ah i see, so 385 bhp on a T34.48 is on low boost and nice and safe

where as 400bhp on the .63 is dangerously high boost.

Phil do you realise why the boost is lower on the modified engine? does it mean the turbo is making less air flow? or simply that the engine is now happily using even more air, so the plenum pressure drops even if the turbo is working just as hard as it was before? or maybe even harder!

 

The .48 can flow safely the amount of air a yb can consume ie around 350 max however a .63 at 400 means higher boost due to the engine restrictions, the .63 would produce 400 at a lower boost if engine is heavily modified thus safer. Thats how i see it??? The .48 spools up really quick but runs quickly out of breath, i always likened the .63 like a t4 very lethagic but diesnt run out if puff.

 

But mike is saying the T34.63 on a modified engine running 400bhp will fail in a short time.

Just because the plenum pressure is lower it doesn't mean it's safer, or that the turbo is working less hard
It just means VE has increased due to the engine mods so the engind uses more air, the turbo can still be pumping just as much volume of air even more so if the power has gone up. It can still overspeed.



I think the T34s in all forms are very well suited to relatively std spec engine. Start porting heads and fitting cams and you start to ask too much from a relatively small compressor and it will start to work too hard.
If you are at the stage where a std engine T34 is not enough, then there are far better options for turbochargers at that point than a T34.

 

T4 ftw, big bang for your bucks

Steve

 

Somebody who actually gets it .

 

What Mike has ACTUALLY said, is that 371bhp is less safe on a .63 housing than 385bhp is on a .48 housing.


Which is what I obviously think is total and utter bullshit.

 

Thats not actually correct for this specific example.

In the case of a changing of back housing it does actually mean that for the same (in this case 385) BHP the turbo is now working less hard to flow that much air at the same rpm the engine was making that power at before.

The reason that the plenum pressure drops in the first place for the same engine at the same power level when you fit a larger exhaust housing is that the back pressure created by the turbo drops.
This drop in back pressure results in a drop in engine pumping losses which means that the engine can now make the same power with less boost.
If you look on the compressor map you will find that flowing the same air but at less boost will result in a drop in turbo speed.



Not to flow the same 385bhp that Mike says was safe on .48 housing but now wont be on a .63 housing it doesnt.

For the same volume of air the speed will drop, for a larger volume of air it will increase.



Im sure we all agree on that one, unless you have some sort of homologation restriction the t34 isnt a good choice of turbo for a modified engine really.

 

IF that power is made at the same peak, THEN you are correct. IF that power is made further up the rpm range, then you are the one talking UTTER horseshit .

You keep making the assumption that the figures are made at equal rpm points when this is clearly not the case. The bigger turbine moves the entire powerband 500rpm higher, which means the 0.63 a/r is working harder due to the extra rpm range it is operating in.

I can't believe you cannot grasp this simple fact and instead are changing your arguement to suit how you "think" a 0.63 works, rather than looking at dyno sheets to actually see what it's operating range is.