Just wondering if you can supercharge something like my weber 45 carbs? can you build a chamber for the trumpets then feed that chamber from the supercharger?

If you did this what would happen to the fuelling, is it just a case of getting different jets and the carbs setup, or is all this impossoble.

I'm just curious, especially as mini chargers are cheap

Cheers

Steve

I believe you can supercharge with carbs or injection. Don't know off hand how it all goes together, but I do know that generally you have to lower you compression ratio.

David

you need to lower the compression ratio if you boost very much (just how much is too much, I don't know).

then you need to enclose the entire carb(s) in a box that is pressurized by the supercharger. Carbs work off pressure differentials (venturi effect) and just blowing through them won't work.

the air rushing past the needle valve is at a lower pressure than atmospheric, causing fuel to be drawn into the air stream (think of blowing across the top of a soft drink bottle). with a blower, the air flow would be at a greater pressure than atmospheric (else, why bother?) resulting in no fuel draw, unless the carb is enclosed in a pressurized box. then the air flow causes the pressure in the venturi to be lower than the pressure in the box.

or, you could draw through the carb - through the carb, then through the supercharger, and into the head.

not simple, but possible.

dave

[Edited on 19/8/05 by dmottaway]

More strictly it is the float chamber of the carb that needs to be presurised. The DCOE type carb has a sealed float chamber with a vent that can be connected to the manifold to achieve this.

Nick

I believe normal practice was to have carb then supergharger then engine, as the supercharger actually helped atomise the mixture. For turbos you pressurised the carbs as the turbo would centrifuge out the fuel droplets.....
That was the old days - your supercharger might not like compressing a mixture (lube probs?).
Bob

The old days still apply, most carb+supercharger combos draw through the carb.

A mate runs a supercharged rover V8 grasser, with a holley carb before an Ex-Jag eaton supercharger.

Here 'tis in action:

and boy is that a monster of a car .........

great to look at and to listen too (from someone who isn't a fan of supercharger whine!)

Phil Irvin has written loads on this subject in his book about tuning classic motorcycles. An excellent read in it's own right it talks mainly about old single cylinder engines but the principals are all there from balancing rotating assemblies to calculations for drag coefficients.

The part concerned with supercharging carbs has the carb-supercharger-inlet-cylinder head set up.

One distinct disadvantage with this is when the throttle is pressed the demand for air increases greatly drawing on the reservoir between the supercharger and the inlet valve, as the rpm has not had a chance to rise significantly and hence produce more pressure to overcome the demand the pressure in the inlet tract reduces significantly. The way round it is to have a large inlet tract that can hold a large volume of air (limited by the size and capability of the supercharger) just the same as a large air receiver on a compressor works. Of course this air is a fuel/air mixture at the ideal 15-1 ratio for burning so the first spit back through the inlet valve and you are driving a bomb. It is not all doom as it is possible to install a blow off valve set to the max pressure the supercharger can produce and which will open in the event of ignition, this is what the supercharged drag bikes used.

As I say the book is an excellent read and unlocks many of the secrets of engine fundamentals and performance enhancements.

Nick

Use the carbs as throttle bodies only, drill and taps holes in your inlet manifold and fit some injectors, then use and after market FI.

However if you charging or turbo'ing, individual throttle bodies won't make too much of a difference. If you don't want to go FI , it should be ok to use the carbs for fuelling, not optimal but should be fine.

quote:

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Originally posted by MikeR
and boy is that a monster of a car .........

great to look at and to listen too (from someone who isn't a fan of supercharger whine!)

---

ok, you take his out in the all comers race and i'll take yours out !



might have a chance of keeping one car behind me if i do that as you'll be too scared of damaging either car to overtake me

me...........scared................nah!

Surely I never fret and worry about crashing

so if you're not fretting about crashing why do you need the toilet about 5 times before a big race?

Aaaah, weight reduction, the true competitive racer!

can't beat a bit of nervous p155 syndrome!

The MG Metro Turbo used a blow through arrangement I recall.

There was a pipe hooking up the float chamber to the carb to pressurize it to increase fuel flow accordingly. (A 1 3/4" SU)

Janspeed did a version with a bow through Dellorto too.

Cheers,

Neil.

Cool,

So I can use the carbs although possibly not the best way to do it.

Am I missing something or basically what you do is,

Buy a supercharger from ebay for £100
Mount it to the car and belt drive it off the crank
Fabricate a chamber for the carbs
Run a pipe from the charger to your fabricated chamber
Run a pipe from the other side of the charger to an air filter.
Possibly fit a decompression plate


Can somebody with a bit more knowledge fill in the blanks and edit this to give a rough step by step guide.

This all seems to easy and cheap, what are the hurdles to overcome?

What power do you think you could get without being greedy, 210 would be great from a standard zetec and cheaper than by cams and a fancy head. Also if it blows up you dont have to worry about damaging your fancy head and cams.

Cheers

Steve

[Edited on 20/8/05 by Monkeybasher]

quote:

---

Originally posted by Monkeybasher
Cool,

So I can use the carbs although possibly not the best way to do it.

Am I missing something or basically what you do is,

Buy a supercharger from ebay for £100
Mount it to the car and belt drive it off the crank
Fabricate a chamber for the carbs
Run a pipe from the charger to your fabricated chamber
Run a pipe from the other side of the charger to an air filter.
Possibly fit a decompression plate


Can somebody with a bit more knowledge fill in the blanks and edit this to give a rough step by step guide.

This all seems to easy and cheap, what are the hurdles to overcome?

What power do you think you could get without being greedy, 210 would be great from a standard zetec and cheaper than by cams and a fancy head. Also if it blows up you dont have to worry about damaging your fancy head and cams.

Cheers

Steve

[Edited on 20/8/05 by Monkeybasher]

---

quote:

---

Originally posted by Noodle
The MG Metro Turbo used a blow through arrangement I recall.

There was a pipe hooking up the float chamber to the carb to pressurize it to increase fuel flow accordingly. (A 1 3/4" SU)

Janspeed did a version with a bow through Dellorto too.

Cheers,

Neil.

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hi i just read this thread as im looking at supercharging my pinto engine, im running a 2.1 litre which has a few mods, fr32 cam kit, and a vulcan racing max flow head, its a 205 cossie block with a shortened sump and pick up pipe, i think it will run at about 160bhp as it has twin weber 40 DCOE's at the wheels.(hopefully) but i want a bit more power! more like 180-200 bhp, which supercharger would you recommend? i was thinking that the m90 from an old merc would do the job or is this too much? i need a supercharger that is small as possible whith a maximum output as i may be a little restricted on space

cheers Alex

You don't always need a particularly low compression ratio. If your engine has a 9.5:1 compression ratio (fairly ordinary) and you boost it by 25% or 0.25 Bar then the effective compression ratio becomes 11.9 - good but not out of the ordinary. This way it can use higher octane fuel as well.

If you want to run 1.0 bar of boost though, the pressures in the cylinder head can start to get a bit large.

vintage "blower" bentleys blew supercharged air through the carbs. It was the charged air through the carbs that made the wailing noise

quote:

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Originally posted by omega0684
hi i just read this thread as im looking at supercharging my pinto engine, im running a 2.1 litre which has a few mods, fr32 cam kit, and a vulcan racing max flow head, its a 205 cossie block with a shortened sump and pick up pipe, i think it will run at about 160bhp as it has twin weber 40 DCOE's at the wheels.(hopefully) but i want a bit more power! more like 180-200 bhp, which supercharger would you recommend? i was thinking that the m90 from an old merc would do the job or is this too much? i need a supercharger that is small as possible whith a maximum output as i may be a little restricted on space

cheers Alex

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Most old style supercharger suck through the carbs rather than blow -- a few excptions pre-WW2 Mercedes, Lotus, MG Montego Turbo. BL managed to get 168ps out the the Montego Turbo just from a single big SU carb so it can't be all bad - but in general blow through is trickier to make work.

If doing it I would either ditch the carbs and go Meg squirt or use a single big SU and inter cooler from a Montego Turbo.

[Edited on 16/1/06 by britishtrident]