Autocross build

[DrewP]

Technically, there would be a benefit. Whether you will even be able to feel a difference let along utilize it, especially with otherwise stock hardware and stock boost, I would say NO, it's won't make a lick of difference.

In my experience, Autocrosses are obnoxious, incessant tinkerers, who think every little demon tweak or 1/2 psi of tire pressure, or taping up body seams will actually make a difference. For me, more seat time and more experience holding the car on the limit is far and away the easiest (as well as cheapest) way to drop time. I don't think I'd even be able to tell the difference between 3-4 psi in the tires until I have been through 4-5 runs just to get a feel for things.

Just get the car running and reliable and sorted and get some time driving it. When you run out of improvement just learning the car and the course, THEN start worrying about the technical details.

The guys who are changing out brake pads for different compounds and fiddling with their shocks at the autocross track are almost never the fastest cars going around. It's the drivers who arrive with the car sorted and set up and dialed in, who just have to worry about their line and technique who do the best.

[Dsp99t]

I feel the same way about seat time vs everything else but more power is always more (lol). I've been playing with race cars since the early 1990s and autocross has been the largest play area for me. I am a tinkerer but stock class has helped with my CLWEA (can't leave well enough alone). I am sure when I do move up it will be because of big changes to this car.



P.S.

I preferr to research things to death rather than waste time and money on experimenting with something someone else has already figured out.

[DrewP]

From what I understand, the biggest benefit of water/meth injection is that you can run more boost with less intercooling than would otherwise be required to keep detonation down. Thus the Turbo S's ran more boost than the plain Turbo's without additional intercooling. There's not a ton of space in the 99 to add an intercooler, which I would guess is the reason they went with water injection.

If you up the boost further you can spray more water at the same time to up the power.

If it will run flat out at the stock boost setting without detonating, the additional water or cooler water won't add any power unless you're mixing a substantial portion of it as methanol.

That was how I always looked at it.

I've always done 900's till now, and there's room for a much larger front mounted intercooler, so I always went that route.

[Dsp99t]

I used to have a drag Datsun 510 running a 2l with a T4 and Holley 750 double pump. In one pass I burned 3 gallons of fuel and 2 gallons of anti detonant. This was at 37psi and the engine could take over 50 psi. I have played with water injection in the past (25 years ago). I'm kind of starting over with this since it is a bit archaic this is why I'm asking stupid questions.

[DrewP]

Not stupid at all, I'll be the first to admit you probably know more than I do!

It may come more down to what will bump you into classes where you won't be competitive rather than what you can squeeze out of it.

[Dsp99t]

I am looking at the water inj as a way to allow a bump in timing up as well, this will help with off boost response. Then there is the on boost advantages water inj can act like more turbo, as combustion takes place any remaining droplets of water will turn to steam and act like more boost without the danger of detonation. Finally the water as an engine cleaner it will remove carbon build ups that could cause detonation. Since its a legal item that has Saab written on it I'm going to use it to the fullest extent possible.

[Geoff]

Doesn't it inject water upstream of the turbo? Water droplets hitting the turbo vanes can't be good. Cold water droplets hitting the turbo vanes might be worse...

[Crazyswede]

Doesn't it inject water upstream of the turbo? Water droplets hitting the turbo vanes can't be good. Cold water droplets hitting the turbo vanes might be worse...

The red rally car runs water injection with the injector downstream from the turbo. The only problem we had (geoff was in the car for this) was that the water was spraying the intake air temp sensor and throwing the fuel injection off. This however was an aftermarket fuel injection system.

Run your water injector after the turbo and you should be ok.

[Jordan]

The non-turbo car Rally car had water injection too. It was more of a pond water/oil mix though.

[Dsp99t]

Compressor damage will only happen if the droplets are large. If the spray is a fine mist there is little chance of compressor damage. I know people who have used pre turbo injection for the last 30 years and their compressor looked just as nice as new.

[SwedeSport]

Most of the heat is generated by the compression??? So I would think injecting it after the turbo would yield the most benefit.

I have seen setups where they also mist water/alcohol onto the fins of the intercooler. But IIRC you are not running one?


I saw a setup on a turbocharged speed boat where they had a scoop built into the hull to intake lake water, and pumped it thru a air/water intercooler. I did not get to poke around to see how it worked, but it ran like a raped ape. You could hear the turbo spool from across the lake. It was quite bad-ass.

[Crazyswede]

The non-turbo car Rally car had water injection too. It was more of a pond water/oil mix though.

Yes, it was injecting to atmosphere though.

[Dsp99t]

Unfortunately in the class I'm building the car for I am not allowed to change where the Injection takes place. This is why I'm looking at ways to make the fluid extract more heat.

[Luke]

The stock water injection is also very low pressure, just enough to atomize the water before the turbo, it takes a much higher pressure pump to inject after the turbo...

[DrewP]

I am looking at the water inj as a way to allow a bump in timing up as well, this will help with off boost response.

Very good point there too.

The non-turbo car Rally car had water injection too. It was more of a pond water/oil mix though.