[Dimman]

Well here’s what I’m getting out of that book so far: Lots of practical testing is in order. Yay…

Seriously though, there is something to this. The authors detail the importance of ‘mapping’ the wave-forms at different rpm, lengths and possibly throttle positions. They even describe how to build a multi-manometer array and how to plumb it to multiple points in the exhaust with a rotary valve physically timed off the engine (yes it‘s about as complicated as it sounds…). Or their more ‘advanced’ electronic way using an oscilloscope and photographing the resultant ‘oscillogram‘. Oh how times have changed. Something could probably be rigged up digitally with a data-logger with MAP sensors and timed off the crank or cam sensors these days. I would also probably gather some EGT data at a few points along the exhaust as well. Maybe IAT at different points in the intake manifold, too. Oh yeah, and a dyno is necessary. D’oh!

The big thing that their graphing shows, and that the formulas don’t address, is the change of shape/length of the waves as well as their amplitude. This becomes even more interesting as we delve into our modern technology.

The formulas can be the starting point and put us in the initial ballpark for what we want. The whole shorter=top end and longer=bottom end generalizations. As well as 4-1 top end short power band vs. 4-2-1 wider low to mid range power band. Now with the ability to ‘see’ the wave shape and amplitude we can make tube length or cross-section adjustments to match the low-pressure return to the overlap period of the cams at the desired rpm or reduce inertia-caused high pressure zones. We can then also see where the corresponding high-pressure return will occur at (flat spot). We can also get an idea of the strength of the scavenging effect from the amplitude of the wave. Then verify everything with power pulls. This would be the limits of the ‘standard’ tuning abilities.

Now for the fun part. Since depending on rpm, and even EGT’s, the shapes change as well as the timing of the returns. Tough luck in the old days, just pick your compromise. But we now have the ability to phase the cams in real-time. So with phasing we can increase or reduce overlap to maximize a longer scavenging return and minimize or eliminate a pressure return. If the wave is arriving a bit early or late we can advance or retard the cams to meet it. Again, the dyno will tell if any benefits of moving the cams around to ‘catch’ negative exhaust waves pay dividends.

Naturally this can then be extended to the intake side and repeated.

So short version: Even if we put a well-designed header and intake manifold designed for max top-end power together, we will probably see even better results in terms of widening the power band with re-mapping the AVCS.

This will be something to be excited about if there is access to the AVCS in a ‘cracked’ ECU.





And in FT86club forgot topic fashion here’s something for the turbo guys:

I got a bit side-tracked by something in the book’s ‘current’ (pre-catalytic converter, still have leaded gas era) emissions control chapter. Toyota used to use an accessory compressor and air injection system for emissions control. And all of this hardware sounds exactly like what is used for a hard-core anti-lag system (the air is injected directly into the exhaust manifold). On a turbo car that has a MAF system venting a BOV to the one-way valve of the air-injection system would be all it takes (well that and plumbing in the air injectors). Since we’ve metered the air, but don’t use it, the fuel injection will be on the rich side, so there will be extra un-burnt fuel in the exhaust, and it meets the air vented by the BOV and now injected into the hot exhaust manifold to create an ‘afterburn’ effect inside the manifold that will keep the turbine spinning while off-throttle. Basically what Mitsubishi’s Supplemental Air System does. So run out and find a late-70s Toyota with air injection (hopefully not disintegrated to rust) to make your own rally-style anti-lag system for your WRX! Just don’t expect your turbo to last very long…