Note to Readers EB (Ted) is a retired machinist who visits us here. He's been also been known to sneak around ovals in the Portland OR area, and wreak havoc with his Z06.

>>>*I said I would offer a few tips on improving the power output of the little 2.4L Toyota engine. For this discussion we are speaking of the 1985 and later engine design, it is the most efficient of all in this series.

So here goes.

The one trouble I had writing this was it started to sound a bit like an advertisement for parts I supply. The problem there is that of course those are the parts I use.

So right off the bat, remember that there are many good venders with many good items, and they may well be every bit as good as what I have. I will say there are quite a few builders out there that this old man spends as much time chasing as vice-versa. In any event, I will try to be as generic as possible.

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Our goal is to assemble the POTENTIAL to produce up to 150 horsepower, but what we usually really want is to improve the torque output within the normal operating powerband.

The basics include a solid short block, a sound cylinder head, an upgrade camshaft, and an improved exhaust system. From this point, we simply tease several areas.

Improvements to the fueling system can also help, but they are way down the list as to real gains, so I will not go into that, other than make sure the system is clean and the mixture proper.

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One very important step is to verify the quench before final assembly, which is often overlooked. Quench is the close collision of the piston head to the flat part of the combustion chamber. Nearly all aftermarket pistons are destroked by about .3mm or around .012" or so. This varies a tad between brands, so installing a new piston set will probably reduce the piston height. Then if your machinist resizes the connecting rods, you just lost even more deck height because they clip the cap and rod to do it. (Well, they do if they are doing it right.)

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There is only one real way to check for quench, you must assemble the short block and measure. So you will need one spare set of connecting rod bearings, they are cheap since all 1975 to 1995 take the same part, only the undersize varies depending on if your crankshaft is machined or not.

Then if the machine shop regrinds the crankshaft, you really could end up with 4 different deck heights in the same engine, unless they index the crankshaft stroke and most simply do not. By the time they get to, say, .030" undersize and have resized all of the connecting rods, it can stack up to a lot, and this just kills power output.

So "dummy" up the short block, and measure how close the piston is to the top of the block. A straight edge and a feeler guage makes this easy. We want it to be zero deck, or as close to that as we can get. Stock, the piston does protrude by about .006" or so, if yours does, this is fine.

The goal here is to get them all to as close to the same as possible and up where they belong.

If this measurement shows the piston is down from the top of the deck at TDC, you will need to disassemble and correct this by having the block decked. Tight quench means you can run proper ignition timing without pinging. A sloppy quench will create more pinging at less timing that the tighter compression ratio will, the blast effect of the close collision atomizes the mixture and distributes it better across the chamber.

Be sure to keep track of exactly how much is surfaced off the engine block, this is important I will get to why later.

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Right here I will insert one theory I have that is at odds with almost ALL other engine rebuilders. This is knife-edging the counterweights. I say this is exactly backwards.

Think of a V-bottomed boat, then a flat bottomed boat. Which one takes less power to get up on top? The knife-edged counterweight slides into the oil, and leads with much more surface area. Oil is kinda clingy stuff, even when hot. Instead, we smooth and blend the leading edge leaving it square. There is a pressure wave ahead of the flat surface, oil moves aside. The shaft spins more freely with less drag. I personally quit doing the knife-edging in circa 1990 on our stock car engines, the result was a drop in oil temp of about 15° on the endurance engines, ALL of them. One gain however might be in weight but the mass is so close to centerline I feel it is of little consequence.

We just use stock crankshafts on our Toyota engines, or our new performance ones, which are really just a nice forged steel upgrade, and so far they work fine.

Here is where I feel is a nice little gain, take some time and some sanding rolls and polish roughness out of the leading edge of the counterweights, and remove any odd flashings and casting flaws on the shaft before you have it remachined. You will see lots of them if you look. Don't get carried away here, but it can help to keep the oil cooler which isn't horsepower but is durability. You were going to rebalance anyway, right?

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Engine size is the next concern. Those with the strokers love them, and if in the budget, go for it. (Mosk cheats, stuffing cubic inches down the top of a big old stroker isn't fair to the rest of us on a budget...*LOL**) That stuff is cool but it would break the bank for many of us. We are trying to be cheap here since the kids are standing around yelling about silly stuff like food, and the wife is waving some piece of paper that says electric bill, whatever that is.

Of course, seeing the number of ladies buying engine parts over the last few years, it just may be HER that is out there overhauling the 4 Runner, so why don't you get up off your dead..(well, you know) and go help her?

*You can find out who won the football game later.

*heehee.

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Normally the block will require rebore, always bore as little as possible to assure round and straight bores. There is no reason to overbore to gain cubic inches, it does gain some of course but about a tablespoon or so is all. You will be better off with the cylinder walls as thick as possible for rigidity, more power can be lost in frictionals than can be gained in size by boring, so I feel around .040" is maximum without checking out the cylinder walls thicknesses carefully.

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Now both Darin's and Larry's engines are .060", but I went through perhaps a dozen blocks to find some I would use there. That is a PIA. The fun part with both of those was that the pistons were NOT destroked, so after decking the blocks they kinda stuck out a tad too much. Putting the head on with it that way would be embarrassing and get me phone calls. So I simply milled off some of the outer raised circle on the piston head, effectively raising the compression ratio by about .5 to one plus the gain from the overbore, those both came out to a shade over 10.1:1 which made me nervous. They haven't sent me any nasty emails though, so it seemed to work. This is easy to do if you can find the non-destroked pistons anymore, if you can, email me and let me know where.

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So now we have the block assembled, the deck height is zero to less than plus .006", and deck is flat, straight, and perfectly smooth. Bag the short block in plastic, let's go look at the cylinder head.

I prefer the Topline head casting because when I measure the ports, I get right at 5cc larger than most stock ones, and they seem to be more consistant. Your stock head will work fine if it is sound, but you must measure the thickness to know exactly how much metal has been surfaced off. Again, this is important, and I will also get to that later.

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Larger valves open up the "window" or area available for flow. They also change the angle of the flow cone as fuel and air enter the cylinder. It is also an improvement in the goodie, which is the initial blast effect past the head of the valve as it opens. Think of your finger on the end of a garden hose, and the spray you see as you take it off, and then it slows to a steady stream.

Exactly the same thing happens as the intake valve cracks open, and this is the best and most important portion of cylinder fill.

So larger is a big asset here for many reasons, following this logic we would think as large as possible would be even better, right? Well, no, too large then creates a velocity drop and now physical energy must be used to recover the flow, too large can actually cost power for the intent of this piece.

We use .033" larger intakes and .024" larger exhaust valves. Since our goal is to add power without paying for some Exxon executive's family vacation, this size is about right.

Of course we must now machine the valve seats larger to get them in there, and we need to make a cut under the seat to open up the bowl. Plus we need to get the valve spring assembled hieght to 1.594"-1.610" so the rocker arm doesn't go out of geometry and things don't bang into things.

To the machine shops that insist in sticking an .060" thick shim under a stock valve spring, I say they should be shot and killed and their bones hung in the Sun as a warning. The setup will handle about .480" lift without mashing stuff, stick in an .060" thick shim and we are now at around .420" or less, then bolt on a .430" lift camshaft? *Well, I bet you can see the problem. At least a half dozen came though our doors this year with exactly that situation.

We use 1.610" installed most of the time, since we are next going to be using a higher lift camshaft. The base circle will be slightly reduced, even on a brand new camshaft. It has to be to keep the rocker arm installed angle close to arc centerline.

We don't bother to port the StreetRV head versions, porting does add power but it begins to move up the RPM band quickly, we are still looking for economy and inexpensive power gain, so porting and racing is a different article.

One trick we do use is dimpling up in the bowl dome. We use a 3/8ths die grinding tip to create little dips or dents, all this does is collect fuel droplets. The idea is to take advantage of the blast effect as the valve opens. Air is easy to move, you see, the fuel would rather not so we just force it a bit. This seems to work, and seems to have stopped some of the hesitation we noticed with the very early setups. Then notice that little vortex ledge under the head of the intake valve. It is there to twist the mixture, and increase velocity at slow speeds. Fuel tends to head that way, there are some tiny gains to be had in the mid to upper RPM ranges by changing this to a slight trough. DON'T cut it out of there, you will be sorry unless you are racing or supercharged/turbo'd.

Oh, go ahead if you wish...*LOL**.

On the camshaft profile, if carbed you may run more duration, EFI is sensitive so about 222° @ .050" lobe lift is the most we will use and I prefer around 218°. The one design we do run the full 222° duration on is our little 261C, and it is only .410" gross valve lift. But that is a fat lobe little critter that is intended to offer almost instant off-throttle torque, folks who haul loads or have huge tires like that one. Still, it has that chattery idle, nature of the creature.

Lifts to .430" stay well within the geometry of the top end, for street use we prefer a bit less. You will need a slightly stronger valve spring, not much, about 5% although stock will work and run fine if in good shape, as long as you don't go teisting her to redline everywhere you go. The only way to know on your valve springs is to test them, if they won't hit 60# at seat, replace them. The stock springs are darned good pieces, though, I have seen them test just fine at 200,000 miles.

Now some venders offer split duration profiles, usually more lift/duration on the exhaust side. This has only the effect off moving the powerband to higher RPM's, we do not advise or produce anything other than single patterns, and I am currently working on a design that has much LESS lift/duration on the exhaust side and it looks extremely promising for a high-torque and economy design. (Don't ask, it's months away still.)

One trick with the cam design is lobe shape. Several venders offer many designs based on the factory lobe shape that will add valve action. We found that while this did add power, it also can add noise due to the mechanical action.

So we used a different lobe shape entirely on our current favorite design, the sudden dropoff on the factory lobe design was almost entirely eliminated. This let us produce a profile that is fairly quiet and short duration @ .050" lobe lift, and still hit .425" gross valve lift and add area under the curve.

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Now we are almost ready to set the head on, it is time to think of valve timing. This also gets overlooked a lot. Let's assume we decked the block by .013" to get the quench back and we are dropping on a brand new head with our personal choice of camshaft design, got the big valves all setup and in place by our favorite machine shop we trust.

We need to correct the valve timing. The easy way to do this is to go back and machine .007" off the head, to get to a total of .020" removed. The reason is now we can drop a 3 position crank gear on in the "A" position, this moves the valve timing ahead by the 2° of the cam movement we just lost due to surfacing. Or we can invest in an adjustable cam gear, that works too and lets us experiment a bit.


All of this is well within the system's ability to compensate so emissions are easy to pass, we don't need to spend a pile on larger injectors, etc.

But now we need to think about the exhaust system. Improving the exhaust system is number one as far as freeing up usuable power, it doesn't "make" any at all. But the factory needed a quiet, smooth, and responsive engine because the driver might be a little old lady going to the store in Hawaii, or a young fellow driving around at 5000 ft altitude in Colorado. So they compensated for this, and for ground clearence on some vehicles.

The best setup cost wise we have found is to use the excellent factory exhaust manifold, then increase the pipe size to 2" all the way to the muffler, yep, the cat, too. Then we increase again to 2 1/4" on exit all the way back.

This creates a bit of directional flow and frees up power, it fairly quiet and smooth.

So here is a recap, like I said, simple and basic stuff, and in the budget.

Tight short block.
Quench set to zero/+.006"
Larger valves and mods.
Single pattern cam, 222° or less @ .050", .430" or less lift.
Restore accurate valve timing.
Improve exhaust flow.

No real surprises here, easy to do, cost should be less than $1500 including the paint. This combination WILL make 140+ H/P and I have seen tests that touch 150 now.

The gains are simple, the larger bore increases compression slightly once the deck height is back to zero, the mild head surfacing does the same. The engine is now right at 9.7-9.8 to one static, still good for regular fuel. The airflow increase is about 6-7%, the flow cone is improved. The largest gain is in the larger area added by the cam profile, and this creates a need for the improved exhaust system to take advantage. Tuning settings remain stock.

Easy stuff you can do yourself with simple hand tools and a book, if the first time though ask questions so you don't mash the timing chain tensioner or ruin your timing cover by forgetting the "secret" bolt in the front.

*And there is a wealth of good information right here on this site, with genuine experts that will answer questions. I know, I learn things almost every day here.......*EB