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Old 01-14-2021, 08:28 AM
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Here's more info to help out.
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Old 01-14-2021, 09:57 AM
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A few years ago I called K&N and asked about the air flow requirements for my my 505 cubic inch engine at 6000 rpm. It made peak power on the dyno at that rpm. They said it required about 745 cfm of air flow. I noted my dyno sheet indicated the scfm at 6000 rpm was 839 cfm. Also with other formulas on the internet to determine the cfm requirements of a engine based on cubic inches and rpm can differ. I mentioned all this to the K&N rep and his reply was they had their own methods to determine required air flow.


.

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http://www.hotrod.com/articles/0712p...tiac-trans-am/

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Old 01-14-2021, 10:22 AM
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This thread seems to tell me that with my stock built 68 YS engine, 068 cam, .040 over that the OEM air cleaner is my best bet ... am I correct? Would I be better off with a "free flowing" OEM dimension filter? Or just a standard off the shelf filter?

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Old 01-14-2021, 10:22 AM
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As it relates to this topic I'm sure just about every single open-element type air filter assembly will meet the minimum CFM requirements for your engine.

The problems I've seen are NOT related to CFM, they are caused by disrupting the airflow into the carburetor. Every single time w/o exception we've done things to raise the carb closer to the hood then have to move air cleaner lid closer to the carb it has caused some sort of performance issue or loss in ET/MPH at the track.

What throws a monkey wrench into some of that sort of testing is running an open element lid or no lid at all and having issues or it not working as well as something else.

In any case guiding air into the carb can have a major impact on power production and vehicle performance, so it's something to think about when you start adding spacers, taller intakes, combinations of both, etc........Cliff

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  #65  
Old 01-14-2021, 10:29 AM
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Efficient high performance well thought out combos / motors will make more hp with less CFM, and them VE numbers well above 100% are the icing on the cake!

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And he was not talking about 1/8 or 1/4 mile ETs!
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Old 01-14-2021, 11:07 AM
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Quote:
Originally Posted by prostreet64 View Post
We are currently using the ram air box on both cars. The Bird has the 14x4 box and my T/A has the 14x3 box. I don't have enough clearance for the 4" with the RPM intake. And we have to use a drop base also. But the real advantage, I think, to using the ram air box is it allows us to run the 4" duct into an area of cooler air. On the Bird we actually were able to cut two 4" holes in the core support and attach the duct right to the grill inserts. Some have said that there is a slight 'ram air' effect when speeds reach 100 mph or so.
Yes that works exceptionally well. My Formula with it's factory ram air ranks up there as one of the better working factory cold air packages, and your theory of ramming air in does happen with a good intake system that is front and center. Those aftermarket ram air boxes work fantastic.

I had problems with mine, at any speeds above about 80 mph, blowing out the little filter element for the crank case that sits in it's plastic housing. Every pass at the track I'd pull the air cleaner lid and it would be sitting at the very back of the air cleaner housing. It would stay all day under normal driving conditions but as soon as I hit higher speeds, either on the highway or the track that thing would be at the back of the air cleaner every time. I ended up wrapping a little chicken wire around it to keep it in place. The air coming in that fresh air setup apparently is pretty strong at higher speeds. I don't have that issue with the other cold air packages on the 2 cars that use the cowl plenum area.

I've tried all kinds of different open element setups on my Formula, with the scoops open (just dumping in the engine compartment) and the scoops blocked. It's never been able to duplicate it's best times with any configuration other than having that factory ram air setup in place, it just flat works!! What I thought was odd, and why I tried other open elements on it, is that the factory fresh air base and lid is so shallow, it only takes a very short 1 3/4" or 2" filter, and the lid is literally right on top of the carb just 1/4" away from the choke horn. I thought for sure that shallow base with it's short filter would choke it, but larger drop base open elements proved to be worse. Just shows how getting fresh outside air to the engine can be worth while I guess.

It's why I suggested early on that Mchell may find even better results if he bought the factory air cleaner setup and made his hood functional, it's basically the same setup my Formula uses, and his scoops are front and center like my Formula, which is said to be one of the most effective hoods for grabbing outside air.
If it were mine, I'd even go as far as porting the stock iron intake and performing the mods that has been done for decades by many, so that I could fit the factory ram air setup on the car. I'd like to see that comparison. My money says that there would be some gains there.

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Last edited by Formulajones; 01-14-2021 at 11:30 AM.
  #67  
Old 01-14-2021, 11:27 AM
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Tid bit from a magazine that might be of interest. And relates to Cliff's comments......

When designing a cold-air package, remember that an optimum entry will provide a nonturbulent air supply above atmospheric pressure. Front-facing hoodscoops typically begin supplying air at lower speeds, while rear-facing scoops supply air at higher speeds with less turbulence. Inside the scoop, all air ducts should be designed so that air entering the carbuertor will do so smoothly- preferably through a air cleaner or other diffusing device. Be sure that the bottom of the air cleaner's lid does not rest too closely to the top of the carbuertor where it will restrict air flow. You should leave at least 2 inches of clearance.
If your building your own scoop, make sure the incoming-air opening is at least 10-15 percent larger than the carburetor venturi size. This typically equates to about a 20- to 25-square-inch opening in the scoop. For optimal performance, the roof of the scoop should be placed about 2 inches above the carburetor. Be careful not to build the scoop too high because additional clearance can sometimes create turbulence. Adding a scoop to the carburetor system can also effect the air/fuel ratio of the existing combination because the incoming air will hold more oxygen molecules. As a general rule, you might want to begin your tuning by jetting up about two jet sizes (from prior optimum jetting) after you've added a cold-air package.

On another note.... and take this one with a grain of salt !

Very successful Pontiac Super Stock racer John Clegg stated that a front-facing hood scoop will work as a ram air source only if the car in question is doing 200 mph. He used a small Harwood scoop mounted backwards on the hood of his 8-second former record holding Firebird ( it looked like a large size Trans Am scoop ).


.

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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 )
Old information here:
http://www.hotrod.com/articles/0712p...tiac-trans-am/

Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine)
5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension
https://www.youtube.com/watch?v=qDoJnIP3HgE
  #68  
Old 01-14-2021, 11:38 AM
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Quote:
Originally Posted by Steve C. View Post
Tid bit from a magazine that might be of interest. And relates to Cliff's comments......

When designing a cold-air package, remember that an optimum entry will provide a nonturbulent air supply above atmospheric pressure. Front-facing hoodscoops typically begin supplying air at lower speeds, while rear-facing scoops supply air at higher speeds with less turbulence. Inside the scoop, all air ducts should be designed so that air entering the carbuertor will do so smoothly- preferably through a air cleaner or other diffusing device. Be sure that the bottom of the air cleaner's lid does not rest too closely to the top of the carbuertor where it will restrict air flow. You should leave at least 2 inches of clearance.
If your building your own scoop, make sure the incoming-air opening is at least 10-15 percent larger than the carburetor venturi size. This typically equates to about a 20- to 25-square-inch opening in the scoop. For optimal performance, the roof of the scoop should be placed about 2 inches above the carburetor. Be careful not to build the scoop too high because additional clearance can sometimes create turbulence. Adding a scoop to the carburetor system can also effect the air/fuel ratio of the existing combination because the incoming air will hold more oxygen molecules. As a general rule, you might want to begin your tuning by jetting up about two jet sizes (from prior optimum jetting) after you've added a cold-air package.

On another note.... and take this one with a grain of salt !

Very successful Pontiac Super Stock racer John Clegg stated that a front-facing hood scoop will work as a ram air source only if the car in question is doing 200 mph. He used a small Harwood scoop mounted backwards on the hood of his 8-second former record holding Firebird ( it looked like a large size Trans Am scoop ).


.
As far as turbulence goes, I can attest to that with the Formula setup, as I mentioned I found the air coming in so turbulent it kept blowing the crank case filter out of it's case at anything over 80 mph. Which also relates to John's quote that forward facing scoops only work at 200 mph. I find that to absolutely not be the case with anything I've tried and tested.

Unfortunately with that factory setup, and the low profile of the Formula hood, the lid is literally 1/4" away from the choke horn and there is nothing I can do about that. I'd love to raise the lid, but you can't even get a mouse fart between the lid and hood as it is now.
I don't like the very thin air filter that fits in there either, I don't even think it's 2 inches tall, but despite my best efforts to try anything else, the car runs best with this setup.

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Old 01-14-2021, 11:55 AM
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If the boundary layer on the hood of your car behaves as one on a flat plate, estimate how far from the front edge of the hood the boundary layer becomes turbulent. How thick is the boundary layer at this location?


Might be of interest....

http://justacarguy.blogspot.com/2011...of-factoy.html


.

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Old information here:
http://www.hotrod.com/articles/0712p...tiac-trans-am/

Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine)
5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension
https://www.youtube.com/watch?v=qDoJnIP3HgE
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Old 01-14-2021, 12:06 PM
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Old 01-14-2021, 12:35 PM
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Quote:
Originally Posted by Steve C. View Post
A few years ago I called K&N and asked about the air flow requirements for my my 505 cubic inch engine at 6000 rpm. It made peak power on the dyno at that rpm. They said it required about 745 cfm of air flow. I noted my dyno sheet indicated the scfm at 6000 rpm was 839 cfm. Also with other formulas on the internet to determine the cfm requirements of a engine based on cubic inches and rpm can differ. I mentioned all this to the K&N rep and his reply was they had their own methods to determine required air flow.


.
Steve,
Remember the SCFM is measured and was for the measured Uncorrected HP. A 505 ci @ 6000 RPM @ 100% VE wants 877 CFM.

Stan

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Old 01-14-2021, 12:37 PM
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Quote:
Originally Posted by steve25 View Post
Efficient high performance well thought out combos / motors will make more hp with less CFM, and them VE numbers well above 100% are the icing on the cake!
Steve,
That is why it is nice to see Fuel lb/hr and BSFC on the dyno sheet.

Stan

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Old 01-14-2021, 01:04 PM
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Stan, you are correct the 839 scfm number is on the uncorrected sheet.

On the 'corrected' sheet at 6000 rpm:

Volumetric efficiency was 106.9 percent
BSFC was 0.491
Fuel A lb.Hr - 144.3 and fuel B lb/hr - 150.9
659.2 HP at 6000 rpm.

At peak torque rpm it was 707 scfm
110.1 VE
0.427 BSFC

My point to the K&N rep was their formula to estimate the required cfm was different to other formulas used. No big deal. just an observation.

.

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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 )
Old information here:
http://www.hotrod.com/articles/0712p...tiac-trans-am/

Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine)
5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension
https://www.youtube.com/watch?v=qDoJnIP3HgE
  #74  
Old 01-14-2021, 02:41 PM
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Quote:
Originally Posted by Stan Weiss View Post
Steve,
That is why it is nice to see Fuel lb/hr and BSFC on the dyno sheet.

Stan
Yep, and quick math will tell you if they are fudging the numbers

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Old 01-14-2021, 02:49 PM
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Quote:
Originally Posted by Steve C. View Post
If the boundary layer on the hood of your car behaves as one on a flat plate, estimate how far from the front edge of the hood the boundary layer becomes turbulent. How thick is the boundary layer at this location?


Might be of interest....

http://justacarguy.blogspot.com/2011...of-factoy.html


.
There was a test of this years back and I can't remember where that came from, but this was a big part of the discussion. It was more about factory hood offerings though. I remember the Formula was up there as one of the better ones, since the scoops are so far forward it was less affected by the boundary layer than scoops further back. I seem to remember the further back the forward facing scoops went, the worse they did. I think the Challenger TA was another decent one because it's raised up off the hood a bit. The higher the scoop the better it worked. It also got into the effectiveness of cowl plenums and how the distance from the base of the windshield affected it's usefulness.

I'll have to see if I can find that test.

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Old 01-14-2021, 03:33 PM
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Within his articles Rocky Rotella has brought up the related subject regarding the Trans Am shaker scoop when functional. Was as it's more than a hot-selling gimmick to draw potential customer traffic onto the showroom floor and whether the factory sales literature aerodynamic drawings showing high-pressure air at the base of the windshield are accurate or not. Whether it actually worked that way is debatable. Some suggest watching water drops roll off the top of the shaker and backwards into the opening prove it works.


.

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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 )
Old information here:
http://www.hotrod.com/articles/0712p...tiac-trans-am/

Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine)
5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension
https://www.youtube.com/watch?v=qDoJnIP3HgE
  #77  
Old 01-14-2021, 05:08 PM
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The pressure developed at 130 mph is 0.3 psi according to Bernoulli's equation and 0.7 psi at 200 mph.

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Old 01-14-2021, 05:25 PM
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So, how fast do you need to go to overcome 14.7 psi atmospheric pressure to gain "RamAir"?

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Old 01-14-2021, 08:21 PM
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Pressure decreases with increasing altitude.


.

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'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 )
Old information here:
http://www.hotrod.com/articles/0712p...tiac-trans-am/

Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine)
5.14 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension
https://www.youtube.com/watch?v=qDoJnIP3HgE
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Old 01-14-2021, 08:57 PM
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Quote:
Originally Posted by Kenth View Post
So, how fast do you need to go to overcome 14.7 psi atmospheric pressure to gain "RamAir"?
Those were gauge pressures, absolute pressure minus 14.7 psi.

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