300 Six Compression Ratio, Intakes, Heads, etc

[Rembrant]

Wow! That is EARLY! I was up at 5:30 to do my computing as the house is quiet then - as opposed to now w/7 year old twins rough-housing w/their father. Boy, am I going to miss that on Jan 3rd when they leave.

So what is the general consensus on the best carbed set-up for a 300/6?

I was just reading this afternoon (New Summit catalog showed up a couple days ago), and I see the different Offenhauser intakes for the 300/6. There is one for small 4bbl carbs (500cfm or less). Are these add-ons mostly for increasing power? Do they help or hurt MPG? Just curious...

And compression...are most running them at stock 80's compression ratio? If one were to boost the CR, would you be swapping in an EFI cylinder head? Or is that even a thing? I guess what I mean is, for those that have had these engines rebuilt over the years, do they usually just do a stock spec overhaul, or are they doing things to bump them up a bit...cam, increased compression, etc?

I've read a couple posts by people in the past that claim they're getting "good" MPG with 4bbl carbs, but I don't know what they consider to be good...

[Gary Lewis]

So what is the general consensus on the best carbed set-up for a 300/6?

I was just reading this afternoon (New Summit catalog showed up a couple days ago), and I see the different Offenhauser intakes for the 300/6. There is one for small 4bbl carbs (500cfm or less). Are these add-ons mostly for increasing power? Do they help or hurt MPG? Just curious...

And compression...are most running them at stock 80's compression ratio? If one were to boost the CR, would you be swapping in an EFI cylinder head? Or is that even a thing? I guess what I mean is, for those that have had these engines rebuilt over the years, do they usually just do a stock spec overhaul, or are they doing things to bump them up a bit...cam, increased compression, etc?

I've read a couple posts by people in the past that claim they're getting "good" MPG with 4bbl carbs, but I don't know what they consider to be good...

I've never owned a 300 six, and certainly haven't had one built, so can't say "this is the way to do it". But, I'll give you my theories anyway.

First, the main improvements you can make with regard to power as well as MPG are raising the compression ratio and achieving an even air/fuel ratio across all of the cylinders. Higher compression ratio makes the engine more efficient, and getting a uniform air/fuel mix lets you tune the carb to achieve best power and/or best economy.

But from what Frenchtown Flyer said the heads for the 300 six all had the same combustion chamber volume, so changing heads isn't going to help the compression ratio at all. Given that, the only way to raise the compression ratio on a 300 is to use different pistons when you rebuild it. However, if you are running a stock engine you have what you have.

That brings us to the air/fuel ratio each cylinder "sees". There is an air/fuel ratio that gives the best MPG, but one carb feeding multiple cylinders with dramatically different intake runner lengths and sharp corners can't possibly give each cylinder the same air/fuel ratio (AFR). This is because fuel tends to drop out of suspension more on longer the runs and around tight corners.

There are at least three ways of combating that: heat; multiple carbs with shorter runners; and rounded corners on the intake manifold. Heat in the manifold helps keep fuel in suspension, but it reduces the efficiency of the engine, so there's a balance. And, you can only make the intake so hot w/o causing other problems.

Multiple carbs can help if they are placed such that they reduce the difference in runner length, but you have to maintain a certain velocity of air across the venturi to get adequate vacuum with which to pull fuel into the air stream. So if you just add on more of the same size and type of carb the velocity drops and the ability to tune the mix goes away.

But, you could use multiple smaller 1bbl carbs. Or, you could go with what's called "progressive" 2bbl carbs that have a smaller venturi that it runs on most of the time and then a 2nd, larger venturi opens when the need arises. Some Webers are progressive.

However, you asked about running a 2bbl, like maybe a 2150, or a small 500 CFM 4bbl in place of the existing 1bbl. Personally, I'd go with the 4bbl. That's because 4bbl carbs are progressive and you'll be running on the small primaries until you need the secondaries. But a 2150 isn't progressive so you have the larger venturi on them always in play.

Well, I'd better quit. I'm sure I've confused you. But, perhaps someone else will chime in and clarify things?

 

[85lebaront2]

I've never owned a 300 six, and certainly haven't had one built, so can't say "this is the way to do it". But, I'll give you my theories anyway.

First, the main improvements you can make with regard to power as well as MPG are raising the compression ratio and achieving an even air/fuel ratio across all of the cylinders. Higher compression ratio makes the engine more efficient, and getting a uniform air/fuel mix lets you tune the carb to achieve best power and/or best economy.

But from what Frenchtown Flyer said the heads for the 300 six all had the same combustion chamber volume, so changing heads isn't going to help the compression ratio at all. Given that, the only way to raise the compression ratio on a 300 is to use different pistons when you rebuild it. However, if you are running a stock engine you have what you have.

That brings us to the air/fuel ratio each cylinder "sees". There is an air/fuel ratio that gives the best MPG, but one carb feeding multiple cylinders with dramatically different intake runner lengths and sharp corners can't possibly give each cylinder the same air/fuel ratio (AFR). This is because fuel tends to drop out of suspension more on longer the runs and around tight corners.

There are at least three ways of combating that: heat; multiple carbs with shorter runners; and rounded corners on the intake manifold. Heat in the manifold helps keep fuel in suspension, but it reduces the efficiency of the engine, so there's a balance. And, you can only make the intake so hot w/o causing other problems.

Multiple carbs can help if they are placed such that they reduce the difference in runner length, but you have to maintain a certain velocity of air across the venturi to get adequate vacuum with which to pull fuel into the air stream. So if you just add on more of the same size and type of carb the velocity drops and the ability to tune the mix goes away.

But, you could use multiple smaller 1bbl carbs. Or, you could go with what's called "progressive" 2bbl carbs that have a smaller venturi that it runs on most of the time and then a 2nd, larger venturi opens when the need arises. Some Webers are progressive.

However, you asked about running a 2bbl, like maybe a 2150, or a small 500 CFM 4bbl in place of the existing 1bbl. Personally, I'd go with the 4bbl. That's because 4bbl carbs are progressive and you'll be running on the small primaries until you need the secondaries. But a 2150 isn't progressive so you have the larger venturi on them always in play.

Well, I'd better quit. I'm sure I've confused you. But, perhaps someone else will chime in and clarify things?

Gary. I suggested dual progressive Holley/Webers like a Pinto or earlier Chrysler 2.2L used. The Pinto carbs have mechanical secondary throttles, the Chrysler ones are vacuum secondary design.

Pinto carb, pluses, has replaceable idle jets for tuning the idle transition, main jets, air jets and emulsion tubes are replaceable for tuning, engine size 2.3L (140 ci). Minuses, mechanical secondary throttle, water heated choke.

Chrysler carb, pluses, electric choke, vacuum secondary, main jets, air and emulsion tubes replaceable for tuning. Minuses, idle jets internal, non-replaceable prone to getting blocked, engine size 2.2L (134 ci).

Aftermarket Weber carbs, fully adjustable jetting, can be had in larger sizes for V6 applications (2.8L or 171 ci), many are hand choke but electric chokes are also available. These will frequently have a larger secondary barrel.

On the 3 one barrels, I would suggest trying to find a matched set of the Ford/Holley 1940 carbs, they have real accelerator pumps, piston type power enrichment systems but hot air or manual chokes only. They also have a dual pontoon float and a pretty much concentric float bowl design. Progressively used, center carb with auto choke, end carbs with manual chokes tied open. Synchronized, all three same style choke and jetted the same.

My personal choice for multiple carbs on an in-line 6, either 3 SU HD8s or 3 45 DCOE Webers.

[Gary Lewis]

Gary. I suggested dual progressive Holley/Webers like a Pinto or earlier Chrysler 2.2L used. The Pinto carbs have mechanical secondary throttles, the Chrysler ones are vacuum secondary design.

Pinto carb, pluses, has replaceable idle jets for tuning the idle transition, main jets, air jets and emulsion tubes are replaceable for tuning, engine size 2.3L (140 ci). Minuses, mechanical secondary throttle, water heated choke.

Chrysler carb, pluses, electric choke, vacuum secondary, main jets, air and emulsion tubes replaceable for tuning. Minuses, idle jets internal, non-replaceable prone to getting blocked, engine size 2.2L (134 ci).

Aftermarket Weber carbs, fully adjustable jetting, can be had in larger sizes for V6 applications (2.8L or 171 ci), many are hand choke but electric chokes are also available. These will frequently have a larger secondary barrel.

On the 3 one barrels, I would suggest trying to find a matched set of the Ford/Holley 1940 carbs, they have real accelerator pumps, piston type power enrichment systems but hot air or manual chokes only. They also have a dual pontoon float and a pretty much concentric float bowl design. Progressively used, center carb with auto choke, end carbs with manual chokes tied open. Synchronized, all three same style choke and jetted the same.

My personal choice for multiple carbs on an in-line 6, either 3 SU HD8s or 3 45 DCOE Webers.

Bill - You know far more then I do about carbs, and I was really just agreeing with you as well as supplying some background.

And, were time not against me I'd like to build a 300 w/3 Webers. Hmmmm, just gotta finish Dad's truck & Big Blue, both with EEC-V, then the Bee and the '50 Chevy. Well, maybe the Chevy will have a big GMC 6 w/3 Webers?

[85lebaront2]

Bill - You know far more then I do about carbs, and I was really just agreeing with you as well as supplying some background.

And, were time not against me I'd like to build a 300 w/3 Webers. Hmmmm, just gotta finish Dad's truck & Big Blue, both with EEC-V, then the Bee and the '50 Chevy. Well, maybe the Chevy will have a big GMC 6 w/3 Webers?

Why don't you go opposite what most hot rodders do, put a built 300 in it, the Chevy/GMC 6s are usually 7 port heads, E II EE II EE II E as opposed to the Ford big 6 (240/300) 12 port head E I E I E I E I E I E I (if I remembered that pattern correctly on the Ford). In addition the dual intake and exhaust ports on GM are siamesed ports.

[Gary Lewis]

Why don't you go opposite what most hot rodders do, put a built 300 in it, the Chevy/GMC 6s are usually 7 port heads, E II EE II EE II E as opposed to the Ford big 6 (240/300) 12 port head E I E I E I E I E I E I (if I remembered that pattern correctly on the Ford). In addition the dual intake and exhaust ports on GM are siamesed ports.

That would boggle some minds.

[Ford F834]

I've never owned a 300 six, and certainly haven't had one built, so can't say "this is the way to do it". But, I'll give you my theories anyway.

First, the main improvements you can make with regard to power as well as MPG are raising the compression ratio and achieving an even air/fuel ratio across all of the cylinders. Higher compression ratio makes the engine more efficient, and getting a uniform air/fuel mix lets you tune the carb to achieve best power and/or best economy.

But from what Frenchtown Flyer said the heads for the 300 six all had the same combustion chamber volume, so changing heads isn't going to help the compression ratio at all. Given that, the only way to raise the compression ratio on a 300 is to use different pistons when you rebuild it. However, if you are running a stock engine you have what you have.

That brings us to the air/fuel ratio each cylinder "sees". There is an air/fuel ratio that gives the best MPG, but one carb feeding multiple cylinders with dramatically different intake runner lengths and sharp corners can't possibly give each cylinder the same air/fuel ratio (AFR). This is because fuel tends to drop out of suspension more on longer the runs and around tight corners.

There are at least three ways of combating that: heat; multiple carbs with shorter runners; and rounded corners on the intake manifold. Heat in the manifold helps keep fuel in suspension, but it reduces the efficiency of the engine, so there's a balance. And, you can only make the intake so hot w/o causing other problems.

Multiple carbs can help if they are placed such that they reduce the difference in runner length, but you have to maintain a certain velocity of air across the venturi to get adequate vacuum with which to pull fuel into the air stream. So if you just add on more of the same size and type of carb the velocity drops and the ability to tune the mix goes away.

But, you could use multiple smaller 1bbl carbs. Or, you could go with what's called "progressive" 2bbl carbs that have a smaller venturi that it runs on most of the time and then a 2nd, larger venturi opens when the need arises. Some Webers are progressive.

However, you asked about running a 2bbl, like maybe a 2150, or a small 500 CFM 4bbl in place of the existing 1bbl. Personally, I'd go with the 4bbl. That's because 4bbl carbs are progressive and you'll be running on the small primaries until you need the secondaries. But a 2150 isn't progressive so you have the larger venturi on them always in play.

Well, I'd better quit. I'm sure I've confused you. But, perhaps someone else will chime in and clarify things?

Gary, the only things I think I can add to this might be that 240 CID heads actually do give you about a half a point increase in compression ratio, which is why people want them. It’s a good idea to have hard seats put in though, as my mechanic mentioned that older, leaded-gas era heads tended to suffer more from valve recession than later ones. As a side note he also said EFI heads are more prone to cracking. If you put a 240 head on a light duty 80-82 engine with 8.9 CR, you would theoretically finish at 9.4 if all parts were original. David says this is at least mid-grade gas territory especially if you want to run a lot of timing advance.

I have only run 1bbl carbs, but from my reading and hanging out in the I-6 FB groups I can say that I have never once heard of anyone gaining mpg by going to a 2bbl, 4bbl or EFI set up. I know from an engineering standpoint the 1bbl in the middle of a long log is atrocious... but at the speeds/revs of these truck engines they seem to do awful well considering the supposedly “horrific” design.

[Rembrant]

Gary, the only things I think I can add to this might be that 240 CID heads actually do give you about a half a point increase in compression ratio, which is why people want them. It’s a good idea to have hard seats put in though, as my mechanic mentioned that older, leaded-gas era heads tended to suffer more from valve recession than later ones. As a side note he also said EFI heads are more prone to cracking. If you put a 240 head on a light duty 80-82 engine with 8.9 CR, you would theoretically finish at 9.4 if all parts were original. David says this is at least mid-grade gas territory especially if you want to run a lot of timing advance.

I have only run 1bbl carbs, but from my reading and hanging out in the I-6 FB groups I can say that I have never once heard of anyone gaining mpg by going to a 2bbl, 4bbl or EFI set up. I know from an engineering standpoint the 1bbl in the middle of a long log is atrocious... but at the speeds/revs of these truck engines they seem to do awful well considering the supposedly “horrific” design.

Came across these Ford 300/6 Badger pistons in my searches this morning.

The ad is not new, but thought I'd post up for the 300 inline crowd.

Says high compression, but no idea what year/generation.

https://www.kijiji.ca/v-view-details.html?adId=1292958620&requestSource=b

Standard size pistons would likely be hard to use in a rebuild that presumably would have to be bored?

[Rembrant]

I have only run 1bbl carbs, but from my reading and hanging out in the I-6 FB groups I can say that I have never once heard of anyone gaining mpg by going to a 2bbl, 4bbl or EFI set up. I know from an engineering standpoint the 1bbl in the middle of a long log is atrocious... but at the speeds/revs of these truck engines they seem to do awful well considering the supposedly “horrific” design.

Good point Jonathan.

Here are some pictures of the 81's engine bay that I'm planning to go look at tomorrow. Looks like it's mostly all intact, minus some smog equipment. Seller says that it needs some carb work, which I am assuming means that the thing isn't running properly/well.

Anything specific to check for on these things? Not sure if these pics will post properly...

 

[Gary Lewis]

I have only run 1bbl carbs, but from my reading and hanging out in the I-6 FB groups I can say that I have never once heard of anyone gaining mpg by going to a 2bbl, 4bbl or EFI set up. I know from an engineering standpoint the 1bbl in the middle of a long log is atrocious... but at the speeds/revs of these truck engines they seem to do awful well considering the supposedly “horrific” design.

Good point Jonathan.

Here are some pictures of the 81's engine bay that I'm planning to go look at tomorrow. Looks like it's mostly all intact, minus some smog equipment. Seller says that it needs some carb work, which I am assuming means that the thing isn't running properly/well.

Anything specific to check for on these things? Not sure if these pics will post properly...

There's some funky wiring in there. Some to the battery, and something to the #1 spark plug wire. So I'd look the truck over to see what has been done to the wiring. Like trailer lights. Hacks back there can be a pain to fix after the dirt and wet have gotten into the wiring over the years.

Anyway, good luck! Maybe this is your Christmas present?

Oh, and there appears to have been a mod to the alternator belts. Perhaps a smog pump was taken off. But two belts to the alternator is unusual from what I've seen, and the back belt appears to sit down further in the waterpump pulley than the front belt. Not good! Not a reason to pass on the truck, but something that needs fixed - if I'm right.