My GTO engine swap

Hi Al.
Joe has asked me to provide a few details of what was involved in my 4g63 conversion on my gto.
It will take me quite a few posts to fill in all the details, so please bear with me.

Please bear in mind that this is not some unlimited budget build. I run my GTO on a budget, and try to keep costs down as far as possible.
Also, when I did this, I was determined to get it back on the road as quickly as possible. I really wanted to avoid the pitfall I have seen others fall into, of trying to do to much at once, and not concentrating on the job in hand. It’s all to easy to get distracted and think…while I am doing this, I may as well do this. You, almost always, NEVER finish what you set out to do!
I cut corners to get the job done. Some I wasn’t too happy with, but it had to be done, to get it running. I have been steadily working my way through them, since I got it first running.
Also, I wasn’t concerned about ‘blinging’ things up as I went. It’s another time consuming distraction, and something I decided to look at after I got it running

In summary:
My car is a 1991 GTO TT.
If I was to do this again, I would use a manual N/A to start with. You will see why as I list the stuff.

Engine is EVO 3 4G63
Prop shaft is N/A GTO complete. Only change is at the rear diff, as the bolt diameter is different . (I will explain later.)
Gear selector is N/A manual GTO
Gear lever is N/A manual GTO
Front RH driveshaft is complete LH N/A auto GTO. I think the manual one will fit also
Front LH driveshaft is a bit more complex. Mixture of TT GTO, N/A GTO and Evo 3. (I will explain later)
Front engine mount is TT GTO with the Evo 3 and TT GTO brackets welded together
The part that bolts to the chassis is same for TT and N/A
Rear engine mount is Eclipse bracket. TT mount, which is reduced in width slightly. More details to follow
Cambelt side is much more complex. Separate subject!
Starer is Evo 3
Power steering pump is evo 3
Ecu is currently evo 8, but I initially ran it on evo 1 ecu
Wiring is GTO TT, modified(not as much as you might think)
Speedo sensor is 2G eclipse. Evo 3 has a shaft drive. The eclipse unit under reads, which isn’t ideal, but I have an N/A manual one to try instead
Coils pack is evo 3, but the coils are same as gto.
Radiator is GTO TT
Thermostat housing is Evo 3, with the 2G eclipse top part(which includes the fill point) Evo 3 has this on the radiator
Downpipe is std evo 3.
Exhaust is aftermarket GTO TT I created a custom cat replacement pipe to act as a ‘joiner’ more details to follow
Oil cooler is GTO TT, with custom AN lines to std evo 3 oil filter housing
Intercooler is std evo 3, modified. Full modified evo 3 pipework.
Maf is evo 3

There is loads more, but I will add in as I remember, plus pics etc.



I used a std evo 3 diwnpipe.
Reason for this was I was certain it would clear the gearbox and transfer properly.
Happily, it lines up with the aftermarket TT exhaust I have, although there is a gap where the cat would normally sit.
The downpipe is 2 1/8" diameter, and the exhaust is 3". So I had the following made.

It’s mild steel, with an off the shelf flange. I welded it together, and coupled with a bit from my old cat replacement pipe, the adapter pipe was complete.
Works perfectly, and although there is a change in diameter, it’s getting larger, rather than smaller, so not really an issue.
Only cost £15 for the pipe, and £8 for the flamge
Longer term, I intend on getting a 3" downpipe made, but this got it running. Works fine so far


Very interesting, looking forward to the next instalment

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Front engine mount.
It’s the OEM GTO TT front mount.
The bracket is the Evo 3 OEM, which bolts to the front of the gearbox.
I modified this, and welded part of the TT bracket to it.
Works perfectly fine, despite my dodgy welding!
I have to clean it up and powdercoat it at some point

Clutch vacuum system

The Evo 3 doesn’t have servo assisted clutch master cylinder

TT GTO does.

I could have swapped to NA , but decided instead to keep the TT set up.

The Evo has servo assisted brakes, and as such, has a larger bore hose nipple on the intake plenum.
The TT GTO has a second one for the clutch.

So, I have joined the two systems together, so I can utilise the single nipple.
I used Gates hose, and cut out the NRV’s from the standard hoses, so the operating of one system doesn’t affect the other. The NRV’s can be ‘encouraged’ into the hose, if lubricated with a little washing up liquid.

Seemed like a neat solution to me, and looks pretty OEM.


This is brilliant. Thanks for going to the trouble of writing it all up :+1:


It’s not problem.
Actually good for me to do it, and have a through account of the process.
If anyone else is wanting to attempt it, i can give part numbers etc.
Much more to follow.

The 6G72 in the GTO came with an oil pressure gauge.
The Evo 4g63 doesn’t have one.

Rather than have a non functioning oil pressure gauge, I decided to fit the 6g72 oil pressure sender.
I already had the oil filter housing off as I was doing lines for the oil cooler, so did thus at same time.
Simply a matter of identifying which bit to drill and tap. The casting was already there for it.
It’s a bsp taper tap, so had to trial fit the sensor a few times, then drill a small hole in the bottom tk connect into the oil gallery.
Once flushed and refitted, I simply extended the gto wiring to suit.
Ps. I’ll find some better pics


Brave move Marty, what was the decision to do it? Is the Evo engine much more power or a different delivery of power?


The decision to do the swap was based on my factors, but cost of upgrading the 4g63 is about 20% of the 6g72.
Weight was a major factor. The swap took 150kg out of the car.
Not all engine obviously, but drivetrain etc too.
It’s MUCH easier to work on and access is good for most tasks.
Power as std is similar, but given the reduction in car mass, it’s certainly lively
Car weight currently stands at 1260kg