what headers are those? cost?

 

Restrictive exhaust will not cause lower pressure reading in the intake manifold.

 

Why wouldn't it?

 

Vacuum in the manifold occurs when the intake system is not capable of providing as much air as the engine wants.

Restrictive exhaust puts some pressure backwards against the piston when it's on the exhaust stroke, reducing the overall power output of the engine.

Actually, if the exhaust were restrictive enough, the piston wouldn't be able to push all of the exhaust out on the exhaust stroke, requiring less air to fill the cylinder on the intake stroke, which would reduce the airflow requirements of the engine. This would actually make the intake system LESS restrictive, making it more likely to hit higher pressure numbers.

 

And a super-efficient set of headers might pull enough extra air through an engine to make the intake the most restrictive component, giving a vacuum kPa reading. (?)

 

Exactly what I was thinking. Increased exhaust flow increases the airflow capacity of the engine, making the intake setup a more restrictive part of the engine.

 

Great idea, but there are a few problems with ALL the data.

First, Elevation plays a HUGE roll in KPA. Some may not hit 90 kpa if they are 4,000 feet about sea level.
Second, The air filter restriction also plays a huge part, not to mention intake tube design, maf location, throttle body style, head style, valve size.
Third, humidity and air temp need to be accounted for.
Forth, pressure IS NOT flow.

Also as mentioned, a larger exhaust restriction would mean a higher intake pressure up to atmospheric, at that point if you have your **** together as in cam, intake, and exhaust you can and should build "boost" in the intake. infact, that is what all the N/A guys should be shooting for.

Runner length, runner taper, plenum volume all play a part in many theorys. Most common is helmholtz theory. Where as pressure waves are tuned via intake to maximize volumetric efficiency. Unfortunately, your map will not show any signs of this theory (or any other) actually taking place.


To me this all seams like a bit of a waste. you will not get any useful data from ten different people, with ten different set-ups, in ten different parts of the world.

 

Which makes sense as to why the guys running a 5.3 with decent LT's and an aftermarket intake system see a nice gain going from a stock intake manifold w/ 78MM TB to the TBSS/SSR/NNBS (4.8/5.3) intake manifold w/ 90/87MM TB. Lower restriction in the inlet allowing the engine to operate at greater potential for the installed cam.

 

I just looked through several of my old logs and hit 100 KPa on every one. I'll get some new ones with the cam once I get the tune for it dialed in. I've thought for a while that my exhaust was too much for my setup but I've never tried to test that theory.

This experiment is interesting but there are too many variables to account for.

 

For restrictive exhaust i would look at he grams/cyl numbers... If they seem to drop off dramtically in the higher RPMs then i would consider that an exhaust restriction because the air is being left in the cylinder.... Also looking at KR and how much the Knock sensors are detuned will also show if you have some exhaust restrictions.... Just my .02....