gt25r

LotusCarlton.co.uk

VXR8

BACK

The following describe some of the modifications and problems I encountered while
fitting garrett GT25R turbo chargers. These turbos differ in one major aspect
in that they have ball bearings instead of journal bearings. Claimed spool up is quicker
because the bearings offer less friction resistance, the geometry for the turbine wheels
and compressor wheels are improved too. Also, because they have ball
bearings, they need less oil for lubrication, which in turn means the oil feed is restricted,
which also means less chance of seal leakage........a major problem I've seen in
almost every LC/LO........smokey exhaust at tickover. I'm not saying now that these are
the magic answer, but it was time to try something different.

1. Flange modification updated 30/08/05

5. Dry fit on car updated 10/02/06

8. Dump Valve updated 07/03/06

9. Down pipes updated 19/02/06

11. Oil feed pipes added 08/03/06

13. Some early results added 08/04/06

So what are the turbo's currently fitted ?

2 Garrett T25's

Part numbers:
TB2544 (Garrett#) 452038-0001 (Lotus Part Number) P530.4021.851AF
TB2545 (Garrett#) 452039-0001 (Lotus Part Number) P530.4021.852AF

Looking at http://www.melett.com/ data sheets provides:-

I always thought that each turbo was mechanically the same, just the clocking positions were different.

Some of the housing/cover part numbers differ too, but I'm not convinced they really are physically different.

Tech specs for the GT25R:-

Std T25 compressor map

A rough rule of thumb, for each 9.5 - 10.5bhp we need 1lb/min of air flow.
This equates for 377bhp, 18.85lb/min each turbo. (using 10bhp per 1lb/min air flow)
I think (because I don't know for sure !) that looking at the maps the GT25R has a little
more capacity in reserve than the T25 the top end of it's range, to get 430bhp then air
flow needs to increase to around 21.5lb/min

GT25R compressor map