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Old 20-11-2003, 07:44 PM
91CavGT 91CavGT is offline
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Default Can water injection effectively replace 100 octane race gas?

I currently own a 2003 Dodge SRT-4 and will be installing water injection on it when funds allow me to. I will be using a 100 psi Surflow pump, 2 selenoids, and 2 McMaster Carr nozzles(one around a 3 gph size and one around a 5 gph size). One nozzle(3gph) will be triggered at 5 psi and the other(5gph) will be trigered at an adjustable boost level(anywhere from 4-20 psi but will probably be turned on at 11 psi). I plan to use a mixture of 50% distilled water and 50% methanol.

The motor this will be used on is a 2.4L DOHC factory turbocharged 4 cylinder motor with 8.1:1 compression, a VERY small TD0416G reverse flow turbo, a decent sized factory intercooler(approximate demnsions are 3" thick, 2' wide, and 7" tall. Peak boost is going to be in the 17-21 psi area(I'm currently running 17 psi).

At 16 psi of boost, the car has already been dynoed at 242 hp and 264 ft lbs at the front wheels with air/fuel ratios being right at 10:1 from 3500 rpm to 5,000 rpm where it start to lean out a bit to 12.5:1 at 6250 rpm(redline).

Now to my question. The Mopar Stage 2 upgrade will be coming out for this car and will include some pretty nice stuff. It is going to be coming with 4 682cc injectors, a tuned PCM for these injectors, and among other things a switch inside the cabin for pump gas or 100 octane race gas. The race gas switch is supposed to alter fuel and timing when activated to give an additional 15 hp and 20 ft lbs. So, will this water injection system be able to replace 100 octane race gas and still give safe air/fuel ratios? I know this is a very broad question and there are many variables involved, but in general, is water injetion as effective as 100 octane race gas?

Thanx..........
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Old 20-11-2003, 08:38 PM
Forum Admin Forum Admin is offline
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Without getting into whether or not an injection of water/methanol injection is the "same" as 100 octane race gas (because it isn't - different length hydrocarbons and other differences), I will say that you can run 92 or 93 octane fuel on a 100 octane map with water/methanol injection.

Keep in mind even though it is a performance tune Mopar is still leaving some level of buffer with excess fuel and a bit conservative timing relative to say if you had your engine tuned on a dyno at the edge - that factor should provide you with even more comfort.

Properly implemented you will not experience knock and any knock learning the reprogrammed PCM has will permit it to run maximum advance. There is no reason that with your system and the stage kit that you shouldn't get the performance results of the tune from pump gas.

I would look into a variable flow kit though. I used dual and tri stage kits for a long time due to a lack of alternatives and it does work, but the difference with a true variable flow kit is night and day.
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Old 21-11-2003, 03:30 AM
Brad Brad is offline
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At a 11.0 to one air fuel ratio the car will most likely make less power with water/methonal. The engineer who set that system up will only let it run rich. If you pull the air fuel ratio down to a solid 12.5/1 power will go up with the use of water.
If my memory is correct that is a speed density system. If it is and it uses a 0-5 volt map sensor you can add some resistance to the MAP sensor out put and it should lean it down. This will also increase the timing. Under stand I have not done this on the SRT-4, but on other cars and added water and increase wheel horse power 25%. I beleive TurboXS has a program to change the computor signals for personal tuning. There web site is www.turboxs.com.
My only true point is running that rich of a mixture may loose power with water/methonal. With water only may work better.
I will post a little information on the intercooler size after I do a little research.
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Old 21-11-2003, 04:04 AM
Brad Brad is offline
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A site that can be used to compare intercooler size flow. Not perfrect but informative. www.bellintercoolers.com
Go to core inventory
click on 3" thick core
Part number 3002400600 is a 3" thick core with 6" tubes and flow entering on the 24" side and exiting on the other 24" side flows 770cfm
Part number 300068240 is a 3" thick core with 24" long tubes 6.8" high
flow entering the 3"X6.8" side flow 171cfm.
All flows are done in the same manor. Different manufacturers measure flow with differing pressure drops. I go here with core size to use it as a standard.
Your car will need more than 171cfm to make the power you are making. Therefore there is most likely a pressure drop accross the intercooler.
If you lower the back pressure by reducing the amount of pressure drop accross the intercooler you can pick up power.
Could you use water injection and not intercooler, maybe. Some people do it.
On my SAAB in installed a 489cfm intercooler to replace the 100cfm intercooler. Exhaust manifold pressure dropped 5psi- power went up. The fuel mixture droped from a 12.5 to 14.0 because there was less spent cumbustion left in the cylinder.
So many things to consider and balance.
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Old 02-02-2004, 08:12 AM
SaabTuner SaabTuner is offline
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Here's something else to consider:

A high resistance intercooler will make the turbocharger "feel" like it's at higher boost than it actually is. A restrictive intake does the same thing. On a performance car this is bad, but on a stock car that's not necessarily the case.

I have a 2002 Saab Viggen which at peak hp runs roughly 13 psi of boost pressure. However the stock compressor for the car is most efficient on the high flow side of the map at a pressure ratio of 2.5:1. If I had no intercooler backpressure, no intake restriction, and no other flow restrictions my car stock would only cause a pressure ratio of about 1.9. This means that Saab engineered the parts to create some resistance so that on the stock vehicle it should always been at a "good place" on the pressure map.

Of course someone will always tell me to put a big intercooler on my car, and I won't argue! The moment I crank the boost up even a little I would be well advised to have one. But keeping everything else stock, the benefit from an $800 intercooler would be very little. Nowhere near that of say an $800 turbo back exhaust.

As Brad said, there are a lot of things to consider. I would actually reccomend a larger intercooler! But I just wanted to post that stuff so that anyone with a stock car doesn't go out and waste $800, unless they've considered all of the variables. 90% of the time it's probably not necessary.

Adrian~
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