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Author Topic: What's the main difference between "IDI" and "TDI" engines??  (Read 44659 times)

June 20, 2009, 07:22:32 pm

Vincent Waldon

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This question comes up often, and I recently found a couple of cool pictures that help explain it.

IDI Engines:

The acronym "IDI" generally refers to "InDirect Injection.  In this configuration diesel fuel is injected indirectly into the combustion chamber via a "pre-combustion chamber" inserted into the head:



The IDI diesel engine was standard VW passenger car fare until mid 1997 and may or may not be coupled with a turbo. Engines of this vintage without a turbo are often referred to as NA or normally aspirated engines.   IDI engines uses a pintle-style nozzle that sprays fuel in a mist and are threaded into the head like spark plugs. Due to the heat-sinking capacity of the surrounding head IDI engines generally require the use of glow plugs on all but warm days. 

The fuel system for an IDI engine is almost always 100% mechanically controlled via a Bosch VE distributor-type pump, although Europe got a late version of the AAZ engine that had some vestiges of electronic timing control.  Throttle control is via mechanical cable to the throttle pedal.


TDI Engines:

The acronym "TDI" generally refers to "Turbo Direct Injection.  In this configuration diesel fuel is injected directly into the combustion chamber formed by a depression machined into the crown of the piston:




The Direct Injection engine started appearing in European VW passenger cars in 1991, in some North American Passats in 1996,  and were in general circulation world-wide by  mid-1997.   In all but rare cases the direct injection configuration is equipped with a turbo, hence the confusion some folks have thinking their turbo-equipped IDI motors is a TDI.  The nozzle sprays fuel in 5 discrete jets and is held into the head with a top-mounted clamp. Glow plugs are not generally needed until the engine temperature drops near freezing.

The fuel system on a TDI generally uses a electronically-controlled Bosch pump with an Engine Control Unit, and the throttle is drive-by-wire using a potentiometer-equipped pedal.

A primarily home-built variant of the TDI pump known as "m-TDI" uses the TDI pump body and nozzles but substitutes parts required for manual (ie cable) throttle control.

A more recent version of the TDI design, commonly referred to as "PD" or "pump duse", uses individual injector/pumps that are driven off the valve camshaft to pressurize the fuel to extremely high pressures and spray it out a nozzle with 7 holes.  North America got PD engines from 2003-2006.

In 2009 VW introduced the so-called "Clean" TDI design... a common rail system with a completely different injection system yet again.

For a variety of reasons, including more precise fuel control and fewer thermal losses, TDI engines generally obtain better fuel economy than their turbo-equipped IDI cousins. 


« Last Edit: August 01, 2022, 06:28:13 pm by Vincent Waldon »


Vince

Edmonton, Alberta, Canada
2001 silver TDI Jetta Malone Stage 1.5 , 2001 blue TDI Jetta SBIII 216s Malone Stage 3, 1970 Bay Window bus

Gone but not forgotten: 1969/1971 Beetles, 1969/1974 Westies, 1979 Rabbit, 1986 TD Jetta, 1992 gas Jetta, 1994 TD Jetta

Reply #1June 20, 2009, 07:35:12 pm

Vincent Waldon

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #1 on: June 20, 2009, 07:35:12 pm »
Great cutaways!  The Passats started getting the TDI engines in '96.

Thanks Andrew...

And, in general guys and gals...  correct at will... I'll update the top post accordingly
Vince

Edmonton, Alberta, Canada
2001 silver TDI Jetta Malone Stage 1.5 , 2001 blue TDI Jetta SBIII 216s Malone Stage 3, 1970 Bay Window bus

Gone but not forgotten: 1969/1971 Beetles, 1969/1974 Westies, 1979 Rabbit, 1986 TD Jetta, 1992 gas Jetta, 1994 TD Jetta

Reply #2June 21, 2009, 10:52:10 am

MJF

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #2 on: June 21, 2009, 10:52:10 am »
1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)
'74 VW Scirocco TD
'86 Audi 80q 1,9TDic
'01 Audi A6q 2,5TDI

Reply #3June 21, 2009, 03:36:57 pm

the caveman

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #3 on: June 21, 2009, 03:36:57 pm »
1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)
Not in North America
" I'm a vegetarian,not because i love animals, it's because i hate plants"
1970 Type 3 fastback
1972 Renault 12
1971 Super Beetle 140 HP 159 ft lbs
1987 Fox
1989 TD Jetta
1990 Fox
1989 Fox
1998 TDI Jetta
1990 T3 German MIL Transporter 1.9 na Giles super pump
1997 Jetta GLX TDI

Reply #4June 22, 2009, 10:46:25 am

foxracer1

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #4 on: June 22, 2009, 10:46:25 am »
Awesome write up. Now i can show people what i"m talking about when then ask what the difference is between the two.

Quote
Quote from: MJF on June 21, 2009, 06:52:10 AM
1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)

Not in North America
  I wish we would have gotten half of the sweet diesels from over the pond.
84 4dr Rabbit 1.6 N/A sold to friend
86 Jetta TD getting raced out AHU 02A
98 Jetta TDI Malone tune stg 3
91 S10 305 TPI T56
86 S10 2WD Prerunner project.


Now offering turbo rebuilds. HP or stock. Any turbo you have i can rebuild it for ya.
Reseal injection pumps PM for det

Reply #5June 26, 2009, 06:12:59 pm

fdnyguy

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #5 on: June 26, 2009, 06:12:59 pm »
Awesome write up. Now i can show people what i"m talking about when then ask what the difference is between the two.

Quote
Quote from: MJF on June 21, 2009, 06:52:10 AM
1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)

Not in North America
  I wish we would have gotten half of the sweet diesels from over the pond.

Amen to this, Brother. Amazing how many American* cars are over there with diesel engines. I'd love to get their cetane numbers as well in our diesel

*Yes, I know some of these cars are made in Canada..... :)

Nice work, Vince..


Stay safe, stay well. Jimmy.
Never forget what a "Religion of Peace" did on 9/11/01.

2015 Passat TDi. 27k
1998 Jetta 1.9TTDi 228k .
2002 F250 7.3 TD   63,000 miles. Sold.
1980 Mack CF Fire Engine. Working on it.
2007 Dodge MegaCab 5.9 Cummins. Nice, but plagued with issues

Reply #6June 28, 2009, 02:26:55 pm

Turbinepowered

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #6 on: June 28, 2009, 02:26:55 pm »
Later TDIs had/have seven hole nozzles, but that didn't start until the PD engines so you're probably not covering that here. :D

Reply #7June 29, 2009, 11:24:41 pm

diesel smoke

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #7 on: June 29, 2009, 11:24:41 pm »
Nice writeup Vince!  8)
'99.5 Bora TDI
'88 Fox Coupe
'71 Tin Top Westfalia Bus
'85 Mercedes 300SD

Reply #8June 29, 2009, 11:54:33 pm

Vincent Waldon

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #8 on: June 29, 2009, 11:54:33 pm »
Thanks all... I've incorporated your various (great) suggestions.  

If I ever find cut-aways for the PD or common-rail design I'll add their own sections... anyone willing to take a bandsaw to their 2009 Jetta??!!   ;D
« Last Edit: June 29, 2009, 11:57:00 pm by Vincent Waldon »
Vince

Edmonton, Alberta, Canada
2001 silver TDI Jetta Malone Stage 1.5 , 2001 blue TDI Jetta SBIII 216s Malone Stage 3, 1970 Bay Window bus

Gone but not forgotten: 1969/1971 Beetles, 1969/1974 Westies, 1979 Rabbit, 1986 TD Jetta, 1992 gas Jetta, 1994 TD Jetta

Reply #9June 30, 2009, 10:39:43 am

lord_verminaard

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #9 on: June 30, 2009, 10:39:43 am »
I'm sure there are enough people with PD engines that have lunched their camshafts, should't be that hard.  ;)

Brendan
81 Scirocco 'S -->Soon to be m-TDI
93 Corrado SLC VR6
'86 Golf N/A Diesel  -->Wife's car
1990 Audi CQ
05 New Beetle PD TDI


"I am a man, I can change... if I have to.... I guess....."

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Reply #10July 16, 2009, 11:41:53 am

sven

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #10 on: July 16, 2009, 11:41:53 am »
Very informative, thanks very much
1990 GOLF GTD

Reply #11February 12, 2011, 01:09:16 pm

spdrace11

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #11 on: February 12, 2011, 01:09:16 pm »
Wow i just got schooled.  Thanks for the info.
91 VW Jetta diesel coupe 1.6 NA 5spd, 91 Jetta 1.6 NA, 81 Caddy 1.6NA

Reply #12March 14, 2011, 12:15:31 am

blackdogvan

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #12 on: March 14, 2011, 12:15:31 am »
PD

1991 Vanagon 1.9 mTDI

Reply #13March 14, 2011, 01:14:12 am

R.O.R-2.0

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #13 on: March 14, 2011, 01:14:12 am »
the PD injectors basically operate just like a Jimmy does, correct? just has electronic correction features too?
92 Jetta GLI - Black, 1.6D w/ GT2056V turbo..
86 GTI - 4 Door, Med Twilight Gray, Tow Machine..
86 Audi Coupe GT - Tornado Red, All Stock.. WRECKED.
89 Toyota 4Runner - Dark Grey Metallic, LIFTED!

Turbo: exhaust gasses go into the turbocharger and spin it, witchcraft happens and you go faster.

Reply #14August 13, 2011, 08:00:20 am

ricosuave

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Re: What's the main difference between "IDI" and "TDI" engines??
« Reply #14 on: August 13, 2011, 08:00:20 am »
those are beautiful pictures!
Now: 00 2dr Golf TDI, 03 Jetta Wagon TDI, 02 2500HD Duramax - :)
Then: 69 SC Transporter, 84 Rabbit GTI, 87 Fox GL, 91 Golf IDI, 96 Passat Wagon TDI, 97 Jetta IDI - :(
"Everything I save by driving diesel I put back due to poor German engineering and crappy Mexican workmanship!"   :P