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Go fast 250 flathead?


martin67

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SBC = cheap..as in more ways than one..upgrading to a larger flathead is averall less invasive..going to a bent engine..lots and alots of mods no matter the coice of donor manufacture..this is a road to many compromises and where I assure one mod will incorporate yet 2 or three other mods to make it all work smoothy and even many many more cuts/welds dimples and reshaped metal and such to dress it up correctly..

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I don't care about racing anyone. I doubt if I would drive over 65 MPH. I think the stock Mopar flathead six costs less to rebuild than a Ford flathead 8. Quite a bit less. I have heard stories of getting it done for $1,800. Who builds the Ford that that little? Jegs offer a new Mr Goodwrench 350 for $1,500 - free shipping and 3 year GM warranty, get one if you like that option. For me the classic Mopar engineering is solid and that is what the car was built with. Chrysler was #2 in sales from 1937 thru 1951 on the strength of these motors. The alloy speed parts look pretty but so does detailed all iron motor. I might add some of that later. I intend to stick with the traditional build as in the Coatney 251. A 140 HP 265 has about the same torque as a stock 318 but at low RPM. I like the looks of these motor, plus my block number matches the title of the car. My grand father drove Dodges and Plymouths with the flathead six. Smooth dependable power.

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The Jegs/GM warranty on the 350 only applies when it is installed in a listed GM vehicle. Still, its pretty cheap for a new motor. I think by the time that the swap were done that the costs for the flathead six build would be less, if you don't use the costly antique speed parts.

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Thanks for the compliments on my engine. It has proven to be very dependable and I do not baby it. I once did just shy of 800 miles in one day and most of that was at 70 MPH.

When I bought my engine the block was stripped naked and all the parts were in a basket so to speak. I was told that all the machine work had been completed but I found that was not the case as the crankshaft needed some additional work. The new valves that came with my engine are from a shiverlay. They work well. I was told that the new pistons were also chevy but I cannot verify that. The pistons are .030" oversize for a final diaplacement of 255 CI.

MVC-026F-1.jpg

MVC-015F.jpg

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On changing to a small block chevy, where's the fun in that? It's like a butt, everybody has one:). I think the flathead 6 is unique, more interesting.

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just to be on the other side of the coin, lots of folks think the best part of the flathead is the ability to swap it out for another powerplant..I have a number of flatheads here on the place and in the past....I have a number of transplants now and in the past..I will admit that most that have been transplanted came with a busted engine or no engine at all making the choice easy...most of these the average person here have proved they would have sent these cars to the scrapyard due to rust in floors and rockers, bad engine and or interior by rip and tear..

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Don, don't suppose you have a pic of those "chevy" pistons do you?.........thanks, andyd

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Don, don't suppose you have a pic of those "chevy" pistons do you?.........thanks, andyd

I would be interested in knowing what piston was used! Also what RPM does the motor turn at 70 MPH with the T-5?

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My 265 with the T-5 and 4:11 gears---at 70 2600---at 60 2300

That's pretty good. I think my S-11 has 3.73:1, your setup is probably better. matched, although the 265 might have enough torque to pull the 3:73 in 5th.

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Hope no one minds me posting this again but I never get tired of it.

If you want to know what a flathead six is capable of read this report. It was done by the original owner of a 1951 DeSoto Suburban 8 passenger sedan who drove the car 180,000 miles between 1951 and 1975

I think this is my favorite part:

'Incidentally, any car loses power at high elevations, It is particularly apparent towing a trailer over Loveland Pass, nearly 12,000 feet, although low gear is more than adequate. But the surprising thing is that the car has no difficulty maintaining high speed with the trailer at high elevation on nearly level ground. The decrease in wind resistance is so pronounced at 10,000 feet in the high Colorado Valleys, that it will run at 70 easily, even up a slight grade. And the compression pressures are so reduced that the engine smoothes out like a perfectly balanced turbine."

70 MPH in a 6000 pound 8 passenger sedan, with a flathead 6 and 4.11 gears, towing a trailer.

http://www.allpar.com/cars/desoto/suburban-1951.html

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  • 5 years later...
On 05/06/2012 at 2:40 PM, michael.warshaw said:

not really a technical one, but wouldnt a small block chevrolet be the easiest and cheapest way to go?

Michael Warshaw, yep a Chevy would be cheaper to build. But that's not as much fun as building a flat head six & fitting a V8 looses the charm of these old girls.

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42 minutes ago, Mickkc77 said:

Michael Warshaw, yep a Chevy would be cheaper to build. But that's not as much fun as building a flat head six & fitting a V8 looses the charm of these old girls.

This is an old thread that Mikey posted this on 

In reality going SBC is really not so cheap in it's totality.

Buying an engine and trans, this could be cheap if used out of a junk yard or whatever.

Then the install.

New engine trans mounts, cross members etc.

New rad or adding a trans cooler for automatic trans.

New trans shifter.

Gas pedal and kick down linkage.

Headers or appropriate exhaust and complete exhaust system.

Belts, hoses and misc wiring etc.

New driveshaft and possibly diff.

Ebrakes if not going to a donor diff .

Diff install and changes.

Brake system upgrades.

And any other hidden and unexpected items that arise.

Not a huge deal for the experienced fabber and welder.

Stock engine build might bot be hugely cheaper. But us hugely easier and simpler even if going to a longer 250 engine.

You guys do the math....lol

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