Single Carb. Conversion, VW Plenum & Modding, the OEM Manifolds

[Dave_J]

In the restrictor plate used in Nascar, the carb is much larger than the plates holes, and as is the runners down to the head. This plate is a CHOKE, not a venturi. It allows only so much air to flow no matter the carb or runner size. But the engine builders have found out that it does cause the air to speed up and causes some turbulence and they have tweeked the runners so the velocity is higher and they make good power.

A second venturi down in the runner could be used as an airflow choke, it will work. The airflow before the venturi may stall some. It will speed up only thru the venturi but as soon as it gets to the larger pipe section it has to slow down again and may stall out some again.

But making the pipe size the same end to end, but smaller works better in prior race car tests. The Chevy Vortec engine has a venturi down near the valve just to cause a vortex/swirl in the combustion chamber.

If the carb has a removable booster ventury on the top, adding a coating of epoxy to thicken it up will make the carb air flow smaller.

 

[joedrum]

good post and totally true ... a little bouncing around ... but all on point dave

kind of explains my deal on other manifold im doing with carb bodies as runners :mrgreen:

 

[Ansimp]

mcgovern61 » Tue Oct 01, 2013 2:07 am[/url]":36m0wbb5]

82a » Mon Sep 30, 2013 10:34 am[/url]":36m0wbb5]
i've also seen 'iggy' used and i think that is short for ignition (systems)

Well that blows apart my interpretation.....I thought "iggy" was a new Member here! :smilie_happy: :wave: JK

I thought that was Joe taking a break and having a " ciggy" :smilie_happy:

 

[Dave_J]

Something you may want to look at is the use of Tumble Generator Valve's (TGV) Subaru, Ford, Volvo and many others are installing them at the end of the intake runners to promote swirl when cold. It is just a butterfly that at low airflow it is closed up some helping mix the air/fuel better. The WRX guys are deleting them for a SMALL amount of power when adding a huge turbo. The gain is about 10 HP when they boost over 20 PSI. WOW! It costs them from $200 to $500 to gain 10 HP on the street. WOW!!! If intrested read some of the posts: https://www.google.com/#q=tumble+generator+valve

 

[westgl]

Ok talked to first fab./welder

He said it would be 2-weeks.

I said ok but can you do it today?

So he gave me the name of another Fabricator/welder, that said he could do it.

Till he saw there was a rubber end of the manifold, that is not remove-able, then he said No way.

Then said wait!, so he is going to put the rubber in a pan of water, while he welds the two piece manifold into one.

If that damages the rubber end, i will be going to plan "B"

Plan "B" is remove the rubber off of the two, port angled manifolds, and have welder weld the Alum. tube directly to the manifold with out the rubber end on it.

Poor Cat, he ain't gunna have no skin on him.

 

[westgl]

I picked up the manifolds they look good.

I got everything mounted

It was 50 degrees out

I started the engine, it does run a little differently.

No leaks Vacuum, or fuel.

It revs differently, it sounds different while revving it.

Hmmmmmmmmmm!!!!!!!!!!!!!

We shall see what happens during the ride report

I did not have a chance to test ride, as i have to hook up the throttle cable, and cable stop, and mount seat and faux tank.

I wanted to make another mount for my cable stop

 

[Steve83]

opcorn: :beg: :clapping:

 

[westgl]

Here are a few pictures, showing the newly cut and twised Oem Manifolds point directly at the VW plenum outlets

You can see the weld bead, but they did a good job welding it.

you can also see the manifold is pointing directly at the Plenum outlet.

This new setup was easier to mount.

While running it sounds a little more Ferocious.

P1020166

• westgl
• Oct 1, 2013

Rev.2 Manifold Runners and Oem manifolds twisted to point right at VW plenum Outlets

Below was my worst cylinder, right front cyl. now it is a piece o cake

P1020165

• westgl
• Oct 1, 2013

Rev.2 Manifold Runners and Oem manifolds twisted to point right at VW plenum Outlets

P1020164

• westgl
• Oct 1, 2013

Rev.2 Manifold Runners and Oem manifolds twisted to point right at VW plenum Outlets

P1020163

• westgl
• Oct 1, 2013

Rev.2 Manifold Runners and Oem manifolds twisted to point right at VW plenum Outlets

P1020162

• westgl
• Oct 1, 2013
• 1

Rev.2 Manifold Runners and Oem manifolds twisted to point right at VW plenum Outlets

 

[KYWinger]

:clapping: West: That manifold looks AWESOME!

A clean and professional look, to be sure! Can I ask you what you paid for the welding?

If I go single carb, this is most definitely how I'll do it...

Did you cut/reweld the oem runners on just cylinders 3 and 4?

 

[dan filipi]

That looks great west!

Ride report, ride report.

 

[westgl]

It does look more like factory, that was what i was hoping for.

Welding, was $40.00 total, so $20.00 per manifold, I had them weld 2ea manifolds.

I cut the Manifolds, then I mounted the lower section to the head, and twisted the upper section to Point at the VW plenum Outlet,

There are only 2ea manifold that need to be twised and welded, The other 2ea manifolds are both straight runs at the plenum outlets.

Well now all 4ea manifolds are straight runs pointing at the Plenum outlets.

It looks like it will be very DURABLE.

I want to pull the tubes out after I do some Road Testing, for some polishing, to dress them up some.

The two cylinders that need to be cut are, #1 & #4, #1 on my engine was the worst.

Cyl.'s #2 & #3 are straight shots already and dont need anything done to them.

KYWinger » Tue Oct 01, 2013 6:16 am[/url]":2wvh5nif]
:clapping: West: That manifold looks AWESOME!

A clean and professional look, to be sure! Can I ask you what you paid for the welding?

If I go single carb, this is most definitely how I'll do it...

Did you cut/reweld the oem runners on just cylinders 3 and 4?

 

[joedrum]

yep looks good west ....revvs different ...hmmmm .... yes ride report .... seems there might be huge difference in how the runners work maybe from rubber to metal ... witch is the omly big difference here ....hmmmmmm ... could it be rubber is better :shock: :headscratch:

 

[KYWinger]

west: We're ALL awaiting a road report! opcorn: opcorn:

 

[westgl]

What I did to get the proper amount of twist was:

1. Cut the alum. tube for the 2ea cyl. that are straight shots and get them mounted and in place this will show you your spacing and keep in mind that some spacing is required between the carb inlet and frame.
2. Mount the 2ea oem manifolds, that are straight shots already from factory (cyl.'s #2, & #3) with the tubing you just cut, you can leave the hardware a little loose.
3. Cut your manifolds above the mounting section, about 1/4" this should be a straight cut, then de-burr with a file, inside and out.
4. Put the top half on to the mounted lower half of cut manifold, now point Centerline of oem manifold to centerline of Plenum outlet, mark with a sharpie, three lines center line shaped like a Romain Numeral I that is your center line.
5. Take to a fabricator/welder, ask for price up front. My welder put the rubber in a water pan, while he was welding to keep the rubber cool.

If the rubber was damaged while welding, I had Plan#B
In case someone has the rubber damaged on those 2ea manifolds,

I was going to remove the rubber completely, then weld the tube directly to the Oem Manifold, this would eliminate this clamp point here.

 

[KYWinger]

westgl » Tue Oct 01, 2013 7:19 am[/url]":1wwipmyf]
I was going to removed the rubber completely, then weld the tube directly to the Oem Manifold, this would eliminate this clamp point here.

This idea seems the best and most solid. It also would allow (after a while) heat transfer up to the plenum; why did you choose to keep the rubber connectors?

 

[westgl]

Yes, removing the rubber would allow much needed heat to the runners and would be the absolute best way to go.

I thought of plan "B" after, I dropped off parts to the welder, and he told me the rubber may not survive, due to 1200 degrees of heat, during welding.

But if your measurement/angle of TWIST is off slightly, Or welder is Off slightly, you have 2ea rubber mounted sections to make up the difference.

KYWinger » Tue Oct 01, 2013 7:26 am[/url]":33te7oh8]

westgl » Tue Oct 01, 2013 7:19 am[/url]":33te7oh8]
I was going to removed the rubber completely, then weld the tube directly to the Oem Manifold, this would eliminate this clamp point here.

This idea seems the best and most solid. It also would allow (after a while) heat transfer up to the plenum; why did you choose to keep the rubber connectors?

 

[westgl]

Chances are, if Not too far off.

You can make up the differences at the VW plenum, rubber mount.

The Tube Between the VW Plenum Outlet and Twisted OEM manifold has Been cut at a angle, to match the canted angle difference between the tube and plenum outlet, this is not critical, just angle as it cannot be a straight cut.

I used a Chop/cutoff saw, to cut everything, as it is really fast, main thing is being able to hold the part very solidly while cutting.

 

[Dave_J]

West, I still would run a rubber coupler in the runners due to vibrations left to right.

In my days of doing a 2004 WRX, some of the "Tuners"would mill or grind off any not needed item or casting lashings just to shave about 40 pounds off the engine (then go to lunch and scarf down 2 Big Mac's, large fries, large coke with two refills and two apple pies). Some of these mods cost over $500 each and others 100's of man hours. One item that was ported and ground down was the heavy cast aluminum intake manifold. They would heavily grind down all the outsides of the runners to polish them. Then only to have them crack from the vibrations. Now granted they did have a huge intercooler on this but all that was rubber hose mounted and supported by brackets.

In our case it would most likely crack at the heat effected zone near a weld.

 

[westgl]

Guys I want a ride report too.

But it is only 44 degrees out, i think i will wait till at least noon.

3 hours from now, I should have some more heat out there by then.

When I started it up last night it was 50 degrees out.

Plenum & Runners, were a little cold.

But my Rev.#1, the runners were also cold, with the silicone hose it was a little harder to feel that they were cold, i think the silicone hose was insulating the cold to the exterior, But I bet they were just as cold.

 

[westgl]

I have two rubber isolated mounts.

If i do have a manifold cracking problem.

Then Plan "C" comes into play.

I like to always have a spare tire.

Hey Zelda, How many Rabbits are in this Hat?

Dave_J » Tue Oct 01, 2013 7:46 am[/url]":1graty3h]
West, I still would run a rubber coupler in the runners due to vibrations left to right.

In my days of doing a 2004 WRX, some of the "Tuners"would mill or grind off any not needed item or casting lashings just to shave about 40 pounds off the engine (then go to lunch and scarf down 2 Big Mac's, large fries, large coke with two refills and two apple pies). Some of these mods cost over $500 each and others 100's of man hours. One item that was ported and ground down was the heavy cast aluminum intake manifold. They would heavily grind down all the outsides of the runners to polish them. Then only to have them crack from the vibrations. Now granted they did have a huge intercooler on this but all that was rubber hose mounted and supported by brackets.

In our case it would most likely crack at the heat effected zone near a weld.