Carburettor Set up for Supercharged x1/9

Road-race engines and ancillaries - general discussion
Post Reply
Charlie
Posts: 19
Joined: June 23rd, 2006, 2:30 pm
Location: Ireland
Contact:

Carburettor Set up for Supercharged x1/9

Post by Charlie »

When I first fired up my supercharged x1/9 1300 after assembly it became evident that the Dellorto Dhla 40 that I was using required proper setting up for the application. I was using the 32mm chokes that came with the carburettor and there was complete reluctance for the motor to take any throttle off Idle. I needed to get some expert information on setting up the side draught unit. After numerous phone calls to several carburettor specialists, including the official distributer of Dellorto "Eurocarb ", "Gower and Lee" and explaning my set up and the problems I was experiencing I got the usual answer off, " Sorry mate I can,t help you with a supercharger application". D'ont get me wrong these are very helpfull people and I deal with them for carburettor parts, but any knoweledge about setting up a carb for a supercharger application was as scarce as" rocking horse poo"!.
After thrawling the net for weeks, including checking the complete Lancia Beta Volumex forums I was still "non the wiser".( Sorry about the Irish slang here).
I had heard about " Guy Croft Racing Engines" from anybody in Ireland that owned a twin cam Fiat and there was nothing but praise for the work and parts that came from this establishmen,t.
After contacting Guy and explaining my problems he immediately hit the nail on the head and told me that the choke sizes that I was using was to big for a supercharger application and suggeted a complete carburettor set up at the drop of a hat. Not only that he went through the complete set up including compression ratio, ignition timing and efficent exhaust design. I fitted the 25 mm chokes that Guy recommended and his suggestions reguarding jetting and at last sucess!. I had ment to contact Guy by e-mail to thank him for his invaluable help personally so I will take the opporrtunity to do it on his own Forum here.
Charlie
Wallace
Posts: 11
Joined: July 16th, 2006, 1:46 pm
Location: London & Lincolnshire
Contact:

Post by Wallace »

I had twin 40 Dellorto's on my turbocharged Montecarlo engine - and they went a treat ! Choke size was 32mm.

I take it you have the fuel regulator on them to give a constant fuel pressure over boost pressure ??
WALLACE
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Post by Guy Croft »

You have to run small chokes on suck thru supercharged units because of the back-flow from the rotors. They are the opposite of n/a engines to tune, as Charlie discovered.
Turbocharged blow-thru are a different animal, you can run as big as you like so long as the fuel signal in the carb will respond. Turbo suck-thru I'm afraid I don't have much exp of fixed choke carb setups, they probably fall somewhere between the two.

GC
Wallace
Posts: 11
Joined: July 16th, 2006, 1:46 pm
Location: London & Lincolnshire
Contact:

Post by Wallace »

Ah - therin lies the difference - mine was a twin blow through. My question about a fuel regulator isn't relevant either then !

The only reason I asked was becasue I had a problem getting the car to run under boost because I'd plumbed it in incorectly - I used a hose from the plenum chamber looped through to each carb (the vent at the top) and thence to the regulator. With hindsight, I should have realised there was a pressure drop along the pipe so the boost pressure hitting the regulator was incorect.

Another problem I had was replacing the cheep steel screws on the carbs with nice shiny stainless ones - unfortunately slightly too long. Under boost, the carbs leaked petrol like a sieve as the tops weren't tight enough - the screws were bottoming out. And of course, the *&^%$" thing caught fire . . . :oops:
WALLACE
Ade
Posts: 13
Joined: September 2nd, 2006, 3:19 pm
Location: England
Contact:

Carburettor setup for supercharged x19

Post by Ade »

Hi Charlie,

I read with interest your supercharged 1300. I've got a fairly standard 1500 and am keen to look at turbo/supercharging.

If you don't mind me asking how did you fabricate the drive for the charger on the bottom pulley and what supercharger did you use?

Also if you lowered you comp. ratio how did you do this? I hope you're pleased with the end result, have you seen a good improvement?

Many thanks,

Ade
Charlie
Posts: 19
Joined: June 23rd, 2006, 2:30 pm
Location: Ireland
Contact:

Post by Charlie »

Hi Ade,
I haven,t been very active on this forum lately and I have just noticed your post , hence the delay in this reply.
The supercharger that I am using is an Eaton M45 from the BMW "Mini cooper S".
The crank pulley is an 8MX20mm synchronous type. These can be purchased with a small pilot bore from most industrial bearing and transmission part suppliers. I just removed the original Vee pulley and sent the new pulley with a drawing to my local precesion engineering shop
and they bored and machined the pulley as required .
One of the biggest challenges during the design phase was obtaining drive for the supercharger while keeping the supercharger properly aligned with the existing inlet manifold. This is why I have a primiary belt and auxillary belt drive system.
Lowering the compression ratio to 8:1 was achieved by fitting a cylinder head from a 1500 engine.
Ade
Posts: 13
Joined: September 2nd, 2006, 3:19 pm
Location: England
Contact:

Post by Ade »

Hi Charlie, thanks for you reply.
I was talking to a friend who went on the X19 Anglesey trip this month (Sept) and I think he mentioned there was a supercharged X19 there, possibly yours?
I¢ž¢ve also been considering using the Mini supercharger, you mention the difficult task of obtaining supercharger drive, what do you think about adapting and using the auxiliary pulley which runs the fuel pump cam? This way the belt can be shorter I figured, the engine mount would have to be negotiated though.
Also please Charlie, how do you get the charged air to your carb, did you have a manifold made up to fit the mini supercharger?
Many thanks for your advice.
Ade
Charlie
Posts: 19
Joined: June 23rd, 2006, 2:30 pm
Location: Ireland
Contact:

Post by Charlie »

Hi Ade,
The car your friend seen at the x1/9 national meet in Wales was mine.
It also was voted " Favourite Modified x1/9" at the meet.
I would not recommend driving the supercharger from the auxillary distributer/ oilpump drive. This is driven by the cambelt which should not be subjected to any extra loading, as the consequences of any failure in this drive would result in majour engine damage. The charger consumes about 6hp a@ 10 psi @ 10,000rpm according to the manafacturers. The supercharger needs to be driven from the crankshaft.
Your query about getting charged air to the carburettor is not relevant
to the set up I have used. I have used a "draw through" carb set up, not a "blow through" set up which you refer to.
If you check out the "Readers cars" section in this forum , you will see pictures of the set up that I have used. There is not enough room in the x1/9 engine bay for a blow through system using this charger.

Charlie.
Ade
Posts: 13
Joined: September 2nd, 2006, 3:19 pm
Location: England
Contact:

Post by Ade »

Thanks Charlie, very useful advice and well done with the recent award! I did check out your photos previously but must have missed the one showing the carbs and suck through setup. A very tidy job I must say.
Do you limit boost can I ask and if so how do you overcome venting mixed air/fuel to atmosphere, looking at the pipe I'm wondering if you use a recirculation system?
Also how did you fabricate the adapter to allow the mini charger to fit to the Fiat inlet manifold?
Sorry for all the questions and many thanks
Ade
Charlie
Posts: 19
Joined: June 23rd, 2006, 2:30 pm
Location: Ireland
Contact:

Post by Charlie »

I am not using any boost pressure limiting device.
I am using a vacuum operated bypass valve, its function being to unload the charger during idling and cruising, not to dump excess boost.
It basically links the supercharger inlet and supercharger outlet.
Boost pressure on a roots type supercharger is generated in a linear fashion unlike a turbocharger or centrifugal supercharger which delivers little boost at low rpm and then will boost up dramitacally at higher rpm where wastegates and overboost valves are required to stop the engine from been overcharged. A draw- thru system is much easier to adapt to a bypass valve system than a blow- thru system . With a blow through roots type system the charger would be pushing boost up against virtually closed throttle plates at idle generating heat and load on the charger without a bypass valve. With the draw-tru system a bypass valve
is benifical but not critical because when the inlet to the charger is closed boost is not available.
You can set up the drive ratio from the crank to the supercharger to give you the maximum pressure that you want to run at.
The 1300 engine will displace 650cc per revolution.
The Eaton charger displaces 750cc per revolution.
For a boost pressure of 8psi you would have to supply each cylinder with
roughly 1.5 times its volume.
It is then a simple calculation to obtain the blower drive ratio.
The charger is fitted to the Fiat manifold with a fabricated 10mm adaptor plate. The plate is bolted to the inlet manifold first with countersunk allen head screws and then the charger is bolted on to this plate.
I have modified this manifold to allow the use of a bypass valve by drilling through the manifold coolant gallery and creating an extra port.
The gallery/ new port sides were welded up and made good. The corresponding ports in the cylinder head were also tapped M10 and sealed using grubscrews and sealant.
A bypass valve was specially designed to fit this application as was the carburettor to charger inlet plenum.

Charlie.
Ade
Posts: 13
Joined: September 2nd, 2006, 3:19 pm
Location: England
Contact:

Post by Ade »

Thanks Charlie, very thorough advice. Hope you dont mind me asking more questions if they come to me.
Regards
Ade
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Post by Guy Croft »

Ade,

This is a good thread that runs itself, that's nice, but before you get too technical and Charlie ends up writing a book about this here at your behest, how about you make a start on your engine and tell us what you're doing?

I speak from years of experience of advising people 'how to do things' only for the line to 'go cold' and and for me to discover years later that after they realised how much work it was - they never went ahead. The list is very long.

You may be very committed on this, that's great, but as the site owner I write for the edification of all members. Many will simply pluck information interminably..because they can. Not here!

GC
Ade
Posts: 13
Joined: September 2nd, 2006, 3:19 pm
Location: England
Contact:

Post by Ade »

Thanks Guy and thanks for letting the thread run, Charlie's expertise has assisted no end.
Having just completed 2600 miles return trip to Italy I'm happy with the reliability of the car. Currently I'm running the standard 1500 engine and car with the following very minor modifications;
-Kent cam and pulley (though I'm unsure of the the exact spec.),
-Larger main jet in carb,
-Uprated copper cored radiator,
-Usual suspension and wheel upgrade,
-Some small bodywork changes to reduce weight,
-I also have a 4 into 1 heat wrapped exhaust manifold and exhaust system but this is still fitted to my other X19.
Admittedly these are all fairly token gestures at improving performance and I would like around 120Bhp whilst retaining driveability.
I'd like to keep the same cubic capacity, 1500cc, and then look at forced induction, that way i can run lower boost with the original internals.
Whereas Charlie has been able to lower his C.R. by fitting the 1500 head to his 1300 block, I will have to lower C.R. by other means.
Guy, is fitting of low compression pistons the only realistic option? What is your advice on fitting a solid thicker head gasket? (I have read your thoughts on skimming the head for increasing C.R!)
Also I've considered Biuretting the head and enlarging the combustion chamber to lower C.R.
Your thoughts are very welcome.
P.S would you mind if i posted some pictures of the car?
Ade
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Post by Guy Croft »

Ade, hi

you can take a lot out of the combustion chamber to reduce CR, plus doing a super valve/seat job will increase the chamber volume.

Be aware that you are taking something of a risk running supercharged on X19 standard pistons. I don't take chances with things like that so I am not going to say, yes, they are strong enough or no, they're not. Supercharged pistons in cast material always have stronger ring lands and thicker crowns - or else forged are used. Your call, I know what I'd do.

I'm also concerned about head gasket, I have been unable to get hold of the old Astadur Goetze X19 injection head gasket for some time, this is incomparably stronger than any OE or aftermarket one. I know about Spesso, but there is a (I think) a 10 off minimum order.

Thoughts on this Charlie if you please..

I can e mail you a CR calculator that will tell you very accurately what the head volume needs to be. Drop me a line at croftengines@aol.com. The head needs to come off and some measurements taken first though. I will talk you thru what to do at that stage.

sure! Good pictures always welcome, especially if well-captioned/described.

GC
Charlie
Posts: 19
Joined: June 23rd, 2006, 2:30 pm
Location: Ireland
Contact:

Post by Charlie »

Hi Guy, Ade,
Guys concerns as he has outlined reguarding the standard OE pistons and cylinder head gaskett have also caused me some concern.
Indeed I have contacted Guy about sourcing a performance gaskett as I plan to remove the cylinder head to check how everything is holding up to its life of forced induction.
I have covered over 3000 trouble free miles so far but this is not enough to proclaim that OE parts are suitable.
Without building a mule engine and testing it to destruction there is no possible way of accessing the suitability of OE parts.
Lets just go back to basics for a moment.
To quote Keith Duckworth who designed the Ford Cosworth DFV Formula 1 engine in the 60,s , " The power of an engine being the size of the bangs times the number of bangs per minute." or words to that effect.
Lets compare a tuned normally aspirated engine for example , the 1500 sohc engine as used in Ade,s x1/9 and a supercharged 1500 sohc unit.
With a ported head, freeflow exhaust, twin carbs and suitable cam, 120 bhp can be achieved easily from the normally aspirated unit.
With a supercharged engine the bangs will be bigger but at a lower rpm to achive the same power, hence the probable need for forged pistons .
This is where professionals like Guy are needed who can provide specially designed pistons for the application.
I am not involved in any form of engine developement on a daily basics and I can't give you any specialised knoweledge as to the suitability of these particular engine internals.
It was primillary the engineering challenge of fitting the Eaton supercharger to the sohc engine that attracted be to this project.
There is a few specially designed components used in the project .
I have an advantage here as I am involved in industrial machine design and modifications so I am well used to designing specialised components using CAD.
My advise to you is that unless you have a strong engineering background or know people who can engineer these components for you, then you should look at other avenues for a performance increase.
In an ideal world a motorsport professional could supply the whole lot as a kit and you would just have to bolt it on.

Charlie.
Post Reply

Who is online

Users browsing this forum: No registered users and 38 guests