Sorry, I don't have much knowledge of the G4ED (more like... none) but if you wanted some info on the 4AG I have plenty.
There were 4.5 generations of the 4AGE engine coming in NA and supercharged.
1: Known as the Bluetop, came in the AE86 chassis, AW11 MR2 and AE82 FX-16.
-Weaker 3-rib block
-Smaller crank bearings, smaller wrist pins, thinner rods, just generally lighter and weaker.
-9.4:1 compression
-Because of it's lighter bottom end, it's VERY rev happy and throttle response is fantastic. This is why the 4AG became so popular. About 115hp for AFM versions (north america), and about 128 for map sensored versions. (japan)
-Earlier models came with a 200mm flywheel. Some came with 212mm flywheel. (but only in FWD transaxles)
-Included T-VIS (Toyota Variable Induction System) which would close off half of the intake ports to increase intake velocity (and low end torque) below 4000 rpm.
1.5: Known as the Bastard engine, Redtop bigport, or 7-rib bigport, Late Bluetop
-This motor is the transitional motor between the bigport and smallport motors.
-Strong 7-rib block, thicker rods, crank and pins. Not as rev happy but very strong
-Maintained the 9.4:1 compression
-Maintained the T-VIS system
-With this bastard engine came the supercharged 4AGZE. It needed the stronger internals to handle the boost. The 4AGZE variant came with 8.0:1 pistons. Found in the AW11 MR2 and made about 140hp.
2: Known as the Smallport engine or Redtop Engine. Found in the AE92 chassis.
-This motor had the stronger block, crank, rods, and pins
-Added oil squirters into the block that blasted oil onto the underside of the pistons to keep them cooler.
-Compression raised to 10.3:1
-Made about 130hp here (using Air Flow Meter) and 140hp in Japan (using MAP)
-Head was redesigned. Intake ports were made smaller to increase intake velocity.
-T-VIS was removed due to hotter compression and smaller ports.
-Cams were slightly less aggressive.
-The smallport 4AGZE variant made about 170hp, and was found in the AE92 and AE101.
3: Known as the Silvertop, found in the AE101
-Now running 5 valves per cylinder for a total of 20 valves.
-Came stock with quad throttle bodies
-Updated pistons for the 5 valves, now running 10.5:1 compression
-Internals were still the strong beefy type
-Introduced VVT
-No more supercharged versions.
-Came only in an AFM version and made about 160hp
4: Known as the Blacktop, found in the AE101
-Went back to the early bluetop character in it's revability
-Lightened crank, rods, ultralight flywheel, non-ribbed lightened block.
-Made about 165hp and only came in MAP sensored form
-Each of the 4 throttles were increased in diameter
-Ran 11:1 compression
In North America, the Smallport Redtop is popular as an AE86 swap because you can buy any part for it at any auto parts store. Swapping in a silvertop or blacktop is cool, but if you break something, you'll be waiting months to get a part in from Japan.
Using the stock ECU, only the blacktop can run open throttles as it is MAP sensored. You can figure a way to run silvertop throttles open by converting to MAP (by standalone or whatever) but it is more difficult as there is not a common plenum to get a good vacuum reading, as it wasn't designed for this in the first place. Some kind of vacuum canister will have to be fabbed up in order to do this. The dilemma though is that the smaller silvertop throttles are much better suited for general use than the too-big blacktop throttles.
Many people love the early, old, weak bluetop for it's revability, and would cringe at the thought of swapping something heavier in with less throttle response. It *is* just a joy to drive, that's for sure. You can rev to 8000 all day long, every day, year after year and it still won't let you down.
For ultimate 4ag builds, north america has uses the bigport 4ag in Formula Atlantic (with some mucho stronger parts of course) and Japan uses the Silvertop for Group A.
For ultimate forced induction, people use smallport, silvertop or GZE bottom ends and it's been proven to reliably handle 400hp.
FWIW, the 4AG is discontinued and an outdated design, and the G4ED is still a current model. But you can still do AMAZING things with the 4AG, and you also have over 20 years of history and builds to look back, learn from, and apply to mate with current advanced technologies. Not to mention, there are RWD, FWD, and 4WD transaxles the "A" series toyota engines are mated to from the factory.
[Edited by AccentAE86 on Dec 20, 2005 1:37 PM]
