The Modified 4AGE Page, page two
Other stuff that's important
On the preceding page, I've talked about such-and-such a camshaft duration, but I didn't mention the actual timing of the cam that should be used. Everyone talks about having a cam of, say, 304°, but the one thing that's very important that they're missing out on is just where to put the 'top of the lobe', as this is the real trick to getting the best power out of your cams & engine.
And fortunately, it's dead easy to do!
The one simple rule that you have to follow is this - For cams with a duration of under about 270°, you want the cam lobes to be at about 110-110, and above about 270° have the lobe centres at about 100-100.
(note that this is a general rule, and each engine will require fine tuning to get the last little bit out of it, but the actual figures will almost invariably be to within 2° or maybe 3° of those numbers, eg, 100-100 may up ending being 98-102, and 110-110 being 108-113)
So what do I mean by 110-110 and 100-100?
Again, quite simple to do - With the engine at Top Dead Centre (TDC) #1 or #4 cylinder, and what you are looking for is to have the inlet cam lobes for #1 cylinder just starting to open, ie, the cam lobes on #1 cylinder must be pointing towards each other. If you wind the crank over 110° in the forwards direction, then the inlet valves should be fully open. This is checked by means of a dial vernier gauge, which can accurately and repeatably measure valve lifts to less than 0.001".
To check the exhaust timing, simply wind the engine backwards from TDC #1 by 110° (or 100° as the case may be)
If you haven't done cam timing like this before it may seem a tad difficult, but it only takes a few tools, a bit of patience, and some time. Note that it must be done as accurately as possible, because a 'degree or two here or there' just isn't good enough!
To get accurate cam timing like this can
be done with standard cam wheels, modified by drilling new holes in
the right spot after the new timing has been determined. Shown in the
pictures below is the other two methods used to give adjustable cam
timing, one of which is vernier adjusters and the other slotted cam
wheels. Both are pretty easy to make, but only the slotted type can be
adjusted with super-fine accuracy.
(The vernier type has, say, ten holes drilled in the camshaft front flange and nine hole in the cam wheel. As you turn the cam wheel and cam around each other, the holes line up in different places so you can often find such an alignment very close to where you want the cam to be. But with the slotted type you can get the timing absolutely spot on. The slotted type are easy to make if you have access to a lathe, but they can also be bought for a reasonable price)
Another important thing to note is that
the closer to 100-100 timing you get, the less and less inlet manifold
vacuum you'll be getting, to the more likely the standard computer
(and aftermarket, for that matter) will be unable to sense that vacuum
properly, thus making the engine run badly and use too much fuel. The
other effect is that the engine will start to idle roughly, compared to
the 110-110 timing. (see later paragraphs on flywheel inertia and inlet
manifold for further info on this, however)
As an example of how a 4AGE idles with 100-100 cam timing, 288° cams, and a stock inlet manifold, have a listen to my AE-86 . Like a rotary, huh? :)
Another important factor to getting good performance in a 4AGE, and any engine in fact, is to reduce the inertia of the engine by as much as possible. This of course means reducing the weight of everything that rotates or goes up & down. This is one of the main reasons why good pistons, con-rods, etc, cost a lot of money - They are made of better metal, made stronger, and weigh less. They also aren't a mass production part like the rest of your engine, so they will cost more per unit anyway.
They are also worth it.
Possibly the best value for the price you pay is a lightweight flywheel, as they affect the ability of the engine to pick (and lose) revs rather dramatically. It's effectively free power, even though it doesn't affect the actual power of the engine at all, ie, if you put two engines on dynos, one with a lightweight flywheel and the other stock, then they'll make the same power. Put the two in cars and go drag racing, the one with the lightweight flywheel will win every time.
The 4AGE is no different, of course, and you can run a flywheel down to about 4.7kgs no worries on the road. I have a 3kg one in my AE-86 and it's fairly liveable ... ;)
It's often said that a lightweight flywheel will also cause the engine to idle roughly, but this is more likely to be something else out of tune. (Eg, my racing car with it's 2.5kg flywheel idles dead smooth, and when I went from the stock 7kg one to the 3kg one in my AE-86 I didn't notice any difference) That something else, in the case of the 4AGE, is most likely to be a combination of cam timing and the inlet manifold. More on this later.
Crank and con-rod
There are basically two sizes with the 4AGE's, and they can be divided up into the ones that the small and big port engines use. (Note that the 20v and the 4AGZE all use the 'big' crank & rods)
Both types are fine to use up to about 200hp, but after that the big crank & rods are less likely to give trouble. For high revving engines though, the small crank will 'give' more power at those high revs due to causing less friction. (smaller crank journals causing less drag, etc) If you've got a high revving engine that makes more than 200hp, you should give serious thought to getting one of those hard-to-get forged cranks, which are of the 'small' dimensions.
You have to live with whatever size con-rods that go with the crank, but the weight of them can be reduced a tiny bit by very careful grinding of the cap and taking the casting flashes off the little ends. The standard rod bolts are good for up to about 180hp, but past that a good set of ARP, etc, are required.
Oils & filters
The oil you use in the 4AGE will also affect its performance, though you won't really notice much difference on the road. The only oil you should use is a full synthetic, such as Mobil One 10W-50 or the like. If you're in a country where the temperature isn't too high and you want that last little bit out of the engine, then I recommend Shell Helix Ultra 0W-40, which can give you an additional 5hp or so over any mineral oil. The only hassle with that oil is that it gets very 'thin' when hot, so it must be kept to a reasonable temperature by using an oil cooler, or if in a road car by not running flat out all the time. (give the engine a break for 30 mins from running flat out by driving slowly)
To give you an example how much difference they can make, I used to use a synthetic oil for regular driving, but when I ran my car in an event at a race track I decided to run a good racing mineral oil (another really dumb thing I've done ...) and much to my surprise it wouldn't start on the morning of the race day, because it wouldn't spin over over fast enough. Luckily I had parked it on a hill and so I could roll start the car.
Note that part of that problem was that my starter motor was a little tired, but this is typical of aging 4AGE starters anyway.
The standard Toyota oil filter is excellent, and they are (AFAIK) the same unit used by TRD for racing. If you feel that you need a larger filter, the one used on the UZ series of engines also fits and has about 48% more volume.
A lot of the current bearing kits for the 4AGE have the main crank bearing shells with only one half being grooved and the other flat. This is not good, as the oil flow at high revs may suffer, and the con-rods may run out of oil. Not good! The grooved ones are the best way to go as they ensure a constant supply of oil.
If the bearing kit that you get from your local supplier is like that, then either don't accept the kit or get two of them to make one good one.
In my RWD 4AGE I run the stock injectors with stock fuel pressure, and when the engine was making 160hp the injectors still had more than enough flow to run richer than what I needed, but they're very close to their limit and to go any further I would need to use either more fuel pressure or bigger injectors.
Copied from my Stock 4AGE page, here is the injector sizes for the (Japanese sourced) 4AGE -
|TVIS big port||182cc/min|
As soon as you get away from using the factory computer with the 4AGE, you will have to find a way to control the spark advance, as the factory distributor has no mechanical advance mechanism at all - The computer does it all. The distributor has two 'trigger' wheels inside it, one for the computer to sense the rpm of the engine and the other for sensing when a piston is at TDC.
The cheap & nasty way to make the dizzy work without the factory computer is to simply hook up an ignitor module (eg, Bosch) and then run the engine without any spark advance. Speaking from about 70,000km experience of this, it's really not big deal - The only hassle is that the engine can be a little hard to start when cold or very hot.
Another solution is to fit the engine with an electronic dizzy out of a 4K-E, as they have an electronic 'reluctor' like the 4AGE dizzy, but also have mechanical spark advance. They require a small adapter plate to be machined up, but it doesn't look very difficult to do from what I've seen.
I have also seen a small black box, when I was living in New Zealand, that hooks up to the 4AGE dizzy that controls the spark as if it had regular spark advance. Unfortunately, I can't remember the name of the box in question, but it was about NZ$400, or about Aus$300.
Yet another way to control the spark, even on a heavily modified engine, is to use the factory computer in parallel with whatever you have controlling the fuel already. All you have to do is run the tacho trigger and power to the factory computer and run the right output wires from it to the factory dizzy and it should control the spark in much the same fashion as a stock engine does. (not sure if the factory computer uses MAP sense to modify the spark advance output or not, but it'll still work ok, and certainly be better than nothing in any case)
The best way to control the spark on a modified 4AGE, however, is to use a good aftermarket computer, such as a Motec, Adaptronic, Autronic, etc. They all have very customisable maps to accurately control the spark advance, and so can be made to give the best possible power at all times. The other methods mentioned above are quite simplistic by comparison, but are fine for road use anyway. A full race engine requires the best possible method available, so there is need to be able to control the spark on the odd occasion by even knowing which gear the car is in ...
The standard inlet manifold is adequate, but pretty far from being good by any stretch of the imagination. I know from one particular race engineer that it's possible to get 190hp from a RWD manifold, but I think that for us mere mortals more like 170hp or so is more practical. (naturally aspirated, of course)
What I'd really like to say though is that if you have the slightest chance of throwing the factory manifold away and using a decent twin Weber style manifold then do it right away! There are a couple of reasons for doing so -
- Since you'll have to be running an aftermarket computer anyway, you won't have any troubles with the complete lack of a decent inlet vacuum to sense off. The only way to go is to use a throttle position only type computer, which schedules the fuel by sensing a combination of TPS (Throttle Position Sensor), RPM, water temperature, and air temperature.
- The airflow into the inlet ports will be a LOT better, as it'll be even for each cylinder instead of having different amounts, as the factory manifold has.
- The engine will idle like 'normal' engine does, ie, smooth! Yep, I've found out that if you use a factory manifold with anything bigger that about a 260° odd cam, then it'll start to idle roughly. By simply using a twin Weber style manifold, the engine will go back to being smooth idler. I'm not totally sure why this is the case, but I think it's due to the plenum chamber in the factory manifold, and the single throttle body affecting the airflow into the engine. (Quick note as I'm doing a site update: I did this mod on my own 4AGE in November 2001 and yes, it really does make the engine idle a LOT smoother. Even with the 288° cams it idles much like a stock engine)
Some people spend a fair few dollars on fitting the factory manifold with a bigger throttle, to try to increase the amount of air going into the engine. This is a waste of money as far as I can see, as I have a dyno report on a engine that has had that mods done and there was a 1hp - 2hp improvement. This is more likely to be dyno error that any actual increase in power as such. The factory TB is 55mm in diameter, and while it may not seem to be that large remember that the engine only has one cylinder sucking at a time, so a 55mm hole is actually quite large. FWIW, a typical twin Weber 45mm set-up for a big HP 4AGE would have something like 40mm chokes for each cylinder, which is obviously a lot smaller (~53% the area) than the 55mm TB.
The Toyota Variable InductionSystem is designed to, and really does, improve the power of a stock engine at low revs. From experience with talking with people around the world, it's best left in the 4AGE with cams smaller than about the 270° size. Past that size, however, the engine will make more torque by removing all the TVIS butterflys, the butterfly pivot shaft, and then block up the remaining holes to the outside world with a good sealer, such as Devcon.
See the next page for a diagram on the TVIS manifold.
Webers & other
Twin Weber kits for the 4AGE are readily available around the world, and they vary in price quite a bit. As described on the first page, it is not too difficult to make a twin Weber style manifold at home, and it'll cost very little. Buying second hand Webers can be a little risky, and if there's any doubt at all they should be rebuilt with any worn parts (often the needle & seat, for example) replaced. Any purchased Webers will also most likely have to be re-jetted to work properly with your 4AGE, and if buying them new you should be able to buy the carby with the jets you want. If second hand, they also most likely need to be re-jetted.
So what jets & emulsion tubes, etc to get?
Well, it's a bit hard to guess because there are that many different possibilities that could be needed for all the different 4AGE's, it's pointless trying. But typically they would use something like 145 main jets, 200 air correction jets, F16 emulsion tubes, and 36mm chokes. That's a start.
Apart from the usual Webers, there is also Dellorto's and a couple of types of Mikuni carby that're a straight bolt-on in place of Webers. All three types have their own plusses & minuses - cost, availability, etc - but Webers are usually the easiest to get bits & pieces for. They are not necessarily the most tuneable or the best, however. Another possible carby to use is the flat slide Mikuni's, which are quite popular in Japan, but are rather expensive. (Though you can get lucky hunting around the motorbike wreckers)
One final word on carbies though - If you have a choice of using a reasonable programmable EFI computer or any brand of carburettor, then in every case use the injection gear, as you'll have far superior tuneability and reliability. Also - if using EFI then make sure to also use a good swirl pot and second fuel pump to ensure that the engine gets a good fuel supply at all times.
Toymods Australia is a good places to go for technical advice.
Back to the
On to the third page
Back to the Index page
Page & contents where applicable © Bill Sherwood