351 windsor head question

[Miker]

?:?
I picked up a '94 f-350 351W and don't intend to tear it down more than I have to as it was a runner in the truck with 62K miles. Can anyone tell me what the compression on this puppy should be and more importantly what size cc's should the factory heads have.
And is there any rule of thumb (sounds weird typing that phrase) that says for this or that many cc's you do away with i.e smaller chamber heads, milled heads etc., it bumps compression up by X factor??

Many Thanks!!

 

[cs_88]

I have read before that if you mill heads .030" it will raise your compression about half a point. By the way that motor should have E7TE heads.

 

[Miker]

does anyone know??

 

[badmuttstang]

From 1985 on their really is not much difrent on 302 and 351w as far as chamber size but as far as yours check your casting numbers like cs_88 said it should be E7TE or E6AE/E6TE which would be a 60cc to 64cc chamber size. If your lucky the casting is F3ZE/F4ZE or F3ZZ-A/F4ZZ-A these are cobra gt-40. If you do mill just make sure to check valve to piston clearance if you are also running a larger cam or 1.7 rocker arms instead of 1.6 hope this helps.

 

[badmuttstang]

sorry forgot your stock compression ratio sould be 9.0:1

 

[Broncobowsher]

Typically 8.8:1 compression ratio. But I have seen a few good sources that I can't find right now that show the 250/350 trucks got 8.3:1 compression and slightly derated power output.

 

[barronj]

I have a 94 F350 351 & my pistons were DISHED! I would be surprised if it were 8.8:1 (happy, really)

 

[broncnaz]

I'd also say it should have E7 heads with 64cc chambers.
Usually for every .005 removed you lower the chamber CC's by 1. And every 5 cc smaller you gain 1 full point in compression. So Take about .030 off the heads and gain at least a full point.
Of course this all depends on starting combustion chamber size and shape.
I wouldnt bother milling the heads on a engine that you dont really intend on tearing down. While higher compression can be good to have as it makes cam choices broader if your not swapping cams that need the higher compression you really wont gain anything.
Read a article a few years ago about compression ratios and the differance in 1 full point in compression ratio was only 10hp with the same cam.
If you have 8.8-1 now I really wouldnt bother. 8.3 or so I might think about it if I was running a cam that needed 8.5-1 or better compression

 

[Hal9000]

Do a google search for compression ratio calculations. They're pretty easy to do and if you play around, you can figure out exactly how much changing your combustion chamber size will affect compression ratio of your engine.

 

[Hal9000]

Here, try this. At the very least, it's good practice and will help you out when you build/modify your next engine.

For what you're doing, you can just assume the deck volume is 0 to simplify the calculation. It won't give you the actual compression ratio, but will tell you how much the CR will go up by reducing the combustion chamber size.

From http://www.greatplainsas.com/icompratio.html

1. Determine the displacement of your engine. Displacement formula is:

BORE X BORE X STROKE X .0031416 = DISPLACEMENT

Example: 92 x 92 x 82 x .0031416 = 2180cc

2. Determine the swept volume of one cylinder:

Example: 2180cc divided by 4 = 545cc

3. Determine the deck volume of each cylinder. The deck volume is the distance from the top center of the piston to the top of the cylinder when the piston is at top dead center. Measurement is made in thousandths.

Example: on cylinder #1 you measure and find you have .020" deck height.

BORE X BORE X DECK HEIGHT X .01996 = CC"s

Example: 92 x 92 x .020" x .01996 = 3.378cc's

Measure each cylinder.

4. Measure the volume in each cylinder head. To do this, use a piece of plexiglass cut to fit in the cylinder head to cylinder mating area. Drill a 1/4" hole in the center of the plexiglass. Lightly grease the edge of the plexiglass and install in the head. (Spark plug and valves have to be installed) with a syringe graduated in cc's fill the cylinder head chamber up with a light weight oil. Record the measurements. Repeat for other three chambers. Average cc volume of a new head chamber is between 47 and 51 cc's.

5. You now have all the measurements to determine your compression ratio.

one cylinder swept volume + deck cc + head cc

deck cc + head cc

Example: 545 + 3.378 + 48 = 596.378

3.378 + 48 = 51.378 = 11.6:1

In this example, 11.6:1 is the actual unadjusted compression ratio for one cylinder. Add cylinder shim thickness which will increase the deck cc volume and refigure compression ratio. This must be done for all cylinders. Average deck height shim for use on a 2180cc engine will be between .150" and .185". We use a .177" shim for AVGAS and a .216" or .256" shim for unleaded premium auto fuel. Lower is better for increased engine life and fewer valve related problems.

 

[barronj]

Typically 8.8:1 compression ratio. But I have seen a few good sources that I can't find right now that show the 250/350 trucks got 8.3:1 compression and slightly derated power output.

When I was rebuilding mine, I got my first set of rings from Autozone, perfect fit the first time. As I was assembling, I boogered one of the oil control rings, and had to source out new rings. Not wanting to pay the $80 for a full set of rings, I shopped every other autoparts store in town. O'Reileys, Advance, Pep Boys, etc- none of them had the right set of rings, but all of their computers showed them to work. Apparently, there was a piston that took a metric sized ring, and pistons that took a standard size.

Is there any way to see what cc dish my pistons are by looking up the ring size application?

 

[broncnaz]

Rings have nothing to do with piston dish as rings can be used on a varity of pistons. Yes there are metric and standard rings early engines had standard rings then sometime in the 80's ford started using metric rings. Probably about the time they went from 302/351 to 5.0/5.8L. Then you can also rebuild using either the metric or standard pistons.
You'd be better off asking/searching for what size dish your year of engine came with.