ACE A350 Header Supporting Mods
 

Hey fellas, I'm preparing to install my ace headers and since I'll have the manifold off the engine I figured I might as well change the mushy stock engine mounts. However I read you need to change tranny mount since they both act as a single unit when flexing. I also heard about diff bushings, subframe bushings, and a grocery list of additional bushings -- my question is, what supporting mods do I need in addition to engine and tranny mounts? I am installing both (STI) for sure so any tips for additional mods is hugely welcome.

You don't NEED to really, though it's recommended.



If you stiffen up one part of the driveline, you should stiffen the rest. Once some areas become stiffer, the softer areas will take on more load and stress, potentially wearing out sooner. Motor mounts, transmission mount, and diff mounts are the most common to be done all together.


As far as subframe bushings, those are considered part of suspension reinforcement.

Remember to bang a bit engine protection pan where header may contact it. You don't need rest of bushings mentioned like tranny/diff/subframe. And if those mentioned, remember that with all of them installed NVH will noticeably suffer. If one installs just one less compliant bushing somewhere, vibrations/noises can be passed to other bushings up or downstream, reducing impact to NVH. If all bushings are non-compliant ones, all the noises & vibrations & rattles are passed to you :).
I don't have ace headers, just wanted to tighten a bit suspension & enhance gear shifting feel. Rear subframe inserts did nothing to NVH, tranny mount & rear bushing added slight gear whine at 1st & 2nd .. but when i added diff bushings & engine mounts to those, i hated result. Gear whine was much louder and now audible in other gears and on car jumps on road defect gearbox rattled a bit, clutch got noisy and awkward to use (due driveline shocks passed now to only springs in it), extra noises from engine vibration .. reverted to just gearbox mount & bushing & subframe inserts. In same way you may leave engine bushings for header, and maybe subframe inserts .. but i wouldn't go all the way changing out all possible driveline bushings. Result might be not to your liking.

Yes, i'm aware I should stiffen the rest. I just wanted to know which the rest were, I guess I'll add diff mounts to the mix. My confusion comes from the fact there are so many damn of them, like just for the diff mounts Whiteline has two different products and they don't explain what they do differently.
https://86speed.com/whiteline-rear-d...gger-mount-kit
https://86speed.com/whiteline-diff-cradle-mount-kit

Do you know which one I should use?

I didn't mention it but I also want to tighten the chassis feel. Your post settles my decision to get STI mounts to keep nvh at minimum but also have responsive feeling. I will hammer the undertray but my biggest concern is header contact with subframe so another reason to get mounts.

Which diff bushings and engine mounts did you add?

@Plumbus : TRD ones (should be same as STI ones). Whiteline subframe inserts & diff inserts. Perrin transmission mount & gearbox bushing. Now left both gearbox's & subframe's aftermarket, rest reverted to stock, and that's what going to stay long-term in relation to driveline.

Either diff mount should be fine, depending on what you're looking for. (The two you have listed are options for the Rear Diff Mounts)

• KDT925 - The "Whiteline Rear Diff Outrigger Mount Kit" should be sufficient if your stock mounts are in good shape still. They are inserts that reinforce the factory mounts.
• KDT924 - The "Whiteline Diff Cradle Mount Kit would be good if your stock mounts are on their way out or you want something more aggressive. These are complete replacements for the stock mounts

Depending on your preference, you might also upgrade the front diff mounts as well. Whiteline only offers a complete bushing replacement (KDT923), but Cusco has a reinforcing insert option similar to how the KTD925 works except for the front (Cusco 965 928 A).


Right now, this is what I have installed:

• Perrin Rear Shifter Bushing
• Cusco Transmission Collar/Mount

I'm waiting to install all the rest in one go:

• TRD Motor Mounts
• Cusco Front Diff Inserts
• Cusco Rear Diff Inserts

What an absolute BOSS of a response, thank you! This made it so much clearer and now I finished adding all needed mods to my spreadsheet. I'm about to buy the KDT922, KDT925, perrin rear shifter bushing, and mtec shift springs, just debating on buying KSR210 steering rack bushings or the Perrin steering rack lock before I order. Also bought both STI engine and tranny mounts and all of that should tighten the chassis really, really nicely. :respekt:

I think most of the folks here got it handled.

TL;DR:

- Hammer out the key points on the undertray for clearance.

- Torque everything well, heat cycle, and torque again. Repeat until hardware doesn't back out.

- Engine mounts optional, but most folks seem to like them.


Tag me if you have questions!