Pistons

[Anonymous]

I think I mentioned this before but I have to replace my rings. I was considering an upgrade to my current dished pistons while I have the motor apart.

According to the Falcon Performance Handbook (pg. 31) I can use either pistons from a 141 CID or the 255 CID in my block to raise the compression. But the manual says the 255 pistons can be used in a 250 but doesn't say a 200. My question is this, can the 255 pistons be used in a 200 block (my block year is 68 and head is a 77)?

Thanks in advance,

Chris

 

[Mustangaroo]

No the 255 will not fit, but you can use the HSC Tempo flat top pistons! There the same size as the stock 200 pistons but will help increase compression! The 255 pistion are taller and would pop out the top of your block with out you decking it!

 

[CZLN6]

Howdy Again Chris:

The stock 200/250 piston has a pin height of 1.50" The 255 V8 pistons have a pin height of 1.585". The reason they work so well in a 250 is that they take up some of the .150" of deck height in those blocks. A typical 200 will have .025" deck height, a composite gasket will add another .050". That means, if the 255 V8 piston is truley .085" taller, it would stick out of the block by .010". That could be exciting.

But, I must ask, what is your goal? If you're doing a complete rebuild, I'd recommend the cheaper, and more efficient small dish 200/250 pistons. Deck the block to zero deck height with a composite head gasket and enjoy a cheaper, more efficient way to go. Once you've decide on the dimensions of the block, you mill the head to your desired CR.

Just be sure to clean the head bolt holes out and use a hardened washer on the bolts.

That's my two cents.

Adios, David

 

[Anlushac11]

8)

Wont the piston actually be sticking .060" out of the hole?

If the deck height clearance is .025" and the piston is .085" higher it sticks out more than .010". The head gasket would take up the dfference but is it safe to stick the piston that far out of the bore?

I was under impression it was not good to have piston sticking up out of the bore. If this is not a problem then I should be able to use the 305 Chevy pistons right?

Just trying to get my facts straight.

 

[xctasy]

Depends on what your doing with your engine! Usually, 25 thou below block face is best with a cast piston in an engine that likes to rev. If valve cuts exist in the piston, and the valves are canted or inclined from the horizontal axis of the piston, sometimes you can close it. Get too close to a valve, and you'll reduce your compression ratio more than you can afford!

(Technically, a zero deck register to piston tdc register is the ideal. A flat top piston or raised dome piston then should have a relief cut to clear the chombustion chamber, and a central trough excavated ( ah, sorry, milled...hard day on the digger today!) to provide flame travel, idealy from the plug to the exhast. Dunno whos got the bucks to check all that with plastercene, and then mill six pistons to suit!)

The 305 Chevy piston ranges from 1.531 to 1.563 inches tall from wrist pin to the top. If its the shallower 1.531 tall number, you may get away with a stock size, 3.736 inch, this piston in a 56 thou bored 200 would be pretty close to touching the head. You'd have to ream the rod to fit a wrist pin 15 thou bigger. All good for another 6 cubes!

The check is blue print rod length, plus blue print stroke divided by two. Then subtract this from the factory blue print depth. Then throw that away and just measure the deck register to piston tdc register with a dial gauge around the anulus of the piston.

I always thought the 200 had a 4.71 inch centre to centre rod. The throw is half the stroke, 3.126/2. Subtract these from 7.808 inches, and you get a 1.535 clear area. If a stock 200 is 1.50 inches, then you got 35 thou clear. A 1.531 Chevy 305 stock piston is around four thou off hitting the chamber.

I used some 229/305 forged pistons for my engine. I felt milling them was a better idea, and the pistons was cleared for a stock chamber so it didn't hit any thing. I'm not sure if I'd work a non-forged piston, I'm not that brave!

 

[Anonymous]

But, I must ask, what is your goal?

Well David.... My goal for this engine is to get the most out of it for the most amount of money I spend on it (if that makes sense).

No, seriously, I need to rebuild the engine. I have had a bit of a smoking problem, carburetor issues, timing, etc. sense I've purchased the vehicle. I just really can't do much during winter (no garage, yet ) yet I need to plan for spring.

I know I am going to replace the rings first chance I get and then go from there with everything else. I thought sense I had to replace the rings that I would also replace the pistons. I thought why not?! Then I got to reading your handbook again and decided that I could only improve my engine if I go with better pistons (just my thoughts).

I think I've said this before the forum last went down, but the engine was partially rebuild before I bought the car. Everything from the head up (water pump, dizzy, carb, valves, etc.) had been replaced or retooled to OEM specifications. Now that I've had it for a few months and have driven it for awhile I now realize that a COMPLETE rebuild can only help.

Sorry for blabbing but I thought it might help to understand my background a little more while still trying to answer your question.

Thanks for answering my question!

-Chris[/code]

 

[CZLN6]

Howdy Back All:

Chris- "My goal for this engine is to get the most out of it for the most amount of money I spend on it". Our goal is to get the most out of an engine for the least amount of money.

Given your goal, my reccommend is still to use a cast replacement small dish piston and deck the block to zero, then mill your head to reach your desired CR. In our engines the small dish piston has several advantages over a flattop piston; resistance to knock, more power, more efficient combustion and cheaper. I'll run some numbers on the Compression calculator and get back to you

Anlushac11- I included the thickness of the gasket in the term "sticks out of the block". Sorry for the confusion. And, no, it is not unusual for race engine builders to have a positive deck height, where the piston actually sticks out of the block. The risks are piston to head deck interference, valve to piston clearance, excessive compression ring heat and excessive compression. Consequently, it is not a good idea for a street type, daily driver engine.

The Chevy 305 piston may have some potential, but only if it were in stronger materials. Where as 200/250 pistons aren't even available in Hypereutectic materials, and forged are ridiculously expensive, Chevy 305 pistons are available in these materials and, relatively cheaper. Ring options and selection is also greater. The down side is boring a thin wall casting block, such as our 200/250s .060". I know that it has/is done, but at high performance/pressure levels, I think that it is pushing the limits.

I'm thinking my next engine will have a cast flattop piston, but with a "D" shaped dish milled into the top that mirrors the chamber in the head. And I want to try some of the high tech piston coatings. The goal is to maintain the highest quench to bore ratio, enjoy the advantages of a dished piston, lighter and the smallest overbore necessary.

Adios, David

[/b][/quote]

 

[Anonymous]

David:

Sorry for the confusion. I just knew my answer for your goal question just didn't sound right.

What I meant to say is this - I want to get the most of this engine. Period. But not brake the bank in the process.

That being said, what small dish piston do you recommend (year, from what block, etc.)? I know you said 200 / 250 but I find it easier for me to have a name for a car when I buy my parts (sorry, limited knowledge).

Thanks again!

-Chris

 

[CZLN6]

Howdy Chris:

The Silvolite catalog lists a small dish cast replacement piston for FoMoCo 200/250, all years, with a 6.5CC dish as an #1120. You'll have to specify your overbore after you disassemble, assess bore wear, and determine the amount of bore to clean up the cylinder walls. I've never ask for a piston by year and make, so I can't help you there.

You may find that the machinist you work with can get a kit that will include everthing, including the pistons, for less money then you can buy all you need seperately. Badger is another supplier of pistons. I don't have there catalog.

What's the casting # on your '77 head?

Adios, David

 

[CZLN6]

Howdy Again:

Assuming a zero deck height, a head gasket with a compressed thickness of .050", a .030" ob, and a 55 cc chamber you'd be at 9.2:1 CR. That's just about right for 93 octane gas. At this level it would be wise for you to polish the chamber too, as cheap insurance.

If your '77 head is stock it will have about 62 cc chambers. A mill cut of .050" will get you to aproximately 52 cc chambers.

Be sure to measure for deck height with the new parts in place. Replacement pistons are built down a bit to compensate for machining. Measure twice- cut once. Measure again.

Assuming a well tuned engine; carb, head, cam, and exhaust, capable of flowing 211 cfm at 4,500 rpm, you'll be looking at about 125 hp. At this level it would be wise to have the engine balanced.

Adios, David

 

[Anonymous]

David,

The casting number off my head is :

D7BE 6080 AB


-Chris

 

[CZLN6]

Howdy Chris:

Great! the D7BE-AB is the best possible '77 head. It should ber a larger volume, flat-top log. With the block decked to zero, you'll have a great combination.

I believe you said you had the head rebuilt before installation. What did the rebuild include?

What will/are you using for a carburetor? What cam? Exhaust?

Adios, David

 

[Anonymous]

I believe you said you had the head rebuilt before installation. What did the rebuild include?

What will/are you using for a carburetor? What cam? Exhaust?

Yes, I had the head rebuilt before I took ownership of the car. The last owner said there where many problems with the engine and thought a complete rebuild was in order. I agreed but only ended up rebuilding the head (time and money was an issue). I had everything cleaned and retooled to factory specifications. New valves and springs where installed. A bit of an unshroading job was also performed at the same time (just to get rid of some burrs). After all was done, I had the head milled slightly to create a nice uniform surface (less than .040 IIRC).

That was the extent of the engine rebuild besides replacing all the hoses and some of the wiring. Plus a little engine paint.

I still have the stock exhaust manifold, exhaust and a rebuild Carter YF carburetor plus same year (give or take a few) dual vacuum dizzy. The distributors advance (not retard) is plugged to the carburetor. All other ports are plugged except the line from the transmission to the manifold vacuum source.

I am currently working on a carburetor and adapter setup. I am rebuilding a Motorcraft 2150 '77 for this procedure. I had a problem with the adapter mating to the carburetor but have solved this problem with using an aftermarket space.

Finally, the cam is stock as well. I want to put in an aftermarket performance cam but I haven't decided which one or what brand to go with for my setup.

I hope this wasn't too much info.

Thanks!

-Chris

 

[Anlushac11]

I used some 229/305 forged pistons for my engine. I felt milling them was a better idea, and the pistons was cleared for a stock chamber so it didn't hit any thing. I'm not sure if I'd work a non-forged piston, I'm not that brave!

So you did mill the top of the pistons?

I wanted to go that route but couldnt find a good answer whether that was damaging to the piston. I know thats the one place you dont want to take material off but I was only planning to take .020"-.030" off. I want to use forged pistons in case I decide to turbo the motor.

 

[xctasy]

My advice is to chat with a good piston specialist. When I talked to my local Ford engineer, he asked me if I knew more than the FoMoCo? The point is, if you want to dabble in the black art of piston swaps, you must ASBSOLUTELY know what your doing. I'm not there yet becasue my little project I6 build isn't on the road, and I don't have the cash to correct an expensive mess up. Heres what I found about the Chevy pistons:-

There are two types of 229V6/305V8 forged piston. Light duty, and heavy duty. Some will handle a cut of 60 thou or more without weakening, others will be compromised strength wise. Because my 229V6/305V8 Chevy pistons were going into an odd ball 250 block with Aussie 3.3/200 long rods and a Aussie/Argentina 3.6/221 crank, I had a situation where the normal 1.531 inch piston was 56 thou out of my cylinder block. OOOCH!

Calcs were 6.275 inch rods, plus 3.46 stroke halved, all subtracted from a 9.48 inch deck register. That leaves only 1.475 inches of piston top to wrist pin space...less if the deck is 9.469 inches like most of your US 250's. I may have had to shave 67 thou off to get the piston level on that block. And remeber, that a six needs more room for rod and piston streatch at 4000 to 5000 rpm range most I6's max out at. 25 THOU BELOW THE BLOCK IS SAFE. (I'm told the latest Gen iii Holden has a plus 6 thou piston/block protrusion with a semi cast piston, but the've spent millions getting the piston to dove tail in with the alloy heads on a stiff alloy block)

The solution for me was to mill 60 thou, which is likely to be too much on a cast piston. On a 200, a 30 thou mill would be fine, and would put a Chevy piston back in the block where it belongs. I can't rationalize it, 30 thou is not much to mill a cast piston, but 60 or 70 thou is a lot more and I'd be pretty scared lopping off that much. Could excecute a good piston!

The thing is, most cast and cheeper forged pistons are optimised designs which may have little margin for 60 though of shaving. After spending out on some left over Chevy pistons, which are rare and expensive down here, I wanted the security of a good forging. My pistons are old TRW forgings, can't remember the exact line number. Down here, theres a guy in Christchurch, South Island, who does custom machining of imported US Ross forged blanks, and he says some off the shelf forgings are not thick engough to get savage with a milling machine.