When porting the base of an intake, do you port maybe 2-3 inches inward. Or are you talking about all the way across the passage. If so, how would you reach the middle of the passage? If not, wouldn't the intake still be a large restriction because it will still be small in that area?

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91 Z28
Best Time Slip:
60' - 2.098
1/8 - 9.137 , MPH - 76.21
1/4 - 14.213, MPH - 97.55
Performace Mods: B&B Exhaust, few free mods.
Appearance Mods: SS wheels, 2.5" Cowl Hood... New 100% Black paint job, Clear Side Marker Lights
Stereo: Alpine 855, Infinity Kappas all around, Infinity 150x2 amp (POS), Infinity Perfect 10 in hatch.
Pictures are Here
ICQ: 1437212
AOL: normalmatt9

 

To get a stock one to breath, you have to port through the entire passage. A bit with a long shaft, or Dremel with a flex attachment lets you get at the middle portion of the base.

 

Seems like it'd be to accidently go through the it when you can't see real well in the middle. Oh well, I'll get one and give it a try.

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91 Z28
Best Time Slip:
60' - 2.098
1/8 - 9.137 , MPH - 76.21
1/4 - 14.213, MPH - 97.55
Performace Mods: B&B Exhaust, few free mods.
Appearance Mods: SS wheels, 2.5" Cowl Hood... New 100% Black paint job, Clear Side Marker Lights
Stereo: Alpine 855, Infinity Kappas all around, Infinity 150x2 amp (POS), Infinity Perfect 10 in hatch.
Pictures are Here
ICQ: 1437212
AOL: normalmatt9

 

Theres no way you are going to accidentally go through the material in the middle unless you do it intentionally, its more than 3/16" thick.

 

I posted this back in Feb, hope it helps.....

When I approached my intake manifold porting, I followed what I had read in David Vizards book on cylinder head porting. You can break the TPI manifold into 3 regions, the head entry, the mid runner section, and the entry to the runner tube. If your goal is to increase the flow through any passage of non uniform cross section you need to look at each area where the cross section is distinct and understand
how each section flows to determine how much (if any!) it needs to be modified. If you look at the stock manifold you will observe the following dimensions:
Cylinder head interface: 1.14" x 1.75"
mid passage dimension: 1.10" x 1.55"
passage at runner entry: 1.48' x 1.55" (one inch into manifold)

These yield the following cross sectional areas:
Cylinder head interface: 1.99 sq. in.
mid passage dimension: 1.705 sq. in.
passage at runner entry: 2.29 sq. in.

As you can see there is a noticeable difference. To put this into flow terms, if we assumed each of these cross sections were the full length of the intake manifold passage, we would observe the following flow rates for a 28" H2O pressure drop:
Cylinder head interface: 245 cfm
mid passage dimension: 200 cfm
passage at runner entry: 294 cfm

Since pressure drop is proportional to the length of the passage, you also need to figure in the length to be exact, but it is very clear that in order to improve the flow of the manifold, you need to work on the center of the runner since it flows the least and is the longest in length. A bone stock intake manifold will flow about 220 cfm. You can work all day long on enlarging the passage to the runner and not change this number at all!! I will discuss each section above and describe what I feel needs to be done:

1) Cylinder head interface: If you are using larger than stock heads, by all means match the opening size to the heads. A common performance head opening is 1.23" x 1.98" and is the std for the Fel-Pro 1204 gasket. This opening area is 2.415 sq. in. and has an equiv flow rate of 315cfm which is already bigger than you need. Make your manifold opening slightly smaller since alignment is never perfect and you in general never want the airflow to hit a "step up" but rather a "step down" if it cannot be smooth. I would like to make note of an important distinction about this area of the passage. At this point in its travels, the air needs to make a rather significant change in direction when it meets the head. This is referred to as "intake entry angle" and is far from optimum on the TPI manifold. It was designed this way so that the engine would fit under the low hood lines of the corvette and F-bodies. Air does not like to make sharp turns and if forced, this will cause turbulence, flow loss and heating. The way to make air turn a corner better is to provide a larger radius turn. The only way to do this on the TPI manifold is to raise the roof of the port. You do not have alot of material to work with here, but always give preference to roof removal versus floor removal when enlarging this portion of the passage as you move into the passage.

2) Mid passage: This area I feel is the most important and the area you will get the most gains in cfm and horsepower. It is also the most difficult and time consuming. I have made measurements on a stock TPI base that was ported by AirFlow Research and the mid port dimensions are 1.22" x 1.625" versus the stock 1.10" x 1.55". This is a cross sectional area of 1.983 sq. in vs. 1.705 sq in. stock. The equiv. Flow rate is 245 cfm vs. the stock 202 cfm. I used a 6" carbide burr for material removal in this area of the passage and worked from both sides. Make yourself a little feeler gauge to measure width and height.

3) Runner interface: Modification in this area depends on the runner being used. This is already a high flow/low velocity area, so don't go crazy trying to open it up. Match it to the diameter of the runner(slightly larger in this case since the air is flowing from the runner to the manifold). You will notice that large tube gasket are larger than the runner diameter. This is intentional, as again, alignment will never be perfect and you don't want the gasket intruding into the airstream. DO NOT match the runner opening to this gasket diameter or you will for sure get a negative step at some point along the runner circumference.
One general note on surface finish. After you finish your port dimensions to the proper size with a carbide burr, always finish sand with sanding rolls. I like to use conical rolls and finish with 400 grit if avail, try to get 320 at least. This will help airflow by reducing the friction factor due to inside roughness. You can see the effect this has by looking into an engineering text on fluid dynamics and using a Moody diagram. It is significant so its worth the extra effort to make the walls as smooth as possible. This work will pay off. My AFR ported manifold flows 255 cfm versus the stock 220 cfm.

Well, that's my 2 cents worth………………….well, maybe 3 cents worth!


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Dave Zelinka

 

Thanks Madmax... and big thanks Dave. I'll give it a try.

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91 Z28
Best Time Slip:
60' - 2.098
1/8 - 9.137 , MPH - 76.21
1/4 - 14.213, MPH - 97.55
Performace Mods: B&B Exhaust, few free mods.
Appearance Mods: SS wheels, 2.5" Cowl Hood... New 100% Black paint job, Clear Side Marker Lights
Stereo: Alpine 855, Infinity Kappas all around, Infinity 150x2 amp (POS), Infinity Perfect 10 in hatch.
Pictures are Here
ICQ: 1437212
AOL: normalmatt9