Feasibility of an AAV turbo as a daily

[cheys03]

I’m seeking more power for my daily driver. Currently it’s a MK3 coupe with original AAV engine (70k) and GT injection added, 239 vented brakes and whole new suspension, plans for an arb’d rear beam too – basically to make sure the brakes and suspension are G40 factory spec or better.
The car currently covers approximately 25,000miles per year mostly on motorway and A-roads, averaging roughly 40-42mpg.
Because of the mileage I don’t really want to go down the G40 route. I think it would mean a charger rebuild once a year even with a standard pulley and probably an engine rebuild at some point. The attraction of a turbo’d AAV is both the turbo and engine can be had cheaply.
Target power would be 125-130+bhp while aiming for ~40mpg on motorway trips. I’d also like to avoid a heavy clutch if at all possible!

How realistic is this?

Just for additional info – the car is post 1992 and so requires a CAT and injection which rules out AFH+bike carbs. 1.6 ABU+ GT injection is a temping alternative but may be a bit lacking in power. My budget is up to roughly £1600, but could be extended if necessary. This would include a remap and suitable exhaust. I'm not really after a list of what I'd need just yet, more opinions on the idea as a whole.
I enjoy driving and maintaining the Polo so prefer to keep it as the daily rather than buy a more sensible diesel Mondeo or something.

Many thanks in advance for opinions, comments etc. Feel free to tell me I’m dreaming on price or mpg or if you think there are more realistic alternatives.

Cheers

[hayesey]

personally I'd get hold of a g40 bottom end to lower your CR a bit to keep long-term reliability, you're far more likely to need yearly engine rebuilds with a turbo'd AAV engine than a turbo'd g40 bottom end.  Although at the same time, a turbo running relatively low pressure on an AAV engine would probably make a nicer car to drive.  If mapped correctly and you resist the temptation to just keep winding the boost pressure up (which is hard to resist because it's just so easy with a turbo) then it should be reliable.

[PeteG40]

wanna do it well cheap? get some g40 pistons in yr bottom end to lower compression.

remember that you'd need management/boost pipes/i/c etc etc

[cheys03]

Thanks for your input gents.
Hopefully I'll be able to resist the temptation on the boost screw as it'd hit the mpg - one of my main concerns with this is keeping roughly 40mpg (which I'm not even sure is possible?).

Pete - I've a rough idea that I'll need G40 ECU & loom, turbo manifold, downpipe, exhaust, G40 throttle body, G40 CO pot, I/C, boost pipes, map sensor (or use current G40 one in the ECU?), injectors, oil feeds, remap plus a few things I've forgotten. Already have a GT cam which I understand is ok for a turbo. I'm not sure what you mean "wanna do it well cheap", but do you feel £1600 is too little for this potential project?

Cheers

[PeteG40]

it'll cost same as ag40 conversion but minus the £350 a second hand g40 head and block costs

[hayesey]

I'd be tempted to do it on your AAV engine and keep boost below 0.5bar, with correct fuelling it should work for sort of 100bhp or so, poss a bit more.  You'll need a complete g40 management system (loom, ecu, fuel pump, all engine sensors etc...), pipe work and what not. Unfortunately not just things you can pick up at your local motor factors, I'd envisage a fair amount of time collecting parts.  I think £1600 is realistic if you can find the turbo parts 2nd hand and stick to the cheap, readily available and known KKK K03 parts.  Unless you have ability and access to the tools to mke your own manifold, downpipe etc... then it'll be considerably cheaper and you can use whatever turbo you want or come across for cheap that's the right size.

[lance]

is there a place for a knock sensor on the aav though?

[hayesey]

it should have the stub sticking out of the block which will just need drilling, tapping and smoothing off. 

[cheys03]

Hmmm...

By the sounds of it 125-130bhp is probably over-optomistic given the level of boost safe for the AAV compression ratio? If it's likely to be 100bhp (or even 110bhp) it doesn't seem worthwhile in terms of time and cash expenditure - especially with a 1.6 (ABU/AEE) engine with GT injection it's possible to achieve ~100bhp relatively easily.

[Justin14100]

Hmmm...

By the sounds of it 125-130bhp is probably over-optomistic given the level of boost safe for the AAV compression ratio? If it's likely to be 100bhp (or even 110bhp) it doesn't seem worthwhile in terms of time and cash expenditure - especially with a 1.6 (ABU/AEE) engine with GT injection it's possible to achieve ~100bhp relatively easily.

power figures are power figures, but its how it makes the power that will make it more of what you want than a abu/aee

[hayesey]

well 100bhp was just a guess really, but I cant see it making more than standard g40 power with less than or the same as standard g40 boost pressure.

[Yoof]

I'm well up for helping out with this project- been thinking about a turbo'd AAV for a while now.

You don't need a G40 throttle body- can use a GT one with a modified elbow.

A small parts list:

G40 Management
G40 Inlet/Injectors & FPR
Rothe Manifold & Downpipe
K03 Turbo & Standard Actuator (Circa 7psi)
Intercooler & Boost Hoses
G40 Management Sensors; Knock, Dizzy, Map, CO Pot, Boost Switch & Full Throttle Switch
G40 Loom
3F (GT) Camshaft

I'd try to get a G40 gearbox if your budget can strech- if not accept the 8P might affect your fuel consumption.

Also a stock G40 clutch (200mm) will be fine, and not be any heavier than your current one.

I'd budget approx £300 for a custom map too.

The good thing is, once you've purchased the above, at a later date you can then buy a G40 engine and wind the boost up to 160bhp+ with that set-up.

[cheys03]

Interesting, for the G40 gearbox it is the ratios or general mechanical efficiency that give it a better MPG than the 8P?

For the throttle body, would it be easier to use an NZ item as this already has an idle switch, with a boost switch working as the full throttle switch normally would? Or is the GT item just as easy to modify? In honestly though if it's a fair bit of work on either the NZ or GT I might try to get hold of a G40 one.

Injectors - G40 or ones with a greater flow rate?

Many thanks for the offer of help Yoof - I'll certainly need it! I agree with Hayesey - it'll surely take a while to accumulate the parts. In the mean-time I'm doing as much research as possible to get my head round it a bit better. The post archive here and various build threads (inc Andy's on CP) are proving very useful.

For the remap and exhaust I was hoping to come to PPP, though these will probably be a while off yet as the last bits on the long list!

[Andy]

NZ only has WOT switch if memory serves, so you'd have to modify it to fit an idle switch. The 3F TB is potentiometer, so that'd need an idle switch fitting too. With that in mind, I'd use a G40 TB!

If you use a K03 and a 3F cam, you'll get something that spools around 1500-1800rpm and starts to choke up by 4500rpm if the same combination on my 9.3:1 CR 1341cc motor was anything to go by. I'd try the 3F cam first, but budget to get something lairer.

As for power, if you run a 'turbo' cam and 6psi of boost with a K03, you should get around 130bhp once mapped up.

When it comes to injectors, G40 ones will be fine for the power you're talking about - however, you'll struggle to get an off-the-shelf chip for them. With that in mind I'd be tempted to go for 250cc/min G60 'greens' - you could use one of our generic chips to get you up and running, and it'd be okay for any boost level up to 15psi. Alternatively, stick with stock G40 injectors, and budget to get it custom mapped before booting it.

For gearboxes I think you'd be fine with an 8P if you still run stock rolling radius wheels - so 175/60R13 or something like 185/50R14. If like me you're running 175/50R13 then you'll want a G40 'box so that the overall gearing remains sensible. Once you decide you want more boost and more power, you'll want a G40 'box either way!

[cheys03]

Thanks for the info Andy. G40 throttle body it is then! Be needing the G40 vacuum brake servo hose too I guess.
I'm running 165/60/R14 atm. Possibly 185/50/R14 in the future. 8P should be ok for the moment going on the above. Will take your advice and run G60 injectors with a suitable PPP chip (#G40008) to get started.

What have you done for a catalyst on your Polo? On your CP blog it looks like you've got a standard CAT welded to the downpipe?

I've done a little research into the knock sensor used by the G40 management. In a couple of other threads here you mention the simplistic nature of this sensor and raise doubts as to it's effectiveness. Clearly it's there for a reason, but in your opinion is it worth fitting? Perhaps in order to fool the ECU into not raising a knock sensor fault a suitable resistor could be attached across the relevant terminals? I'd happily avoid having to remove the engine and get the block tapped if knock can be addressed using another method...?