Modified 2-1/2" Outlet Rams Horn Manifolds (1 Viewer)

[B y r o n]

Many who use SBC engines use rams horn manifolds. A lot use the 2" outlet version to take advantage of the 2 into 1 crossover exhaust pipe. Some of us want a little more, and use the 2-1/2" outlet version used on mid 60's Corvettes.

There are companies like Cast Iron Heads that will sell you modified rams horn manifolds at a premium price. They use CNC machines to port the manifold to match Fel-pro 1404 manifold which open the port from approximately 1-5/16" to 1-1/2" opening.

Dorman offers early Corvette manifold reproductions at a very reasonable price and you can enhance them yourself with a simple die grinder and 1/4" carbide burr.

Here is an example of the factory exhaust manifold gasket and the Fel-pro 1404 that is 1-1/2" x 1-1/2" ports.

So you take the Dorman manifolds, left side or drivers side, and open them up.

And you end up with this.

Now it took me two days to port both manifold because you have to open up 8 port and I also open the exit port to allow unobstructed flow.

Now the purpose of all this work is to create a 2-1/2" into 3-1/2" exhaust system for a healthy 350+ motor. Mine is 0.030" over with Edelbrock EFI being added.

My old system was 2" dual exhaust with cross over H-pipe and a carburetor. My plan is to build a 2 into 1 system with 3-1/2" single exhaust. I want to place the O2 sensor in the 2 into 1 collector so it can read the 02 levels from all 8 cylinders instead of only 4 cylinders from either side.

 

[Weber Sarge]

Unless that's a really short y-pipe the O2 sensor may have a hard time reading correctly .....nice porting work , btw .
Sarge

 

[B y r o n]

Here is a picture of the collector I was going to mount the O2 bung on.

My thought was to place it near where it joins into the 3-1/2" outlet pipe where the exhaust from both side would be merging.

 

[pb4ugo]

Interesting, How did the gasket ports compare to the cyldr head ports? Did you need to port the heads too? By the way, chevy did not use gaskets between the head and the stk exhaust manifolds.

 

[Mace]

By the way, chevy did not use gaskets between the head and the stk exhaust manifolds.

??? I've seen this for Diesels, but never gassers..

 

[B y r o n]

Interesting, How did the gasket ports compare to the cyldr head ports? Did you need to port the heads too? By the way, chevy did not use gaskets between the head and the stk exhaust manifolds.

The exhaust ports on the head were larger than the silver gasket in the above photo but smaller than the Fel-pro gasket. The exhaust ports on my heads are 1.375" x 1.375" (1-3/8" x 1-3/8"). This was done years ago when I had a shop Cc and port them. The intake side actually had more extensive porting done than the exhaust. I believe the stock 350 port size is probably 1.375" (1-3/8") high by 1.25" (1-1/4") wide. I didn't touch the head porting.

The porting I did on the exhaust manifolds was to allow them to flow more than their original 1.3125" (1-5/16") would allow. A secondary benefit I picked up on is that with the manifold port larger than the head port it sets up an anti-reversion dam. Basically it keeps exhaust from being sucked back into the head.

As previously stated gaskets have always been used on the Chevy exhaust manifolds I've worked on over the years.

 

[pb4ugo]

I port matched a couple of my engines & it helped. Simply And easy, it's only labor. I've pulled my share of GM exh manifolds ,heads & engines on unmolested vehicles for repair or parts & have never found exhaust manifold gaskets installed. I currently have 3 sbc's, w/stk cast iron manifolds & a 6.5td, none of them had or have gaskets. Cast iron heads & manifolds w/good straight surfaces & your good to go. I have a 1993 GMC Service Manual. There's no reference of gaskets or pics of exh gaskets in the componet diagrams. The installation steps in the manual does not reference or lists gaskets either.

Edited.

 

[yotafj]

Your o2 sensor needs to be about a foot farther back in your exhaust pipe to get a proper reading of the air to fuel ratio. I did this conversion With a 94 302 but it was the fast system. It kept giving false readings at the collector so we moved it back into the exhaust pipe more and it smoothed out way more, fast said the turbulence at the Collector was to much moving it into the pipe it is a steady constant flow out the exhaust, they compared it to the newer cars how it's placed before the cat to get the reading hope this sorta helps. We had BBK headers with 2 1/4 cross over to a 2 1/2 out the back

 

[terrx]

Good info.

Running without gaskets is a trick used for years on motorhomes with big block engines that were prone to cracked manifolds. I don't use gaskets on a SBC but probably will once the surfaces no longer seal without them.

Check the EFI kit, more than likely the O2 sensor is heated (three or more wires) and you'll be fine with that location.

Does your engine have vortec heads?

 

[B y r o n]

Good info.

Running without gaskets is a trick used for years on motorhomes with big block engines that were prone to cracked manifolds. I don't use gaskets on a SBC but probably will once the surfaces no longer seal without them.

Check the EFI kit, more than likely the O2 sensor is heated (three or more wires) and you'll be fine with that location.

Does your engine have vortec heads?

The Edelbrock E-Street EFI supplied O2 sensor is a heated unit (0 258 017 025 or 17025 version).

No on the Vortec heads, 76 Cc version to keep compression down with flat top pistons.

 

[bikersmurf]

I'm running a 350 chev from a Sept '69 Belair... Neither side had gaskets till I pulled one manifold that had a broken stud. After 38 years, it wasn't sealing perfectly anymore, so I reinstalled it with an exhaust gasket. FYI, it came stock with Ram Horn manifolds, and the second one hasn't been off the head since it left the Factory. I'm the third owner of this motor, and the second owner grew up riding in it.

BTW, never mess with a motor built on a Wednesday... Mine was built on a Tuesday... But close enough. 45 and still going strong, all it's had was a cam, lifters, rockers, and a timing chain.

 

[B y r o n]

Well, today it was time for some refinishing. These were brand new manifolds with 0 miles on them. I've read where some recommend baking the manifolds before coating to make sure there is no moisture inside the metal that could get trapped by any coating. Here is what they looked like coming out of the oven after 1 hour of baking at 300 degrees verified via infrared heat gun.

Seems the baking was a good idea as none of that brown was there before going in.

I was going to use Cerakote but before I made my purchase I found out the VHT had a Very High Temperature Flame Proof paint that is Silica- Ceramic coating and rated at 1300 - 2000 degrees Fahrenheit.

Here is an example of manifold to cap of can which is supposed to represent the final look.

Here is what they looked like after applying.

I still have to bake or cure the paint but have to wait for it to fully dry before they go back into the oven.

 

[bikersmurf]

Best of luck... I've yet to find any paint that won't burn off mine... something about glowing manifolds burns off the paint.

 

[B y r o n]

Well I baked/cured the manifolds last night following the instructions on the can. FYI, it took less than one can to paint both manifolds. Last temperature was supposed to be 600 degrees but my oven only would get to 550 degrees so I guess if there is any thing left to cure it will be done with the manifolds on the engine. Here is a before and after photo for color/finish comparison.

Size and lighting are slightly different but as you can see it was a very good paint match to the original finish. Only time will tell how well it hold up but with a 2000 degree rating it should do pretty well.

 

[B y r o n]

Here they are mounted on the engine.

New grade 8 mounting hardware. From what I was able to find out bolt torque is 20 lb ft on the outer 8 (short) bolts and 30 lb ft on the 4 (longer) inner bolts.