7AGZE - waste gate and other options?

[PrettyCoolWagon]

Hi guys,

Just discussing this with some other toyota fans at recent winterfest (Vic)

Building a SC14 7AGZE with forged internals, running 9.3 comp ratio, bigport head and cams and adjustable cam-wheels.

Not sure if I should use the sc12 snout pulley and over drive pulleys with this comp ratio.. or play it safe and run with standard sc14 pulley.

On the other hand with torque and longevity in mind.., I mentioned I want to protect the supercharger by letting the bigger flowing ports, forged internals and higher revs take over the top end, some one suggested I use a waste gate that has a set pressure rating, for example 10-12PSI

Interested in discussing this further.
Like the outcomes of the various combination I could set up, If using a waste gate, how to choose where to locate it?..how to set up the waste gate and magnetic clutch to work with each other and so on.. (or does the ECU take care of this?)

Still learning so go easy..

Thanks..

[Duk]

Using a waste gate on a supercharger is pretty damn inefficient. You have all of the power consumption of compressing the air + the thermal loading on the supercharger only to then bleed it off to maintain a lower pressure. It's a very backwards way to go about it.

If you want to use the SC14, I'd suggest getting rid of the clutch and using a proper solid pulley, but make sure you have a decent bypass valve like the butterfly valves used in Eaton superchargers. That way you'll kill 2 birds with 1 stone. No bypass valve that tends to open (tho that's easy enough to deal with) and a much simpler puller set up to change drive ratio's to get your desired boost pressure.

BTW, use a minimum 60mm throttle body before the SC, anything less will hamper the performance potential.

[PrettyCoolWagon]

Yeah, I've read some threads that say similar to you - like.. what's the point ? (lots of to-ing and fro-ing between posts and opinions)
Depends on desired result I guess.., as other posters have suggested the main point would be real strong torque down low using the sc12 pulley...
Fitting to 4wd corolla with oversized wheels - want it to be able to climb some decent dirt tracks.
I'm looking for opinions on using the sc12 pulley with the 9.3 comp ratio (&under drive kit for accessories..)



So you're saying a bypass valve can be used to protect the supercharger from over revving in a fixed pulley set up??
One reason for sticking with a magnetic clutch is longevity of the supercharger.

[AE25]

blow thru or suck through throttle body? big difference!
aftermarket ecu or gze?

yes, clutched sc benefit of longevity, less belt wear/tear. More involved to setup with aftermarket ecu to replicate oem operation. best to switch on sc with engine load rather than rpm or throttle activation as it smooths boost transition. with a delay in switch off for momentary decel' and gear changes.

Do i read this correct... you want to overspin the sc to get boost earlier and use a relief valve to reduce boost back to atmo at higher rpm?
why? why not gear boost to 10-14psi throughout the rev range? you afraid to break something? overheat the sc? If i recall correctly, 'tiny' was running an internally stock 20v ST + sc14 which shows the 4a is good for it at high comp. Tuning is everything! aftermarket ecu could even allow possibility to set up boost bleed activated from manifold air temp.

Using a waste gate on a supercharger is pretty damn inefficient. You have all of the power consumption of compressing the air + the thermal loading on the supercharger only to then bleed it off to maintain a lower pressure. It's a very backwards way to go about it.

Have to disagree with that.. depends which sc is used. A twin-screw charger sure, as it makes boost internally and so the pressure in the plumbing at exit has little affect. running un-clutched off boost is inefficient too hence the diaphragm operated butterfly bypass. A Roots (toyota) sc is different. By using a pressure relief valve, the loss in exit pressure also unloads the sc. ie zero pressure difference across the sc is like spinning the sc with no plumbing. It is just passing air from one side to the other.

But should note, there is a big difference between blow and suck through systems- where suck through puts the sc and plumbing in a vacuum with a shut throttle, therefore no air can be sucked in, and no danger of over pressurising the system with throttle closed, (unless leak occurs between throttle and sc!). But using just a pressure relief valve vented to atmosphere wont equalize pressures effectively. due to less than atmo pressure at sc intake varied depending on throttle position, and variable vacuum/boost at the exit- from full engine vacuum with shut throttle to full boost... therefor pressure differential across the sc. Also an atmo vented valve needs to be closed before the system reaches vacuum otherwise it's sucking air and bypassing the throttle body. all good reasons to use a *recirculating* bypass system to equalise pressures, or none at all which relies on throttle body alone to control boost.

Blow through system has atmospheric pressure at the sc intake so a relief valve can be used to reduce sc exit pressure back to atmospheric, (there will always be positive pressure at the exit). or should i say a valve MUST be used to vent pressure, otherwise pressure build up against a closed throttle body is catastrophic. vented externally is loud and annoying. This system type is noisy by design, due to not having a throttle body up-stream of sc to contain the rotor pulse noise. Best to plumb relief valve back in after the air filter somewhere or after the afm if one is fitted. Venting pressure after the intercooler and recirculating the air can aid cooling the sc after a heated run. If you have room for the extra plumbing that is.

Suck through, (as fitted to toyotas and most oem's) the bypass/recirc valve is not as critical. but it does help smoothness of transition onto boost, pressure equalisation and has overboost protection.
could use the std 4agze poppet valve (maybe a bit too small?) or an external wastegate style poppet valve. if aftermarket ecu fitted, could possibly setup the stepper motor bypass valve as found on supercharged estima/tarago 2tz-fze sc14. down side to suck thru is if you increase plumbing diameter and/or fit big front mount cooler, the volume increase also increases boost lag and also when throttling off, increases the run-on affect.

Blow through, **VERY** important to run a bypass/recirc valve. and even a backup overboost valve incase of bypass malfunction. a large bov with spring tension set to max boost and no vacuum input could work as overboost safety valve?
Benefit of blow thru, is that you can run a front mount intercooler without the run-on effects. also with the right bypass control, boost is more instantaneous, as the plumbing doesn't need to transition from vacuum to pressure.

the researching you've done.. have you read any posts on the eng-tips forum? I find them very useful especially comments by user warpspeed.

[PrettyCoolWagon]

AE25
Will have to read your comments a few times over ..to digest it all.

A's to your Q's
Standard setup - 3SGTE throttle body before SC14 supercharger.
Management is: Factory GZE - ECU with HKS piggyback Fuel Controller, HKS graphics control computer and HKS twin ignition booster.
Definitely want to keep the pulley clutched.
Looking for opinions on sc14 pulley vs sc12 pulley with the 9.3 CR.

A link to tiny's 20v ST sc14 build / posts would be good...

Quote: Do i read this correct... you want to overspin the sc to get boost earlier and use a relief valve to reduce boost back to atmo at higher rpm?

That's precisely the idea I'm posting for feedback... It's not a definite want... just a general idea which prompted someone else to suggest the wastegate.
Yes - I'm concerned about overheating the supercharger, would like it to last for as long as possible ...but also my build is with the 4wd wagon in mind... fully loaded with camping/fishing gear, esky n all that, then hitting some off-roads.
Inspired by old subaru L-series with suspension lifts. i want strong torque way down low...
(have already sussed out my suspension lift steering gear set-up. Also bought a custom bull-bar..)

So, no... it's not a street or track car..

I should also explain, the bottom end is 'built. Forged H-beam rods and GZE (8.9:1) ceramic pistons, with oil squirters machined into the block and 3 x hardened steel dowels mating the crank and flywheel.
So I should be able to comfortably rev it up to 8k quite sustainably.

Agreed! Tuning has to be spot on..

The current thinking is to do a mock-up with SC on exhaust side to reduce piping lengths (and keep centre diff-lock vacuum drum) ..fit modest sized FMIC with possibly a slight gradual taper down in pipe diameter after the intercooler to help maintain pressure.

[Hen]

Just size your pulleys based on the boost you want or your redline and max RPM you want the SC to see. I can't see the point of a wastegate or similar.

Also in my opinion stories of SCs melting are exaggerated. Those I've had have stood up to prolonged flogging without melting/imploding/stripping teflon.

[trdee]

i have seen quite a few go the way of the dodo.. with large chunks of the rotor coatings missing, bearings having shat themselves, etc etc. but it can get a bit exaggerated at times.

so long as you arent flogging it well past it's efficiency point you are ok. also make sure you arent living above the supercharger's max rpm (14000 or so iirc) for very long. size your pulleys accordingly and you will be right...

[PrettyCoolWagon]

OK, side step the wastegate question for a sec.

About the pulleys.
Bought different parts over the last 2 years, so there's a few options, what I don't use goes to another build - same wagon but for street.
Sorry can't quote exact pulley sizes right now but I have 1 x sc12, 1 x 'Non Stop Tuning' 4AGZE pulley kit, I x smaller clutched pulley for sc12 (cheapo one not many ribs on the wheel) and 2 x sc14's (previa and soarer)

It's my first engine build so I don't know anything about calculating pulley sizes and sc14 maximum rev's nor do I know about the tuning and if there's tuning room for adjusting where the pulley clutch disengages and switches over to NA revs power.

So that's why I'm asking about the sc14 w/sc12 snout pulley with 9.3 CR...

[Drew]

I agree with what everyone else is saying ,gear the blower so it is not oversped.
Forget switching off the clutch at higher revs to make more power, it won't happen.
You will make more power on boost than off.

measure the pulleys when you can, somebody here will know how to calculate the speed for you.

cheers Drew

[Hen]

Totally agree with Drew. Switching off the SC at high revs will not help power or make for anything other than a disappointing experience.

SC speed = engine speed x (crank pulley diameter / SC pulley diameter)

Plug in your redline, desired max SC speed and find some pulley dias that suit. If you're using factory bits I'd guess biggest crank pulley and smallest SC pulley would still be safe. I ran an oversized crank pulley and stock SC14 pulley for 16psi on a 4AGZE. Ran fine, though only briefly before I moved OS.

9.3 CR will not cause an issue. Late stock 4AGZE is 8.9 so the difference isn't huge. As always, just make sure your tune is good and all will be merry.

[PrettyCoolWagon]

Totally agree with Drew. Switching off the SC at high revs will not help power or make for anything other than a disappointing experience.

SC speed = engine speed x (crank pulley diameter / SC pulley diameter)

Plug in your redline, desired max SC speed and find some pulley dias that suit. If you're using factory bits I'd guess biggest crank pulley and smallest SC pulley would still be safe. I ran an oversized crank pulley and stock SC14 pulley for 16psi on a 4AGZE. Ran fine, though only briefly before I moved OS.

9.3 CR will not cause an issue. Late stock 4AGZE is 8.9 so the difference isn't huge. As always, just make sure your tune is good and all will be merry.

With the built bottom end, I'd like to think that 8k revs is a good limit, but I'm no expert..

Eons ago I recall reading somewhere about super chargers becoming increasingly innefficient as the revs creep up. ..And reading about the magnetic clutches purpose to stop over revving the sc.
Being a noob, I guess I got it into my head at this stage (when the sc clutch disengages).. that there was still somekind of transition into NA revs power with torque increasing as the revs did.
Taking the idea further, I thought the bigport would suit this best..

But now.. based on a bit more experience and the comments above, I can see that there'd probably be a dip due to a lesser volume of air (VE) being sucked in naturally..
- right??

The first article I read that inspired me down the 7AGZE route was this one:
http://horsepowercalculators.net/tun...series-engines
..which many of you have probably seen..

In it, there's a descripton of 'the Boffins' set up..
Quote:
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!


Now..
I've seen 'Terra Operative' comment a couple of times on other threads regarding sc14's that 14 psi ..is the 'SAFE' limit these sc14's can be revved to..

So who's right and who's wrong? OR what are the determining factors?

..if this guy (the Boffin) gets away with running it at 18PSI, what's keeping his SC together?
Is it just a matter of time till it wears out, one way or another..

My main focus is a smart balance between real low down torque because of
4wd mud and snow use. ..And.. longevity of the supercharger.

I'll get some measurements of my various pulleys (& possible combinations) to you guys soon...

Thanks for everybody's input so far..

[Drew]

Thanks Hen ,I new it was a simple calculation.

I know 8000rpm sounds reasonable for the bottom end you have, although with bigport cams on a 7a you might find it running out of puff a bit earlier maybe 7ish ,don't be too concerned tho you still will have enough power to break stuff.(what driveline are you using ?)

Ok the next thing , read AE25's post about t/body placement.
Then consider this, some more thoughts about t/body before or after supercharger.

With the throttlebody before the blower & a frontmount cooler, idle control is difficult,
think of it this way, you have a large volume of air between the throttle & engine , your ecu is trying to make adjustments but it is setup for a small volume not a large one.(it makes a change & doesn't see the change it expected in the time it expected it so makes a bigger change then the engine stalls or big flare or hunting.)
When you start the eng all that air falls out of suspension & into the engine causing a startup idleflare, before you get oil pressure,bigger the volume the bigger the flare .not a good thing & hard to tune around no matter what ecu your using it is never good only just barely acceptable.

Also that air is going from vacumn to boost quite rapidly when driving & while under vacumn the soft cooler hoses have to be very short or the they will suck flat + when you go from decel to accel the hoses the can blow off.


With the throttle on the manifold after the blower the biggest issue is the horrible noise if the blowoff valve is not plumbed back with some thought put into it.
Idle control is much much easier.
While driving you have either no boost or boost,you don't get vacumn in the cooler piping
Plumbing is also far less of a headache, ask anyone who has put a front mount on a gze about the noise they make after blowing a cooler hose off .

hopefully this makes sense to you, it takes me a long time to try & type things out so they can be understood.

[knightrous]

The SC14 (Ogura TX15, repackaged for Toyota) is spec'd as below:

Displacement: 1.46 liters per revolution
Max Flow: 187 Liters Per Seconds
Max Cont. RPM = 10000 RPM
Max Pressure Ratio = 1.8

12PSI (1.81 PR) is approx 190LPS @ 7000RPM on a 1.8L motor, which seems to be right up on the upper limits of the SC14 once you factor in all the loses.

[oldeskewltoy]

properly deshrouded chambers allow FAR higher static CR.... remove the machining marks allows you far less chance of detonation

[PrettyCoolWagon]

Thanks guys,
Just a quick reply for now..

Drew ..Re:
Drive line I'm using re-built E-series box. The early E-series had some issues with synchro's and also there were upgrades in later years to oil cooling and clutch forks, so the internals will be upgraded, possibly with custom gear sets if they're swappable.. still investigating .. Also researching whether I want LSD up front or not.
I have bought cusco LSD for the rear and the rear axle in AE95's is T-series like the AE86's... just uses a different PCD (4 x 100)

AE25 - When I get a chance away from the boss of my household and the ongoing joblists.. I'll do some more reading up on eng-tips forum / warpspeed..

OST, What's static CR mean exactly? (what other types of CR are there???)
I've followed all your porting / build threads - love the AE95 sedan Bud!
Have bought a range of porting tools, Will hit you up for specific info when the time comes..