V6 Mitsubishu 3L - carburettors vs fuel injection?

Competition engines and 'live' projects only. Good photos to illustrate your post are expected.
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Beek
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V6 Mitsubishu 3L - carburettors vs fuel injection?

Post by Beek »

I am in the process of installing a Mitsubishi 6g72, into a Lancia scorpion. (I have 2 current scorpion projects)
The 6g72 is a 4 valve / cylinder, 4 ohc, V6 in 3.0l displacement. The factory claims 222hp in naturally aspirated versions, and 330hp in Twin turbo applications.
The engine is almost complete:
10-1 compression, ported heads, +1mm stainless valves with a 30deg back cut. My dilemma is to adapt the fuel injection system to the scorpion, or to fabricate an intake manifold and install (3) 42 dcnf's. I envision the intake to look something like the 246 dino manifold. It will be a very short runner versus the 12+ inch runner length of the fuel injected manifold. Unfortunately I am not a learned engineer; I do realize that shortening the runner length will have some effect. My questions are:

1. How will horsepower be affected by deleting the fuel injection and going to carburetion?

2. Should I not try and reinvent the wheel, and just install the EFI system.

3. If I go with carburetors, how will the camshafts match up, as far as timing goes?

My goal is to have 220hp on tap in a less than 2000 pound vehicle.


Here is a picture of where the project is today.
6g72 -1.JPG
6g72 -1.JPG (513.63 KiB) Viewed 7312 times
6g72 -2.JPG
6g72 -2.JPG (492.91 KiB) Viewed 7312 times
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nickp
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Re: carburetion vs fuel injection

Post by nickp »

Welcome fellow Lancia owner, I have a Monte here in the UK.

Personally I'd stick with the EFI, either in standard form (if you can get it to work OK) or preferably with a standalone ECU (Emerald, megasquirt etc etc).
DCNF's will cost you a small fortune and be a backwards step in my opinion. If you want that look then go for a Jenvey (or similar) DCNF throttle body setup.
Either way, good luck and I look forward to seeing some photos of this project.

PS. I resisted putting a V6 in my Monte and bought an MR2 instead and popped a Camry V6 in that.
Beek
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Re: carburetion vs fuel injection

Post by Beek »

Here is a photo of the progress today. I am still up in the air as to induction. I already have the carburetors, and have the ability to make a manifold. But im still unsure which way to go.
6g72-3.JPG
6g72-3.JPG (173.68 KiB) Viewed 7256 times
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Guy Croft
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Re: carburetion vs fuel injection

Post by Guy Croft »

Injection as a rule of thumb gives 10% more power and a broader spread of torque than carbs.

The thing to remember is that - as with carbs - inlet tract length really matters. This the length of the inlet port,the manifold runner and any rampipe measured from the junction of the valve stem to the head along the axis of the tract right to (rampipe) entry at atmospheric pressure (wherever that is eg: at the plenum).

The length of the OE tract will have been carefully matched to the characteristics of the standard engine (principally the cams and ex manifold), to give the torque right where it is specified, irrespective of whether it is on a single throttle body (on a plenum) or not.

I am not saying that deviating from standard runner length - with the STANDARD cams - will destroy the torque curve, but it will alter the shape of it, mainly in terms of where peak torque is developed.

Now - change the cams- and those runner lengths will no longer be optimal. Changing both inlet and exhaust cams on an atmo engine is almost always undertaken to get more 'top end' power by capitalising on the overlapping (scavenge) effect where both valves are open at TDC at the end of the ex stroke. Just giving a cam more 'duration' and/or more lift on their own will not develop morepower higher up, though altering the cam timing will do that but to a lesser extent.

With competition cams you really don't know what to expect from the standard design & length inlet tract. It might be too long and all the torque is 'low down'. It certainly won't be too short! Usually one finds that engines with very long inlet runners have rather short primary ex pipes. In altering a setup the rule to follow is the converse of that: extend the primary runners and shorten the inlet is a good bet. If your primary pipes are at least 17" long (which is the critical minimum) you will find you can shorten the intake manifold runners, eg to fit carbs - and tune the torque curve with different rampipe lengths. On DCNF you'll be very limited for choice unless you make your own - to optimise your torque curve, depending on the tract length between carb and valve, you might need very long rampipes indeed, 8" or more.

I struggle to give much qualitative advice because I have no idea what the intake setups do/will look like. Sketches may help.

Unfortunately, getting a good match betw inlet tract length and header is a costly iteration requiring lots of spare parts and dyno time. However, looking at the quality of your build this may well be something you care to engage in - as I have - and I shall help all I can,

G
Guy Croft, owner
Beek
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Re: V6 Mitsubishu 3L - carburettors vs fuel injection?

Post by Beek »

Thank you for your kind replies. The exhaust I am Planning to use has 24" primaries, where the OEM was a very short 3-1 manifold. Unfortunately I do not want a 6 large rampipes sticking out of the engine compartment lid, as in the old can am cars. Unless I use sidedrafts which i do not have, it appears as i will have to keep the EFI system. This should not present a large problem, as tuning it should be on the same guidelines as the original vehicle it came from.
6g72-4.JPG
6g72-4.JPG (226.73 KiB) Viewed 7223 times
I do intend to cut the header system right after the mating of the 2 collectors. At that point i will have to add bends and such to keep the system inside of the chassis. I plan to use the flex section to keep the stress off the exhaust system.
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Guy Croft
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Re: V6 Mitsubishu 3L - carburettors vs fuel injection?

Post by Guy Croft »

Looks fine by me!

G
Guy Croft, owner
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