Back

 Supercharging A Carby - whats involved  

Post Topic
EUniqe
  • EUniqe
  • trip'n since '11
  • Member No.: 86,090
  • Joined: 3-November 07
  • Posts: 2,433
  • From: South Australia. Heaps Good.
Post #1 post 1st July 2009 - 03:56 AM
hey everyone,

in the near future i am (possibly) buying a car that contains a 2.0l na four with dual carbies. i had an idea that i could buy a supercharger and whack it on, as it would be a project car.

ive read up on some supercharger brands, and ive seen some models for engines smaller and bigger than 2.0l, and i would choose one thats appropriate.

now as far as i've understood, with an engine with carburettors, all thats involved with attaching a supercharger is bolting it on, setting the belts up properly, attaching a pipe from the outlet of the supercharger up to the carbies - i would take out the filter and attach a hose to the beggining of the airbox - attaching a filter on the inlet of the supercharger, and away you go.

i know that with an injected engine, there is more to it i.e changing ecu maps etc but since it has carburettors, i thought that all that was involved was hooking everything up and thats it.

my question is, what is exactly involved? depending on how easy the installation is, i would be installing it myself, with custom brackets and belts made up of course.

i would like to know whats involved in installing it really

cheers

--------------------
TOP
pipster11
Post #2

def not a bolt up job by any means

to add boost (turbo or s/c) to a carby you need to do a bit of work to the carby otherwise the float inside will colapse and other bad shit will happen

this is presuming you go for a blow though (the carby) set-up like you described

another option is to go for the suck though set up
this involves having the carby before the s/c and the supercharger drwaing the air through the carby
this means the carby only sees a lot of air going through it rather than lots of pressure
only down side is that anything after the carby will have fuel in it = no intercooler or long pipeing as a backfire will blow the pipes up and half the motor = bad

my personal suggestion is to go with a suck through turbo setup
t25g (s13 stock turbo) can be had for $100 and will be a good match for low boost (plus the cost of a turbo manifold and dump pipe of course)

lil_bobby_260
Post #3

I would go a draw through setup where the supercharger pulls the air through the carbie. Being an older motor it will be fairly low compression anyway, which means you could run a lazy 6-7psi of boost without having an intercooler or anything. I would ditch the twin carbies and run a single downdraught weber (same as you can find on 4.1L falcon sixes from about 1984 onwards), or a 350 holley. Will be easier to tune and rup piping for than a set of twin carbs.
Make sure the carby is getting as cold an air feed as possible and keep your inlet piping as short as possible to increase response.
Make sure you do the math with the pulley ratios and start with a larger pulley on the supercharger, so you can start of with lower boost and work your way up, as opposed to running a small pulley on the SC and pumping too much boost.

EUniqe
Post #4

ok, thanks for the replies, has made muh sense to me. although, "otherwise the float inside will colapse" how do you mean by this? and wouldnt suck-through be compressing fuel inside the supercharger as well? id imagine that would be bad for it. i have thought about going to single carburettors, but hasnt seemed to be an option i would like to choose. if i decided to stick with the blow-through set up, would stronger/strengthened carburettors be necessary?

i have also thougth about turbocharging, but i dont want custom manifolds etc made up for it, in other words, supercharging seemed alot easier.

pipster11
Post #5

there is some float thing inside the carby
add boost to that and it will colapse (unless you replace it with a foam filled one or something like that)
suck through the carby just sees a shit load of air going through it instead (i think)

zorak
Post #6

best go talk to a carb specialist who has had FI experience. Getting a boost referrenced carb is from what I gather a bit of an art. Ill ask a mate who had one built for his XF ute who he went through, that thing with boost went like the proverbial.

lil_bobby_260
Post #7

A carburettor is designed to have air sucked through it, which draws the fuel in etc. It is designed to run at NEGATIVE pressure, ie a vacuum. If you have a supercharger PUSHING air through it, then you are now running at positive pressure, which completely alters how a carburettor is meant to work. You can have your carbie/s modified to work, but it is simpler to run a draw through setup.
No it isnt bad for it to have fuel/air mix going through the supercharger. Buy the time it hits the supercharger, the fuel is atomised, ie a vapour not a liquid.
Have a look at any old v8 with a supercharger - where are the carbies? sitting right there on top as a draw through setup.
As said, id recommend a single carbie conversion, draw through setup. Piss easy to do, and good results.

EUniqe
Post #8

mmmmm the vaporisation stuff makes much sense now. ok i understand all lol thanks heaps

pipster11
Post #9

yer
but just think of it this way
the longer the pipeing
they more chance you have of the vapor settling and pooling which is bad
cos if you get a backfire you get a boom

zorak
Post #10

QUOTE (pipster11 @ Jul 3 2009, 09:48 AM) *
yer
but just think of it this way
the longer the pipeing
they more chance you have of the vapor settling and pooling which is bad
cos if you get a backfire you get a boom


what piping are you reffering to? PD S/C blows to the carby, a roots styles sucks through, either way the carby is going to be right on the manifold and once in the runners wont have a chance to sit still. also at the rate of airflow pooling is hardly going to be an issue with vapourised air/fuel unless you got a large dia pipe about 20m long.

EUniqe
Post #11

ah yes. i can understans why that would be bad lol

lil_bobby_260
Post #12

What piping...? Realistically there wont be any more piping than standard... the supercharger will sit directly between the inlet manifold and the carby, you would just have adapter plates....
and i guarantee that the temperature of the inlet tract, being that it is full of compressed and therefore WARM air, which will be moving at a decent flow rate through the setup, will prevent any "pooling".

pipster11
Post #13

QUOTE (lil_bobby_260 @ Jul 3 2009, 03:46 PM) *
What piping...? Realistically there wont be any more piping than standard... the supercharger will sit directly between the inlet manifold and the carby, you would just have adapter plates....
and i guarantee that the temperature of the inlet tract, being that it is full of compressed and therefore WARM air, which will be moving at a decent flow rate through the setup, will prevent any "pooling".


just emphasising my point
the best physical placement may not be the easiest in terms of arranging the drive belts

wrench
Post #14

I've had a fair bit of success using SU carbs on blower setup, used a 1 3/4 inch SU when doing suck through on my Datsun 1200, worked great. Mate built a 2 litre escort with a blower running a 2 inch SU, he had a crossover pipe ( to get it over the other side of the engine ) and it worked great too. Carb choice is vital, I find the SU's great, easy to tune.

lil_bobby_260
Post #15

Im gonna have to take some pics of a friends ute and send it to you...
Its a WB ute with a 202, that its running two sc14 superchargers( yes, one on each side of the engine), each with its own draw through carburettor, using a twin throttle body plenum on a redline race manifold.
The thing is absolutely silly, hey. Looks impressive, and sounds phenomenal, and it is PANDEMONIUM when on the throttle haha... and it is a complete home job.

pipster11
Post #16

QUOTE (zorak @ Jul 3 2009, 09:54 AM) *
what piping are you reffering to? PD S/C blows to the carby, a roots styles sucks through, either way the carby is going to be right on the manifold and once in the runners wont have a chance to sit still. also at the rate of airflow pooling is hardly going to be an issue with vapourised air/fuel unless you got a large dia pipe about 20m long.

i know its an efi 3 litre but

http://wiki.r31skylineclub.com/index.php?title=Supercharging

that has long piping
and its not practical to put the s/c on the intake side cos of the shape of the mani and what sits on that side of the motor

lil_bobby_260
Post #17

QUOTE (pipster11 @ Jul 4 2009, 09:48 AM) *
i know its an efi 3 litre but

http://wiki.r31skylineclub.com/index.php?title=Supercharging

that has long piping
and its not practical to put the s/c on the intake side cos of the shape of the mani and what sits on that side of the motor


The guy is asking with regards to his 2.0L twin carb engine - draw through setup will be fine.
As for supercharging an R31, easiest way is to get the kit from CRS (castlemaine rod shop) and do it in half a day

pipster11
Post #18

yeah i was just using that as an example of how or why you would have a fair length of piping

zorak
Post #19

QUOTE (pipster11 @ Jul 4 2009, 09:48 AM) *
i know its an efi 3 litre but

http://wiki.r31skylineclub.com/index.php?title=Supercharging

that has long piping
and its not practical to put the s/c on the intake side cos of the shape of the mani and what sits on that side of the motor


That system still has no fuel passing through the piping or the blower.......
A Vortech off drive setup for example still would need to be blow through, hence my comment earlier that you get a purpose built carb you will be right. Plenty of them around.
Id imagine the OP would want to do something similar to say a Torana setup, get a small GM style roots blower and have a suck through system which is ideally what you want.

lil_bobby_260
Post #20

Id just run a toyota SC14 and the twin barrel vac sec weber off a 4.1L falcon. Easily enough fuel and they are about 250CFM. Easy to tune, easy to overhaul.

  • Member Login

    If you have a BoostCruising account enter your user name and password into the yellow box.

    Alternatively, you can quickly login with Facebook.

    If you don't have an account create one below.

    Create Account
  • Forgotten your password?
  • Login with Facebook

    Login using your Facebook account!

1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:
Loading...
x