Three pondering questions on 4.6 DOHC and IRS swaps

a_penquin · 07-02-2009, 07:54 PM

Alright, first off Im working on a 98 GT. Ive been looking into swapping the straight axle for IRS from an 03-04 Cobra. From what Ive seen it looks almost like a straight bolt in with minimal modifications. I understand the cat back would have to be swapped out and possibly some odds and ends. If anyone has done this or has experience with it I would greatly appreciate it.

The second one is if they have changed heads or intakes on the DOHC engines over the years like they did with the SOHC 99 PI change?

The third deals with the donor car and both above questions. I would prefer to find a salvage cobra for the parts car for ease (like any of this is going to be easy lol) but my grandmother has a 94 Thunderbird with a 4.6 DOHC and IRS. If her car dies out before I find the parts cobra I was looking into trying to use the IRS and rebuild the engine along with supercharging it with most likely a salvaged Cobra Whipple or KB. Would the IRS swap be possible from a 94 Tbird to my 98 GT and if so any major problems that would arise during the conversion?

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Jazzer The Cat · 07-02-2009, 08:51 PM

I will address the IRS question

What are your goals and why this swap? If your goals are nicer ride for a DD, than you are good. If you are looking to run some high HP numbers for good launches on the 1/4 OR improvement on the twisties, you will be better off keeping your current SRA. Of course, you will need to invest $$$ into the SRA to out perform the IRS on the twisties, you will need to beef up the IRS to handle the 1/4. Even with IRS upgrades, you will never be rid of its wheel hop.

I say, keep the SRA and go CO's/PHB or WL and beat the IRS silly on the track AND the corners.

Jazzer

a_penquin · 07-02-2009, 10:36 PM

My goal overall is a street sleeper and DD that is comfortable both on the road and highway. Dont get me wrong its great right now, until I get a big speed bump that rattles the hole back end at 5mph. I was looking into the IRS swap due to handling and the rear pinion is starting to wear out on my straight. I was planning on control arms and better sway bars, but with the thought of the engine swap I could just bang it out at the same time with the same parts car.

Aereon · 07-02-2009, 11:22 PM

IRS from the tbird won't fit, the dohc from the tbird will, but the ecu will need to be either reprogrammed or grab an ecu out of a cobra. IRS out of a cobra is a straight bolt in procedure and if you don't have issues like we had with mine, it'll take maybe 5 hours tops. The different year cobra's/dohc's have diff heads, don't know specifics but the 00r has the best flowing heads, the termie 2nd, mach 3rd, and 99-01 rounding out the bottom.

I know they aren't in order but I was too lazy to reorganize my thoughts=P

a_penquin · 07-02-2009, 11:38 PM

Thanks for the info on the IRS. With the DOHC Im more concerned about the intake working right than head flow right now, but thanks for that bit. I just dont want to put a supercharger off a cobra onto the 94 engine and it not hold a seal.

HEAVYMETALMATT · 07-03-2009, 12:44 AM

IRS swap is a pain in the ass. I did it into an 01 GT, and in order to get it to seat up in there right I had to put jack stands under the IRS, load the car(3 toolboxes, and 2 friends) and forcefully wiggle it. It does ride like a Cadillac now though.

4.698GT · 07-03-2009, 06:44 AM

The T bird has a SOHC unless someone swapped that DOHC in there before you.

Xemeth · 07-03-2009, 07:58 AM

The DOHC swap isn't as hard as everyone makes it out to be. It's just you need to gather a bunch of little parts if you don't get an entire motor.

The 96-98 (93-98 if you include Lincoln) heads are the B heads. Not the best choice.

99/01 Cobras have the C heads, which are pretty damn good and there's tons of them floating around. I have them on my car.

03/04 Cobra and Mach 1's have the same heads, which are slightly re-designed C heads. They're usually more expensive than the 99/01 heads.

The FR500 heads are the next step up from the 03/04 heads, but are really expensive and aren't special enough to be worth the price.

Same goes for the '00 Cobra R heads. They flow the best stock for stock, but are crazy expensive and hard to find.

Here's your bible for info on 4v heads:

http://modmotortech.com/forums/showthread.php?t=295

a_penquin · 07-03-2009, 01:06 PM

Ok so let me try to see if Im on the same page, I can swap intakes from year to year, however with the port matching involved Im better to just get heads and matching intake.

Xemeth · 07-03-2009, 01:17 PM

Quote:

Originally Posted by a_penquin

Ok so let me try to see if Im on the same page, I can swap intakes from year to year, however with the port matching involved Im better to just get heads and matching intake.

No, heads and intake have to match. The B heads need a b head intake, the C heads need a C head intake. The 99/01 Cobra and 03/04 Mach 1 have the same basic intake. So 99-04 heads use one intake, 93-98 heads use another.

That guide I posted lists all possible intakes you can use for each head.