I've noticed my car is running underpower. It doesn't have the kick it used to have.

I can't spot any leaks and today I stuck on a boost gauge and went for a spin. The gauge read just shy of 0.9bar (probably about 0.87bar).

Would this give a significant reduction in bhp if 1 bar= 220bhp?

I'm just wondering if I'm a few bhp off target or about 20+bhp down.

Also, can I manually adjust the boost (there is a manual boost control valve fitted) to 1 bar by revving the engine whilst stationary and checking the gauge, or do I have to tweak the boost control valve a bit, go for a drive, check it and tweak again etc etc etc. i.e. do I have to be physically driving the car to get an accurate boost reading.

I'm not a modder so this kind of stuff is competely new to me. I nearly sh1t myself cutting into a pipe today to temporarily fit a boost gauge, in case I'd cut the wrong pipe

if you want to start pissing about with the boost and your not sure leve it alone our get a pro to do it for you,also you say your car feels like its under power hot wether will do that mate,

You won't get any boost when revving the engine whilst stationary, the engine needs to be under load.

On a standard engine 1.2 bar is generally agreed to be the safe maximum boost, but it's always best to get your fuelling checked on a rolling road if you have been tweaking things.

Thanks guys,

I haven't been tweaking things nor do I want to increase boost over standard. It's just that the car has a manual boost controller (only noticed the valve last week), I've just had the turbo changed the car feels a bit less progressive than before I changed the turbo.

The previous owner of the car told me that I probably need to adjust the boost slightly for the new turbo. I think I'm correct in that the boost should be 1 bar as standard.

I'll try to find a RR somewhere. It's just that they're not easy to come by in these parts. I've found one online which is about 40 miles away. Maybe I'll try and book the car in and get a full checkup.

Daithi

Which turbos have you switched from and to?

Hi MattW,

Standard knackered smokey T28 to new T28 from Turbo Technics

Daithi

You should get more boost on the same boost controller setting when switching from a knackered turbo to a new one.

Is the wastegate adjusted correctly? (pulled over by half an eye)

Are all the boost pipes done up nice and tight?

You still getting -0.6/7 bar on idle?

Pipes seem okay. The car idles at -0.6 Bar.

If there was a leak would the idling pressure be different?

Dunno about the wastegate. I don't know much about my new turbo except it was nice and shiney and weighed 6.2kg

But if the car is idling at -0.6 then does it not mean pressure is okay, it's just that the prv is closed slightly too much, hence giving the 0.9 bar reading with foot to the floor?

Maybe a stretched throttle cable?

It depends if you have altered the PRV at all, if it gave you more boost on the old turbo at that setting.

What I would do is bypass it by connecting the two pipes to each other, that will give you base boost (actuator only). That should be 0.5 bar (+/- 0.05). If it is, then just set the PRV to whatever you want and that will be fine. If it's less than 0.5 bar then you might have a leak, or the actuator might not be adjusted correctly. Then fix whatever problem is causing low base boost before reconnecting the PRV. Hope that makes sense




If the leak was between the turbo and the throttle body (through the boost pipes and intercooler) then it would not be any different on idling. If it was after the throttle body in all the fiddly places then it would normally affect the vacuum on idling, depending how much air was getting in/out.

Hi MattW,

I've never touched the PRV. I bought the car recently with a smoking turbo and I had it replaced within a week or so. I didn't even realise there was a PRV until last week when I posted a "what's this valve" thread.

I've just phoned a RR centre to get the car checked out for bhp, fuelling, airflow etc.

As a by the way, I always let the engine warm up before going over 3k rpm and I'm not a foolish driver. However, a couple of times I've accidently gone over 3k in say 1st or 2nd when the engine is stone cold (for example pulling out of my carpark at work onto a busy uphill road) and when the turbo accidently kicks in, the power is ridiculously strong like a kick in the back of the head!!! It's caught me by surprise twice.

Is that normal???
Progressive accelleration when warmed up?
Kick in the head acceleration from cold?

It sounds fine to me. You'll be 10-15 bhp down running 0.9 bar. I'd just tweak the PRV so that you are running a bar of boost - which is the standard boost.

Mine is a tiny bit more eager on boost when cold, but not that much of a difference. Always a big kick in the head, whatever the temperature

I dont give it beans when it's cold, just the odd split second like you say.

When it's cold then it seems to be taking more effort to spool up the turbo below 3000rpm, doesnt feel very smooth, but after a minute or two it spools up brilliantly.

When the engine is cold it wont perform. You should not ask it to....end of story - leave it off boost until it's warmed up.

I know that suba. If you look at my post you'll see that the "cold" boost I mentioned was only momentary and completely unintentional. Like I said, I always let the car warm up properly before doing any spirited driving and I always let it cool sufficiently before switching off.

I'm not that

I was not having a go, but the car will always run differently going from closed to open loop fuelling, i.e. off boost to on boost when it's not warm.

Cheers Suba

I would get the car rolling roaded anyway, to make sure it's performing as it should when it's hot

If the turbo is a hybrid it may have quite different characteristics to the std turbo and may require more boost to be as efficient as std (e.g. cut back turbine wheel)

Std boost was 1.1 bar falling to 0.6 bar at the redline (which is base boost).

As far as I know the new turbo is simply a T28 (made to T28 spec at least).

At least that's what I ordered...

I'll leave everything as is and get the car RR'd next week.

Is std boost not 1.0 bar falling to base boost 0.6?

no 1.1 bar is std.