Featured Technical Best Flathead Build for a 150 HP+ Cruiser

I like this idea. I've recently been using stainless steel scrubbers/SOS pads stripped down and chucked in a drill to clean inside smaller stuff and it works great. Too small for a flathead block, but I get the picture!

3blap.

 

150 hp isn’t difficult?
So what is your receipt form an honest ! 150hp Flathead?
Sounds easy for you.
Ever put a built Flathead on the Dyno?
I am curious
Regards
Micky

 

Since the later (1952) Mercury 255 was rated @ 125HP with 7.2 to 1 compression, 150 HP should be fairly easy to obtain. I am going to try to get there with my build.

 

Be careful with those factory figures. I think it was the late John W. Lawson that put an 8BA flathead rebuilt to factory specs on a dyno and the most he could get was 83 or 87 HP (I am not sure of the exact number, but it was a lot less than the factory quoted 100 HP). I do think a Merc crank is an important first step in getting to 150, and don't overlook a reasonable overbore (.125"). 276 inches will give you a hell of a head start.

 

^^^^ my formula right now is 276 CI, modified Mercury intake with a 2G carb., Chevy dizzy, port job, and headers. HP will land where it lands.

 

I think you'll make it.

With a relatively heavy car, just don't over-cam it.

 

My last flathead was a .080 over 3 3/4 stroke that I spent lots of time openening up the exhaust ports to the max and reaching way up (6 in deep) to lessen the dogleg on the end exhaust ports. I also fitted a big bore intake gasket to a matching big ported Edelbrock slingshot(one of the better flowing 2-2 intakes I my opinion)and fitted a 3 port Weber style K & N intake filter from a flat six Porsche and pulled 150 h p at the flywheel. I also only relieved ONLY the intake side of the combustion chamber tending to believe since the exhaust was expelled under pressure that it didn’t need to LOSE the little bit of compression to still flow well. Ran a .350 lift cam and .047-.048 jets in the STROMBERG 97’s. Ran strong enuf to run 80 in the 1/8 mile in a fender less hiboy Henry 32 cabriolet.Flatheads Forever!!

 

Let me suggest that while you chase parts and perform other time consuming build efforts, pressure wash the bare block to remove grease and oil, and then set it in a plastic barrel filled with water and some citric acid. Get one of the plastic drums with a removable lid. After about 2 weeks, tilt it over to drain the mixture and hose the block with fresh water. Then fill the drum again with some more citric acid/water and let it set a couple more weeks.

It will get into all the little places inside the engine and it will not harm the block. I had made a mark with a permanent marker on a block, and to my surprise it was still there a month later, but the citric acid did the work. I don't think I made my mixture strong enough. Amazon sells powdered citric acid. Mix half of it in the first bath and save the other half for the second bath.

Edit: 30 gallon drum if you can find one or don't fill a 55 gallon as full. Stronger mixture that way.


Olboy's Flathead




My old Cadillac

 

On my avatar I dug out everything I could through the water jacket holes with the heads off and vacuumed up everything before flushing it. Did each side 5x and collected a one gallon bucket of sand and rust particles. Each flush always ran a funky color until the 5th time - that’s when I stopped. She never once in the 18+ years ever overheated - at the salt flats, LA Father’s Day Show, or running hard @2800 rpm and 85k plus miles. It definitely pays to do this ….

 

Always. Henry left a lot of **** in those blocks after casting. I sand blasted inside, then hot tanked. No over heating issues at all and I am bored .125 over. Moral of the story? Clean out the block! Everything you do to it for performance is futile if it going to run hot.

And put a blower on it.

 

I don’t need to drive it every day… I have options including a 24 Tundra Limited Hybrid and a hotrod 911 Turbo. I am looking for something a bit different and hate leaving the 930 Slantnose parked downtown while I’m at the office.

 

Thank you to everyone for their ideas, suggestions, and thoughts. I’ve done a ton of research and ordered some books. While I can’t get a copy of Lawson’s book, AI seems to have ‘read it’ so I can get some of the details from it. The suggestion that an 8BA cam is optimal is surprising for a smaller engine.

I’m currently considering the following:

Stock Bore
Stock Crank (or **** 4” crank)
Stock Pistons (or pistons for the 4” crank)
Edelbrock 1115 heads for just over 8:1 compression
Ported block (Tardel’s book will be here next week)
Edelbrock 4bbl intake
MSD or similar distributor
Merc cam or the stock 8BA cam or potentially a high lift Merc cam

Machining delays will kill this project. I’m planning to buy a valve grinder and seat grinder to do that work myself.

The stock crank may not get me to 150 HP, but is should still be decent.

What are your thoughts? Am I going down a bad path? What would you do differently? Machining will add 6 months to this project.

 

This is why I mentioned „put it on the dyno“ …
Dont believe in advertising brochures or tales from people.
You spend so much money on a Flathead engine… so $100–$200 for one or two
Dyno runs won’t matter . Be prepared to water in your eyes from the result…

 

Micky,

I agree with your thoughts and have not dyno'd the engine, but it is built very similar by the builder to another one that he did that was dyno'd. Came in at 160 hp. After driving it, I believe it is close. Eventually I will get it on the dyno, but I'm prepared to bring tissues as well. Rear wheel HP is probably pretty low.

Here is what I did to the motor.

1.7 high flow ***anium intake valves
1.6 high flow SBC exhaust valves
Intake ports opened up, size matched, the lower hump is removed
guides cut down
Edelbrock Slingshot intake ports opened to match the intake ports
Block relieved
Exhaust ported, matched and opened up to 1.75". Front and rear dog leg removed as much as possible without needing an insert.
Bore- 3 3/8ths +.030" X 4" stroke
Potvin 3/8ths (thinking of swapping it out for a Potvin Eliminator cam).
Ross pistons with metric rings
Heads matched for correct squish
Petronix ignition
Weber flywheel

Next build, I plan to knife edge the crank and reduce some of the counter weights width.

 

Reading/following along as I have a similar project that I’m playing with.
It’s a 1953 ford f100 with a flattie.
Luckily for me it’s already a driver (kinda).
It’s my first flathead powered vehicle and I gotta admit that I’m really enjoying it.
Given that it’s a stocker, it’s ‘comfortable’ top speed is about 45 mph which makes route planning in and around my city fun, fun, fun. Thought about a t5, and that may still happen, but I’m enjoying the 3 on the tree for now. Takes me back to my youth.
As part of my current ‘speed solution’, I’ve found a complete 9” rear end out of a late sixties F100 that I’m going to fix up and put in next spring. Try some 3.0 or 3.50 gears and we’ll see how that goes first before I do anything more drastic. Wish there were some taller gear options for the stock rear, but putting in a 9” isn’t a bad idea anyway.
I usually go gung-ho on new projects, but trying really hard not to rush this one.
FWIW, sharing my experience/plan as food for thought only.

 

I believe there are better gears than the stock 4:11's. I seem to recall Bob Drake was advertising gears for these early Dana rears. I just tried to find it and wasn't able.

 

I'm a little late to the party. I had Frames on here build me a mild FH. So far it has run great on the test stand for an hour. Put it in the bare metal deuce roadster I just sold which is now in Florida. Hopefully I'll hear something when he gets it on the road?

 

There is no replacement for cubic displacement. Those words were never truer then when discussing trying to tweak horsepower from a flathead ford V8. It will be interesting to see if you come close to 150 HP with stock bore. But I get it, the machine work is spendy, all of the porting, relieving, boring, big valves and those CNC mains to hold the Merc crank in place cost me more than any other engine I have ever built.

You have to do what you can afford, just remember to make it breathe, inhale and exhale. They don't do a good job of it from the factory.

 

Ok, I am going to jump in & comment again. U guys like a target - blast away. The OP has changed spec: not looking for a daily driver 90 miles a day, 450 miles a week. Flathead should be fine. Since he owns a slant nose guess he not worried about $ per horsepower, but he stated does not want to bore block. Can I mention: quick google shows SBC of 250 hp for bit under $4000. No wait for machine shop or parts; just a plug in & play. I can only say again: 30 years with no engine, please rebuild suspension, brake system ( lines ), fuel system, & do not forget heater core ( ask how I know ). Have fun flatheads do have the look. Ok, attack!!!

 

If you do decide to run the aluminum heads, putting on those kind of miles you should re torque the heads once a week when stone cold (this is not something you want to skip)
To get 150HP out of 250-ish CI (***uming stock crank) or even 270-ish CI is going to require some rpm. A lot more RPM than anybody under 60 has experienced. 5o years ago we towed a drag boat all over the western US at 75 + MPH with a 283” no problem. However it was done with 4:11 gears and no overdrive. Modern driver’s will go insane driving at 3,750 rpm, they think that anything over 2,500 and the motor’s about to explode (it’s not). Your ear will have to be able to adjust to that. I think that what you aim to do can be done but it will not be like driving a modern F150 by any stretch.

 

Seems funny to read that post ^^^^^. Years ago buddy’s car & My car both knew 3000 rpm was 60, 2500 was 50. Speedo always wrong. Gearing? Maybe 4:11 do not remember

 

To be clear, I already have a 08 Crown Vic cop car. I bought it to do a suspension and power plant swap into this truck. The trouble is that I don’t have the time to dedicate to that swap right now and won’t for the foreseeable future.

I feel like I could put the flathead that I just bought into this truck and have it moving under its own power in a weekend.

I would love to bore the flathead.125 over and put in a stroker crank and … the issue is not cash, it’s access to a machine shop that can do this right away. It’s a 6-9 month wait and that kills the flathead idea.

I can buy a **** 4” crank, heads, intake, 4 bbl carb for about $3k usd and have it before Christmas. If I do the porting and valve job my self, I could have this thing rebuilt by February and able to use the truck next spring.

 

Hoping you bought some parts as part of Black Friday. Lol! I just ordered some stuff from Speedway yesterday and saved a few hundred on a USD$1.5K order plus free shipping within USA. Speaking of ordering parts, you might want to look into the bits for the T5 and T5 itself if you haven’t. Could be lead times on adapters. Got my T5 adapter for my C69A from Modern Driveline. There’s a guy near Montreal that rebuilds and sells T5’s. He told me he’s pretty much the only guy doing this on a regular basis in Canada and has clients from out west. Typical rebuilt one is CAN$1.5 K. PM if you want his phone number. As far as minimal effort to get the Flathead going, I’m always amazed by Jamie from Dead Dodge Garage and his “budget friendly” approach to some of his engine builds. If bores are decent, and you can get a decent finish with some DIY honing, then no excuses really other than getting parts. If you’re getting new lifters, then get USA made Hylift-Johnson from Michigan. I would also get the original cam reground as well. Seems lots of issues with bad lifters and cams for these engines from all the suppliers over the years.