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
