Engine Build-up

[mysavioreigns]

I have been thinking a lot lately about going to a junkyard, or finding someone with one, and getting a 250. I would do a complete rebuild of it, while using my current 200 as my everyday driver - the plan would be to build this engine up, and do the whole swap (hopefully without problems) in a matter of days.

A few questions I have about availability/building/fitting:

1. Will the 250 fit all stock and everything into a mustang, or will I need new mounting? If I remember correctly, it is the same physical size - may be wrong though

2. If I got to a junkyard, how can I tell it is a 250? Any vehicles I should look at in particular?

3. Are there any certain range of years I should look for?

4. This is even crazier - is there any advantage or disadvantage to using a 250 or 200 compared to using a 200 with a 250 head?

5. How is the availability of getting all this together? I know classicinlines has a lot, but does it have it all? and, are they any other places?

 

[shetland]

The biggest issue I know of is the height. The 250 is taller and can present clearance issues in a 65-66 Mustang.
IMHO it you would be better with a 200 with a 78 or 79 250 head.
look at the posts from Mraley. He is in Arlington and has some great contacts in the area.

 

[addo]

The one thing really holding up hot 250 builds, is lack of a multi-keyway timing set. Az will have them available soon enough (I would imagine about ten weeks) but presently there are none manufactured.

Other than that, height and centre link clearance, and the deck height are main issues.

 

[CZLN6]

Howdy Back:

We've been down this road several times over the years. This is a gtreat opportunity for you to become familiar with the "Search" feature of this forum.

1. Will the 250 fit all stock and everything into a mustang, or will I need new mounting? If I remember correctly, it is the same physical size - may be wrong though.
A- The 250 is about 2" taller because of a taller block. Is is about an 1" wider at the pan. It only came with the longer waterpump and pulleys, making it about 1 1/2" longer. It has a different bell housing and mounting system.

2. If I got to a junkyard, how can I tell it is a 250? Any vehicles I should look at in particular?
A- all 250 have a low mount starter. The starter is located below the oil pan mating line. 250 water pumps are fastened to the block with 4 bolts. 144. 170 and 200s use three bolts to fasten the pump to the block.

3. Are there any certain range of years I should look for?
A- The 1st 250s arrived in 1969 in Mavericks and Comets. Later in Granadas and Monarchs. They were produced until 1980. Earlier years have a more performance friendly block because of later cam timing manipulation. Later years have a better head and electronic ignition.

4. This is even crazier - is there any advantage or disadvantage to using a 250 or 200 compared to using a 200 with a 250 head?
A- Clearly an additional 50 cubic inches is an advantage in a performance application. I think it's called the "Dolly Parton Principle". Bigger is better. Unfortunately there are several Handicaps to be overcome with a 250 that don't exist with a 200.

1st is an enormous deck height. The pistons are typically down in the block .125" to .150". For a more efficient combustion, ideally that dimension should be zero. That can be overcome by using the 255 V8 pistons which are a direct swap and are .85" taller in pin height. The block can be machined, or decked to zero. The problem now is an excessively high compressions ratio. That can be dealt with by machining a dish into the V8 pistons to match the combustion chambers, or relieveing, opening up and reshaping the combustion chambers- OR a combination of both. Deck height effects the quench effect and is important in controlling knock and combustion efficiency.

2nd is the lack of a premium quality cam timing set. The best is to use a set from '69 - '71. It will be straight up. All other years advance the cam timing.

A swap to a later 200 is definitely easier.

5. How is the availability of getting all this together? I know classicinlines has a lot, but does it have it all? and, are they any other places?
A- It would be best to find a donor vehicle for everything from the aircleaner to the oil pan, and from the fan to the driveshaft. I'd look for a '77 to '80 Granada or Monarch with the tranny you want and start building from there.

FYI- 200 and 250 heads are basically identical. Best heads are D7xx (casting code found on the intake log behind the carb.)and later. They have the largest valves and hardened valve seats. They have a 1.75" carb hole.

Sorry to be so long in answering, but as always, the devil is in the details.

Hope that helps.

Adios, David