Supercharger Performance and Engine Performance Parts

Posts Tagged ‘Positive Displacement’

In 1986, Toyota released a supercharger car based on the stellar 4age motor found in the corolla. The MR2 with its mid engine rear wheel drive platform was a great everyman’s supercar and was powered by the 4agze supercharged motor… 

Now, everybody’s heard of unicorns, these mythical creatures that somewhat similar to horses, but possess more beauty and more power with their visually distinctive uni-horn. However, nobody’s ever seen a unicorn. Some of us may even begin to doubt that this mysterious creature every existed. The same goes for the 7AGZE engine. Almost everyone I know who’s interested in Toyota has either heard of it, thought of it (and thought it was original), or thought of actually trying it? But to date, very few people have seen it.

The 7agze is a hybrid engine of:

4age:  a 1.6 liter rev happy engine first introduced in rear wheel drive corollas. Coupled with a 5 speed manual , a Front/Rear drivetrain configuration, and a very light chassis (no airbags, no crumple zones, no sound deadening, no seat massagers, no nonsense) made for a fun commuter car that later became a drifter’s modern classic.

7afe: a 1.8 litre stroker version of the 4age that was used on early 1990s celicas. The 7afe increased displacement by 12.5%, brought peak torque at a very low 2800 rpms. However, the 7afe differs from the 4age in that is uses the Toyota ‘F’ head design with a narrower 22* valve angle for increased low rpm fuel efficiency at the cost of high rpm exhaust scavenging and peak performance.

4agze: The ‘Z’ in 4agZe stands for a positive displacement roots style supercharger. The supercharger was a good compliment for the high revving 4age in giving it better torque at lower rpms and increasing peak power potential to take advantage of the high flow , large port head.

3 way compare:

The Toyota 1.2 Liter SC12 is a positive displacement roots style blower, with teflon coated rotors and a computer controlled electromagnetic supercharger clutch.

The 7agze is not a motor produced by Toyota. The 7agze is a ‘unicorn’, it is an enthusiast concoction similar to installing GT-40 heads on a mustang small block ford to come up with a ‘factory parts’ hybrid car that outperforms both the original engines. The goal of the 7agze is to create a hybrid motor using the 7a stroker bottom end with the high flow ‘g’ head from the 4age (with its matched cams and intake/exhaust manifold that are optimized for peak power delivery at 6600 rpms, which is much closer to the 7afe’s redline of 6300 than its current peak power rpm of 5600) and to produce a car that supercharged to about 10psi of boost will produce:

203 hp @ 6600 rpms @ 10psi and 180 ft.lbs of torque at 2800 rpms

By doing so you create a motor that has higher peak power than all three of the original motors, and have a wider power band of 3800 rpms compared to 1800 , 2500 , 2800 powerbands for the 4age, 4agze, 7afe respectively. So not only do we have a more powerful motor, but we now also have a more usable motor that is better performing in mid-gear passing acceleration and on corner exits on the track!

Coupled with a light bodied race-car, and some sticky rubber, 200 measly horsepower can run circles around much more powerful cars with heavier less poised bodies.

The 7agze is a unicorn that is seldom seen on the road for many reasons:

In 1986 Toyota introduced a mid engine rear-wheel-drive car powered by a supercharged 1.6 liter with a 7300 rpm redline. The people's superchar of its time!

1-      It requires a unique blend of junkyard sourced or Japan sourced parts from THREE different motors. This scavenger hunt style engine build can take a long time in planning and sourcing parts before the build can even begin.

2-      There is no factory computer that will work for this hybrids as the stroke, piston speeds, peak power figures, and volumetric efficiency of the motor shift all over the place from the unique mix of a shorter bore/stroke ratio, a higher flowing head, and clutched supercharger that can be switched on/off at the user (or the ECU’s desire).

3-      Due to the differences between the ‘F’ series head (that utilizes dual overhead cams driven by a single cam gear and a ‘master and slave’ gear set between the intake and exhaust cam), and between the ‘G’ series head (that utilizes a true dual overhead cam setup with two cam gears) then neither the 7afe nor the 4age nor the 4agze timing belt is a direct swap for this hybrid motor. The proper installation and timing of the engine requires an enthusiast with the patience and understanding of cam and crank timing to make sure the rotating assembly is put together properly.

Because of these three reasons, the 7agze has usually been left to enthusiasts that want to showcase their mastery of part sourcing, engine tuning, and engine building as all three skill sets must be present to build one of these (in stock form). Building a modified 7agze with more power requires even more wizardry.

One such example of well put together 7agze is the beast put together by ‘The Boffin’, the list of modifications includes:

Engine
7agze
1800cc 7afe block 1996 celica st overbored & decked
4age big port head polished & ported
HKS 1.0mm steel head gasket
Oil cooler pistons jets machined in
Arias 81.5mm oversized forged pistons
Pauter forged rods w/oil feed to small end
Porsche 924/944 1986 117x19mm timing belt
NA inlet manifold
Celica GT 55mm throttle body
Supra 1ggze/previa sc14 1435cc supercharger w/sc12 125mm small pulley fitted
Fensport oversized pulley kit
HKS adjustable cam gears
AE92 4agze dli & ecu
PFC HKS f-con & gcc
400cc black supra injectors
HKS super header 2 s/s 4-2-1 manifold & super drager exhaust
HKS intercooler

The 7agze sitting happily in the AE86 corolla and ready for battle.

Some of the most notable parts on this particular install is the use of the larger SC14 (1.4 liter) supercharger combined with a Fensport 176mm crank pulley and 125mm supercharger snout pulley. The resultant pulley drive ratio is 1.408:1 so with each revolution of the motor we have 1.4 revolutions of the supercharger and a total of 2020.5 cc or air. In comparison, the 4 stroke 1.8 liter 7agze breathes in about 900cc per revolution (half of its displacement) of air depending on its exact volumetric efficiency at that rpm range.

The result of this combination is an easy 18psi of peak boost pressure and a potential peak power figure of 270 horsepower @ 6600 rpms!

Also notable here is the use of a 4-2-1 exhaust manifold. Four into two into one (4-2-1) exhaust manifolds merge adjacent firing cylinders together first, and then merge the two resulting exhaust branches into the final exhaust collector. This creates two distinct exhaust pipe lengths (one equal to the length of the primaries, and one equal to the total length of the header tubes from flange to collector). This in turn produces two resonant peaks (or two rpms where power and volumetric efficiency) is boosted which goes well with the promoting a wide and linear power-band between those two peaks. This header design then matches our engine build with a wide 3800 rpms power band. On cars where power is more peaky or the power delivery is over a narrower rpm range (such as a normally aspirated 4age with only 1800 rpms between peak torque and peak power), then the use of single merge 4-1 header usually does a better job of exaggerating that single power peak, however for this application the choice of a 4-2-1 header is perfect, and it doesn’t reduce any top end power as the high boost and high flow head can take care of those tasks.

Final thing to notice here is the use of the fully programmable HKS F-Con and GCC which give the user the ability to completely remap the fuel and ignition timing delivery during high power demands, but leaves the stock ECU in-place to take care of items better fit for the OEM ECU such as idle speed control, and closed loop fuel tuning (for good mileage and efficiency) during cruise and low load conditions, such as other more delicate controls such as knock detection and active timing retard to save the motor in case of a bad fill of gasoline.

Very neat little motor (that would be a great learner experience for a father-son build due to its coverage of all things automotive from engine assembly , to timing, to EFI and tuning , to supercharging …etc) and also a great example of supercharger performance boosting the power output and competitive nature of a frankly small displacement motor.

Here is a video of a NON SUPERCHARGED 7age taken to 7000 rpms…. just imagine 18psi on top of that!

For more information on the remainder of the modifications on this car or to contact the owner directly please visit: Driftworks

Technorati Tags: 4age, 4agze, 7afe, 7agze, Fennsport, HKS, MR2, Positive Displacement, roots, SC12, SC14, Toyota

Positive displacement superchargers do not usually compress air inside the supercharger but rather better described as air pumps. Positive displacement superchargers are usually rated in liters or cubic inches (or a similar measure of displacement). The reason behind that is that a 1.5L rated positive displacement supercharger moves 1.5 liters of air per revolution and so to produce 15psi of boost (or a pressure ratio of 2.0) on a 1.5 liter engine, the supercharger would have to be geared to double the rotating speed of the engine. Thus for every round of the engine, the engine would normally ingest 1.5 liters of air, at the same time for every round of the engine, the supercharger completes two full rotations because of the gearing between the engine crank and the supercharger, and thus the supercharger puts out 3.0 liters of air for every 1 revolution of the engine.

The result is that the supercharger pumping and feeding 3.0 liters of air to a 1.5 liter engine, which results in the air being compressed inside the intake manifold between the cylinder and the supercharger, and effectively forcing the engine to breathe twice as much air, simulating a motor that is twice as large, and producing double the horsepower.

Based on this theory, the easiest way to raise the boost and thus increase the power of a supercharged car is to increase the gearing between the engine and the supercharger, making the charger spin faster and force more liters of air into the engine for each revolution.

However, superchargers are limited due to the size and weight of their rotating assembly, the tolerances between the tips of the rotating rotors, and the adiabatic efficiency of the supercharger to a certain maximum operating rpm. Exceeding the maximum rpm causes the supercharger to become inefficient, producing extremely hot output air which isn’t good for performance, possibly over-vibrating and overheating its internals and permanently damaging the rotors or having them contact the housing, and increasing the supercharger drive requirement excessively (the horsepower required to spin the supercharger to that rpm).

One of the solutions to increasing the performance of your vehicle is to upgrade to a larger supercharger, that can pump more air per revolution and so produce more boost and more power at its maximum operating rpm. However, having most supercharger kits incorporate the supercharger and intake manifold or the supercharger and throttle inlet in one mechanical package it becomes difficult to just swap to a bigger supercharger as you would with a turbocharger.

The next best solution available in such a situation is modifying the existing supercharger to make it more power friendly. Since the primary utilization of positive displacement superchargers is for factory vehicles and OEM manufacturers, there are many provisions built into the manufacturing process of the supercharger geared towards reducing the supercharger’s manufacturing cost as well as improving its NVH (noise, vibration, harmonics) performance such that the factory vehicle can adhere to local or international design standards.

Now if we’re willing to spend some money to improve our supercharger, and we’re willing to put up with (or better yet yearning for) more of that iconic supercharger whine, then supercharger performance porting becomes a viable option.

The goal of supercharger porting is to essentially turn our 1.5 liter supercharger into a 1.8 liter supercharger for example. So in simple terms, modifying the supercharger so that it is capable of pumping more air volume per revolution, and so producing more peak airflow (in CFM) at the same maximum operating rpm.

The modifications typically performed when modifying a supercharger include:

·         Enlarging, blending and smoothing the supercharger inlet port

·         Casting protrusion elimination

·         Raising the roof

·         Enlarging and reshaping the outlet port

·         Rotor coating

·         Plugging the silencer ports

A brief overview of the twin rotor supercharger:

The supercharger typically has two helically twisted three prong rotors encased in a dual chamber housing. Air enters the supercharger from the back of the charger through the inlet port, and is guided to the top part of the rotor housing called the roof. As the rotors turn in opposite directions, they grab the air that is available in the roof of the charge, and trap it in tight tolerance between the rotor blades edges and between the supercharger sidewalls. No compression is performed to the air, it is just trapped against the supercharger wall and pumped downwards with the rotation of the rotors.

As the rotors reach the bottom (the floor) of the supercharger they release the air into the manifold through the supercharger outlet port. The fact that the supercharger is overfeeding the engine causes the air to compress as it exists the outlet port (as explained earlier) through positive displacement of more air than the motor can breathe.

Now in light of that, let’s review our modifications:

·         Enlarging, blending and smoothing the supercharger inlet port

The supercharger inlet port is where our modifications will give us the most improvement result because it reduces restriction in the intake path of the supercharger. With reduced restriction, the supercharger can flow air more easily and that reduces horsepower drive loss and increases flow per revolution. Since this part of the supercharger has no fuel in it, and thus there is no fuel atomization requirement, the internal walls of the inlet port can be polished and smoothed. Any sharp turns or transitions between the throttle body or the supercharger inlet and the supercharger housing should be smoothed, also any rough transitions between the inlet port and the rotor housing should also be smoothed especially on the top half of the charger (opposite the outlet port) as that is where the rotors get their fresh air.

·         Casting protrusion elimination

Due to cost reductions in supercharger production, sometimes there are some materials protruding the inlet port of the supercharger. Any such protrusions should be removed, and then the housing refilled with aluminum putty filler or JB Weld, and then resurfaced smooth.

·         Raising the roof

Slightly raising the roof of the supercharger gives the supercharger more volume of air to grab per revolution.

·         Enlarging and reshaping the outlet port

Depending on the target pressure ratio for the application, there is an obvious relationship between the area of the inlet port and the area of the outlet port. If air enters the supercharger at 0psi (which is 1 atmosphere) and exists the supercharger at 15psi (or 2 atmosphere) then the exiting air although it has the same mass, has half the volume. So it makes sense that if our inlet port is 20 square inches large that at a target pressure ratio of 2.0 our outlet port need only be 10 square inches larger. Thus enlarging the outlet port doesn’t necessarily have much power gain potential because inherently it is less of a restriction.

When porting the supercharger outlet port, there is a limitation to how much we can enlarge the port or reshape it. The supercharger has a helical twisted rotor and for eaton this is a 60 degree twist. If you visualize a twisted rotor spinning, capturing air between the rotor and the housing, and then as the rotor’s blade reaches the floor of the rotor housing the rotors blades create a V shaped contact area.

This is why the outlet port is V shaped or triangle shaped to match the twist of the rotors and to make sure that air stays trapped properly till the rotors reach the floor of the housing to force the air into the manifold.

Enlarging and smoothing the outlet port is possible however, the maximum that we can enlarge this port to can be found by tracing a line around the exact point where the rotor touches the housing floor of the charger housing and porting to that line.

·         Rotor coating

One of the changes between the earlier and later generation Eaton superchargers is that the newer blowers have coated rotors. The rotors are coated with Teflon/Ceramic/Carbide abradeable coating. The coating does two things:

1-      Helps the rotors withstand, distribute, and manage heat better especially when using the supercharger at higher rpms.

2-      The  coating adds thickness to the rotor. When the rotor is heated by its normal operation it expands to a certain extent. If the rotor expands too much within the housing then rather than having a proper seal against the housing wall (to trap air) it may touch the wall causing the whole assembly to catastrophically seize. To prevent this seizure, there is typically a tolerance (a room for error if you will) left between the rotor tip and the housing. This room is bad for performance because it allows the air to escape rather than be trapped by the rotating rotor and thus reduces the superchargers pumping and adiabatic efficiency. To improve efficiency on the later generation superchargers the Eaton engineers have come up with an abrade-able teflon-carbon based coating that makes the rotor slightly thicker. When the rotor expands it now basically touches the housing, but this is now not a metal on metal contact, but rather a metal (housing) to carbon-teflon (rotor coating) contact. What happens here is that the harder material (which is the aluminum housing) wears down the softer material (the carbon-teflon coating) shaping it to the exact shape of the housing and giving a more exact seal between the rotor tip and the housing, better trapping air, improving supercharger flow per rotation, reducing pumping losses, and thus reducing outlet air temperatures. This idea can be used on any twin rotor charger to improve rotor seal and is really a great engineering solution.

·         Plugging the silencer ports

Besides the supercharger outlet port, there are typically two or more smaller ports called the silencer ports. Depending on weather whether the air in the supercharger housing or the air in the intake manifold has a higher pressure, then these ports allow air to flow in and out of the supercharger housing around the rotors to faster equalize the pressure between the two chambers. Reasons for having pressure differences between the supercharger and the manifold attached to it would be like having a throttle body in the system after the supercharger for example. If this throttle plate is rapidly opened (jumping on the throttle –full throttle) or rapidly closed (going from wide open throttle immediately to no throttle) then positive and negative pressure waves will travel back and forth between the throttle body plate up the intake system and reflect off the supercharger outlet back and forth. These pressure pulses and fluctuations caused by the dynamics of the engine are unavoidable. As we all know, sound is created from pressure waves and so these waves reflecting back and forth in the intake system create some unwanted noise in the engine bay, more so if we have a sealed system where the pressure waves are trapped to reflect back and forth multiple times. The supercharger silence ports are small bleed ports between the outlet of the supercharger that bleed air back into the supercharger housing. This is obviously bad for pumping efficiency because some of the air pumped in by the supercharger is not held as boost, but always being bled back (as a designed air leak) back into the supercharger housing. But as we said before, in situations where there are dynamic pressure changes between the supercharger housing and the rest of the intake system, having this air bleed allows the pressure to equalize faster (rather than waiting for it to reflect and die out) which improves noise performance.

Since we are interested in improving the pumping efficiency and are not required to adhere to noise, vibration, and harmonics standards like original equipment manufacturers, these ports are typically plugged with aluminum putty or JB weld and surfaced down to a smooth finish. Now that we’ve done so, 100% of the air pumped by the supercharger is trapped in the engine which increases our boost pressure and our positive displacement of air per revolution.

Results of all of these modifications are typically in the 10 to 15% range, so depending on whether we are talking about a 200hp capable Eaton M45 or a 500hp capable Eaton M120 gains will vary between 20 and 75 hp which are sizable increases. Further performance gains can be found by increasing the supercharger rpm (now that it is able to flow more air at higher RPMs after it has been ported) and so higher gains are possible for race applications. I would be reserved though about exceeding supercharger manufacturer stated peak operating RPMs for road going vehicles that will see extensive use of the supercharger at those RPMs.

Technorati Tags: engine performance parts, Porting, Positive Displacement, Rotor, supercharger performance