Poor Guy

Hi all, I know how supercharging and turbos work. Now Ive found the ideal supercharger to go on my Triumph GT6, an eaton M45 as found on the new Minis.
Now, i notice that when supercharging everyone has the carb, supercharger then engine.
I want to put on the supercharger, then have a pipe from the chargers outlet to an airbox over my carb trumpets.
would this work?

any ideas?
cheers

davegtt

Que?

GC8

Yes it would; but you would have to find Webbers that were pressure sealed to enable pressurised blow through. Even when carbs and turbos were common this was an uncommon way to do it. The first place to try will be a Webber concessionary, if they still do carbs..........


Simon

J4CKO

iTrader: (1)

wont you have to lower the compression to make it work ?, I am sure it will take a bit of boost as standard but to make it worth the effort I would imagine a complete rebuild would be on the cards.

I suppose its a better method than your other way of getting improved accelleration, you know the one where you use a Fiat Punto......


Sorry, couldnt resist, is it all fixed now ?

GC8

You can lower the compression by using a precision cut plate sandwiched by two headgaskets, or two copper headgaskets... It isnt an unsurmountable problem, the trickier bit is knowing how thiick to make it all to achieve the correct compression ration. Itll take a little boost without being altered but it wont really be worthwhile and you can only really adjust the amount of boost by machining new drive wheels..... I hate maths.


Simon

Poor Guy

shes getting there.
http://putfile.com/pic.php?pic=11/30710154136.jpg&s=x11
shes on SUs at the mo, so i was thinking about using gasket seal on them. not looking to use to much pressure either. The compression at current is 160-165 PSI and can take up to 200 on standard stuff. The heralds used to have shorrocks as an aftermarket mod advertised by dealers. so they can take being blown as the triumph 6 pot is a triumph 4 pot with another half enigne on there.

Poor Guy

I can machine new drive wheels no probs. Am an engineering student at the mo so have access to a college full of machines and tools.

warrenm2

the lotus esprit 2.2 used pressurised carbs - not sure on the pros and cons - i suppose that way gives better mixing....

GC8

Machining the drive wheel is the easy bit and making the sandwich plate wont be too hard either. Calculating the dimensions is the bit that will f*ck you. That and finding a pair of sealed Webbers. I havent even thought of, or heard of these carburettors since the late 1980s!


Simon

GC8

If the early Espirits used them, they will have been Del'Ortos wont they? Theyll still fit on a Webber manifold though.


Simon

Poor Guy

they dont make webers at the mo i think. as i remember the staff in spain have been on strike for months.
Any ways, im wanting to use SU's. better for torque. if i made a plate it would be about 15thou to give me another 20/30 psi. so that could mean the compression ratio would be about 135/145psi.

Brendan Hughes

You're going to copy Lotus engineering?

An old Triumph with a Lotus-designed engine component. Are you going to join the AA as a member, or just as staff and keep the tow-truck for yourself?

GC8

The SUs wont work; look at an old Montego Turbo, they used carbs because AR couldnt get fuel injection to work..... They may well be sealed SUs.

Without wanting to appear to be too negative and on the strength of the substantial mistakes that youve made in your posts so far; Id advise you not to bother, you arent going to make it work.


Simon

Poor Guy

hmmmmmmmmmmm, might have to use single 2" SU then before the charger

andypugh2000

I would use a webber 38dgas before the supercharger, I know of a few applications that have used this setup. Using a carb after the supercharger is asking for all sorts of problems plus the vanes are considered as a good mixing pot before it goes into the engine.

CrisPDuk

I'm with Andy, get a decent weber, SU's being better for torque is a load of bollocks originally dreamed up by BL engineers when the R & D dept was too cash strapped to buy and develop a proper carburation system, SU's are only one (very small) step up from putting the fuel in yourself with a jug

The theory says that the closer you can get the introduction of the fuel to the inlet valve, the better the engine response will be, the practice says that pressure sealing a carb is a ballache, so sticking it upstream of the charger makes practical sense. Although IIRC R5 Turbos had a pressure sealed carb?

You normally can get away with quite high boost levels on older design engines if they're in good nick because they were over engineered and were designed with with low compression ratios anyway.

J4CKO

iTrader: (1)

Wouldnt it be better to get a new injection system, i.e. throttle bodies and mappable ecu that could be set up properly ?

Poor Guy

looking at £2k at least for a proper motec one.
I on the SU front, I know a guy with a spitfire who runs a single mini SU and the torque is insane. driveshaft twisting insane. hes gone through 3 shafts.
I think I would be sticking with a single 2" SU as i find webers a little more temprimental to setup.
This is going to be nuts lol.

Mini-Performance

The easiest method would be to use either the SU or a weber in suck through configuration as used in the Vmax conversions (see pic)
Depending on engine size the Eaton M90 might be the better option.

Poor Guy

already checked that pic
its a 2 litre which the M45 can cope with.

NotoriousREV

Metro Turbos definately used pressure sealed SU HIF44's

andypugh2000

I would consider the weber setup far easier to rejet etc than an SU plus both venturies can be jetted differently to get the afr's spot on, you can pick up a 38 DGAS from breakers everywhere as they were fitted to the Essex V6 engine which was put into the 3.0 capri and granada and maybe even some early 2.8 cologne engines,(stand to be corrected) should set you back no more than 15 quid I reckon

Leslie

It is certainly a lot easier to stick the carb on the front end of the supercharger. Too much complication the other way with having to equalise the air pressure in the carbs and the float chambers unless you can box all the carbs in totally. You might consider fuel injection, I did that on my racers when I turbocharged them.

Les

Poor Guy

AHAHAHAHAHHA!
how did i not see that? box up that carbs to cancel out the pressure difference. one problem is that the supercharger has to be fitted on the other side of the engine to the inlet. so would require a big pipe for the fuel and air to travel down.
I could easily box the carbs up and seal it to the manifold.

ALi-B

iTrader: (1)

Have you ever looked at the Megasquirt EFi??? DIY...build it yourself, MAP based, so ok with boost. Very basic simultaneous system, just need a good trigger source (electronic conversion to the dizzy is ideal). Could use TR6 throttle bodies, which can be "made" to fit, which would just nessitate the need to swap the injectors for more modern electrical ones and fitting of a throttle pot.

Although that little lot would take some time to set up properly before you even dream of bolting on the supercharger, but is a hell of alot cheaper to make than the off the shelf aftermarket EFi system that are currently knocking about (although its worth looking at some USA based parts sellers such as Summit racing as American aftermarket stuff is miles cheaper to buy compared to the rip off tat we get offered here).

Leslie

The length of the inlet pipe from the supercharger is not significant as long as you have room to fit it in. It will help by losing a bit of the charge heating effect before it reaches the engine anyway.

Good luck

Les

vindaloo

One reason for carb then turbo is supercharger efficiency. Dunno how much it applies these days but the fuel acts to improve the supercharger's seal, improving pumping. Also, the carbs are on the atmo. side of the s/c so don't require any special attention other than setting them up.

I'd suggest that you think how you want it all set-up. If you want to be able to run bypass off the s/c and select boost when required, I don't think that carbs and clockwork ignition is the way to go. Maybe convert to EFi first...?

Regarding the mechanical set-up, every article I've read stresses the need for accurate alignment of the drive pulley and the s/c or belts fall off and/or shred.

J.