Supercharging a old VW


Chester uk
8v k-jet MK1 GOLF
Hello all,

Sorry for a long post, thought it best to give a detailed explanation to my questions :)

so here is my setup. - I have a 1986 MK1 Golf GTI with its original DX Engine, Bosh K-Jetronic 1.8 8V.

I love the engine, I am a fiddler, and tinkering on the car throwing money at it (down the drain) is my hobby and i don't want to swap it, for me its not about getting the most HP from the car - if that was the case I would put a 1.8T or VR6 in, what i want to do is get the most out of the stock engine.

so far the engine has been fully rebuilt, rings, bearings, pumps, belts, valves etc - the lot. I have swapped out the warm-up regulator for a 16V model and swapped the throttle body to match - giving the engine better throttle response and a tiny bit more top-end power. the head is ported and polished and so is the inlet manifold. its got a 4-2-1 manifold and sports exhaust and Its running a 276 performance Newman Tarmac Rally Sprint Cam with a vernier pulley.
I have not had it on a dyno since the cam but i expect its making a whopping 120BHP at the crank. (on the last run it managed 92 wheel HP)

So i have taken the engine about as far as i can get it now without swapping to a turbo or supercharger.

There were both supercharger and turbo options for the engine in the 1980's, either a turbo technics or a couple of supercharger kits - these were made for the Golf and Scirocco that both shared this engine.

Turbo technics and supercharger kits are super rare and when they do turn up are way overpriced so i have given up looking and i am thinking to do my own.

The DX engine is a 1.8, and has a compression ratio of 10:1 (Less than ideal) i don't want to bore it out or swap the bottom end to a 2L, i would prefer to leave it stock and i presume that some boost can be run because the kits back in the day could run on this setup.
I would be willing to get a Decompression plate manufactured if needed but would love to run with the 10:1 if possible - again to just keep it stock as possible.

Comments on my thinking so far;
Fabrication of mounting brackets etc and fitting etc i can handle all that myself no problem + there is plenty of room in the engine bay. Turbo or supercharger will go into the system between the throttle body and the K-Jet as this is where it joins on all kits and it's also more simple (So it's sucking through the metering plate and blowing into the manifold) and from research, the K-Jet and stock injectors should be fine for the kind of power I can expect so no need to fettle any further on fuelling apart from the usual rolling road setup after any install.

Now then, to the questions;

1- The Supercharger
If i am going to do it myself I would prefer the supercharger because of its good power delivery through the range and its simpler. I was thinking of getting a scrapper VW supercharger from a 1.4TFSI or similar and building around this but a local guy showed me his Beetle running a AISIN AMR500 Roots Supercharger and it looked ideal? What are peoples thoughts on this?
Its not big so fabrication and fitting should go better and as I have a 10:1 ratio I cant exactly crank up the boost so this could be a good option? –
What do you think?
I will post more info on the AMR500 at the end of my post.

Pulley, how do I calculate the right ratio to boost? Is there an online calculator for this where I can input pulley sizes and rpm so I can get the right pulleys?

Where would you drive the belt from? I am thinking to add an extra pulley onto the main crank shaft and drive from there as its got the best access for me, are there benefits / cons to where the supercharger would be driven from?

Engine knock / pump fuel / Water meth – I will be fuelling with regular pump fuel and I am working with 10/1 so would water meth be worth considering helping with this as well as retarding timing etc?

What am I forgetting here? – what advice do you have for me? – what are your thoughts?

Info on the supercharger I am thinking of getting.

Application: to increase performance on motorcycles, snowmobiles, ATVs, VW engines, Mini Coopers, Subarus, Nissans, Toyotas or any engine under 3.0L.

500cc/ revolution (30.5 With straight, 2 lobe rotors. It could be over-driven, and make good boost on a 650cc-1000cc drag bikes or larger if RPM is kept low. Or it could be under-driven for smaller engines.

On a 500cc two stroke, with the blower being driven 1.5:1 with the crank, it would produce approximately 7 psi boost.

On a 750cc four stroke, with the blower being driven 1:1 with the crank, it would produce approximately 5 psi boost.

On a 750cc four stroke, with the blower being driven 1.5:1 with the crank, it would produce approximately 15 psi boost.

On a 1000cc four stroke, with the blower being driven 1.5:1 with the crank, it would produce approximately 9.5 psi boost.

On a 1600cc VW engine, with the blower being driven 2.1:1 with the crank, it would produce approximately 5 psi, but the engine RPM must be limited to 8000 rpm.

Additional Info:
Max blower continous speed is 16,000 RPM Before this, these were only available in Japan!
This would be a great blower for any small engine up to 1200cc ( depending on RPM ).

Over all length is 6.75", Width is 8", Height from inlet to outlet 5.5" The 4 bolt inlet & outlet flanges makes it easy to fabricate custom mounts for manifolds, and carbs. The drive pulley diameter is aprox. 3" but could be changed out to a cog belt drive quite easily. We have no info on what modifications are needed to mount this unit on your engine. You will need to be capable of doing custom fabrication.
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