Project 6G72, bitsumishi mashup.
Hi folks,
Got a spare engine for cheap for my van, so I figure I can go a little crazy on it. Mitsubishi 6G72 SOHC 12 valve, 3.0L V6. This one is a '92 with the roller cam, so hoping that's a slight MPG gain before I start.
Just in the preliminary stages of planning the atrocities I want to wreak on it so far.
Here's what I'd like to work in. High compression, with Singh grooves and "edging" to handle it. "Velocity porting" for improved induction and exhaust (And it's about the only way to handle it on this, very little meat to play with) Deshrouding the exhaust valve might help too. Concentrating charge/burn over exhaust valve. Shown to be effective in many concepts. Piston mods to enhance tumble when piston low, and to enhance swirl at top of stroke. Also hope to work in a wedge shape to the piston to offset toward the exhaust valve.
Now the highest compression pistons available for 6G72s are 10:1 and it's a PITA to make sure that those are actually the ones you get. Very confusing info on the applications of those. I'm not sure those will be "enough" since by the time I've done any grooving, edging and deshrouding, the compression will probably be back down to 9:1, heads apparently have very little to skim to claw any back. I'm looking at the possibility of using pistons from the 2.6L 4G54 Mitsubishi Astron, which are the same bore and have the same pin diameter. The compression height on those is 35mm vs 31.8 for stock 6G72 pistons. I think that would work out at 14:1 if they don't pop out of the deck (Gotta find that out, and double check it on the engine when I've got the heads off) Now 14:1 is a bit [b]too[/b] much in all likelihood, but I think that by the time I've carved at them a bit and taken a few CCs out of the head, that it all might work out nice and have me sitting at 12:1.
Trying to figure something out for the fuelling is giving me "conniptions" at the moment, dunno whether 88 should be 27 psi or 48 psi (conflicting info in the net) Can't use the injectors that came on the '92 'coz they're high impedance when my 'lectronics expect low impedance. Now I want to make provision for extra fuel, since I wanna make sure that nothing is toasted when the gas gets mashed. It's reputed that the SMEC can tune for up to 50% more and not lose MPG if you "keep your foot out of it" Also thinking that at lower engine speeds, normal driving, that getting all the fuel sprayed earlier in the induction cycle may have benefits for encouraging a stratified charge type of burn. Might turn back the fuel a bit later but want to be real careful at first.
I'm hoping that I can make a lot of power with these mods too, aiming to get 30% more flow out of the ports than anyone else is getting on these by using various tweaks to manage flow. Goals are 30 mpg (on 6 cyl) 225HP ...... and 14 second 1/4 miles. :twisted:
Other mods will include a crank scraper, intake plenum and throttle body porting, spacers and mods, ignition upgrades. Also trying to work out a "reliability" mod which is something like a windage arrangement for the camshaft, something like what's on K engines, (To solve PCV oiling and clogging problems on this one) which may give a fractional efficiency increase. Might try porting the headers, not sure yet, they appear to be doing something that's desireable for reasons of making 3 cylinder DOD work, and I don't want to mess that up.
Van will also (eventually) get an aerodynamics package, hmmm well maybe some of that will get on there before I finish with it's "new" engine.
Anyhoo, getting excited planning it, never seriously thought before about getting a spare engine at the $500+ the wreckers usually want around here, but I've got one now so can "go nuts" :D
Van will probably get emergency surgery shortly, and be on the road for a few months before this engine is near ready, and I may be testing some of the bolt-ons, some of the DOD stuff, some of the aerodynamics etc on it before it get's it's new motor.
So, that's the next thing in the works. Really need to get going on stuff though, Escort project is stalled still/again. I was celebrating winter's departure too soon the other week, had a couple of warm days, but this week it's been snowing a bit again, not hanging around though, and snow in the forecast for the next week too, grrrr. That makes 6 months of winter here, got our first snow early on October 13th, warmed up after until Jan but it was mostly that raining sideways blowing a gale weather I couldn't use either. Feeling like I've got screwed out of about 3 months of "doing stuff" weather with all that :roll: Figure as long as it's at least 7 or 8 C though I can tear into front end work on the van, whether it's raining or not, though I guess a couple of degrees above freezing is just as good if it will stay dry too, and at least get that in running shape, then pressure's off a bit and I might be able to concentrate better on the Escort and get that finished.
Road Warrior
Comments
Project 6G72, bitsumishi mashup.
[quote="RoadWarrior"] "Velocity porting" for improved induction and exhaust (And it's about the only way to handle it on this, very little meat to play with) [/quote] [quote="RoadWarrior"] aiming to get 30% more flow out of the ports than anyone else is getting on these by using various tweaks to manage flow. [/quote] Are you sure these 2 statements are compatible? I'd be honored to learn what you know if you can pull that one off.
Mike
Project 6G72, bitsumishi mashup.
Well I can aim :D
Yeah, that's too much of a boast, what I meant was that most folks porting these are getting barely anything. Seen some numbers posted that were about +15% now I think about it. Really mean I want to try and get 30% over stock. Not a lot of numbers around really but there's folks say they've ported them who're only claiming about 5 or 10 HP more than folks who haven't with approximately the same other mods. Then there's an attitude that there's "no point" porting them.
What I understand by "velocity porting" is to work the shape above all else to allow high speed flow, avoid flow stalls, avoid large seperation vortices at high flow. Then use induced turbulence to "fix" bad shapes that can't be worked around. I am under the impression that all that can actually gain flow at the top end for the same port area. I guess "velocity porting" is used to mean situations where port size is restricted but that flow rate is kept near the best stock flow numbers, but at higher velocity, with the objective that torque and ram effect is improved. I'm using that term to mean I want to use those techniques to make the best out of limited port area, hence get more flow out of it at higher velocity. In other words, I can't get 30% more area, so I'm aiming to make it 30% faster.
I'm not quite going to be flying blind on this though, there's some cross sections on the turbo mopar forums that I think I can figure out how to import into a fluid dynamics simulator program I found a while back. I figure I can do a lot of experimenting with shapes in that. Then when I've got what flows best on the computer, I can make templates to work with to hopefully get the same shape on the actual ports.
Haven't tried this with the Escort ports to see what I'm doing because I can't figure a way to get the cross sections, and because the shapes of those ports are more complex to start with. On the 6G72 they are basically tubes, I figure that simulation will be easier and more likely to apply to real life.
Oh BTW, some of that flow increase I'm thinking is coming from one of your tricks with the valves. Grooving the back of them. Can't remember what you said that gains in flow, but there was someone else doing it commercially in the UK back in the 90s, claiming up to +40% flow.
Anyhoo, doubt there's anything much I can teach you really, I'm stealing all your best ideas :D
Road Warrior
Project 6G72, bitsumishi mashup.
"Anyhoo, doubt there's anything much I can teach you really, I'm stealing all your best ideas"
Actually, stealing means taking something that isn't yours without permission. You have permission so it really isn't stealing.
I'm waiting for the second set of test results to confirm my "variable boundary layer" theory with the Powre Lynz. The first test came back showing that at low demand levels, flow numbers are low, thus velocity is high. As the port increases in flow, the numbers increase accordingly up to the physical limitations of the port size. More on that when the rest of the data comes in.
You can make a lot of power from the combustion chamber side of the heads. I have a head that will be going on a TBI Dodge where I didn't touch the ports. All of the work is CC side, including milling it for increased compression. This will be a telling story.
Mike
Project 6G72, bitsumishi mashup.
Yeah I'm hoping to get a nice shape in the chambers, take it to a deshrouded heart shape. Wish I had some of the material I used to have on tuning BMC "A" series engines from the UK, that was an engine that got a [b]lot[/b] of combustion chamber tuning done to it. 1275cc motors were making 150HP, bored and stroked 1400cc ones were hitting 200HP. Think I had an earlier edition of this book out of the library a few times... http://www.aptfast.com/APT_Parts/Books/Book_Info/B-01_info.htm I figure if I could apply the lessons from that engine to mine I should do real well.
Project 6G72, bitsumishi mashup.
[quote="RoadWarrior"]Yeah I'm hoping to get a nice shape in the chambers, take it to a deshrouded heart shape. Wish I had some of the material I used to have on tuning BMC "A" series engines from the UK, that was an engine that got a [b]lot[/b] of combustion chamber tuning done to it. 1275cc motors were making 150HP, bored and stroked 1400cc ones were hitting 200HP. Think I had an earlier edition of this book out of the library a few times... http://www.aptfast.com/APT_Parts/Books/Book_Info/B-01_info.htm I figure if I could apply the lessons from that engine to mine I should do real well.[/quote]
Hmmm 'David Vizard' books. Me thinks MPGMike forgot to mention talking to him in his name dropping article on FET!
Project 6G72, bitsumishi mashup.
I've had some new ideas for this build...
Looking at using 136mm Nissan SR20 connecting rods, as far as I can figure they have identical wrist pin dimensions, and are 51mm at the big end without bearing and 48mm with. Stock on the 6G72 crank is 50mm, and most undersize is 48.5 mm. I think it would probably be okay ground down to 48 with the nissan bearings in, since it can handle a lot of power in the nissans. Not sure yet what size the hole is on the stock rods. Got 2 specs for width at the big end, 19mm and 17mm, need to find what width a 6G72 one is.
So, thinking of combining those with a 4G54 (G54B) piston, that's 3.5 mm too tall, leaving me 0.5 off stock deck. But then with 2 mm undersize crank grind I can have that offset and get at least 1mm more stroke.
This has several advantages. i) brings rod ratio close to ideal. ii) lets me get compression without having to take too much off the head, which ends up complicated for figuring the right angle grind for the intakes and getting them to fit properly (Vee engine) iii) lets me use the astron pistons which seem to have a good shape for tumble. iv) the pistons are cheap, the rods are cheap, and the crank grind may be cheaper than the head machining that would otherwise be required.
Got 76mm stroke, 140mm rod, ratio=1.84, with 77mm stroke and 136mm rod that would be 1.76
Don't quite "have all the figures in" to determine exactly what my offset will be on the grind. Might depend on what my head volume is.
Anyhoo, figuring this makes it more efficient at lower RPM with better scavenging, also gets the piston velocity near constant in the mid part of the stroke. Also thinking it will have a stronger tumble action.
It's said that longer rod needs less timing and shorter needs more timing. Also said that higher compression can be run with a longer rod... however.... I've got a gut feeling that this balances some of the characteristics of grooving, and that shorter rods will cope very well with a smooth fast burn, and timing will not be affected.
Be aware that the V8 people who are always saying "longer rods! longer rods!" are in the 1.5-1.6 range stock, so let's not get sidetracked on "long rods are better" on V8s where they are coming up to the same ratio I'm coming down to.
Also seems like I will get a better piston seal, think the ring pack is well spread on a 4G54 piston compared to a 6G72 stocker.
Thinking I should get more midrange with this. Midrange should be good for mileage, and should feel "peppy" I want power where I can use it, any gains over 6000 rpm are a waste IMO.
Gonna be trying to get good ram effect in the intake tract to complement this.
Crazy but Cool Idea.. :)
This is a crazy idea at the same time a cool idea. But I think this will need a lot of mitsubishi accessories and parts before you can pull this off.