Flatty rebuild advice........

Hi guys and gals.
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I’m doing a bit of planning for my upcoming and first Flathead build.
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I’m planning on doing a full overhaul so I’m looking at cranks, cams, heads, intakes, dizzys and carbs at this stage.
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It’s going to be a long term project so I’m going to be building it 100% correctly.
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No short cuts!
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I want something more than a stocker and want to build it so that in the near future I will be able to throw a 4/71 blower on it.
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These are some parts that I have been looking at:
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• **** crank. 4 1/8 or 4 ¼. Not sure if pistons will suit the 4 ¼.

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• Isky 400 Jr. race cam.

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• Tommy Thickstun 2 x 2 intake repop (original if I can find one).

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• Edelbrock Hi flow finned heads.

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• Dual 94 or 97 carbs.

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• Dizzy. Not sure. I know a flatty loves a nice hot spark.

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All you big guns out there, please feel free to contribute your ideas and experience.
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I’m all ears……….
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Thanks
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HC.

 

Sorry, I traded mine for SBC... but I'd like to see some pics if you build one!

 

I would strongly urge you to research blown flatheads BEFORE you buy parts. For example, since blowers raise compression, you might reconsider lower comp. heads. Too much cam overlap isn't too helpful. An advance curve that is too quick may not help either. I ran my flathead with 5/16 bore and 1/4 stroke. center main support, stock cam and polished "Canadian" stock heads. The real key is to keep in mind that a normally aspirated flathead has different requirements than a blown one. Smaller blower with around 5 lbs boost max worked for me. Loved it! Good luck.

 

Thanks for that Bill.

I understand where your coming from.

I'm not jumping the gun, just getting an idea of what is the best for my purpose.

Ok, what about if I forget about the blower.

What would be needed to get the absolute most out of a naturally aspirated Flathead?

I'll add again that I want it to look as period as possible.

HC.

 

We are building a flathead at work. I'll post some pics tomorrow. We've done a bit of reasearch while trying to decide what to do with ours. It's not a super high performance build, but we are doing port work, relieveing the block, and a few other tricks.

Flatheads run better with lower compression. of course, the higher compression heads, the less flow you have and from looking at other poeples experiences, it seems the most hp gained is with low compression and improved flow.

 

These Edelbrock heads that I'm looking at feature 74cc combustion chambers.

What does that sound like?

As I said, since there won't be a blower, does it matter if you go for the big crank etc, which will result in higher compression?

Thanks again.

HC.

 

Also, would the 4 1/4 crank be okay to install into the un-blown 49-53 Flathead 8BA?

HC.

 

You will get conflicting advice - what I can tell you is if you want to supercharge the flathead, you need to talk to Joe Abbin at Roadrunner Engineering. Get his books - both of them.

The Edelbrock 74cc heads are no better than stockers, really. They are more effective for blown engines - stock heads are around this size, so you won't get any increase in compression.

The blanket statement above that you want low compression is misleading. You want the highest compression you can get without sacrificing flow. Make no mistake, it is a compromise. 8.5:1 seems to be the practical limit - after which, you do tend to be restricting flow - particularly on a normally aspirated engine. Consequently, the best way to build compression in a flatty is with bore and stroke increases instead of making the chambers smaller on the heads. Again, there is a practical minimum.

On the street, a smaller cubic inch engine with a small blower will normally still make more power than a big inch normally aspirated engine. Yes, there are certainly exceptions, but we're talking streetable engines. So, you'd be better off to build a 239 with a modest overbore and spend your money on a small blower kit (forget the 4-71 unless you're getting it free - besides, 4-71 is overkill for the street for many reasons) instead of the big inch stroker kit.

You can build a normally aspirated engine and later put a blower on it with careful parts choice. If that were my goal, I'd probably build a 276" engine (4" crank and .125" overbore - probably the most common combo) and use stock EAB heads on it. I'd run an Isky Max-1 or 400Jr cam (depending on the car), 1.6" valves, a mild relief, and a nice port/polish clean-up (not hog out) job. Then, when I got the blower, I'd consider running Mercury heads or 8RT heads - these heads have lower compression than the EAB (highest stock head CR) heads. For ignition, I'd run MSD or one of GMC Bubba's converted SBC distributors triggering an MSD box. With the blower, put a boost retard unit on. I'd run a steel center main cap if I ever even thought I'd run a blower. Ross pistons are almost mandatory for the blower too.

If you decide to stay normally aspirated, once you get beyond 4-1/8" stroke, you really have to start looking at connecting rod to block clearance and often requires grinding for clearance - on these old blocks, there are 70+ year old water p***ages right behind there, so be careful. Spend your money on the internals - you can change heads and intakes easily. Run EAB heads - if you really want finned aluminum heads, you can always put them on later. You will need to check valve to head clearance, as well as piston to head clearance. Over the valves, you probably want about .100" and over the pistons, about .050". You'll be able to run cast pistons and stock main caps on a normally aspirated engine w/o any worries.



It ain't cheap. It won't make a lot of power (even blown). But it is addictive.

 

Flat Ernie stole my thunder. Joe's last book is almost a recipe book for building a flathead. Very detailed and parts selection backed by dyno performance. As for not making a ton of power, it's true. Joe built a normally aspirated at just under 300 hp and blown at 325 if I remember the book correctly. I don't know where he ran the dyno, but I would think he did it in Albuquerque... a mile above sea level.

Stock heads, a very good porting job, mild cam, modest compression, electronic distributor. It's all in his book, very easy to find exactly what you are looking for for a build now and a blower upgrade later.

 

check out my web site www.flatheads-forever.com

 

Check here also:
http://blown49.com/index.html
Jim Leis knows a lot about blown flatties.

 

I would keep stroke down to 4 or maybe 4 1/8. More is I believe too much, leading to too much rod angle and side thrust/ring issues.

 

Bill Boomer's engine, one of the ones profiled in Joe's latest book, is for sale...

What I like about Joe's approach is he did years of flow research, modeled engines with computer software, and was running his original blown engine with good results. Then he took all that info, modeled an engine, built it, dynoed it, then raced it - each step validating the previous. There is no doubt he's making the HP he claims because he's backing it up at the strip.

 

What about a 4-71 blower? Would that work ok?

 

BTW: $17,500 gets Bill's motor delivered from Canada to US. You seriously may want to consider buying a proven engine like his than doing a full out blown build like you want.

I can get you the specs. and all the info on it if you'd like. It is a serious engine. It makes 300 h.p. on premium. This was backed up on Joe Albin's dyno with 30 pulls.

You'd be surprise how quickly you'll go over $17,500 to build a motor like his.

 

IMO, a 4-71 is too big for a street flatty and has to be underdriven too much. Can it work? Yep.

A 3-71 is a far better choice for a -71 series blower. The -53 series blowers are better still (what the Weiand, B&M, Holley, etc are all based on), but you'll likely end up fabricating your drive system...

 

Here are some links that should prove helpful:

http://www.btc-bci.com/~billben/flathead.htm

http://www.vanpeltsales.com/FH_web/flathead_home.htm

http://www.fordflathead.com/index.html

Flat Ernie's advice is spot on!
Get Joe Abbins books they are a very useful resource with lots of testing on various engine combinations.

 

Why would you fabricate if you get the little Weiand blower? Isn't that what Joe Albin's set-up is based upon?

 

Flat Ernie:

Please correct this info that I have for using GMC 71 series blowers on flatheads:

6-71 run underdriven

4-71 run at crank speed

3-71 run overdriven.

Can you share where you are getting the need to underdrive a 4-71 on a flathead? I'm curious on this as well.

 

Thanks everyone for the ideas and input.

Many useful links there!

I also was a bit confused when you said about the 4/71 because I know a few guys who are running flatty's with a 4/71 and seems like they've done a good job (in terms of power output).

Flat Ernie- you mentioned that 8.5:1 seems to be a good compromise.

Is that for the blown and unblown?

I'm going to go for the unblown option and try get some good power so what what would be the best for unblown?

If I'm not going to go blown, is it worth going the big stroker kit?

If I need the highest compression possible, is it worth 'decking' the heads of a hi flow set of Edelbrock heads?

Thanks.

HC.

 

HC, I agree with everything Bruce and Ernie have said, they know their stuff.

Decide WHAT you want, then build accordingly.

8.5:1 is a high CR for a blown FH, its nice for a NA FH though. As mentioned, there is an inverse relatonship b//w breathing and compression on a FH. The higher the CR, the LESS the engine will breathe. Compression is SECONDARY on a FH, BREATHING IS PARAMOUNT as these engines do not breathe and while CR is good for TQ, the engine will run out of breath early in its usable rpm range.

Here's my advice.

If you want to install the engine in a light car (say a T or stripped A roadster), a nice stout, decently ported and relieved 4" x 3 5/16" bore FH will move it along nicely, be reliable and be fun. A bigger stroke increases piston speed and rod angles change therefore adding more friction/wear into the equation. 4" arm is fine. Inf act a lot of blown FH back in the day ran 258ci combo with the stock 3 3/4" arm.

Shoot for around 8.5:1 or so CR, a decent Schneider or L100 cam, 1.6 valves, Offy 425, Sharp or Navarro heads, unshroud the valves in the head's chambers, a Edelbrock Super Dual (flows beter than a PM7) decent headers/exhaust and ignition and you should end up with around 175HP or so but that will be about it.

If your gonna have a heavier ride (say a coupe or fat ride), build a nice blown FH and make more power.

You need to figure out what car the engine will go into first, do a LOT of reading (Joe Abbins books are the ones to read, esp the most recent one) and go from there.

You will never make mondo HP/TQ with a FH blown or unblown BUT....its not all about mega HP/TQ with a FH anyway....know what I mean?

Rat

 

Everyone here has given you great information.

A few things to contemplate;
What kind of boost are you going to shoot for?
What kind of RPM are you going to limit the motor to?
How much money are you willing to spend?

Personally, I think Joe Abbins setup is the best on the market for the price. It uses the Weiand 142/171 cfm blower. Joe's setup comes with everything you need and is around $3k.
Depending on your budget, I would use a set of Norm Frick heads, or Tony Barrons if you have deep pockets.....................if your pockets are not deep, I would search out a set of stock 8CM (Merc) heads and do a little work to them. The Edelbrock heads are just not worth putting on a blower motor......in my opinion.
Again, depending on how much boost you are going to feed to this motor, I would go with replacing all the stock mains with Doug King steel mains and ARP studs. If you are going to use the 4-71 and crank the boost up over 7psi I would think about a bottom end girdle.
I would use the ****/Eagle/C.A.T. H beam rods, although you could have the stock rods polsihed/shot peened/resized if you are on a budget.
The other thing to think about is the exhaust. The headers on a naturally aspirated motor can be about anything you want, but a blower motor is a VERY LARGE air pump, and you want to get everything out............scavanging is pretty important on a blower motor like a flatty......................your normal Reds Headers are just not up to the task...IMHO
Also, when you put the blower on the motor, two 97's are not going to be up to the task, and with a blower motor detonation/missing/running lean is the KISS OF DEATH....running a boost retard is the only way to go.......IMHO
So in closing, if you ARE going to put a blower on this motor at sometime, remember to put the bottom end together right the first time.............don't skimp, you can use a **** crank if you like but I prefer a "Real Merc" crank and message it from there, have it mag'd, shot peened, ground, index'd and clean it out good, use H-beam rods and forged pistons with good Moly top rings............and use steel mains with studs........IMHO
Oh yes, if you do use the 4-71/3-71, the best manifold is the Navarro............bar none!

So, get a copy of Joe Abbins book and read it cover to cover.................then call Joe to answer your questions.
Good luck and let us know which direction you go.

 

Thanks Rat and Chopped coupe!

Appreciate it.

I've planned to go unblown.

So I think I'm heading towards the 4'' merc or **** crank (?), 3 5/16 bore (.125''), edelbrock super dual intake and the rest still to be thought out.

I love the look of the merc heads but will see what happens.

I am on a bit of a budget but it is a long term project too.

Want it to be done properly!

Off to do some more reading.............

HC.

 

Try calling Mike Davidson in Adelaide he's the Aussie guru on flatheads.

Pretty sure he has a website Flatattack racing.

I'm running stock crank pistons ect with davidson ground cam, mallory electronic ignition, adjustable lifters, Edelbrock heads, thickstun manifold and a pair of demon 98's on my jailbar engine and it runs beaut.









The T is stock internals with adjustable lifters edelbrock heads, toyota MR2 supercharger on 4 barrel manifold with a pair of 1 3/4 SU carbs and goes great.

 

Yes, absolutely. That was my point which I failed to make!

The 4-71 is designed to pressurize a 426" diesel engine at 2:1 ratio at about 3000 rpm. It's simply too large - I think most folks get away with running it 1:1 simply because most of these blowers have a fair amount of leakage and rarely see the other side of 3500 RPM. But if you spin it to 5000 RPM or beyond, you're probably making well over 7psi on your standard 276 flatty.

Barney Navarro set most of his records with a 3-71.

They can be made to run effectively on the street - lots of people do it. But in general, for a street engine, you want a smaller blower spinning faster. For racing, you want a larger blower spinning slower - gross generalizations.

Unblown. I'd move toward 7.5:1 for a blown engine...

Yes, but you're not far off what a blower kit costs...

Edelbrock makes two heads - a 65cc chamber and a 75cc chamber - if you must run Edelbrock heads naturally aspirated/unblown - run the 65cc chambers.

Budget and flathead don't go together well!

If you're on a budget - no need for the **** crank - find a good used Merc crank - if you shop around, you should be able to find one <$250. If you like the look of the iron heads, the EAB Ford heads are actually the best ones - the Merc heads have lower compression. A 4" stroke and .125" overbore = 276" engine - with EAB heads, it should be around 8.2:1 - if you use the Merc heads, it'll drop the CR down to 7.3:1 (those are approx numbers and will vary a little bit, but the ratio is the same - almost a full point).

I'd put some 1.6" Chevy valves in the ports - you can get some inexpensive stainless valves from Summitt for about $100 for all 16.

I'd use a GMC Bubba converted SBC distributor.

I'd run an Isky Max-1 cam or a 400 Jr (depending on your car and gearing). Run the solid adjustable lifters (no need for the expensive lightweight ones). Lincoln valve springs (or Isky singles).

Mild port/polish clean-up job.

Red's headers for your application.

If you like the 2x2 look - hard to beat the Super Dual. If you use 94s, you can keep the costs down (they're still cheaper than Strombergs).

Cast 3-ring pistons from Patrick's will be fine if you're certain you'll never put a blower on it.

I'd run a nicely rebuilt late 8BA-style oil pump (look for the spiral gears, not straight gears).

You can get brand new late rods from SF Flathead for about $125/set (last I looked) - hard to beat, but weigh that against the cost of reusing your stockers - no real reason not to if they're in good shape.

Best composite head gaskets.

Bob's your uncle.

 

I'll just p*** along a few tips here with respect to looking for longevity and power!

1-Make certain whoever does the machining has a block-plate to do the final hone.

2-Use the "metric" ring setup, 1.5, 1.5, 3.0 mm! Ross uses this configuration. Moly rings are "mandatory" in any decent build!

3-Use "coated" cam bearings, will close up the cam clearances by .0005" and all but eliminate normal bearing wear!

Thanks, Gary in N.Y.

P.S. Am building 2 units now, possible 3rd pending, just had all the cam bearings "Teflon" coated!

 

Thank you very much for that Ernie! I appreciate all your input along with everyone elses.

Also thank you Gary.

With the heads- will the 65cc edelbrock heads bring up 8.2:1?

I know I said I am on a budget but I mentioned that I will be doing this 100% properly. No short cuts!

So whats gotta be done is gonna be done.

I've printed off all your posts and am going of to read them inside out!

I'll be back tomorrow with more questions.

Thanks again......

HC.

 

Since the flatty Gurus are all here, I'm following this thread as I'm in the process of building a flatty for my roadster. Question, I have a very nice 3 3/4" crank and rods, am I going to notice the difference on the street in a normally asp., relativly mild motor, witout using the 4" stroker crank and H beam rods, (Speedway kit)? Or is this just money thrown at bragging parts?

 

You may. If you've never had a built flathead before, you won't know what you are missing. In a light car, probally not that noticable.

Again, everything being relative. A shaved or aluminum flywheel would make this set-up even snappier.

Some guys love the 3 3/4 with a .060 overbore. Makes a nice street engine.

Cam choice is going to be crucial with this set-up. Guys like Ol' Ron love the Isky 1007B for this size motor.

 

The 4" crank is noticeable; don't forget it is also a multiplicand in your displacement formula, too! Stock rods plenty OK, though early rods with floaters offer a tiny bit of free power from less friction and a major dose of insurance against high RPM failure...even though the rods are lightly stressed by the low RPM of a normal flathead, they offer some bragging rights. A good Merc can be cut for 4 1/8 of course, and that gets you the lighter version of the floaters. Stock heads are definitely an option if your displacement is sufficient to get compression you want and have multiple benefits...better flow with properly placed (the flow from valve goes UP) p***age volume between valve and bore and I strongly believe they improve the whole package by serving as a girdle for the deck, a weak spot on just about all stock based engines.
Most reciprocating/rotating part stress is from RPM, NOT power, even at high levels of soup. This is probably the reason for racing flathead survival, along with the mandatory floaters in race cars of the past. Supercharger is nice because it can boost power at low RPM's, so no great stress with a big performance boost.
I once saw a stress chart from GM on a Z-28 302 engine...stress of course went up rapidly with RPM, highest loading by far was at top of exhaust stroke from the undamped movement...
RPM kills via the stretching of the lower ends on locked type rods, other failures come from detonation pounding in stretch in rods and mains, all causing locked bearings to curve inward at parting line, leading to a very loud mess. Detonation is not something that can realistically be fought by girdles and such...it remains lethal and just has to be eliminated, not resisted, according to Yunick's studies. Adding more metal just postpones the failur or moves it to another part..