Monkeybasher
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 posted on 18/8/05 at 10:50 PM |
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Can you supercharge carbs
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
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DavidM
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| posted on 18/8/05 at 11:51 PM |
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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
Proportion is Everything
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dmottaway
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| posted on 19/8/05 at 12:24 AM |
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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]
Somewhere, in Texas, a village is missing its idiot.
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Doh!Nut
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| posted on 19/8/05 at 06:45 AM |
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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
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Bob C
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| posted on 19/8/05 at 07:28 AM |
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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
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NS Dev
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| posted on 19/8/05 at 07:51 AM |
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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:
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MikeR
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| posted on 19/8/05 at 07:59 AM |
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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!)
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Nick Davison
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| posted on 19/8/05 at 08:34 AM |
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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
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darren(SA)
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| posted on 19/8/05 at 08:44 AM |
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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.
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NS Dev
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| posted on 19/8/05 at 10:24 AM |
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quote:
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!)
It is lovely isn't it!! I think I need to talk Rik into letting me take it out in a race!!!
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MikeR
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| posted on 19/8/05 at 11:11 AM |
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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
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NS Dev
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| posted on 19/8/05 at 11:13 AM |
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me...........scared................nah!
Surely I never fret and worry about crashing
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MikeR
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| posted on 19/8/05 at 11:15 AM |
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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!
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NS Dev
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| posted on 19/8/05 at 11:18 AM |
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can't beat a bit of nervous p155 syndrome!
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Noodle
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| posted on 19/8/05 at 11:36 AM |
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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.
Your sort make me sick
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Monkeybasher
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| posted on 20/8/05 at 01:41 AM |
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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]
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Monkeybasher
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| posted on 21/8/05 at 11:37 PM |
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NS Dev
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| posted on 22/8/05 at 07:21 AM |
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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]
Sort of but not quite.
You want to run a "suck through" setup on the carb(s) to keep it simple, so you fabricate a way of mounting the charger, preferably in a
way that makes it easy to then mount the carb fairly directly to the intake side of the charger. Then pipe the charger outlet to the engine inlet
manifold. This is the easiest way to to it.
A single carb, either 38DGAS (up to 150hp) or single 48 IDF weber (up to 200hp ish) would be the easiest method of carburation.
The mini superchargers on ebay are small, that needs to be borne in mind. I looked at using one on my XE 16v vauxhall, but they just won't shift
enough air (it makes 200hp naturally aspirated, the charger will only supply enough air at it's max rpm for approx 220hp, and then it's
way over on the efficiency curve and heating up the air a lot, which you don't want) you are better looking out for an ex-merc one (they turn up
fairly often) which is a bit bigger (M90 instead of M45 blower)
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NS Dev
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| posted on 22/8/05 at 07:27 AM |
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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.
The metro did indeed use such a setup, but the carb is slightly different. The whole setup was hardly a paragon of engineering excellence!!
The dellorto setups used carbs originally designed by dellorto for the Esprit Turbo, which had this setup from the factory. Again, the carbs are not
std ones, they have pressure ports fed by the inlet manifold pressure to keep them in pressure balance.
Best to steer clear of blow through on an amateur basis if using carbs. Use Injection if you want that type of setup.
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omega0684
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| posted on 16/1/06 at 11:49 AM |
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supercharging carb'd pinto
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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smart51
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| posted on 16/1/06 at 12:48 PM |
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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.
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smart51
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| posted on 16/1/06 at 12:49 PM |
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vintage "blower" bentleys blew supercharged air through the carbs. It was the charged air through the carbs that made the wailing noise
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NS Dev
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| posted on 16/1/06 at 04:04 PM |
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quote:
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
For a pinto you won't go far wrong with the cheap Mini M45 blower, that will supply plenty of air for 180hp and will push enough for 200 but
that's about the limit when I did the maths on it a while back. We were looking at using one on a cavalier 2.0 8 valve engine in a manta, I can
see if I can find the spreadhseet with the calcs on it for the pulley sizes etc, took me a little while to do it and I calced it all through properly
but I think it may have been lost.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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britishtrident
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| posted on 16/1/06 at 04:22 PM |
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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]
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