Big Turbo Emails

----- Original Message -----

From: John Clark
Sent: Tuesday, July 20, 2004 3:19 PM
Subject: GT28RS Vs GT28R


I'm building a V8 Lotus Giugiaro Esprit - details here:

The 3.5 litre Lotus type 918 V8 has been assembled with forged Mahle pistons (Keronite coated), ported/polished heads, an ex Le Mans Lotus GT1 plenum and a specially fabricated twin chargecooler, based on the Lotus Carlton unit. I'm expecting power of 600 bhp and over (I've sourced a transaxle upgrade to cope with this!), so the standard T25s will be insufficient and I'm sold on the quick spooling benefits of ball bearing turbos.

It seemed to me that the 2 x GT28RS would be perfect, but I'm looking for your advice on the best route.

AET Turbos in Wakefield in the UK, have a specially adapted GT28R with different A/R (housing change?) they say they've tested the GT28RS on the dyno and it's laggy on engines under 2 litres (1750 per bank on the 918) in the mid rev range - so they've got this modded GT28R that they've tested on up to 370 bhp race applications..... they say the compressor housing is large, but they've got another kit to reduce it to approx T25 dimensions, whilst only loosing a small bit of flow. He's quoted me 820 each for the lot.

You seem to quote the max flow for the GT28R differently in 2 places on your site - 290 bhp in your GTR "line-up" and 310 bhp in the buy online page - I want to break the 600 bhp for twin turbos on the V8, so do you think the GT28R would cut it?

Looking at the Garrett brochure, I also see there's also a turbine option for the GT28RS with an A/R of 0.64 - would this give me the best combination of power/spool-up?

I need the turbine/compressor inlet/outlets to match the T25 (the GT28R compressor outlet looks different bolted)

Thanks for any help - I'd love to buy online, as your prices are good and the exchange rate is in my favour! also, there doesn't seem to be much expertise on the GT28RS in the UK yet.

John Clark

>> >----- Original Message -----

From: "" <>
To: "John Clark" <>
Sent: Wednesday, August 04, 2004 7:30 PM
Subject: Re: GT28RS Vs GT28R


Our opinion is this: If you were under 3.0L, then there may be some concern, but with that much displacement, definitely go with the GT28RS pair.

Here is what we know:

- Most people only know of the GT28RS when combined with the default housing (.86 A/R) and this can feel laggy on the 1.6 and 1.8L engines. We have run the .64 A/R GT28RS on the 1.6L and 1.8L and the housing makes all the difference in the world. You are one of the few to see the potential for the .64 A/R housing and your intuition is right. We proved to the Garrett engineers that the.64 A/R is adequate for 1.8L use and still get well the 350HP mark on the single turbo application.

The GT28R comes default with a .64 A/R housing. The GT28RS with the .64 A/R hits full boost just as quick as the GT28R on the same engine even though it is "larger". The reason for this is because if it's superb wheel aero and excellent wheel match.

With the exception of where packaging is an issue, we have stopped using the GT28R in our kits and have put the GT28RS in place.



----- Original Message -----

From: John Clark
Sent: Wednesday, August 25, 2004 1:07 AM
Subject: Urgent GT28RS questions


The turbos arrived safe and sound - but I have some queries:

1) The new GT28RS turbos do not have the same exhaust outlet as the old T25s - in fact they have no output flanges at all on the turbine/wastegate output. Actually, I'm having a completely new exhaust system fabricated, so I'm thinking the V-Band adapters would be ideal:

Do you agree?

Are bolts or studs/nuts supplied?

Is there a gasket?

Would you expect the V-Band clips etc. to be commonly availble to specialist exhuast fabriactors in the UK?

2) The alignment of the oil inlet/return and coolant banjo fittings are rotated with respect to the existing T25s, if the exhaust flange is held up to the manifold. The Compressor oulet is also not aligned with the inlet pipe-work to the intercooler.

Now it looks like this rotational alignment of the turbo centre to the turbine/compressor could be altered by unbolting them and rotating - is this possible?

Would I be in danger of affecting the rotational balancing (I'm guessing not, as it's only the housing that would move)?

How is the float (i.e. gap) between the compressor/turbine wheels and housings controlled (looks like a register/groove in the machining)?

What's the torque setttings for the bolts?

Does this need to be done by a turbo specialist or can I do it? (I see you sell a GT2871R upgrade for the GT28RS that's a turbo centre and compressor housing, so I'm guessing it's OK for me to do this - maybe I need the installation instructions for this kit?)