250 Build Plan Specs (help me check my figures)

[mike1157]

All right then.

I'm getting ready to order my pistons, and the deck height is now coming into play.
The block I'm using is unmolested, (well,...unmolested up until I got a hold of it ) and never has had any machine work. That said, I guess I now assume, that my deck height is stock @ 9.469".
If it is the same thickness on the big end as a stock 250 rod, at Xctasy's suggestion, I plan to use a 1986 2.5 HSC rod. Length is advertised @ 5.990".
Now, doing some simple math, and dividing the stroke in half, ( 3.91/2 = 1.955) Adding 1.955 to the rod length of 5.990 (5.990 + 1.955 = 7.945). When you factor stock compression height of the piston of 1.511, and add it to the previous,.....you get 9.456.
A piston that will be .013" still down in the hole.

Am I right in my thinking here?

Now, this block is gonna have all six cylinders sleeved, and remain factory standard bore 3.68. Ultimately, I'd imagine they're gonna have to deck it to square it. So If I give them .030 ( plus the stock .013, I'll have normally) to deck the block back to true,..I modify my pin height requirements "up" into the piston commensurately, so my new requested pin height on my custom piston should be......1.481, and it should still be .013 down.

1). So my first question is,...is it safe to assume that a corrected pin height .030 higher in a custom piston will be sufficient to have ample room (.043) to deck the block to zero deck?

You guys getting what I'm sayin',.....you painting what I'm priming here?

Next, I'm using a Crossflow head (HF2 to be exact) Trying to determine what I have from simple internet research yields little about whether or not the head is good or bad based on chamber design considering I'm going to be turbocharging it. It looks "open" to me, but when a gasket is placed on the face of the head, there is clearly two quench areas on both side of the chamber, so maybe I'm wrong in thinking that? I hope to hell that the head I have is gonna work, I'ts waay too far along to be second guessing myself now. Two of the stock valves are bent, which brings me to the quest to correct that. While I thought that there was a bagillion replacement stainless valves out there, the opposite holds true. As long as the intake valve is on a crossflow head, the ONLY valve you can use for an intake replacement is the 1.88 exhaust valve for a BBC. From what I'm reading, I'll have to have that dude undercut to a maximum of 1.84 to not go "too big". Conversely, the exhaust valve can be readily replaced w/ a 1.54 351W sized FMS replacement SS piece.
Trying to research chamber volume yields somewhere in between 53-56CC's. Obviously important to my final piston design, as to be able to figure out how to get a final compression ration of 9.0:1.

I'm planning on using a custom made Cometic head gasket ( will not be a wire-lock design, more of a sandwiched tool steel thing-a-ma-bob from what I'm understanding) Anyway, a .040 compressed thickness will be the targeted design requisite.

So,... Question #2.

All things considered, Is there enough information here to give my piston guy so that he can determine how much of a dish I'm gonna need to yield a final compression ratio of 9.0:1?
3.68 bore, 3.91 stroke, 53CC head, zero deck, .040 compressed gasket?

 

[CNC-Dude]

I ran into this all the time when I worked in a race engine shop. You need to create a bucket list of priorities to get completed and stick with it because you never build an engine on assumptions, only absolutes! First, you need to get the head completely machined and finished so you can determine if the compression is doable based on it. Second, get the block sleeved and rough bored and rough decked so you can take a piston of known compression height and verify the actual deck height with the rods you intend to use, again, never assume it based on theoretical math or assumptions, custom pistons are not returnable. Maybe get the crank ground at this time also, it will just remove another possible error out of the equation. Once you do that, you can then give the piston company the exact measurements of compression height, dish volume, ring stack, etc...because they will not make your pistons on assumptions either, only absolute numbers and measurements. Its only after you do this that you can know beyond a shadow of doubt that all your number crunching will have real world meaning and work out like it should. The only math you will be doing is based on the difference between the setup pistons to the corrected new pistons. Your removing the assumption of the stroke, the assumed rod length and assumed deck height your assuming on these other assumptions and replacing them with real hard data, that's the only way to do it correctly.

 

[mike1157]

I ran into this all the time when I worked in a race engine shop. You need to create a bucket list of priorities to get completed and stick with it because you never build an engine on assumptions, only absolutes! First, you need to get the head completely machined and finished so you can determine if the compression is doable based on it. Second, get the block sleeved and rough bored and rough decked so you can take a piston of known compression height and verify the actual deck height with the rods you intend to use, again, never assume it based on theoretical math or assumptions, custom pistons are not returnable. Maybe get the crank ground at this time also, it will just remove another possible error out of the equation. Once you do that, you can then give the piston company the exact measurements of compression height, dish volume, ring stack, etc...because they will not make your pistons on assumptions either, only absolute numbers and measurements. Its only after you do this that you can know beyond a shadow of doubt that all your number crunching will have real world meaning and work out like it should. The only math you will be doing is based on the difference between the setup pistons to the corrected new pistons. Your removing the assumption of the stroke, the assumed rod length and assumed deck height your assuming on these other assumptions and replacing them with real hard data, that's the only way to do it correctly.

Thanks,....and you know I kinda knew that the whole time,..it's just tha I have a little extra money, and pistons are 3-4 weeks out after they are ordered,...I just wanted to get them bought, and behind me. I agree w/ your steps 100%, and that's the way I'll do it.

 

[drag-200stang]

Your math seems fine to me. What I'm concerned about is that these blocks are thin, lightweight designed - not made for what we're doing to them. I would do the very least to compromise strength in the deck area. I'd only deck it a few thousandths. I would also not slot the block like you're thnking. I'm sure something else can be done. I would go with holes in the side before I'd cut the deck. It almost looks like the groove and pin lifters, maybe done from underneath may be simpler. Have you mocked up the valve train for push rod clearance? It may not be as bad as the gasket indicates. For some reason Ford seems to make everything bigger than necessary.

What thickness sleeves is your builder talking about? I did 6 sleeves once on a 200. When I got done boring all 6 cylinders there was virtually nothing holding the bolt bosses. I swear I could grab and rip them out barehanded. Granted this was on a 0.070 overbore, but that still only gives you 0.035 more meat. Good chance installing 6 sleeves will distort the block and need line honing. Hate to sound like a negative Nancy, to make the power you want you'll need as much strength in the cylinder walls as you can get. I thought about thin wall sleeves boring the block just enough to clean up for the sleeves and reducing the bore. You can make a lot more power with a little more boost than you will worrying about a few cubic inches. Isn't the cross flow head designed for a smaller bore anyway?

I looked into using the already produced turbo barra multilayer steel gasket. They said they could increase the bore size to accomodate my 3.700 bore with minimal charge. I would think that would be very close to fitting the head you have. May be worth looking into it. They say they can do custom stuff but until its in your hands, I would try to use something off the shelf first.

Have you looked into SI Industries? One of the guys had a log head that they lengthened the valve stem. I don't believe the price was too bad. Maybe they can make something custom. Is there any gain to use 5/16" stems?

I typed too slow and I agree with CNC. Get everything positively ironed out first.

Good luck.

 

[mike1157]

Your math seems fine to me. What I'm concerned about is that these blocks are thin, lightweight designed - not made for what we're doing to them. I would do the very least to compromise strength in the deck area. I'd only deck it a few thousandths. I would also not slot the block like you're thnking. I'm sure something else can be done. I would go with holes in the side before I'd cut the deck. It almost looks like the groove and pin lifters, maybe done from underneath may be simpler. Have you mocked up the valve train for push rod clearance? It may not be as bad as the gasket indicates. For some reason Ford seems to make everything bigger than necessary.

What thickness sleeves is your builder talking about? I did 6 sleeves once on a 200. When I got done boring all 6 cylinders there was virtually nothing holding the bolt bosses. I swear I could grab and rip them out barehanded. Granted this was on a 0.070 overbore, but that still only gives you 0.035 more meat. Good chance installing 6 sleeves will distort the block and need line honing. Hate to sound like a negative Nancy, to make the power you want you'll need as much strength in the cylinder walls as you can get. I thought about thin wall sleeves boring the block just enough to clean up for the sleeves and reducing the bore. You can make a lot more power with a little more boost than you will worrying about a few cubic inches. Isn't the cross flow head designed for a smaller bore anyway?

I looked into using the already produced turbo barra multilayer steel gasket. They said they could increase the bore size to accomodate my 3.700 bore with minimal charge. I would think that would be very close to fitting the head you have. May be worth looking into it. They say they can do custom stuff but until its in your hands, I would try to use something off the shelf first.

Have you looked into SI Industries? One of the guys had a log head that they lengthened the valve stem. I don't believe the price was too bad. Maybe they can make something custom. Is there any gain to use 5/16" stems?

I typed too slow and I agree with CNC. Get everything positively ironed out first.

Good luck.

Thanks, I appreciate your input. All of the issues you're concerned about have been hashed out in various threads throughout the forum.

I do not know the exact sleeve thickness, but they are thicker than what you used, (something like .160 bigger I believe) leaves a .080 wall. ( and nothing of the original cylinder, I'd imagine) The sleeves are there to restore the bore back down to standard, as two of the cylinders are scored so deeply, they are beyond saving even at an .030 over bore. I'm not trying to get bigger, I'm trying to restore block integrity. There are several arguments out there as to whether or not sleeving a block will add, or detract to that, but I'm going to go w/ the "adds integrity" side of that coin.
The slots in the block have also been a conversation on another thread. Once cut, I would have a equally thick replacement to go back in the slot. I looked at cutting access holes in the side of the block, and may still do that. To tell the truth, I haven't committed myself one way or the other.
As for pushrod clearance, and the block grinding to get that clearance, I'm just following previous examples set by others.
The head gasket is a 125.00-150.00 custom piece. I can deal with that. Getting the roller from OZ is a big enough hassle as it is,..I'll try to keep everything local everywhere I can otherwise.

 

[Gene Fiore]

Using the c/r program I have I plugged in your specs...using a 56cc chamber and pistons down .013. If the pistons were flat top you would be looking at 11.37 to one...so you will need quite a dish on those bad boys to get you to 9:1 static compression. I played with the program and found a 19cc dish would get you to 9:1...maybe others will chime in. Is a 19cc dish feasible? Here is the link to the program I have.\

http://www.csgnetwork.com/compcalc.html

Good luck with the build!

 

[rbohm]

8) everything that has been posted so far looks good, from everyone. a couple of things;

1: i wouldnt worry as much about the thickness of the sleeves you are having installed, so much as the material you use for the sleeves. for instance you can use a thinner sleeve made from something like 4340 steel as opposed to say 1018 or 1020 steel, and after they are normalized to the block you will actually gain strength. this is just an example, the actual material will be up to you.

2: i also recommend that you triple check your compression ratio numbers very carefully, especially since you are going to turbo the motor.

3: since you are sleeving the motor, i would go with a standard bore size to give you more room for rebuilding in the future.

 

[CNC-Dude]

Yeah, those numbers are right Gene. A 19cc dish in a piston with that small of a bore will be a huge and deep dish, not sure if it is doable and still have any quench area left on it that would do anything.