Pre turbo injection on RX7

[Tintin]

I've been playing around with idea of pre turbo injection for a while now and started reading the big pre turbo thread last night but haven't got anywhere near the end yet , anyway I have a few questions that will help me get underway with planning

Firstly , is this going help me acheive my main goal which is to raise my boost level past the current limits of my turbo ? I have an RX7 ( FD ) with standard twin turbos ( working non sequentialy ) and the boost is currently set at 13psi , this is around the effeciancy limit of these turbos , orgionally I just thought I'd up the boost and use the WI to cool the charge however I'm thinking this will not only cause excessive heat in the charge but also the coolant and the oil which is not what I want this is why I started playing with the idea of pre turbo , I'm not looking at a massive hike in boost but would like to see how far I can saftly push these little turbos

From what I have read here and else where there seems to be some discrpency as to the best location to inject and when , some say as close to the impeller nut as possible , others say further away to help atomisation , some say inject early , others say inject late . Is there any conclusive evidence as to which method works best or is it more a case of personal preference and what works for the individual ?

One of my other main worries about this project is if something fails I want to be able to cut boost fast , my origional idea is to locate a temp switch after the IC and set it to operate the wastegate solenoid if the temp exceeds a set limit , probably about the 60C mark , my ECU also starts to retard ignition at 60C so was hoping the two combined would give me a good saftey net , opinions please

Last question is regarding injector sizing , I was thinking of starting with 2 3mm jets ( one for each turbo ) and seeing how it goes , will the 3mm jets be adequate to start with ? I'm also a little concerned with enlarging the jets to the limit where the pump can't produce adequate pressure for good atomisation especially if I continue to inject before the throttle body aswell


Probably should hae mentioned I'm currently using an aquamist 1s kit injecting about 6in before the throttle body with a 4mm jet injecting at 10psi , this is mainly a saftey feature that I only really use on the drag strip , my intercooler is doing its job at the mo so the WI is more to help cooling the rotors as opposed to cooling the inlet charge

I haven't spoken to my tuner about this yet but intend to do some testing and fine tuning on his dyno once its up and running , getting him to agree to raising the boost may take some persuading as he is a cautious tuner ( very good but cautious ) can't blame him really after all blowing engines due to tuning on the edge wouldn't help maintain his reputation

[Tintin]

I've managed to read a few more pages on the big thread today and come up with some ideas and more questions

Due to the amount of bends and unequal length of my two inlet tracts I have decided it would be better to inject directly onto the impellor blades both turbos have 90degree bends at the turbo inlet so I should be able to mount the jets so they spray right onto the blades , if this isn't a good idea someone please tell me now

As I don't know enough info about the air consumtion of my turbos I am unable to work out 2% to give me a starting point for jet size so I'm going to stick to plan A and start with 3mm jets and so where it takes me and probably going to start injecting around the 10psi region

Alot of you guys seem to be running quite sofiticated systems ( compared to the 1s ) , this got me thinking if my kit is up to the job or would I need some extra components ( high speed valve , acumultor , ect )

Regarding cutting boost if temps get too high I'm having trouble finding a temperature switch to open the wastegate solenoid , any ideas ? am I just looking in the wrong places or do these even exist ? can't really think of another way to achieve what I'm after , my current idea would cover me in two areas , firstly no water being injected for whatever reason thus making the charge too hot and secondly not enough water to keep the compression isothermic ( or there abouts )

[Richard L]

Thereis a thread somewhere discussing the pre-compressor injection. In general, avoid letting water droplets creeping along the turbo inlet flange and meet the tip of the compressor blade.

You can:

1) spray the water well away form the turbo, for example, direct teh water spray toward the air filter (opposite to aur flow) and allow the incoming air to atomise the water further.

2) Spary the water as close to the compressor nut as possible. Every % increase in diameter yields ~3x% the tip speed. Pi*D