250 XFlow Rockers

StarDiero75

StarDiero75

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Howdy guys,

So i recently acquired a 250 xflow and im in the process of gathering parts. The rocker bolts look like 5/16" so I know that ain't flying. I'm looking to push it to 6500 RPM. I'll be using Molnar 300 rods and custom forged pistons. Possibly larger intake valves. Supercharger. Still researching cams. I am planning to use a 1.73 roller rocker off a 351C/460. They typically use 7/16" studs, which I don't think there's enough meat in the head boss to hold that together just by looking at it. What is the typical thing done here? Machine the tops off and install 3/8" or 7/16" studs? Adapter plates? Whats the secret? I would also assume for this setup to run 3/8" pushrods, right?

Thanks!
 
There are already rod and piston kits out there rather than using custom 300 rods and custom pistons, your application doesn't look that ground breaking.

3/8 to 7/16 all depends on cam and spring pressures etc, at 6500 with a reasonable cam 3/8 will still be ok. If you are thinking over .550 lift id suggest 7/16 studs.

Yes machine them off drill and tap, sometimes you need to do a bit of welding to build up the areas and if you are trying to make a decent amount of power you will be welding the top of the intake port to raise the runner.

Again pushrods thickness and diameter depend on your setup, 5/16 will do most but sometimes with boosted applications I use a larger diameter or thicker exhaust pushrod because of the high cylinder pressures.
 
rocklord said:
Are these the some of the rod and piston kits you are talking about?
www.spoolimports.com

250 XFlow Conrod + Piston Deal

Australian online store selling genuine Spool conrods, crankshafts and performance parts worldwide.
www.spoolimports.com www.spoolimports.com
Click to expand...
Thats what Id suggest, the 200 rods are 6.27 long. The dished piston would be a good start. Crow is a good source for cams, I doubt you will find anything stateside for the crossflow. Yellaterra do a line in rockers for them. Aussiespeed have blower manifolds. I doubt you will need 6500rpm to get what you desire. The EFI crossflow heads have about the biggest valves you can fit, 1.84/1.54, they hay silicon bronze inserts in the head. Pushrods are the achilles heel of the crossie, they are long and spindly. I'sure you can find something localy.
 
aussie7mains said:
Thats what Id suggest, the 200 rods are 6.27 long. The dished piston would be a good start. Crow is a good source for cams, I doubt you will find anything stateside for the crossflow. Yellaterra do a line in rockers for them. Aussiespeed have blower manifolds. I doubt you will need 6500rpm to get what you desire. The EFI crossflow heads have about the biggest valves you can fit, 1.84/1.54, they hay silicon bronze inserts in the head. Pushrods are the achilles heel of the crossie, they are long and spindly. I'sure you can find something localy.
Click to expand...
I also stock and supply all of those brands. I am also paid sponsor that supports this site...
 
Cox Custom Mechanical said:
There are already rod and piston kits out there rather than using custom 300 rods and custom pistons, your application doesn't look that ground breaking.

3/8 to 7/16 all depends on cam and spring pressures etc, at 6500 with a reasonable cam 3/8 will still be ok. If you are thinking over .550 lift id suggest 7/16 studs.

Yes machine them off drill and tap, sometimes you need to do a bit of welding to build up the areas and if you are trying to make a decent amount of power you will be welding the top of the intake port to raise the runner.

Again pushrods thickness and diameter depend on your setup, 5/16 will do most but sometimes with boosted applications I use a larger diameter or thicker exhaust pushrod because of the high cylinder pressures.
Click to expand...
So whatever setup I get will end up being "custom". The kits are like $1700 a set. The Molnar 300 rods are like $650 and unless custom pistons are $1000, then whats the benefit? Just curious. Also, I noticed they are for 0.040" over, I have a standard bore motor and would really prefer not to take off more than necessary, especially if I am boosting.

Currently I am trying to find an engine builder who's willing to touch this. The very reputable one I'd like to take it to wants me to get all this info ahead of time, otherwise he won't touch it because he hasn't dealt with one before. He has a few more questions:
1. Any torque plates? He's not super excited to machine without one since he knows what power goal I want.
2. Forged cranks? Any worries with stock cranks, why or why not?
3. Special harmonic balancers to allow to spin up to 6500?
4. Any known cooling issues? He believes the #6 cylinder is known for getting hot like on the old 200s/250s.
5. Any other issues or concerns to build to this kind of power?
 
aussie7mains said:
Thats what Id suggest, the 200 rods are 6.27 long. The dished piston would be a good start. Crow is a good source for cams, I doubt you will find anything stateside for the crossflow. Yellaterra do a line in rockers for them. Aussiespeed have blower manifolds. I doubt you will need 6500rpm to get what you desire. The EFI crossflow heads have about the biggest valves you can fit, 1.84/1.54, they hay silicon bronze inserts in the head. Pushrods are the achilles heel of the crossie, they are long and spindly. I'sure you can find something localy.
Click to expand...
You would suggest the yellaterras over anything normally for the 351C motors?

I was thinking of trying to sneak a little larger valve for either the exhaust or intake as it looks like I can do one or the other. Are the silicon bronze seats better than a normal "hardened" seat that gets installed?

I have read that about the pushrods. I was planning on using something from Summit racing's site.

I currently have a crow cam but I don't think it's gonna be enough for the plan. I'll try and find the number on it unless Rocklord knows offhand which one he gave me. I can have my crow reground to something different, right?

I do have the 6.27 200 rods already. pmuller suggested not using them b/c they won't hold up to the power and to look at the 300 molnar.
 
StarDiero75 said:
You would suggest the yellaterras over anything normally for the 351C motors?

I was thinking of trying to sneak a little larger valve for either the exhaust or intake as it looks like I can do one or the other. Are the silicon bronze seats better than a normal "hardened" seat that gets installed?

I have read that about the pushrods. I was planning on using something from Summit racing's site.

I currently have a crow cam but I don't think it's gonna be enough for the plan. I'll try and find the number on it unless Rocklord knows offhand which one he gave me. I can have my crow reground to something different, right?

I do have the 6.27 200 rods already. pmuller suggested not using them b/c they won't hold up to the power and to look at the 300 molnar.
Click to expand...
YT rockers can be obtained in a direct bolt on form, plus you get a kit with everything you need. Stock rockers work ok up to a point.
Silicon bronze is what everybody uses here, Id stick with them, I dont think there is much to gain with the slightly larger intake valve, and exhaust is good as it is.
Pushrods, somethings needs to be done there.
Crowcams, need to know the PN.
Many guys race with the 200 rods in 250s, they run then out to 6500, you here of occassional blow ups. If you can get better rods at a reasonable price, do it.
 
Last edited:
StarDiero75 said:
So whatever setup I get will end up being "custom". The kits are like $1700 a set. The Molnar 300 rods are like $650 and unless custom pistons are $1000, then whats the benefit? Just curious. Also, I noticed they are for 0.040" over, I have a standard bore motor and would really prefer not to take off more than necessary, especially if I am boosting.
Click to expand...
Racetec will make a piston, I'm sure for less then $1000. My custom pistons were about $700.
 
StarDiero75 said:
So whatever setup I get will end up being "custom". The kits are like $1700 a set. The Molnar 300 rods are like $650 and unless custom pistons are $1000, then whats the benefit? Just curious. Also, I noticed they are for 0.040" over, I have a standard bore motor and would really prefer not to take off more than necessary, especially if I am boosting.

Currently I am trying to find an engine builder who's willing to touch this. The very reputable one I'd like to take it to wants me to get all this info ahead of time, otherwise he won't touch it because he hasn't dealt with one before. He has a few more questions:
1. Any torque plates? He's not super excited to machine without one since he knows what power goal I want.
2. Forged cranks? Any worries with stock cranks, why or why not?
3. Special harmonic balancers to allow to spin up to 6500?
4. Any known cooling issues? He believes the #6 cylinder is known for getting hot like on the old 200s/250s.
5. Any other issues or concerns to build to this kind of power?
Click to expand...
Torque plates probably not,
Forged cranks, can be sources but VERY expensive, not really needed, barra is similar and they will go 750kw on stock nodular crank.
Special balancers, yes ROMAC in Adelaide have them.
Only cooling issues known is when there is a lot of corrosion in the system, otherwise usually no problems.
These things are like a brick shithouse, people have got huge power out of them, they seem to be able to handle 500bhp fairly well, the Barras are known for up to 2000bhp with factory blocks and heads, there are NO aftermarket blocks or heads ATM
 
aussie7mains said:
Torque plates probably not,
Forged cranks, can be sources but VERY expensive, not really needed, barra is similar and they will go 750kw on stock nodular crank.
Special balancers, yes ROMAC in Adelaide have them.
Only cooling issues known is when there is a lot of corrosion in the system, otherwise usually no problems.
These things are like a brick shithouse, people have got huge power out of them, they seem to be able to handle 500bhp fairly well, the Barras are known for up to 2000bhp with factory blocks and heads, there are NO aftermarket blocks or heads ATM
Click to expand...
Thanks for going through the list. I'll get this info back to my guy. I'm also gonna start talking to Jeff Jones. I have heard he's a pretty impressive builder of the Ford inlines in California. Just wish he was a little closer. Just gives me an excuse to use some hotel points lol.

Maybe Matt Cox or Jeff have torque plate since they build hopped up motors. Then maybe this will work out.
 
aussie7mains said:
YT rockers can be obtained in a direct bolt on form, plus you get a kit with everything you need. Stock rockers work ok up to a point.
Silicon bronze is what everybody uses here, Id stick with them, I dont think there is much to gain with the slightly larger intake valve, and exhaust is good as it is.
Pushrods, somethings needs to be done there.
Crowcams, need to know the PN.
Many guys race with the 200 rods in 250s, they run then out to 6500, you here of occassional blow ups. If you can get better rods at a reasonable price, do it.
Click to expand...
I'll do yoy one better and include the cam card. Its 2800-6000rpm range. This is a rompy cam. Its a Crow 14650 cam. This is just what came with the motor (not installed).
 

Attachments

  • 20240123_204743.jpg
    20240123_204743.jpg
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StarDiero75, the cam you have is a Crow Cam 14650.
Attached is the cam specs.
 

Attachments

  • Crow Cams 14650 Cam Sheet.pdf
    4.9 MB · Views: 4
StarDiero75 said:
Thanks for going through the list. I'll get this info back to my guy. I'm also gonna start talking to Jeff Jones. I have heard he's a pretty impressive builder of the Ford inlines in California. Just wish he was a little closer. Just gives me an excuse to use some hotel points lol.

Maybe Matt Cox or Jeff have torque plate since they build hopped up motors. Then maybe this will work out.
Click to expand...
Matt does not build anything...

If Jeff does as many small sixes as people say then id imagine he would have or his machinist will have a torque plate. For a Small six it is necessary to torque plate hone engines as the bore distortion can be up to .001 at the top of the block, granted its less on a crossflow block than a pre crossflow.

Your cam is on the small side for 450fwhp unless you are jamming in some boost.
 
aussie7mains said:
Torque plates probably not,
Forged cranks, can be sources but VERY expensive, not really needed, barra is similar and they will go 750kw on stock nodular crank.
Special balancers, yes ROMAC in Adelaide have them.
Only cooling issues known is when there is a lot of corrosion in the system, otherwise usually no problems.
These things are like a brick shithouse, people have got huge power out of them, they seem to be able to handle 500bhp fairly well, the Barras are known for up to 2000bhp with factory blocks and heads, there are NO aftermarket blocks or heads ATM
Click to expand...
Close but not quiet true, there are a few people making aftermarket Barra blocks.

As for crossflows there was one or two aftermarket crossflow blocks made, I know where one of them is as for the rest. No idea.
 
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