Gonna build this spare 2.6 I have. Got most of the parts, NJV head, valves, heavy springs, lifters etc etc. Can a guy do like a .020 over bore, slap a header and free flow exhaust, and a Weber 38 on it and see any increases? Or is that a waste of time?
Or is there a little more that should be done. Trying to keep it as close to stock as I can, and find a nice balance of improvement to budget ratio.

Colt Racing Bulletin - NA 2.6L Tuning

Link above courtesy of mitsubishilinks.com...leave a donation (so that he can upgrade his computer system).

Appreciate it. Anyone else with any real time experience doing slight mods?

Way back when, I used that bulletin on the 2.6 as a starting point for modding the engine in a Fire Arrow I used to have.

That probably goes back to the 80's.

What Worked:

If you had the combo catalytic converter exhaust manifold, anything was an upgrade!

The factory tri-y exhaust manifold is pretty hard to beat. On the street, I never saw an improvement when I swapped to a 4 in 1 header.

A good exhaust from the last Y back can help.

Milling the head, seemed to work very well. I cut the heads up to .040" with good results (.025 was typical). I also reworked the valve bowls a bit to smooth out the sharp edge on the short side radius. No radical gain, but again it seemed to add a bit of snap.

Distributor advance springs from a Starion. Quicker initial advance, again a bit more response. I also upped the initial advance 5? to 7?.

Bigger cam (John Baker performance cam). Bad mod... No noticeable gain. Less bottom end, not enough gain on top to offset it.

Dual side drafts. Nice increase in response, some gain on top, horrible fuel economy and poor cold starting. An expensive experiment that didn't pan out.

Working secondary barrel on the stock carb. Best mod ever!!! The power loss from a non working secondary is amazing.

Upgrade downdraft: I never tried one, but the reports are generally positive and its a lot less complicated than the factory carb.

Roller cam from the AU motor. On my turbo 2.6 it added mid range TQ but is hard to find.

I fooled around with the NA 2.6 for four years. Small improvements can be made that add a bit of pep. The EFI system from Australian 2.6 would be a nice score. The down side is the water port on the head is different and it needs to be modded for a fore-aft motor layout.

Balance shaft elimination: There are some outrageous claims on HP gains from taking them out. I never saw a enough of a gain to make it worthwhile. That and I like having a smooth feeling four.

I've read a bit on how boring over doesn't do much. For every little bit of displacement you add, your adding more friction surface with bigger rings or what not. Again, just somethi ng I read.

Not trying to argue, but milling the head to increase compression won't work as you offset the timing chain. The thinner the head, the more off your valve timing is, hence you didn't really feel a difference. With an adjustable cam gear you can degree in your cam and see some actual performance gain s. I feel its even documented in the fsm. Same goes for a cam, if you dont degree it there's not going to be a real gain.

Correct me if I'm wrong, but running the Aussie cam doesn't increase output, it just lets you run roller rockers and mechanical valve train, hence a more responsive engine. Its when you get it with the actual aussie head that flows more air that you gain power. My buddy has an aussie head, cool mod, but the gains are minor, so its only worth it as part of a no cost spared performance build. Plus they are like $500 and about as easy to track down as 4.875s.

How about using FI to relieve some of the carb issues?

The hardest thing to change is the sorry intakes, both n/a and turbo share the double wye design and I'm positive the two inner cylinders get less fuel than the outers. It's hard to change because of the three different water passages, the main tstat flow, the tstat bypass to the carb plenum floor, and the bypass flow to the heater inlet.

I wish I had the fab skills to make up a long tapered tube ram manifold for FI+efi, with a plenum with internal velocity stacks. Long tube to match the undersquare long stroke motor, because long tubes enhance low end torque. You could use a thick flange and what ammounts to plumbing fittings for two water flows (no need for plenum floor heating when you squirt at the back of the intake valve) with a remote thermostat.

I disagree that boring is wasted effort. The ring contact area varies directly with the increase in bore, and the cylinder volume varies by the square of the increase in bore. Mo inches is mo power.

Compression increases also aways mean more power, as long as you stay under the detonation limit of the fuel without having to subtract timing.

It's fairly easy to correct the cam timing to match the head cut, either by using an adjustable cam sprocket or by drilling out the index hole on the stock sprocket and use a bushing with an offset hole.

I betcha Kevin would agree that the most effective mod for a 2.6 is the turbo from a starion. Doubling the hp is easy with only minor mods to the stock starquest system. If you want to play n/a games, I'd start with a 4g64 2.4 swap and get a much more modern engine with 4v per cyl, dohc available, turbo available, mucho aftermarket available, as most of the 2.0 4g63 stuff fits. I think 300 very docile streetable hp is readily available FI, and 150 n/a.

Eddy. You not the first to mention the intakes unevenly dividing fuel. Just out of curiosity, does the magna one have the same problem? It isn't a y design, so I'm guessing no.

I also feel that boring would make more power, but a few articles presented some interesting points. Cant remember and dont care enough to look.

I agree increasing compression adds power. But if you cut the head or block as the way to increase it and dont fix the timing like you said, yourn making matters worst. Its how many honda guys mod their rides just for the sake of modding without actually thinking about what does what. Like how an oversized throttle body creates a lean condition. You feel more power, but its not a good mod.

And lastly, yes the starion turbo swap is the easiest way to make power. I did it and its so much fun to drive. However, its unreliable. I didn't do my research, so I'm turns out almost everything for it is discontinued. I have everything from a spare afm to relays in the trunk as nothing new is available. I even had to use up my spare injectors as both already died. However, the carb was very reliable for 8 years, just outrageously slow.

I say best performance mod for a g54b is a swap to something better.

The issue that I see, is that trying to gain enough displacement to make overboring worthwhile is difficult. That and some motors lose some sealing as cylinder wall become thinner.

.040" oversizes gets you a 56 cc disp inc (about a 2.2% inc in disp). Every bit counts, but I would rather trade wall thickness and potentially better sealing for a small size increase. The upside is the 2.6 has decent wall thickness. That and I like leaving something to cut for the next rebuild.

My current turbo motor is .040" over. Thats was what it took to get the rust pits out. I did however bore and hone the motor using a deck plate to predistort the bore. Its worth a HP or two. Using my dial bore gauge I measured the bores before and after torquing the head, it gets you a at least five to seven tenths better roundness. Years ago I listed my test results, I'm pretty sure Randy (aka Dad) followed my lead and started using a deck plate when honing. I remember him asking me to make one for him.

You cant beat displacement... Its getting it thats the issue.



Critical thinking skills: If you are making two changes at once, don't automatically assume that they cancel each other out. Another approach would be to analyze each change and try and figure out what will happen.

In a perfect world, you mill the head and compensate the valve timing exactly.

Real world... 2? is too small to notice. 4? of cam timing change is when you will see a difference. What happens when you mill the head? The cam timing gets slightly retarded. At the same time you gain compression.

The compression gives you a small across the board power increase, retarding the cam shifts the power band up slightly. The compression increase adds more low end and midrange power than the cam timing shift takes away. At higher RPM's (WAG...above 3500RPM they combine 3-4 hp or so).

How do I it know it works? I tested it. Where does the 2? rule of thumb rule come from? Comp cams and my own testing.

Also, I did calculate the cam timing change. Cut the head .040" gets you about 2.2? change at the crank. My personal recommendation is to cut the head .025". A cut of .040" bumps the CR up 1/2 a point and is good for a couple of HP. I wish I had my engine build notes from when I build my original Fire Arrow (1985 or so). I worked all this out a long, long time ago.




Ok why would you put in a roller valve train? Typically it's to reduce friction. As a percentage of developed HP, figure a friction loss of about 10-15%. 110 HP engine would have about 11-15 HP of friction losses. As a wag, 17 % of that loss is valvetrain. The roller rockers easily cut that in half for a 1+ HP gain.

That and the roller cam has about 8? less overlap. Less overlap increases mid range hp, in exchange for less hp at higher RPM's (above 5000 RPM).

Thats what I get from a some quick calculations. Real world, I swapped the roller cam in my Raider and I got better throttle response, a stronger mid range pull and less pull after 5000 RPM.

I'm just listing my experiences of whats works and what doesn't. If you can score the parts for a good price, go for it.

Other changes to the 2.6: Inside the crankcase there are a set of ears that help to isolate the bottom of the number three cylinder. This was for an emissions device that was dropped in the early 80's. The block kept the feature even though it was no longer used.

Removing it, decreases windage losses and takes weight out. Not a big gain, just one of those things you can do. A few guys on the Starion board did the same thing to their motors.

I also dropped my oil pan and pickup down .75" using a giant aluminum oil pan spacer. Again to reduce windage losses and add oil capacity. No noticeable gain but the extra oil capacity is nice.

Coated piston skirts might get you another HP. Same with thinner cross section rings. With the long stroke on the 2.6, piston and ring friction (and windage) is more of an issue than with other motors.

That long stroke is why you get that nice pulsing when you take the valve cover off. Its an odd thing with piston kinematics, the crankcase volume is not constant. Because the piston accelerates faster off of TDC than BDC, the crankcase volume changes twice per revolution. The long stroke of the 2.6 make this effect more pronounced. This is also why 4 cylinder engines have a second order vibration, unequal piston acceleration BDC VS TDC.

You might notice that a lot of the changes don't have some outrageous HP number attached to them. Without raising the RPM or adding boost, large gains in a NA motor are hard to come by. My experience says you get modest gains by making a lot of small improvements. A 1-2 hp gain may not seem like much, but if you combine a handful of them to get a 10 hp gain it does matter. That a lot of what successful motor building is, is optimizing and getting small changes that add up.

The other way to get HP is spin the motor faster... That means more cam and is not where you want to go on for a 2.6 on the street.

Thats what led me to look into swapping in a turbo motor. The small gains were nice and helped but its so easy to do with a turbo.... The dual carbs were what convinced me that a turbo was the way to go. <img src="/forums/images/graemlins/rodent.gif" alt="" />

Skip the heavy valve springs... No gain and all you get is more friction.

Have the piston skirts coated with a dry film lube.

Run a wider gap on the second ring. Run the top gap in spec.

Lightly port the head, short side radius cleanup and remove casting imperfections and flash.

Try and get a 9:1 CR. Most aftermarket pistons are "decked" to reduce the CR by 1/4 to 1/2 a point. Pretty much the wrong direction for a non turbo motor.

Find a good shop to bore and hone the block. One that understands how to hone a performance motor. A plateau hone seems to be the best thats readily available.

web page

You might find a difference in how well this works compared to say a motor done with a hone from Harbor Freight. A good shop will match the honing abrasive grit to the type of rings you run. Whatever you do, avoid using plain cast iron faced rings.

Fit the piston clearance before you have them coated.

Once you have the head on shim the timing chain tensioner for minimal clearance.

Verify your cam timing. My gut feel is the 2.6 is a bit over cammed for a truck. You can look for a smaller cam (the stock one from a 2.0 would be a good experiment), or try advancing the stock cam 4?. A crazy future idea I have had is a simple RPM sensitive cam advance for the 2.6. Dial in 4-8? advance at low RPM, and 4? retard above 4000 RPM.

Remove the ears in the #3 cylinder bay ( bottom of the block).

MAG check the block for cracks in the deck before you have it bored and honed.