Supercharging Through Bike Carbs

[Guest ianjenn]

This is just what I have found to work after hours of searching the net. Please do your own research if contemplating a charger. I have adapted the principle used by the motorbike boys and their turbos.

 

Essential components

Plenum or airbox (I made mine and also made outlet and inlet manifolds of supercharger after getting plates laser cut)

pitot tube

fuel regulator that can adjust according to boost (I use a mallory 4309)

high pressure fuel pump at about 45psi (I use MSD 2225)

supercharger (I use eaton M62 from mercedes 230)

 

 

The key to supercharging through bike carbs is being able to pressurise the float bowls to the same pressure as boost. Without doing this the pressure from the charger would force fuel out of the bowls as boost pressure increases meaning that you would run lean. You will all be aware that the fuel level regulated by the floats plays a critical role in fueling with bike carbs and works in unison with the jets.

 

So how do you pressurise the float bowls? If you have a look at your bike carbs they will have a hole in the side near the top that you have never noticed before its about 5-6mm in diameter. This goes straight down to the bowl. The key then is something called a pitot tube which is a small (I use 8mm) facing the incoming flow of air from the supercharger. This link tells you everything you need to know about pitot tubes

link to pitot tube

 

Okay so you have pressurised your float bowls next you need the fuel pressure to be higher and mirror boost pressure. The mallory 4309 (needs an unrestrictive return line) keeps fuel pressure 1psi above boost and hence you need to use a higher pressure fuel pump. So I take another line out of the plenum to the fuel pump and set the baseline pressure to around 2psi. This link covers pressurising R1 carbs but I am using ZX6R carbs

carb pressurising

 

There are lots of options regarding the charger. There are loads on ebay at a range of prices, I paid £120 but it did need new bearings. I first of all tried with an M45 found on some minis and mercs. This outputs 0.75litre of air per rev and is supposed to be good for 2.5l engine but it just doesn't have the umph for a 2.0litre zetec. The next one up is an M62 which outputs 1litre/rev and this would be my recommendation. The one I have has an electric clutch which is brilliant because I can control with a megajolt and also have a switch to turn on and off. When the charger is switched off the pulley just freewheels. Superchargers are very noisy and being able to switch it off is brilliant. Be careful to identify the correct charger as they do get listed incorrectly on ebay. This is a good site to identify the differences.

eaton charger date

 

To mount the charger I cut off the front lugs and then had a plate laser cut to match the front cover. I would be happy to share the drawing.

 

The key to boost is being able to spin the charger up to about 10,000rpm. Anymore than this and you don't get much air increase. To get 10,000rpm you need to adjust pulley ratios and this is not so easy on the M62 due to the clutch. One option is to get an oversize crank pulley or as I have done to retain the harmonic balancer in the existing crank pulley, is to machine off the ribs on my existing pulley and machine a new outer ring to take the diameter up to 155mm (from 132mm) 155/93 = 1.66 *6000rpm = 10,000 at charger.

 

The only other thing I have is a boost bypass valve that opens to release boost at vacuum i.e. closed throttle, my theory being that it would reduce the pressure on the carbs when the throttle is closed as plenum pressures can get up to 20psi when coming off throttle at high revs. The slight downside is that the valve will open at gear change which then means pressure has to build back up but this takes fractions of a second.

 

Do you need to make any other engine mods when charging? I honestly don't know for sure. There is a chap running a supercharged pinto in a capri with no mods(search google). Chargers run at much lower max PSI than a turbo, but time will tell and its not as if zetec engines are expensive anyway. I will post pre and post charger rolling road results in a week or two but first drives are amazing and to be honest I suspect my pre charger jets will be fine if not a little rich. If things get too rich I will adjust jets and drop the floats accordingly.

 

There are detailed pictures of my install here

detailed pics

 

Would be good to compare notes with anyone else contemplating charging

cheers

alex

 

the only other thing is that I might fit an intercooler at some point. I have one from a Mazda Bongo that looks suitable

[Guest woolly]

thanks for you time in posting it has helped me to understand more as it has been crossing my mind. any ideas of compression ratio recommendations. mines a pinto.

but considering this on our project puma.

[Guest ianjenn]

thanks for you time in posting it has helped me to understand more as it has been crossing my mind. any ideas of compression ratio recommendations. mines a pinto.

but considering this on our project puma.

 

found the link to the pinto. click here

[Grim]

good interesting post, even for those of us not considering it

[Guest Tim Norman]

mmmmmmmmmmmm Supercharged V8? Must check whether my life policy is up to date!

[Guest snotfart]

very interesting post, will look forward to the dyno figures.

[Guest Robin Allison]

Is that an ST170 engine?

[Guest ianjenn]

Is that an ST170 engine?

 

yes it is, I had a standard blacktop before the st170 and to be honest there has not been much performance difference (needed totally different carb jets and is worse on fuel) whilst normally aspirated between the two of them. The ST170 does have a stonger bottom end which may be useful for charging. From my first drive the charger elimated the flat spot before the cams kick in at 2400rpm.

[Longboarder]

I have my spare ST engine in bits at the moment doing some head work on it. First impressions were that the intakes were fine, big, reasonably clear of steps and narrow areas, goodish shapes and quite well finished. Three angle seats throughout. The exhausts are tiny, poor shape, very narrow at the throat by the valve stem and far to small for the valve size. 20mm only in diameter. My friendly neighbourhood head grinder who usually says put 80% of your effort into the inlets and 20% into the exhausts said I need to open them up by 6mm. I only managed 4mm before I lost my nerve. The inlets just needed cleaning up a bit without major reshaping.

I have found the ST seems to be good from about 3500 and runs out of puff at about 6500. I thought this was down to cam timing as I can't do PWM with omex 600 but I wonder if the small exhaust ports are a factor. I shall see when the spare engine is back together and mapped up.

 

Nigel

[Guest ianjenn]

Had the rolling road today and I am quite pleased with the results topped out at 172BHP at the wheels (probably around 200bhp at flywheel) which by anybodies money is fairly decent. But the most noticable difference is the increase in torque and power accross the rev range. Also I can flick the switch on the dash and turn the charger off for general driving

There is a picture of the graph compared to car without the charger here

rolling road graph

 

and a video of the rolling road session here

rolling road

[Guest Robin Allison]

Don't see how the st was not far better than the black top. Are you sure it's an st170 and not an st150?

 

A mate of mine has one on bike carbs and that did 172bhp at the flywheel. They do need the vvt to be working to get the best out of them.

 

I'm looking to turbo an st170. As they are ideal for turboing.

[Guest ianjenn]

Don't see how the st was not far better than the black top. Are you sure it's an st170 and not an st150?

 

A mate of mine has one on bike carbs and that did 172bhp at the flywheel. They do need the vvt to be working to get the best out of them.

 

I'm looking to turbo an st170. As they are ideal for turboing.

 

you have answered your own question. 172bhp at the flywheel will be about 145bhp at wheels and if you look at my graph I was 150bhp at the wheels normally aspirated and 172bhp with charger. Big difference between bhp at flywheel and at the wheels (about 15-20%). to get an extra 20-30hp on an st170 without spending mega bucks is very tricky. The VVT kicks in at 2400rpm.

 

An st170 is about 10hp better than a blacktop if you improve the inlet manifold and use bike carbs because that is what they did to make the st170. I had a blacktop in before the st170 so know exactly the difference. (although ford engines are notorious for the variability)

[Longboarder]

I have a N/A ST170 and to be honest they promise much with their steel internals, large head ports, VVT, bigger inlet valves but they have sort of already delivered in the focus. They certainly look as if they will deliver loads of power. There is more to come but at a big price on the pocket. I felt my blacktop had the edge on power spread but not quite on overall top end. If using an ST you need to think about getting an ECU with a PWM outlet that will control the cam properly. DTA S60 or Omex 710 for instance. Next problem is when swapping cams the buckets are sized and do not come with shims. So it's new buckets from ford or lashcaps to get cam to follower clearance right. Which is a pricey way to go. Obviously one route you can take is to go to fixed cams and save on the more expensive ECU.

Probably a more sensible route is a decomp plate, decent pistons and a blower of some sort. Much more power for less cash than staying N/A. This also spreads the narrower powerband of the ST. Probably not much in it between an ST and a blacktop and the blacktop's a cheaper route to follow. Just my opinion!

 

Nigel

[Guest ianjenn]

If using an ST you need to think about getting an ECU with a PWM outlet that will control the cam properly.

 

Just wondered why you say you need an ECU with PWM outlet? The megajolt can do just as good a job since the VVT is basically an on/off switch. You switch it on then it is oil pressure that controls the advance. The ford vvt is very basic nothing like the honda vtec.

[Guest gdc]

but to get the best from the vvt it needs controling ,dinger prob has the best set up . the controle is even on tickover .

 

dad