Boost and Bushings

[jeepmor]

I'm trying to find the STI mounts. The numbers I had were wrong at the dealership. I had ST41022AS000 and same ending 010 for left/right. Subaru didn't even have the number.

I'm not sure which STI model matches our mounts, but I guessed at 15 WRX STI, but didn't make an order. Subaru parts counter gave me a number of 41031VA000 and same ending in 010. He couldn't find N group or anything when I asked. I was kind of puzzled, am I looking for a Aussie/UK part instead that's not on US books? I'm confused.

Moreover, what STI year range match the BRZ/FRS platform?

[Decep]

ST41022AS000 and ST41022AS010

When i bought these, cheapest place was rallysportdirect. Maybe a Japan part number? You don't want to pay their markup anyways.

[jeepmor]

I had those part numbers, thanks for confirming. Went to Rallysportdirect, punched in the number and got it. Still puzzles me the dealer couldn't find it, but oh well. Thanks for sending me the right direction. Just ordered them.

We're having a cold snap in April here in the PNW, those TorqueSolution mounts really lay on the NVH when cold. Look forward to alleviating that, as much as I like them, I have to peel back a level for my car.

[jeepmor]

Just had the Group N mounts put in today. No more parking lot speed NVH. The Group N put the power down well, but nothing like TorqueSolution mounts that I just took out. Definitely lost some of the racecar feel and sound because the TS models were so direct and stiff with 75 durometer bushings. Lift or press throttle with the TS mounts and you had instant decel/accel feel. The Group N makes the in/out throttle response softer and not as direct or instantaneous. Group N feels about 1/2 as firm and the in/out throttle feel is no where near as good as the TS mounts.

Again, this car is a SC'd commuter and wanted to get better bushings, but went too far with the TorqueSolution mounts. I like how they drive, but the NVH was just a bit much for my daily. I hate rattles, these created a lot of them at takeoff and driving at parking lot speeds.

Next, I'm going after the bushings that mount to the rear of the diff. Bushings are still too soft back there even with the Whiteline insert kit. Saw STI parts for that. Can anyone comment on that end?

I have the MCA traction kit, just haven't got it in yet. No time today.

[jeepmor]

Recent updates

STI Group N engine mounts traded out for the Torque Solutions. NVH is gone. In/out throttle isn't as crisp as the torque solutions.

I was still having suspension hurky jurkies occasionally in first when trying to feather the clutch around the parking lot or freeway start stop traffic. The Whiteline insert kit helped, but I still had a problem Still not happy, I ordered a Cusco rear diff brace.

Just installed it this morning. Took about an hour from start to finish in the driveway. You cannot use the Whiteline kit and the Cusco brace together. Pull your LCAs down for access, worth the room to reach inside the rear housing to mount the bolts.

I'm impressed, it appears it fixed that occasional diff flop, clutch chatter, wheel hop suspension bind I was getting in the back. And there is no discernible difference in NVH, really impressed with that. I have to admit I was a bit nervous thinking I was going to reintroduce the Torque Solution level NVH. You can still feel the deflection of the whole system, it's just stiffened quite a bit stiffer and no longer floppy soft feeling in first gear.


In the end, my boost and bushing journey has landed me here.

JDM STI engine mounts
Whiteline trans bushing insert
Whiteline rear diff outrigger mount bushings
Whiteline rear subframe insert bushings
Cusco Rear diff brace

I do attribute my low speed problems to my South Bend 350 ftlb clutch. It bites harder than the OEM rating and deflects the bushings more making this issue more prevalent. I put the clutch in before the boost and don't regret it. But it took these parts to make the new clutch and boosted power feel similar to the OEM car manners again.

The Torque Solution motor mounts are a bit too stiff. I couldn't find any softer urethane bushings for them. 75 durometer only, a 50 or 60 might be a good compromise, but I haven't found them yet. I also appreciate them for what they are, true race car gear. Their driving feel was really superb, the NVH was just too much for my commuter. As for the Whiteline diff inserts I removed, these were a big help, but still too soft with the stiff clutch. The Cusco brace really shines here now. I was nervous I'd bring more racecar NVH into play, but that was a pleasant nothing burger. NVH is same as it was before. The stiffer bushes in the rear have me hearing the diff more, but it's not obnoxious like the TS motor mounts could get.

[jeepmor]

Still have the herky jerky behavior with this setup when you have to feather the clutch too much. Still not thrilled, too soft in 1st.

Looking for feedback on Whiteline, Megan Racing or similar full bushing changes. I see solid aluminum inserts like the whiteline urethane insert kit, but just for other cars.

Megan Racing
https://www.rallysportdirect.com/par...-diff-bushings

Whiteline
https://www.rallysportdirect.com/par...-diff-bushings

I've seen STI bushing for these mentioned, but cannot find them on any JDM resource I have reviewed.

[Decep]

I never solved the herky jerky problem at low speed. These cars have it stock, and adding boost and an aftermarket tune i guess doesn't help. Doubt it's your clutch tbh.

At cold temperatures it could be pretty bad if i wasn't careful.

[jeepmor]

Originally Posted by Decep

I never solved the herky jerky problem at low speed. These cars have it stock, and adding boost and an aftermarket tune i guess doesn't help. Doubt it's your clutch tbh.

At cold temperatures it could be pretty bad if I wasn't careful.

I didn't have these issues before the higher rated clutch, which came many miles before the HKS supercharger. The harmonics are the issue with the bushings.

Leaning toward Megan being they state their urethane durometer and I have the subframe bushing connection to buffer the extra stiffness they'll bring. Might be Torque Solution race gear all over again, not sure. Still appreciate that ripping racy feel the high durometer brings, but I'm going for touring car, not a track car.

[jeepmor]

Originally Posted by Decep

I never solved the herky jerky problem at low speed. These cars have it stock, and adding boost and an aftermarket tune i guess doesn't help. Doubt it's your clutch tbh.

At cold temperatures it could be pretty bad if i wasn't careful.

I didn't have these issues before the stiffer clutch. The first gear low ratio really brings it out. May not pose the same issue as the motor mounts going stiffer due to the subframe connection providing some NVH barrier as well.

[StraightOuttaCanadaEh]

The jerky first gear is a problem when grippier tires are fitted. I just went from summer to winter tires and the jerkiness went away. But I am putting in diff bushing inserts on the weekend so that should fix the problem for good

[Calum]

Originally Posted by StraightOuttaCanadaEh

The jerky first gear is a problem when grippier tires are fitted. I just went from summer to winter tires and the jerkiness went away. But I am putting in diff bushing inserts on the weekend so that should fix the problem for good

Are you sure it wasn't cured by more compliant side walls? Remember these cars were designed for some pretty compliant tires.

[StraightOuttaCanadaEh]

Originally Posted by Calum

Are you sure it wasn't cured by more compliant side walls? Remember these cars were designed for some pretty compliant tires.

Definitely possible, not an expert. All I know is I didn't have this problem when I had the Whiteline diff bushing inserts installed. Then I took them off cause they were making my 1-piece driveshaft vibrate at higher speeds and it became jerky. Took off the driveshaft and that made it even worse. Now the inserts are going back in