Top Speed Increase for 1Z Engine

Hello,

Is it possible to increase the top speed of a 1Z engine without engine tuning? I'm particularly interested in modifications that might slightly reduce acceleration, but potentially achieve a higher top speed (possibly even at the same maximum RPM). Is it possible (in layman's terms) to install a different gear ratio or something similar?

Hello Edward,

There was already a discussion about a longer 5th gear here, even with part numbers. However, I don't know if those parts would fit in your gearbox -> the search function is your friend.
Tires with a larger rolling circumference are likely to be cheaper and easier to install (if you happen to need new ones).
The Ulfs calculation tool includes a calculation of tire rolling circumferences on the second page.
You should check what is registered in your vehicle registration document, or ask your TÜV (technical inspection agency) what options are available regarding rim and tire sizes.

Best regards, Rainer.

Hi,

For the 1Z (90 hp), the aerodynamic drag (air resistance and rolling resistance) is likely the main factor limiting the maximum speed. I don't know of any 1Z that reaches its maximum RPM in fifth gear on a flat surface (at least not in its stock configuration)!!
If you extend the overall gear ratio or even just the fifth gear without any modifications (tuning, weight reduction, improving the drag coefficient...), your car will likely become slower.

@Bertil:
Well, that could be it... I certainly have that feeling myself when I try to reach the top speed. On a flat road, I'm slowly reaching 180 km/h according to the speedometer. That should correspond to about 173 km/h according to the vehicle registration document. However, if there's even a slight incline or invisible headwind, I have more problems (-> 170-175 km/h according to the speedometer). Do you also have a 1Z? How is it for you? Have you modified it? Can a lower ride height result in a better drag coefficient?

'I would have said: adjust the fuel injection pump to increase the maximum engine speed. However, this would also require increasing the idle speed. But if the maximum speed isn't even reached in 5th gear, then it was probably just a cold engine, right?'

joergs wrote:

Adjusting the fuel injection pump to maximize the engine speed will also likely increase the idle speed.

Huh? He has a TDI engine, and if it weren't, you wouldn't need to adjust the idle speed either.

Sorry, I probably didn't explain myself clearly. Of course, it's a process; increasing the upper RPM limit also increases the lower RPM limit! Is that better?

Hello,

I don't want to overstep, but how about you try starting with a sentence in German first?
I don't understand what you mean.

Best regards, Rainer.

Okay, so about the German language...

My friend has an Audi 100 2.5 TDI with the MKB engine. He also experimented a lot with things like that. Eventually, he went to a Bosch service center, and they somehow adjusted the injection pump. They increased the locking speed by about 100 or 150 revolutions, which made a difference. The result was, first, an increase in the idle speed, and second, a top speed that was about 5 km/h higher.

If needed, I'll ask about what and how exactly? Is that better?

P.S.: Of course, a prerequisite for this is that the engine is also capable of reaching the upper RPM.

What is the production year and original horsepower of the Audi 100?

Sorry, it was an A6 model from 1995 with 140 horsepower.

Okay, but with a proper TDI engine, I don't understand the procedure. Why would you adjust anything directly on the injection pump? Shouldn't the engine control unit (ECU) be responsible for the rev limiter? Or is it still the same as with a TD engine, where the injection pump determines the rev limiter?

Stukov wrote:

So, when it comes to a real TDI, I don't understand this procedure. Why would I need to adjust anything directly on the injection pump? Shouldn't the engine control unit be responsible for the shut-off? Or is it still the same as with a TD, where the injection pump determines the shut-off speed?

Hi.

You are correct, at least for VP37 engines (I don't know what it looks like for VP 44 engines).

You can only adjust the fuel injection curve ("RWG characteristic curve") at the pump itself, which would result in injecting slightly more fuel than the engine control unit expects.

This can result in a slight increase in the rev limit, in addition to a few more horsepower.
However, this approach puts you in a precarious situation, with one foot in the "jerking" problem and the other in the error memory (due to exceeding the RWG tolerance range).
More details can be found in the technical article about the RWG.

edward wrote:

@Bertil: Well, that could be the case... I certainly have that feeling myself when I try to reach the top speed. On a flat road, I slowly reach about 180 km/h according to the speedometer. That should correspond to approximately 173 km/h according to the vehicle registration document. However, if there's even a slight incline or invisible headwind, I have more problems (-> 170-175 km/h according to the speedometer). Do you also have a 1Z? How is it for you? Have you modified it? Can a lower ride height result in a better drag coefficient?

Wow, I'm not going to complain about a poorly performing 1Z anymore! Mine easily reaches 170, and I struggle to get to 180, at which point it's completely done (speed read from the navigation system - speedometer shows just under 190 - hopefully!). I achieve these values with the auto-hold box turned off. With the box on, it easily reaches 180, and then up to 185, sometimes even 190 - it depends entirely on the weather.
Lowering a vehicle can have benefits, but it doesn't necessarily have to. Similarly, a front oil cooler can be advantageous, or it might not be.
By the way, the vehicle is in my signature, and you can see it as a 2.8T on the picture on the right .

I have 205-size tires on - could a corresponding loss of top speed be the reason? That's almost 10 km/h difference, is that really possible? (I have to say, these are Vredestein Sportrac tires, size 205/60R15, which of course have a lot of grip).