Turbocharging an N/A engine

[Jack4688]

I am doing research for a potential project later in the year where I intend to do as much of the work as possible. I accept that doing this sort of thing could cost around £5k in parts alone but I don't want to spend money unnecessarily - such as replacing engine parts or transmission parts that are capable of handling the increase in power and torque.

The engine in question is a 2.3 20v VR5 to which I intend to add a K04 or something similar to get B5 S4 levels of power and torque, so not going nuts but still from what I've found out so far some intrenals will have to be changed. I know it's been done before as I've found some videos and forum posts from various vw forums etc. on specifically the VR5 being turbocharged, though no useful technical info from which I can learn and make decisions. Annoyingly there seems a lot more info and support (in terms of complete turbo kits etc) for the VR6.

I'm getting conflicting info on things like the pistons, rods and cams. From what I've read/watched so far this is my understanding of said items:

• Pistons - Smaller pistons required to alter the compression ratio, though the same can be achieved with a spacer plate in between the head and the block. I would go with pistons instead of a spacer plate all day long as it seems an inelegant way of doing it. Are forged pistons required for strength reasons too? Remember I'm looking for about 100bhp increase and somewhere over 100 lb/ft increase at whatever boost would be needed to provide that from a K04 or similar.
  
  
• Rods - As far as I can tell only needed if you're increasing power/torque/boost to very high levels to provide extra strength. But would they need changing from standard the moment you add any form of turocharging?
  
  
• Cams - Need replacing with custom made ones to alter valve overlap and stop boosted intake simply going back out the exhaust valve.

I've found quite a few VR6 turbo kits online as a reference for what requires modification or replacement but have thus far found no examples with new camshafts and some that don't offer new rods. This VR5 turbo kit offers forged rods as an option and a spacer plate, so standard pistons, and claims 550hp is possible - though I don't know the credibility of the company and their products... I have even seen an MX-5 turbo conversion where power is claimed to have been doubled, with a 'safe' map with no risk of detonation etc., but with completely standard internals!

I have sent off an enquiry to turbodynamics.co.uk as they seem to have the knowledge I need on this type of project - i.e. turbocharging an engine that was never offered in turbo format from the manufacturer - though I have had no response. I was thinking AutoMark would be a good place to go to get the thing mapped and I may ask if they have any pointers for engine prep. Anyone else got any suggestions on who to ask or even experience of their own that will help me?

If you're going to tell me "don't bother, you'll spend thousands and thousands" I don't mind so long as you can give me good reasons that I can consider

If you're going to tell me "just buy an S4" please modify that to "just buy a Legacy GT-B" as I still intend to leave the UK for NZ ......Forever!

[Error404]

If you are only going for "260-270hp maybe you can get away with the stock pistons. Plenty of factory turbo engines don't use forged pistons.
What is the stock CR? Not that high I bet. Easy way to drop the CR a touch would be skim the piston crown.
Maybe you can re-clock the stock cams to reduce / remove the overlap. Or maybe you can recalibrate the cam control if they have VVT?

[Jack4688]

I think it's 10.8:1 standard and that's another thing I don't know - I've read that "between 7.5:1 and 8.5:1" is the compression ratio you need. How do you work out what it actually needs to be? Sending out the cams to be machined sounds preferable option so long as I can figure out what profile is needed. I thought those engines didn't have VVT but this shows they do.

[Jack4688]

Looking at this my guess, with the limited knowledge I have at the moment, the VVT mapping should be able to be modified to give the desired effect i.e. reducing valve overlap as there are two conditions stated where there is none whatsoever.

[Error404]

You don't need to run that low CR unless you're going for big boost.
I would say you will probably be fine on 10.8:1 to reach your target as you won't be needing to run much boost. If the bottom end is coming apart anyway, then you could skim the pistons down a tad pretty easily.
You will be able to re-calibrate the active cam control to better suit the boosted engine so I wouldn't worry too much about that to be honest.

If I was you I'd get the turbo & associated ancillaries fitted up to the stock engine, pick some injectors, find a competent tuner and see how you go.

[quattro-nick]

with alex

[Jack4688]

Sounds like a good idea, as this is also an engine swap project it's a matter of when I do it; before or after I've removed the engine from the donor car - I have no intentions of making a 270hp FWD Passat

[sandman1111]

I don´t think the compression ratio is 10.8, it is probably lower. Doesn´t matter that factory figures say so, check it out (for excample, vw and audi 2.0 16v engines were actually 0.5 lower. Factory states 10.8). With that kind of power levels, I think double head gasket is enough, should land somewhere around 9.5?

Since it is a budget build? I would just replace bearings, oil pump etc. Would not change pistons, crank, rods. Are you sure you need upgraded internals? Those power levels are low.

[Jack4688]

Are you sure you need upgraded internals? Those power levels are low.

That's what I'm trying to find out, it would appear I can get away with just reducing the CR and remapping the VVT

Since it is a budget build? I would just replace bearings, oil pump etc. Would not change pistons, crank, rods.

I wouldn't say 'budget' as such. I just don't want to go mad and buy parts that are not needed if the standard parts will cope. The idea is I will do as much research as I can and it will be down to either I will or I won't go through with it - skimping on cost for any reason seems irresponsible on my part!

[sandman1111]

So what you want from the engine? Just a fun ride or reliably daily driver?

[Jack4688]

Daily driver, not a hot rod. Also I want a 5 cyl again plus I'd like to teach myself to undertake this sort of task.

[Error404]

Fabricating the exhaust manifold will be the biggest job I think

[Jack4688]

Yeah I wanna learn how to do that It'll be another skill I will have learned during the process.

[Jack4688]

Although I'm starting to think the transmission may cause problems - I'm starting to think there is now way the 01A DWR box in my B5 quattro sport isn't up to the job (or at least I cannot find any technical sheets to guarantee it) and 'simply swapping' in B5 S4 box, prop, driveshafts, diff may not be all that simple. Trouble is B5 S4s seem to be climbing in value at the moment and it's just too tempting to do it to my car as I already own it (reducing GST applicable for importing it to NZ), it was a cheap quattro avant, the bodywork and interior are in good condition for a 174k car, it's an interesting colour and I prefer the more subtle look to the quattro sport compared to the S4.

[sandman1111]

Gearbox is fine. You need thicker head gasket, or double. I would leave internals stock. Change bearings, oil pump, gaskets etc. Bigger turbo than k04, its just too restrictive for those power levels. Custom exhaust manifold, downpipe 2.5". I would do full exhaust. intercooler piping air outlet size to intercooler and a bit bigget to throttle body. Stock intake manifold. Modify stock intake, better flowing air filter. Plugs. intercooler cheap chinese or used OEM from something similar power level. BOV. Injectors?? Higher fuel pressure regulator?? Management?? Clutch. Modified sump. Turbo oil line.