Looking at the OBD2 reader I've got hooked up, shows a peak airflow of 236 g/s air from the MAF, working out to about ~80.4% volumetric efficiency at peak RPM (6300). Anyone? Induction system in good shape, reasonable shape, or needs a cleaning? (I've no issues or complaints, I'm just curious...)
03-13-12, 06:20 PM
The standard automotive airflow calculation uses a VE of 80% - most wonderful for a stock engine.
I'm not going to post it all - Google "automobile engine airflow calculations" and do the math yourself.
3 years ago I screwed around with a mechanically modified MAF - JET Performance - and got exactly nothing worthwhile. This was done over two 821 mile round trips from MD to FL and I actually lost a half mpg, set mixture codes, and introduced a low speed/off idle stumble.
So..........In answer to your opine, your engine and intake system is just fine..............but go ahead and work out the formulae - you'll convince yourself that the MAF/throttlebody modification idea is pretty useless on these engines: they already have a cold air intake tract and panel filter which flows more air than a 279 c.i. engine can handle as-is.
Aw, heck - here are the formulae..............
CFM = CID X RPM X VE / 3456
VE = 3456 X CFM / CID X RPM
For a NA engine, use a VE of ~80%.
Huh? I'm not interested in modifying it, but it could perhaps be an early indicator of exhaust cam wear for the pre-2000 engines. The only way to get more suck (without a blower) is to get a tuned (variable length) intake along with finding space for a bigger crossover pipe (there is no space), and that's not happening :rolleyes:
03-13-12, 06:35 PM
get more suck (without a blower) is to get a tuned (variable length) intake
Your engine already has a tuned intake manifold with 8 variable sized individual intake runners coming off the distribution log. Everything before the center lower distribution log is designed for maximum cold air flow.
.........not saying you're looking at modifications - just that a few of us have been there, and there isn't a gain to be had from fooling with the intake. You would have to have some pretty severe intake manifold sludge buildup before there would be ANY performance losses there - but a clean air filter and throttlebody is of prime importance.
For anyone coming along, to go from g/s to CFM depends on air temperature (and humidity), but using 15C air is 1.225kg/m^3, going from g/s to CFM
m^3/s = g/s / 1225
m^3/min = m^3/s * 60
CFM = m^3/minute * 35.31
Oops! I did my calculation wrong. It's about 80.4% for 236g/s - displacement is 0.0045648 m^3 and max rpm 6300 not 6000
Variable as in changing length, the runners help but to get everything possible the size needs to change...