Flatty rebuild advice........

Thanks guys.

I think my plan up to now is to go:

4" Merc crank.

400 Jr/L100 cam?

.125" bore.

EAB or Edelbrock (65cc) heads.

Edelbrock super dual manifold.

cast 3 pistons.

1.6" chevy valves.

MSD SBC ignition?

Comes to about 276 ci.

I know that N/A Flathead's aren't the best revvers but I would like to get the best revving range as possible.

What will help achieve this?

Thanks.

HC.

 

You just stated you want to bore and stroke and get the highest revs you can. In some ways that is a contradiction. Back in the days when the flathead was king of the race track, many racers used the 3 3/4" crank, believing that (for racing anyways) the key to higher revs was in the shorter stroke. This theory is borne out I guess by the fact that todays engines (japanese) are running short stroke and turning astronomical revs.
In the 60s I was friendly with a guy here in NZ who was a successful racer. He said the Edelbrock Super Dual was the only manifold you'd ever need, and he was also adamant that the reason his single seater with 239" was #1, was down to stock displacement and an emphasis on good breathing, allowing high revs.
Food for thought.

 

I really appreciate the straight out correction!

As I said, It's my first build and I'm only just learning the technical side of things.

So the 3 3/4" crank sounds to be the best for high revving, but obviously you don't have the higher HP.

A lot of room for thought for sure........

Thanks again.

HC.

 

Basically, a flathead is considered a torque mtor, as opposed to a revvy motor. They produce low down torque, as the revs increase the lack of breathing makes itself evident. Think tractor motor. Most guys build them up with this in mind, improving breathing is the golden rule. Hence the recommendation for the longer stroke; a nice long intake cycle to cram as much fuel/air mixture as possible into the cylinders, combined with an overbore and porting job. Relieving the block was once considered essential towards this goal also, however, as other guys have said, the flow from the valves goes upward, which contridicts that earlier thought.
You have asked how to get the best revving range out of your flattie. Possibly [this is opening a can of worms], you would be better off to destroke [from 3 3/4"] and run the lightest possible rotating ***embly you could.
What I can tell you is I drive a 221 cu in + 0.060" bore, 21 stud, water pumps in the head, twin 97's on a Fenton intake, Isky 88 cammed, lightened flywheel with 9" Auburn clutch, fully balanced of course, and regularly wind it up to to 7000 RPM!! [In 2nd gear-stock 3 speed trans] It is a rev motor, but doesn't have much down low, although it is pretty responsive; it is not your typical flathead. It runs [repop] Eddie Meyer heads that I modified to provide maximum breathing whilst retaining a tight combustion chamber [60cc volume]. So, that's how to build a revvy flathead; keep everything as small and light as possible.
I think the general consensus, gained over the past 70 odd years, is to build a flattie as a torquer and gear accordingly. My opinion only, Tooratly

 

Thanks for that guys.

That is very handy info.

Well I have been thinking about what car this will be going in.

I think it will almost definitely be going in an 'A' roadster so going small might not be a bad idea?

Is it maybe a better idea going the .125" bore and going the 3 3/4" stroke (for higher revs) or won't it make a big difference?

Rockabilly B***man-You said that a nice long intake cycle would help, is that aiming at a long neck intake manifold (e.g, PM-7)?

What I've heard and read on this thread is that the super dual seems to be the best at flowing the gas down the manifold.

Keep them coming guys.

Really appreciate it!

HC.

 

Remember that HP is a mathematical construct using a formula that means HP will be low below 5200, about the shift point for most typical FH rod motors. The motor is definitely limited by airflow at the narrows of the ports, not by lower end...lower end is probably fine for 7,000 but normal engines (not nitro, high boost, porting by geniuses, etc.) but can't get there in terms of flow...noticing that got Duntov thinking, by the way.
Lower displacement will allow higher revs only because you run out of air a few r's higher.
Think in terms of the total area beneath your power and torque curves on a graph...I think the rewards grow smaller as you try to move the RPM curve past the breathing limits, and no matter what you do you won't have a true high RPM motor.
And displacement...any displacement the flathead can reach is tiny in the overall world of rodding. You have to think about weight...if you want fast, you are talking 2,000 pound roadster, really (though Flatdog's 12 second car weighed 3,000. What could that motor have done in a Model A??). The displacement becomes a killer factor in a big '40's car. It can be a peppy street ride, but the weight is too high for the displacement.
The early overheads had rather poor high RPM breathig too, for the first several years, and the flatty continued to rule in light drag cl***es til '56 when the hemi and the SBC really began to use the advantages of OHV, but the flathead was outcl***ed rapidly in heavier street cars. The first generation OHV's were largely faster because they were quite substantially bigger than a flathead.

 

Check the H&H Flathead site..There really isn't any good way to scrimp on a GOOD flathead. The money spent up front is probably money saved in the long run. They'll even dyno the thing for you. It's really hard to do, but try and differentiate between a flattie for full throttle lakes use and one for the street. Been there, done both.

 

As always, it comes down to how much money you want/can spend and how much street HP you want to use. I think the 276 cube street flatty is an ideal size for a light car --- 4" stroke, 3 5/16 bore . . . great combination, reasonable price and lots of fun! Don't make RPM your goal - make max and usable torque your goal! You're far better shifting when the torque and HP is dropping off, then continuing to rev it just to say you did. There are VERY few street flatheads that should rev much past 5200 - 5500 (on the outside) . . . just no need to do it. Having the larger cubes without some good porting, relieving work doesn't make much sense either -- take time to learn what a good street port job is, plan on spending 30 - 40 hours if you know what you're doing, or paying somebody who does . . . makes a big difference. Make sure you have headers, a great ignition, etc.. Also, compression is your friend on the street - try to get to 8.5 - 9.5 to one . . . really helps the low-end.

Have some fun . . . ask a lot of questions along the way! If you want to see a good set of porting, relieving and valve guide rework pictures, let me know . . . maybe I'll post a set from a recent build.

Dale

 

A correction to Flat Ernie's comment about the displacement of 4-71's. Probably a typo on his part.........but the 71 series GMC diesels are 71 cubic inches per cylinder, hence a 3-71 is 213", a 4-71 is 284" and a 6-71 is 426". However, what may not be fully undestood by all fans of Jimmy blowers is that they are not superchargers as used on Jimmy 71 series diesels. Those engines are 2 cycle and the "blower" is just that....it blows pressurized air into the cylinder thru side ports in the cylinder wall to scavenge the exhaust so the incoming charge is fresh(er) air. While the increasing number of cylinders from a 3-71 to a 4-71 or 6-71 require more blower volume, I doubt the volume output of the blower is as directly related to the displacement of the Jimmy engine as it will be when used to actually fill the cylinders of a 4 cycle engine. The physical size of 71 series blowers, the height and width are the same, only the length varies, is a bit m***ive for a flathead ford/merc.

 

I built one in the late 60's. Started out with a 53 Merc 8BA. Bored it 60 over. Turned the crank 100th and used the pre war rods (40 Ford). That gave it a 4 1/8 stroke. 296 cid It was in the coupe in my avatar. The biggest and one thing that gave this motor life was a full balance. I used an Isky full race cam with J&E pistons. Edelbrock heads and Edelbrock 4bbl intake. That engine ran ***ume and wish I never would have sold it. Back then I had about $200 in the build but today, you better taken on a second job. I have a friend with a blown flathead in his 46 Ford coupe and you would never know it's a flathead by the sound. He is running a little B&M blower. He has around $10g in the motor.

 

Thanks for that Bruce.

I think the concept with the light roadster sounds good!

Don't worry Dale..... I'll spend 100hrs if I have to. I'll be doing whatever I can on the build so probably only the machining side of things will be done by a professional.

Those photos would be good.

Thanks.

Useful info there.

Thanks.

Some useful info there too!

If I ever decide to build a Flatty for a heavier car, which I think is very likely, the info above would be useful.

Off to do some more reading.

Thanks again everyone........

HC.

 

Bored&Stroked, love to see a thread on that street port and polish. I've kinda' developed my own methods over the years which are probably crude at best. Post away as I'm going to start on my new block for my roadster in about two weeks.

 

Very useful info here

Would apreciate pics and Info about porting, too.
Building a 276 Flatty for my 53 Ford and in near future a 21stud for the 35

 

Do a search guys - AV8 and others have put up killer threads about porting/relieving etc along with other useful info on FH builds.....

S E A R C H it - theres heaps of info ....

Rat

 

Got a quick question.

What do you have to change on the motor if you want to change the crank from a 4" to a 4 1/8" or viser versa?

Thanks.

HC.

 

If you offset grind a 4" Merc crank to 4-1/8" you will have to use early Ford full floating rod bearings and 21A rods. The mains stay the same. I don't know about the new stroker kits being offered. It's no easy task. You have to find 8 good 21A rods that are straight with good wrist pin ends, 3 ring pistons, and a set of standard rod bearings. The radius on the crank rod bearing throws is critical for proper bearing clearance. Frankly I'd pop for a new complete stroker kit. Just my opinion.

 

Thanks Bill.

Well that's what I'm planning on doing but I was thinking of was maybe trying out both cranks and see which one I personally like best.

Just ideas.........

By the way, I'm planning on throwing a 5 speed gearbox behind it as a will be putting plenty of miles on her!

HC

 

As noted, new rods, bearings and pistons . . . quite a lot of money just to experiment with a few more cubes. If you take the combination I mentioned below --> 4" stroke and 3 5/16 bore - and change to a 4 1/8" stroke, you only pickup 8 cubic inches of displacement. Chances of you being able to tell the difference on the street are pretty slim. If you already have a 4 1/8" stroke crank - go ahead and use it, but to just pickup another setup to try it seems like a waste to me. If you're going to buy a new crank from ****, then why not buy the 4 1/8 stroker -- as long as you know what rods you'll be running.

PS: Port and Polish article -- there is lots of information on the HAMB on this. I'm going to put 'yet another' article together in a couple weeks.

 

With the Oz $ heading to parity with the u s ,why not wait a little while longer and get the whole rotating ***embly fully balanced for about $1800 .save a whole lot of h***le .And on the subject of heads , Edelbrocks are the only brand , to my knowledge ,that has the correct cc difference between left and right heads. Yes ,there should be different cc s

 

"...will be putting plenty of miles on her!"
Good reason to stay sane on the stroke. I would stay at 4", if you want to play with crank cut it down for 21A rods without offset. That way you can strengthen by getting a generous fillet radius on crank, lose some rotating weight, lose a tiny amount of friction. And...you can buy a Merc crank that is cheap because it is worn out for rebuild with the big rods!

 

H.C. Don't take offense but you remind me of myself when I started putting our sprint car together. I started buying a bunch of engine parts then realized I really didn't know squat about dry sump race motors. Sold the parts and bought a professionally built motor. Much better off in the long run. Hot Rodding has a lot of "head scratching" built in. Dreaming is fun but buying the wrong stuff is expensive!

 

The best thread on how to do a quality flathead porting job by far IMHO is the one Mike Bishop put together.

Do a search on here for it. I've used it, printed out and given it to all my flathead friends and keep a greasy copy out in the garage to use while porting and a clean one for reference in the house.

Yes, it it that well done. Find it at all cost.


****, I took pity on a fellow flathead brethern.

I searched and found the link to Mike's article:

http://www.jalopyjournal.com/forum/s...ad.php?t=23305

Double poop: The link isn't working. Sorry, man. I tried.

 

Bill:

As much as I'm sure we all can appreciate your trial and error experience with a flathead, I don't agree with the need to buy a motor pre-built by one of the pro-shops.

The poster is looking to put together a good street motor and not a full out race motor.

I believe that by taking your time, asking questions, and doing your homework there is no reason the average guy couldn't put together a flathead on their own.

It is important to keep in mind that this isn't a NASCAR 355 c.i. race motor we're talking about. It is basically 8 Briggs and Straton's engines cast together with a common crank and cam.

Sure, some guys may do a better job than others, but, aside from the machine work, it all can be done fairly well at home.

I think what happens to some folks is their logic gets clouded by what a flathead is and what it is certainly not.

Sometimes taking or getting advice from internet forums can be helpful, but we can't deny that some folks jump in to the fray without really having any real-world experience to back up what their statements.

I beleive if someone is willing to learn while they wrench it back together (sounds like this guy is) it should turn out just fine.

Just my two cents...

 

Ha! This one works! http://lonestar.texas.net/~mcdaniel/porting.pdf

 

And crazy amateurs in dirt-floor garages got roadsters up to 130 or 140 before there were any pros to turn to...

 

Bruce:

So true. My own personal flathead guru (my dad) showed me a dog-eared B&W photo of him doing a rebuild of a customer's flathead in the sand pit of the Sinclair Station he worked at when he was 16.

(BTW: I still have his shirt from those days)

After seeing that picture, I've learned to trust his advice regarding flatheads.

Tim

 

This post contains some limited super-secret pics from the research bunkers of Flatdog, who never revealed more than hints about his Uberflathead:

http://www.jalopyjournal.com/forum/showthread.php?t=247729&highlight=ports&showall=1

Also a couple other posts he entered into:

http://www.jalopyjournal.com/forum/showthread.php?t=138917&highlight=ports&showall=1

http://www.jalopyjournal.com/forum/showthread.php?t=237203
&highlight=ports&showall=1

http://www.jalopyjournal.com/forum/showthread.php?t=76445&highlight=ports&showall=1

 

And Bishop...he knows Bingelli, early Guru and builder of VERY fast flatheads. Could there be secrets of the past in that porting article???

 

Thanks everyone for the links and info.

I'll be going for the merc 4" crank.

Probably the 270F schneider cam.

Are the 7.00" H-Beam connecting rods from Speedway any good?

Thanks.

HC.

 

H.C.:

Do your homework on H beam rods. Last thing you want is to add more weight to the recipricating m***.

If you are not going with a blower you don't need them.

Some folks who run a blower would even argue the need for them at that point as well.

Is it safety and insurance? Sure. Just be smart and put your money where it really counts.