Looking to add a stroker kit to my flathead. According to Scat's website, the 274 cu. in. kit yields a 9.4:1 compression ratio vs. 9.7:1 for the 286" version with a 74 cc combustion chamber. Will regular fuel work with either kit? What's best for an everyday street driver?
The gain that you get with the extra 12 cubic inches is not worth what you lose with potential heating issues. IMHO.
For an everyday street driver the smaller 276 stroker option is the way to go. You have to bore the block that much further to get a 286 flathead and this gives the engine that added chance to run warmer now that there is less material on the cylinder walls. Just so you know SCAT products are all made in China. Some of the cranks are OK but some others are out of balance and require another trip to the machine shop to correct the problem. My personal preference is to get a genuine Henry Ford 4 inch Mercury crank and 8BA rods and build up a 276 using genuine Made in USA parts.
Good advice from quickchangev8. I run a 286 in my 50 and on regular gas. No problems if you tune it right. Go with the 274 and that leaves you with the option to do another rebuild if you have to clean up the cylinder walls.
OK, gotta ask the question one more time. Why does the thickness of the cylinder wall affect the steady-state heat transfer and cause the engine to run warmer if the walls are thinner? The heating/cooling is a system that takes the heat of combustion and transfers that to either metal or oil. The metal heats and transfers its heat to both water and air. The water carries the heat to the radiator to transfer the heat from the water to the radiator metal and then to air. For the cylinder wall, the heat doesn't know how thick the wall is, it is trying to equalize the heat throughout the wall....heat flowing from hotter to cooler or vice versa. When the engine is cold, I can see how the resistance of the thicker vs thinner wall can affect the system response. Anybody have an explanation that is not simply "that's what everyone says"?
Think about it, the larger bore means more surface area of the piston. More surface area means more friction. More friction means more heat created that transfers to the cooling system.
3 3/16 bore vs 3 3/8 bore, both with 4 inch stroke Piston contact area for 3 3/16 is estimated to be 20.03 sq inches Piston contact area for 3 3/8 is (using same piston height) estimated 21.20 sq inches 5-6% difference in contact area. Most heat generated is heat of combustion, not friction.
Actually, this phenomenon has occurred with every flathead that I've bored in excess of .060". The 5/16" X 1/4" (bored an 1/8", 4" Merc crank; 274") ran somewhat hotter than stock, .020", .030", .040", and .060". I can say that with certainty, as by the time I settled into the nice 5/16 by quarter standard I was well worn from the 304", 296" 'horses' I had suffered thru the heat spells with. After my 'heat adventures' with the 304 in my fenderless hiboy '32, (1960) I was gun shy as hell! Consequently, I made note of temp after break in, and the adage is true: "Thinner the walls, hotter the water." Never heard of 'wet water' or other modern devices then...the hot rods never ran fans, either. Fans were for '40s, and '46s... Not getting too technical here, just a 'timely' practical observation...
I recall reading that as the cylinder walls get thinner, the cylinder walls actually flex causing cavitation which reduces the efficiency of heat transfer and dissapation thereby causing the engine to run hotter. Goinng with the minimum bore possible is a better choice along with a 4in. Merc crank. Look at this video to see what it looks like inside a Ford flathead V-8 when the engine is running. Pretty neat.
I believe that people see the affect of boring a motor. My 59L block is 3.385 bore x 4 inch stroke and measures 0.100" on the thinnest wall (sonic check). We ran testing last summer in Tucson on a 106 degree day, hottest was 195 deg water temp in town and 190 deg on freeway. Running water with Dupont racing coolant additive, Fryer's pumps, and a new Brassworks radiator, no thermostats, no restrictors, no hood sides. Aluminum heads, stock oil capacity with full flow filter. Unfortunately, the block was already bored 3 3/8" when I got it so I have no baseline to compare to. My findings is that the motor is slow to warm up this time of year, we are only in the mid 80's now in February.
[QUOTE=" For the cylinder wall, the heat doesn't know how thick the wall is, "?[/QUOTE] This is not true. Check any engineering handbook, heat transfer text, etc, and you will find that heat transfer in a cylinder varies directly with temperature difference between the inside surface and the outside surface and the area of the cylinder, and inversely with the cylinder wall thickness. The wall thickness acts as a barrier to heat flow. The thicker the barrier, the greater the resistance to heat transfer. Otherwise, the recommendation by heating and cooling contractors to increase the thickness of your attic insulation would be a big scam. Farmalldan
Street engine , my preference is 4 inch crank and .040 over bore. you will not gain a significant amount of USABLE horsepower with an aftermarket rotating assembly. You will spend a lot of money though. 9.7 to 1 comp ratio will probably be more of a hindrance than a help. Just my 2 cents worth. Post your question on Ford Barn, there is a wealth of flathead info there.
Wish we had thermodynamics/automotive engineer who could give us the real low down on heat transfer and cylinder wall thickness.
If you are going to spend the money why not go with the 293 cid kit (3 5/16" Bore with a 4 1/4" Crank) If you use the low compression Edelbrock heads you would have approx 9 to 1 compression. perfect for the street.
OK, I appreciate all of the input, but I'm a bit confused by some of it. According to Scat's website, the only difference between the 274" and the 286" is the stroke of the crankshaft. The cylinder bore remains the same at 3.313" (3-5/16"), so the thickness of the cylinder walls remains the same. The only difference in my mind that would impact the temperature might be the difference in compression ratio. Also, unless I'm missing something, the Edelbrock heads with 74 cc would yield a lower compression ratio than their 65 cc version, and the 74 cc chambers is what Scat is using to calculate compression ratio for the different rotating assemblies. I like the idea of using an original 4" stroke Mercury crank and my stock rods to save $, but I'd need to find a good Merc crank, and that may be a challenge.
The longer the stroke an engine has, the faster the piston speed it has.In theory, the faster piston speed will "wear out" the engine sooner than a lesser stroke with a slower piston speed. Dyno tests indicate a 4 1/8 stroke engine(in a flatmotor) is not appreciably more powerful or stronger than a 4 in stroked engine. RoadRunner Engineering,Albuquerque,N.M. has dyno tested many flathead engines of various displacements(different bores and strokes) and I believe the more efficient and powerful engines utilize a 4 in stroke. Joe Abbin is a certified engineer; has a flow bench and a dyno and has many hours testing different combinations.His best (highest h.p.) in his 34 sedan has 335 h.p with a blower and pushes over 200 h.p in an unblown state using the 276 cu in.
FWIW, the 286 built by the previous owner in my '39 runs just fine as a daily driver. It has a Scat rotating assembly, which had to be re-balanced at a macine shop before installation. The PO never got it running quite right, and while it required some doing, I got it there with little consternation, just constant fiddling until I found the right combos of ignition and carburetion. It runs on 92 octane pump gas. If I were to build another motor for the car, I would probably do a size smaller, but the 286 hasn't given me trouble since I got it to play nice.
I have a 293 or 296 depending who is selling the scat setup but it is 4 1/4 x 3 5/16 and it is powerful. I was extremely surprised how it ran after the build. Hills I was topped out at 30 mph by the top now have no limit except rpm. I also live at 8500ft of elevation and go as high as 11k ft and the car is a 48 4dr sedan. That doesn't tell much of over heating or not. I had a new radiator built during the engine build. My car does just fine on hot days in stop and go traffic and stays just under 200. The only time I see it get too hot is when my rpms are too high at speed. I went to Salina ks for the leadsled one year and it was 116 air temp, who knows what the temp on the road was, and I traveled at 65 mph with the temp gauge at 205. No problem at all. I put thermostats in and that made a huge difference but I think my reared gears are just too low and the rpms are making it overheat. I could be wrong but I want to put in 3.54 gears this spring and see how it works out
Old post I know, you really need to know how thick the walls are to start with. Only way to do this is by sonic testing. Current block we are working on is a 59L. It was already bored to 3 3/8ths. Here are the results after our tests. CYL Top Front Bottom Rear #1 .130 .156 .161 .111 #2 .122 .151 .173 .122 #3 .142 .146 .178 .118 #4 .178 .155 .198 .188 #5 .165 .134 .158 .167 #6 .115 .129 .177 .130 #7 .119 .134 .166 .143 #8 .192 .105 .177 .182 Next, my builder measured the bores and found there is a good amount of taper this dimension is the worn oversize #1 is an additional .009 worn #2 .008 #3 .008 #4 .007 #5 .006 #7 .006 #7 .006 #8 .008 So, you can see this particular block is still very thick even after being punched out to what many believe to be the outer limits for a street engine. We are hoping a .010" hone will clean it up. Egge offers 3 3/8" pistons in + .010, .020, .030" sizes. Getting the block absolutely clean by baking and other manuals methods and other "tricks" will allow this block to run as cool as a smaller bore motor while putting it is 292 c.i. range.
My 4" cranked, 3-3/8" bored, 286" flathead runs really cool. Mostly 170 to 180 on the highway, and it only gets hot when stuck in standstill traffic on a blistery day in July. It is a 99A block, so it might have a bit thicker cylinder walls. I think the key to its coolness is the block was thoroughly sandblasted inside the water jackets from every hole available. Getting it clean is very important.
Agree 100%. Even after getting baked and boiled, I was able to pull stuff out of the water jackets. I think a lot of folks miss this part when rebuilding. It's easy even to see if you've got junk in there if you look down into the coolant holes.
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