What mods should I do to the bottom end of a 250.

I plan on ditching my 200 and using a 250 I just bought. I will be using my alum head and other parts from my last build. Just seeing what other have done to the bottom end to make it strong. I plan to raise C/R to 10.5(either flat top pistons or deck the block), cam would be a 274/274 110(Unless I should go bigger). I have seen where guys have used 255 piston and 300 rods. Will the rods match perfect or do I need to machine them. ARP bolts but which part number?

Thanks Brian

Are you installing a hood scoop or lowering the engine? I have hood clearance issues with my 200 in a 67 coupe and the 250 is decently taller. I've considered the change in the past myself so I'm curious.

cr_bobcat":2h4r5sqm said:

Are you installing a hood scoop or lowering the engine? I have hood clearance issues with my 200 in a 67 coupe and the 250 is decently taller. I've considered the change in the past myself so I'm curious.

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Yeah plan to lower mounts the best I can and a hood scoop. Might use the passenger side of the hood scoop from a 69 firebird just on one side

Yes for sure any way you go use the ARP rod bolts it's a very low cost to the amount of benefit. On the cam it all depends on your planed use and goals for this engine? I.E. street use, street and race, or racing only, that said generally a cam is milder in the bigger engine vs the smaller one. For the rotating assembly an early 300 rod (.912 pin and no oil hole) a standard rod rebuild plus add polished beams and shot peened then used with a custom piston is the way I would go or if your budget is higher yet you could use a set of custom made Billet rods instead. The 300 rods are almost "a bolt in" there are two different pin sizes (on the small end) depending on the year of the castings they would each need a slightly different piston (on the Pin sizes) to fit in a 250 block, I have not done the math yet on using the 255 pistons with a 300 rod combo so not sure about what it takes, but probably uses the later style 300 rod. I do like to keep the block deck as thick as possible for best head gasket sealing, so prefer not to machine the 250 block deck very much beyond a light clean up cut, with the 300 rod and the right pistons. Good luck

Street engine is the plans. So the 300 rods changes piston location? They are not longer or shorter? With my head having a 51 cc chamber I do not have to machine much at all. I think the 255 piston will raise the C/R to much.

for some general tips, start by taking a cartridge roll and a hand drill and deburr the block and remove all the casting flash you can find. then with a proper sized ball mill, also in the hand drill, chamfer all the bolt holes. then run a bottoming tap in all the threads to make sure they are clean.

for the rods, have them checked for straightness, and have the ends resized as needed. then remove the casting flash along the beams and then have them shot peened. also install ARP rod bolts.

for the pistons again deburr all the edges.

as for the crankshaft, once you have the rod and main journals checked and machined if necessary, polish the journals and chamfer the oil holes.

have the rotating assembly balanced.

I have seen some say the rods need to be replaced. Will they hold up to my build? That is my biggest concern with it.

65-coupe":zc264dq0 said:

I have seen some say the rods need to be replaced. Will they hold up to my build? That is my biggest concern with it.

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as long as the rods are properly rebuilt and straight, and as long as they are properly prepped, they will handle anything you throw at them up to about 400hp or so.

65-coupe":2yretxzo said:

Street engine is the plans. So the 300 rods changes piston location? They are not longer or shorter? With my head having a 51 cc chamber I do not have to machine much at all. I think the 255 piston will raise the C/R to much.

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Yes the 300 rods will change the piston location they are quite a bit longer then a 250 rod. A 250 rod measures 5.880 a 300 rod measures 6.21. If your 250 rods are forged castings they will hold up when prepped and rebuilt as in the above posts. Good luck

I'm using the stock 250 rods and .040 over 255 V-8 pistons and with a 57cc chamber that puts me at about 10.5 to 1 static compression ratio.

6.21" rod won't work at all with 255 pistons. 1.585" compression height, 6.21" rod, puts the piston 281 thou out ofthe 9.469" block. You'd need a block 281 thou taller to capture that in the block.

I like the custom 6.21 300 rod and forged Racetek or CP piston, but there are other options. It will work


Some rods, like the stock 1978-1980 D8's a re cast iron, don't use them. Use forged rods. Best option is 4 cylinder Taurus 6" 2.5 HSC rods and a deep dish piston so you can reduce compression. The 9.469" deck gives a 103 thou short. With the HSC rod, the shortfall is gone in one hit. Victor Reinz head gasket or actual deck will propably get the piston clear of the head.


Factory Aussie pistons with 27.9 cc deep dish are avaliable from Silvolite 3332H on page 33 of the catalogue.

6-250 4.1L 3.6807(IN) 93.49(MM) AUSTRALIAN FORD ENGINE Hypereutectic, Dish 2.843” dia. .276” deep 28.7 cc calc, but chamfered, so its 27.9 cc.060” Offset Pin Unleaded Fuel
COMP HT: 1.530
PIN DIA: .912 Offset
3332H part number STD. .020 .030 .040 or .060
top ring 2-5/64
Second ring 1-3/16
Assy Interchange no RA4106


Ak Miller said the 250 piston short fall gave extra room for higher lift cams, but when closed up, you needed a custom Jahns piston. Well, this was Ford Australias cross flow piston, and it will help reduce compression, and clear the lift of a 490 thou cam. And its tough as.

And is US made.


Slot the 51 cc chamber, 27.9 cc #3332H dish, into a 20 thou over 250 with 6" rods and a Chevy LS1 like +16 thou piston stick out, and you still get a fairly good compression ratio.

http://wallaceracing.com/cr_test2.php

(Your displacement is 252.24 CID The Compression Ratio is: 8.72)


Problem solved.

what setups are good for higher compression like 10.0:1 with stock 250 rods and tempo flat tops? or what is a good option?

autoX65":20qaz7n2 said:

what setups are good for higher compression like 10.0:1 with stock 250 rods and tempo flat tops? or what is a good option?

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None. The rods are crap if they aren't forged, and the pistons are too shallow and not strong enough. Although Does10's did do pretty good before the gudgeon pins froze and took the block out with a turbo engine.


Bascially, the track record on using stock US 250 Ford 6 conrods with 4 cyl parts isn't good. The 103 to even 125 thou piston shortfall still exists, and the compression and ideal dome ins't there. They do allow for over 500 thou lift. They were economy engines after 1969, and thats when Ford started down grading the wall thickness and materials on the economy engines.


There seams to be a prevading need to steal and off the shelf Ford piston while using all the stuff ups that Dearborn put there to make it an economy engine. If they fixed that, it would have been like the Aussie 250, only even better.

All the 250 cranks are underweighed with too few crank counterweights. ( Its an ecomomy engine crank!). It does have a huge crank spigot, good sized main bearings, and can take 302 SBF timing gears, and all that profile cut crank girdle stuff to make it stronger when oil splash is an issue. On a nearly 4" stroke 250 engine, it has 400 Ford style oil splash, and needs some ARP studs, an girdle, and smoothening over. If they made a US 12 counterweight crank, it would be the next option, but they didn't, and the Aussie 1993 to 1997 4 liter 12 counterweight engines were 1.25" crank spigot, not 1.375", so they won't interchange in a US block easily. The thrust bearing is different too. Basically though, the US 250 crank is fine, Ford did a good job on it, just make sure its crack tested, indexed, and prepared right.


The rods, shallow dish 200 piston choices, there all wrong from Ford in 1968, and common almost flat top 255/2.3 HSC piston thinking is wrong today for any 250. A methonal burning 340 HP 250 Aussie engine uses flat tops, and they get torched right through, you can't reduce the compression enough.

None of the info relating to a US 200 engine relates to the 250, as that engine marked the racheting down of the component strength each year, with the 1979 Granada or Monarch being the thirstiest, lamest 250 ever. But it sure makes it a cheap base for an engine that almost has the potential of a 240 or 300. Almost!


The 250s best press was in a February 24, 1979 "Quarantine" episode of ChiPs where Linda Lawrence as Lori says she gets over 27 mile to the gallon out of it. Not that anyone ever did...

In order to make your engine the least prone to detonation use the 1964 - 1968 forging# C5TE 300 rods (No Oiling Hole and .912" pin)
and order custom dish pistons from Autotec with a CH just under 1.300" so you have a few thou to deck the block.
Of course check actual deck height before ordering.
This will give you zero piston to deck clearance and a very light piston.

With the 274/274 cam degreed straight up, keep the compression ratio at 10:1
depending on the head gasket thickness you should need around 18cc in the piston dish.

.. from a 2012 forum discussion:

I'm not sure if this will help but may add to your choices:

The US 250 performance engine I'm running, uses TRW/SealedPower # 470NP's pistons. The application is 79-89 AMC 4.2(258).

Ford 250: bore = 3.68 / comp distance = 1.5 / dish volume = 13cc
AMC 258: bore = 3.75 / comp distance = 1.633 / D-Sump = 21cc's

This utilizes the bore at @ .070 over and raise the piston toward the deck .133 . The specs list the pin diameter of the ford rods at .9122 and the AMC's at .9310 which the rod can easily accomodate.

The cc volume of the recess is 21ccs. With the .070" overbore the bore is 3.75", stroke of 3.91, a Felpro head gasket at .050", a zero deck height, chamber volume of 60ccs and a piston recess of 21 ccs, gives a street compression ratio of 8.8:1 with @ OEM deck/head before any milling. milled head chamber volume , gasket crush variable will raise CR.



2015:

I've been running the .070 overbore 250 for @ 10 years to local cruises, interstate trips and quite a few trips to Lebanon Valley Dragstrip. A few weeks ago I drove the 2 hour trip on NYS Thruway to the drags, ran half a dozen hard ass' I could launches and then drove it home. The 250/AMC piston .070 overbore seems quite manageable. 8)



. .


have fun

Hi Powerband , love your manifold, I am working my log 250 head, for drag race only, plan to turbo charge and run on E-85, how well does your modified log work? It looks like it would work very well. Looks like you used 2 by 4 rectangular tubing. How is the fuel distribution, has to be much better? As much information as you can give please. Thank you Randy

hotrodguy":1pa6mi7t said:

Hi Powerband , love your manifold, I am working my log 250 head, for drag race only, plan to turbo charge and run on E-85, how well does your modified log work? It looks like it would work very well. Looks like you used 2 by 4 rectangular tubing. How is the fuel distribution, has to be much better? As much information as you can give please. Thank you Randy

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I also am working up Forced Induction versions, thats why the single 2Bbl on multiple intake port Offy' setup. There's lots of info on many variations of mods for the log head in the forums including my own. Here's a few links to recent discussions:

viewtopic.php?f=1&t=72684&p=558707&hilit=offy#p558707

viewtopic.php?f=1&t=72684&p=558599&hilit=offy#p558599

viewtopic.php?f=2&t=72662&p=558485&hilit=offy#p558485

viewtopic.php?f=1&t=72571&p=557760&hilit=offy#p557760

viewtopic.php?f=101&t=72395&hilit=offy

.

HAve Fun

Thank you

A good, "cheap" street engine would be to use 2.5 HSC pistons with custom dishes milled into them and deck to get 7.7-8.7 DCR with your chosen cam and the size of those aluminum head combustion chambers with the thinnest gasket you can get. Rotating assy balance if you want or can afford. Longer duration, low end torque cam grind with a bit more lift than stock, 3.5:1 rear or shorter with overdrive trans or 5 spd. Stock forged rods.

Cal @ calspeccnc.com can mill custom dishes in any piston and is very reasonable. Will they hold up? I couldn't say yet. He's confident they're more than adequate for a street motor.

@65 coupe,

I went the early 300 rods and custom RaceTek pistons route, and have never regretted it. The pistons are at nearly zero deck height, which discourages detonation, and the excellent quench makes the engine run more efficiently. I also used ARP main studs, ARP rod bolts, and had the entire rotating assembly statically and dynamically balanced. The cam is a Clay Smith 274/274/108.

The only issues I've had with the engine are fan to radiator clearance (had a fan spacer machined down and used a 14" low profile fan to improve that), and DUI ignition failure. Replacing the DUI with an MSD 6AL/DS2 setup.

Thanks
Bob