TDI rev limiter
- Thread starter jayb1103
- Start date
cage
Top Post Dawg
- Joined
- Mar 25, 1999
- Location
- lakewood, ohio
Diesels are naturally rev limited. They lose the ability to inject and ignite the fuel at anything more than 4,000rpm. About the only way to redline them is if they ingest oil from a blown turbo then they'll really rev!
Slave2school
Top Post Dawg
Cage, I really have to dissagree with you on that one...maybe a tdi startst o lose the ability to inject fuel much past 4300 rpm or so, but that isn't true for all diesels. Diesel fuel will ignite plenty fast enough for revs past 8k, you just have to inject it much earlier than our pumps could ever allow AFAIK.
whitedog
Veteran Member
Interesting question. Interesting due to that 1999.5 number. Where does th at come from? Redline is 5100 or 4700 depending on the model.
rdkern
Top Post Dawg
- Joined
- May 21, 2004
- Location
- Humboldt Co CA
- TDI
- Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
One test of the MAF is to put the foot down while in neutral and in the driveway, and if the engine stops at 4700-4900, the MAF is probably bad. Should go to 51-5300. The ECU limits the TDI's rpms well below maximum possible for the engine.
compu_85
Gadget Guy
Tim, 1999.5 referrs to the 1999 model year A4 cars (like mine for example
the 1999 A3 cars are just '99s)
I believe the redline is 4700, but it looses major steam around 4000.
I believe Jeff of Rocket Chip is working on increacing this on his car.
-Jason
I believe the redline is 4700, but it looses major steam around 4000.
I believe Jeff of Rocket Chip is working on increacing this on his car.
-Jason
Birdman
Top Post Dawg
- Joined
- Apr 7, 1999
- Location
- Near Hagerstown MD.
- TDI
- Jetta 2001 Died by Truck one snowy day. Jetta 2003
Mine with chip (Unnamed) redlines past 5200 RPM ANd would go more if i let it.
whitedog
Veteran Member
Oh. That makes sense now. Sorry, I made a mistake and assumed there was a typo. Thanks for clearing that up.Tim, 1999.5 referrs to the 1999 model year A4 cars (like mine for examplethe 1999 A3 cars are just '99s)
I believe the redline is 4700, but it looses major steam around 4000.
I believe Jeff of Rocket Chip is working on increacing this on his car.
-Jason
cage
Top Post Dawg
- Joined
- Mar 25, 1999
- Location
- lakewood, ohio
My point is that if you are driving the car try taking the engine to redline. It will be impossible under load. Unless, like the old Subaru commercials said, "You are going down hill in a hurricane." So the engine is self rev limiting without having a rev limiter.
These are considered high speed diesels but 4,000 rpm is about it for diesels. By the time the pressure gets high enough to ignite the fuel the piston is on it's way back down. You would have to incorporate a spark plug to get higher revs like a gas engine. They are infact experimenting with just that. I was reading an article about it in an industrial magazine while waiting for an appointment.
These are considered high speed diesels but 4,000 rpm is about it for diesels. By the time the pressure gets high enough to ignite the fuel the piston is on it's way back down. You would have to incorporate a spark plug to get higher revs like a gas engine. They are infact experimenting with just that. I was reading an article about it in an industrial magazine while waiting for an appointment.
cage
Top Post Dawg
- Joined
- Mar 25, 1999
- Location
- lakewood, ohio
Oops I meant Isuzu commercials
Slave2school
Top Post Dawg
I can get my car to redline under load, not down a hill either. Flat, uphill, whatever.
Slave2school
Top Post Dawg
Indicated, never tried to make it go past that and it is an auto, to do that I'd have to put my selector into 1-2 as I can't afford the ticket I'd get in 3rd or 4th at that rpm
Maybe if the car is all warmed up come this next week I can give it a shot if there is no one around, but I'd rather not as the 12mm pump I have won't like it...
Normally the car will take it all the way to 4600 (give or take a little bit, I don't usually stare at the tach as there isn't much point in an auto, that and it is a good way to crash) when you put your foot to the rug.
I don't see why we should be trying this though, there are people trying to increase the rev limiter, and I can only guess that it is because it it indeed possible to peg the tach at 5300 rpm and they want a bit more speed form each gear before shifting. At any rate, I do not think, nor do I ever want to see my poor little car with fat pump get anywhere near 5300rpm now that I think about it!
Maybe if the car is all warmed up come this next week I can give it a shot if there is no one around, but I'd rather not as the 12mm pump I have won't like it...
Normally the car will take it all the way to 4600 (give or take a little bit, I don't usually stare at the tach as there isn't much point in an auto, that and it is a good way to crash) when you put your foot to the rug.
I don't see why we should be trying this though, there are people trying to increase the rev limiter, and I can only guess that it is because it it indeed possible to peg the tach at 5300 rpm and they want a bit more speed form each gear before shifting. At any rate, I do not think, nor do I ever want to see my poor little car with fat pump get anywhere near 5300rpm now that I think about it!
Bob_Fout
Oil Wanker
You'll find that while you can physically run at past 4600, it would be just like you hit the brakes, the car slows quite a bit, either due to horrible combustion, or the car is forcibly decreasing fuel to get back under 4600. Since out-of-gear you can go all the way to 5300, I'm betting it's the former and not the latter.Indicated, never tried to make it go past that and it is an auto, to do that I'd have to put my selector into 1-2 as I can't afford the ticket I'd get in 3rd or 4th at that rpm
Maybe if the car is all warmed up come this next week I can give it a shot if there is no one around, but I'd rather not as the 12mm pump I have won't like it...
Normally the car will take it all the way to 4600 (give or take a little bit, I don't usually stare at the tach as there isn't much point in an auto, that and it is a good way to crash) when you put your foot to the rug.
I don't see why we should be trying this though, there are people trying to increase the rev limiter, and I can only guess that it is because it it indeed possible to peg the tach at 5300 rpm and they want a bit more speed form each gear before shifting. At any rate, I do not think, nor do I ever want to see my poor little car with fat pump get anywhere near 5300rpm now that I think about it!
Folks who in-the-know with street racing etc. etc. say it's best to shift at 4000 RPM to get max. acceleration in each gear, with a stock setup.
n1das
TDIClub Enthusiast, Veteran Member
- Joined
- Jun 11, 2002
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- Nashua, NH, USA
- TDI
- 2014 BMW 535xd ///M-Sport, 2012 BMW X5 Xdrive35d, former 3x TDI owner
A4 TDIs redline at 4700RPM.
The ECU cuts fueling at 5100RPM (rev limiter) to protect the injector pump and engine.
~ n1das
The ECU cuts fueling at 5100RPM (rev limiter) to protect the injector pump and engine.
~ n1das
Slave2school
Top Post Dawg
Good stuff, so I guess now that it has been said that Jeff can tune TCU as well, if I ever get the car chip[ed it would be prudent to have him set the gear change under WOT to ~4000rpm so the poor beast dosn't keep going (like you say, it does feel like someone puts on the brakes after about 4400 in my car). As it is if I want to go really fast, as I approach about 4100 I pull my foot a up a frraction off the go-pedal and then it will shift and I get back down on it the rest of the way...rather irritatring.
Drivbiwire
Zehntes Jahr der Veteran
- Joined
- Oct 13, 1998
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- Boise, Idaho
- TDI
- 2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
A TDI can safely rev in excess of 8,000 rpm without throwing a rod, pump or anything else based on physical limits of piston speed etc etc.
The TDI is RPM limited not by a "Governor" but the smoke map. To prevent smoke due to the very small injection window required to meet emissions fueling is restricted and limited so as not to allow rpm's in excess of 5100.
At or around 4200 rpm fueling begins to be reduced. At 4600 there is a rapid reduction in permissable Injection Quantity that limits any further increase in RPM at 5100. This can be interpretted as a "Governor" but in fact its the emissions controls kicking in to prevent excess smoke.
Due to the high rpm range of the TDI motor injection and combustion must occur in some instances within 3 miliseconds, in comparison an F1 race engine running at 17,500 rpm has up to 5 miliseconds to accomplish the same thing! The TDI in order to meet emissions must reduce the maximum fuel injected per stroke since there is no longer sufficient time to inject fuel nor is there enough advance range remaining within the Injection pumps range of adjustment.
The PD motors since they are not mechanicaly limited like the VE pumps can offer more range of adjustment but you find yourself limited by peak cylinder pressure to to the extreme range of advance needed to make the motor work at much more than 5100 rpm.
When you look at a modified TDI's performance chart you can see that there are ways to trick the ECU into allowing higher fueling longer in the rpm range. I have personally gotten 5300 rpm from a TDI with reasonable smoke output and power bands continuing into the 4600 rpm range (11mm & .216 injector combinations which trick the ECU into thinking there is lower IQ values than actual).
Bottom line, RPM's are limited by the Smoke map rather than actual rpm inputs.
DB
The TDI is RPM limited not by a "Governor" but the smoke map. To prevent smoke due to the very small injection window required to meet emissions fueling is restricted and limited so as not to allow rpm's in excess of 5100.
At or around 4200 rpm fueling begins to be reduced. At 4600 there is a rapid reduction in permissable Injection Quantity that limits any further increase in RPM at 5100. This can be interpretted as a "Governor" but in fact its the emissions controls kicking in to prevent excess smoke.
Due to the high rpm range of the TDI motor injection and combustion must occur in some instances within 3 miliseconds, in comparison an F1 race engine running at 17,500 rpm has up to 5 miliseconds to accomplish the same thing! The TDI in order to meet emissions must reduce the maximum fuel injected per stroke since there is no longer sufficient time to inject fuel nor is there enough advance range remaining within the Injection pumps range of adjustment.
The PD motors since they are not mechanicaly limited like the VE pumps can offer more range of adjustment but you find yourself limited by peak cylinder pressure to to the extreme range of advance needed to make the motor work at much more than 5100 rpm.
When you look at a modified TDI's performance chart you can see that there are ways to trick the ECU into allowing higher fueling longer in the rpm range. I have personally gotten 5300 rpm from a TDI with reasonable smoke output and power bands continuing into the 4600 rpm range (11mm & .216 injector combinations which trick the ECU into thinking there is lower IQ values than actual).
Bottom line, RPM's are limited by the Smoke map rather than actual rpm inputs.
DB
DIESELprogrammer
Veteran Member
While that may be true for your car, it is definitely not for mine. My stock Golf sees redline everyday. Plenty of pull all the way to 4750rpm and beyond. I often run to 5krpm between 2nd/3rd shifts, and just barely see a flattening out of speed past 5krpm to governed.
Before I adopted DBW break-in procedures my Golf wheezed and started loosing speed at 3800rpm. It took a few weeks of continually increase shift points to get the speed loss point to increase. Now almost 2 years later – increased speed (UNDER LOAD) all the way to 5krpm.
Golf_GTDI
Veteran Member
bump... for the simple reason that this is a very good thread.