Hi all,

My son and I are sorting through our fuel injected Corvair and have confirmed one of my earlier observations that the i.d. of the intake runners are smaller than the carb base diameter that they bolt to and would like to correct this.

We’ve started to poke around for flanges and pipe to have some fabbed up and are curious to know what sources are available for these parts more so for the flanges than the pipe, but any info would be appreciated.

Thx,

Mike

I know of no one offering Larger flanges. Others will comment.

Find a local shop with WaterJet or Plasma cutter.

MODERATOR
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Please post pictures of what you are talking about.
You spoke of Fuel Injection, and then went on to mention Carb. Bases, and Runner Diameters.

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WA. state, 1 mile south of the Canadian border, I am not at the end of the world, but you can see it from here.

As requested, here’s a pic. The i.d. Of the runner is 1 1/8” and it is not mandrel bent.

I think you're fine since you're only carrying air through those runners. You can run the math but I think you're way plenty. 164 cubic inches can only move so much air.
Just my opinion and I could be wrong. I'm not much of a bigger is better guy. Velocity comes to mind but I'm not prepared to argue it.

Jim Brandberg
Isanti, MN
CorvairRepair.com

this may get you started down the right path;

[www.ebay.com]

Dan Central MN
1968 Convert

Thanks Jim,

Hadn’t thought about the volume - only the cross sectional area. Think I will put pencil to paper and run the math!

Thanks Dan - exactly!

You would do well to bore the carb pads out to 1.5" and have new tubes to match that. Your heads will now flow close to what they do with individual runners, as the integral manifold has a larger cross sectional area than do the holes for the carb pads. Gm's experiments with fuel injection all used tubes that were 1.5" and larger. Theres a real good reason for that!!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]

That air flow meter is probably the restriction not the tube or port ?

1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1998 Honda Prelude Dirt track car
1967 Crown V8 under construction
Mike Levine
Cumming Georgia
North of Atlanta

There is a formula floating around somewhere that you can use to calculate mean gas velocity to figure out runner size and length based on valve size and RPM. I had it years ago and designed some kart intakes that really worked great. I lost it.
I think the website was a motorcycle road race group called Army of Darkness but it is long gone.

Joel
Northlake, TX
5 Ultravans, 144 Corvairs and counting...

63turbo Wrote:
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> You would do well to bore the carb pads out to 1.5" and have new tubes to match that. Your heads will now flow close to what they do with individual runners, as the integral manifold has a larger cross sectional area than do the holes for the carb pads. Gm's experiments with fuel injection all used tubes that were 1.5" and larger. Theres a real good reason for that!!


Great info Kevin - Very much appreciated!

v8vair Wrote:
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> That air flow meter is probably the restriction not the tube or port ?

Thanks Mike,

I’ve been thinking about the throttle body diameter and hadn’t chased it back to the AFM, but I will now.

joelsplace Wrote:
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> There is a formula floating around somewhere that you can use to calculate mean gas velocity to figure out runner size and length based on valve size and RPM. I had it years ago and designed some kart intakes that really worked great. I lost it.
> I think the website was a motorcycle road race group called Army of Darkness but it is long gone.

Thanks Joel - it’s gotta be out there somewhere in the way back machine.

You're just carrying air not a fuel air mixture. What's 12/1, like 8% more volume available for air?
The intake manifold is an additional plenum that each cylinder is drawing from.
It can all be big and smooth up above but the last steps into the intake valve will slow it all down.
I have no math to back it up. I'm just not a bigger is better guy without thinking it through.
Years ago I got the notion that the plenum under the Holley 390 in my 6-tube manifold might be better off bigger. I did some research and ran the math which showed the Warren LeVeque design was spot on.
I could be wrong, I find this interesting and would love to read more. Where did GM locate their injectors? Adding the fuel at the end of the line is a wonderful thing, especially with our 120 degree or more change in direction.

Jim Brandberg
Isanti, MN
CorvairRepair.com

JimBrandberg Wrote:
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> I think you're fine since you're only carrying air through those runners. You can run the math but I think you're way plenty. 164 cubic inches can only move so much air.
> Just my opinion and I could be wrong. I'm not much of a bigger is better guy. Velocity comes to mind but I'm not prepared to argue it.


Hi Jim,

I ran some math last night.

The existing 1 1/8" diameter runner area is .994 square inches and a 1 5/16" runner area would be 1.352 square inches.

That's about a 35% difference.

The 4 runners are about 17 inches long.

The 1 1/8" one yields 68 cubic inches and 1 5/16" one yields 92 cubic inches which carries the 35% delta forward from the area noted above.

Given the 1 1/2" diameter of the intake plenums as Kevin notes below, figured at 12" long, they yield 42 cubic inches.

Plus the plenum just past the throttle body is about another 32 cubic inches.

92+42+32=166 cubic inches.

The GM fuel injection set-up basically had the injectors at the top of the ports, these heads had the whole integral manifold machined off, and all 140 heads done like that tend to flow around 200 cfm that way. With the integral manifold, you get to the same head flow if the carb pads are bored to 1.5"... of course this lets the engine breath a lot more, so the power goes up. but the engine must rev higher now, and can because of this extra head flow. Doesnt happen with those tiny little stock carb pads, and making the tubes only the same size as those stock pads just makes it worse, because of the extra length!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]

63turbo Wrote:
-------------------------------------------------------
> The GM fuel injection set-up basically had the injectors at the top of the ports, these heads had the whole integral manifold machined off, and all 140 heads done like that tend to flow around 200 cfm that way. With the integral manifold, you get to the same head flow if the carb pads are bored to 1.5"... of course this lets the engine breath a lot more, so the power goes up. but the engine must rev higher now, and can because of this extra head flow. Doesnt happen with those tiny little stock carb pads, and making the tubes only the same size as those stock pads just makes it worse, because of the extra length!

Hi Kevin, I’m not sure I understand what you mean by extra length. Would you mind explaining a bit more?

Mike Doiron Wrote:
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>
> Hi Kevin, I’m not sure I understand what you mean by extra length. Would you mind explaining a bit more?


The extra length I'm referring to is the tubes you have that are attached to the stock carb pads. If these tubes are the correct size to match what the heads will actually flow (meaning the carb pads bored to 1.5"), then the extra length, meaning that tube length from the carb pad to the throttle body actually helps get some wave action, but with them too small, this extra distance exaggerates the flow loss from the original undersized carb pads, basically a pressure drop due to length.
Another example of this is the turbo cross over manifold. Someone a few years ago converted their 110 to fuel injection and used a stock turbo manifold to mount their injectors on it, deleted the stock carbs and attached a large throttle body on the cross over manifold. He said that while he was real happy with the throttle reponse, smooth running and instant starting ect., he noticed no increase in power, which is impossible unless the loss due to the tube length on the turbo manifold cancels the gain that comes from deleting the carbs!! On the turbo manifold its 3 feet long to the drivers side head and 2 feet long to the passengers side head. On the Turbo application, this undersizing of the tube is so severe that by the time the head manifold gets to 20psi, the turbo has to put out 25psi to do it!!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]

63turbo Wrote:
-------------------------------------------------------
> Mike Doiron Wrote:
> -------------------------------------------------------
>
> >
> > Hi Kevin, I’m not sure I understand what you mean by extra length. Would you mind explaining a bit more?
>
>
> The extra length I'm referring to is the tubes you have that are attached to the stock carb pads. If these tubes are the correct size to match what the heads will actually flow (meaning the carb pads bored to 1.5"), then the extra length, meaning that tube length from the carb pad to the throttle body actually helps get some wave action, but with them too small, this extra distance exaggerates the flow loss from the original undersized carb pads, basically a pressure drop due to length.
> Another example of this is the turbo cross over manifold. Someone a few years ago converted their 110 to fuel injection and used a stock turbo manifold to mount their injectors on it, deleted the stock carbs and attached a large throttle body on the cross over manifold. He said that while he was real happy with the throttle reponse, smooth running and instant starting ect., he noticed no increase in power, which is impossible unless the loss due to the tube length on the turbo manifold cancels the gain that comes from deleting the carbs!! On the turbo manifold its 3 feet long to the drivers side head and 2 feet long to the passengers side head. On the Turbo application, this undersizing of the tube is so severe that by the time the head manifold gets to 20psi, the turbo has to put out 25psi to do it!!

Thanks Kevin.

Coincidentally came across the pics of the system in your second paragraph earlier this week.

Much appreciated.

Mike