MrJ

I've got the base off the car, and I have a generally idea about what to do. But is there any kind of guide that I can refer to, that has info on what areas to focus on, where not to focus on, etc? It would be really helpful if there were.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

Kevin91Z

iTrader: (1)

Here's pics of what my dad did to mine:

http://24.1.139.249/images/101500/DCP_0028.JPG
http://24.1.139.249/images/101500/DCP_0029.JPG
http://24.1.139.249/images/101500/DCP_0030.JPG

Basically you just open it up so it matches the gasket. But if you're not doing the heads too, then dont open up the intake manifold larger than the heads. Air hates it when it hits a wall, and if the intake is larger than the heads, they'll create a wall. Also make sure you dont port it so much you go thru the casting!

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West Coast GM Shootout 2001!
1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

MrJ

thanx Kevin.

IrocStan

I ported the chit out of my base. I inserted ***** in each port to gauge each one to the next. I opened up the opening the most, I used a yellow foam "Nerf" ball to gauge that. Then I used a ping-pong ball to gauge the inside the port about a inch of the way in. I mostly tried taking out the bends on the entry and exit. In the middle I just enlarged it. I used TPIS's Large mouth Base gaskets. I didn't use those as a guide though, because they are HUGE!
I know that it isn't the most scientific approach, but what else can you ask for when you are on a budget.

Austin

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87 IROC 350
Mods: 3:42 Torsen, pocket ported 083 heads, complete Edelbrock exhaust, Most free mods, Most little mods, aluminum d/s. Edelbrock STB, boxed rear suspension pieces, urethane bushings everywhere.
Stock cam, chip, runners, base, and trans
13.94@103mph, 2.25 60'
Recent stuff: SSM sfc's, Homemade relocation brackets, Ported SLP runners, ported base, EGR!
Current/future projects: homemade torque arm, and 27x10 Hoosiers (need wheels!), and Prom Burning
Planning new engine build, possibly 383 w/ TFS 23*

MrJ

OK, I started porting. I began by adding a better transition from the runners to the base. I'm using a Dremel w/ a flex shaft attachment and the drum-shaped high speed cutting bit. Where should I be concentrating on? It looks to me like the biggest restrictions are found right after the air enters the manifold, since it has to make a quick turn before heading toward the head port. And the other restrictive spot, even worse than the other one, is found about an inch into the manifold, if you look into it by looking through the head-side openings. The air has to make yet another turn. So the bottom line is, it seems to me like I need to give the air as straight of a shot as possible, from the runners to the head as it passes through the manifold.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

Yelofvr

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 fiqure 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

88IROCs

Dave,
Really excellent info! Has the makings of a good article for the tech section if you feel up to it(hint, hint).

I port-matched all the intake components last spring, and felt a substantial improvement for my efforts. But I figured I'd have to buy an aftermarket base to get any more worthwhile improvements. Now, I'm questioning if that makes sense(your ported flow numbers are very close to those of most stock aftermarket bases).

And if you don't mind me asking: how much did AFR charge to port your base?

Thanx,
Andy

Yelofvr

Andy: I did not pay to have the base ported. I bought it that way on ebay for $180. Az Speed and Marine gets $475 to port a stock manifold.

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Dave Zelinka

88IROCs

Dave,

<u>$180 ?!?!?</u>. For a professionally ported base manifold? That's a steal!!! I've bought a fair amount of tpi and thirdgen stuff from online auctions in the last year,... and I thought I had gotten some deals. You lucky dog!!

Guess I'll have to call AFR and see how much. As for AS&M,... I like their stuff, but it's way too rich for my blood(read: I like my toys but, I'm a cheap old bastard at heart )

Andy

IrocStan

Very interesting Yelofvr, thanks for sharing. One question:

How did you measure this? This is in the middle of the port, and isn't a very common shape to calculate area from.



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87 IROC 350
Mods: 3:42 Torsen, pocket ported 083 heads, complete Edelbrock exhaust, Most free mods, Most little mods, aluminum d/s. Edelbrock STB, boxed rear suspension pieces, urethane bushings everywhere.
Stock cam, chip, runners, base, and trans
13.94@103mph, 2.25 60'
Recent stuff: SSM sfc's, Homemade relocation brackets, Ported SLP runners, ported base, EGR!
Current/future projects: homemade torque arm, and 27x10 Hoosiers (need wheels!), and Prom Burning
Planning new engine build, possibly 383 w/ TFS 23*

Yelofvr

IROCstan:
I bulit a set of inside feeler gauges by taking a posicle stick and I cut little pieces of zip tie at varying lengths like 1.50", 1.525", 1.55", etc. I attached these at right angles to the end of the sticks. That way I could insert them into the ports to get a measurement for width and height. I performed all these measurements on a Accel high flow base manifold to get a direct comparison. The ports are not perfectly rectangular, but for making a estimation of area increase, I thought this was fine.

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Dave Zelinka

shaggy56

This is one of the most informative reads I have ever seen and is chock full of porting info. Its a shame it never became a sticky. Good stuff here too.

https://www.thirdgen.org/forums/tech...d+port+porting

Mark 89Formula

Second that. This should be a sticky.

shaggy56

I think its great how he points out how a stock performance port is 1.23" x 1.98" and is capable of flowing 315 cfm. It shows how just about any head would better benefit from some porting in the correct locations as long as their is enough material in those areas to do so.

1989GTATransAm

iTrader: (3)

For $400 you can also get the manifold extrude honed which not only opens up the manifold but makes for a very smooth finish. I have seen where an Accel Extrude Honed TPI manifold flowed 273 CFM. That will get it done.