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Old 07-10-2016, 05:09 PM
sambeeb sambeeb is offline
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Default sizing a pre comp boost pressurised system

Hi,

I need some advice on a boost pressurised pre comp injection system. The engine is a VAG 1.8T BJX with a borg warner K03s turbo. This turbo pushes 12 psi peak in standard form and in its stage 2 flash tune guise pushes 20+psi (1.45 bar). The exhaust manifold has been ported and port matched and the wastegate pretty radically ported too. This along with the 3in dump should have reduced back pressure substantially, so would it be fair to assume it is not hot side limited but rather compressor limited and a good candidate for pre comp injection?

The aim is to increase the turbos upper range/efficiency whilst still running a generic flash tune where fuelling can't be altered and only global timing can be adjusted.

So here's what my train of thought has been so far:

1. I want to do a purely mechanical boost pressurised system using a spraying systems atomising nozzle. From what I can gather this will give excellent atomisation which will allow me to inject well upstream of the compressor which is all I have access for, and will also give variable flow

2. Based on the standard 2.5in MAF peak readings of 185g/s, if I inject at the recommended 2-3% of air, calculated on 2.5% of max MAF flow = 4.625g/s = 277g/min = 3.66 gal/h.

3. There are 3 spraying systems nozzles that fit the bill with working air/water pressures from 5psi up to 20psi. The SUE15B and SUE18B both give between 1.4-2.0 gal/h between 10-20psi. The SUE18A though is between 2.2 and 3.0gal/h between those boost levels. Given that I will likely inject only above 1 bar (my spool is already pretty aggressive and ZI don't really need to enhance that) which nozzle would be more appropriate?

4. I was going to run WM 50/50. I would have preferred water only from a reliability point of view but considering that I can't 'tune' for the injection other than adjusting global timing advance, then incorporating meth seems to be the way to go. Is 50/50 sounding about right for this kind of brief or is more meth needed considering that I won't be able to add much timing?

5. I have read that in these systems when under boost, the air orifice in the atomising jets can be large enough that they can actually represent a boost leak. I can't really see how that is the case - it may be one until vessel filling is complete and then stop being one surely. Either way i'll be running small diameter hose and may even use a solenoid/valve in the air line to be activated when the injectant solenoid is activated to prevent this. likely to be an issue or not?

6. One thing I'm unsure of is the best way to design the reservoir. I was actually going to use one of the VW/audi ball shaped coolant tanks since the design is baffled, will handle the pressures, see through, has all the tappings to use and will not be out of place in the engine bay. The only issue I could think of was that perhaps volume of the chamber may not be right. Is there any rule of thumb for determining what air:injectant volume ratio works best in a boost pressurised tank?

7. lastly from what I can gather I will likely not see an increase in MAF g/s even though the engine may be making more power ie the engine will draw in the same amount of air its just that (if successful) it will be using it more efficiently. I just wanted to verify this so that I can change the way I measure progress as to date I've always looked to MAF readings/curves as a way to gauge power increase - crude I know but free!

again, the aim is to run a system that will give me more mid range to top end on my maxxed out turbo that will have the best chance of working with a fixed fuelling tune. any help greatly appreciated.

thanks
sam
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Old 07-10-2016, 09:30 PM
rotrex rotrex is offline
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Default Re: sizing a pre comp boost pressurised system

in order to take full advantage of water methanol injection, you need a fully mappable ECU. with the litte you can add without, you won't gain much.
Then as a second measure, I would propose a T04 size turbo.
These two will get you to 260 to 300HP without any water methanol on your VAG engine.

Regarding the air assisted systems I suggest you read riceracing's thread in the sticky section.

the reservoir is pressurized through a check valve, so no back flow into the plenum.
The fluid flow is controlled by a solenoid close to the nozzle.
This way the system stays pressurized and ensures minimum delay for spray onset.
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Old 08-10-2016, 09:48 AM
sambeeb sambeeb is offline
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Default Re: sizing a pre comp boost pressurised system

regarding the set up of the system that is exactly what I was envisaging. I was debating swapping out the air check valve for a solenoid but you've rightly pointed out that when that is off, that pressure can't ever build beyond what the pressure in the reservoir was at the time that it triggered. Check valve it will be.

I know that to take FULL advantage of pre comp injection that a programmable ECU is needed and also that a bigger turbo is the way to go, but funds simply will not allow that. My turbo is grossly undersized. For instance I believe that a version of it is the turbo used on fords little 1.0L ecoboost triple. Its a little weapon on really tight hairpin riddled hillclimbs - I nearly got the class win against some pretty mental road registered V8's but is nowhere at places like the Bathurst hillclimbs and its that that I was hoping to help a tad.
I'm surprised that given how hard my turbo is being pushed that you don't think there is some potential there. I can see that I am kind of snookered - I won't be able to add much timing which would make the addition of methanol rather than 100% water seem necessary BUT in using methanol I'm adding another fuel to a system that I can't lean out.
Thinking about it, with my car I can feel that when I add timing that the spool rate drops off presumable due to lower EGT's but the top end picks up despite timing pull starting to appear. That's making me wonder if spraying early instead of only at the top end will work eg I could get my spool back (not too much hopefully because the car is traction limited) but help out the top end. Considering that I can't add much timing and fuelling is fixed I even wonder if going from 98 ron to 95ron could help considering that methanol will be in the mix. But like you say whether or not I'd see a net gain from all this is debatable.
I'll go through Rice Racings' thread. I'm actually in Sydney so who knows I may have to try to track him down. the input is always welcome
sam
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