Anthony Hyde's Volvo TURBO information page - last update June 2007
Garrett ball bearing turbo, Flange dimensions, Lotus Turbo Exhaust Housing

Mitsubishi Evo turbines - advanced backward curved impeller

Turbo Bearing Checks for excessive play - floating SLEEVE TYPE (not ball bearing type)

General tolerances - Sleeve bearings - (access the shaft from compressor air-in end) -> typical maximum shaft end play (thrust) (back and forth, not sideways) is 0.008"inch or 0.20 mm (play should NOT be noticeable using your fingertips). Shaft side play no more than 0.022" inch or 0.56 mm (very noticeable sideways movement using your fingertips). The oil pressure should self-centre the bearing within wear limits. Too much play would result in the blades rubbing the side of the housing. Look out for wear (small chips, rough edges ) on the very tips of the compressor blades that give an indication of your air filtration quality over the years, and for rub marks on the alloy turbo housing from scraping outer side blade edges. Rough tip edges should be carefully smoothed if possible.
It has been stated that
approximately 40% of all turbocharger failures are oil-related. Contaminated or dirty oil leads to bearings being scratched and scored resulting in excessive wear and premature failure. Lack of lubrication due to low oil pressure to turbocharger bearings (even a momentary loss of pressure) can quickly cause overheating and damage to the bearing system.

Regular synthetic oil and filter changes are essential for long turbocharger life. A magnetic sump drain plug is also recommended.
Dimensions of Exhaust Manifold flanges for Garrett T3 and T25:

Garrett TB03 mount flange four attachment STUDS are on rectangle 85 mm x 45 mm c/c apart - typical flange outside dimensions are approx. 90mm x 82mm.
Garrett T25 mount flange four attachment STUDS are on rectangle 72 mm x 40 mm c/c apart - typical flange outside dimensions are approx. 92mm x 62mm

Latest and greatest - Garrett anti surge compressor housing #BBGT 30375. Click to enlarge. Act quick if you see one for sale.

Typical Garrett Exhaust housing with internal wastegate

Free flowing 3" exhaust exit form Garrett Turbocharger

Good exhaust builders can fashion up some neat custom pipework. Pre-cut flanges, like in the picture opposite, can be bought from turbo suppliers to give the exhaust builder a good accurate head start to form his pipework around.

On completion, spend a lot of time to carefully hand file dead-flat the new welded 'exhaust to turbo' flange before bolting-up. We don't want any deadly exhaust flange leaks do we.

Use bearing blue (or a texta) and a very flat piece of metal (or sheet of glass) to indicate the high spots to file down.

This diagram of an exhaust housing conveys the general idea.
(Pic by Paul Grimshaw)


A/R =The Area / Radius ratio
A = Area of throat at intake
R = radius of scroll in the housing of either the compressor or exhaust turbine

TRIM -turbine wheel trim can effect an increase or decrease in turbine pressure for a given housing A/R

A Turbo COMPRESSOR produces heat (exothermic). An INTERCOOLER strips heat out (endothermic)

TURBO Exhaust HOUSINGS - Garrett

LOTUS ESPRIT (TB03) exhaust housing (Made by Garrett) also fits the Volvo Garrett Turbo centre cartridge & features a much better placed internal wastegate positioning for better exhaust flow, plus the best feature - a large 3" dia exhaust pipe exit
A Ford Cosworth exh housing is reportably similar to the Mitsubishi used on the Volvo 850 Turbo (TD04HL-16T)

In 2004 it was discovered in Sydney Australia that a 'LOTUS ESPRIT Turbo' (2.2L, 16V, 246 hp, 1988 era) exhaust housing (on carton - Garrett #413617-0001, cast number on turbo 43097) is a good performance upgrade for the Volvo Garrett equipped (740) turbos. Volvo/Garrett TB03 internals fit the Lotus housing which is A/R 0.48 in size. My secret informant tells me the exhaust housing is of a free flowing design with the main outlet being approx 1/2" bigger in diameter, enabling a 3" exhaust (dump) pipe to fit straight off the back of the turbo which eliminates that much cursed 2 1/2" bottleneck. The wastegate pivot is in the main body of the housing, not on an attached sub flange that the exhaust-pipe attches too. The internal wastegate casting dia is a large 30mm and the gas exit path after the flap is also improved.
Modifications required to fit the Lotus housing to the free-flow 940T manifold are that the manifold flange step (for Mitsub) is machined off, the flange is milled a little inside to match the Lotus housing exhaust path, and that 10 mm attachment studs are used as per Lotus sizing (replaces Volvo 8 mm). An appropriate gasket fits in-between.
This info is basically for US people, as remaining spare part supplies of the Lotus housing are very limited in Australia already, with no more being imported. Anthony Hyde, Australia

TURBO UPGRADE DISCUSSION - Written by Philip Bradley, [Turbobricks]
Responding to an identification question: The 0.52 cast marking is the A/R of the compressor housing. It is not the trim of the impeller within.
From information provided, you have an 0.48 A/R turbine housing. The A/R means more on the 'exhaust turbine' end. Small ones like the 0.48 help response and are best for automatic transmissions and can be ordered in two "stages" of modification that reduce backpressure and sort of result in a compromise between a 0.48 and a 0.63. The 0.63 will spool up slower, but has the potential to make more power due to less restriction. It works well on manual trans, and can also be ordered in two stages of modification (that probably compromise a 0.63 and a 0.82, which would be too big for a street 2.3 liter). There are only two turbines, and I think Volvo uses the larger one, so you don't have to worry too much about that.

At the compressor end, the A/R does not mean so much. It is the trim of the impeller that is most important. You have a 50 trim now. A 60 trim will flow significantly more. A ball bearing centre section doubles the price and can be bought only as part of a new turbo, so figure on $1400 or more. They increase response, reportedly at least as much as would be gained by using one size smaller impeller trim, so you can get more power potential without sacrificing response.

A 60 trim T-3 compressor will support an easy honest 300 Net Hp, enough to push your Volvo around 104 mph in the quarter. A stock 50 trim will still comfortably get you to 95-98 mph in the quarter before you should really break the piggy bank. From Bill Watson, USA.

Choosing the perfect turbo is hard. I would tend to go for response, particularly on an automatic. In daily driving, having boost at 2,500 rpm rather than at 3,000 rpm or 3,500 rpm, is really nice. You may even end up with a car that is faster except at the dragstrip or under specific conditions like 4-6,000 rpm in the upper gears at full throttle. As we have recently read, even the much smaller turbos used on 90-95 cars can turn very low 14 second quarter mile times at 95-96 mph. I doubt they can do much more than that, however.

If you want more, you will probably have to sacrifice some response. If you want to deviate from the standard T3, a few shops are modifying the more modern T28 (which is a little bigger that the T25 that was fitted to some 90-95 cars and smaller than the T3 that was fitted to many 81-89 cars). Check out the Flyin' Miatas website for more information.

If you are hoping to modify your engine to handle about 300 hp, you sort of straddle the biggest T3s and the smallest T3/T04E hybrids. You can go either way to get up about 325 hp efficiently. I am not sure which way is better. I have seen magazine reviews of turbo upgrades on cars, where at the same boost level, the larger turbo adds about 30 hp. It does so because it is more efficient at the higher flow level so the pressurized air is cooler. But there is almost always a downside - slower initial spool up. My advice is to accept some, but not too much, slower spool up. In other words, if you make a giant jump in turbo sizing, the decreased response will be pretty dramatic, but if you make an impeller trim increase of just one step, you may not even notice it. END.

COMPARISON between a Garrett TB03 and Mitsubishi TDO5 Turbocharger

Question by Anthony Hyde : I compared the Garrett TB03 & the Mitsubishi Turbo units on the workbench and they are dimensionally nearly exactly the same. The compressor blades were quite different though. The Garrett had the tricky convoluted spiral, whereas the Mitsub had the old style straight blades. Do you have any comment or knowledge on the Garrett vs Mitsub change?

Answer by Paul Grimshaw in Canada (author of Volvo Performance Handbook): The difference which you noted in the impeller design between the Garrett TB 03 and Mitsubishi turbo chargers is very important and helps explain the different ways in which these turbos work.

The Garrett's convoluted spiral blade design is known as a backward-curved compressor impeller. In this design, the blade elements are not arranged in a strictly radial pattern, but are curved backward from the direction of rotation. This blade style is designed so that the air entering the impeller is at the same angle as the pitch of the blades. This reduces the shock losses at the inlet and allow the impeller to operate very efficiently at high rotational speeds. Despite their efficiency, however, these type of impellers do not exhibit as high a pressure ratio as radial-patterned impellers. Furthermore, centrifugal force at high speed tends to bend the spiral blades at their roots. So in essence, a turbocharger equipped with a backward-curved impeller helps an engine produce power in the upper-end of its rpm band (where its high efficiency in best appreciated), but is subject to severe stress which may affect its lifespan.

[ Extra comment; A turbocharger equipped with a backward-curved impeller reduces the shock losses at the inlet and allows the impeller to operate very efficiently at high rotational speeds that in-turn helps an engine produce power in the upper-end of its rpm band (where its high efficiency is best appreciated.]

The straight, or radial impeller as used in the Mitsubishi, provides a higher pressure ratio at low rpm than the Garrett. As turbine speed increases, however, the straight blades give rise to inlet shock since the slower intake air strikes the intake's high-speed turbine blades at a sharp angle. This reduces compressor efficiency at high rpm. A Radial impeller used in housing of the same area ratio as a backward-curved impeller tends to result in improved low-end engine torque, but with less overall potential for power.

Interestingly, we see these two types of impeller designs being used in different ways in industry. Jet engines tend to use backward-curved impellers due to their high operating speeds. Large volume industrial blowers (such as those used in ventilation) use straight radial impellers.

It is likely that Volvo switched from the backward-curved and straight radial to improve the low-end response of its turbo motors. An added benefit, however, is that the (straight) radial impeller is cheaper to cast -- making the Mitsubishi turbocharger more cost effective. Given the strengths and weaknesses of each design, I would prefer the Mitsubishi turbo for street use and the Garrett for track use. Given that most Volvos live on public roadways, I would say that the decision to use the Mitsubishi turbo was wise.

Ball bearing turbo - GARRETT GTBB25 TURBOCHARGER upgrade (Fitted to B230FT)

The A/R .60 compressor and exhaust housings are so much larger than .45 size

On Road Comments: The conventional 45 trim Garrett T25 provided good boost levels at low rpm, and packed real mid-range punch between 3-4,500 rpm, falling off soon after. The larger 60 trim Garrett GTBB25 Ball Bearing turbo is a larger air-pump that spools up fast, giving boost from lower rpm. Garrett claims ball bearing models are 40% faster on spool-up, a fact I was counting on, as I did not want to 'lag around' by loosing bottom end grunt coming out of tight corners on the hillclimb track.

Left - Garrett GTBB25 'Ball Bearing Turbo'. High flow A/R .60 gives output rated at 250-300 HP. These special BB turbos are 'Made in Japan' by Garrett, and use a mix of GTBB30 compressor and exhaust sizings. Note the T25 uses a smaller attachment flange than a T3 (see flange info below).Weight - 13.2 lbs (6 kg).
The use of a smaller exhaust housing combined with latest wheel impellor design is part of the trick for rapid spool-up with these newer models.



Right - Old Garrett T25 A/R .45. Was still alive after many years of 'both' friendly use and abuse. 45 trim seems miniature compared to 60 trim.
Weight - 8.8 lbs (4 kg)


Good Link - Pro Turbo in Finland
Technical Link - general article clearly explaing the following
Compressor bypass valve (CBV) / Turbo Blow off valve (BOV) / Dump valve / Vent valve

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