[250 w/ AL head] Theoretical limit of camshaft lift and its benefits

62Ranchero200

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Greetings Ford Six Fans,

'74 250, CI/VI aluminum head, milled down to 47 cc chambers and with stage 1 porting, in the process of having new valve guides installed, without the steel spring locators that originally came pressed onto the guides, to switch to dual valve springs. Still running the valves that came with the aluminum head (manufactured in 2013/2014). Although at present installing a 280/280/110 hydraulic cam (.512 lift @ 1.6:1), according to my machinist, after all the work on the head is done, I should be able to run at least .550 lift (at the valve with 1.6:1), maybe even .575. Schneider has a couple of solid lifter cams in this range.

As I understand it, to run any more lift than that, I would have to install longer valves (for retainer to seal clearance and more travel before coil bind) ... which would probably also require different springs and perhaps other valve train mods as well, since the longer valves would alter valve train geometry.

Questions:

What ultimately limits possible valve lift? Piston to valve clearance (my pistons have 15 cc dishes) ? Valvetrain components being too tall and hitting the underside of the top of the valve cover? Is there a limit on lift with solid lifters in a small six? I know it's not possible to install roller lifters in a small six without extensive custom machine work. I don't intend to go that far in the foreseeable future.

With the aluminum head and its large ports and valves, would more lift always be beneficial to mid-range torque and high-end HP, or can you reach a point of diminishing returns?

If relevant, my machinist says that he would recommend a rev limit of 6,500 RPM on this motor, unless I'm willing to tear it down to replace the "early" forged 300 rods with stronger custom rods.

Thanks
Bob
 

xctasy

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Nothing but coil bind, valve stem length and component failure limits lift. Lash caps allow more lift if the right retainers are used, and already new retaining systems exist if you want to spend.

Back in the early 80's, Big Sixes and 292 Cebbies were hauling 900 thou gross valve lift for 8500 to 9000 rpm.

Thankfully, the shaft rocker is 98% FE Ford, just lacking pedastool height and perhaps end support on really big valve lifts and duration that demands huge full lift spring "poundage's".

There are times it becomes ineffectual, like when curtain area and throat percentages make a point of diminishing returns.

The FE used 1.73 rocker ratios and its just a case of making sure the rocker gear is not going to bend. Guide plates are not really needed for shaft rocker engines.

One thing.

The 250 uses approx 9.62" FE push-rods, so it has big heavy rocker gear. But the valves on an FE are 5.45" tall, and heavy because the head diameter is much bigger. The optimum is over-sized Holden 253/304/308 valves and conical springs and they are just longer Chevy small block race valves with 5.16" being the ideal valve stem length.

The thing is that the FE was a LeMans winner, and Ford umped money into it. So copy the FE solution's.

The Holden V8 was a 40 year champion of 500 and 620 mile endurance racing, as well as Formula 5000. So the Chev style taller valves (which were used by Alan Root and TFS and Ford on its special alloy head aftermarket heads) are a good option. Chev in name only.

For the other parts, well Mike1157 and Does10s used the Toyota 18R/308 Holden/ A series 1275 Cooper S timing gear, known endurance champion form 1966 to 1990, also fits one certain pitch of timing gear for 302 Fords.

And that's how it is. The parts that break can be fixed.

The issue is that the aluminum head cannot have is spring seats thinned down 275 thou like we Kiwis and Aussies did on the old Holden racing sixes and V8's, so you have to go for longer valves.

Bill has been an advocate of taller valves; hes right.

Observation:

In the United States, you guys don't use 200's and 250's as endurance engines, so the 1966-1968 US Drag and 1969-1977 Australian Ford Endurance Racing solutions dreamed up and supplied by the likes of Al Turner aren't options Americans consider because of expense.

It's un-American to be on the inferior end of a financial expenditure unless it has perceived value. In line sixes are econo engines, so no one thinks out side the box on a SWOT analysis.

Enjoy your quest. Its like the crank and induction questions. Mr David Halverson got it right in 1987. If you keep playing the Agent K against the Doomsday argument, your gonna end up like the Nissan Motor Company. Were K is the knowledge operator, p and q, like r and s, are propositions.

You need to mind you P's and Q's so your engine doesn't end up like and R's. S is speed. How much you get is based on What you Spend.
 

pmuller9

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62Ranchero200":2wp4uk86 said:
Questions:
What ultimately limits possible valve lift? Piston to valve clearance (my pistons have 15 cc dishes) ? Valvetrain components being too tall and hitting the underside of the top of the valve cover? Is there a limit on lift with solid lifters in a small six? I know it's not possible to install roller lifters in a small six without extensive custom machine work. I don't intend to go that far in the foreseeable future.

With the aluminum head and its large ports and valves, would more lift always be beneficial to mid-range torque and high-end HP, or can you reach a point of diminishing returns?

If relevant, my machinist says that he would recommend a rev limit of 6,500 RPM on this motor, unless I'm willing to tear it down to replace the "early" forged 300 rods with stronger custom rods.

Thanks
Bob
Piston to valve clearance shouldn't be a problem unless the pistons have a dome but you should always check the clearance anyway.

I don't think that valve cover clearance is an issue with shaft mount rockers. We run into the valve cover on the big six when going to a roller rocker because the locking adjusting nut for the rocker sits high in which case we use a double cover gasket or a cover spacer.

The one limit for lobe lift is the lobe height. The lobes can't be higher than the cam journals or it will not fit past the cam bearings in the block. Once you hit that limit the lobe's base circle has to be reduced for more lobe lift but you don't want to reduce the base circle too far because it weakens the cam. At some point you increase valve lift using a higher rocker arm ratio but that also increases the pressure on the camshaft.
In most cases a cast iron cam core should not be pushed beyond .600" lift.
A roller cam is made from steel and will handle more pressure which is another reason for going with a roller cam.

As long as the ports supports the valve lift with increased flow you should see torque improvements with increased lift.
The piston in a 250 six reaches max velocity at 74.5 degrees before and after TDC.
By opening the valve sooner and quicker you take advantage of the piston motion as it is accelerating for better cylinder fill.

The primary reason for needing longer valves in the aluminum head was for spring selection.

The 200 six with the aluminum head have the potential for 7500 rpm on the street with aftermarket rods and pistons.
The problem is the valve springs required to support that rpm have an installed height of 1.750" and beyond.
They also require steel locators to protect the head which also allows shims to correct any height discrepancies.
By the time all of that is stacked under a retainer you need at least 1.800"

Manley Valves was the go to for longer valves.
 

62Ranchero200

Famous Member
@pmuller,

What do you think the RPM potential of a 250 with the aluminum head is, with a solid lifter cam (similar to the high lift, long duration Schneider cams) and the forged "early" 300 rods I have? Could the RPM range be increased even more with stronger custom rods?

It sounds like .600 is the theoretical limit of lift for a small six, unless you want to do a lot of custom machining to run a steel roller cam.

Do you think the dual springs (from Clay Smith, used to be listed on the CI/VI site) could adequately support 6,500 RPM with .600 lift?

Thanks
Bob
 

pmuller9

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Bob
The 300 six crank has a 3.98" stroke and the 250 six has a 3.91" stroke so I would call that the same.
Members like FTF push the 300 crank to 7200 rpm but I believe it is a forged steel crank.
At even higher rpms the steel cranks vibrate and break around the last main journal.
Bruce Sizemore destroked his to 3.75" to eliminate the problem

I don't see anyone pushing the 300 iron crank past 6000 rpm and there haven't been any reports of breakage.
I wouldn't feel comfortable pushing the 250 crank past 6500 even with a long rod and lightweight piston.

62Ranchero200":2e7gxyxb said:
Do you think the dual springs (from Clay Smith, used to be listed on the CI/VI site) could adequately support 6,500 RPM with .600 lift?
Not even close!

A solid lifter cam with near .600" lift has a very steep ramp.
The spring needs at least a 150 lb seat pressure and 400 lb/in spring rate.
This is what I was explaining at the bottom of my last post.
You would need valves that are around .250" longer.
 

62Ranchero200

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pmuller9":1go73k29 said:
Bob
The 300 six crank has a 3.98" stroke and the 250 six has a 3.91" stroke so I would call that the same.
Members like FTF push the 300 crank to 7200 rpm but I believe it is a forged steel crank.
At even higher rpms the steel cranks vibrate and break around the last main journal.
Bruce Sizemore destroked his to 3.75" to eliminate the problem

I don't see anyone pushing the 300 iron crank past 6000 rpm and there haven't been any reports of breakage.
I wouldn't feel comfortable pushing the 250 crank past 6500 even with a long rod and lightweight piston.

62Ranchero200":1go73k29 said:
Do you think the dual springs (from Clay Smith, used to be listed on the CI/VI site) could adequately support 6,500 RPM with .600 lift?
Not even close!

A solid lifter cam with near .600" lift has a very steep ramp.
The spring needs at least a 150 lb seat pressure and 400 lb/in spring rate.
This is what I was explaining at the bottom of my last post.
You would need valves that are around .250" longer.

@pmuller,

Thank you for the clarification! Last question (for now):

Do you think the dual springs above could adequately support 6,500 RPM with the Schneider 142F solid lifter cam (.544 lift @ 1.6:1, 240 degrees @ .050, 284 degrees advertised) in my 250? If not, then you're really saying that I'd need longer valves and different springs to utilize a solid lifter cam with significantly more lift and duration than the 280/280/110 hydraulic I'm installing now (.512 lift, 231 degrees @ .050).

Thanks
Bob
 

bubba22349

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pmuller9":3qqkqixg said:
Bob
The 300 six crank has a 3.98" stroke and the 250 six has a 3.91" stroke so I would call that the same.
Members like FTF push the 300 crank to 7200 rpm but I believe it is a forged steel crank.
At even higher rpms the steel cranks vibrate and break around the last main journal.
Bruce Sizemore destroked his to 3.75" to eliminate the problem

I don't see anyone pushing the 300 iron crank past 6000 rpm and there haven't been any reports of breakage.
I wouldn't feel comfortable pushing the 250 crank past 6500 even with a long rod and lightweight piston.

62Ranchero200":3qqkqixg said:
Do you think the dual springs (from Clay Smith, used to be listed on the CI/VI site) could adequately support 6,500 RPM with .600 lift?
Not even close!

A solid lifter cam with near .600" lift has a very steep ramp.
The spring needs at least a 150 lb seat pressure and 400 lb/in spring rate.
This is what I was explaining at the bottom of my last post.
You would need valves that are around .250" longer.

To the best of my knowledge FTF only runs the cast cranks without any problems with breakage. (y) :nod:
 

pmuller9

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62Ranchero200":fe7zf7lp said:
Do you think the dual springs above could adequately support 6,500 RPM with the Schneider 142F solid lifter cam (.544 lift @ 1.6:1, 240 degrees @ .050, 284 degrees advertised) in my 250? If not, then you're really saying that I'd need longer valves and different springs to utilize a solid lifter cam with significantly more lift and duration than the 280/280/110 hydraulic I'm installing now (.512 lift, 231 degrees @ .050).
Thanks
Bob
6500 rpm plus some additional rpm for margin is a tall order and requires a stiffer spring.

The problem is the 1.600" (or less) installed height.

I looked through most of the spring lists again.
At 1.600" seat and .550" lift anything that came close to having enough pressure runs out of coil travel and binds because it is starting out compressed more than it's intended installed height.

I did find one spring that would work on your head with the valves you have but you're going to pay for a chrome silicon spring.
The Isky 5105.
https://www.jegs.com/i/Isky-Racing-Cams ... 5/10002/-1
 

62Ranchero200

Famous Member
@pmuller,

That spring is $170 per set - is a set just one outer and one inner coil - does that mean I would need 12 sets?! ($2,040)

Should that spring install with no further modifications to replace the dual valve springs I am installing now?

Thanks
Bob
 

pmuller9

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62Ranchero200:lg7fildo said:
@pmuller,

That spring is $170 per set - is a set just one outer and one inner coil - does that mean I would need 12 sets?! ($2,040)

Should that spring install with no further modifications to replace the dual valve springs I am installing now?

Thanks
Bob
That is for a set of 16 giving you 4 extra.

These are the spring dimensions.

OD 1.000/1.430 in.
ID 0.730/1.075 in.

Once the spring locator is removed from the head they will fit just fine.

I don't know what your valve spring retainer dimensions are.
You will need to measure the retainer outer diameter and the two inside steps to see if they will work or if you will need different retainers.

Also really need to know what the retainer height actually is. I'm kinda working in the dark.
Example:
d1da136ac85e6a4b3d3243d2057a8525.jpg
 
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62Ranchero200

Famous Member
@J_Mustang65,

Currently running Ford dual springs with 280/280/110 hydraulic cam. I don’t see myself upgrading from this any time soon. It required much more time and money than I expected to get to this point.

Thanks,
Bob
 

Jmustang_65

Well-known member
@J_Mustang65,

Currently running Ford dual springs with 280/280/110 hydraulic cam. I don’t see myself upgrading from this any time soon. It required much more time and money than I expected to get to this point.

Thanks,
Bob
Great thanks for the replay. It sure adds up quickly.
 
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