Ahhhhhhh what enjoyment I've just got out of reading through this giant topic.

I've just got one thing to say - and this is not to offend anyone just a point that I'd like to make - :

Its very easy to tell which guys on here have spent too much time at uni with their head in a book looking at everything from a scientific, theoretical, complicated technical viewpoint.

Then you have the guys who are QUALIFIED tradesmen with years of "hands on" experience, knowledge and know how, skinned knuckles , chasing intermittent problems under pressure while listening to someone tell them they know a guy who done that in 5 mins whats taking you so long etc etc ##$@ etc................

You could spend an eternity at uni doing degrees in mechanical engineering or whatever but it can NEVER teach you "HANDS ON EXPERIENCE"

So get a spanner in your hands and get a feel for it because sometimes I think you can actually be so smart that you're stupid

This is what I think of turbocharging.

Here in Finland we have mostly blow through systems, not many of suck thru.
The reason why we go blowthrough is that after you have build the system
and got it working well it works much better than suckthru - of course we have
coulder winter here and carby goes freesing if you use suck thru.

Also it is also good to use always intercooler - and thats possiple only with B/T.

It is bossiple to bressure every carburator, and you don

the english isnt too bad, there is a couple of wrong letters but it was understandable anyway

it was a good description of what is required for a blow through setup

Sorry to keep this topic going.

Some people have some of their wires crossed abit. And I am not trying to doubt anyones knowledge but I have read a couple of things that to me in someways are making a blowthrough setup seem to difficult for anyone to even bother seting up.

One is " a need to supply a boost signal to the float bowl on a standard carbie"
first this isn't really needed but it won't hurt. Secondly on a standard carbie if you look straight down the top of the carbie inside you will see to pipes, these are float bowl vents and plain and simply by connecting the carbie to the turbo the float bowl will get a boost signal.

In my own experiences the only things to worry about with the carbie is sealing all the gaskets so boost will not leak out, because when this happens your fuel will be sucked out along with the boost, and this will make the engine lean out and go bang.
Another thing is the float has to be solid plastic, not the copper kind because under high boost it will crush and go bang.
The only other thing is with the carbie is the right jets for the right job, this goes for any carbie.

Another thing Dodgeman you say for blowthrough setup when useing the standard fuel pump it has to be boxed and supplied with a boost signal could you explain your reasoning for this?
Like I have pointed out in other threads of this topic the standard fuel pump doesn't supply enough pressure to over come the effects of boost ie; the fuel will be pushed back down the line.
The only time I would recomend a standard fuel pump for a b/t setup is like what GoTheDatto did and I think this is now on 1200rallycars 1200, this is where a pressure switch is used to trigger a higher pressure pump as the boost pressure rises.


Like I said I am not doubting anyones knowledge, Just don't try and make one kind of setup sound more difficult than it actually is to setup. Cause each has there own pluses and minuses.

One other thing to anyone who thinks a turboed car can't leave the start line on boost. go for a ride with someone who knows how to drive a turboed car and you will see it is possible to stall up the boost.

THANKS EVERYONE!!! Keep the posts going, i'm learning somthing new everytime someone submits one, all different opions, all valueable information.


"THESE DAYS THE ULTIMATE POWER IS.....
KNOWLEDGE!! "

Finn
Your spelling & your english is better than some of the local illiterates that use this forum. You write darn well my friend. Please come back often.

Screwdocspock.
You are right about the fuel pump. If the boost pressure is greater than pump pressure, then it will not pump, but if the air pressure UNDER the diaphragm is the same as the pressure over the fuel, then it equalises, & the spring under the self same diaphragm will add the 3 or 4 psi above the ambient [boost] pressure & the fuel will flow. All we are doing is making the carb & pump see the same air pressure, the same situation that exists in unblown configuration.
Chris

Dodgeman whats with the name calling

I can now see in what you describe is that by supplying a boost signal to the bottom of the diaphragm it will keep the diaphragm at its maximum height in the pumps fuel chamber, by doing this you will garantee the pumps maximum flow and any backwards pressure on the fuel outlet will be cancelled by the supply to the bottom of the diaphragm.

At first I couldn't see this but after much thought it would work.

Also one other question you could probably better explain to me is - I don't see how the spring under the diaphragm would keep the fuel at a slightly higher pressure its job is to keep the diaphragm in a regulated position to regulate fuel flow
eg; on a naturaly aspirated engine when the engine is running at high speeds the carbies fuel bowl is constantly filling , so there will be hardly any resistance pressure ontop of the fuel pump diaphragm, this will make the spring push the diaphragm up height enough as much as it can till it reaches whatever resistance pressure is being placed ontop of the diaphragm, this will make fuel flow enough for these high engine speeds.
But at low engine speeds when the float in the carbies fuel bowl keeps the needle and seat closed longer there is a greater pressure above the fuel pump diaphragm. this pressure pushes the diaphragm and spring down but this pressure willnot totally over come the spring it will just place the diaphragm in a lower position, and this will make the pumps stroke be reduced this inturn reduceing the pumps flow in a situation when hi flow is not needed.
Otherwise the flow would over come the needle and seat.
This is why no return line is required when a mechanical fuel is used.

The only problem I can see is now on a boosted engine you will probably not have enough flow for the increased fuel requirements.

Also one other thing, if you were to seal the pump lever like you previously describe you would have much difficulty in actually haveing a pump that could be operated.
The only way I could see this problem overcome would be to run a pulley driven mechanical pump. but if you go to that much trouble you might aswell go electric.

Dodgeman you have got me thinking!
Cheers Steve.

Yes I have a turbo for sale its a t25g off an SR20DET Red Rocker Cover as far as I know its in fine condition, however I would prefer to put new bearings in it. Fuel injection has a price but it sure pays off in the end, I've seen heaps of results from various performance backgrounds.
Regards Allan

There's no doubt that this has been one of the best posts for ages, and I have to say that there is a lot of stuff that I didn't know or hadn't considered that has floated to the surface.

I'd like to toss a couple of points into the middle
1. The super- or turbo has to be matched to the engine. If too big the engine won't generate enough power to turn them at low revs.
2. The speed v. output of the compressor has to be considered. Positive displacement pumps like roots and vane units work best at lower rpm and performance (i.e air delivery) falls off as the rpm goes higher. On the other hand, centrifugal blowers suffer from slippage at low rpm and really don't hit their straps until higher rpm.

Conclusions (Mine!)
For Dragsters this is why the PD type is preferred.
For road cars, my guess is that Turbos present the cheapest way of getting bang for your buck.

If the above is true then why does Mercedes and Holden use Roots Blowers?
Someone better tell me because I don't know.

good question about mercedes, but i wouldnt put anything past holden

nah, um, i thought it would be good to describe the fuel setup i used for a "blow through carby turbo setup" (gothedattos advice), for starters the standard mech pump is removed and blocked off, then an electric pump is installed near the tank which as i intended to run 10psi or slightly higher i bought a holley black pump which would supply 14psi ($180, dont be ripped off by repco or such that sell these for $330), this pump runs constantly feeding fuel to the engine bay

after the fuel filter there was a t piece with two lines (plus a line to a pressure gauge but not important), the 2 lines met again at a t piece just before they entered the pressure box to go to the carby

the first line was regulated with a fixed pressure regulator, set at 4psi, this to feed petrol when the car was "off-boost"

then the second line had a solenoid in it (opens up when power is fed to it), this solenoid was controlled by a hobbs pressure switch which was conected to the manifold, basically power is fed to one side of the pressure switch and it is set so that as soon as the car hits boost (pressure in the manfold) it switches to allow current to pass, this current goes to the fuel solenoid which opens up and allows the full 14psi pressure to run to the carby

the reason this is required is that the standard carby is only designed for 5psi fuel pressure and anything above that will overcome the needle and seat, and its not until the carby is pressurised that you can increase the fuel pressure to a point where it will be higher than the boost and therefore not "be pushed back down the fuel line"