Conventional TPI's utilize the 48mm throttle body for air metering applications. Along comes the Ram Jet 502, which also uses the 48mm throttle body, and makes 510 HP doing so, all the while laughing in the faces of those who bought 58mm TB's for their 305's.
The one significant difference between the Conventional TPI and the RAM Jet 502 is that the Ram Jet advertises a significantly increased Plenum Volume. Is this plenum volume the sole reason the 48mm throttle body can be used?

The way I see it, the TB feeds the plenum. The Plenum feeds the rest of the total engine airflow needs. Therefore, by increasing plenum volume, you increase the store of air at your disposal. Engine airflow needs assumed to be linear, this means that, in order to reach a predetermined RPM, the throttle body can actually flow less cfm to feed the plenum because of the relatively greater volume of air initially stored inside the plenum.

Now, if you are exceeding your throttle body's capacity to flow air into the plenum, this RPM cannot be sustained.

In conclusion, assuming the TB is a restriction to RPM, the presnce of the plenum will extend the RPM range above that of an engine being fed directly off the TB. By this logic, the plenum volume of the super ram would be a good choice for an engine limited in RPM by the airflow of the throttle body than the conventional plenum (or you could just change throttle bodies).
What do you think?

 

http://www.sallee-chevrolet.com/Chev...m_Jet_502.html

The new undisputed heavy weight champion, the Ram Jet 502, makes 502 horsepower at 5100 rpm and 565 ft.lbs. of torque at 3200 rpm. The instantly throttle responsive Ram Jet 502 drives like no other big block you've ever driven. With over 500 ft. lbs. of torque from 2,200 to 5200 rpm, the Ram Jet 502 is a tire shredding monster making more torque throughout its operating range. This is possible because Ram Jet has a larger plenum and runners than would ever be possible in a carbureted application. This means greater intake efficiency and greater torque without sacrificing driveability. The Ram Jet manifold is so efficient that we're able to make all of this horsepower and torque with a production L98 throttle body assembly, you know, the one that Firebird and Camaro owners always replace when trying to make more power in their 350 engines. It's all about airflow quality, velocity, and fuel and spark management. You'll just have to drive one to appreciate it. If the one-second cold starts, no stalling, instant throttle response, and the solid pull from idle to red line don't convince you that a Ram Jet 502 is for you, then maybe we could interest you in a 100 mile per gallon, 0 to 60 in a week eco scooter.

 

what's the scooter got for hp?
heh.. just kidding..
i was just wondering about the TB thing yesterday.. or before yesterday.. tnx for the info!

------------------
87 formula
LB9, Automatic
K&N
3" mandrel bent exhaust,
v-force muffler
Hypertech preformance

 

Again, you're oversimplifying. Air doesn't move w/ a fixed velocity at any airflow (HP) or engine speed (RPM). Each intake stroke is a pulse. Each pulse feeds off the plenum. As this happens, this propagates a low pressure pulse area through the plenum which gets alleviated when it hits the TB. The frequency of these pulse is easy, 4 per revolution (in a 4 stroke V8.)

See the inter-dependency yet?

Think of a 251ci baby V8 that makes the same HP as the 502 ram jet at twice the rpm. It will see a bigger restriction at the TB than the RJ 502 at the same HP (total airflow same +/- deviation of BSFC) because the small TB has a harder time refilling the plenum when the pulses come twice as fast even though the total airflow is the same.

Again, this is an oversimplification on my part, but i'm just trying to vaguely illustrate another factor to you. In all of your analyses, you are well intentioned, but you never take into account any effects other than the one you are interested in. You never seem to see the whole system and just try to isolate one variable.

Anyhow, your final statement about a larger plenum volume not needing as much TB is true, but not really in quite the way you stated it. The 'buffering' effect you are looking for does not exist as you put it. The plenum does not buffer the 'total airflow' into the engine. The plenum buffers each pulse. This is a convoluted relationship as i barely touched above.

 

And damn you all to hell for making me think, lol. I hope you appreciate the brain teasers

 

Ed, you're killing me here. I don't agree with this:

Air doesn't move w/ a fixed velocity at any airflow (HP) or engine speed (RPM)

If the Plenum were isolated by the throttle body, and there existed a total perpetual vaccuum inside the plenum, the atmosphere will attempt to fill the plenum at a certain rate.

This rate is determined by the throttle body, or more specifically, the cfm rate of the throttle body.

That is to say, as the engine approaches an infinite RPM, the frequency of the "pulses" also approach infinity, creating a total engine vaccuum.

Because vaccuum is a volumetrically dependant quantity, the larger the displacement per cylinder of the engine, the fewer RPM the engine will have to spin to create a total engine vaccuum.

These "pulses" to which you refer are, no doubt, equivalent to the column of air that rushes in to fill the cylinder.

Your way of thinking about it is kind of a backwards way, and I'm going to change the the way we are engaging the subject. The pulses can then simply be quantified then as low pressure zones, or vaccuum in each runner. These vaccuum signals then migrate into the plenum to form one large vaccuum signal.

At a certain RPM, the pulses will become frequent enough to create total vaccuum in the plenum. Whether this vaccuum is created by at x rpm 502 or a 251 at 2x rpm, and assuming all else equal, the vaccuum signal is the same.

Now,it is the atmosphere's job to fill this vaccuum. We are lucky to have an atmosphere that does not discriminate between the filling of a 251, a 502, or our lungs when exposed to the same vaccuum signal. Once again, the atmosphere cannot discern between equal vaccuum signals.

Given this information, explain how you can come to this conclusion:

It (the 251) will see a bigger restriction at the TB than the RJ 502 at the same HP (total airflow same +/- deviation of BSFC) because the small TB has a harder time refilling the plenum when the pulses come twice as fast even though the total airflow is the same.

Once again, unless this is due to some terminal velocity property of air, I'm not seeing it. I agree with the idea that, at low RPM, the plenum will buffer each "pulse," but at low RPM, the TB is not a restriction.
The TB only becomes a restriction at the point where total engine airflow requirements after the TB are greater than the airflow capicity of the throttle body.

 

By the way, somebody else chime in here and stop making Ed do all the work. I'd like to hear from Yelofvr or BadSS if you are out there.