7AGZE - waste gate and other options?

[trdee]

static compression ratio and dynamic compression ratio.. static compression ratio doesnt take into account camshaft phasing and the like, whereas dynamic compression ratio does.

[Duk]

OST, What's static CR mean exactly? (what other types of CR are there???)

Dynamic compression ratio is the real compression ratio that the engine experiences at any given time.
When you cruise down the road at part throttle, the engine is inhaling bugger all air. If each cylinder is 500cc and the combustion chamber is 50cc then the static compression ratio is 11:1. But at part throttle, the engine isn't going to be inhaling all 500-550cc (per cylinder). Lets say it inhales 100cc (per cylinder). So if it's actually got 100cc of air inside the cylinder and the combustion chamber measures 50cc, the part throttle dynamic compression ratio is more like 2:1.

This shows why an engine that is throttle will easily tolerate heaps of ignition advance.
It's also for this reason that you can't compression lock a petrol engine. Well, not without filling it with more liquid than the combustion chamber can accommodate .

Obviously the force fed side is similar, but on boost the engine doesn't inhale more volume into the cylinder (that's fixed by the cylinder and the combustion chamber's volume), but denser air. So rather than measuring compression ratio as a volume ratio, compression pressure is (probably) more appropriate.

[trdee]

depends on what you're trying to analyse. if you're trying to figure out how close to the detonation limit you are then peak cylinder pressure is the value that what you want to be looking at (iirc??)

[PrettyCoolWagon]

aaahh...

far out.. so much to learn!

[AE3SGTE]

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

I too would like to read through this, link please!
Ali

[PrettyCoolWagon]

Quote from AE25:
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.


Sounds like exactly what I want.
Can this be done using factory ECU and HKS piggy back?

[trdee]

you need a time delay relay and something that switches with MAP

time delay relay can be purchased from farnell/jaycar etc

MAP switching - you need to check your ecu.

also, piggybacks are the devil.

[PrettyCoolWagon]

Reached my spending limit so sticking with HKS piggyback and HKS GCC for the time being... may upgrade engine management at a later stage.... but have far exceeded my budget and still intend to upgrade seats re-spray and a few other items.

But...
I have a choice of using the map ECU smallport head (with bigport cams) and I recall reading the HKS piggy back unit also uses a map sensor.

Any links that I can read up on regarding switching the sc on with engine load?

[Drew]

Without an ecu to do it , you need to be even more oldschool & evil than piggyback if you want load switching.

Vacumn switch maybe , not sure if hobbs do vac switches or only pressure switches, that with a relay & timer circuit .

Throttle would be much easier to setup & will do the job good enough .

i've even just had them switched on all the time & let the bypass valve sort the transition out.

[AE25]

yah, if you're running 4agze ecu. you've got the sc clutch control sorted. wire it in! The ecu controls sc relay.
Or an adjustable pressure switch operating a relay with "off delay". web sources say sc12 kicks in about 8-10" of vacuum but this is where the adjustability comes in. The pressure switch should have some differential built into it, otherwise the thing will hum if the engine vacuum stays at switching pressure.
Smooth boost transition is more the job of your throttle and bypass valve. But allowing the sc to engage too late means as soon as it engages it will feel like a jolt in power when you're accelerating. It wont be smooth. This is why a throttle position switch cannot beat a load measuring system. Although the load operated sc still has a power surge if the revs are up and charger has turned off, and you suddenly stomp the gas again.
You could use revs to switch it.. but the engagement point would need to be rather low.. like 1300rpm. boost is usually seen by 1500 or so? So basically it becomes an idle switch. It doesn't account for coasting down hills or cruising.
Theres some good reading on eng-tips forum. I came across it all when researching twincharger setups.

Re max pressure and calculating boost pressure...
there's too many variables to be able to predict accurately how much boost a system will make or can handle. variables like intake air temp, engine bay temperatures and engine bay air flow, barometric pressure (elevation) air density, max revs, end usage. hey someone could state they run 16psi perfectly fine, then another guy races up pike's peak with same setup and wonders why he's lost boost half way up.

18psi and *potential peak power*... doesn't that speak for itself? find someone that can run this pressure for any decent amount of time and can proove it's longevity.

Re tims 20v sc, my memory did fail me... tim's (tiny) old 86 20v had an *sc12* according to the build thread of new owner. that can be found here..
need to register to view i believe.
http://forums.toyspeed.org.nz/viewto...charger#548009
The original build thread was on garagedori.com but is long gone.

sc 20v guise
http://i126.photobucket.com/albums/p...e/100_1014.jpg
before that was 16v sc
http://toycrazy.net/gallery/d1nz/rou...nzr505-153.jpg
http://toycrazy.net/gallery/d1nz/rou...nzr505-154.jpg

toyspeed thread states the following:
--------------------------
Engine:
Super Charged 4AGE 20V Silvertop
SC12
4agze MAP / DLI- multicoil ECU with a Gizzmo piggy back (now Link ecu)
V-Mount Intercooler
Twin core custom radiator with electric fan
Custom alloy Inlet manifold and intercooler piping
Oil Catch can
Ignition coil's mount inside car
De-loomed, Engine loom minimised, engine bay wiring hiden, anything forward of drivers seat not required removed.
4-1 Exhaust manifold lagged
2 1/4 inch exhaust
----------------------------------

new owner zac has this to say:
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The short block is dead standard, as far as I know the head has never been pulled off.

The fuel injection runs off a standard ae92 4agze ECU with a Gizzmo Cam FC. It allows you to alter the fuel every 500rpm, and run the VVT on the 20v head. It Run's 1jzgte injectors, with the coil packs from the 4agze. It uses the pick ups from the 20v dizzy with the cap and rotor removed so it clears the firewall....

To run the standard ecu you need to make a new manifold to convert it from quad throtal to single throtal body. The one used on mine is a 3SGTE one. You need to make the top mount for the supercharger too, as it mounts to the manifold. You need to find a bracket off some thing that sits the alt on the exhaust side as the charger sits where it was.
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