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piston dish relief
- Thread starter robbinsj
- Start date
A
Anonymous
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You sure????
Have you checked all of your measurements/volumes/gasket thickness yet?
Have you checked all of your measurements/volumes/gasket thickness yet?
The stock dish is listed as 6.5 to 7 cc's depending on manufacturer. Bringing the 250 to zero deck raises the CR pretty high. What are the chamber cc's?
Howdy Joey:
Jacks got the small dish volume for you. There is also a large dish piston at 13 cc. for C/E applications. If you were to use the 13cc dished pistons with zero deck height and 51 cc chambers you'd be in the 9.1 - 9.3 CR range in a 250.
When you deck a 250 block to zero you should not mill the head too, other than to level it.
How did you achieve zero deck height? What head are you starting with? What is your goal CR?
Adios, David
Jacks got the small dish volume for you. There is also a large dish piston at 13 cc. for C/E applications. If you were to use the 13cc dished pistons with zero deck height and 51 cc chambers you'd be in the 9.1 - 9.3 CR range in a 250.
When you deck a 250 block to zero you should not mill the head too, other than to level it.
How did you achieve zero deck height? What head are you starting with? What is your goal CR?
Adios, David
When I ordered my cam from Mike I could have sworn he said zero deck the block AND mill 60 off the head. I've got an email and voicemail in to him to see if he said OR not AND.
At any rate, I will now have an engine that has a calculated CR of 11.5:1. I had the guy at the machine shop make sure there were not potential hot spots in the chambers and smooth things out. Beyond getting the thicker head gasket, cooler plugs, 93 octane, and careful timing, what else can I do to avoid spark knock and detonation?
I use this car as a daily driver and intend to continue. (Worst case I can rebuild the head that's in it now and chalk the other one up to experience.) I plan to get one of Mike's aluminum heads to run a triple Weber DCOE setup as soon as they are available. Until then I've got to rejet the Weber 38 that's on it now to make sure 1 and 6 aren't too lean for this CR. Anybody got any other suggestions? Thanks in advance.
-Joey
At any rate, I will now have an engine that has a calculated CR of 11.5:1. I had the guy at the machine shop make sure there were not potential hot spots in the chambers and smooth things out. Beyond getting the thicker head gasket, cooler plugs, 93 octane, and careful timing, what else can I do to avoid spark knock and detonation?
I use this car as a daily driver and intend to continue. (Worst case I can rebuild the head that's in it now and chalk the other one up to experience.) I plan to get one of Mike's aluminum heads to run a triple Weber DCOE setup as soon as they are available. Until then I've got to rejet the Weber 38 that's on it now to make sure 1 and 6 aren't too lean for this CR. Anybody got any other suggestions? Thanks in advance.
-Joey
A
Anonymous
Guest
Use the shape of the bore (not the gasket) and scribe on the head where the cylinder wall is (have to come up from bootom through piston hole)
Then use a carbide burr to open the chamber around each vavle - this is called "unshrouding" and allows air to flow around the head of the valve with more ease. It removes some chamber material (good for you) and helps airflow a lot.
Use a junk valve so you don't accidentally nick the seats.
Then use a carbide burr to open the chamber around each vavle - this is called "unshrouding" and allows air to flow around the head of the valve with more ease. It removes some chamber material (good for you) and helps airflow a lot.
Use a junk valve so you don't accidentally nick the seats.
What Linc said. Go to Geezer's website and there should be some pictures of the area he ground away, but basically you are laying back the walls on the spark plug side of the chamber so that more air can flow in and out. It makes the chamber larger and helps the engine breath. The only trick is to be consistent so they all end up about the same.
Howdy again Joey:
I'm curious. How much did the machinist have to deck the block to achieve zero deck height? Most 250 have between .100" and .150" of deck height stock. That's alot to machine off.
What head gasket are you using? According to my calculations the Felpro composite is the thickests at about .050" - .055" compressed.
The small bore and zero deck height are in your favor for avoiding pre-ignition. Be sure to polish the chambers, valve and piston faces. Polished and smoothed surfaces in the combustion chambers are less likely to create hot spots and less likely to allow carbon to be deposited.
With a 250 taken to zero deck height it is best to start with a 62 cc chamber head, milled only enough to get it flat and true, and then unshroud the chambers to your goal CR.
What was your goal CR for this engine?
What cam are you using? A little more duration than stock will help to lessen cylinder pressures.
I hope you used washers under the head bolts.
Adios, David
I'm curious. How much did the machinist have to deck the block to achieve zero deck height? Most 250 have between .100" and .150" of deck height stock. That's alot to machine off.
What head gasket are you using? According to my calculations the Felpro composite is the thickests at about .050" - .055" compressed.
The small bore and zero deck height are in your favor for avoiding pre-ignition. Be sure to polish the chambers, valve and piston faces. Polished and smoothed surfaces in the combustion chambers are less likely to create hot spots and less likely to allow carbon to be deposited.
With a 250 taken to zero deck height it is best to start with a 62 cc chamber head, milled only enough to get it flat and true, and then unshroud the chambers to your goal CR.
What was your goal CR for this engine?
What cam are you using? A little more duration than stock will help to lessen cylinder pressures.
I hope you used washers under the head bolts.
Adios, David
A
Anonymous
Guest
CZLN6":1j6l0gg5 said:How much did the machinist have to deck the block to achieve zero deck height? Most 250 have between .100" and .150" of deck height stock. That's alot to machine off.
Good point. Sounds unrealistic.
The cam I ordered from Mike is the 264/274 with 112 lobe center. I'll check tomorrow with the machinist to see if the block was truly zero decked. Hopefully you're right and he didn't take that much material off. The engine has not been reassembled yet so some of the additional head work could be done if needed. I did ask him to polish up the chamber to minimize any hot spots.
The gasket I originally ordered was the thin crush gasket (.038) Mike offers, in my message to him I said I might need the thicker one (.052). I was expecting to get around 10:1 or 10.5:1 after the work. I should have run the calculations beforehand, my mistake.
I don't mind running 93 octane as that's what I'm running in my current worn out engine (timing well advanced). Is anybody else out there close to this CR?
-Joey
The gasket I originally ordered was the thin crush gasket (.038) Mike offers, in my message to him I said I might need the thicker one (.052). I was expecting to get around 10:1 or 10.5:1 after the work. I should have run the calculations beforehand, my mistake.
I don't mind running 93 octane as that's what I'm running in my current worn out engine (timing well advanced). Is anybody else out there close to this CR?
-Joey
A
Anonymous
Guest
A basic alcohol/water injection kit would fix any ping problems.
Howdy gain Joey:
A couple more thoughts.
What size overbore did you go to? Did you measure the pin height of the new pistons compared to the original. Most replacement pistons are down an additional .005" over stock specs. Did your machinist measure for deck height using the old pistons or the new, with the new bearings? That will make a slight difference.
I'm looking forward to the exact details of the new block and piston dimensions.
What head casting are you working with? Did you measure each chamber for cc volume? If you did good. If you didn't it is a good idea; to know what you actually have, and how much they vary. If they vary much, more than 1 cc, it is a good idea to do some grinding to match all to the largest. The eyelid above the intake valves is a good place to take material.
That cam will be a big plus in reducing cylinder pressure.
Hold off on selecting the head gasket until all the other dimensions are in. .038" is a better gasket compressed thickness for quench, if you can stand the extra CR.
Adios, David
A couple more thoughts.
What size overbore did you go to? Did you measure the pin height of the new pistons compared to the original. Most replacement pistons are down an additional .005" over stock specs. Did your machinist measure for deck height using the old pistons or the new, with the new bearings? That will make a slight difference.
I'm looking forward to the exact details of the new block and piston dimensions.
What head casting are you working with? Did you measure each chamber for cc volume? If you did good. If you didn't it is a good idea; to know what you actually have, and how much they vary. If they vary much, more than 1 cc, it is a good idea to do some grinding to match all to the largest. The eyelid above the intake valves is a good place to take material.
That cam will be a big plus in reducing cylinder pressure.
Hold off on selecting the head gasket until all the other dimensions are in. .038" is a better gasket compressed thickness for quench, if you can stand the extra CR.
Adios, David
First off thanks to you guys who have the patience to put up with an idiot like me. And I do feel like an idiot for not doing my homework, not doing the MATH, before I had this work done. I've got enough age and experience to know better...
The shortblock I got from ebay for $225 already rebuilt. It was bored .030 over and since I was putting a cam in it I had it taken apart just make sure all was OK. So, David, the machine shop zero decked to the new pistons that were in it. Those guys are getting tired of me too, ("Hey Doug, it's the dumbass with the Ford 6 on the phone again!") As soon as it gets back from the machine shop, the mechanic helping me do the swap and I will measure each chamber and also verify that the block is decked to these pistons. The head (also from ebay $50 rebuilt) was an early 80s casting so the original chamber size should be 62 ccs, now down to 51ccs. The guy only measured one though.
It was not Mike at FSPP that told me to do both, it was the guys at Clifford. Yeah I know everybody just rolled their eyes into next week. I know what the general consensus is regarding their customer sevice is, but what about their actual knowlege? The guys there say that this was the standard practice on the Ford 250 when they were doing builds and the numbers came from Jack Clifford's research. They also say they know the math comes up looking really high but the engines work. ????
Could they be that far out of line with reality?
Basically this thing will work or it won't. If what they say is true, then great. If not then I've got several work arounds until the alloy heads are available from FSPP. I also fly so I've got access to 100 octane low lead. I figure if it knocks with 93 octane I can put a few gallons of the 100 in to bring it up to where it won't knock. $3.68 per gallon but I can't just fill up there because no highway tax is paid at that price.
I really like Linc's idea of alcohol/water injection and that may be my first choice. I've also thought about running 185 proof ethanol as the fuel as an experiment and an alternative to gasoline. The plan was to do it in my Studebaker pickup (flathead inline 6) but if suddenly I've got a Mustang with a 11.5:1 ratio and a Weber carb that is easily rejetted and the jets on hand....
I'll also have the head that's in there now that I can measure FIRST, and then mill to a 10:1 ratio which is about where I was aiming for. I once had a Honda CRX HF model that had a 10:1 1300 cc carburetted engine that got 67 MPG on the highway. That car has been on my mind lately.
Thanks again for the advice and I promise not to screw up this bad again. I'll let you guys know more once I get it back in my hands.
-Joey
The shortblock I got from ebay for $225 already rebuilt. It was bored .030 over and since I was putting a cam in it I had it taken apart just make sure all was OK. So, David, the machine shop zero decked to the new pistons that were in it. Those guys are getting tired of me too, ("Hey Doug, it's the dumbass with the Ford 6 on the phone again!") As soon as it gets back from the machine shop, the mechanic helping me do the swap and I will measure each chamber and also verify that the block is decked to these pistons. The head (also from ebay $50 rebuilt) was an early 80s casting so the original chamber size should be 62 ccs, now down to 51ccs. The guy only measured one though.
It was not Mike at FSPP that told me to do both, it was the guys at Clifford. Yeah I know everybody just rolled their eyes into next week. I know what the general consensus is regarding their customer sevice is, but what about their actual knowlege? The guys there say that this was the standard practice on the Ford 250 when they were doing builds and the numbers came from Jack Clifford's research. They also say they know the math comes up looking really high but the engines work. ????
Could they be that far out of line with reality?
Basically this thing will work or it won't. If what they say is true, then great. If not then I've got several work arounds until the alloy heads are available from FSPP. I also fly so I've got access to 100 octane low lead. I figure if it knocks with 93 octane I can put a few gallons of the 100 in to bring it up to where it won't knock. $3.68 per gallon but I can't just fill up there because no highway tax is paid at that price.
I really like Linc's idea of alcohol/water injection and that may be my first choice. I've also thought about running 185 proof ethanol as the fuel as an experiment and an alternative to gasoline. The plan was to do it in my Studebaker pickup (flathead inline 6) but if suddenly I've got a Mustang with a 11.5:1 ratio and a Weber carb that is easily rejetted and the jets on hand....
I'll also have the head that's in there now that I can measure FIRST, and then mill to a 10:1 ratio which is about where I was aiming for. I once had a Honda CRX HF model that had a 10:1 1300 cc carburetted engine that got 67 MPG on the highway. That car has been on my mind lately.
Thanks again for the advice and I promise not to screw up this bad again. I'll let you guys know more once I get it back in my hands.
-Joey
A
Anonymous
Guest
The people at Clifford's were right on--for 1969-- when 100+octane leaded gas was pump gas and cost 31.9 a gallon. Those kind of comp ratio's were not a problem with just a little prep work. That was then now ain't. A little head work and a big head gasket should get you back in modern gas life pretty easily though. Course you could add a bigger cam etc etc etc oops there's another $1000.
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