Asiandude

Hi everyone
Like the title says, my S4 auto needs a new engine and my only choice at the moment is the motor from a scrapped GT (hotter cams and a faster idle at least). Is this practical? Or can I simply put my original S4 cams in and turn the GT motor into an S4 one? I see from the Parts manual that the GT heads are a different part number to the S4 ones so that may not be possible.
Anyone any experience with this?
My S4 engine is M28/42, the GT is M28/47
Thanks for any advice.
Joe.

fraggle

Bah flop in the GT and you'll be fine. Don't bother switching cams and such.

soontobered84

I don't think you'll see a higher idle if you use your original computers (LH and EZK)

Asiandude

Thanks. I'm thinking that the 675 rpm idle with GT cams might be a struggle.

blown 87

That is easy enough to fix.
Find some one who has sharktuned a GT and buy the UVPROM they took out.

fraggle

+1 it will be a ton easier than a cam swap. But if you want to get rid of those GT cams I'm sure you have a lot of volunteers.

the flyin' scotsman

The idle speed is controlled by the LH eprom and in an auto gbox car provides the necessary 'stronger' idle when in reverse or any forward gear.

Leave all alone and drop in the GT engine . IIRC the flywheel will have to be swapped......good luck.

Asiandude

Ok, so the consensus is just drop in the GT engine and keep with the S4 LH and EZK? The GT it came out of was an 18,000 ml abandoned pile of misery in guards red. You guys would be saddened at the state of the many 928s here in Brunei (not much left on the road now).
My original engine suffered hydrolock which cracked #6 cylinder, so I have S4 heads (already skimmed) and cams etc as a back-up.
Best
Joe.

Rich9928p

Joe,

If you find that you need a higher idle for the GT motor to run well, just change the S4 EPROM to a GT EPROM. I can provide one if you need it.

Kaz

I, or rather the shop I used at the time did this very swap on my 89 S4 a few years ago. We didn't change cams or anything else, it all just bolted right up. The GT was a manual of course and my 89 was an automatic.

Things I noticed, it was much louder, so much so that my then gf wore ear plugs for highway cruising. Second, it was just a much faster car. I could keep up with certain cars that I previously could not. Someone gave me the right price and I sold the car, new owner wrecked it within 4 months.

The donor car had 80,000 some odd miles on it, my 89 had over 220,000 at the time.

Rob Edwards

Huh. I presume your '89 was white? Mark Anderson bought that wrecked '89 and I bought the GT engine out of it. It's now the stroker engine in my GTS. Did the shop rebuild the engine? It had an oil pan from an '83 on it, and the main bearings had been replaced before, when I pulled it apart.

The guy after you did a real number on that car.

John Speake

The "problem" with a GT idle speed in an S4 with auto box is that you don't get the 50rpm idle speed drop of the S4 (from 675 to 625rpm) This is to reduxce the "clonk" when you engage 2,3,D or R.

With a GT LH EPROM you'll be sticking it in drive at 775rpm. "Big clunk" This can be quite unpleasant in everyday use.....

Lizard928

But John,

Putting a GT engine into his S4 he would likely be using the S4 LH and therefor have the lower idle.....

jon928se

That may not be a good thing - don't higher lift/aggressive cams like the GT ones not like slow idle speeds - leading to lobe pitting etc.

daveo90s4

My understanding is that the GT head casting and the late S4 head casting (1990/91) are the same, with the main difference from earlier castings being some additional 'meat' / stengthening in the later heads. If that is indeed the case then your earlier (??) (what year is your S4 engine by the way) S4 cams would fit in place of the GT cams, and you would have the lower idle with the S4 LH eprom matched with the lower lift cams etc.

You could I guess make sure that the GT cam cover bolts are easy enough to undo before fitting the GT engine in the car, then drive the car and if necessary / desireable swap the cams over later?? Just a thought.