351w rebuild or stroker?..

[project.65]

I have a '69 351w layin around the garage. The motor came from a tired cougar and needs a rebuild. I was planning on just doing a master rebuild and adding some nice top end parts like intake, heads, cam, dizzy, carb, ect. I was looking through some old threads and was reading how some people were building 393 strokers by simply getting a 393(3.850) crank, and 302 pistons. Does anyone have any personal experience or opinions with a build of this sort. Theres no way in hell I can afford $1200 stroker kit rite now, but was just wondering wich of the 2 coices would be better? pros & cons.
1) 351w with a master rebuild and some nice top end parts.
or...
2) 351w stroked to a 393 by changing to a 393 crank and 302 pistons and some nice top end parts.

How much of a diffrence (power/reliability) will the "budget 393 stroker w/ power parts" make compared to a nice rebuilt 351 w/ power parts ?
This will be a hard driven daily driver and Im looking for some decent power.

 

[shelbe67]

I did the stroker route, make sure you get low compresion 302 pistons I screwed up and ended up with 13:1 compression. I like the 393 stroker b/c if you have your stock crank sent out and cut for a litlle more you get a new crank. either way you need to get your rods done and new pistons so to me the stroker only makes sense.

 

[rbohm]

understand a few things;

1: the inexpensive 393 stroker cranks need to be balanced.

2: you will need to triple check the clearance between the piston and the counterweights.

3: you will need to check the clearance between the rods, and the oil pan rail and the cylinder walls, as well as the cam.

the thing about building a stroker motor is to match the motor to the intended usage. if you are looking for a mild engine that makes a ton of low end torque, the stroker is the way to go. if you want an engine that will pull hard past 6500 rpm then the stock stroke engine is the way to go. flattop pistons with 64cc chambers should net you a compression ratio around 11:1, you can further reduce this with an extra thick compressed thickness head gasket, say around .063". that should drop the compression to around 10:1. milling .003" from the tops of the pistons will lower the compression a bit as it changes the deck height. one more thing you can do is run a cam with narrower lobe centers like a 108 degree cam. this will allow the engine to bleed off more cylinder pressure at low rpm to avoid detonation, and yet will still allow the engine to pull strong to around 6000 rpm with little problem.

 

[project.65]

so 393 crank, 302 low compressions pistons, and heads. Do i use the stock rods?

 

[SoCalCruising]

Yes, on the low-buck 393, the stock rods are re-used.

 

[stonecoldtx]

You need to be really careful about the amount of space between the top of the piston and the bottom of the cylinder head--the flat area just outside of the combustion chamger.

That particular area is known as the "quench" area, and you really need to keep that distance at around .040" or less, or you will start encountering detonation issues.

I hate to disagree with someone with the credentials of rbohm, but using thicker head gaskets or milling the top of the piston to gain more deck height clearance are NOT the ways to lower compression ratio.

I recommend you go to the KB website, and check out their tech articles--they discuss this issue (and many others) in great detail--AND--they sell a hypereutectic piston that has a decent compression ratio specifically for the 392-393 stroker.

 

[danny clemens]

milling the top of the piston to gain more deck height clearance are NOT the ways to lower compression ratio.

I'm not disagreeing just wanting to learn. What would be wrong with milling the top of the pistons?

 

[brianj5600]

It moves the piston away from the head. Running the piston close to the head makes for a lot of turbulence at TDC. The movement of high speed air cools hot spots and helps vaporize any droplets of fuel. Efficiency and detonation reduction are the benefits of running the piston close to the heads.
Engines with a lot of boost or nitrous will run better with a greater distance between the head and piston. This is because the flame travel is so much faster that needs more room to spread. Some of the top nitrous motor builder use .125" or more piston/head clearance.

 

[rbohm]

You need to be really careful about the amount of space between the top of the piston and the bottom of the cylinder head--the flat area just outside of the combustion chamger.

That particular area is known as the "quench" area, and you really need to keep that distance at around .040" or less, or you will start encountering detonation issues.

I hate to disagree with someone with the credentials of rbohm, but using thicker head gaskets or milling the top of the piston to gain more deck height clearance are NOT the ways to lower compression ratio.

I recommend you go to the KB website, and check out their tech articles--they discuss this issue (and many others) in great detail--AND--they sell a hypereutectic piston that has a decent compression ratio specifically for the 392-393 stroker.

feel free to disagree with me, i dont know everything, and some of my insights on engine building can be dated compared to what is available today. i will say that small changed in head gasket thickness, or in compression height have little effect on the quench area. also at one time the quench area was used to do two things;

1: to cool the combustion area on the opposite side of the spark plug to help prevent detonation.

2: to provide air movement in the combustion chamber. in the old days before high swirl combustion chambers, and tumble port technology, you essentially had dead air moving into the cylinders, and you needed something to create a cyclonic action in the chamber to provide for best combustion. this by the way is why the older hemi head engines were not as good on the street in a normally aspirated form as a wedge chamber engine.

as for keeping the quench area at .040" or less, that was indeed true at one time, but today if you look at the compressed thickness of head gaskets normally being .053", and the piston being down in the bore as much as .020", getting the quench clearance to .040 it rather tough.

i will say that for a low compression engine, a reverse dome on the piston is the best way to go for best combustion when running nitrous or forced induction.