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Turbo Information, Feel free to add any info or websites that you might know or have

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The science of Turbos is enough to cover several books and then some. Please consider this a simple introduction and if you would like to do further research refer to the books and web links below.
Before we get started on the turbo, it would be helpful for you to have a basic understandings of a couple things. First of all, turbochargers make torque, not horsepower. Horsepower is a function of how much torque the engine has at a given RPM (ie. It is speed related). In order to increase HP without increasing torque, you will need to increase the RPM. Most of the wear, tear, and abuse in a engine is going to come from increasing the RPM because of a simple law of physics: Force increases with the square of the speed increase. In simpler terms, as you double the speed of an object, it's force increases fourfold. These are the forces that tend to tear an engine apart not add power so be aware of that when you design and build your engine. They are also the same forces that require you to spend the big bucks on the expensive high RPM parts.

A much safer and cheaper way to make the car go faster is to increase it's power output while staying in the same RPM range. This can only be done by increasing torque. With a properly sized turbo you could double the torque of the motor at a given RPM while only increasing the peak force on the engine 20% or so. Yes it sounds far fetched but here's how it works:

Keep in mind that the pressure in your combustion chamber is a combination of the how much pressure your piston created when it compressed the fuel mix and the pressure from the burning mix. This fuel mix will burn in your combustion chamber at a certain speed depending on mixture, pressure, and other factors, but for simplicity sake just be aware that it does not burn instantly. In a combustion engine the peak pressure is reached near the top of the stroke when only a small portion of the fuel mix has burned. After that point the piston is accelerating downward and the cylinder pressure drops off rapidly while the fuel is still burning.

In a turbo engine under boost, you may have twice as much fuel mix in the combustion chamber, but since it does not all burn at the same time this additional pressure does not add much to the total cylinder pressure that would have existed in a normally aspirated engine. Now as the piston is accelerating downward there is more burning fuel in the combustion chamber and this burning fuel mix pushes harder than a normally aspirated motor. This is where the real power increase in a turbo takes place. At about 90 degree crank angle the turbo engine's fuel mix is pushing on the piston 3 or 4 times harder than a normally aspirated engine would push. The pushing pressure is still less than the peak pressure which occurred near the start of combustion so it does not create the "overload" to the engine that most people would expect.

Ping, pong, knock, detonate: When the turbo compresses air, the air gets hotter. Most of this heat is due to a law of nature that says when you compress something it will get hotter. Some additional heat is due to inefficiencies in the turbo itself. What's important to understand is that the hotter intake temperature increases combustion chamber temperature. The higher combustion chamber temperatures, higher pressures, and higher compression speeds (RPMs) can lead to deadly detonation. Detonation can be thought of as a spontaneous explosion in the cylinder, rather than the more desirable even burn. It is for this reason that you must use good quality fuel especially at higher boost pressures and never ever let the engine detonate. Fix the source of the detonation immediately.
So you see that while the peak pressure in the cylinder has not doubled, the average pressure pushing on the piston over the entire stroke has doubled. This higher average pressure translates into more torque at the rear tires at the same RPM.

If you've read the previous sections, the above may also help you further understand why the racers use low compression motors with turbos and why turbo cams have different valve timing. In short, you want as much fuel/air mix as possible in the combustion chamber and you want it to push on the piston harder and longer.

As an added bonus, a properly designed turbo car will be more drive-able at low speeds than an equally fast non-turbo car with the same size engine. Remember turbos like relatively docile cams. The low overlap turbo cam will provide better low speed driving and more low speed torque than a high overlap "race" cam. When you hit the gas and the turbo kicks in though . . . watch out.

27,927 Posts
Discussion Starter · #2 · (Edited)
One of the problems a lot of people have with turbos is the dreaded Turbo Lag. How do you pick the right turbo for a motor and and how do you minimize turbo lag?
Lag: Some define turbo lag as a big hole when coming off of idle. Others define it as when you come into boost. With a carb suck-through setup, you will have a big hole off of idle, and to get rid of it, you usually have to be about 2500 RPMs. With fuel injection, there is no hole, it just runs like a naturally aspirated engine until you get to enough RPMs to build boost.
You will never have instant power off of idle unless your running a blower. Even a good running naturally aspirated engine will not pull good until it gets into the RPM range where the cam can do it's magic. Same holds true for a turbo setup.

Until you get to the point where there is enough air going through it, it cannot produce any boost. Do not confuse this with a stumble off of idle. I think the lag that the carb boys talk about is the lean-out stumble, or hole off of idle. Fuel injection works just fine as if the turbo wasn't even there until you get to the point where the turbo starts to push the engine, then of course, the engine wakes up and the fun starts.

The point where the turbo comes in depends on a lot of things, cam, compression ratio, design of intake and exhaust manifolds, and the turbo itself. Different snail shell housings change the "Turbine Map" of when and how it pushes air. The lower the AR number(.42, .48, .6, .8 etc.), the less CFM it takes to get it going. The disadvantage of too small of an AR number is that you will exceed the limits of what it can push at higher engine RPMS. You want to match the output of the turbo to that of the cam profile of your engine. A good example is say you have an engine that you don't want to go above 5500 RPM. Well, for a VW 2276 with an Engle Turbo grind of their 120 cam, using the Chrysler T-3 off of a 2.2 Liter Daytona, the engine will be into full boost by about 2400 RPM (12 PSI) and by the time you get to a little above 5000 RPM, the engine starts to quit pulling so hard, kind of like someone put a nail in the tach. What we found out to be was the exhaust was starting to back up and couldn't get out fast enough, to produce more on the intake. This is where the "Pumping" losses take over. To correct this, say I now want my engine to go to over 6000 RPM (providing that the rest of the engine stays together), all I need to do is change the exhaust snail shell from an AR of .48 to .6. What I just did was slide the turbine map upward. Now what happens is I don't make full boost until about 3300 RPM but hang on all the way through 6000 RPM!

Pay attention to what kind of motor you want. From the example above you can build a good play motor with good bottom end and loads of fun at the top, or, by changing the cam, and other engine components to handle extreme RPMs, you can build an 8000 RPM engine at the cost of loosing bottom end. So again, are you a drag racer, or all around play car?

Use the IHI RHB52 or Ford Probe turbo for anything under 1835cc's. Use the Chrysler T-3 for 1915cc's and bigger. On big engines or high RPM engines, you will have to change the AR of the exhaust to a larger number so it will not exhaust lock on you. Exhaust lock is when no more exhaust can get out, so no more boost can be put in. These are things that the individual has to play with. If you just start with these initial pieces, you will be happy. Then start modifying and you will see what effects what and when.

When you find a turbo at the junkyard, what should you check before you pay for it?
When you go to the the junkyard, do an overall assessment of the turbo vehicles. Look at their mileage, pop the hoods and focus on the best one. Check to make sure there is oil in the motor, and look for signs of obvious engine damage. In my opinion, it's better to find a car with obvious body damage because that will tell you why the car is likely in the junkyard.
Remember, the turbo charger was typically an afterthought to the auto manufacturers so it will be stuck wherever they could find a little bit of space. Before you bust your knuckles taking it off, pull off the air intake and put your fingers on the shaft. It should rotate smoothly all the way around without the blades rubbing on the housing. Now move the turbo shaft side to side. A little tolerance is built into the oil bearings so it should have slightly noticeable play. For sleeve type bearings, look for less than .022" side play which is a noticeable wiggle, and less than .008" end play which is not very noticeable. (A match cover is about .015" thick to give you an idea) If there is too much play, the turbo is either shot or needs a rebuild. Also check for signs of the blades rubbing on the housings, chips and rough edges on the blades and check the turbo outlets for signs of oil leaking past the seals.

Disconnect the wastegate rod and check the operation of the wastegate valve. Look for signs of major cracks on the wastegate port and check for a good sealing valve. Small cracks are to be expected on the wastegate port but if they are opening then scrap the unit or buy it for parts.

Pull off the oil lines and look for heavy deposits of charred oil in the ports. Heavy deposits may indicate that the turbo has had a rough life. Watercooled turbos will probably be in better condition.

The turbo will usually be tucked away in a tight space and the exhaust nuts may be rusted tight. Now would be a good time to spray the nuts with penetrating oil and look for other parts in the yard. When you remove the turbo, keep the oil lines on because they will help keep the dirt out. Whether you use them is up to you, however keep this in mind: That small line on the top of the turbo is the life blood of the turbo. You do not want a cheap or worn line to fail.

Depending on the application, some turbos may have an exhaust outlet that makes a hard bend toward the exhaust pipe. The housing I have seen are cast steel not cast iron so they can be cut and re-welded if need be.

While I'm thinking about it, remember to take a look at the ports where the intake air and exhaust flow through the turbo. If you see any roughness from casting marks or other defects, polish them out before installing the turbo and get a little more free performance.

Expect to pay between $35 and $100 for a used turbo at a junkyard.

Bypass Valve:
The Bypass valve is installed between the turbo and the Butterfly valve. The purpose of the bypass valve is to release the pressure on the output of the turbo when shifting. What happens is when you are racing up the hill, and the turbo is putting out full boost, then you take your foot off the pedal to shift gears, the air pressure can't go down into the engine, and the turbo doesn't have any exhaust driving it anymore, so the air tries to go back out the way it came in. Sometimes under high boost conditions it can actually unscrew the nut holding on the compressor turbine wheel. Anyway it either stops the turbo, makes it go backwards, or at least it slows it down. Now the turbo has to start all over again to get back up to speed.
The fix is the bypass valve. It has a sensor hose connected below the throttle plate. This valve is normally closed to the outside world. When a high vacuum signal shows up, like when shifting gears, it pops open, and blows off the extra boost. As soon as the vacuum signal goes away (like putting your foot back on the gas), it closes and the turbo did not see any back pressure this whole time, so it stays spooled up ready for action.

Turbocharger Vehicle Application Table
This list is by no means inclusive. Please note turbos such as T03 and RHB5 are "family" names. Within that family you will have somewhat similar max air flows, but different boost characteristics. There is no best turbo for any given engine because that depends on the driver, the engine, it's volumetric efficiency, the vehicle, and your right foot.

For each turbo that you may choose, you also have the option of different A/R ratios, different wheel trims and different housings. These aftermarket options will change the airflow and efficiency characteristics of the turbo to suite your particular application. Generally speaking, the turbos that you find on the typical consumer car are designed to provide moderate boost in the mid RPM range. If you desire higher boost levels at the upper RPMs, then look for a turbo off a vehicle that has a slightly larger engine.

27,927 Posts
Discussion Starter · #3 · (Edited)
Turbo Vehicle Compressor A/R Turbine A/R Notes

IHI RHB31 Chevy Sprint 1.0L Possibly good size for smaller motorcycle engine or a twin turbo.
Under 1835CC:
RHB52 84-86 Ford Escort
Ford Laser, Capri

pre 91 Mazda 323, 626 or MX6, RX7

87-88 Thunderbird*


84-86 Mercury Lynx

84-87 Isuzu Impulse

85-90 Isuzu I-Mark

85-90 Chevy Spectrum 1.5L (RHB521)

Ferrari GTO
Fiat Spyder
Generally found on 1.6 to 2L vehicles
One distributor has told me that the bearings are too small on these and that Garrett Turbos are easier to get parts for.

Good for 73-208 HP

Turbine Wheels: VJ20 - 1.8L Mazda GTX

12-R - 1.6L Mazda

Subaru: 15-R or 20-R

RHB models have been replaced by RHF

*Late 80s T-Bird has a higher flow compressor wheel. Could Boost 2.3L to 13-15psi to redline

**Early WRX models had slightly larger RHB52

Warner ISHI
RHB52 VJ11 89-91 Ford Probe
Garrett T2 84-86 Pontiac Sunbird GT 1.8L
88-90 Pontiac Sunbird GT 2.0L

1990+ Ford Fiesta 1.6L Engine 8.3:1 CR

Pontiac J-2000

Over 1912 CC:
Garrett VNT15 New VW 1.91 TDI Bugs or can be bought aftermarket
Mitsubishi TD04
Some 88-89 Volvo 740,760 others used TD05

Volvo 940 2.3L used TD04H-13C-6

Volvo 850 T5 used TD04HL-15G-7

Volvo S70 and V70 used TD04HL-13G-7
smaller compressor and smaller shaft than Garrett T03,
Identifiable by bend in wastegate arm.
Flow at 15psi for different compressor wheels and exhaust housings:
TDO4-9B-6CM2 / 265 CFM TDO5-12A-8CM2 / 320 CFM TDO4-13G-5CM2 / 360 CFM TEO4-13C-6CM2 / 360 CFM TDO4L-13G-6CM2 / 360 CFM TDO4L-15C-8.5CM2 / 390 CFM

Compressor Flow Maps

Mitsubishi TE04H
Similar to TD04??
88-93 Chrysler (Turbo 1) 2.2L and 2.5L
After 1989, 2.5L turbos had larger exhaust outlet
Smaller and faster spooling than T03. Exhaust Flange interchangeable with T03

Uses small shaft and small bearings.

Turbo Info

Garrett TB22
300ZX Twin Turbo T3 Housing
50 Trim T25 Housing
.53 manual
.48 auto
62 Trim
Garrett T25 1990 and later Volvo 740,760,940
(some of these also had the TD04), 95-xx 2nd Generation Mitsubishi Eclipse, Talon (Manual), possibly Nissan after 93
1990 and later Saab 9000T

89-90 Pontiac Grand Prix 3.1L V6
.80 .68 good for 125-210bhp, maybe up to 250HP
Garrett TD05H 14B 90-94 Mitsubishi Eclipse, Talon, Laser Slightly larger than T25
Garrett T03
AiResearch 83-84 Ford
Thunderbird, Mustang GT .60 .48
T03 Compressor Maps

Garrett T03
(60 Trim??) 85-86 Ford Thunderbird .60 .60

(The compressor AR numbers may be reversed)

Garrett TB0344 Mercury 85-86 Capri, Cougar
Merkur 85-88 XR4Ti
.60 or .62?? .63??
Turbocharger Map
Not watercooled.

Garrett T03
45 Trim 84-87 Chrysler 2.2L (Turbo1) .42 .48 84'-pneumatic dual port wastegate actuator
85'-87' computer controlled single port wastegate actuator.

used on Non-intercooled cars 7.5-10PSI boost stock


Turbo Info

Garrett T03
40 Trim
Pre 90' Saab 8 Valve 900 and 9000T Compressor Map
Some Saab owners will swap the compressor wheels with a 60 or super 60 trim

Garrett T03
45 Trim
Pre 90' Saab 16 Valve 900 and 9000T Compressor Map
Garrett T03
(modified?) 1987-1990
Chrysler 2.2L (Turbo II) With Intercooler
86' Shelby Omni GLHS .42 .48 1986-1988 have weak wastegate actuators springs.
1989 switched to bigger exhaust outlet and better wastegate actuator

Exhaust housing marked with M4 (some 1987-1988s) is less prone to cracking than M3


Turbo II

Garrett 25 Variable Nozzle (VNT)

89 Chrysler Shelby CSX, 90 Le Baron GTC, Shadow ES, and Daytona Shelby
(Turbo IV)
High Output .48 .63 variable Excellent idea but carbon on moveable vanes can lead to sticking and overboost.

(very rare but Garrett may still have some new units)
Read This
Garrett TB03
(50 Trim??)
91-93 Chrysler
DOHC engines (16 valve) Intercooled
Spirit RT, Daytona IROC RT
(Turbo III) .52 .48 Larger compressor wheel and housing
Stock engines rated at 225hp



Turbo III

Garrett T03B Volvo 240
pre 87 740,760
(40 Trim??)

.48? Factory Volvo 240s had between 127 and 162HP
Garrett T04

Whether this one will work on a typical 2276 depends on the specific model, AR ratio and trim. No other data yet.
Over 2500 cc:
Warner ISHI
RHB6-A 88-92 Isuzu MPR Truck 135-322 HP
probably best for a 3 Liter


642 Posts
i thought that the wrx's ('93 till 2004) ran a mitsubishi turbocharger (early models ran a td05 and mid 98 onwards ran a smaller td04). the ihi units are used in sti's, and they are the vf series of turbos, not the rhb.

other wise, sweet thread, mods should make it sticky.

Premium Member
4,971 Posts
SixSick6 said:
good info deserves to be read, and posting a link usually isnt the best option, usually no one clicks a link
Yeah, but without the link @ the end, it's a forgery. I know you had good intentions.

4,334 Posts
black_tx5 said:
i thought that the wrx's ('93 till 2004) ran a mitsubishi turbocharger (early models ran a td05 and mid 98 onwards ran a smaller td04). the ihi units are used in sti's, and they are the vf series of turbos, not the rhb.

other wise, sweet thread, mods should make it sticky.
Maybe that is only in Aussie... because I know that the earlier subaru's (Liberty's etc) had TD05's....

642 Posts
tripharn, i did say the earlier ones ran a td05.....either you missed it or meant a tc05 (used em on the cordias, good turbo for the day).
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