a 50 to 100shot of NOS on standard internals?....


what about FMIC?.....does that really aid?

[colVR4]

Hmmm, AFAIK power from boost is turbo dependant. Running 1 bar on a smaller turbo is going to give you less volume of air than 1 bar on a larger turbo. The limiting factor with the VR4 is the size of the turbo and therefore the volume of air that it can get to the engine. Is that right?

Therefore, the engine will probably be able to cope with higher boost levels but the vanes in the turbo won't and will start to disentegrate. I think I read somewhere that you can change the vanes in our turbos to get higher boost. Is that correct?

[triniVr4]

what about upgreaded fuel delivery?...what factors ami to take into consdieration?

[Quail]

Fuel Pump
Fuel Lines
Fuel Pressure Regulator? (not sure on this one)
Injectors
Fuel Rail?

[colVR4]

There is a great article by BDA (Dave) in the members area about the problems that our cars have with OVER-fuelling. It seems that the problem is not as clear-cut as not enough fuel/too much fuel as members who have run high boost have also experienced fuel cut.

This is not necessarily due to not enough fuel being delivered, but could be the engine management seeing higher than normal boost and cutting the fuel as a built-in safety measure.

There is so much information and so many threads on this subject and those related to it in the members are that you would be better searching in there to be honest.

[Kenneth]

Hmmm, AFAIK power from boost is turbo dependant. Running 1 bar on a smaller turbo is going to give you less volume of air than 1 bar on a larger turbo. The limiting factor with the VR4 is the size of the turbo and therefore the volume of air that it can get to the engine. Is that right?

Not quite. 1 bar of pressure in a space is the same volume of air so long as the air temperature is the same. It does not matter what size the turbo is that compresses the air.

my understanding of the issue with turbos is that they have an efficiency range, if you start pumping air above the efficiency range, they heat the air up much more.

so, a bigger turbo that can pump that volume efficently will heat the air less and as such, you WILL get some improvement in the actual number of oxygen atoms going into the engine. If 1 bar is still in the efficiency range of the standard turbo, you probably wont get much difference.

A big intercooler should reduce the effect of running smaller turbos a bit harder as the air is still cooled effectively.

Big turbos of course will be able to hold that 1 bar (or more) to a higher RPM.

If you do a search (you might need to be a member) there is at least one thread that discusses this in quite a bit of detail.

[colVR4]

Not quite. 1 bar of pressure in a space is the same volume of air so long as the air temperature is the same. It does not matter what size the turbo is that compresses the air.

Which is my point exactly. According the Boyles Law, pressure is inversely proportional to volume, i.e. as volume decreases pressure increases. So a mass of air in a smaller turbo (read smaller turbo chamber) at 1 bar will have less density (less air molecules) than a larger turbo (larger chamber) at the same pressure (assuming temperatures of the corresponding air masses are identical).

Compressing air makes it hotter, and less dense. Now as the whole point of compressing the air is to get more of it in the cylinders, this is bad. For this reason almost all turbo cars cool the air down after the turbo by means of an intercooler. Interestingly a common misconception is that the turbo heats up the air because it is physically connected to the hot exhaust. In fact the vast majority of the heat comes from compression.

It's often said that the boost pressure alone determines the power increase. Not true. It is the AMOUNT of air that you can get in the cylinders that determines the power the engine will produce. All the energy to drive the car is locked up in the fuel. A certain amount of fuel needs a certain amount of air to burn - if you can fit more air in, you can burn more fuel.

The pressure of the air is linked to it's temperature, amount and volume:

pressure x volume = amount x temperature (well with a constant stuck in there as well but you get the idea). Since the volume of your engine isn't going to be changing, it's easy to see that the amount of air you can fit in is proportional to the pressure (bigger pressure = more air) and inversely proportional to the temperature (lower temperature = more air).

erm....does that make it any clearer 'cause my heads hurting now!!

[colVR4]

Found this article that may clear it up:

Turbo performance and efficiency

You hear many numbers thrown around describing turbos, but perhaps the most misleading are the hp numbers. "This is a 500hp turbo" doesn't really mean anything. You can guess from it that it's a pretty big beast, but there's no way you can guarantee 500hp from it. You will also hear turbos described by the size of impeller wheels, exhaust turbine wheels, A/R ratios etc.

A hefty flow of (relatively) cold, dense air is the aim with a turbo. Generally the bigger the turbo the easier this is. This is because the larger turbo is a more efficient compressor of air at the sort of values we are looking at (say approx 7 - 30 psi, which is approx 0.5 to 2 bar). The shaft of a turbo spins very fast (typically > 100,000 rpm at stock max boost on a CT20b), and the bigger turbo's shaft can spin slower to flow the same amount of air.

It's a widely believed myth about turbo sizing that (say) 15 psi on one turbo is 'equal' to 15 psi on another. This isn't true. A large turbo will be able to flow a lot more air than a smaller one at any given pressure. And it's amount of air that counts.

[Kenneth]

...
It's a widely believed myth about turbo sizing that (say) 15 psi on one turbo is 'equal' to 15 psi on another. This isn't true. A large turbo will be able to flow a lot more air than a smaller one at any given pressure. And it's amount of air that counts.

thats true.

but if there are no other mods, your engine cant consume that air, so because of the wastegate, your turbo just does not produce that extra air it is capable of.

I think we are talking about the same thing, just in different terms. there are many many variables to take into consideration with turbos, my post was aimed at what the net effect would be with NO other changes. that means air temp, intake restrictions etc.

I thought I had been specific about the temperature issue in my post, but I should have been more specific about there being no other mods (which in real life would most likely not be the case) to improve how much air was being consumed by the engine.

However, if you take away any variable air consumption and any vairable temperature, 15psi is the same volume no mater what sized pump you use. (assuming the same continer volume )

[triniVr4]

this is some great stuff guys....my first step is to get an Emanage and Boost Controller instaleld. and then take it from there...

[Nick Mann]

Flow rate only becomes an issue when the engine is capable of using more than the turbos can flow. Until that point 1 bar is 1 bar. The temperature variable may come in to play if the turbos are spinning at massively different speeds to create that 1 bar, but then turbo lag would probably out weigh any temperature difference anyway.

Flow rate is an issue in the VR4 because the fuelling is relatively easy to upgrade to the point where our turbos cannot flow enough air to increase power. This happens before injectors need to be upgraded and before internals need to be stronger.

[zentac]

Which is my point exactly. According the Boyles Law, pressure is inversely proportional to volume, i.e. as volume decreases pressure increases. So a mass of air in a smaller turbo (read smaller turbo chamber) at 1 bar will have less density (less air molecules) than a larger turbo (larger chamber) at the same pressure (assuming temperatures of the corresponding air masses are identical).

But you dont read the pressure from the turbo`s you read it from the plenum so 1bar is 1bar no matter which turbo you use.... The only difference may be the temperature of the air.

[colVR4]

Point taken...I'll shut up now