I have a full fendered 1928 CC Pickup that I finished doing an AV8 conversion on this spring. I bought the 8BA engine as an assembly locally with a 3/8 Potvin cam, headers, Offy heads and dual carb intake. I pulled the heads to clean it up before installing it in the truck and noticed 2 things. First, it is only a .030" overbore and second, it still has the Ford script valves in it. Overall the truck runs great , stays steady at 180 degrees, even in the Hot Texas summer!! I do have a little bit of valve train noise and I am getting a lot of blow by out of the breather. It is consuming about a quart of oil every 300 miles. So, I believe a full overhaul is in order. I know the block is good, no cracks, not losing coolant and not overheating. What is the best combination of bore, stroke and valve size to work with my truck? Should I stay with the Potvin 3/8 cam or go to the Isky 400 Jr? My heads are stamped .400. I do want it to continue to run cool!! I was thinking of going to an 1/8" overbore and a 4.25" crank with 1.6" valves. Too much for a strong street motor? What else should I consider? Or, should I just rebuild it with the stock 3.75" crank? Money is not the limiting factor, but I do not want to spend a bunch for no real gain either.
Nice lookin' truck. I just finished a 255" Merc for my '51 Ford, not really the same thing except I wanted an engine that would be suited to the street and reliable. I found two things that probably apply to your situation. The first is cylinder head preparation. Try to get your "squish" (clearance between the head and piston) to between .040-.060". This is the first flathead that I built where I paid real attention to head preparation, and it seems to really have paid off. Getting the proper "squish" adds efficiency and that helps both performance and economy. I don't know what the compression ratio is, but all cylinders ended up at 160 lbs compression. The second may not apply to you because of personal taste, but I stay away from multiple carbs. I have run 4-BBLs on flatheads in the past with good effect, and I was going to do that with this one. However, I came across an aluminum Mercury 4 bolt manifold that I bored out and used with a Rochester 2GC, and I like it even better that the 4-BBL. I do have the advantage of having my hood closed most of the time, so how it looks isn't important to me, but it may be for you. (I am going to run two carbs on a Navarro Universal on the "Tub" I'm building, because a Hot Rod just doesn't look right without multiple carbs.) I built this thing for maximum torque and minimum maintenance and I am happy with the results. I would have liked a bigger engine, but this was an economy build and was built on a proverbial shoestring with mostly used parts.
Joe Abbin does know good combinations that work. I have the book but don't really need it, I just pick his brain while he hangs out here at the shop! I personally wouldn't go 125 over, I'd stick to 60 over. Once you go 125 that's it plus I believe bigger bores tend to build heat faster. That said I had one with a 125 bore and no heating issues. I wouldn't spend the money on a 4 1/8 crank either on a street motor. Much cheaper to find a good Merc crank and I dought you'll really feel that extra 1/8 stroke on the street. I just finished a 51 block, 60 over with a Merc crank, mild cam, Offy heads and 3 carb manifold and it feels good in a heavy 51 F-1 truck! Probably feel real good if it was in a light model A. My 2 cents.
The truck pulls hard as is and I am mostly satisfied with the power except cruising in Overdrive at speeds over 70mph. With my current trans, rear end and tire combination I am only spinning 2000rpm at 70mph and I guess the flathead just isn't making enough power at that RPM to pull the truck up hills at 70+ with that amount of wind resistance. I do have a set of 4.44 gears to swap in for the current 3.78s so that should bring me into the 2400 range at 70. But I figure if I can gain another 20hp or so with the rebuild that it should really drive well at any speed. But, just to clarify, the truck is by no means sluggish or under powered feeling running through the gears, just looking for a little more.
Isn't is amazing that after all the massaging and modifying of the old Henry flathead someone with a car that has a 4 cyl. engine with half the displacement pulls up beside you and blows your doors off.
I went with the merc crank and tied it down with some help from H&H .125 , go big or go home. Relieved and ported, a lot lighter now. shoved in some of these ... and some of these Ross pistons in it and topped it with one of these If you build it, they will run. I basically took everything Joe said in his book and combined it with H&H's go fast goodies for a ferocious forty-nine flatty. Call Mike at H&H, he is a good resource.
From all of the old time flathead guys I ever met, they said the following things were most important: 1- flatheads need heat so go with 180 thermos 2- the flathead is at its best between 22-2800 rpm. Anything above or below and you are either creating too much heat or the engine is lugging. 3- simple is better. Progressive 2 carb setup, 4bbl, or Roch 2bbl 4- get all of the sand you can out of the block from when Henry cast it. Hey, there are exceptions to any/every rule-of-thumb but I tried to keep within these guidelines with my roadster and so far, it's worked. For others, different criteria were followed and it works for them. Every car is built to do different things, driven by different drivers - I built my car to run long distance and at speed so at 2250 I am at 65, 2550 at 75, 2800 at 85, .86. 5th gear, 3:54 gears, 32" tall tire. 59ab with stock cam, 3 3/4" crank, original split guide valves, stock lifters, Pertronix Ignitor II in my crab dizzy by Bubba, 50 lb oil pressure spring (I run 48+ lbs at speed, no less than 15 at hot idle), new sealed bearing water pumps, progressive carb setup by Charlie Price with his "Y" adapter on a stock manifold, and I collected a gallon+ bucket of sand out of the block I am presently running, and my best fuel mileage was 17 mpg, 15.5-16 more the average when I keep my foot out of it. Is it a speed demon off the line? No. Does it sound good? You bet through 2.25" un-mufflered or baffled exhaust pipes and can it run 85 for more than 2 minutes? You bet and at 170 engine temps from 80 to 130 degree ambient heat. Is it fun to drive? You bet - so much so that it is almost sinful and very tough to NOT want to drive it at every opportunity. So I do, more so than my DD. Decide what you want and build accordingly - stoplight to stoplight or long distance runner. For most of us, having both would be a very expensive proposition with a flattie but I will not take that off my bucket list just yet!
If your having problems pulling the gear you have now I would only add stroke which sounds like a 255 crank. If you want more go to a SCAT. I'd leave the bore at .030" for your cooling. If you need bigger just go to what you need to clean it up. Relieving reduces compression ratio and you will need to find it somewhere. But if your adding stroke all things considered you should be close to what's there now. Bigger valves are good at higher RPM and smaller for torque, you need to make that call. I like compression, yes it makes heat, but over all makes a car just run better at lower rpms. If your happy with the cam leave it. The added stroke will give you the torque needed to pull the gear at 2000; a bigger cam will work higher in the rpm range but if your not there it's only hurting you..good luck.
i don't think those 400 heads will have enough clearance for a 400jr. probably need at least a 425 head. gotta measure. isky's next step "down," the 88, is a low lift (.320 i believe) that can be used with stock 8ba heads. your heads also should be no problem with a max1 cam...
Part of my problem is my .68 overdrive gear. In 3rd at 70 I'm at almost 3,000rpm. Pull it into 4th and it drops to 2,000. I have decided to change rear gears instead of messing with the tranny (Ford RTS). But more power is always better right? Haha.
Ok... the potvin 3/8 is too big. No torque below 2800 rpm (there it kicks in) I would use an isky 1007b from Pete here on the Hamb . And i would go 4 1/8 stroke and 3 5/16 , because this is where there power comes from. 1.5 inch valves are enough. Cam will clear your heads. Less cam is more in the flathead world.
I've built flatheads of all sizes over the years and my favorite combination for the street is a 3/ 5/16ths by 4. It works out to 276 and is strong enough to pull well and reliable. A SCAT kit makes short work of shopping. I like Edelbrock or Barron heads with an Edelbrock 4bbl. Intake. For a cam, I only use Schneider. I call Jerry and tell him all he asks about the application I am using AND VOILA the right cam appears! Carb the engine to match the heads and cam and all will be good for a long time provided you choose the right machinist, and careful assembly.
So I got the book and it looks like 3-5/16 x 4-1/8 with an Isky MAX1 or 1007B cam and 1.5 or 1.6 valves, block relieved and minor porting. I should be OK with the Offy heads and intake I have (because I have them). I'm not looking to maximize the horsepressure, just get good strong reliable power on a reasonable budget.
Just want to run one down I-20 to I-10 then up thru lower Cali up to Sacramento. Will be using a 255 block hopefully out of the stash I have. Plan on using a Ford TOD and an 8" rear end.....in a 1939 coupe....sorry for the high jack.
1.5 valves are enough and dont relieve the block.... In my option a Max1 is wasted money. The i would rather have a stock merc cam....
well been running this since 2001, and just love it.........276 ci, C4, 9" with 3.0 gears somewhere around 200hp, over 30k on it now, Joes Blower kit, my own head work and dist work, and engine work.......Can't say enough good words about Joe Abbin over the years though........
I built a 286 with Scat rotating assembly . I had Jim Linder build me a distributor, I ran modified EAB heads A two pot Evans intake and a 1007B grind cam that Pete recommended. It would pull like a freight train at highway speeds and never ran hot. I had a quick change but usually ran a 3:12 gear with tall Firestones. If I ever have a need for another 8BA I'm building that exact same combo again.
The Jalopy Journal
