I've spent the last couple of weeks researching this very topic, although I am interested in using a MegaSquirt. I THINK it should be doable, but I haven't yet found anyone who has done. If you guys do go down this road and make progress, please post it here.

DropDead, how far into this project are you?

 

And another question for anyone, but maybe DropDead knows, are the front 5 lug hubs and 4 lug hubs the same Inner Diameter and spline count? Will 5 lug hubs bolt right up to my 4 lug car?

 

I checked the specs for a 2004 Ion 2.2L on RockAuto, and looking at the Moog hubs for 4- and 5-lug, the number of splines is the same (33), but just about all the other specs are different. The 5-lug hub flange diameter (where it fits into the knuckle) is 136.9mm, vs 131.8mm for the 4-lug version. So it's not a direct bolt on.

 

Thanks OldMarine!

Also on RockAuto, the they only have the left side GM knuckle, but it shows the same part number for Ion (4 lug) and Ion Redline (5 lug), which I had looked at previous to posting here, and implies that they use the same diameter hub. They have both sides by Dorman, and those are different part numbers, implying that the hubs are not directly interchangeable. So maybe if I were to buy a set of the correct knuckles for the 5 lug hubs then I cold bolt them up and since you verified that the spline count is the same, maybe? Anyone know if that would work to adapt 5 lug hubs to my 4 lug car?

 

I'm going to try and cover everything you just asked in this.
I'm not far along. I have an explosion of parts, and my rack got taken up by my buddies Honda that blew up. I've been collecting parts for years though as deals came to be.
My previous ion was 5 lug swapped.
I swapped the rear axle/beam out of a junker cobalt SS I bought. Had to use the rear disc e brake cables and I believe I needed new soft brake lines. So yes, I rear disc swapped as well.
Car was a 5 speed. And as the redlines only came 5 speed, front hubs were a direct swap. Axles/splines fit correctly. I don't remember off hand of the automatic axle splines are the same or not. I don't see why they would be different as GM has always been cheap. That car was also non abs, so I just plugged the abs holes on the hubs.
Overall simple swap I pretty much did in an evening besides needing to order those rear brake lines.
That's another thing. I swapped to front redline calipers/pads/rotors as well. Notice a difference with braking? Nope.
03/04 you can get away with a bit more in the bolt on aspect then the 05/06 due to them being iat cars vs MAF cars.
My 04 was a custom true 3 in intake, ported throttle body, 2.4 big runner intake manifold, 27# injectors, full exhaust. I was getting ready to cam it when the trans blew. I swapped that, then the engine started knocking, swapped the engine, lost that and 2 other cars in a fire.
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Thanks DropDead!

Didn't mean to hijack the thread. I recently bought a rear axle assembly and brakes out of an '04 Redline and am planning to swap that all in to my '04 sedan soon. Fortunately I also got the e-brake cables. Trying to decide if I should just run the rear drums with the 4 bolts, or go to 5 bolt all the way around. Also considering running the Redline disks all the way around, and getting the rotors drilled to the 4 bolt pattern. Thanks for the info, its very helpful!

 

Go 5 lug all around. The cost of redrill will be more than the cost of just swapping hubs. Check out Detroit axle. That's where I get most of my parts from for pretty cheap.
It's an easy enough swap to just do it and not look back

 

Dropdead you have a DM.

 

I have a 03 sedan, they run the same setup. Mine runs but slaps and taps. Same goal in mind eventually I want to swap the trams. Ac works and all it'd sick to lose a nice car with no rust

 

Biggest difference in 03/04 is speed density vs MAF
What's your goal?