All Small Six Which cylinder head?

[Otto]

My original pathway needed to change after closely checking the carb base. I removed one of the brass plugs and it uncovered drilled passageways from the slots to the idle mixture screw. The original direction would have intercepted this passage and ruined the base. There was another route on the other side of the slot passage where I was drilling through solid material at a different elevation and would miss the passage.




I cleared an area with a small burr and then used a spot facing bit to create a flat where I could measure carefully and mark where the hole was needed. This was the most stressful hole I think I’ve ever drilled.



The hole came through the base just where I was hoping it would- just above the throttle blade. It felt a bit like operating a tunnel boring machine!



Placed a vacuum hose nipple into the outside of the hole with some epoxy; when that cures, I’ll reassemble and try it out. Fingers crossed!



m

 

[Frank]

My original pathway needed to change after closely checking the carb base. I removed one of the brass plugs and it uncovered drilled passageways from the slots to the idle mixture screw. The original direction would have intercepted this passage and ruined the base. There was another route on the other side of the slot passage where I was drilling through solid material at a different elevation and would miss the passage.
View attachment 24457

View attachment 24458

I cleared an area with a small burr and then used a spot facing bit to create a flat where I could measure carefully and mark where the hole was needed. This was the most stressful hole I think I’ve ever drilled.

View attachment 24459

The hole came through the base just where I was hoping it would- just above the throttle blade. It felt a bit like operating a tunnel boring machine!

View attachment 24460

Placed a vacuum hose nipple into the outside of the hole with some epoxy; when that cures, I’ll reassemble and try it out. Fingers crossed!

View attachment 24461

m

That's impressive work. I feel bad, had a "subconscious unrest" about the original route and didn't say anything. What bugged me was, the factory ports are always on the side you drilled, not the inside. Glad the carb wasn't ruined, we almost led you to it.

Hole placement and size looks good! This should work well. Nice job!

 

[Otto]

That's impressive work. I feel bad, had a "subconscious unrest" about the original route and didn't say anything. What bugged me was, the factory ports are always on the side you drilled, not the inside. Glad the carb wasn't ruined, we almost led you to it.

Hole placement and size looks good! This should work well. Nice job!

Frank, you shouldn't feel bad about anything; you've given me stellar advice all throughout this problem solving exercise and been extremely helpful. Thank you and everyone else who has contributed, it's much appreciated!

I'm happy to report that the van's engine runs much better- I put the carb on and gave it a try tonight. I connected the new ported port to the vacuum gauge and when the engine was idling, no vacuum. The slightest little blip of throttle showed vacuum on the gauge. It even has a decent idle now (not perfect, but something I can work on or live with).

Plus I learned a few things I didn't fully know before, so hopefully those lessons will stay with me. My only automotive training is in body & paint, so I can make things pretty and can make things run but struggle with getting them to run well.

 

[Otto]

Now that the carburetor is working normally, I’ll try jetting it. I was told that 2G jets were different and won’t interchange- they were right!


I found some sources to reach out to for alternatives to buying expensive boat jets. I’m fairly confident that Mercury Marine isn’t making their own jets and is probably buying from another carburetor manufacturer. If I can’t find jets that will work, drill bits are cheaper than boat jets.



The Mercarb on my van has 145 jets. From the chart, it states these are for high elevation use and the 3.0L is usually set up with 155s for general use so I’ll start there.
n

 

[Otto]

The drill bits arrived and I labeled the bags they came in with their sizes and started with the 1.55mm bit. I made a jet holder from scrap aluminum and tapped it for the jet- at least the hole will be drilled plumb. It appears we’ll have a dry spell here for a time, so test drives look possible.



I also discovered the Mercarb doesn’t have a fast-idle cam for the choke. There are no steps or ramps to the little movable piece at all. I swapped this for the fast idle cam from one of the other 2Gs. Not sure why this is, but I’ll try something here.

 

[Frank]

Keep in mind when calculating jet changes- square the jet sizes and divide the two numbers to get the % of area/fuel change.

Example, going from a .050" jet to a .055" jet. 50x50= 2500. 55x55= 3025. 3025 over 2500= 1.21. 50 jet to a 55 jet, the change will increase fuel thru the jet by 21%.

Like all area of a circle changes, the difference is more than "meets the eye".

 

[DON]

I found that when drilling these small holes, if I put the bit in the chuck that comes with some sets. Then put the chuck in a dremmel tool, the higher speed works better, less pressure needed to cut, less apt to break when it first starts to break thru the drilled material. It’s hard to tell how much pressure you are putting on it in a drill press.

 

[Otto]

We’re having a rare spell of dry weather here so I took the van for a lengthy test drive. The carb’s main jets are at an equivalent of the 155 jet; that’s two steps up where it was according to the chart. Data from today’s drive:

• Idle= 12.5 - 13.0 AFR
• Cruise= 14.5 - 15.0
• WOT= 11.5 - 12.0

Overall the engine ran very well- I was very pleased. Very smooth throughout the RPM range without any flat spots or hesitations at all. It would lug down and recover easily; it pulls quite well for what it is.

I’m going to leave the carb alone for now. Later on, I would like to open up the carb hole in the intake and my adapter. There may be some jetting changes to do after that, or not.

 

[Otto]

Getting back to where this topic started, the 2V conversion.

It’s more like a 1.5V with just opening up the intake manifold carb hole a bit. The full 2V could still happen if I feel there’s some more power potential on tap. But for now, I’ll try this and see how it goes. Really don’t want to do any welding on the head and introduce localized heat and risk a crack.


I was surprised with how much cast iron was removed, yet the casting is still pretty thick.
c

 

[Frank]

Getting back to where this topic started, the 2V conversion.

It’s more like a 1.5V with just opening up the intake manifold carb hole a bit. The full 2V could still happen if I feel there’s some more power potential on tap. But for now, I’ll try this and see how it goes. Really don’t want to do any welding on the head and introduce localized heat and risk a crack.
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I was surprised with how much cast iron was removed, yet the casting is still pretty thick.
c

As pointed out in post #66 above- opening up a hole increases the area more than the mind's logic calculates by sight. What you've done there looks great, and is a HUGE increase of airflow, probably close to double what it was before. An opening of 2.12" flows twice as much as 1.5" . 1.83" flows 50% more than 1.5". Nice work! I've been putting off doing the same to a 300 log intake. What tools did you use?

 

[Otto]

Yes, the circle math is impressive and deceiving. Upsizing a pipe from 6" to 8" is not a 25% increase but closer to 80%.

As for tools, I just used a die grinder with a carbide burr- and ear plugs.

 

[funkaholik]

As for tools, I just used a die grinder with a carbide burr- and ear plugs.

That new opening is impressively well shaped for just using a carbide burr! It looks like it was CNC'ed. You must be a patient man.

 

[Otto]

Thanks Funkaholik, it did take a bit of work but the burr is fairly new and sharp, so not so bad.

While I was in the engine compartment, I noticed significant a restriction in the exhaust. The van has a 2” pipe system, but there is this portion of the manifold connection where it necks down to 1 ½” for the donut. I’m going to re-do this part so there will be an unrestricted 2” pipe that connects to the manifold. With the bigger intake hole and full-flowing exhaust, I’m hoping for a little more performance improvement here.

 

[TrickSix]

You'll probably craft something way cooler than the factory parts anyway. But in case you don't know, the C8 exhaust manifold you should have gotten with your C8 block has a 2" outlet for a 2" pipe. Earlier cars have an exhaust manifold with a 1-3/4" outlet for a 1-3/4" pipe, maybe even 1-1/2" for the earliest ones. Might your downpipe be a left-over remnant of an old system re-used because it fits in the engine bay? That doesn't look like 2" pipe. My 2" system has a healthy flare on the pipe there as well as a good sized bevel around the exhaust manifold outlet for the donut to sit in. The donut probably has an id a little smaller than 2", but not by much. Not as small as in your pic.

Something like this -
https://www.oreillyauto.com/detail/...e-car-1969-ford-mustang?q=exhaust+donut&pos=2

 

[Otto]

You hit the nail on the head TrickSix, this was a example of “I don’t know what I don’t know”.

I have three exhaust manifolds that will fit a small six- a C3, C5 and a D8. The C3 is the one that was on the van’s 170 engine and is tiny with a gasket to the headpipe. The C5 and D8 manifolds are very similar in size, but the D8 has fittings for emissions stuff. I’m using the C5.
I did booger on a short piece of headpipe, likely from the spare engine just to get this project moving forward and I forgot how small this pipe was. Silver lining I guess finding this again.


A section of 2” pipe slips inside the manifold and seats up to a lip or ledge inside and a 2” donut fits the pipe snugly. I modified the existing two-bolt flange by welding a 2” three-hole flange onto it. When tightening the nuts, this seems to hold everything together like a ferrel on a compression fitting. I’ll add some two stroke exhaust springs as cheap insurance. I tend to solve problems with fabrication.

 

[TrickSix]

Another detail you may not be aware of is the downpipe strain relief. There's a little bracket that bolts to the block that lets a simple u-bolt style pipe clamp hold the pipe fast to the side of the block. Keeps exhaust system movement from putting strain on the flange and gasket.

Here’s a pic. Frame reference that’s the back end of the starter on the left.

 

[awasson]

Another detail you may not be aware of is the downpipe strain relief. There's a little bracket that bolts to the block that lets a simple u-bolt style pipe clamp hold the pipe fast to the side of the block. Keeps exhaust system movement from putting strain on the flange and gasket.

Here’s a pic. Frame reference that’s the back end of the starter on the left.

View attachment 24699

I’ll just interrupt and thank you for posting that. I wondered what that was. I’ve used it to hold the starter wire away from my headers on my mustang.

 

[Frank]

I’ll just interrupt and thank you for posting that. I wondered what that was. I’ve used it to hold the starter wire away from my headers on my mustang.

They're very beneficial! I discovered them factory on an AMC flathead 6 and wondered why all vehicles don't have it. That or use a flex pipe. Most systems are in reality depending on the manifold bolts in the head to handle the weight, movement and varying vibrations. I fabricated one at the bellhousing on a HD manifold (donut style) / custom exhaust on a F100/240. Adds life to donut for sure.
Exhaust leak:

You hit the nail on the head TrickSix, this was a example of “I don’t know what I don’t know”.

I have three exhaust manifolds that will fit a small six- a C3, C5 and a D8. The C3 is the one that was on the van’s 170 engine and is tiny with a gasket to the headpipe. The C5 and D8 manifolds are very similar in size, but the D8 has fittings for emissions stuff. I’m using the C5.
I did booger on a short piece of headpipe, likely from the spare engine just to get this project moving forward and I forgot how small this pipe was. Silver lining I guess finding this again.
View attachment 24697
View attachment 24698
A section of 2” pipe slips inside the manifold and seats up to a lip or ledge inside and a 2” donut fits the pipe snugly. I modified the existing two-bolt flange by welding a 2” three-hole flange onto it. When tightening the nuts, this seems to hold everything together like a ferrel on a compression fitting. I’ll add some two stroke exhaust springs as cheap insurance. I tend to solve problems with fabrication.

I did the exact same thing on the truck mentioned above, LOL. Found an HD ex manifold, but no flange. A generic from Summit and welded the 2 1/2" pipe to the flange, compression sealed with the donut. The pipe also extends into the manifold

 

[Otto]

Another detail you may not be aware of is the downpipe strain relief. There's a little bracket that bolts to the block that lets a simple u-bolt style pipe clamp hold the pipe fast to the side of the block. Keeps exhaust system movement from putting strain on the flange and gasket.

Here’s a pic. Frame reference that’s the back end of the starter on the left.

View attachment 24699

Nope, wasn't aware of that either; thanks for posting.
My van didn't have anything like that on it and I'm curious if all 6 cyl applications had that or if it was more likely found on passenger cars. I had an early Mustang 30 years ago, I don't recall that having one either. It does make sense though, the engine will shake a bit.
I'll look for a threaded hole in the block.

 

[Otto]

I decided to hit the "easy" button and follow the lead of what was there originally.
The exhaust is now a full 2" from end to end after cutting off the old connector and welding on a short piece of pipe. While I was doing stuff, I added a temperature gauge with numbers on it. Should be able to quantify temperature better than the gauge in the dash.

I made a little offset bracket like TrickSix showed and attached a muffler clamp to it. Made the exhaust very sturdy. Should be able to start it up tomorrow.