The Mega Supercharger 4AGZE thread, using twinscrew charger

[jondee86]

Hey Rob... I bought that stuff off and auction site from a guy who was clearing out his shed. I haven't pulled the head yet to inspect the bores, but the way I see it, if I'm going to the trouble of fitting new pistons and rings, I might as well bore to the first oversize and change all the bearings at the same time. That way I can pound on the thing with confidence

Not a lot of reference material around on T/B size vs hp. If I was able to use one of your huge "No restriction here" intakes I would use a 65 dia T/B. But My intake will not be so free-flowing, and I think I will compromise on a 60 dia if I can find one at the junkyard.

And I'll definitely look at a meth injection setup. Since I don't want to try and muscle an intercooler under the hood, meth injection that kicks in at 6psi would seem like good insurance/fun

Cheers... jondee86

PS: That piece of hardware she is holding is known as "the invisible T/B".

[jondee86]

Just trying to get my head around the real world difference between supercharging a lower compression (8.9:1) engine compared to a higher compression engine (10.3:1). The Sprintex selector does not require compression ratio as an input... it just says if you poke this much boost in, you get this much hp out.

Reading elsewhere, I see that you can run more boost with a lower compression engine, while achieving the same effective compression ratio as a higher compression ratio engine with less boost.

Putting these two pieces of information together tells me that the lower compression engine will make a fair amount more power than the high compression engine, while placing similar loading on the engine components. Is that actually how it works in the real world ??

I regularly read about stock GZE engines boosting 20-25psi, and seeing 15psi every day for years without destroying themselves. So I'm thinking, why go to the trouble of putting a supercharger on the 10.3:1 engine in my car and run 6psi, when I could build the 8.9:1 engine and run 10, 12 or even 15psi ??

Anyone got any solid pros or cons for high vs low compression on a road car ?? Is there anything that I am missing that makes one choice better than the other ??

Cheers... jondee86

[jondee86]

While pondering the above, I also got thinking about the alleged loss of off-idle response caused by lower compression. I can see this being a problem with exhaust driven turbo's and centrifugal superchargers, where the engine is off boost at idle. But with a positive displacement charger, the charger is spinning and pumping air into the engine even at idle. So, boost should be available pretty much instantly when the throttle is opened, making the effects of lower compression a non-issue ??

At least that's how I figure it And I think that it is inevitable that I will want more than 6psi... so I shall go with the engine rebuild and GZE pistons. That way I will have a bit more tolerance for error when I am learning how to tune for boost.

Cheers... jondee86

[trdee]

All things being equal (which they rarely are). Achieving the same peak cylinder pressure using less compression and more boost will mean more overall power. This is because you are squashing more air and fuel into the combustion chamber compared to a higher compression engine running less boost to achieve the same peak cylinder pressure.

***HOWEVER!*** All things are not equal!

You need to keep in mind that, as discussed previously, most superchargers don't like running with high pressure ratios. The harder you push the charger, the more parasitic loss you get, as well as much higher intake temps, which means your ultimate power will be less than what you might expect. With higher comp and less boost, you might not have the same *potential* power, but you may be able to get very close whilst not having to punish the supercharger anywhere near as hard.

Then there is the other side of the coin! The pistons are not equal either! As previously mentioned, the stock 10.3:1 pistons can last under boost but they do seem to be a fair bit weaker and if you get any decent det events you will smash the ringlands pretty damn quick. So, even though you **could** run them to the same overall cylinder pressure as GZE ones, I personally would be less inclined to do so, simply because I would prefer not having to rebuild an engine if I didn't have to. If you really wanted to you could get some high comp forgies made up, and you might even be able to run 6psi or so with 12:1 comp forgies and make a very decent amount of power whilst also maintaining optimum efficiency, but that's a lot of money and a lot of fuckaround for what will realistically not be a hugely significant difference.

Summary: Taking cost and safety margins and everything else into consideration, I would recommend using those 8.9:1 GZE pistons you have there with something like a TRD 0.8mm headgasket and some ARP headstuds, and running as much boost as is reasonable for the supercharger. This will also give you headroom if you decide to go turbo or something else later down the track As you yourself mention, it will give you a bigger safety/error margin, and it's a tried and true method which has been proven to work in many setups for decades.

Edit: Also, if you find you are pushing too close to the det ceiling, it's a lot easier changing supercharger pulleys and lowering the boost pressure than it is to go to a lower comp piston!

[jondee86]

Thanks for the input !! Even with the GZE pistons I would still start off with a pulley geared for lower boost (6-8psi) and do my setup and learning with that. After playing with that for a while, I would gear up for 15psi and look at implementing a water-meth injection system.

Turbocharging is not on my agenda, but I am interested in the reason behind your suggestion of a TRD gasket and ARP studs. Is there a threshold where a MLS gasket and ARP studs beome necessary ? Or, if you like, where a standard Toyota gasket and head bolts are no longer up to the job ?

Cheers... jondee86

[trdee]

It's not much more money and provides extra insurance, and if you already have an engine pulled apart then why not! The common figure thrown about for standard head bolts and head gaskets is that they don't like going past 20psi. In reality I think it depends a lot on your setup. Once again, detonation plays a part here and the stock head gasket will be more susceptible to shitting itself than the TRD one which is a multi layer steel unit. The TRD head gasket is also a bit thinner than a stock one which helps bump compression up a little bit. It isnt a huge difference though, just consider it an extra bonus

edit; if you really truly don't think you will ever exceed 15psi, then the stock gear will be more than adequate for you. But it is cheap insurance in case you do ever decide to go full retard on this motor. Up to you I guess.

[maj]

8.9 0.50 OS GZE pistons, stock HG and TGP head studs along with stock boost is all I'm aiming for. i.e. AE101 style except without the smaller pulley. Then can start playing with overboost or smaller pullies to find a sweet spot, and eventually think about engine management.

If none of it eventuates, I'm sure running Aussie 98RON with the base config should be safe enough and keep the supercharger lasting a while.

[jondee86]

What head gasket is found in the AE101 smallport GZE ? Is it anything special, or just the same as the N.A. smallport ?

Cheers... jondee86

[jondee86]

if you really truly don't think you will ever exceed 15psi, then the stock gear will be more than adequate for you. But it is cheap insurance in case you do ever decide to go full retard on this motor. Up to you I guess.

While moar powah !!!! is always tempting, I have drawn the line at shooting for more than 1 bar of boost. Even at that level I am pretty sure that the brakes, gearbox and diff will be close to the limit for a 30 year old car.

Cheers... jondee86

[trdee]

all 16v 4As run the same part number headgasket if you do a toyodiy search.

ok then, if you are set on staying at or under 1 bar then the stock stuff will be more than fine

[trdee]

also, this may be interesting for you http://www.toymods.org.au/forums/eng...or-2087-a.html

[maj]

I don't think they would bother making a HG with 0.50mm piston accuracy, especially since its a squishable item.

[trdee]

u wot? headgasket thickness is a pretty important measure as it affects the engine's compression ratio.0.5mm can be a decent difference. it is in fact almost the entire difference between the TRD 0.8mm headgasket and the standard 1.2mm headgasket

[maj]

I'm talking STD vs OS pistons? Or is there an OS HG?

I'm not talking thickness of the HG, I mean combustion chamber size.

[trdee]

Oh right. You can get head gaskets with specific bore sizes but IIRC the TRD unit is only available in standard bore size.