[NoDOHC]

Originally Posted by vex

I think you're missing my point. I do not believe your throttle body is doing what you think it is doing. The throttle body is altering the flow itself just by being the stream. Reducing the intake diameter or further 'restricting' it will cause an increase in intake velocity (hurrah for area flow rates). This will do two specific things. One it will increase the vacuum on the manifold, and two the intake velocity will speed up. Since we're doing this the ideal fuel combustion will amount to a slightly better ratio. The harmonic tuning will further increase your volumetric efficiency. This in turn means increased 'bang' for your buck.

You are coming at this problem from your aeronautics background. I am attacking this problem using thermodynamics and engine controls experience. Call it a restrictor or throttle (which means narrowing or restriction), it still creates a pressure drop that I have to pump air across to get it to the exhaust. This means that I do more work to get the air that the engine needs for combustion, while decreasing the temperature ratio of the thermal cycle (lowering efficiency).

Higher vacuum in the intake manifold is all bad (think about the flow work to pump air through the engine from that pressure to the exhaust manifold pressure, without even considering the chemical and thermodynamic implications).

Helmholtz tuning could possibly help, but the required intake runner size to get enough air velocity to see any appreciable benefits from Helmholtz would give up way more power than I am willing to give up. If the intake runner can provide even 0.1 Mach at 2400 rpm and 45 kPA pressure drop, They would have a tiny cross-section and would be something like 5 feet long. On top of that Helmholtz would only help for a very limited speed range.

I really should have done a better job of explaining my goals for this plan, I want my cake and I want to eat it too. I want a 250+ Hp rotary that will still give 35 or even 40 mpg.

Originally Posted by vex

If you're serious about doing this I wish you the best of luck. I personally feel however you'll find more gains in a properly designed intake manifold, restrictive set up, and harmonic tuning. That said those will only net you so much. Consequently your low rolling resistance wheels aren't really all that great for improved gas mileage but they're probably the best balance for the buck. When I say low rolling resistance I'm talking about solar power car wheels a-la:

I wonder how those wheels do on the corners?
I really do sound like I am being unrealistic, but I have a Metro if I want to drive for cheap, I want the RX7 to get decent mileage to see if I can. I also want it to retain some semblance of pleasure to drive, otherwise I might as well drive the Metro.

Originally Posted by vex

Granted those aren't going to work for you, but those will reduce the friction acting on the car dramatically (which technically speaking is a hell of a trade off). As for the aerodynamic effects I completely agree. If you really wanted to improve your MPG at speeds over 60 MPH you'd want to install a couple of these:

The ideal location I would think would be directly in the front of the hood... but that's just a guess. Possibly putting them on the rear roof line might actually prove more beneficial, but both might be tested on the highway for verification of greatest increase.

These basically perform the same function as a spoiler and are a very good idea. I might look into this (I really couldn't care much less what the car looks like).

Originally Posted by vex

Drag reduction by use of the vortex generators will have significant effect on the Cd. The idea is that it sort of 'trips' the boundary layer causing it to not necessarily reattach to the surface but follow the contours still. In essence rolling along on bearing of air over the skin of the car. If you don't care too much about looks you might be able to try some artificial 'shark skin' which is used on marine hulls to reduce drag. The effect is going to be similar... but I don't know any place that would sell 'em.

Unfortunately, this sounds like more work than I am willing to go to. Still not a bad idea.