406oc.co.uk

Have just bought a 98 Sri turbo in blue, totally original and only 83k with history, looking for more power on a budget. Have bought it as a cheap runabout to replace a Bluebird Zx Turbo, i also have an St220 as a better car. Have a new boost controller left over from the Zx as a start but not fitted it yet, looking for ideas and cheap mods. Would like to see 190bhp+ can anyone give me some advice as i dont want to kill her, Thanks Karl

To be dead honest the best answer is leave it alone. Your engine can be modified to around 180 BHP but not without a LOT of heartache and trial and error. Particular weak points are the turbo, cooling system, head and fuelling - not a good starting point really

The 8v head, ports, inlet and outlet just weren't designed for big BHP indeed the 2.0 16valve found in 306gti's has 167BHP without a turbo! it's all in the design of the original concept really and the 2.0T was just mildly uprated with a low pressure turbo for more low end torque to compete with other marques of that era in fact the turbo only adds 20 BHP over a N/A 2.0 but does add more torque.

mjb on here ran his standard tubby upto 180,000 miles with basic servicing (if that)

I'd say leave it alone any enjoy comfortable and very cheap motoring.

Welton wrote:mjb on here ran his standard tubby upto 180,000 miles with basic servicing (if that)

What's servicing?

mjb wrote:

Welton wrote:mjb on here ran his standard tubby upto 180,000 miles with basic servicing (if that)

What's servicing?

Ditto

Ok will take that on board.
Another minor problem is starting. When starting if you touch the accelerator pedal she is an absolute mare to start she turns over and over and finally starts. If you start the car without touching the pedal she starts straight away, is this correct as i never had this problem with my old one 5 years ago.
Has the car an underlying problem ? i know the answer is dont touch the pedal.

Of course if you want to try and get more performance out of your car, don't let the naysayers put you off completely

Electronic boost control is going to give you the most control over the shape of the boost curve, so go with that if you can. Just don't go over 1 bar. The map sensor doesn't have the range and you'll just trigger the fuel cutoff. The end result is you may not increase peak power very much, but you can lift the boost in the middle of the range for more responsiveness.

you shouldn't press the accelerator when starting a car with a cat. It sends unburnt fuel through the engine into the cat, causing an early end to the cat!

just start it with out pressing the accelerator, problem solved

Not to mention revving the engine with no oil pressure

Welton wrote:To be dead honest the best answer is leave it alone. Your engine can be modified to around 180 BHP but not without a LOT of heartache and trial and error. Particular weak points are the turbo, cooling system, head and fuelling - not a good starting point really

The 8v head, ports, inlet and outlet just weren't designed for big BHP indeed the 2.0 16valve found in 306gti's has 167BHP without a turbo! it's all in the design of the original concept really and the 2.0T was just mildly uprated with a low pressure turbo for more low end torque to compete with other marques of that era in fact the turbo only adds 20 BHP over a N/A 2.0 but does add more torque.

The ports on the had and the valves are actually quite large and certainly large enough to flow 200bhp, the problem with getting big power is basically the turbocharger is way too small, great for response, crap for top end. It also has a very low compression ratio for a 'modern' turbocharged engine.

Comparing it to a 306Gti6 engine is pointless, because that engine has a much higher compression ratio and a head designed to flow well at high revs, 8 valve heads will never flow aswell top end by design, but can still produce good power at a lower rpm than a 16 valve. Where it will excel is torque and thats far more important than outright bhp on the road.

So although 'adding' a turbocharger only gave 20bhp it doesnt tell the whole story.

You can safely up the boost to 12psi with a manual boost controller, it gives a big improvement in mid range and turns a tardy car into a swifter one.

406's and Xantia's are heavy cars, and to make them perform you need to do more than the basic mods of boost control, exhaust and filter. By perform i mean faster than 15 second quarter mile times.

whats the average bhp increase when running 12psi boost from standard? 170bhp from the standard 150bhp?

jason1987 wrote:whats the average bhp increase when running 12psi boost from standard? 170bhp from the standard 150bhp?

Yes i would say that would be about right, the best thing about getting rid of the original boost control valve is the increase in torque, specifically mid range which does make it quicker point to point. Your not going to get much more out of the standard turbo unless you can cool the inlet charge significantly, and then you'll br running it out of its range, remember it was specced for driveability and smoothness not outright power.

i would change intercooler first, cause the original sitting near rad.
give car more air and decat exhaust, change fuel regulator + boost controller. these mods shouldnt cost alot and improve bhp.

I'm getting another Activa tomorrow which will see the following mods.

Boost to 12psi on MBC

Air-con and rad removed, massive intercooler to be fitted replacing the stock. Stock is OK at standard boost though. Generally all intercoolers sit in front of the radiator, once your moving air goes through this first, then the air-con rad, then the radiator. Heat soak is the issue rather than the position. Shielding must be made to ensure air is properly channelled and doesnt go past the intercooler/rad at speed.

2,5 inch exhaust, single box at the rear, decat.

Fuelling to be checked on the rollers after to make sure its safe, aiming for around 190bhp/210lb ft, to be run on V-Power 99 only. Its doable, as someone has got 180bhp/200lb ft just from putting the boost up.

Beyond that, your going to need a bigger turbo. Might as well get a Volvo T5 15g as it bolts straight on but will need a different downpipe made up as the outlet is different.