Ram air?

[Weasel73240Z]

I'm changing back to the stock air cleaner box as part of my Winter upgrades. Which got me thinking...has anyone tried a ram air set-up with the SU's and stock air box?

I was thinking about running a 3" +/- duct from the intake of the air cleaner box to a collector (maybe 3" x 24") above the front valance, below the bumper. I work in construction, so getting a collector box fab'd should be pretty easy. Seems like it might be a pretty cheap and easy way to pick up some HP's, and help with the problem of overhead heat affecting engine performance.

Anybody tried a set-up like this, any results?

[sblake01]

Don't know about carbs but I've had a cold air intake on my 78 (EFI) for years. I don't know what it does for performance/mileage etc. but it seems to have marginally improoved both. It's not really the same thing you're describing but mine does draw air from right behind the center of the grille.

[gnosez]

You can do it but it would help if you set the carbs to match the new A/F mixture you will see as a result of your mod.

There's a picture of a 240 in Japan taken in the early '70s that has an aftermarket grille insert that directed air to just the radiator (with addition mods) and had an opening for SU induction hosing.

I have a K&N cone filter attached to a hose running to the cold air box on my triple Mikunis. The cone sits in front of the radiator. Works nice.

You could also drill 1-inch holes along the top of a stock air filter box, as per Dave Rebello's instruction to me a few years ago when I ran 2-inch SUs on my earlier set-up. That worked fine as well. The intake air isn't as cold but it let more air in without a whole lot of work on my part.

[Weasel73240Z]

You can do it but it would help if you set the carbs to match the new A/F mixture you will see as a result of your mod.

I was thinking that in order for it to work right, the carbs would have be set pretty rich at idle, so that the AF mix was right at speed (when the ram air was working). I may fab one up and see what I get. If I do, I'll post pics of the process.

[gnosez]

The best way would be to tune them on a dyno and have a fan blowing air directly into the intake tube/filter array.

We'll be having a Z club dyno day sometime in late spring here in New Hampshire so that might be something to consider.

[Walter Moore]

I was thinking that in order for it to work right, the carbs would have be set pretty rich at idle, so that the AF mix was right at speed (when the ram air was working). I may fab one up and see what I get. If I do, I'll post pics of the process.

I can see a "ram air" system increasing the airflow into the carbs, but why would that change the mixture? Isn't the point of the mixture setting on any carb to set the ratio of air to fuel? If the air flow increased wouldn't the fuel flow pretty much increase at the same rate because of the velocity of the air passing through the venturi?

I really do not know the answer to that question. I am asking because I want someone who does understand to explain the process better.

[Weasel73240Z]

I can see a "ram air" system increasing the airflow into the carbs, but why would that change the mixture? Isn't the point of the mixture setting on any carb to set the ratio of air to fuel? If the air flow increased wouldn't the fuel flow pretty much increase at the same rate because of the velocity of the air passing through the venturi?

I really do not know the answer to that question. I am asking because I want someone who does understand to explain the process better.

I don't think so, because the carbs actuate by engine vaccuum, they wouldn't compensate for the "forced-air". But I'm not sure either.

[ozconnection]

:classic:

I can see a "ram air" system increasing the airflow into the carbs, but why would that change the mixture? Isn't the point of the mixture setting on any carb to set the ratio of air to fuel? If the air flow increased wouldn't the fuel flow pretty much increase at the same rate because of the velocity of the air passing through the venturi?

I really do not know the answer to that question. I am asking because I want someone who does understand to explain the process better.

My understanding of this is that it's the temperature of the air that the engine sees which determines how much fuel to add.

Cold air is more dense than hot air at the same elevation above sea level. It carries more oxygen by volume so therefore needs proportionately more fuel added to keep the same AFR's as before. Without adjusting or compensating for this added, colder air (because the mouth of the new ducting is usually placed outside of the hot engine compartment), the engine will run leaner than before with the possibility of some lost power. An overly rich carb calibration before the mod may actually run closer to optimum with the mod, picking up a little torque/power. Either way, it's important to realise that some minor adjustments could/should be made to the tune after fitting an effective cold air/ram air induction setup.

There's a lot more to it than just a few lines written on a page and grad students could write a thesis on the topic!! However if you're going to the trouble of creating a cold air intake, make sure you place the mouth in an area of the car that experiences high air pressures! Mounting the air induction pickup in a low pressure area is counter productive. A good spot for high pressure is under the wipers on the front windscreen, for example.

Just as a final point, 'ram air' induction really only works when driving at super high speeds. The effect from sedate around town speeds is minimal. Like I said before, it's the temp. of the air that has the greatest potential for more power and torque. (Have I put you all to :sleep:?)

Cheers!

[Friar-Tuck]

This may be of interest,

http://www.sportrider.com/tech/146_9508_ram/index.html

These were actual measurements, (pretty good for backyard experiment)

The speed at which it becomes effective may be a bit for your average grocery getter.

High end bike tuning shops have ducted fans capable of 200mph wind speeds

on their dyno's for jetting/mapping (like you guys spoke about earlier).

Tuck\o/

[gnosez]

I have attached a picture of the Rebello suggested stock air box mod and the fiberglass insert once sold in Japan (this is Alan's picture). It did two things; 1) reduced the air flow into the engine bay by directing it to the radiator and 2) it had an inlet for a ram air duct to the SUs or triples.