Best 250 to get?

[Anonymous]

Sorry, I am new to this forum... just starting to get used to it.

I was wondering what the best year to get for a 250 is.. I have a 69 Ranchero that I want to put a 250 in. I'm gonna go looking in the junkyards soon. I have the handbook, but I was a little confused about some things. Do all the heads with hardened seats have the hex log? And only the hex log heads have the bigger valves, right? I would prefer to have a flat top log for carb mods.

I'm mostly looking for something with good power and economy. The Ranch will be my daily driver and work truck.. I'll probably be carrying a little bit of weight in it most of the time also..

I plan on adding a cam, and would like to get a header but they are a little pricey new (I'm used to being able to get headers for a V8 for under $100).

Are the bigger valves worth that much more power?

Thank you

 

[rbohm]

8) i would recomend you use a 300 instead since you want to carry a load. if you however you have your heart set on a 250, any of them will work. the best head will be the later ones.

 

[CZLN6]

Howdy 6T8:

The 1st flat-topped log head was the '69 "M" head. It's down side is that it had 1.69 intake valves and non-hardened seats. A C9XX-M head can be upgraded during a valve job with larger 1.75 valves and hard seat inserts.

The flat-top log heads came in several later casting- D5XX-BA & D7XX-AB. These heads will have 1.75" intakes and the D7 will have hard seats. The D5 will have at least induction hardened exhaust and possibly intake. A D5 could still have 1.69" intake valves. Check to be sure. Yes, this was a transition year. D7 and later will all have 1.75 intakes for sure. We're still looking at heads, trying to figure out the suffix code.

The advantage of the Flat-top log is in modifying to directly mount a two barrel or multi- carb. If you're not doing that than the advantage over a late model hex head is slight. Just 120cc in total intake tract volume.

If I were you, I'd be looking for a '69 to '72. They had better cam gear timing. If you're building a block, it won't matter, just know that earlier timing gears were less advanced. A '69 will have an Autolite 1101 carb, 70 to '73 will have a Carter RBS. Both have good and bad qualities. You will want to upgrade to a '76 or later DuraSpark II ignition system, under any circumstances.

Hope that's what your needed.

Adios, David

 

[Anonymous]

Just adding in... if you are looking for a new block, beginning in '78 Ford used cast rods in the 250 versus the previous forged rods... if that's even a concern.

 

[sefus]

so when im out at the junk yard, what should i look for if i want a 'good' 250 head. i mean what vehicles did they come in and which years were those better heads on? i figured the mavrick, granada, and falcon but how do i know its a 250? thanks?

 

[Anonymous]

a 200 has 3 bolts holding the water pump and a 250 has 4 bolts.

 

[CZLN6]

Howdy All:

In addition to Deeebo's tip about the water pump attaching bolts, which are hard to see in some engine bays, check to location of the starter, All 250's had a low mount starter location, below the oil pan gasket line. Most 200 had a high location, or above the pan gasket line. The exception is later. '80 -'82 Fairmont, etc.... those 200's had the later big bell attachment and a low mount starter.

And the 250 block is about 2" taller than a 200. 250 measured from the pan gasket line to the head gasket line is about 10 1/16" tall. A 200 is about 8 1/16" tall.

I'd be looking for a '69 - '72 Maverick/Comet, low miles, that is in beautiful condition, except for the fact that it had been rear ended in a crash. Cars are in the Wrecking yard for two reasons. Either the engine/trans is shot and the owner didn't want to spend the money to fix it, or it has been in an accident and declared totaled by the insurance co. You want to find the latter. If you find a "good" donor, get everything, front to back, from the fan to the driveshaft, top to bottom, air cleaner to the oil pan, and side to side, frame mount to frame mount.

Check the inside of the engine by pulling the plugs.

If an otherwise good donor car doesn't have the head & ignition system that you want, keep looking else where for that and swap later. You would have to be very lucky to find all that you want in one package.

What engine was in your '69 Ranchero? What trans? What rear-end?

Adios, David

 

[Falcon62]

Just a thought, but wouldn't a 300 fit the engine bay of your Ranchero? If it will fit, I'd go that way over the 250, unless you want it to be a simple install. You'd probably have to fabricate stuff to put a 300 in it.

 

[Anonymous]

I already have the mounts and brackets for a 250... I really wouldn't wanna spend all the time to fab up the stuff to fit a 300. I was kinda leaning toward the gas mileage to do the 250, the 300 just kinda seems to defeat that. I have a 289 I could put in it if I was gonna do that.

The Ranchero currently has a 351w FMX(yuk) and a 9 inch in it. My whole idea was I was gonna take out the 351 and put it in my 68 Stang(which currently has a 302 that's starting to get a little old) and swap the 9 inch into the Stang also. The FMX I'm gonna trash out of the Ranch, I'm gonna put a spare C4 I have in it now... I'd like to eventually put an AOD in it with the 250... I plan on putting my old Stang 8 inch in the Ranchero, cause the 9 inch is kinda overkill with the 6, and I'll need it in the Stang with the 351w. I got the Ranch for $500, needs a little work... but the motor in it is good, I just thought it would make a good driver/light work truck... I'm not going to be carrying that much weight all the time. I'm just going to be helping a friend with his pool biz. I'll be carrying supplies and sometimes pumps & filters.

I really don't mind about the timing gears, I'll just be replacing them anyway. I assume you can just replace them with an earlier set and get the better cam timing right? I was a little familiar with that cause I know Ford did that to the V8's also in '72 I believe.

Are the earlier blocks(69-72?) any stronger than the later ones?

Thanks guys for all of your help

 

[CZLN6]

Howdy Again:

6t8 asks- Are the earlier blocks(69-72?) any stronger than the later ones?

No, I was just thinking of matching with your '69 Ranchero chassis- motor mounts and trans mounts, but it sounds like you've got that covered. Other than minor accessories, like water pump length, and pulley diameter and the already discussed cam timing, all 250 blocks are pretty much the same. Oh, and the rod material, John already mentioned.

If you're rebuilding the block, know that one of the greatest shortcomings of the 250 engine is the massive amount of deck height Ford used get the CR down to their advertized 8.2:1. Actual CR came out to be 7.8:1. Mine measured .150". So much for quench turbulence. If you're rebuilding, this problem can be minimized with 255 V8 pistons, which are .085" taller, off set crank journal grinding, and decking the top of the block. Now your problem might be too much compression. Oh Darn! What a problem.

Adios, David

 

[rbohm]

If you're rebuilding, this problem can be minimized with 255 V8 pistons, which are .085" taller, off set crank journal grinding, and decking the top of the block. Now your problem might be too much compression. Oh Darn! What a problem.

8) sure. use the early 250(69-73) with the late head, and 255 pistons. deck the block only the amount you need to make the deck flat and your compression should be right around 9.5:1

 

[CZLN6]

Howdy All:

rbohm- My goal was to reduce deck height to zero to improve quench turbulence. You scenerio solves the CR problem, but still leaves too much deck clearance for good combustion quality. And if you add more deck clearance with a thicker than OEM, compostie type head gasket, you haven't solved much. In theory, quench needs to be in the .030" to .040" to be effective. The curse of the composite gasket makes that goal difficult. .050" deck clearance has to be a bunch better than .150".

A 250 of stock bore and stroke with 255 V8 pistons, with 2 cc eyebrows, leaves .065" deck clearance, assuming a .150" original deck height. If the deck were machined to zero, and it was assembled with a composite head gasket of .050", the CR would be 10.3:1. I'm thinking that's a bit too high for 6t8's intended purpuses.

If you add to bore in a rebuild you add to the problem. I'm looking at offset grinding the crank to reduce the amount needing to be removed from the top of the block, but that adds to CR too. Also note that the 62 cc chamber head may be less if it is milled at all, again, adding to the CR problem.

The trade offs are CR, or quench. Or, custom machine a "D" shaped recess or dish in the top of the 255 pistons- but that's another post.

This may be all too acdemic for 6t8's goal of a good work truck engine that gives good gas mileage.

Happy New Year!

Adios, David

 

[rbohm]

8) good points, one thing that can be done though to add quench in my idea is to angle mill the head to reduce the openess of the chamber in the late model head. that along with a composite gasket should give the quench you are looking for and still keep the compression a streetable 9.8:1

 

[CZLN6]

Howdy all:

Rbohm- Angle milling the head will decrease chamber volume, but it won't improve the quench effect. Quench is created by the proximity of the flat surface of the head, not the chamber, and the top surface of the piston. It is created by a combination of deck clearance, the distance from the top surface of the piston and the deck surface of the block, and the compressed thickness of the head gasket.

When the piston comes up on the compression stroke, fresh mixture is squeezed out of this area at high velocity and turbulence into the combustion chamber and is simultaniously ignited. Less deck clearance more quench. More deck clearance less quench effect.

Less deck clearance, up to a point, and more of the quench effect is better for more turbulence, better combustion, more power and economy, and less tendency for pre-ignition.

Other factors enter in, like the ratio of combustion chamber to bore, and piston crown to dish ratios, but for the most part, on a wedge-shaped combustion chamber engine, a quench of .040" or less is better. The trade off is piston to valve clearance. Pistons and valves must not occupy the same space at the same time or bad things will happen.

The only ways to improve quench is to reduce the deck height of the piston in the block, and/or reduce the compressed thickness of the head gasket

The huge deck clearance on the 250 engines is one of it's performance shortcomings. Composite head gasket add to the problem. But it can be dealt with.

How are you doing 6T8? Is any of this helping in your quest?

Happy New Year!!!

Adios, David

 

[Anonymous]

Oh yes, you guys have helped quite a bit!

About the Comp ratio, the handbook says to use 8.7:1 if you want to use 87 oct gas right? Where I live we kinda get both extremes.. it can get up to and over 100 degrees in the summer.. and it can get freezing in the winter (no snow or nothing tho).. I was thinking of shooting for about 9:1, but do you think that would be too much for 87 oct?

I went to the yard yesterday(50% off day).. all I could find were Fairmonts with 200s and hex logs... I did get a DS2 dist tho.. There was a '74 comet there that HAD a 250 w/ C4 in it... but someone took both of those already.. I'm probably gonna head to a neighboring town today to see if I can find anything in that yard(they have 50% till Sunday too). I guess what I'm gonna have to do is get a flat log then put the bigger valves in it.. Are the 144 intake valves(to use as exhaust valves) hard to come by?

Thanks again!

 

[CZLN6]

Howdy Back:

A good running, well tuned 250 should be able to run well with a 9:1 CR on 87 octane all most all of the time. The exceptions would be summer heat, under load and too much initial advance. In those conditions you may have to mix every other tank with 92 octane, or reduce initial advance.

Make sure your cooling system is working well, A/F mixture is not lean, exhaust is open. Better if you can provide a cool air source to the air cleaner intake.

If you're doing a valve job, campher, or round and sharp edges where the deck transitions to the combustion chamber, polish the chambers, and piston tops.

The DSII ignition system will help too. Use one step colder plugs and gap to .050". Set initial at 10 degrees for a stick and 14 for an auto trans. You may be able to use more depending on your circumstances.

144 intake valves are very hard to come by. I think I got mine from Kanters, but that was 3 years ago. I think a better choice now is the SSIndustries 1.5" exhaust valves from Ford Six Performance Parts. They are a drop in for stem dia and length. They were'nt available when we did the 144 intakes as exhaust valves. Our next head will have 1.5" SSIs from Azcoupe, aka Ford Six Performance Parts. Check out his website.

If you're using an early flat top log make sure your machinist know what you're using when he does the hard seats.

Are you rebuilding the whole engine? trans? What's your elevation?

Adios, David

 

[Anonymous]

The elevation here in the city is 296' above sea level(had to look that one up!)

I got a good exhaust manifold at the yard(C8 casting), I figure I can use it until I get a header(or I might just make my own, I got a MIG).

I also pulled a D7 head off a wrecked '77 Comet, so I'm pretty happy about that(got the bigger int valves and hardened seats)..

I already have a good C4 to put in the Ranch... I eventually want to put an AOD in it.. I'll probably get one in the yard pretty soon and rebuild it... I figure I'll wait until I have the 250 in there a little bit and sort all the bugs out... sounds better than starting off with a new engine and trans.. especially because of the Tv cable adjustment on the AOD.. I'll probably make my own bracket for that...