4agze Twincharger Conversions

[AE25]

Ahh.. the beauty of a twincharger.. is having a smallish capacity engine that has effortless acceleration and feels like a larger engine due to the low end boost from a supercharger, yet has the ability to ram copious amounts of air into the engine for awesomeness and top end power from the turbo. YET be able to turn the s/c off for fuel efficient naturally aspirated motoring at cruise and idle :cool: I see this as a performance ideal we will see more of in the future as engine emissions and also engine capacities will be getting more and more restricted.

 

i've been doing a bit of research into this as I'm seriously keen to build a 20v twincharger in particular myself.

 

I would like anyone that has any decent links or info to add to this thread

 

So, in my searches.. there have been three main twincharge concepts worth discussion.

#1: compound boost. where a turbo blows into the SC without a bypass. the s/c compounds the incoming pressurised air via it's compression ratio so a larger total boost is seen. both chargers can be setup to run in their peak efficiency zones, and inlet manifold and exhaust pressure ratio can be tweaked, which gives better cylinder scavenging, better knock resistance, less residual heat etc.

#2: Turbo into SC with a bypass. ie a sequential setup. The SC is there purely to get the turbo up to speed quicker, which then does all the work.

#3: SC into Turbo with a bypass. again, SC is there to spool turbo quicker, and then SC is bypassed.

 

 

Fensport bought an hks twincharged front cut and installed it in their project ae92 and are were modifying it.

they had a diagram of it on their website (below). (unfortunately their site has not been updated in a while???)

http://gama.main-hosting.com/~logabyte/twincharge1.html

This would be the turbo into sc sequential setup. throttle before SC.

diagram not by fensport.

 

 

has anyone got ideas on control systems for SC switch on/off and controlling the bypass valve in a sequential setup?

 

one solution (as 'twincharger' has done on his ae86) is use a one way valve as a bypass so that when the turbo out flows the s/c, the sc is switched off and the bypass flap opens to bypass the SC. The valve will not open by itself is the SC is running due to the compound effect as theoretically the valve will always have more pressure behind it than before. It will be tricky to get the SC to switch off at the right point and back on again. if not done right, then a definate drop in boost will occur at the switchover point.

 

'twinchargers' setup in ae86 (turbo on intake side)

 

If doing a sequential system, it seems better to use a diaphragm operated poppet valve (wastegate style) or butterfly.. like the nissan march superturbo (have found a good source for one too, the toyota 2L-T diesel has one). this runs off vacuum so will likely require a replacement dual diaphragm like found on an external wastegate. i was thinking to have it operate similar to the one-way, ie have it operate on pressure difference, ie once the pressure behind it raises above the pressure before it after a set boost threshold, then it will start to open. ie set a spring load on the diaphragm shaft so it stays shut until say 1psi more than the maximum sc boost pressure, then gradually open until just before maximum boost is reached.

 

as to s/c clutch control.. i have limited experience of the 4agze system apart from a fang in a mates aw11 mr2 supercharger.

the sc clutch relay appear to run off the ecu.. so likely be controlled either by afm position or map. 8" vacuum is apparently where the s/c turns on.

If a clutched SC is used, it is better for efficiency and durability to have it turn off at idle and cruise/coast conditions. some form of pressure activated relay with a time delay will do this. (time delay for gear changes and short duration decelleration).

it is debateable whether it is worth turning the sc off at high rpm when a sequential system is used. the sc will be free wheeling basically, so load on the sc should be minimal. depends on use of the car.

 

another idea for clutch control, would be to make use of the std map gze ecu controlling the s/c clutch on/off events yet intercept the relay at higher rpm and/or once turbo is boosting to switch it off if you desire, yet cut back in when intake plenum has vacuum and rev's dropped below the turbo's operating range... wouldn't want the sc clutch to engage as you back off the gas at 7000rpm every time.. this is another hurdle to overcome. was the HKS system somehow similar to this? complications... meh. keep charger on.

 

VW have recently put into production their 1400tsi twincharger engines which won awards. 125kw and 32.5mpg

Edited August 22, 2010 by AE25

[Sam_Q]

the vw idea I think is the most superior option by a long way, but you ideally want to have supercharger turn right off when not used. Fitting a supercharger on the side of a 20v would be tight

[AE25]

yep it is tight.. you have to modify the pipe that comes out of the head into the water pump for a start... but it will fit under there once thats done and you move the vacuum pipes under the throttles and make a new top mount for the charger. this is 'twincharger's one on the link in first post

 

 

soo many ways possible to do it..

 

i'm tossing up wether to have the turbo outlet plumbed over the top/rear of engine into the charger or just have the charger non intercooled so it's plumbed into a normal turbo setup :cool: (chargers on opposite sides of engine)

will be making up various design sketches soon...

Edited May 18, 2007 by AE25

[AE25]

after looking into it further..

the water system of the 20v with supercharger needs to be totally rerouted. you could mount the charger further away from the block to retain factory 20v cooling system but most rwd conversions will be out of room.

using the factory 4agze bottom mount and pulling the charger up close to the quads, theres just enough room to squeeze the water pump inlet pipe past the sc to a remote thermostat sitting behind the charger under the intake. the factory 20v head-to-waterpump pipe will not fit. is a bit too much of a squeeze to get even a custom pipe made to fit without it going down past #3 cylinder and back to the front. no reason this couldn't be done but will have to also move the vacuum piping under the quads for enough clearance. there is a limit to how close the charger is mounted to the block due to the knock sensor (in pic)(edit.. have found gze have knock sensor fitted between #3&4 cylinder rather than #2&3 as found in smallport 16v and 20v). the std sc12 bottom mount had to have the rear bolt hole milled 8mm off the underside so it mounted flush with the block with an ae86 engine mount sitting underneath it. a custom engine mount could otherwise to be made to bolt on top.

 

 

 

what I'm looking into doing now is have a manifold off the back of the head that joins the two holes together (rather than grind a water passage out of the back of the head and weld the holes up) so that the hot water coming out of the block goes thru the head under the quads and out the front hole above the water pump... this is then the hot out to the radiator and has enough room (if you design the top sc mount to fit around it). this should also get rid of any possible airlock problems that could be caused if the hot out were to come off the back of the head and then down under the charger etc. hot out should stay high so all air in the system can easily get to the radiator.

 

it would look something similar to this awesome drawing

from this

 

to this

Edited August 3, 2007 by AE25

[mlaser]

There's actually a 4agzte for sale in NSW at the moment on ebay

 

http://cgi.ebay.com.au/AE92-Corolla-levin-...1QQcmdZViewItem

 

who knows you might be able to email the dude and get some better pics.

 

after looking into it further..

the water system of the 20v with supercharger needs to be totally rerouted. you could mount the charger further away from the block to retain factory 20v cooling system but most rwd conversions will be out of room.

using the factory 4agze bottom mount and pulling the charger up close to the quads, theres just enough room to squeeze the water pump inlet pipe past the sc to a remote thermostat sitting behind the charger under the intake. the factory 20v head-to-waterpump pipe will not fit. is a bit too much of a squeeze to get even a custom pipe made to fit without it going down past #3 cylinder and back to the front. no reason this couldn't be done but will have to also move the vacuum piping under the quads for enough clearance. there is a limit to how close the charger is mounted to the block due to the knock sensor (in pic). the std sc12 bottom mount had to have the rear bolt hole milled 8mm off the underside so it mounted flush with the block with an ae86 engine mount sitting underneath it. a custom engine mount could otherwise to be made to bolt on top.

 

 

 

what I'm looking into doing now is have a manifold off the back of the head that joins the two holes together (rather than grind a water passage out of the back of the head and weld the holes up) so that the hot water coming out of the block goes thru the head under the quads and out the front hole above the water pump... this is then the hot out to the radiator and has enough room (if you design the top sc mount to fit around it). this should also get rid of any possible airlock problems that could be caused if the hot out were to come off the back of the head and then down under the charger etc. hot out should stay high so all air in the system can easily get to the radiator.

 

it would look something similar to this awesome drawing

from this

 

to this

[beerhead]

I haven't heard the best thing about those HKS twin charge kits on the GZE, apparently they drive full throttle for 2 seconds after you throttle off. Fine on a race track, not so good on the street. The VW setup is far superior.

 

Nice to see someone having a go at a twincharge motor, I hope you get this thing running well.

[bullet79]

-drove a Nissan March superturbo (k10), MA09 1000cc twincharged,.. ssshitting in pants too... super nice response with these twin-charge motors... plus a feather weight chasis.. hmmm :evil:

[Jordan]

the easyest way to go twin charger is to run the turbo before the super charger and have it blow throught the super charger in a compound setup. it avoids and complex bypass valves, and there's no issue with it switching from supercharger to turbocharger, since the SC is always on and the TC just shows up when the time is right. No lull in power.

 

It's best to have and intercooler and an aftercooler in order to avoid super high intake tempreatures, even water injection can work well here.

 

The supercharger runs all the time (eg off at cruze, but on all the way to the limiter)

 

Cheers

Jordan

[AE25]

thanks guys :) yeap the more I'm researching into twincharging the more i'm getting interested in it. i've read thru countless forums and the amount of bullshit theoretical info is incredible :o i'll probly have to edit some of what i've said but meh.

 

soo.. to add more to this thread:

Most superchargers (ie roots type) will require a recirculating circuit or air release system that operates when the throttle is shut.. used when engine at idle, when braking or between gear changes. the air that the sc is passing needs to go somewhere otherwise bad shit happens... belt slip, popped piping or blown intake gaskets/manifolds!

 

Toyota use an Air Bypass Valve (ABV) in their 4a-gze/1g-gze/1kz-fze(?) engines which operates via a diaphram connected to intake plenum and also controlled via an ecu controlled solenoid. more info on that here http://www.mr2supercharger.com/ABVmods.html

 

To explain the ABV: when supercharger is engaged and throttle is shut, high vacuum in the plenum pulls the abv open creating a recirculating circuit through the SC. once throttle is pressed.. depending on intake vacuum the ABV gradually closes which directs more and more air into the engine until the ABV is fully closed creating pressure in the intake plenum. as you back off the throttle, the intake is under vacuum again which open the bypass circuit allowing the charger to spin freely. the ABV is held shut by a spring rated at the maximum boost pressure which will allow the ABV to open once full boost is reached (8-10psi in factory 4agze system). this is a safety mechanism to relieve any overboost.

The toyota system also has a time delay (5secs?) of full vacuum before the charger is disengaged via the electromagnetic clutch (so it doesn't cut the SC whilst changing gears etc). The clutch is re-engaged at 8" of vacuum, ie when throttle is pressed.

 

The best bypass/recirculating valve to use is an external wastegate off a turbo as these use a diaphragm operated valve which is smooth in operation. (tho expensive) an external wastegate measures the difference in pressure before and after the throttle. The air line connected after the throttle is attached to top of the wastegate actuator so it pulls the valve open.. the air line before the throttle connects on the underside of wastegate diaphragm so any pressure before the throttle helps open the bypass valve. Unlike a BOV (blow off valve) which is designed to open and close suddenly and harshly which can cause flutters and other issues so is not suited as a ABV.

Using a BOV solely to release air to atmosphere from the SC system is both noisy and a waste of power/petrol. imagine your sitting at idle and your engine is constantly pissing air! it WILL get annoying.

 

A BOV is still required when using a turbo.. and in a twincharger system, when used in conjuction with a ABV will only open when the tract after the turbo is under pressure. ie when the ABV is open there will be no pressure in the supercharger circuit to cause the BOV to hiss air. (a plumb back BOV could be a solution to this if noise is an issue)

 

i think some explanatory diagrams are required here :D

Edited November 1, 2007 by AE25

[AE25]

re the HKS 4agze kit problem (first ive heard of this). i can only assume this is happening due to it retaining the factory 'throttle before charger'. if bigger intercooler and piping is added i could only assume that extra volume between the throttle and engine is causing this? ie say (after the throttle) you've got 10psi feeding thru a big front mount intercooler.. after you back off the throttle.. that 10psi of volume needs to be sucked thru the engine before the engine sees vacuum so it can slow down again :o

[AE25]

I see benefit in 3 twincharger systems. none of which are running the chargers in 'parallel' which seems to be the first thing people think of doing! the problem with a parallel system is the supercharger is trying to blow back out the turbo until the turbo sees enough exhaust flow/pressure to spool it up. yes you can fit extra valves and flaps to bypass and divert air but it will only ever increase turbo lag and add complexity. so i think.. why bother when a 'sequential' or 'in series' twincharger system has been proven to perform :D

 

the 3 systems are...

#1 turbo into S/C continuously.

as described previously. This is by far the simplest way as it does not require bypassing the SC or turning off s/c at higher rpm. the supercharger sucks it's air through the turbo which gives bottom and midrange torque.. then turbo comes on boost and blows into the charger (compounding boost) for top end power. A higher total boost pressure is created compared to sequential systems due to the compound effect. the turbo's wastegate controls total boost pressure. Ideally run two intercoolers, one after the sc and one after the turbo.

It needs to be mentioned that this system must run a sufficiently sized recirculation valve on a positive displacement (roots) charger. The air flow through the roots needs a way out if the throttle is shut. The consequences of not bypassing air can be blown piping/gaskets or worse a bent/broken throttle shaft (uncontrolled full throttle and full boost is potentially fatal if occurs at the wrong time!).

 

Also, feeding a sc hot (non intercooled) air straight from a turbo could cause damage to some sc if the sc's pressure ratio is too high. For instance the toyota sc12/sc14 have coated rotors which can melt/delaminate at high temperatures. anywhere above 14psi (boost created by the sc only) can create enough heat to do this. If you run a single I/C after both chargers, the hot air from turbo will add to the heat made by the sc, so a decrease in sc pressure ratio (smaller crank pulley) will likely be required to keep heat under safe levels. This is also required to get a good balance of efficiencies from both chargers. 8psi sc / 15psi turbo etc.

Intercooling and/or water-meth injection before the sc is a good idea. Cameron-datto on toymods forums runs this system in his sc14 4agzte 1200 datsun.

 

#2 turbo into S/C with bypass.

(Nissan March superturbo and HKS 4agze twincharger kit).

The sc provides low rpm boost until turbo matches it for flow. a bypass valve around the sc is gradually opened until the turbo provides all the air. once the turbo out flows the supercharger then the charger can either be left free wheeling or disengaged via electromagnetic clutch.

The bypass valve operation is the crucial bit... it's the GRADUAL opening of the bypass that is essential to a smooth transition from sc to turbo. the bypass valve is set to start opening at anything *above* atmospheric pressure before the SC. The idea here is that the turbo will be matching the flow of the supercharger at the point when pressures balance out, measured before the sc. You will then need to be able to control the rate of valve opening in relation to turbo boost pressure. If the bypass too slow to open it will act like a compound system. you will want a measured amount of this but if the compounding pressure exceeds the maximum overall boost pressure then a spike and resulting drop in pressure will be seen once the switch to turbo is completed. If the bypass acts too fast there will be a pause or dip in boost pressure. the perfect boost curve is one that raises gradually without dips or spikes. Under full acceleration, (going by other peoples experience), the turbo spools up quickly and the bypass change over period happens fast. A poor changeover is not so apparent under full acceleration but shows it's ugly head under other conditions.

The downside of this system is more complexity, more components, more expense, more space used.

A single intercooler system can be used...

1: cooler after turbo.. a low pressure ratio on the sc should keep temps down enough not to require intercooling. The IC needs to be efficient enough to reduce temps entering the sc for safe operation and reliability.

2: cooler after SC.. Turbo boost pressure (heat) needs to be low enough not to overheat the SC. This could kill the benefit of a twincharger system in some setups.

Other options to reduce air temps or knock resistance are to lower engine compression ratio, water/meth injection, better cooling systems, cam adjustment to reduce valve overlap (turbo boost only). if engine is already built then you're left with tuning, ie reduce ignition advance and richen fuel.

 

Throttle BEFORE the sc.. as used in factory 4agze engine and HKS twincharge kit.

This takes away the danger of blowing things up if the sc recirculation valve malfunctions. It's also quieter than throttle after sc due to blocking the noise from charger inside the intake pipes. throttle before sc is the safer option if only a small intercooler is required for the SC and short piping can be used. Throttle before SC does not suit a big intercooler and long plumbing. Increasing the volume of intake tract after throttle and before engine increases sc lag. Along with that, it creates a potentially annoying ability to continue accelerating for a second or two after throttle is released. Any leaks in the supercharger's intercooler or piping is also a big issue, due to air bypassing the throttle. Instant redline from a burst pipe at the wrong time is not good for the health! :o

 

#3 SC into turbo with bypass

SC blows through turbo until turbo matches it for flow then a bypass around the sc or from a separate air filter opens to free up intake air before the turbo. otherwise the sc will restrict air entering the turbo. A single intercooler setup is used, both chargers are before the cooler. The bypass valve is also a crucial part and needs careful calibration on opening rate to prevent any dips in the boost curve. If bypass opens too slowly, the turbo sucks a vacuum into the piping before it (after the sc), thus restricting air flow to the turbo and reducing power. Also a vacuum created before the turbo compressor can cause oil leak issues and increased thrust bearing wear. If bypass opens too early, ie before the turbo matches flow rates, you'll get a dip in boost.

Edited January 16, 2011 by AE25

[beerhead]

the easyest way to go twin charger is to run the turbo before the super charger and have it blow throught the super charger in a compound setup. it avoids and complex bypass valves, and there's no issue with it switching from supercharger to turbocharger, since the SC is always on and the TC just shows up when the time is right. No lull in power.

 

It's best to have and intercooler and an aftercooler in order to avoid super high intake tempreatures, even water injection can work well here.

 

The supercharger runs all the time (eg off at cruze, but on all the way to the limiter)

 

Cheers

Jordan

 

Yeah easy, but highly restrictive. I always thought the idea of twin charging was to be able to benefit from both the positives that most supercharger and turbo charger owners love to pledge as why their kind of boost is better - instant boost of the S/C and and top end power without mechanical load on the crank of the turbocharger.

 

If you're not turning off the supercharger once the turbo is on boost, your wasting power, without a bypass valve the most your motor can make is governed by how well the super charger deals with being force fed. Also, if you know anything about Toyota roots superchargers you'd know they're Teflon coated. Hot air straight out of a turbo onto the blades would cook off the Teflon in no time.

[Jordan]

Also, if you know anything about Toyota roots superchargers you'd know they're Teflon coated. Hot air straight out of a turbo onto the blades would cook off the Teflon in no time.

 

Quite true, that's why you need an intercooler and an aftercooler.

 

Things to remember:

 

all chargers are simply air pumps.

 

a roots type blower is just that. All it does is pump air, it does not compress air. The compression of air is due to the restriction that the motor provides. hence they tend to be inefficient. SC12 and 14 are of this style.

hence if using a total compound setup (simplest) once the turbo is in business and pressure before the SC increases. The SC still only pump 1.2L of air each revolution. It just happens that each 1.2L of air is no longer at 14.7PSi absolute, but rather some number higher.

(I'd have the throttle plate (plates for quads) afterthe SC because, then you cna run a BOV after the SC which sounds amazing.)

 

A better option than the Roots blowers are the Lysholm twin screw suberchargers, which come on such cool engnes as Mazda's 2.3L V6 miller cycle. This particular SC is made under licence by IHI and they are a real nice peice of kit. they're much more efficient and over come many of the short commings of roots style blowers. They're (the one on the Mazda miller cycle engine is) also of a larger displacement then the toyota SC's. Meaning you can run it at a lower speed (less drag/heat) to pump the same amount of air.

 

Low static compression works well for Twinchargers. a nice 7-8:1 is just right.

 

Cheers

Jordan

 

P.S: Twinchargers are dirty, overly complex, hard work, not fuel efficient (ever due to low static compression) but ever so rewarding.

[AminGZE]

Hi AE25,

 

has anyone done their homework on s/c controlling and controlling the bypass valve?

a simple solution (as 'twincharger' has done on his ae86) is use a one way valve as a bypass so that when the turbo out flows the s/c, the one way automatically opens to bypass the s/c

 

I'm a newbie and very blurr about this item (one way valve). Please advise me if you have any product name and where I can get it?

[Luckie_Steve]

Surely a one way valve on a pressure set spring would not be too hard to set up as a bypass valve for the SC...

 

Ya know like getting a spring that collapses at any pressure higher than say 1-1.5psi and fitting it like a waste gate before the SC intake... i know it sounds fairly simple and mechanical but it should be fairly effective as a bypass valve being as a lengthened spring has flex for the variation in pressure and open amount you want...? :P

Edited August 20, 2007 by Luckie_Steve