This (hopefully) qualifies as advanced tech. I have minimal understanding of fluid mechanics so hopefully someone can offer some input.

After datalogging my GM847 on the dyno with HPTuners, it looks like my car is still pulling vacuum at WOT. I don't have the datalog on-hand (will post later tonight once I get it from Louis). You can see my setup here.

I did some preliminary reading online trying to figure out whether the cam was choking from my CAI, unported MAF, 52mm TB, or unported stock intake. While searching, I ran into some interesting information:

http://dtcc.cz28.com/flow/index.htm

Note that all of those CFM numbers were obtained on the same flowbench.

Without having a solid concept of describing airflow beyond CFM, the flowbench numbers make it look like the flow capacity of a stock MAF negates the purpose of going from a 48mm to a 52mm TB.

I'm guessing that to locate the intake restriction I'd need to pick some area (such as the TB) and assume that the airflow at that point is adequate for the needs of the motor. What can I do to figure out if the restriction is before or after that point?

Thanks

 

The flow test data you published is incomplete. It needs to be stated in terms of CFM flow at a specific pressure loss (e.g. - 28"H2O).

The flow number is not an "absolute".... it doesn't mean that a stock 48mm TB can flow 822 CFM with no impact on engine performance. It means that IF the TB is flowing 822 CFM, it will contribute a pressure loss of 28"H2O (or whatever depression they measured the flow at).

Any pressure loss in the intake - ducting, MAF, TB, etc. - will show up as a lower pressure in the cylinder at the bottom of the intake stroke, and a corresponding lower mass of air in the combustion chamber when the mixture is ignited.... less mass of air = less HP.

You can approximate pressure loss by looking at the velocity of the air. If that same TB was flowing only 411 CFM, it would only be producing 1/4 of the pressure loss, or 7 "H2O. Less, but still a pressure loss. The 52mm TB could flow that same amount of air, while only causing a pressure loss of (approx/simplification) 6" H2O. The 52mm TB will give you a denser charge in the cylinder, and allow you to add more fuel and make more HP.

But is 1"H2O "significant"? Standard atmosphere is 14.7psi = 407"H2O. A savings of 1"H2O will increase the density of the air charge by only 0.25%, or increase the power in a 300HP engine by 0.74 HP.

All of the above is a simplification.... it is not a rigorous technical analysis, but it is intended to illustrate the points in response to your question. I'm not sure what you are after with regard to locating the restriction.

Each and every piece of the intake track contributes to the total pressure loss in the system, the filter, the ducting, bends in the ducting, sudden enlargements and contractions, the MAF sensor, the rippled wall of the typical intake bellows, the radius of the turn the bellows makes, the throttle body and the flange of the intake manifold all contribute to the pressure loss. Look at each component, and reduce its contribution to the point where it is no longer "significant".