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Reducing charge temperature

Introduction to Engine Tuning

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Discussion and questions related to the course Introduction to Engine Tuning

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I've talked with a few guys at the drag strip, who are running turbochargers, and experimenting with injecting meth/fuel, into thier intake air supply to reduce thier charge temperature.

I compete in a foot brake only class, and am curious about the affect this independent injection of "coolant" will have on my staging rpm? I push though the lights at 1800 rpm.


Depending on how you set water/meth system arming, it may or may not spray while staging.

Arming is typically based on engine speed or manifold pressure.

If it does spray while staging, it's not likely to significantly alter stall speed if the nozzle is reasonably sized and does not spray until there's enough engine airflow that the kit coming on doesn't bog the engine out. This is quickly tested as long as you have a wideband air/fuel meter, and many systems can be adjusted by turning knobs, so you can quickly tweak it to your liking.

You will need to take into account the enrichment from the added methanol/fuel, first, to avoid an over-rich mixture.

What affect it has on your particular setup is hard to estimate - I would expect it to be of most benefit with high stall, high boost engines with a transmission brake to take the torque, as that is going to be producing high charge temperatures that need the additional cooling, and the fuel demand is high enough to make the fuel quantities high enough to get substantial evaporative cooling..

If you're in a class that bans transmission brakes, and is purely stalling against the foot brake, I would expect that the gains would be minimal. You mention 'pushing through the lights' at 1800rpm - does this mean you'r using a low stall torque converter that is already producing enough torque to move the vehicle against the brakes? If so, I would not expect a noticeable change off the line, but perhaps a small gain after leaving the line due to the fuel charge cooling reducing net temperatures and increasing density.

If you're looking at using a water/methanol mix, as Mike said, you may need to tailor the supply to the load/airflow - making sure the nozzle(s) have good misting properties should help over those that have larger droplets.

In the end, though, you're going to have to experiment to see it it actually makes a difference for your specific application.

Oh, it may be relatively temperature sensitive, too, with the best effects on hot days, when the ambient air needs more cooling.

Thanks for the input guys! I did talk with one of the guys who is still experimenting, and he is having problems with his motor bogging down. He did say, the other guy "drilled out his thottle body!???"

My thoughts would be to control the injection of fuel/coolant, by temperature, along with miscellaneous safety sensors, rpm, etc.

I run a 10R80 transmission in my car. And will be able push the RPM up to 2500, once I change my differential gearing.


Drilling the throttle body is an old practice which should have been left behind and is not necessary with proper tuning.

Controlling injection based on an intake air temperature threshold, to avoid spraying when it's not needed, along with RPM and engine load, or airflow based volume injection control, integrated with your engine fueling so your total fueling is appropriate for your total airflow, will avoid bogging as well as over rich or over lean conditions.

When I first read that, I was thinking of the old carb' trick where the butterflies would have small holes drilled in them to increase airflow without having to open the butterflies to the point where they impinged on the progression/intermediate circuit.

In this instance, I believe it's referring to the practice of boring the throttle body to take a larger area butterfly. It can give a small increase in power, if done correctly, at the expense of off-idle control, and isn't really worth-while in most cases unless chasing down any restrictions, if bigger options aren't available. Even then, there are often more critical areas, such as charge cooler matrix and end tank designs, that restricting flow.

The stall speed on the transmission is down to the engine torque and torque converter characteristics - changing the diff' doesn't affect that.

Thanks Guys for sharing your knowledge!

My roots go back to dirt oval racing and until 4 years ago, I never built anything without a carburetor. So I'm still learning about Electronic Tuning and Turbocharging (plus Fuel Injection, E85, Methanol, etc.).

I'll have to check my notes and time slips, concerning launch and 60' ETs. I did some testing last racing season, first launching at 1750 rpm in 1st gear (4.70 ratio), and then launching at 2500 rpm in 2nd gear (2.99 ratio), with Ford's 10R80 Transmission and OEM 3.15 differential gearing.

Thanks again for the help!!

Another option is an "Interchiller", and controlling refrigerate flow (from the car's a/c system) by intake manifold temperature or charge temperature.

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