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Pitch stop rod upgrade not pointless, but it is noisy!


Gripless

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Ok so Ive been having a think about this, and looking at the AWD system used in Subaru compared to say an Audi system.

The Subaru system has direct connection to the gearbox/engine, similar to a FWD car, Where the Audis have another driveshaft/diff. So in essence the torque form the Subaru system will have a twisting/rotation of the engine same as a FWD, so the pitch stop seems to help with keeping the engine and gearbox from becoming out of line with the rear drive shaft.

You could run without it but I would think that the engine and gearbox mounts will fail faster.

Thats my 2 cents worth

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But in other fwd cars the motor pitches (forward, backwards) due to the crank being in line with the front drive shafts. Even stationary revs in neutral will pitch the engine.

The Subaru crank is 90 degrees out from the front driveshafts so the main force is roll. But again the mounts are in place to stop that.

Though isn't that the AWD vs 4WD having a seperate transfer case box that can split 0/100 to 100/0 or disengage half the drive train.

 

@SpeedySub it could be to keep the driveshaft in line as you said but maybe limits factory mount movement. 

Now you've said that it maybe a secondary damper or movement limiter to the engine mounts. Explains why it's not overly strong as it's just taking part of the load at the extremes.

 

 

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On 07/02/2018 at 1:04 AM, boostin said:

 

You had your answer days ago.

On 07/02/2018 at 1:04 AM, boostin said:

Front axle torque lifts the gearbox and engine.

 

Edit - front axle torque tries to rotate the engine and gearbox assembly backwards, engine up and gearbox down. Yes pesky prop shafts and whatnot also get in the way, but the torque reaction is there.

 

Edited by boostin
Phone double post
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6 hours ago, Gripless said:

@boostin So is the upgrade worth it and what improvements would you notice?

Depends if you're a cheap bastard like me, and power levels, driving style/habits etc. I would expect a better launch, possibly better acceleration, but with increased NVH. 

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Pulled sti rod today.

It's glass fibre reinforced plastic so actually pretty strong.

The little end hardly moves forward and backwards. It does pivot to allow the engine to rotate.

The large end is soft rubber and moves about 4mm under about 75kg.

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That 4mm is one way so on rebound the engine can move the same so about 8mm travel in total. 

The way the bush is designed the insert kits wouldn't do much as the solid rubber section where it moves is very soft.

Edited by Gripless
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As for the aftermarket rods, this is what I've noticed in two days!

 

Pluses

  • off throttle slight bucking like bunny hopping is almost eliminated, not that it was bad before
  • inside front wheel skips and squeaks more on polished concrete so guessing less drivetrain loss somewhere
  • handbrake seems to be a little more effective (not sure how)
  • gearshifts at high rpm changes are way more positive, finding the gear is easier
  • acceleration may be increased but doubt to a point you could measure it, though more aggressive power delivery and reduhced loss when high rpm shifting
  • engine start seems quicker from cold
  • raspy almost boxer rumble engine note
  • feels more solid over sharp bumps, engine has solid mount to the chassis now

 

 Minuses 

  • masssive increased noise. Both engine and gearbox. On deceleration you can here the gear whine. On acceleration above 3500rpm it gets loud. It's like race car loud, with no sound deadening, sharper raspy engine noise comes through the whole firewall and Drones a fair bit.
  • on startup you can here the firewall mount creaking
  • gearshifter vibrates a bit more
  • pretty sure the firewall mount is taking a hammering and may fail prematurely
  • did I mention the noise? It's like a droning exhaust, in town it was fine but longer higher rpm driving its loud, about 4 times the engine noise. Luckily it's mostly above 3500rpm so not horrible at 100kph cruising
  • its like driving with the window open, more white noise with the engine noise mixed in

For $65 and 30 minutes that anyone should be able to do.

(2 bolts for rod and intercooler takes... 2 bolts, 2 BOV bolts, 2 pipe clamps, 2 hose clips, and 3 pipes that pull off)

 

If you can deal with the noise and future firewall mount rewelding it's makes a noticeable difference and is worth the money.

 

ps I already have sti group N mounts and the whiteline diff and gearbox/shifter mounts all replaced. If you don't you make get bigger benefits and more noise.

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3 minutes ago, Subru said:

Where did you get yours from?

Just got a kW one since they had the lowest price is case I didn't like it.

 

I may get another type though as while the results are good the noise is getting irritating fast.

that or modify the kW one to allow some twisting and hopefully reduces the noise.

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  • 4 weeks later...
2 hours ago, Jono24 said:

Is there any difference between the 5 spd and 6 spd pitch stops?

(I have a clunking sound during engine braking which has occurred since my 6 spd trans swap.)

Sent from my E5823 using Tapatalk
 

 

Not in my experience, put an ebay one in my gc8 with a 6 speed, can't remember what it was meant for but fitted fine. 

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I had a glass fibre one on a car I used to own, didn't seem to have as drastic an effect on NVH as Gripless has said. Have a solid alloy Whiteline one floating around, might biff it on when I fit a front mount next week and chime in.

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