4.1L 250 cid L6 w/ integrated head -- Need Help w/ Rebuild or Upgrade

[Biscuit Blanco]

BLUF (Bottom Line Up Front): I need help to improve performance of my 4.1L 250 cid inline 6. Specifically, where to find parts/alternate parts and any suggestions for improved performance.

BACKGROUND: I inherited my grandfather's 1975 C10 Longbed with a 4.1L 250 cid L6 motor. He bought it off the showroom floor in '75 and I inherited it in '08. After many years of running poorly, I finally managed to find someone who could help me get her going again. Which we did. She runs smoothly, but she still has no balls and she smokes a ton at operating temp. Now, I am not a mechanic in any form or fashion. My new brother-in-law, however, is. He has committed to helping me completely tear down and rebuild the engine and saginaw 3-speed transmission when he travels to see me in late summer. After some research, I have discovered that 1975 was the first year Chevrolet began using an integrated cylinder head/intake manifold on their L6 engines. These manifolds are notorious for cracking even without overheating. Additionally, my carburetor is only a 1bbl. Overall, I want to increase the performance of the current engine and keep the 3-speed column-shift transmission for nostalgic reasons.

DISCUSSION: 1) In addition to rebuilding the engine, do I bother with the integrated head and find/fashion a bracket to move from a 1bbl to a 2bbl carburetor?
2) Do I abandon the current integrated head and get a remanufactured integrated head from 1979-1983 which accommodated a 2bbl carb? I did find a remanufactured single-barrel (c 1975) and 2-barrel (c 1979) integrated heads from alliedmotorparts.com, but I don't know if the later-model head will fit.
3) Do I abandon the entire integrated head concept and replace the original head monstrosity with a non-integrated head and intake from, say, the 1974 model of L6 engine? If so, where do you recommend I find one? I've "combed the desert" and I "ain't found sh*t." Also, what intake manifold would you recommend? Lastly, if I change the head/intake, do I also have to change the exhaust manifold?

ASSUMPTIONS: Money is an object. I have some cheddar but my '75 is my heirloom and toy. The wife isn't going to let me go nuts buying parts (I'd appreciate suggestions which will help me keep the parts under $1K-1.5K. (Labor is only going to cost me pizza and beer.)

OVERALL: I want to get the biggest bang for my buck and improve the performance of the engine while keeping as much of the original parts as possible. I'm a novice (at best) and, unfortunately, my brother-in-law doesn't have the time to help me do the research right now. I want to have a firm plan in mind and all the parts I need to do the rebuild and performance mods by the time he gets here. I appreciate any and all help, research, websites, suggestions, etc that you can provide!

Cheers,

-BISCUIT

 

[Vbb199]

@jjester6000 or @WamboJambo might have some input.

 

[idahovette]

@DoubleDingo , would know something about this

 

[CorvairGeek]

The exhaust manifold is absolutely different between integral and non-integral heads.

 

[DoubleDingo]

I don't anything about the integrated head, except they are not well liked, and non-integrated is preferred to swap in. You can find exhaust manifolds and intakes on craigslist or ebay. Check 12bolt.com too.

Lump port kit. 1.84/1.60 valves. Offenhauser or Clifford intake. Headers. Cam. These will cost extra, but could be done further down the road.

Since you'll be rebuilding it, at least upgrade the cam to an RV style cam.

Offenshauser and Clifford intakes both allow for bigger carbs to be installed, but they need to calibrated to run on a 6.

No matter what you do, it is going to cost a few hundred dollars at a time. I'd plan for the cam during the rebuild, and source the intake and exhaust too. If you can afford the lumps and valves and reworking the head, go for it. Then upgrade other stuff as money allows. These engines have a nice flat torque curve with the right upgrades.

 

[Ricko1966]

So I guess a v8 swap is out. My way would be find a 292 inline 6. Head problem solved more displacement and still looks and sounds relatively stock.If you can find good used its probably cheaper than rebuilding the 250. Leave it damn near stock and if you need more balls later you can blow through turbo it. 8psi you won't need intercooler or internal mods.

And since the truck is kind of a legacy thing, and also probably has a good chance of being 100 percent original the original engine can easily be put back in and the truck returned to 100 percent original status in the future.Survivor vehicles and very original vehicles always have demand and usually bring good money.

 

[WamboJambo]

I've got non-integrated intake and exhaust manifolds and rochester monojet carb from my truck you're more than welcome to have. I swapped them out for an offenhauser quad barrel intake manifold, a set of long-tube headers, and a four-barrel carb. The monojet is probably the same you have, so not sure that's helpful, but if you find a non-integrated head you could use the intake and exhaust manifold with it just to address that issue.

As for the head, I remember seeing a few in nearby junkyards; several of the chain ones (LKQ, pull-a-part) will have inventory searches you can do for just the pre-1975 head so you can swap it out.

I've read that the exhaust manifold is the actual issue; the stock one is too restrictive and can't evacuate gases fast enough, so even if you were to go to a bigger 2bbl carb you may not be able to realize any performance gains from it. Maybe it would be worth seeing if you can replace your exhaust manifold with the cast iron 12bolt ones that Tom Lowe sells, then either plumbing intake heat via one of the intake plates (which Tom also sells, works great in my install) or welding on some sort of bungs to the manifold. I assume (might be wrong on this) that only the intake is integrated into the head, in which case you could do just an exhaust upgrade with your current setup, but I might be wrong; I've never actually seen an integrated head in person.

 

[jjester6000]

BLUF (Bottom Line Up Front): I need help to improve performance of my 4.1L 250 cid inline 6. Specifically, where to find parts/alternate parts and any suggestions for improved performance.

BACKGROUND: I inherited my grandfather's 1975 C10 Longbed with a 4.1L 250 cid L6 motor. He bought it off the showroom floor in '75 and I inherited it in '08. After many years of running poorly, I finally managed to find someone who could help me get her going again. Which we did. She runs smoothly, but she still has no balls and she smokes a ton at operating temp. Now, I am not a mechanic in any form or fashion. My new brother-in-law, however, is. He has committed to helping me completely tear down and rebuild the engine and saginaw 3-speed transmission when he travels to see me in late summer. After some research, I have discovered that 1975 was the first year Chevrolet began using an integrated cylinder head/intake manifold on their L6 engines. These manifolds are notorious for cracking even without overheating. Additionally, my carburetor is only a 1bbl. Overall, I want to increase the performance of the current engine and keep the 3-speed column-shift transmission for nostalgic reasons.

DISCUSSION: 1) In addition to rebuilding the engine, do I bother with the integrated head and find/fashion a bracket to move from a 1bbl to a 2bbl carburetor?
2) Do I abandon the current integrated head and get a remanufactured integrated head from 1979-1983 which accommodated a 2bbl carb? I did find a remanufactured single-barrel (c 1975) and 2-barrel (c 1979) integrated heads from alliedmotorparts.com, but I don't know if the later-model head will fit.
3) Do I abandon the entire integrated head concept and replace the original head monstrosity with a non-integrated head and intake from, say, the 1974 model of L6 engine? If so, where do you recommend I find one? I've "combed the desert" and I "ain't found sh*t." Also, what intake manifold would you recommend? Lastly, if I change the head/intake, do I also have to change the exhaust manifold?

ASSUMPTIONS: Money is an object. I have some cheddar but my '75 is my heirloom and toy. The wife isn't going to let me go nuts buying parts (I'd appreciate suggestions which will help me keep the parts under $1K-1.5K. (Labor is only going to cost me pizza and beer.)

OVERALL: I want to get the biggest bang for my buck and improve the performance of the engine while keeping as much of the original parts as possible. I'm a novice (at best) and, unfortunately, my brother-in-law doesn't have the time to help me do the research right now. I want to have a firm plan in mind and all the parts I need to do the rebuild and performance mods by the time he gets here. I appreciate any and all help, research, websites, suggestions, etc that you can provide!

Cheers,

-BISCUIT

If you need a non integrated head/manifold, I have one laying around.

You can have them for the cost of shipping.

It's a 1 barrel manifold, but with no EGR, so it isn't too bad.

When it comes to a head, there are two to choose from, both identical, but both could use a valve job.

 

[Grit dog]

I think your grandfather would have liked for it to have a small block!
Lol
Seriously, that’s your best bang for the buck. And dime a dozen.
If you want it to sound like a 6 banger keep the single exhaust and put a huge muffler on it.

 

[Michael Benardo]

BLUF (Bottom Line Up Front): I need help to improve performance of my 4.1L 250 cid inline 6. Specifically, where to find parts/alternate parts and any suggestions for improved performance.

BACKGROUND: I inherited my grandfather's 1975 C10 Longbed with a 4.1L 250 cid L6 motor. He bought it off the showroom floor in '75 and I inherited it in '08. After many years of running poorly, I finally managed to find someone who could help me get her going again. Which we did. She runs smoothly, but she still has no balls and she smokes a ton at operating temp. Now, I am not a mechanic in any form or fashion. My new brother-in-law, however, is. He has committed to helping me completely tear down and rebuild the engine and saginaw 3-speed transmission when he travels to see me in late summer. After some research, I have discovered that 1975 was the first year Chevrolet began using an integrated cylinder head/intake manifold on their L6 engines. These manifolds are notorious for cracking even without overheating. Additionally, my carburetor is only a 1bbl. Overall, I want to increase the performance of the current engine and keep the 3-speed column-shift transmission for nostalgic reasons.Get rid that Integrated head and replace it with a conventional head. You will need an intake manifold and an exhaust manifold

DISCUSSION: 1) In addition to rebuilding the engine, do I bother with the integrated head and find/fashion a bracket to move from a 1bbl to a 2bbl carburetor?
2) Do I abandon the current integrated head and get a remanufactured integrated head from 1979-1983 which accommodated a 2bbl carb? I did find a remanufactured single-barrel (c 1975) and 2-barrel (c 1979) integrated heads from alliedmotorparts.com, but I don't know if the later-model head will fit.
3) Do I abandon the entire integrated head concept and replace the original head monstrosity with a non-integrated head and intake from, say, the 1974 model of L6 engine? If so, where do you recommend I find one? I've "combed the desert" and I "ain't found sh*t." Also, what intake manifold would you recommend? Lastly, if I change the head/intake, do I also have to change the exhaust manifold?

ASSUMPTIONS: Money is an object. I have some cheddar but my '75 is my heirloom and toy. The wife isn't going to let me go nuts buying parts (I'd appreciate suggestions which will help me keep the parts under $1K-1.5K. (Labor is only going to cost me pizza and beer.)

OVERALL: I want to get the biggest bang for my buck and improve the performance of the engine while keeping as much of the original parts as possible. I'm a novice (at best) and, unfortunately, my brother-in-law doesn't have the time to help me do the research right now. I want to have a firm plan in mind and all the parts I need to do the rebuild and performance mods by the time he gets here. I appreciate any and all help, research, websites, suggestions, etc that you can provide!

Cheers,

-BISCUIT

 

[Michael Benardo]

BLUF (Bottom Line Up Front): I need help to improve performance of my 4.1L 250 cid inline 6. Specifically, where to find parts/alternate parts and any suggestions for improved performance.

BACKGROUND: I inherited my grandfather's 1975 C10 Longbed with a 4.1L 250 cid L6 motor. He bought it off the showroom floor in '75 and I inherited it in '08. After many years of running poorly, I finally managed to find someone who could help me get her going again. Which we did. She runs smoothly, but she still has no balls and she smokes a ton at operating temp. Now, I am not a mechanic in any form or fashion. My new brother-in-law, however, is. He has committed to helping me completely tear down and rebuild the engine and saginaw 3-speed transmission when he travels to see me in late summer. After some research, I have discovered that 1975 was the first year Chevrolet began using an integrated cylinder head/intake manifold on their L6 engines. These manifolds are notorious for cracking even without overheating. Additionally, my carburetor is only a 1bbl. Overall, I want to increase the performance of the current engine and keep the 3-speed column-shift transmission for nostalgic reasons.Get rid of that integrated head and replace it with a standard head. You will need an intake manifold and an exhaust manifold. Unfortunately, the only way you can get a 2 barrel manifold is to buy one for Aussie Speed in Australia for about 450.00. The other alternative is an Offenhauser twin 1 barrel intake, almost as expensive, but you will have to replace the steel freeze plugs in that manifold with aluminum pipe-thread plugs that will have to be welded in. You biggest headache will be finding brackets for the Air Pump, and if you have it, the Power Steering pump. You might have to change the harmonic balancer to 74 and older style, as the groves won't line up if you have to use 74 and older style brackets. You will have a straight-forward, trouble-free engine. About the smoke, is it blue smoke, (burning oil), or black smoke, (running too rich)? Do not put a 2 barrel on a 2 to 1 adapter, as it will probably lean out a full throttle that way. Another problem is the gearing- 70s and 80s vehicles had ridiculously tall gearing, which hurts acceleration. Change your rear end to something like 3:54 or 3:70. You will have much better acceleration. Any head will fit any block.

DISCUSSION: 1) In addition to rebuilding the engine, do I bother with the integrated head and find/fashion a bracket to move from a 1bbl to a 2bbl carburetor?
2) Do I abandon the current integrated head and get a remanufactured integrated head from 1979-1983 which accommodated a 2bbl carb? I did find a remanufactured single-barrel (c 1975) and 2-barrel (c 1979) integrated heads from alliedmotorparts.com, but I don't know if the later-model head will fit.
3) Do I abandon the entire integrated head concept and replace the original head monstrosity with a non-integrated head and intake from, say, the 1974 model of L6 engine? If so, where do you recommend I find one? I've "combed the desert" and I "ain't found sh*t." Also, what intake manifold would you recommend? Lastly, if I change the head/intake, do I also have to change the exhaust manifold?

ASSUMPTIONS: Money is an object. I have some cheddar but my '75 is my heirloom and toy. The wife isn't going to let me go nuts buying parts (I'd appreciate suggestions which will help me keep the parts under $1K-1.5K. (Labor is only going to cost me pizza and beer.)

OVERALL: I want to get the biggest bang for my buck and improve the performance of the engine while keeping as much of the original parts as possible. I'm a novice (at best) and, unfortunately, my brother-in-law doesn't have the time to help me do the research right now. I want to have a firm plan in mind and all the parts I need to do the rebuild and performance mods by the time he gets here. I appreciate any and all help, research, websites, suggestions, etc that you can provide!

Cheers,

-BISCUIT

 

[justhorns]

Same problem here. Except mine currently runs great with only 80,000 on the engine (except valve ticking). I even have the cat! Anyone still have a 250 6 cylinder head (non integrated) and intake / exhaust manifold leads? Or, perhaps a 292?