Flathead help

James Rogers

James Rogers

Well-known member
I have just obtained a 51 8BA that my uncle bought about 61 and owned till he passed last year. I am going to need some help with the rebuild and the performance upgrades that go with it. I will need help understanding such things as relieving and blowers. Any help with publications will be much appreciated. I do Model T/A/B engines and am well versed in the four bangers but am just getting into V8's.

BTW I will be selling the shoebox 51 the motor came out of soon. Anyone interested in it can PM me for pics and details. It will be priced reasonably.
 
i would not relieve the engine, thats making a path from the valve pockets to the cylinder on intake and exhaust, supposed to make the engine breath better by not having the fuel mixture go up so far before it enters the cylinders, truck motors had that done at the factory, but it lowers compression because you are removing metal from the block, and in my opion makes the metal to thin and prone to cracking the block where the relieving is done , i dont have a picture of the relieving location but i know some one in here does and will either post it or email it to you, also to add i dont recomend a blower on a flathead, they have only 3 main bearings and thats the weak point, they wont hold up under a heavy load usually break the webs on the center main, for carburation i would use a 350 cfm 4 barrel instead of two two barrels, easier to adjust
 
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Trying to make an engine breathe better by relieving is about like trying to run a foot race with your head held against your chest-your breathing is restricted! Basic physics says an object in motion tends to stay in motion in a straight line unless acted on by an outside force. The air coming in through the port is flowing upward and wants to continue up to the head where it is directed across the transfer area, then down into the cylinder. You want changes in direction of airflow to be as gradual as possible, in the shape of an arc. Forcing the intake flow down against the deck surface is going to slow it down, restrict it. Maybe on an all-out high RPM Bonneville engine you want the last little bit of airflow from relieving but on the street (or dirt track) you want low and mid-range response. This calls for compression-which you gave away by relieving!---Just my 2 cents!
 
ford1 said:
also to add i dont recomend a blower on a flathead, they have only 3 main bearings and thats the weak point, they wont hold up under a heavy load usually break the webs on the center main, for carburation i would use a 350 cfm 4 barrel instead of two two barrels, easier to adjust
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Not wanting to satrt an argument here but I tend do dissagree with your blower statement. I installed mine in 2003, about 17,000 miles ago and have had zero problems. Pretty easy to put your foot into it though and it does add a lot of power.

James I recommend you order Joe Abbbins new supercharger book available on his website http://roadrunnerengineering.com. Much usefull information there as to releiving, heads, and blowers just fot flatties.
Jim
 
I have to go with Blown49. I do have a center main support and have had no problem what so ever. The power is incredible after driving stock flattys.

Just my .02

Fourdy
 

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I'm with blown49.
I have two friends with blown flatties, and they love 'em!

I also have to disagree on the relieving issue. In the 50s it was not uncommon for street driven roadsters to run 125-145mph at Bonneville (for instance Ray Brown, 143mph) and if you look at spec sheets, they pretty much all were ported and relieved. How many flatties today are driven to Bonneville, run 125-145mph, and drive home again? Even with technology today, we are not running as hard as they did in the 50s.
 
Here is a photo of the factory relief on my NOS 99A block that I am going to put in my '42 Sedan Delivery. These blocks were used in a wide variety of military applications during WWII. This one came in it's original military packing crate too which is going to make a really great coffee table. I am looking forward to getting the motor running, hopefully not in the too distant future! :)
 

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Bassman/NZ said:
I'm with blown49.
I have two friends with blown flatties, and they love 'em!

I also have to disagree on the relieving issue. In the 50s it was not uncommon for street driven roadsters to run 125-145mph at Bonneville (for instance Ray Brown, 143mph) and if you look at spec sheets, they pretty much all were ported and relieved. How many flatties today are driven to Bonneville, run 125-145mph, and drive home again? Even with technology today, we are not running as hard as they did in the 50s.
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Bassman has it right....It is easy to get 9 to1 with a relieved block and that is too much for todays no lead fuel..The only disadvantage to relieving is doing it for the average builder who doesn't have access to a machine shop.
Doing by hand takes about 10 hours...Doing it on a mill takes an hour.
I drove my 32 coupe to Bville in 1954, ran 137 and drove it home..Drag raced it many times after that besides driving it to work every day and ran Bville the following 2 years with the same engine...Oh and don't forget all the Saturday night street races...3 of my friends were doing the same thing at the time also.
The average guy with a flathead today has no idea what they are capable of.
RELATIVELY, it doesn't cost any more to build a fast flathead today than it did in the 50's....It does however cost a lot more for the same performance than bolting in a stock Chev crate engine...You either have "cool" or you have cheap.
Ah, but I preach to the wall.
 

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On relieving, I have seen examples of where the valve areas were contoured towards the bore; not really relieved, but the natural pocket where the valves sit chamfered. My pea brain thinks if it travels smoothly and in a straight line, that's the most efficient path. On any engine I build I will cut out the molding slag (very crumby casting on the block I'm working with) and try to eliminate any sharp corners. I did this on both the intake and exhaust and also did the chamfering so as the air/fuel mixture leaves under the valve it has less sharp angles. The same is true for the exhaust as all that hot gas tries to crawl under that little valve; less angle equals better transition.

I was surprised that the intake path isn't as retrictive in appearance as I thought it would be. It's not modern engine architecture but except for the last transition at the valve, it doesn't seem that bad. As I was grinding and smoothing, it appeared to me the exhaust is the real holdback. Those end cylinders and the 90d wall the gas hits as it flows towards the exhaust flanges is horrid. Anyone ever do anything with smoothing those far corners of the exhaust in the block? The siamesed center is bad but it looks like that's just one of those things you have to learn to live with. From what I've read, opening up the "fourth outlet" at the manifold heater doesn't really seem to help.

I'm using an Eddie Meyer 2X2 manifold with 94's. Its high rise and runners looked in photos like it was the straightest shot to the intake ports. Wrong. It may look cool, but my intuition says this one loses considerable horsepower to more conventional appearing manifolds. Looking into the manifold resembles a map of an LA interstate exchange. Experience?
 
I think Blown49 has it right and Pete has experience with these modifications. P personalty think relieving the block is a waste of time from a performance point of view, especially for a street engine. Relieving the head is more important in a competition engine. Cuz mentioned shaping the exit from the valve for better flow, I've done some flow bench work here and this works best. HOWEVER, regardless what you do it's hard to measure the change. Probably build two identical engines, one with and one with out a relief and see what the improvement is.
 
I never had a blown flathead but I once had a blown smallblock C word. Fantasic perfomance and very streetable. Low compression pistons with mild manners at lower rpm stand on it then it comes to life. Very costly but much nicer than 12 to 1 compression all the time. I would think a blown flathead would be a pleasure to drive on the street as well. In this case $ can buy happyness. If a bag of cash fell in the yard I'd do it. Gene
 
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