Originally Posted by
edwardb
When talking about 4-links, I think it's important to say there are differences. Very often a "4-link build" is a straight up donor build with Mustang donor control arms, donor quad shocks, etc. This was (and still is) the most basic and cheapest build, and also deservedly has the worst reputation. Worst ride, worst handling, bad manners, etc. A very common upgrade was to replace the quad shocks with coilovers. This made them a bit better. At the other end of the spectrum is a 4-link build with aftermarket control arms, bushings, coilovers, etc. When pushed to the limit, these also would exhibit some of the 4-link bad habits. But I would agree with previous posters that for street cruising, works quite well. My first build, Mk4 #5125, has this setup. I didn't know any different at the time and drove it thousands of miles for a couple seasons with no issues. It didn't have any problems with wheel hop. It's still going strong today with its new owner. Given the choice, I'd probably agree with the comments to go with another option. But just wanted to say, in regards to the poll question, not all 4-links are created equal.
Regarding the high cost of IRS, I get asked this question a lot. My answer always is "it depends." It's possible to get a donor or salvage 8.8 solid axle for a very reasonable amount. Many do. Often they do require some work though, and usually it's not of the DIY variety. At least for many. It's also possible to buy a ready to use 8.8 solid axle (Moser, Forte, etc.) but now you're talking about much more serious money. You can buy the 2015+ Mustang IRS center section for around $800 NIB for the non-Torsen version, which is the same as most 8.8 solid axle diffs. The knuckles are $300+ brand new as well. The parts are also now pretty widely available in salvage for considerably less. It's a very different picture compared to what it was like over the last few years finding and rehabbing the older style IRS components. Yes, the IRS option adds to the kit price. But depending on the direction you go, it may not be as much of a cost adder as expected. As far as complexity, I didn't find the job of installing the various IRS parts any more difficult than installing a solid axle. Having owned and extensively driven the 4-link (mentioned earlier), a 5-link, and now the new IRS, I highly recommend the IRS. The ride is very noticeably better. I don't push my cars that hard, but I've found the handling to be outstanding with nothing negative to report. No one every wants to talk about resale value ("I'll keep this thing forever...") but there's no question an IRS build has more interest and value than a solid axle. I'd give IRS a hard look for any build.