The 6G74 Conversion - what you need to know.

Why put a 6G74 in my N/A?
The increased displacement means plenty more downlow torque. The proper engine to use, from a 1992-1998 Mitsubishi Debonair pumps out an impressive 191 kW or 256 hp according to Wiki (I’ll confirm this myself when I hunt down a debonair brochure!) So not only does the bigger engine produce more torque, but it also produces more power. It’s a win-win situation!
Advantages vs Disadvantages

Advantages of a 6G74 DOHC

• To any Jo-blow it’ll look like a stock 3L
• More torque
• More power
• More return for the same mods done vs a 6G72
• Plenty of potential to stroke, or turbocharge, with fantastic results.
• Parts are NOT hard to come by as some may think. Timing belt is simply a Pajero/Montero 3.5L DOHC belt. Not available in Kevlar though.
• Price is similar if not the same as a 6G72

Disadvantages

• You MUST ensure the engine you buy is complete. Alternator/power steering brackets, crossover pipe, and water tube from the water pump is a MUST.
• You will get the bug for more power and more torque from your engine....it’s a very fun drive!
• Lower stock rev limiter on the debonair (6200RPM) means the powerband isn’t as wide.
• Taller engine means it might interfere or come close to your front strut brace/tower bar.
• Your stock downpipe will bolt up with some 1cm spacers from your local exhaust shop. You’ll need 4 gaskets in total and she’ll bolt right up.

6G74 Specifications

6G72 6G74

• Bore: 91.1 93
• Stroke: 76 85.8
• Crank Offset Radius: 38 42.9
• Rod Length: 140 152
• Piston Compression Height: 31.75 31.75
• Deck Height: 210 228
• Main Bearing Diameter: 60 64
• Rod Bearing Diameter: 50 55
• Compression Ratio: 10:1 10:1
• Piston Pin Diameter: 22 ??
• ROD Ratio(L/S): 1.84 1.77
• 
  
• Engine Size: cc 2972 3497

Correct vs incorrect engine to buy
You are wanting as a direct bolt-in solution an engine from a FWD Mitsubishi Debonair. Ebay ads will list these incorrectly as Montero or Pajero engines. Regardless of what they say, if the engine looks like that out of a 3000GT then that’s the engine for you. However to be sure I would always confirm with the seller it’s 100% a FWD layout engine and is the one for sale in the pictures.
6G72/6G74 head compatibility
I have read many things stating heads are different which we need to clear up!
IF the engine you are using is from a RWD Pajero or Montero, YES the heads are different!
IF the engine you have is the proper JDM Debonair engine, NO The heads are 100% the same!
I have confirmed this with ASA (The Mitsubishi parts program) so there should need to be any more false information floating around the forum anymore.
To put it simply, if you have the FWD model, you are 100% good to go.
Parts interchange-ability with a 6G72
I have been working on my 6G74 for a few years now and I now have a good idea of what fits and what does not.
Here is a list of parts I know of that WILL fit onto your 6G74 weather right away, or if you need spares
Intake (from air cleaner up to TB)
Throttle body
Upper intake manifold (it is actually 3mm longer than a 3L one so technically different but for argument's sake, it’ll work with no problems)

• Front rocker cover
• Front timing cover
• Coil pack and PTU
• Exhaust manifolds
• Alternator
• Power steering pump

If your 6G72 is a 93+ with dual serpentine belts, the Crank pulley will work
Parts which are different

• Lower intake manifold on the 6G74 is wider for the wider V of the block
• Rear rocker cover and rear timing belt cover are different. One solution is to use your 3L ones. They are different in that the bolt hole spacing is closer on the rear rocker cover/timing belt cover than they are the 72 ones. I cannot confirm if 1993+ 6G72 rear rocker cover’s and timing belt covers are different/the same as the 1991-1993 models.
• Alternator/Power steering bracket
• Sump is 2 piece. 6G72 is one piece.
• Lower timing cover is taller aswell.
• Injectors will fit however DO NOT use 6G72 Injectors.

Modifications to enhance your N/A 6G74
Adding adjustable cam gears and setting them around the normal -3 +1 adjustments will give you a lot more mid and top-end power. I noticed the power would drop off sharply around 6300RPM before adding them, with them installed it would rev nice and smooth all the way to 7000RPM

A/C Delete. I did this as I cannot really be bothered using my A/C. Deleting it saves close to 20kg in total. I kept the upper pulley. I used a 6PK1035 belt. Fitted perfectly.

272 camshafts. I have recently installed a set of DR 272 reground camshafts w/shims. I haven’t had a good chance to take the car out for a test’n’tune so I cannot comment on these. Let’s just say that you won’t be making LESS power with them that’s for sure!

Common Q’s and A’s
Will it bolt right into my 3000GT/Stealth?
If you own a FWD Model, YES, this engine will 100% bolt right up
Will my fuel system need upgrading?
If you are upgrading from a SOHC 12v 6G72 then YES, your fuel pump will need upgrading.
If you are upgrading from a DOHC 24v 6G72 then NO, it will not need upgrading.
Will it work in a 1993+ car?
Yes, All electronics will plug right up if your car/engine harness has the two separate plugs for the separate crank and cam angle sensors on the timing belt side of the engine
If you have a 1991-early 1993 engine you will need to perform a wiring modification to adapt to the new harness
Will my 3L ECU run right away?
Yes, your 3L ECU will fire it up right away.
Due to the aggressive timing of the 3L it is recommended to only run High octane fuel to prevent any chance of knock. There have been cases of a few 6G74 engines running 6G72 ECU’s failing because of this.
Will my Transmission bolt up?
Yep, no worry’s here. Your manual gearbox will bolt right up, as will your automatic transmission. The bolt pattern is exactly the same.
I have some spare injectors from my 6G72, can I use these?
Technically, they will bolt up and work. However they are a smaller capacity so refrain from using them at all costs. Playing around with fuel injectors without proper fuel control can turn nasty. It’s best to avoid these hassles in the first place.
I have a spare 6G72 Oil pump, can I use it?
Only if it's from a 1993+ onwards car. In fact most of the lower timing belt components will work aswell, timing tensioner, idler pulley, hydraulic tensioner, that swing arm that is being pushed on by the hydraulic tensioner. Even the lower CAS plate and sensor will work.

References;
6G74 3.5L Engine Main Swap details!...JOHN MONNIN'S PERSONAL 3000GT/STEALTH FAQ
Mitsubishi Debonair - Wikipedia, the free encyclopedia

I made this to be a quick stop for people considering this conversion as there is an influx of basic questions always asked. If ANYONE has something to contribute, please PM me and I will modify it and/or add/remove things.