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

may B silly Q on my part but...
do all (rod, piston) that make a difference - when he has a 250 & it looks like U have a 200?

also

seems like all of us R strayin some from "bottom end" mods.

I, on the other hand, have no thing to offer (beyond these types of process Qs).
I AM all ears & hopin to learn more!

Oh, may B this:
I heard U could "knife edge" the crank - for weight and oiling assistance?
 
chad":3pqxt07o said:
may B silly Q on my part but...
do all (rod, piston) that make a difference - when he has a 250 & it looks like U have a 200?

also

seems like all of us R strayin some from "bottom end" mods.
Click to expand...

bottom end mods are the same for every engine, in general. there are specifics that apply to a particular engine though.

Oh, may B this:
I heard U could "knife edge" the crank - for weight and oiling assistance?
Click to expand...

knife edging the crank is actually done for both reasons. you take weight off the counterweights, and you make it easier to prevent oil from wrapping itself around the crank and making it harder for the crank to pass through the windage.
 
I'm going to recommend the same as 62Ranchero200 (Bob), Bubba22349, and xctacy. Go with the early 300 rod and Autotec/Racetec piston
I did a similar deal on a 300 where I used the longer 240 rod with Autotec pistons.

The pistons are a forged 4032 alloy so the piston to wall clearance is still fairly tight (<.003") and they are cheaper than the 2618 alloy pistons.
You get to set the CH so the piston is at zero deck clearance without having to machine a lot off the top of the block deck.
You have the option of using the more modern/thinner ring set.
Pistons come with an accumulator groove between the top and second ring
With the longer 300 rod the piston will be shorter and lighter
Here what one of mine looks like with a 10cc dish

viewtopic.php?f=2&t=71491

Find a set of the 1964 - 1968 forging# C5TE 300 rods (No Oiling Hole and .912" pin) and grind the forging lines off the beams. Then polish the beams and have the rods shot peaned.
Then have them resized with ARP bolts

https://dl.dropboxusercontent.com/u/393 ... G_0009.jpg
 
Econoline":1b4gm3iz said:
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.

c9hl.jpg


mvbBGp.jpg


TLOcw8.jpg
Click to expand...


sounds good. what timing gear are you running on that 250?
 
pmuller9":140lo6m0 said:
I'm going to recommend the same as 62Ranchero200 (Bob), Bubba22349, and xctacy. Go with the early 300 rod and Autotec/Racetec piston
I did a similar deal on a 300 where I used the longer 240 rod with Autotec pistons.

The pistons are a forged 4032 alloy so the piston to wall clearance is still fairly tight (<.003") and they are cheaper than the 2618 alloy pistons.
You get to set the CH so the piston is at zero deck clearance without having to machine a lot off the top of the block deck.
You have the option of using the more modern/thinner ring set.
Pistons come with an accumulator groove between the top and second ring
With the longer 300 rod the piston will be shorter and lighter
Here what one of mine looks like with a 10cc dish

viewtopic.php?f=2&t=71491

Find a set of the 1964 - 1968 forging# C5TE 300 rods (No Oiling Hole and .912" pin) and grind the forging lines off the beams. Then polish the beams and have the rods shot peaned.
Then have them resized with ARP bolts


sounds like the best way and what power level would you rate that bottom end art. great for nitrous?
https://dl.dropboxusercontent.com/u/393 ... G_0009.jpg
Click to expand...
 
Just stock. Mild cam, Erson 280101. Trying to optimize a bit and have a good reliable motor for the old Econo. Would be nice to drop an aluminum head on it or some 1.6 ratio rockers. Where do those stock ones come from? I think with at least 54cc chambers it would work out OK. 56 would better. Even at 54cc with .053" gasket I'd be at less than 8.1:1 DCR(10.2+ SCR) with the aluminum head. Trying to keep the compression and the squish in hand is tough with a 250. Esp on a budget ;) Compromise. It's a weird cam grind if the numbers hold out. It always 2 pts lower dynamic. I'm going to be at 9.5+:1 c/r as it is with 62cc chambers and a victor gasket. Going to lose at least 5 thou in the clean up. So it's going up. 3.7:1 in the rear w/25.5" wheels and an AOD for pure convenience not matter the cost and being my DD and all. And retroing a 5 spd into an Econoline, I don't want to go there right now. It's never going to see the track
 
that sounds real nice. Im sure the early 300 rods will hold up great. but just curious does anyone make a set of H beam rods for the 300?
 
i as well have been working on a 250 build so this sure will help! decided to use the small log head that ive made the aluminum intake and plenum on in another thread. figured the extra 50 cubes will give the mod head its best chance. im thinking about the 274/274 on a 112 with a c4 and need to get a hi stall converter or possibly the 280 grind from classic inlines.


I was leaning toward the 300 rods and autotec pistons to make it really easy to get a custom sized dished piston. I dont think Ill get low enough Compression with the HSC piston even if its milled for a dish since its a small chamber opened up to 54cc. thinkin to run a autolite 480cfm and above 10 to 1 is the plan just a street strip build.
 
autoX65":2o6wudgx said:
Im sure the early 300 rods will hold up great. but just curious does anyone make a set of H beam rods for the 300?
Click to expand...

The only "off the shelf" H beam rod that can be used for the 300 is the BBC 6.385" with the 2.100 rod journal. Eagle CRS6385B3D
It has the same .990" big end width as the Ford six.

If you use it on the 250 six the piston CH ends up around 1.130" depending on the actual block deck height.
You would need a custom Autotec piston with a .990" wrist pin.

Option 2
Scat makes a 6.00" H beam rod for the Chevy 250. Scat 2-250-6000-2000
Big end width is 1.050"
Rod journal is 2.00"

Narrow the big end about .060".
Off set grind the crank for a 4.010" stroke with a 2.00" rod journal.
 
Im sure 250 aussie crossflow rods are useable, if thats the case you can then buy spool or argo rods, I’m about to explore the same possibilities with my build for the supercharged motor, 250, custom forged pistons and aftermarket arp bolted rods. For the cost of shipping etc, if thats the case 6 rods will cost sweet fa to buy from us.
 
spool also do custom conrods starting at 145 each including ARP bolts, look at conversion rate right now for Aussie parts guys
 
here is a thought, 265 Hemi rod can be used with a little crank offset grinding, gives 275 cubes and good for 7200 apparently, must be true as i read it somewhere lol
 
how about piston rings what are the best these days. especially for the power adder builds. when to use chrome rings? and cast are the only options right?
 
xrwagon":3p6vvls0 said:
here is a thought, 265 Hemi rod can be used with a little crank offset grinding, gives 275 cubes and good for 7200 apparently, must be true as i read it somewhere lol
Click to expand...


I dont see the specs for these what would need to be done?
 
@65-Coupe

the 250ci is a stout engine... if street use, even light racing, you'll never stress the components... I recommend keeping it simple and easy.
 
aside from the pistons to get the correct compression/squish, the 250 is very over engineered for a bottom end. having just finished mine, i really have ahard time seeing why a double roller chain is needed, or any beefier rods, etc. for a street car.

mine will rev to 6K with adead bone stock bottom end, fine. im seeing 60 psi oil pressure under normal driving, and 20 psi hot idle in gear. bottom is stock on my car. Have cam, autolite 2bbl, hei ignition, lots of head work and a 6 into one.
 
.. 'bottom end' discussion :

The rescued legacy performance built 250 in my 61 uses "shot peened and balanced" rods in the engine build literature I obtained. I'm wondering if this early performance hardening technique is still used and viable ? ...

have fun

'kudos Wiki ...

" It was common practice for blacksmiths to hammer peen the concave side of leaf springs, which enhanced their life, although the exact mechanism was unknown. The maximum tensile stresses are located on the surface of the concave portion of leaf springs; the peening effectively offset the maximum tensile stresses, also located on the surface, when the compressive stresses were induced by peening with a ball peen hammer. Shot peening was independently invented in Germany and the United States in the late 1920s and early 1930s. The first commercial implementation was done in the United States on automotive valve springs.
Peening a surface spreads it plastically, causing changes in the mechanical properties of the surface. Its main application is to avoid the propagation of microcracks from a surface. Such cracks do not propagate in a material that is under a compressive stress; shot peening can create such a stress in the surface... Depending on the part geometry, part material, shot material, shot quality, shot intensity, and shot coverage, shot peening can increase fatigue life up to 1000%."

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