Without a 200-250 flattop piston, how did Ford do it?

[WerbyFord]

I have a question about factory pistons & compression in the 200 and 250 and hope I can ask it clearly because the numbers out there are confusing. I read the following in FAQ:

viewtopic.php?t=1027

But it leaves open the questions:
1. If the 200cid had 9.2cr with a 52cc or so head, what happened in 1969 when its head went to 62cc? That would take the compression down to 8.2 unless something else changed - like a flattop piston instead of the 6.5cc dish.

And yet, most of the specs I see still show torque of 190ftlb just like the 9.2cr pre-1969 version, and compression does not drop to 8.3 until 1972 (though the numbers here show some scatter from 1969-1971). This implies the compression was still "up there" from 1969-71 even though the 200cid was running a 62cc head. What was done to keep the compression up? :

2. Similar question for the 250cid. With its 6.5cc dish piston, .123" deck clearance (from the Classic Inlines site, and it jives with the deck height of 9.469"), and 62cc head, I get compression of about 8.25, close enough to the 1972-up rating. But in 1969-71, the 250 was rated at 9.0cr. Was that a bogus number, and if not, then again, how did Ford do this with a 62cc head and 6.5cc piston dish? :

I figured if anybody knows this history it will be here!

 

[CNC-Dude]

What has probably happened is that some of the specs are wrong, either by a typo error or just some other form of misinformation. I know, I know, "If its on the internet, its got to be true". Well its not always that way. Just follow the rest of the specs and you see that even though it states the HP and torque remain unchanged as with the previous 9.2-1 52cc head, a red flag should tell us that this 62cc head was probably supposed to also be a 52cc head, just a typo. We all would expect that if you lost a full point of compression, that the HP and torque would also loose some amout of each, not remain the same. So I think its just an old fashion honest mistake in the data that was copied to the FAQ's, or in the original data source.

 

[WerbyFord]

CNC-Dude,
THanks for the reply.
I agree about the web, ya never know. The sources I was looking in were "Complete Ford Book", from 1972, and "Fearsome Fords" from 1982 [hard to believe I think of that one as a "new" book] - and the Classic Inlines site.

1. On the 200, there is some hint that it maybe as you guessed - maybe the 200 was 9.2cr thru 1968, and then in 1969 with the 62cc head, it was just plain 8.3cr from then on. The first appearance of a 115hp rating (down from 120hp) was in 1969. This about equals the reduction from 9.2cr to 8.3cr. Torque was still typed in as 190ftlb, didn't drop to 180ftlb in the specs til a few years later. I just wanted some confirmation on that theory if anybody has measured a 1969-71 62cc 200cid for compression.

2. On the 250cid, the March 71 Hot Rod is an article with Ak Miller, discussing the amounts to mill and use the 170 head to raise compression from 9.0 to 10.5. These guys usually knew what they were doing so I assume they measured - or trusted - the 9.0 and the 10.5. Hard to find a much better source you'd think. So that mystery remains as well - was there ever really a 9.0cr 250cid, and if so how did they do it? :

 

[CZLN6]

Howdy Werby:

That is a mystery that has eluded us since the beginning. To add to the "bad data" thread, you should add a thread on "Over zealous admen" at FoMoCo. And then add a thread on FoMoCo infamous "Empty bin" policies.

We've perused many sources, with the year and model shop manual, being the most reliable and consistant- however, there are still exceptions. For example- with the 1st assembly line appearance of the 200 engine in 1964, the advertized CR was 8.7:1. Unlikely as it may seem, castings from170 C1 & C3 are most common on '64 200 engines. These casting, that we've been able to measure typically cc out at 48 to 51. Ironically, in the '65 200s with C5 castings are rated at 9.2:1. Most of these castings measure right at 52 cc. More cc AND higher CR!!! That's not right, but it probably sounded good in the showroom.

Another anomolly is in the '69 to about '72 change-over years. In the '69 castings only the C9xx-M castings were, POSSIBLY, 62 cc. The "M" suffix castings were supposed to only be on 250 engines, however they have been found on 200s. All other C9xx suffix castings that we have been able to measure are 52. '68, '69, & '70 200 engines are rated at 8.8:1, WITH THE SAME BORE, STROKE, GASKET THICKNESS, PISTON DISH AND CHAMBER VOLUME as a '65 casting????????? The advertized CR dropped again in '71 to 8.7:1 with no apparent change in specifications. And Advertized CR dropped again in '72 & '73 to 8.3:1. The final drop to 8:1 occured in the '74 model year. From '69 to '74 things were a changin' at Dearborn. From '74 on engine specifications and advertized CR became fairly accurate- the exception being the "Calif. Emmissions" engines with large dish pistons.

The CR difference between the 200 and the 250 was in the deck height- about .025" on most 200s and .150" or so on 250s. C9 to D5 castings are frequently a suprize, somehow. That's why we recommend D7 and later castings to be able to reliably predict chamber volume, valve size, hardened valve seats and less crack prone castings.

The changes in HP and torque in this era had to do with lower CR, and the newly mandate requirements that all automobile manufactures use a "NET" HP and torque rating rather than a "Gross" rating. Net HP is measured at the rear wheels. Gross was on the dyno- sans trans, alternator, water pump and fan. So it's likely that the rating standard switch accounted for a25 - 30 hp drop while the drop in CR, from 9:1 to 8:1 accounted for the rest.

Obviously, there was more going on at FoMoCo, in those days, then accurately measuring and dividing. Ak Miller has always been a good source, but editors edit.

So, to answer you question- "Was there ever a 9:1 250 engine" from the factory? No! Not based on what we have seen, so far! With FoMoCo, i've learned to avoid words like "always" and "never".
If a C9 head casting other then an "M" suffix, it could happen. Did it ever happen from Dearborn????????????

Sorry to be so long, but it's been a long time getting this far.

Adios, David

 

[jamyers]

Remember, these were Ford's lowest-cost and probably least-engineered, economy engines.

Heck, from looking at the high-quality (NOT!) castings and clearly wide margins-of-error Ford used on these engines, my bet is that the true compression ratios are all over the place - and the variance in published data simply shows that. One guy's engine was 9.5, another was 8.2, and the guy next door's was something else.

Oh yeah - and don't forget that Ford was also making "export" engines, some with CR's as low as 6:1, iirc.

 

[fordconvert]

Wouldnt just a different pin height on the piston be a reason for different cr's?

 

[WerbyFord]

Thanks for the replies -
David, thanks for the long response. Werby's Wife is supposed to get me your book for Xmas but I might have to make it an early Xmas. After all, she ends up getting most of her Xmas presents early. Sounds like I need that book.

Fordconvert -
Yes, I wondered about pin height. A change in compression distance from 1.511 to 1.500 might explain the drop in compression of the 250cid from 8.2 down to 8.0 in about 1974. Was this trick used other times too? Don't know - but, explaining away more than a couple tenths that way seems unlikely.

Unless - - -
Jamyers, your comment about export gave me an idea.
I am totally new to the Aussie Falcon six, but somewhere "on the web" I saw a comment about a 9.380" deck height. Was this lower deck height (if it exists at all) ever used in the USA? :

I mean, it seemed odd to me that Ford would deliberately set up the hot new 250cid six, in 1969, the hottest year of the 60s, and give it an anemic .123" deck clearance, killing off any chance of quench or swirl. I know Ford did this later in the 70s - deliberately large deck clearances to create an "open chamber" - but in 1969 wouldn't they have wanted a decent (small) deck clearance for good quench? :

It then occurred to me - if the 9.380" aussie deck height block is real, then that "shorter" block, with a 62cc head, 13cc dish (the deep one), and .022 steel gasket gives - 9.0cr.
Did Ford do this (or maybe just plan to do it) and that's where they got 9.0?
Just thinking aloud. :mrgreen:

I hear the Aussie 250 is 9.5cr, I will try to find the combination that created that CR.
Perhaps we will never figure out all the history, since by now, anything could have been milled any number of times.


EDIT:
viewtopic.php?f=3&t=21001


This is a link to the alleged 9.380" deck height Aussie 250. Any chance there was an early 1969-1970 250cid USA with 9.380" deck height? : Maybe not.

 

[CZLN6]

Howdy Back:

Piston pin height is the same on 200 and 250 pistons @ 1.50". Pin height, dish shape and size and deck height are all variables that must be considered when figuring CR. One godsend in pepping up the 250 is to use pistons from a 255 V8 with a pin height of 1.585" to help reduce the huge factory dimension.

As far as FoMoCo using and/or intermixing Aussie parts into USA production- that is very likely a stretch. Unfortunately, the Aussie sixes got all kinds of performance oriented upgrades that we could only drool over.

Most likely the advertizing dept. didn't spend alot of time with the engineering dept. in the late 60's and early 70's. And the 200 and 250 engines were not a performance image by then. All good thoughts though, and it is a fun brain trip trying to figure it all out.

Adios, David

 

[early ford fan]

Howdy Back:

Piston pin height is the same on 200 and 250 pistons @ 1.50". Pin height, dish shape and size and deck height are all variables that must be considered when figuring CR. One godsend in pepping up the 250 is to use pistons from a 255 V8 with a pin height of 1.585" to help reduce the huge factory dimension.

could i use the 255 pistons in a 75 250 with a 78 head cut 60 thousands?[after checking for valve clearance]?the reason i ask is i have the head on a 170 now but want an aod so i bought a 75 250 to rebuild and swap in.what cam would give the best gas mileage with this?

 

[CZLN6]

Howdy EFFan:

Yes, you can use the 255 V8 pistons to help reduce the excessive deck height on a 250. THe combo can be farther enhanced by decking the block about .070" to zero. The down side is that CR will become too high. The ideal solution is to mill a "D" shaped dish into the top of the 255 pistons to match the shape of the combustion chambers. Since you've already milled the head for the 170 you may need to do some chamber reshaping, unshrouding and polishing to gain back a more civilized CR. We advise milling the head last on any mix and match combo to achieve the desired CR.

Let us know how it all works out.

Adios, David