Turbo Talk

Basically... i am fairly new to the Turbo scene.. (been more of a supercharger man)

Anyway i was after some info really on what the specific dimensions of my Turbo mean..

I know the T3 Flanges refer to the Mountings etc etc.. its everything else that i wouldnt mind learning a bit more about.. and maybe working out flow rates,cfms,possible hp outputs produced etc etc.

Spec of my GT25 T25/T28 :

Hybrid T25/28 with a T3 flange .48 hot side with .68 cold side,3" intake with 2.5" V Band outlet

I was assured the turbo was a gooden, which i have no doubt it is... but i myself would like to make a few calcualtions.. or atleast understand a bit about what the figures above actually correspnd to...

I hope i dont sound too thick

Shaggy wrote:Basically... i am fairly new to the Turbo scene.. (been more of a supercharger man)

Anyway i was after some info really on what the specific dimensions of my Turbo mean..

I know the T3 Flanges refer to the Mountings etc etc.. its everything else that i wouldnt mind learning a bit more about.. and maybe working out flow rates,cfms,possible hp outputs produced etc etc.

Spec of my GT25 T25/T28 :

Hybrid T25/28 with a T3 flange .48 hot side with .68 cold side,3" intake with 2.5" V Band outlet

I was assured the turbo was a gooden, which i have no doubt it is... but i myself would like to make a few calcualtions.. or atleast understand a bit about what the figures above actually correspnd to...

I hope i dont sound too thick

Not thick at all mate! I still don't really understand how to spec a turbo for an engine, or indeed how different specs affect the characteristics of an engine

I'd also be very interested in getting my head around this mysterious subject

yeah skool us turbo guru's.

this is a usfull site for turbo tech .

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CorradoVR6-Turbo wrote:this is a usfull site for turbo tech .

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That's quite a good calculator that, I'll add it to the resources forum.

Shaggy wrote:

Spec of my GT25 T25/T28 :

Hybrid T25/28 with a T3 flange .48 hot side with .68 cold side,3" intake with 2.5" V Band outlet

I was assured the turbo was a gooden, which i have no doubt it is... but i myself would like to make a few calcualtions.. or atleast understand a bit about what the figures above actually correspnd to...

I hope i dont sound too thick

Usually the above translates to a T25 housing with T28 trim wheel inside it (larger wheel). Cold side ratio will determine the overall cfm capability of the turbo (bigger more air in simpleton terms) and the hot side ratio will determine where in the power band it starts to spool (smaller the quicker spool up in simpleton terms).
You then get a whole new equation to think of and that is that a VW 16v head flows depending on casting approx 45-50% on the exhaust of the head than the VW 8v head. This would mean on a .48 housing spool up will be much quicker on the 16v head as it's shifting more air. Similar logic applies to porting the heads.

If you go on the garrett website there is some 101 tech articles that explain the working of the compressor maps. To calculate what turbo you need for your application this background maths is crucial as different engines will have different efficiency ratings based on cyl head flow, cam spec, bore size and stroke of the crank. So although opne turbo might be good for 1 type of 1.8ltr engine it will not be good for another because of the other variables.

The last time I accuratelly had to match a turbo for an unkown application it took over 6hrs of maths. So generally you tend to work out from experience based on what you know different turbo's have done on different applications.

Cheers guys! getting really interested in all this now! ;-)

Cheers for the heads up on the Garrett stuff. Just been on and had a look, very interesting site with loads of info even for a thicko like me!

Linky for everyone else to enjoy... [You must be registered and logged in to see this link.]

That site with all the Math confused the hell out of me a long time ago.