dyno question

so has anybody thought about testing some sort of hood /airpan on the dyno to duplicate that sort of restriction ? or even a a height distance between the top of the carb and the hood ....just curious on what kind of an effect takes place on the carb with different scenario's ......


probably not even feasible but i was just curious

wouldnt it need to be moving to get a real good idea of how it worked?

Nick, put you car on chassis dyno with wheels and put sprocket from your rear wheel to the dyno wheel and take it for a ride
And then tell us the dyno read out

i being serious guys ......

bruno wrote:i being serious guys ......

me too?

I had this same discussion yesterday with my dyno guy when I was dropping my motor off! I told him that I had a fabbed pan that pretty much sealed up my air cleaner to inside the cowl hood and wondered how much it would affect performane. He said it would slightly restrict airflow into the motor but it all depended on the size and type of my air filter (paper element or gauze like K&N) also the speed at which I was going. In my case of a mud truck a cowl hood really isn't helping me much more than simpkly keeping the mud out of my air cleaner.

ok. but IMO it mite be a little restriction over not having anything on it.

true, but how do you reproduce the affect a cowl hood has on a stationary dyno? it's not really a possible solution.

kjett wrote:true, but how do you reproduce the affect a cowl hood has on a stationary dyno? it's not really a possible solution.

only way I can see, is put a dyno in a Wind tunnel.

bruno wrote: so has anybody thought about testing some sort of hood /airpan on the dyno to duplicate that sort of restriction ? or even a a height distance between the top of the carb and the hood ....just curious on what kind of an effect takes place on the carb with different scenario's ......


probably not even feasible but i was just curious

On NHRA Super Stock engines we use a simulated hood, (usually a 24" by 24" section), over the carb at the same distance AND the same angle as what it is in the car, while dyno testing.
Those hoods can get as close as 1" in places; especially with carbs which must have the choke and choke horn remaining in place.
The hood is measured from the valve cover rail and duplicated on the dyno. Now we can work on the spacer package. Because of limited space, sometimes a spacer which normally makes more power will make less because of that space limitation above the carb.
It's all a balancing act...

I have spoke with racers and read a few articles that may offer a bit of information as to the function or dis-function of scoops and/or distances between hoods and carburetors. I will attempt to explain my experiences as best as possible.

On the topic of hood to carburetor distances, the racers I spoke with didn't seem to have concerns of most setups involved with NHRA SS and SS/GT combinations, to a point. It seemed popular belief as long as the air had an opportunity to enter the carburetor in normal fashion and wasn't disturbed before entering the carburetor, it was explained most applications did not suffer from the carburetors close proximity to the hood, considering the carburetor did not contact the hood.

On another note, the addition of fresh air or air at a temperature cooler than air contained in the engine compartment would obviously enhance performance.

An article I read several years ago of hood scoops, mainly NHRA P/S and NHRA Competition Eliminator entries did have interesting information as to the increased performance offered by a properly designed and located hood scoop. Aerodynamics of the vehicle's frontal area played a major role as how the air was captured and placement of the hood scoop's opening. A few years ago when the more aerodynamic front areas appeared in drag racing, and stock appearing body lines were maintained, the leading (opening) edge of the hood scoop was extended near the front of the hood where air continued to move past the opening with some force (speed).

Another article included information from Warren Johnson as to the effects of a properly designed and located hood scoops function. Warren mentioned, the hood scoop on his Pontiac of the time, produced one pound of boost at 200 MPH.

Last but not least a testament of my own. My 1970 Mustang drag car has the factory type non-ram air hood scoop, for that model. I installed a data gathering system on the car several years ago and located one of the sensors in the air pan attached to the carburetor that sealed the carburetor to the hood scoop's opening in the hood. If I remember correctly the air temperature passing by the sensor dropped by 20 degrees from the starting line to the finish of the 1/8Th mile run.

To make a long line of B.S. brief, I do think scoops that are located and designed properly are worth their weight and abit of performance.

Just my line of B.S.!
Dave.

I can see me explaining that bill to the wife now. Dyno tune for the full day = $700, price of the wind tunnel to make sure my motor is tuned with the scoop tray and cowl hood = about the same of the lawyer that will help me through my divorce for spending too much money on a mud truck.

kjett wrote:I can see me explaining that bill to the wife now. Dyno tune for the full day = $700, price of the wind tunnel to make sure my motor is tuned with the scoop tray and cowl hood = about the same of the lawyer that will help me through my divorce for spending too much money on a mud truck.

02

For most applications, don't worry about wind direction or pressure; just be SURE the air is much cooler than regular underhood air.

kjett wrote:I can see me explaining that bill to the wife now. Dyno tune for the full day = $700, price of the wind tunnel to make sure my motor is tuned with the scoop tray and cowl hood = about the same of the lawyer that will help me through my divorce for spending too much money on a mud truck.

Now that is just PRICELESS INFO right there