250 "Freshen Up"

So I started the Falcon up the other day and it immedeately started running really bad. I found that it had a dead #3 cylinder caused by mechanical damage to the plug I used a bore scope and magnet to remove two small slightly curved rectangles of metal out. Further scope inspection showed a nice half crater along the edge of the piston. I'm deducing that the metal pieces are my top ring breaking as it fatigues from the non supported area where the crater is. I have no history on this engine other than its a 74 250. I found on Craigslist a 72 250 from a wrecked Mustang with 77k on the odometer. I have it disassembled on the stand right now. The bottom end looks really good for 77k no scuffing on the piston skirts. Cylinders all look good, cam is fine, head has been replaced with 69 head according to the casting #, Bearings all look good. I still have to mic everything to insure its all within specs. Then I plan to hone it and install new rings, bearings, oil pump and timing set. I know the 72 had the lowest compression and least HP rating. Will the 69 head help get me a little more power and should I consider in investing in a mild cam and lifters. Its a daily driver 62 Falcon, I'm a motorhead that likes to go fast but wants good fuel economy too.

The bottom end looks really good for 77k no scuffing on the piston skirts. Cylinders all look good, cam is fine, head has been replaced with 69 head according to the casting #, Bearings all look good.

The anvil strong small six will often stand some abuse and still be servicable. My current turbo 250 six project had odd damage to top of one piston like detonation pockmarks ( @ 30K engine). A machinist friend saw it thought a spark plug let go or nut dropped in carb. He recommended pulling piston to check cylinder, rings and skirts. Nothing else looked affected and so far runs fine after re-assembly.

250 from initial Mustang application '69? head could be OEM I think, what's 250 block number? .

Milling the head to accommodate modern composite head gasket thickness and finding good-running carb' suitable should meet basic performance/economy demands for a daily driver that likes to go fast but wants good fuel economy too., A freshened 250 built to your needs' is a good project for pictures here. 8)

My redundant opinion is that engine upgrades need to be matched to a final Gear Ratio suitable for modern 'daily driver' needs. If any distance or Interstate travel is planned, concern about HiWay cruise RPM is critical. 70's cars used tall-geared rears with the 1:1 trannys with economy and performance sacrifices. For performance and economy, OD trannys' are better suited to the torquey small block six' powerband.

have fun

The head has a machine shop overheat button in the rear freeze plug and has that rebuilt look to it. The head casting lacks the patina that the valve train and hardware has. IIRC head = C9DE and block = D2CE. The coil bracket had the factory aluminum tag stating 72 250 MT.

OK so I took the crtical measurements and I need to bore it .020" over. Crank, cam and lifters are good. Pistons are still within specs but the cylinders are .002" oval at the bottoms. I have a question, since its going to the machine shop should I consider decking it to 0 deck height. If so can I measure using the stock pistons and trust the new ones to be the same just bigger diameter. Would it get me noticeable power increase? Would it cost in fuel economy? Would I still be able to run 87 octane? I have a little time to mull it over while I wait for tax refund and then engine kit.

Almost forgot. I'm running a Mustang II 8" with 3.00 gears 205/70 14s and a C4. The 250 is running an RBS carb and stock exhaust manifold. It gets 17MPG when I don't beat on it.

cobraguy":y4vwi22a said:

OK so I took the crtical measurements and I need to bore it .020" over. Crank, cam and lifters are good. Pistons are still within specs but the cylinders are .002" oval at the bottoms. I have a question, since its going to the machine shop should I consider decking it to 0 deck height. If so can I measure using the stock pistons and trust the new ones to be the same just bigger diameter. Would it get me noticeable power increase? Would it cost in fuel economy? Would I still be able to run 87 octane? I have a little time to mull it over while I wait for tax refund and then engine kit.

Click to expand...

If You zero deck it you probably will end up with too high of a compression ratio for 87 octane fuel with a stock type piston and a milled down 1969 head. Have you measured the 69 head casting's chamber size (CC) and measured your deck height yet to calculate your current compression ratio? As a general rule the new stock replacement pistons have a little less deck height then standard size pistons if you know what brand you will get you can look up the specs in their catalog. Sounds like a very good combo and quick (the 250 with a C4 and 3:00 gears) in an early Falcon, good luck on the build

Deleted-not relavent
Myway

I have not measured the head. Where do I take the measurement (head surface to valve cover surface?) and what should I be looking for

Keep in mind a 250 has about a .140 deck height, I would not want to mill that much.

Ignore that it's a brand X V8 head in link below, but its still the same method that is used to measure most any combustion chamber in any cylinder head. Once you have that measurement, along with the head gasket CC, bore size, stroke length, the deck height, with the piston dish CC volume if any, you can calculate the true Compression Ratio. Good luck

CC a cylinder head
https://m.youtube.com/watch?v=V7V40ZWNgCo

Comp. Calculator
https://www.rbracing-rsr.com/compstaticcalc.html

cobraguy":3flyshrs said:

I have not measured the head. Where do I take the measurement (head surface to valve cover surface?) and what should I be looking for

Click to expand...

if ... you can be sure head has NEVER been touched, you can use OEM figures. Otherwise the only reliable way is to measure the size of the heads' combustion chamber volume . The simple but accurate way is to fill combustion chamber with a measured fluid amount. typically machine work should cut head @.030 - 070 for composite gasket and CR boost if planned.

http://www.classicinlines.com/SmallSixS ... #SSgeneral


; this head is OEM Maverick 250 verified at @ 62 cc chambers with OEM deck height and head not re-surfaced - with "modern" composite gasket at @ .050" for doggy static CR @ 7.8:1 - not good for non-turbo. (used for low compression turbo six build)

. .




have fun

Thanks for the links bubba. I will play with that calculator and see if I can't dial in a deck height to land at around 8.5 -9.0:1 CR. Would I start killing my gas mileage putting a bigger cam in it?

cobraguy":2ommc5lv said:

Thanks for the links bubba. I will play with that calculator and see if I can't dial in a deck height to land at around 8.5 -9.0:1 CR. Would I start killing my gas mileage putting a bigger cam in it?

Click to expand...

Stock my 77 Maverick 250 had 8.0 C.R. C4 with 3:00 gears it's a heavy car 3000 + pounds. The stock cam stopped pulling around 70 MPH. In my OPINION a little more cam and CR would help it and should not hurt MPG to much.

Sorry Cobraguy -my mind deviated to the 200 relationships and confused the whole issue- as the more conscious posts indicated, your starting out with a piston about an 1/8 th of an inch in the hole. The point I started out to make is that cast replacement pistons are shorter than cataloged in most cases and with a thicker head gasket you will end up with considerably less comp. Do the calculations the guys are indicating and see what steps can be taken.
That 255 ford V8 piston that is a .085 taller might not be that tall in a replacement?? and could be easily be turned shorter to get where you want to be.
Forget the quench as without some head work and piston machining that could get you close to 11 to 1.
Apologize for making the water muddy

I ysed a 10ml syringe and got 47ml/cc for the chamber and 7ml/cc for the dish in the stock piston. Deck height .145 Head gasket .045. Bore 3.700 at .020 over and 3.910 stroke equals 8.87:1 if all I do is bore .020 over and new pistons are just .020 bigger. Decking .020 gets me to 9.2:1 as long as new pistons....... So it looks like I get my rebuild kit first and measure the dish and piston height and recalculate. Thanks for the help In the past I've always just threw the parts together and hoped for the best. This time I feel like I will know exactly what I want the machine shop to do. I would like to get the CR close to the upper limit for 87 octane. Where would that be?

The CR is a little more complicated. Your static CR as calculated will always be higher than your dynamic CR, due to (and depending on) your cam profile and how well your head breathes.

At 47cc the head has been mill or it is a late model 170 head. does it look like power bands head or does the chamber look larger? or your measurements are off.

Powerband have not seen a 250 head with that small of chamber , looks like a 170. maybe I have not seen a early 250 head.

drag-200stang":2rkdlgoc said:

Powerband have not seen a 250 head with that small of chamber , looks like a 170. maybe I have not seen a early 250 head.

Click to expand...

... you're good, I checked my pictures and you are correct!.

The head in the measuring pic' is from a 1971 Maverick 170 and has @ 52cc chambers. The picture was mixed up with the head I verified at 62cc's for the 250 turbo project.

here's the straight poop:
viewtopic.php?f=1&t=71133&p=546047&hilit=chamber+picture#p546047


have fun

I would believe that the head has been milled. My measurements may be off a little off due to where I put the syringe plunger on the 10ml line and small bubbles in the syringe but not a whole lot. I can always recheck.