just a little more info...
difference between a petrol and diesel turbo is its seals, diesel turbos dont have positive seal turbo seals, which means that if u we put it in a suck through system they can leak oil under extreme vacuum, which happens when throttle is closed in a suck through setup, while in blow through extreme vacuum is not build up, so they r ok for blow through, but could give problem in suck through.
barpk

Much respect to ddgonzal you sound like a wise person!
But where the hell were you before! lol!

Thank you for summerising this long subject!

Cheers Steve!

Summary of technical points. One thing to remember is that a method that works well isn't the only good way. Let's see if I understand this (I'm sure you'll correct me if I misunderstood something)

Intercooler
- Not needed. The first three years of the Porsche 911 Turbo didn't have one (75-77), yet this 3.0 liter turbo outperformed 7.5 liter NA cars.
- Intercooler is worth it as it significantly reduces the temperature of the compressed air, which increases the boost possible with a given octane fuel
- Using an aluminum radiator should be better than nothing. Unless someone actually tested this, we are all just guessing. Radiators can flow a lot of water, and air is easier to pump ... so air should flow through w/o significant restriction. Putting this in front of the car should allow some cooling effect, although obviously not as a much as a purpose-designed cooler.
- An alternative is to use water or alcohol injection. Some OEM applications used water injection (ex. 1962 Oldsmobile Jetfire)

Wastegate
- Used for adjustable control over boost pressure. When the set pressure is exceeded, exhaust is routed around the turbine to go out the tailpipe
- Not needed if you carefully size the turbo to the application (ensuring that at maximum rpm, design boost is not exceeded). Older OEM applications used this method.

Blow-off valve (or recirculation valve)
- preventing the turbo from surging, for example during gear shift or whenever throttle is closed
- Porsche uses these, so obviously they work
a Blow-off intake boost to atmosphere. Boost is lost. Simple, inexpensive
b.Blow-off to compressor inlet (recirculate back through turbo inlet). Used to enhance throttle response: Boost is kept in circuit for immediate availability when throttle is opened again

Carb setup
- Injection is better, allowing better control of mixture
- Draw through was used by many OEM setups. It is reliable, and the simplest otpion. The downside is you can't use an intercooler, as the fuel will condense in the cooler.
- Blow through works well. The main reason to use this over a draw-through is so an intercooler can be used.
a Boxing carb. This allows a more or less stock carb to be used, the outsided pressure balancing the inside pressure
b Unboxed carb. This was a popular OEM method. phunkdotaspok says this can handle 10 psi with a good top-gasket seal. In an NA application, a warped top is not a problem, as there is no pressure in the float chamber. This only becomes important in boosted application.
- Need richer jets to keep air charge cool and prevent detonation

Fuel pump
- Stock fuel pump is good for draw-through setup. It's not enough for a blow-through setup, as 2.5 boost would overpower the fuel pressure
- Using a low-pressure (15 psi) electric pump oughta be good for a 10-12.5 psi boost.
- Needle and seat has trouble holding more than 10 psi fuel pressure. Better to use a secondary 15-psi pump to cut in only when needed.
- Best setup is to use a rising-rate regulator with a high-psi pump. Excess fuel is returned to the tank.

Turbos
- T3 is pretty big for an A12. Needs high rpm, head work, etc
- Mid-80s Nissan Pulsar turbo (E15 engine) has integral wastegate
- go_the_datto actually tried Daihatsu diesel 1.0 turbo on A12. Good response in lower rpm ranges. Two make better twin-turbo application for A12

Boost pressure
- 6-7 psi is what a lot of OEM applications use.
- 10 psi should be possible with a stock A12/A14
- 14.7 lbs gives theoretically double the airflow so max. power would be about 2x stock, but this isn't actually the result. The reason is that the stock induction and exhaust system won't flow this much air under pressure. However, the low rpm torque could approach 2x (at about 2250 rpm) if a small turbo is used. So a 130hp turbo engine will have much more performance than a 130hp NA engine
- 1986 Honda 1.5 liter ran boost of 4.0 bar - that's 300 bhp ... per cylinder with special fuel

Toyota 4A 1600cc engines
- Word is that the the 4AF has not much more power than an A15
- 4AGE (double-overheard cam) Impressive power
- 4AGEZ supercharged. Use this motor and its fuel system and computer for a turbo setup. The advantage over the supercharger is that boost can be variably controlled per the wastegate. A supercharger has a fixed design boost.

Harry there is no hard feelings from me mate!
The only thing I find to be offensive is if someone tells me I am wrong and their way is better! especially if they have never experienced their way or even mine!
( None of which you have done or meant!)
But others yes!
I respect people doing different things as then they have stuff to share to make others understand of different possibilities!

There is no problem which can't be over come with any setup! It just takes knowledge, Thinking and finally money!

As for the draw through disadvantage you mentioned ( Re backfire!)
All you need to do is look at the big supercharged engines and copy their burst plate design into your manifold!
I know of an A14 inlet manifold setup like this! ( This one has the plate underneath the manifold ( don't know what this was originally for?) Spring loaded so in the event of a backfire it will blow open! ( Springs are rated to compress around 20 psi of pressure)

As for EFI this is what I am fiddleing with now on my Turbo A15 1000!

Cheers Steve!

not intended as a personal attack phunkdokta. I'm sure I haven't upset you have I? I'm flatter if I did, cause barpk couldn't manage it --just kidding-- All of what you have said in here is right, and you obviously know what you're doing. I just think there's a better way. Don't close your mind to the possibility.

You have described the limitations in detail yourself; amount of boost limited by the amout of fuel pressure you can achieve and control, and also limited by what the carb or box seals and float can withstand.

The real drawback of the draw through carby system is that you can't really intercool it. Most of the unlimited category speedboats run drawthrough carby turbo V8's with intercoolers, but it obviously only takes one backfire to turn them into a bomb. But there are ways around that, up to a point.

true EFI is the ultimate for performance, driveability, fuel economy and reliability. But for most people like you and me, the cost of the ECU and tuning is still prohibitive. I'm still after the maximum performance I get get out of what I can afford to do.

Besides, it's much more fun doing it all yourself. I'm sure you and I are really on the same wavelength on that score. Hell, the more fast little 1200's out there the better! "To each their own" is fine by me, just offering my perspective.

Harry

Much respect for what you say!

No Doubt each setup has its advantages and disadvantages!

You say " No contest"
I say " to each their own! "

I don't understand these limitations you mention of either?

And as for no contest! OK if you are not after maximum performance but if any of use were after this we wouldn't be messing with carbies!
We would go EFI!

the "saturday night special" comment was very tongue in cheek...

ahh I see what you mean now, dissconnect the wastegate actuator ROD so that the wastegate is free to open all the time. Rather than disconnecting the wastegate actuator from the compressor housing!

Fuel pooling is not a problem when the compressor wheel is actually being driven. You may get some wetting of the manifolding after the turbo, but I never saw any evidence of pooling in the compressor housing on my motor.

Back to the actual point of blow through vs draw through...
Personally, I prefer the simpler and cheaper draw through system. And from an engineering perspective, the best solution is the one that does the job effectively with the least complexity and minimal number of additional components. Not only does the draw through system have fewer components and less unnecesary complexity, it also does not suffer from the limitations of the blow through system. Extra capability from a cheaper simpler system - No contest really.

Mate there is no agro here just saying my point of view!

As for this suprise you say of!
I have had to do this as intercooler hoses have burst on me a few times and the noise is very annoying if you have to drive for an hour before you are somewhere to fix it!
Also the car will run like a dog with such a big exhaust no doubt! but if the exhaust has to go through the wastegate first this is causing a bit of back pressure whick would be better than just going straight to a big exhaust!
Also only the carbies secondaries are larger! yes this will cause the car to run rich but only when the secondaries are open! so you just have to take off slower so the car doesn't bog down! then once you are going you won't be bothered as much ( yes I agree it would still run like ####! )
But even changing one jet ( 5 mins ) isn't to much to ask!
Your webber would still have the same dramas!

As for fuel pooling in the turbo! this is one of my points exactly!

One thing I should point out is I never said the car would be the best to drive!
I did say why would you bother doing this!
And you gave your reasons and I acept them!
( Just don't agree with doing it all just so on a Saturday you can have a turbo car!

Not Agro just saying the facts!
Steve

yeah, your system would be quicker to change. the point I was making was that with a draw through system using a downdraught Weber instead of a better sidedraught Weber or SU, and the standard inlet manifold instead of a better fabricated item would give you that option albeit at the expense of a bit of power. It wasn't supposed to be a benefit of draw through over blow through, but I can see how you interpreted it that way. let's not make this thread any more agro than it already is

45 minutes is an outside estimate. I could put up with that. Some of the racetracks I compete at are 2.5 hours drive away and undoing a couple of pipes and moving the carb is a small price to pay to avoid having to tow the car home if you happen to blow the turbo at one of those events.

Quote: how about you try that and see what happens! I think you're in for a surprise...

as for your suggestion of sucking the fuel through the turbo when running in aspirated form, I reckon it would be very sluggish and horrible to drive. You would also have problems with pooling of fuel in the compressor housing which would't be a very good idea when you connect it back up - liquids don't compress very well

Mate I respect your feelings

As for being simple to change back! Maybe
But what makes you think any other setup would be any different? If you have an exhaust pipe adapter there is no difference!
maybe my setup is even quicker to change back! ( but really why would you want to?)
My carbie is in the right place to start with! so it is only the turbo you need to take off!
and put an aircleaner instead of the intercooler pipes!
The carbie is set up to run good at no boost or with boost! Nothing needs to be done here!
And If all you are after is a car that runs no boost in the week! just disonnect the wastegate actuator and this is what you will have! Nothing else is required!

But in the end to each his own!
Think about it and tell me now if 45 mins is better then 5 mins!
You too could just disconnect the actuator but then you still have to suck the fuel through the turbo all the way to the manifold!
Just though I would point this out!

But to each his own!