Question: RPM Air Gap Porting

[BOOT]

I clean up & prep every intake that I use, don't like doing it or think it helps some much but... no stone unturned. Casting can hide flaws until you sand it.

This is basically what I do and why https://youtu.be/xQpwhGJ1ID4

[1980RS]

Here is my results with an RPM Air Gap this year.

Best 1.53 60ft.
11.30@117.5mph
Divider cut out and port matched to a 1205 gasket.

Sportsman II heads mild ported 2.05 and 1.6 valves
.600 lift 250° duration on a 108° LCA solid cam

4.88 gear with my old 10" TCI converter, my 8" that I broke this year would have been 2 tenth better.

Now I have 3 other intakes to test with this combo,
Ported (old school) Torker
Victor Jr. ported
Holley Modified Single plane Street Dominator
4 If I decide to run the 300-36 again but I don't think it will be any better than the Air Gap.

[forphorty]

Not too impressed with the dyno results for the ported Air Gap on this one: https://www.motortrend.com/how-to/hrdp- ... d-porting/ Unported version outperformed it below 6000.

[skinny z]

Kevin,
I have mentioned this before,
In 2019 my 383 combo
10.6 comp
Dart cast iron 165cc (178cc)
Comp SFT 235-242 @ 0.050" 500" lift 106LSA-106INCL
As cast airgap 950hp carb
Tried alot of spacers the best I can not really say
Engine made around 430hp
Car weighs 3650 with me streeter 255/60/15 MT ET STREET
Testing for approx 9 months
11.75 - 113.23 mph
1.58 - 60ft
7.43 - 91.10 mph
Gear shifts @6000 rpm and 6000 rpm finish line
Engine falls flat at 6000
As far as porting a airgap good luck would be extremely difficult.
Same combo changed to Vic jnr was not port match and just removed casting flash no porting.
11.71 @ 114.48
1.60 - 60ft
7.44 - 91.73
Still 6000 rpm shift 6200 finish line
Had tested with shift points from 5800 - 7000 and 6000 seemed to be where it liked.
I understand you are set on gear and converter
I went from a 9" 4200 converter to a custom 8" 5600 converter and it is worth 3 tenths in the 60ft on all my different combo's .
450hp won't be hard for a 355 cube
But with a set rear gear and converter you will get to a point of flogging a dead horse so don't get caught up to much as it will wear you down.

Looks to be that the Air Gap is well suited and given that you're feeding more cubes than I would be, perhaps that puts me in even better shape.
I can see that "porting" in the strict sense of the term isn't likely given the runner configuration. I'm also inquiring about whether there's anything to be gained from addressing the obvious like stated here.

I clean up & prep every intake that I use, don't like doing it or think it helps some much but... no stone unturned. Casting can hide flaws until you sand it.

That said, digging through some of my earlier build pictures, I came across the gasket to head interface. These are Vortec style ports and a FelPro 1255 gasket.

IMG_6340.JPG

IMG_6342.JPG

IMG_6343.JPG

This is something I never addressed but by the looks of it, I probably should.
Now that the engine is out of the car and the heads off, I can start examining these details I overlooked the first and second time through.
I haven't checked but I'm guessing the manifold side is equally mismatched.

[skinny z]

Not too impressed with the dyno results for the ported Air Gap on this one: https://www.motortrend.com/how-to/hrdp- ... d-porting/ Unported version outperformed it below 6000.

Thanks for the link.

[skinny z]

Here is my results with an RPM Air Gap this year.

Divider cut out and port matched to a 1205 gasket.

I've got the divider notch as it came out of the box.
Have you modified yours further? If so, to what extent and for what kind of benefit?

[1980RS]

As my buddy used to say, quit testing and lets race those intakes. He should know, his 505 BBC made 802hp with an out of the box GM Performance dual plane non-air gap intake (rpm copy).

[1980RS]

Here is my results with an RPM Air Gap this year.

Divider cut out and port matched to a 1205 gasket.

I've got the divider notch as it came out of the box.
Have you modified yours further? If so, to what extent and for what kind of benefit?

Yes mine is cut almost all the way down, it will pull 7K pretty easy. I did notice that 2 cyl were a little fat so I may need to cross jet the carb a bit. Not a big deal though. Here is a picture of what I did.

[skinny z]

... out of the box GM Performance dual plane non-air gap intake (rpm copy).

I have one of those on the shelf from an original ZZZ crate engine (1st edition).
They seem to have some performance value if the internet has anything to say about it. It's the wrong bolt pattern for me but maybe it should be for sale at one the local tracks here.

[steve cowan]

Are you going to port the cylinder heads?
The opening is not the restriction, I would not gasket match.
If the heads are as cast so to speak or you hnock off casting flash on heads and intake I doubt you would notice any difference.
I find the biggest port and size the others to that.Port match intake if you wish,you will find roof alignment of head and intake probably won't line up as well.

[skinny z]

Are you going to port the cylinder heads?
The opening is not the restriction, I would not gasket match.
If the heads are as cast so to speak or you hnock off casting flash on heads and intake I doubt you would notice any difference.
I find the biggest port and size the others to that.Port match intake if you wish,you will find roof alignment of head and intake probably won't line up as well.

That picture was before porting. They've had a new valve job and work on the bowls as well. Nothing done to the ports otherwise. Nor has any attention been given to the port alignment other than trying to get in there with an inspection camera for a look see. But it was impossible with the tools that I had. There could be something there.

They're small heads like a Vortec. One of the things on my agenda is to get in there and get a few measurements. I've no idea what the MCSA might be or the volume since the pocket porting. Not that I'm going to do anything about right now but the information is useful. Especially in the virtual world and discussions here at ST.

For the record, like the gearing and converter, I'm going with the heads the way they are as I've never had any of the combination sorted out before a lifter went sideways. They did flow 254 @ .550" so there's something in them to exploit.

[skinny z]

Then there's this from another forum:

When comparing a Dual vs a Single Plane Manifold...
If the Engine makes peak HP at 6,500 RPM...
and the Single Plain Manifold produces less HP below 7,000 RPM...
Well there is no point in using the Single Plane for that application.

The Vortec Performer RPM Air-Gap Manifold, and the Super Victor Manifold produce results of a similar nature.
Also by removing the Dual-Plane Divider (increasing Plenum Volume), adding a 1" Spacer, preferably a HVH Spacer (increasing Plenum Volume), and some minor porting...
The Vortec Performer RPM Air-Gap Manifold can beat out the Super Victor Manifold, in Peak HP (below 7,500 RPM), while retaining the higher Average HP of the Dual-Plane design.
Not to mention, keeping the higher Average and Peak Torque of the Dual-Plane design (not as important with 400+ Inches... but i would never actually use these Heads for an Engine that size).

When I modify those Intake Manifolds...
I TIG weld the HVH Spacer to the Manifold, and re-shape, contour, port, and blend the Plenum opening and Spacer into one uniform opening.

The material/ areas that have Black Lines outlined, are removed and re-shaped to be more like a Single Plain opening:

manifold1_835df41e90e4eaadbcaef2b6aed43fb9addcfa30.png

The taller Manifold/ larger Plenum area, with the transition from the ported HVH Spacer into the ported shared Plenum space...
along with some Runner transition porting, and Port-Matching... really improve the already great performance of the Intake Manifold.
The HVH Spacer is shown Upside-Down in the Image Below:

hvh_ss4150_1dpal_hp_xl_bf2d193e6265f874f7d6435722de1b89eaf78f9e.jpg

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Seems opinions are all over the map.
But, the divider and a spacer look to be a common theme.

[steve cowan]

they do not say what cubes and or AVG CSA of cylinder head,the statement is misleading in my opinion

[skinny z]

they do not say what cubes and or AVG CSA of cylinder head,the statement is misleading in my opinion

Sorry about that. In my editting, I excluded that this poster was working with Vortec heads on CID from 350 to 383 to 400 (although 400 was later described as not ideal).

[F-BIRD'88]

Might want to consider trying out a custom made spacer that includes a plenum divider that fits your cut down divider. Essentually restoring the full divided 180° split plenum. Then experiment with various spacers styles above that spacer/divider.. It seems many many times that the higher up the carb is on the manifold. the better on all manifold types. Something to think about and try.

Gives you an excuse to cut a hole in the hood.