Silly Turbo Question...?

[Guest]

Gents
Very confused here.. I have a friend Thomas who has an '87 Turbo ... The turbo is shafted. She is a 220bhp. He has sourced a turbo K26-8 which is from an '89 on. Hes going to fit this to the '87.

He Says
This will give me 250bhp like an '89 on. The later turbos give more boost. Its just a matter of bolting it on and thats it sorted.

I Say
He will have to change the map of the engine and boost control as the wastegate will still react in the same way. Max boost at 3.5k rpm and tailing off as the revs increase. It wont make one bit difference chaging the turbo for the later version.

We have argued the above points until we are both blue in the face so who is right ...? Me ... Him or none of us....! [&:]

 

[xenon]

I'd say you're more right than him! Certainly (and I'm no expert on the turbos. - or any of them, come to that) but there is more difference between the 220 and 250 models than the size of the turbocharger. They certainly have different maps and PET says that the cams are different too.

 

[Diver944]

It will still work okay but as it is the larger K26/8 it will spool up a bit slower so he will notice more lag. The KLR map will control the wastegate to carry on opening at the lower boost level of the K26/6 car so he will not get 250bhp.

A modified chipset (both DME and KLR) will enable him to run higher than standard boost and take advantage of the slightly larger K26/8.

Best solution (and most expensive) would be to fit a modern turbocharger, maybe ball bearing and get much quicker spool up, vastly reduced lag and a higher top end as well []

 

[sawood12]

Is that right? Given that the wastegate is the primary boost control system and as far as i'm aware the spring in the 220 turbo wastegates and the 250 turbo wastegates are the same (because the wastegates are interchangeable), so the wastegate operation will be the same. All the KLR does is to monitor boost to look out for potential problems and decide when to initiate the overboost protection via the cycling valve. I always thought that the extra 30bhp came from the fact the K26/8 holds boost a bit longer than the K26/6 i.e. more area under the curve and not necessarily from more boost pressure??

 

[Diver944]

My understanding was that the KLR controls the maximum boost pressure allowed in the system. Looking in the factory manuals is a bit unclear but it does state on page 21-10 that the K26/6 car hits a maximum boost pressure of 0.75 bar at 3000rpm but will drop down to 0.52 bar by 5800rpm. The K26/8 car also peaks at 0.75bar but it holds that level until 5800rpm and then it tails off.

The big question is whether it's the turbocharger holding the extra boost or the KLR controlling it?

 

[Guest]

Thanks for your help lads ..[]. We are for fitting the turbo this weekend (dependant on our respective partners of course []). The car is off the road at the minute and its our only option to getting it mobile again.... I'll let you all know what way it performs with the K26/8 and the standard '87 engine management... []

 

[sawood12]

Paul,
How does the KLR actively control boost though? The only control the KLR has over boost is via the cyling valve and the cycling valve is a safety device as far as I understand it. If it wasn't then how does the Lindsey Boost Enhancer work as the cycling valve would be performing the same funcion i.e. hiding the true boost pressure from the wastegate until the target boost pressure was achived?

I think you have confirmed my understanding in saying that the K26/6 and the K26/8 achive the same max boost pressure (i.e. controlled by the wastegate) but the K26/8 holds it longer therefore achieves more power as a result.

 

[Diver944]

ORIGINAL: sawood12

I think you have confirmed my understanding

Bu66er, I was always rubbish at this debating lark.

I'll be interested to see the actual result when Donal and his mate fit the new turbo this weekend. I'm wondering if the extra boost over 3000rpm will keep triggering the 220 overboost protection.

 

[sawood12]

Yes but the overboost only monitors boost pressure and not BHP, so whether your achieving 500bhp at 0.75 bar boost or 220bhp at 0.75 bar boost it is invisible to the KLR - it only sees boost pressure.

EDIT: Ahh, I see what you're saying Paul - yes it will be interesting to see if the KLR has a boost map in there as well. I know it looks at rate of boost buildup as that was what was kicking in the boost protection in my car when I was running DPW with stock chips - the boost was building too quickly and the KLR thought it was going to overboost.