4A with high revs and boost?

[tedium]

I'd like to combine the 4A's capabilities as a naturally aspirated engine with the SC14 supercharger - yes I know the SC12 comes as standard on the 4A-GZE but the extra 200+ cc's per rev are just too attractive to pass up - and I've done some math to come up with the following:

4A-GZE engine
Rev limiter @ 9500rpm
Max power @ 9200rpm
Blower @ 1/2-bar
...all to produce approximately 260hp at the crank, so ~220 at the wheels assuming 15% loss - don't turn on the air con.

This would also mean the supercharger is underdriven, at about 4:5 (-ish), so it doesn't seem to be working that hard, but it's still moving a s**tload of air - I figure about 390cfm. This is the point where V8 owners say, "390cfm is a lot is it? You wuss." I come from a motorcycle background. 390cfm isn't just a lot, it's a hell of a lot.

Now I know all about the theory that enough money makes anything possible, but how possible would this be for the backyard mechanic on a budget? I've set the rev limiter in the example above at a point that I consider too high, but for all I know the 4A is perfectly capable of regular excursions to 9000+ rpm. I have the engine producing similar power at 1000rpm less with 10psi.

Or a 7A would do it @ 6800rpm with 12.5psi, but where's the fun in that?

Thoughts? Should I put my flame suit on?

edit: I should also add that I'd be running the supercharger on an electromagnetic clutch, which would in turn be operated by a TPS, so if I wasn't gunning the living bejeezus out of it the supercharger wouldn't be running at all. It'd be something of a concealed weapon, I suppose.

[TERRA Operative]

A quick rundown of the SC14.

Rated RPM: 10,000
Max short term RPM: 11,000

Rated boost ratio: 1.8
Max short term boost ratio: 2.0

So, as long as you don't go beyond 10,000 RPM at the charger, and keep it below 12PSI, the charger will love you.

At 9500RPM, you have the following easy options:

4AGZE crank pulley, Stock SC pulley: 11020RPM @ the charger
4AGZE crank pulley, 103mm SC pulley: 13374RPM
4AGE crank pulley, stock SC pulley: 10260RPM
4AGE crank pulley, 103mm SC pulley: 12451RPM

So, with stock pulleys, you're riding right on the edge of the maximum ratings of the bearings. (Better make sure they're well lubricated, you can only replace the rear ones).
With a 4AGE crank pulley, you'll be safe. (disregarding boost ratio of course, you'll have to work that out too).

Don't forget to replace the rods etc. I know the stock 4AGZE is good for 8000RPM, but I wouldn't be taking a stock motor beyond that. Besides, the charger will be sapping about 12-15Kw from the engine at that speed, with a supercharger you want to build a torque monster, not a screamer.

[trdee]

Why does it need to rev to 9500rpm? The gze is all about making a good spread of power from low revs. At high revs you are just sapping power from the engine with the s/c, plus shortening the lifespan of both the engine and the charger

You can make that kind of power using the sc14 with more boost and a lower rev limit, and it will be more reliable because you wont need to rev it as high anyways

[TERRA Operative]

My SC14 install will have a pulley bros 103mm pulley, stock redline, and Adaptronic and will be plenty enough go before the new engine.

[Sam_Q]

I was under the impression that 4agze engines have a sharp power drop at the higher end of the power curve, but hearsay only.

Sounds like you need a centrifical charger

[dangdang]

5500, its in the tune

[senn]

if you're going to go high revs and boost, go a turbo. a 20 year old supercharger is a big gamble when you're talking about upping the rev limit by that much. If you leave the rev limit stock, it should be better but those chargers are still getting on in age.

[tedium]

Thanks for the feedback guys. It was more of a thought exercise than anything else.

One question, what's a boost ratio? I've never heard that term before. I'm assuming it doesn't mean the SC14 is rated to run a constant 1.8bar, because everything I've read about both the SC units says don't go past 14psi.

[TERRA Operative]

To convert boost ratio to PSI, you subtract 1 and times it by 14.7.

Ie A boost ratio of 1.8

1.8 - 1 = 0.8
0.8 * 14.7 = 11.76 PSI

[mookschank]

I was under the impression that 4agze engines have a sharp power drop at the higher end of the power curve, but hearsay only.

I had an AE92 4agze SC12 (the one with no rev limiter) where the power wouldn't bring it on much above 5500. SC14 in it now though is a different ball game, it loves high revs no end. If I was in spending money mode, a set of cams in the mix would be great...

[oldcorollas]

boost ratio is

output pressure : input pressure

these pressures are absolute (and typically rated for 1BAR going in)

so if you have 2 bar going in, you should get 3.6bar coming out = 2.6 bar boost

[tedium]

Cool, cheers for that. More math!

[cartledge_uk]

At high revs the roots style chargers are grossly inefficent (they are actually inefficient at all revs in comparison to others) they effectively turn into a hair drier! Its not worth building a a high reving sc14 engine. If you were to get a twin screw charger, or a rotrex, then it will be entirely different. Or as stated above go turbo.

With my SC14 4agze (if/when its finally running) due to the pulley sizes I will have to lower the rev limiter to maintain reliability.

[tedium]

Now that I've started thinking about this I can't stop. So I've come up with this:

20-valve blacktop
Aftermarket pistons & rods based on GZE items
Stock crank (this is the part that worries me most)
GT25 turbo from a SR20DET set around 0.5 bar
Max power tuned to come at about 8500rpm - maybe a bit later - rev limiter set to 9000
Compression higher than a standard GZE but lower than a standard 20V, so like...9.5:1. I'll figure this out later
Standard intake cam & leave the VVT alone as much as I can
Longer duration & greater lift exhaust cam, (1) to help the turbo spool up and (2) to compensate for the lack of exhaust cam VVT when the high revs come
Stronger valve springs, blah blah blah, basically a more robust head

The idea here is to make better than 200hp at the wheels and have an engine that just screams its way there.

I've read Billzilla's advice on how to make a 4A get up and dance but I really am the blind man with the lantern when it comes to this stuff, so any help y'all are willing to give is very much appreciated.

[trdee]

perhaps start by reading up on some of the tonnes of already completed 4A-GZE/4A-GTE builds that are around, instead of just pulling things out of your arse?

just saying, do some research so you dont sound like such a stooge