Extreme Engine Tech, Technosquare’s Monster Naturally Aspirated Toyota 4AG

Extreme Engine Tech: Technosquare’s Monster Naturally Aspirated Toyota 4AG – Part I

by Mike Kojima, photos by Jeff Naeyaert

The Toyota 4AG is a historic engine, one that was essential in launching sport compact car culture in the USA.  In 1985 the 4AG first rocked the automotive world.  It was the standard engine in the Toyota Corolla GTS, the famed Hachi Roku AE86.  The AE86 was the last of the RWD Corollas and Toyota made history by equipping it with the revolutionary A4G engine.  The AW11 MR2 mid engine sports car was powered by the 4AG as well.

For serious motors Technosquare starts with a later model second generation, post 1988 4AG block as found in the supercharged AW11 MR2 or the AE92 Corolla.  This block is important for a all out effort 4AG because the older AE86, NA AW11 and AE82 4AG block is much weaker and block integrity is an issue for high powered 4AGs.  The late block has beefier construction and deeper external ribbing for strength as well as piston cooler oil squirters.  Milder motors under 180 hp can use any 4AG block.  As the first stage of block prep, the interior of the block is polished to remove any stress risers where a crack could start, speed oil return and to remove embedded casting sand.  This is a big issue with iron blocks and an amazing amount of sand is removed while polishing.  The sand can break off and end up in the oil, not good.   The block is checked to see if align honing and is needed. The interior of the block is shotpeened to stress relieve it and to help improve fatigue strength.

At the time the 4AG was like nothing that had ever been offered for sale in the USA in mass quantities.  The engine was exotic, with 4 valves per cylinder, dual overhead camshafts and direct port injection with a variable intake tract.  The redline was a stratospheric for the time, 7500 rpm.  Remember most cars at this time didn’t rev over 5500 rpm.  To allow the high revs the 4AG’s injectors were batch fired in groups of two as the slow ECU’s at the time could not keep up to fire the injectors sequentially at that high engine speed.  At 116 hp and 97 lb/ft of torque, the 4AG out powered its compact car rivals, most of which only produced about 80-90 hp.

This piston cooler nozzle squirts oil on the underside of the piston crown, helping to keep it cool.  This greatly reduces the chances of detonation and piston failure.  The notch cut right below the cooler body and  the other notch in the blocks internal reinforcing rib to the far left care cut by Technosquare to clear the rod bolts due to the 83mm stroker crank that will be installed in this engine.

In racing the 4AG enjoyed a great deal of success in SCCA’s SSC and GT3 sedan classes. Later the 4AG became the spec engine in Formula Atlantic. The 4AG enjoyed a great deal of development by TRD, Hasselgren and Jennings pumping out up to 250 hp in Formula Atlantic trim. Recently there has been a resurgence of interest in the 4AG as the AE86 has become a coveted collector’s car due to the popularity of Japanese drift videos and the enigmatic Initial D cartoon series.  Formula D ace Taka Ono still fights the V8 funny cars in his 4AG powered AE86 with some success.

The pebbly texture of the main bearing saddle shows the surface finish that shotpeening leaves.  A critical area to watch on a 4AG is the area where the main cap meets the block.  The 4AG block is prone to flex in high power applications causing bearing and crank problems.  When the block starts to flex, this surface starts to get a polished look and the main cap gets loose.  In this case the block must be align bored to save it although some engine builders will probably feel that the block must be discarded.

Technosquare in addition to being the official shop of MotoIQ, has had a lot of experience with the 4AG from day one.  Howard and Richey Watanabe of Technosquare were some of TRD USA’s original technicians and were involved with the development of the 4AG from day one.  The Technosquare crew can build 4AG’s from mild to wild and perhaps there is no one better at the job on this side of the pacific.

The block deck is fine milled for flatness and then lapped on a surface plate for absolute flatness.  This is important for seal when using MLS (Multi Layer Steel) performance head gaskets.  The block is bored 2mm from 81mm to 83mm for this monster 1800cc stroker engine and honed with a fine 600 grit stone.  The bore is then plateau honed for good ring seal with modern low tension rings.  You can’t see it but before machining the block’s water jackets were filled 1/2 of the way to the deck of the block with Hard Bloc, a cement based block filler.  This material helps support the cylinder walls while still retaining heat conductivity.  With a big bore, this is an important step to ensure longevity and good ring seal in the thin wall somewhat weak 4AG block.

Lets take a look inside one of their creations built for a customer’s under construction Time Attack AE86.