So, I just purchased some bushings on FB marketplace and I'm waiting for them to arrive by mail. I thought I was buying a complete set of Mazda competition control arm bushings, but looking at the part numbers in the picture I think two of them are actually Mazdacomp differential bushings. These are the ones that go on the two ears at the back of the diff.

This is perfectly fine by me, since those bushings are pretty old on my car (original to the differential, not to the car). They're definitely due for replacement, but I have been putting it off since I am going to swap the entire differential soon-ish. The new differential will also probably need mounts since all FC rubber is old now, but hey, I can dream.

Anyways, this leaves me with the question of how much NVH should I expect from the Mazdacomp bushings? I already replaced the front diff mount with OEM non-comp and it dropped the vibrations a lot while also tightening up the rear.

Any insight about the control arm bushings is helpful too, although they can't be stiffer than the poly bushings I'm using now.

 

i did the control arm bushings last summer with comp bushings, in the front. in the rear i did the subframe bushings and regular control arm bushings. my old ones were totally knackered.
so on my car its been a 100% improvement with no downsides. its quieter, and smoother. ride got better. basically you can read that as 'changing to rubber bushings from stone helped a lot'
handling is better, but of all the things it changed the least

i do have he diff bushings too, and they have been in the car since i put it together. i do like it, because it gets rid of the rubber bandy drivetrain the FC tends to have.
mine is noisy though, and i've done everything wrong here, no rear carpet, and the diff is a 200k unit and it came out of a 12 second car, so its hopefully just shagged.

 

I was in a similar spot 6 years ago, but I just used the full Energy Suspension poly kit. They work fine and they aren't terrible as far as NVH, but it's certainly noticeable.

It was always a cost-driven decision though. I didn't buy the Energy kit because I wanted poly bushings, I bought it because it was $100 for the whole kit vs $800 or so for a complete set of new OEM bushings.

I grabbed these comp bushings because the price was crazy good.

Fortunately I have full sound-deadening and carpet, so I'll probably be fine then. I am definitely getting noise from the (original) diff and subframe mounts at present, so I suppose the comp mounts can't be worse.

I have noticed the drivetrain in our cars likes to move a lot. I'm using new OEM vert mounts for both engine and transmission, and they might be a bit better than coupe mounts but there is still a lot of flex. Meanwhile there is still more vibration than a normal car at idle.

I've been thinking a lot about making a front strut brace and adding another engine mount that picks up on the air-pump mounting points. It should stiffen the engine under acceleration without adding NVH, since the engine only mounts in two places and they're both at the bottom. The whole thing can pivot quite a bit side-to-side.

 

yeah, the suspension bushings are so nice i'm thinking about either Comp mounts for the engine/trans or maybe even solid ones(!)
the FC Tweaked Power FC runs so smoothly its amazing, its making my think solid mounts might be ok.

 

I've had the Mazda Comp (MC) differential bushings, both front and rear, in my FC since 2003 and haven't noticed any increase in NVH. I've also used the MC front control arm bushings and MC upper strut mounting blocks in my FC on a couple occasions and haven't noticed much if any increase in NVH. The MC front bushings improved the car's handling. At one point, I had Energy Suspension PU bushings in the front, but after a couple months swapped them back to rubber due the increase of NVH.

 

One thing I want to do is install a MAF (I'm thinking Z32) and Rx8 air pump. The air pump is an important part of how the stock ECU helps the idle, and the MAF will just help the car run more smoothly overall.

Running MAP is fine, and it's really smooth at steady-state. But it seems to not like transients or idle and needs a lot of tweaking of the compensation tables (after-start enrich, accel-enrich, etc). Plus it's hard to find a place to put the IAT sensor where it is accurately reading the temp but not heat-soaking. I think this is why Power FCs work so well out of the box compared to other ECUs. Most of the time, people installing a standalone are also converting to MAP at the same time.

It's a poor carpenter who blames his tools, but I've spent enough time tuning it at this point that I think I've found the practical limits of the system. I want to achieve OEM idle speed and smoothness.

That's exactly what I was hoping to hear. I was concerned about taking the time and money to install the new bushings, then finding out I don't like them and have to do it over again.

 

Running solid engine mounts with a rotary is nowhere near as violent as with a piston engine.

I even forgot I’m running solid engine mounts until you mentioned them.

 

the power FC is nice because its sort of like a tunable stock ecu, AND the FC Tweak software is really good (i just log a run and hit A for autotune)
so that combo has been a nice tool set!

the Power FC is funny though, its like a carburetor, but instead of two jets (idle and main) its got 256 (16x16 table, or whatever it is). its also got a bunch of compensations, but they kind of work like the Emulsion tube on a Weber

ive thought that using a MAF would be easier too although i've never done it. i've also thought about the Rx8 air pump, but maybe with a variable speed controller? the early 2000's Fords used a fuel pressure sensor, and then a variable speed fuel pump controller, so basically they keep fuel pressure constant by changing fuel pump speed the ford ones are inexpensive because they bolted the aluminum module to the steel frame and put it under the truck, so it rusts out....
so anyways, i think one of those running the Rx8 airpump would keep the pump happy (in the Rx8 it only runs on cold starts), but also supply enough air to work for an older rotary

 

There's a lot less info out there on it than you'd think. There's plenty of info on the theory, but it seems like very very few people who run standalone EFI systems choose to go with MAF.

I'm guessing this is because more performance-oriented users are less concerned with drivability. The few people I can find running MAF seem to have had excellent experiences, and most of them don't seem to need the compensation tables.

There is also this theory that MAFs are restrictive, which is probably true. But when there are abundant quantities of 90mm Q45 MAFs, I doubt it's a real-world issue for most people.

The Z32 one should just fit into the stock intake tube, and I think the bolt pattern on the other side may even mate to our airbox outlet.

I was thinking a simple relay would do it. The OEM FC pump freewheels above a certain engine speed, and also just dumps to the silencer under some conditions (I forget which). The MS3X and most other standalones can just switch a certain output on or off depending on multiple logic conditions. The ACV and other solenoids should also all be controllable in the same way.

 

i think Mazda's SAE paper on the FD lists going from the AFM to the MAP sensor was a 3% gain, but that is the sliding cone style. i'd think the hotwire sensors would be less than that, like 1% or less
and 1% or less and you'd be better off upgrading the intake hose, its big on the outside, but small on the inside