Bmsluite

iTrader: (1)

What is the normal manifold vacuum pull on the VQ35HR engine?

I am going to cap off the vac port and install an electric vacuum pump and I want it to be lower vacuum than stock for a stiffer pedal on track. Also, electric pump should take away the varying vacuum from the engine revs changing.

Has anyone does this? If not, that's ok, I am going to try it anyways.

icer5160

iTrader: (4)

This should be something available in the troubleshooting section of the FSM. I don't have a copy for the 07-08 HR equipped Zs, but I don't think the numbers would be vastly different between the DE and HR.
Cheers!
-Icer

Bmsluite

iTrader: (1)

I ordered an electric vac pump, an adjustable vac switch, and a vac reservoir. I guess I'm going to he be the Guinea pig on this one and set it up. Seems pretty straight forward. I guess this is what Porsche and audi have been doing for years which is why their brakes are so consistent

icer5160

iTrader: (4)

I think VW products do this with their clutch system as well (not sure). But I have driven multiple manual VW and Audis that have the smoothest clutch systems, very little pedal effort required and buttery smooth. The complete opposite of what I have experienced with Japanese vehicles. Maybe I'm wrong and it's not vacuum related, could be another fundamental change in design. My buddies B5 S4 appeared to have a traditional clutch master cylinder and slave cylinder setup, no vacuum lines. But what I did find odd was the reservoir for the clutch hydraulics was shared with the brakes and Audi used an internal tank partition (bulkheads) for the fluid. So perhaps it's all in their clutch pedal design or pressure plate. My brother had an 04 VW GTI VR6 6MT, that had the best feeling clutch pedal I've ever experienced. Very comfortable to drive and that VR6 sound was fantastic. I miss that car, I think it was one of the best GTI generations. The turbo model that came after just wasn't the same.

Let us know if your efforts pan out, I'm curious to know how this improves braking across the RPM range.
Cheers!
-Icer

icer5160

iTrader: (4)

Here's the DE Brake booster vacuum testing specs (procedure calls for inspecting the rod length).

1) Using a handy vacuum pump, apply a vacuum of −66.7 kPa (−500 mmHg,−19.69 inHg) to the brake booster.

2) Standard dimension when vacuum −66.7 kPa (−500 mmHg, −19.69 inHg)
With TCS : 10.4 mm (0.409 in)
With VDC : −6.2 mm (−0.244 in)



I know this isn't the exact manifold vacuum, but since the booster utilizes the manifold, I would imagine these numbers are pretty close to what you should be aiming for. I also noticed in the FSM that the line feeding the booster has a one-way check valve to maintain vacuum on the booster. In theory if this valve is functioning correctly, then you should have a very consistent brake pedal throughout the RPM range.




Take these numbers with a grain of salt since I pulled from my 06 FSM.
Cheers!
-Icer

DarkZ03

iTrader: (11)

His thing is he's on a Porsche 6/4 piston setup, which has probably changed the interaction with the stock MC/booster.
His inconsistencies are on track I believe, only time I've had inconsistent braking was when I removed one of my check valves

DarkZ03

iTrader: (11)

Funny you say that, yes the clutches are smooth in operation but I hated it SO much, as do most GTI owners.
Smooth is often vague, and does not relay info that people like for performance cars.
In the GTI (mk7.5) there are 2 delay valves, and the pedal is spring assisted on the way down and up!
That is one of the first things I did was delete one of the valves and remove the springs, ive been driving manuals for over 20 years and this car felt so unnatural, and was hard for me to drive smoothly in a spirited manner.
Even the dealer was like "you have an aftermarket clutch?" I'm like nope, this is how it SHOULD feel lol.

icer5160

iTrader: (4)

Hey Dark,

Thanks for chiming in. I agree with you, but it's all situational. As a daily driver in SF Bay Area commuter traffic, a light clutch pedal is a huge quality of life bonus. But for open roads or spirited driving scenarios, I would prefer more feedback (sensitivity) over an easier pedal stroke. A sports car trying to be both luxurious and sporty often achieves neither. I'm happy with how my Z feels, hell the whole reason I upgraded to the RJM clutch pedal was to get better engagement feedback.

Also, I just realized an error in my above post. My brother didn't have a GTI, it was a 2004 R32. One of my close friends at the time had the GTI VR6 (either a 2001 or 2002). Doh! Either way, the clutch was very soft/smooth and for daily driving in stop and go traffic, it struck a nice balance between comfort and sportiness. One thing I did not like about the R32 or GTI was how tall the front seat positions were. You got great visibility, but the higher position meant you got tossed around a lot during sharp cornering. I guess that's just the nature of a hot-hatch chassis. Not sure of the newer Focus RS, Corolla GR, or Golf R have similar setups today. I haven't had an opportunity to drive one of those yet.
Cheers!
-Icer

DarkZ03

iTrader: (11)

I definitely get that, the Zs clutch is much stiffer than the GTI, even taking in consideration that the Z is also sprung both ways I've gotten used to it over the years.
For me I feel since it's stiffer it's easier to modulate, granted my Z doesn't have the delay valve, (guess it was not on all models)
The delay valve seems to be what I don't like, I can delay it myself if need be, I don't need that assistance lol.