Pajero Owners Club of South Africa

I am currently developing a range of performance components for the V6 Mitsubishi 6G74/6G75 single cam 24 valve non-MIVEC engines. (However pistons, cranks and rods would suit MIVEC). As a semi-retired race engine engineer I know what I want for these engines and now I would like to invite your forum members to provide their input so that their needs can be accommodated. I’m after good sports road performance, not race engine. Also good low rpm torque for these heavy vehicles. My AWD sedan is nearly 1700kg (3750lb) and the 4WD and pickup models are as heavy or heavier.

I purchased a AWD model Magna (Diamante) here in Australia but was quickly disappointed that virtually zero parts existed, and those that were available were of dubious value. Very frustrating, considering the excellent potential of these engines; very robustly engineered and with pretty good cylinder heads.

Cams were available but unfortunately were very low lift and with inconsistent timing between banks (mainly due to the complex valve geometry and the cam developer not actually bothering to get an engine to work with. He relied on Cam Doctor software and had no idea that “at the valve” motion was nothing like that occurring “at the cam lobe”. He was mainly using copies of BMW and Lancer EVO cam lobes so some cams had noisy operation as simply reversing the lobes for use in the opposite bank placed the closing ramps on the opening side of the lobe and the opening ramps on the closing side.)

My first development was with mild head work. Flows recorded showed excellent potential for easy HP using quite mild cams (see attachments of recorded flow).

The next problem to overcome was the limited lift that the factory valve spring could accommodate, about 9.8mm. I now have beehive style ovate wire springs made in USA that easily accept the nearly 11mm lift of my mild road cams. These springs will work up to 13mm valve lift (probably more than will ever be needed.)

Current tune is I’ve removed the 6G74 engine and built up a hybrid 6G75. It has lightly modified heads that drop CR to 9.8:1, and my TSR 196 cams and valve springs (I have designed and had another 2 sets of cams ground but haven’t yet tested them). The block is 6G74 bored to 95mm and fitted up with 6G75 crank and pistons. That engine has a nice flat torque curve and max output of 232HP at the wheels with HM 6-2-1 headers and factory exhaust and air filter on 95 RON E10 fuel (about 90 octane by US standards). I’ve modified the upper inlet manifold, cutting runner length by 50mm and increased plenum volume from just under 2.0 ltrs to 3.7ltrs. Plus I’ve flashed stock ECU. All Magna AWD are 5 speed auto. The dyno manufacturers Mainline reckon that would be 300-315 HP flywheel. Power fall off is only about 6% at 6500 rpm and the road engine will run to 7000rpm without trouble. (Stock EVO IX generally record about 215-220HP at the wheels on the same dyno using 98RON premium fuel). Fuel economy has improved slightly around town; going from 13 ltrs/100km to 12.3ltrs/100km. Highway economy has improved from stock 11.8ltrs/100km to 8.5ltrs/100km over my 345km test route (about 80% at 120-130kph, the rest a mix of 60, 80 and 90kph plus a few sets of traffic lights and road works. Note ECU is tuned full open loop).

I wanted to do a big cube engine but couldn’t get any manufacturer of MLS head gaskets on board, or else the minimum order was 100-150 gaskets. That is now in the past. A manufacturer will now make small runs of MLS gaskets and first big bore gaskets were delivered last week. Both 6G74 and 6G75 blocks are very rigid and thick walled. I am about to bore my 6G75 block to 99.5mm to bring capacity up to 4.2ltr. Physical measuring and sonic testing shows that is a workable size with room for future rebores. (I think the 6G74 block will be suitable for 97.5mm bore; 3.84 ltr with stock crank).

I’m also interested in doing a 4.5-4.7ltr stroker engine. I’m welding up a crank and offset grinding it with 98mm stroke to check clearances with the early heavy rods. The cylinders are long enough and block height is OK for close to 100mm stroke, so we’ll see. After a lot of searching I’ve now got a crank manufacturer lined up to do 4340 billet cranks for sensible money. Most weren’t interested or wanted $5000 and more just for writing the CNC machining programme. Only catch with this manufacturer is that minimum order is 3 cranks at a time.

I’ve contacted ARP regarding their rod bolts. Those they supply are not suitable for the early heavy 6G74 rod. They are 1.5-2mm short. Apparently ARP made them for the 6G72 and didn’t understand big end journal is 5mm bigger dia on 3.5 engines. Their bolts are OK, just, for the lighter ‘74’ rod fitted about post year 2000 to 3.5 engines and all 3.8 engines. I’ve had both rod types spectroscope tested for steel composition. Results attached, results between rods are slightly different due to steel batch variations but steel type is EN43b/1045 medium tensile carbon steel. The circuit race boys here in Australia are using the light rods with stock bolts up to 7300rpm in their 3.8 engines without any problems, so the early heavy rod with much stronger beam and thicker big end eye should handle higher rpm, or more stroke. Alternatively I could go for billet rods. Then with billet crank I could use an alternative big end size for better quality race bearings (Clevite make heavy duty 50mm bearings for Ford/Mazda Duratec 2.3, ACL make 52mm for Subaru 1.8-2.5, and there may be good 52mm bearing available for Nissan 350Z). Smaller big end would also provide more clearance in crankcase for extra stroke and would reduce crank loads.

So if forum members would like to discuss among themselves what parts they are wanting for these engines and then nominate someone to email me with that request and questions I would be happy to hear from them. Please, I don’t have time to answer emails from lots of members.

Very best regards,

A.Graham Bell

PS. Please contact me and I will email attachments