TL;DR: Looking for a strut that is suited to 4.5kg/mm front and 4k rear springs on a GC8... Planning to use stock top hats. Tired of overly stiff coilovers which are super planted on perfectly smooth roads; but rather "slow" on "real" roads due to all the slowing right down for bumps that don't even exist for other motorists! :P ..However still would prefer stiffer than stock, as I thought that feels like an SUV...

For a crappy old GC Impreza (front and rear McPherson strut), may I please ask what struts do you think would be good to pair with Manzo (i.e., Megan racing, i.e., manufactured by same company as BC) lowering springs^, which are F 4.5kg/mm, R 4.0k ?

The ideas I have so far are between used Pedders (Monroes) for $300 off gumtree (hehehe) or maybe some KYB AGX adjustables ($920 off ebay from America inc. shipping) or some Koni Yellow adjustable ($1040 off ebay from America inc. shipping); what would be a good pick? How big is the gap in quality between the AGX and the Koni Yellows?

I would be inclined to prefer the AGX if only because it's a complete strut; not an insert like the koni yellow where the stock strut needs to be cut up. Maybe that shouldn't be a big consideration?
BTW the local price I saw for Koni Yellows was $400 PER shock - talk about a rip-off!

I found the stock suspension (well they were some kind of lowering springs, but not much stiffer than stock), highly comfortable but for cornering totally unacceptable, rather SUV-like, so don't want to go back to something that soft. It's interesting to note that a subaru club enthusiast sets *very, very, very* quick hillclimb and track times in a GC STi on Kings lowering springs, which are progressive springs, with Front max rate of 4.0k and Rear max of 2.8k; obviously very effective indeed!

The stock spring rates, for reference, are around F 2.8 kg/mm R 2.6k (so I would presume that OE replacement KYB struts, or just the orginal struts themselves, would be a no-go with the Manzo springs as it's nearly an 80% increase in rate ); while if I got the Pedders "SportsRyder" strut set I would be taking out the stock 02 STi springs from the set; which are the early GDB STi rates of F 3.3 kg/mm and R 3.0 kg/mm (if I am not mistaken; >04 STi is not compatible, but these 02 struts should be compatible with the first gen Impreza; presuming I swap on the stock GC rear top hats). By the way, feel free to find it unusual that the owner replaced the OE monotube inverted STi shocks with non-inverted twintube Monroe/Pedders shocks -- presumably the stock ones were worn out and Pedders rip-off prices were cheaper than subaru genuine parts rip-off prices! :P

May I ask please also if maybe there is an entry level non-adjustable sports shock that would perform well with the Manzo springs that I am overlooking?

^ I have no idea where to get STi gymkhana tarmac springs (F 5k R 5k - which are presumably the stiffest oem shape springs for this chassis), so these are the best I can locate; any other suggestions? Or would it better to get some entry level coilovers? The existing coilovers are a bit tiresome -- they are very, very good on perfectly smooth roads -- but too stiff for some urban & backroads (certain roads and routes are fine thankfully; heck some roads are good but only in one direction! :P).

Go Konis any day...they are excellent quality and a proven strut for WRX/STi for both road and competition use (ask Jamie Lister). Combine with some suitable springs (eg Eibach, KW etc)...talk to John at John Fowler Autsports 0416 105 911. Pay a bit more for quality and reliability...

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No Subarus currently owned

Check these threads out;

http://www.perth-wrx.com/vb/mechanic...vs-struts.html
http://www.perth-wrx.com/vb/general-...et-driven.html
http://www.perth-wrx.com/vb/mechanic...coilovers.html

+1 for Konis 8610-1351 Sport front and 8610-1352 Sport rear

Only other shocks Id look at are Bilstien B8 or the adjustable KYB AGX . Had all 3 and Konis were defiantly the best all-round and good adjustability .

If you do go to the stiffer springs id go the Bilstiens as the other option . The Kyb struts do give you the adjust ability but on the highest setting I found them not a spot on match for the stiffer spring rates.

Bilsteins work well, Monroes were cheap and not worth it, came with the car and couldn't sell them second hand, so they went out on the curb.

If the Bilsteins make a clunking noise there is usually nothing wrong with them, they are a quality unit, I think they use a OEM top hat with the Bilstein body.
To fix the Bilstein clunk if you have it. My springs were a bigger diameter than the standard springs and can touch the strut tower when going over bumps or cornering. Couple of taps with a hammer where the paint was rubbed off inside the shock tower fixed my clunk permanently. I like Bilsteins on the front because they seem to cope with bumps and potholes well with the typical front end heavy Subaru, have KYB's on the back.

Koni shocks were sold to one of the other big shock manufacturers years ago, cant remember which one. The original owners who made the name famous, now use the name Ikon if your looking for high quality or custom made shocks. They will sometimes completely rebuild the shocks you have with much better internals. Found some Bilsteins at a very good price just before ordering a set from them.
Sway bar choice is important too, I make my own now to get what I want.