Straight Six performance upgrades?

[Racer-X-]

Are there any "Sixers" hanging out on this forum?

I've got a Chevy 250 Straight Six engine/TurboHydramatic 350 drivetrain (transplanted into "not exactly a Chevy Truck").

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"Not exactly a Chevy Truck" powered by Chevrolet 250CID Straight Six (at the front of the line in both pix)

The codes say it's most likely from a 1978 model year car or truck. It's had a head swap for the one with the separate intake.

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Engine ID pad on our Chevy 250 Straight Six

 

[Racer-X-]

This thing has a few problems. It's had several "Chineseum" replacement "Monojet clones" put on it over the past few years, and the fuel pump had a cracked diaphragm and was leaking, as well as not flowing enough fuel. New fuel pump has been installed, and owners are on board with an ethanol free diet for this one in the future.

The #6 intake valve was intermittently sticking open in the latest issues, and belching flames out the carb when every 5 to 10 seconds. Removing the valve cover revealed that the nut had backed off the rocker arm on the #6 exhaust valve, allowing that rocker arm to pivot off the valve and pushrod, and it was sometimes interfering with the rocker on the #6 intake. The #6 intake rocker arm had a cross-threaded nut on it, and wasn't completely locked down either. I also suspect a damaged lobe on the #6 exhaust lobe of the cam. I haven't dug into it that far.

The complaint with this car has been, even when it was running better, before the current set of issues came up, it lacked power. It was incapable of maintaining speed up some of the steeper hills on our local 2 lane country roads.

The current plans are to get some larger intake valves installed (either 1.84" or 1.90", whichever are available quickly)in the head, and a Clifford Performance intake/carb/header package (with a single Weber 38/38 DGES carb).

We also have a "HIFLOW" lump kit from Tom at 12bolt.com to install in the head while the other machine shop work is done.

We're also awaiting a Competition Cams 260° "Hi Energy" camshaft which seems to be tailored for towing and heavy duty applications (212°/212° at 0.050" lift, .489 total lift, 110° LSA).

I'm basically thinking of this like I'm building a truck engine for hauling a significant trailer. The vehicle weighs 6,500 pounds +/- when fully loaded with passengers and a little bit of luggage.

I'd like any feedback on what's planned so far.

Also, we've run into an issue with the head, and I'll probably post on the "want to buy" section here. The head we have has 3 (yes 3!) crack repairs that extend into a valve throats on 3 different cylinders. This is not the head we want to use for this project. So I'm looking hard right now for a "never been cracked" cylinder head without the integrated intake manifold for this engine.

 

[Bextreme04]

Are there any "Sixers" hanging out on this forum?

I've got a Chevy 250 Straight Six engine/TurboHydramatic 350 drivetrain (transplanted into "not exactly a Chevy Truck").

You must be registered for see images attach

You must be registered for see images attach

"Not exactly a Chevy Truck" powered by Chevrolet 250CID Straight Six (at the front of the line in both pix)

The codes say it's most likely from a 1978 model year car or truck. It's had a head swap for the one with the separate intake.

You must be registered for see images attach

Engine ID pad on our Chevy 250 Straight Six

You would need the engine block casting date code on the block to know which application you actually have. CCK was always for a 250/TH350, but could have been from a taxi/police application in 1970, as well as several applications in 1974 and 1978.

 

[Bextreme04]

This thing has a few problems. It's had several "Chineseum" replacement "Monojet clones" put on it over the past few years, and the fuel pump had a cracked diaphragm and was leaking, as well as not flowing enough fuel. New fuel pump has been installed, and owners are on board with an ethanol free diet for this one in the future.

The #6 intake valve was intermittently sticking open in the latest issues, and belching flames out the carb when every 5 to 10 seconds. Removing the valve cover revealed that the nut had backed off the rocker arm on the #6 exhaust valve, allowing that rocker arm to pivot off the valve and pushrod, and it was sometimes interfering with the rocker on the #6 intake. The #6 intake rocker arm had a cross-threaded nut on it, and wasn't completely locked down either. I also suspect a damaged lobe on the #6 exhaust lobe of the cam. I haven't dug into it that far.

The complaint with this car has been, even when it was running better, before the current set of issues came up, it lacked power. It was incapable of maintaining speed up some of the steeper hills on our local 2 lane country roads.

The current plans are to get some larger intake valves installed (either 1.84" or 1.90", whichever are available quickly)in the head, and a Clifford Performance intake/carb/header package (with a single Weber 38/38 DGES carb).

We also have a "HIFLOW" lump kit from Tom at 12bolt.com to install in the head while the other machine shop work is done.

We're also awaiting a Competition Cams 260° "Hi Energy" camshaft which seems to be tailored for towing and heavy duty applications (212°/212° at 0.050" lift, .489 total lift, 110° LSA).

I'm basically thinking of this like I'm building a truck engine for hauling a significant trailer. The vehicle weighs 6,500 pounds +/- when fully loaded with passengers and a little bit of luggage.

I'd like any feedback on what's planned so far.

Also, we've run into an issue with the head, and I'll probably post on the "want to buy" section here. The head we have has 3 (yes 3!) crack repairs that extend into a valve throats on 3 different cylinders. This is not the head we want to use for this project. So I'm looking hard right now for a "never been cracked" cylinder head without the integrated intake manifold for this engine.

This is always an option too:
https://www.powernationtv.com/episo...oids-boosting-a-chevy-292-inline-straight-six

 

[Racer-X-]

You would need the engine block casting date code on the block to know which application you actually have. CCK was always for a 250/TH350, but could have been from a taxi/police application in 1970, as well as several applications in 1974 and 1978.

Where do I find the date code?

I thought blue paint (which looks factory original) rules out 1970. Although a taxi/police engine would kind of cool, if that's what it is.

And it has HEI, which is more likely 1978 (standard equipment that year) than 1974, although someone could've upgraded it. Somehow I doubt that happened.

I have to confess, I'm more of a LS swap guy lately, but this "antique" 1965 has developed into a very interesting project. In this vehicle, with the narrow hoods and the narrow frame, and with air conditioning absolutely required, an LS swap really won't fit.

And the turbo setup looks mildly interesting, but I don't think we need quite that much. The owner would like to see better performance, so a 150-180HP (ish) "towing" engine will get the job done.

 

[Vbb199]

I dunno alot, but I've heard of people taking 350 heads, cutting them down, welding them together, and making 1 straight 6 head

Seems like if you're gonna go thru that much effort, why not go up 100 more cubes for the aforementioned 350.


There's a guy somewhere out there on the internet that sells performance heads for the straight 6.

HEAD Lump Ported Intake 70.5 cc Stage 1 250 / 292 Chevy Inline 6 Cylinder

Mrhotrod6 Motorsports Stage 1 70.5 cc Intake ported Lump Porthead. T-6 Racing Often Imitated Never Duplicated! Fits all the generation three 230 250 292 Chevrolet Inline Six-cylinder engines. Only after passing our strict 67-point inspection process by our GM Master Certified, ASE & I-Car...

mrhotrod6.myshopify.com

Maybe thats him ^ I can't remember


@WamboJambo knows the website

 

[Racer-X-]

Seems like if you're gonna go thru that much effort, why not go up 100 more cubes for the aforementioned 350.

If a 350 would fit, I'd go with an LS engine.

I mentioned above, air conditioning is required for this vehicle, and there's no way to fit a V8 with AC between the frame rails at the bottom and within the narrow front section of the hood at the top. We'd have to cut holes in the hood for clearance, and that kind of detracts from the Rolls Royce Limousine experience. The people in the back seats are paying for this, and they really just want to enjoy the ride. They don't want to see what's under the hood, or even be aware of it, as long as the thing goes where they want to go.

And that head in your link is "Sold out." If it wasn't, I'd buy it for $700 in a heartbeat. The machine shop bill alone on this project will probably come to twice that. I'm aiming for that setup with the head we'll use in this one. I'm using a different, but very similar "bolt in lump kit," and that page doesn't say what valves were used, but we're going up to 1.84" minimum on the intake valves (stock is 1.72"). We're targeting 72cc for the chamber volume, and that one promises 72.5cc.

 

[Vbb199]

If a 350 would fit, I'd go with an LS engine.

I mentioned above, air conditioning is required for this vehicle, and there's no way to fit a V8 with AC between the frame rails at the bottom and within the narrow front section of the hood at the top. We'd have to cut holes in the hood for clearance, and that kind of detracts from the Rolls Royce Limousine experience. The people in the back seats are paying for this, and they really just want to enjoy the ride. They don't want to see what's under the hood, or even be aware of it, as long as the thing goes where they want to go.

And that head in your link is "Sold out." If it wasn't, I'd buy it for $700 in a heartbeat. The machine shop bill alone on this project will probably come to twice that. I'm aiming for that setup with the head we'll use in this one. I'm using a different, but very similar "bolt in lump kit," and that page doesn't say what valves were used, but we're going up to 1.84" minimum on the intake valves (stock is 1.72"). We're targeting 72cc for the chamber volume, and that one promises 72.5cc.

Someone here will post up the link. I can't remember who it is, but there's a guy out there on the web who builds performance heads for these motor.

Maybe that was it, but I cannot for sure recall.

 

[richard A lindner]

I have an83 short fleetside ,89000 org miles . 250 3 speed with overdrive. I was going to put more power to I decided to leave org. Has every thing under the hood from factoty

 

[Racer-X-]

You would need the engine block casting date code on the block to know which application you actually have. CCK was always for a 250/TH350, but could have been from a taxi/police application in 1970, as well as several applications in 1974 and 1978.

Coming back to this. Here's a pic of the back end of the block on the (British) driver's side, behind the fuel pump and behind the motor mount. just behind the dipstick tube:

You must be registered for see images attach

Is that the casting number you were referring to?

And doesn't the F mean June, the first 8 means 8th day of the month, and the last 8 means the year ends in 8?

The only year ending in 8 that had a CCK code would be 1978.


Also, I've got a head casting on the way right now that was sold as "no cracks or repaired cracks." We'll see what we get when it gets here.

 

[Bextreme04]

Coming back to this. Here's a pic of the back end of the block on the (British) driver's side, behind the fuel pump and behind the motor mount. just behind the dipstick tube:

You must be registered for see images attach

Is that the casting number you were referring to?

And doesn't the F mean June, the first 8 means 8th day of the month, and the last 8 means the year ends in 8?

The only year ending in 8 that had a CCK code would be 1978.


Also, I've got a head casting on the way right now that was sold as "no cracks or repaired cracks." We'll see what we get when it gets here.

Yep. So that is the month/day/year of the casting. So F=June, 8=8th day of June, and 8 is the last digit of the year. Since all of your suffix codes were in the 70's, this is 1978. So your block was cast June 8, 1978.