Blow Through Carby Set Ups...Disadvantages?

[andrew_mx83]

yeah very similar mate, was a 32/36 weber with a sealed alloy box on top where the air cleaner would normally sit, with about a 2" inlet for a turbo/cooler pipe on the front

not sure what else was done to the carby, the bloke bought it out of a running car and put it in his shell

was just a shitty g161 anyway.... poo!

[andrew_mx83]

was just a shitty gemini anyway.... poo!

fixed for me

[StuC]

so would i be right in saying that for a 1600 a 32/36 weber would be the go? Im looking at getting a little suzuki vitara for thrashing around and it will need just a little more poke than the stock SOHC 1600 canput out.

[andrew_mx83]

i am (slowly) in the process of putting a 34/34 on a mates 1600 golf, i reckon it will be shit hot

the carby coming off it looks to be under an inch lol

[astro boy]

32/36 is a good carby for anything from 1300 to 2300cc, providing it's jetted right.

[AdrianS]

Maserati ran a "weber in a box" blow through setup on their '80s biturbo : 2l / 2.5l / 2.8l twin-turbo v6.
It makes some things much easier - no need to worry about boost leaks through throttle shafts, rising rate fuel pressure, etc.
Some things harder - you have to take the box off to get to the carby to set the idle and so on.

I work with a bloke who used to tune them - said it worked pretty well, if jetted right.

I could probably dig up more details if you're interested.

[andrew_mx83]

like this?

[Duk]

It makes some things much easier - no need to worry about boost leaks through throttle shafts, rising rate fuel pressure, etc.

They would still need a rising rate fuel pressure regulator. Most carbies only use 3-5 psi of pump pressure, without a RRFPR, the pressure in the float chamber wouldn't allow fuel past the needle valve once on boost.

[AdrianS]

They would still need a rising rate fuel pressure regulator. Most carbies only use 3-5 psi of pump pressure, without a RRFPR, the pressure in the float chamber wouldn't allow fuel past the needle valve once on boost.

True, but since the pressure in the float chamber matches the pressure in the carby (pre venturi), there's less issues with mixture change on boost.

Otherise you have to pressurise the float chamber somehow.

[NME308]

[They would still need a rising rate fuel pressure regulator. Most carbies only use 3-5 psi of pump pressure, without a RRFPR, the pressure in the float chamber wouldn't allow fuel past the needle valve once on boost. Finally someone making sense!

True, but since the pressure in the float chamber matches the pressure in the carby (pre venturi), there's less issues with mixture change on boost.

Otherise you have to pressurise the float chamber somehow. And now for someone else to throw more mud in the water...

Hi there Duk, I wouldn't bother wasting any more of your time trying to correct people...
Whenever the topic of boosted engines and carburettors comes up the thread always gets filled with nonsense from peeps who have never done blow through and obviously do not understand the concept...

Anyhow Duk is there a blowthrough guide for webbers similar to the holley guide I have linked to above??? People obviously cannot relate the holley operation to a webber! That or they damn can't read or are too proud to bother...

Cheers,
Jason

[Duk]

Whenever the topic of boosted engines and carburettors comes up the thread always gets filled with nonsense from peeps who have never done blow through and obviously do not understand the concept...

I've never done 1 either tho

Anyhow Duk is there a blowthrough guide for webbers similar to the holley guide I have linked to above??? People obviously cannot relate the holley operation to a webber! That or they damn can't read or are too proud to bother...

I think people come unstuck because they don't really know how carbies work. Until I read Hugh McInnes TURBOCHARGING, and a couple of books about Weber carbies, I didn't really know either.
Where most people get confused is thinking that engines suck air into themselves during the induction stroke. It doesn't, atmospheric pressure fill the gap left by the descending piston.
And a turbo/superchargers pump air into the engine. They don't (well they do, but not in the context that most people think of), they just add extra 'head pressure' to help get the job of filling the cylinder done.
That, and people always seem to think that the engine sucks fuel out of the carby.

What I think would help people out a lot when understanding engines and carbies, is to throw out the idea of 'vacuum' and understand pressure differential. Higher pressure fluid flows to lower pressure fluid.
*Gasses and liquids are both fluids.

[Hurricane]

Anyhow Duk is there a blowthrough guide for webbers similar to the holley guide I have linked to above??? People obviously cannot relate the holley operation to a webber! That or they damn can't read or are too proud to bother...

Cheers,
Jason

i dont know were there is a guide. but when i ran blow through webers i had a box bolted to the front of the carbys were the fillers would go, allowing boost pressure into the fuel bowl breathers also (the 1 or 2 holes on the front face of the webers thats would normally breather through the filters).
run the solid plactic floats and run fuel pressure higher than boost pressure using a rising rate regulator.
and thats it.
make sure all the shaft seals and carby gaskets are in good condition also.

dan

[AdrianS]

No need to get shirty. I acknowledged that a RRFP is needed, and mentioned that the float chambers need to see boost pressure, as hurricane also pointed out. I have a very good idea of how carbies work. Save the insults for another forum.

[NME308]

No need to get shirty. I acknowledged that a RRFP is needed, and mentioned that the float chambers need to see boost pressure, as hurricane also pointed out. I have a very good idea of how carbies work. Save the insults for another forum.

No insults here mate.
This is the technical forum and the OP had a serious question. Since the OP was asking a question to build his knowledge how is this supposed to work when well meaning but uneducated people keep posting up half truths and mis information?

Technical threads need to be accurate or they are useless!

Cheers,
Jason

[Bigblue2]

If the dude who started this thread has done his build considering its been nearly three years i'd be curious how he went na dsome pics! please