This looks interesting... V8 Caldina

[vvega]

Wont it change because the temperature IS different between different sized turbo's... as much as you discount it in your discussion, thats why bigger turbos exist, because it does make a difference. The point I made in my very first post was about charge density...

the temperature difference will only be significant if you're operating the smaller turbo outside of its efficiency. If it's properly specced then the smaller one wont be heating much more than the larger one.

of course when you use terms like properly specced then you cant be wrong. You have a greater probability of being outside the high efficiency islands on a smaller turbo.

well no
cant agree there
if youve read the map and worked out were you sit then you cant be outside
thats teh whole point of working it out properly
as off star trek
ya canne bend teh laws of physics

everthign can be worked out matmatically
and if it dont work out
youve $&#$% up teh equasion somewhere
those turbo's hes running wont even get into full effiancy zone till he hits about 700-1100 hp :S
a couple od tdo5's or gt28rs's woudl be there at around 250-700
thats the point i was tring to make

[4000GT]

Wont it change because the temperature IS different between different sized turbo's... as much as you discount it in your discussion, thats why bigger turbos exist, because it does make a difference. The point I made in my very first post was about charge density...

the temperature difference will only be significant if you're operating the smaller turbo outside of its efficiency. If it's properly specced then the smaller one wont be heating much more than the larger one.

of course when you use terms like properly specced then you cant be wrong. You have a greater probability of being outside the high efficiency islands on a smaller turbo.

well no
cant agree there
if youve read the map and worked out were you sit then you cant be outside
thats teh whole point of working it out properly
as off star trek
ya canne bend teh laws of physics

everthign can be worked out matmatically
and if it dont work out
youve $&#$% up teh equasion somewhere
those turbo's hes running wont even get into full effiancy zone till he hits about 700-1100 hp :S
a couple od tdo5's or gt28rs's woudl be there at around 250-700
thats the point i was tring to make

Again, yes properly sized, what I am saying is the islands are proportionally more forgiving on larger turbos.

I cant say what efficiency zone he is in as I dont have any specs other than GT35.

[4000GT]

http://www.lextreme.com/GT.html

Looks like someone has done it all before...

[vvega]

lol lextreme has been around a looooong time now

[mister2]

Pretty much sounds like its all been said RE: turbo sizing. Only thing that hasn't been clarified is the extent that turbine sizing plays.

The Garrett catalog has some turbine flow maps which illustrate it fairly well. Basically flow asymtotes with increasing pressure ratio across the turbine.

The way I think of it is that the engine makes power proportional to VE, RPM, and p(inlet)/p(exhaust) ratio. Bigger turbos lower the ex manifold pressure, so at the same inlet boost increase the p(i)/p(e) ratio.

Cheers

Nick

[Lith]

Provided your smaller turbo is operating within it's efficiency range (learn to read a compressor map), then it shouldn't be producing much more heat than the big one.

To conclude, stop making up shit and pretending you know what you're talking about.

The only way the big turbos might make the car feel more powerful is that they're so laggy that because the power increases rapidly it feels more powerful than it really is.

Thanks, I only just got back to this thread and was basically going to have a rant to this effect... so ^^^ what he said.

There is confusion about bigger turbos making more power on the same boost level, I think this comes from when people have run stock turbos on 18psi (probably pumping hot air to reach this boost level, and probably not holding to redline) and then upgraded to some larger unit which CAN flow efficiently on given motor at that boost level, ie - compressor is still efficient, or turbine is not choking the poor thing....

Wont it change because the temperature IS different between different sized turbo's... as much as you discount it in your discussion, thats why bigger turbos exist, because it does make a difference. The point I made in my very first post was about charge density...

When I was first learning about turbos I thought this way as well.... there's a lot more to learn though Unfortunately its not so cut and dried that "A bigger compressor will always supple denser air". Funnily enough if you look around at enough maps, there are plenty (if not most) cases where a smaller turbo would be more efficient (ie, denser air) at lower flow levels than the bigger turbo - hell, I'd not be surprised if GT28s on a 1UZFE would operate efficiently at a point where GT35Rs could be surging. Fortunately the 1UZ would never spool the GT35Rs hard enough to reach the surge zone at a low pressure ratio.

The reason there are bigger turbos is they have efficiency ranges which cover a higher flow area. This doesn't usually encompass a stretch (ie, still be efficient at the lower flow levels) but more like a shift across to higher flow levels, the surge point and the choke point both more or less get a shunt upwards. This is essentially why Garrett seem to like to say "Suitable for 2.5-3l" etc on their turbos, as there are certain turbos most friendly to the flow capabilies of motors in that range - ditto with ones suitable for "5l+" etc.

The reason people CAN use much bigger turbos on smaller motors and get power isn't because of the "cooler air" by default, they've made the motor breath more - basically running high lift cams and porting heads etc allows bigger turbo choices because the motor will be able to breath at a given pressure in the higher efficiency areas of bigger compressors.

Pretty much sounds like its all been said RE: turbo sizing. Only thing that hasn't been clarified is the extent that turbine sizing plays.

The thing is, you don't have different trim choices for GT35Rs. They all run the same trim compressor and turbine wheels, though different turbine a/rs. We don't even need to go into Turbine A/R matching (which I normally consider the last bit for fine tuning where/how you want the whole shebang to operate) as the thing is obviously that far off what most would consider optimal.

[Akane]

Bravo.

vvega has finally cleared it up for everyone.

[BlakJak]

Actually I think Lith's last post explained some misconceptions nicely.

Anycase, thats enough of that now I think.