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Old 10-31-2018, 12:37 PM   #1
GOSFAST
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Default Flathead Overbore/Size Feedback

Hi guys, looking for some feedback on preferred o'bore sizes on the '59's and the 8BA blocks.

The sort of "accepted" size has always been .125" over, we sell most kits at this bore size, but with decent blocks getting much scarcer now and me personally never really being all that comfortable going out close to the "max" from the "get-go" we decided to try to change the "norm" from now on.

We are considering somewhere in the neighborhood of .070", .080", or .090", this would allow some "wiggle" room on the next o'haul with the same block and would also make any blocks already at .060" more eligible to be saved still with a lesser size o'bore than the .125"??

We will still be keeping Ross' .125" overs for either the 4.000", 4.125" or the 4.250" strokes

Thanks, Gary in N.Y.

P.S. I do realize there are already larger than .060" o'size pistons available but we're talking "staying the course" with Ross forged pistons and only with the metric (moly) ring packs. Am at the stage of needing about 10 add'l sets of pistons from Ross as I type!
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Old 10-31-2018, 01:01 PM   #2
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Default Re: Flathead Overbore/Size Feedback

Building a performance engine you want displacement...a block that canīt take .125 from start is not for racing...
Why not go for oversizes between .125 and .3 3/8 gives you the option to build a 3 3/8 light or reboring a .125. a couple of times.
Have a 3 3/8 in the shop now and enough meat left in the cylinder walls to make me sleep at night.
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Old 10-31-2018, 01:10 PM   #3
Tim Ayers
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Default Re: Flathead Overbore/Size Feedback

I have a 59 block I got from an old racer that is also at 3 3/8ths currently. Definitely need to get it sonic checked and eventually will do that just to see. I'm curious if there is any meat left on the bone.
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Old 10-31-2018, 01:11 PM   #4
51 MERC-CT
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Default Re: Flathead Overbore/Size Feedback

Just my thoughts, what is really being gained by going to the max. over-bore or longer stroke?
Who are Ya' going to beat?

In today's world there are 4 cyl. cars with half the displacement that'll blow your doors off.
The most I care to go is the next clean-up/over-bore and drive it till the next one (if I'm still around) Don't care to impress anyone.
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Old 10-31-2018, 02:19 PM   #5
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Default Re: Flathead Overbore/Size Feedback

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Originally Posted by 51 MERC-CT View Post
Just my thoughts, what is really being gained by going to the max. over-bore or longer stroke?
Who are Ya' going to beat?

In today's world there are 4 cyl. cars with half the displacement that'll blow your doors off.
The most I care to go is the next clean-up/over-bore and drive it till the next one (if I'm still around) Don't care to impress anyone.
It's that close to asking why mess with flatheads at all when there are technically more advanced car/trucks out there? Just about any vechile after the mid-50s has better everything (engines, performance, brakes, transmissions, rear axles, etc). You build/drive flatheads for the love of the nostalgia of bygone years. A hoped up flathead is not going to "beat" or out perform much on anything, that is not the point. It cost more to get much less performance wise out of a flathead, it's not because it is going to out perform something else on the street, it is for the love of the flathead itself and the love of improving the performance of the flathead just because.

I spent a ton of time and money building up a quick-change rear end in mid-fifties style. I'm not racing, I don't need the capability to change gears, I would never be able to get enough power out of a flathead to break it and there are a ton of later model rear axles that would swap in for much less expense and effort. So why do it? Because I like it, I think it is cool, I have always wanted to build one and now I can.

I want an early to mid to mid-fifties Hot Rod, that includes as much performance as I can get out of a flathead (big bore and stroke) and all the tricks I can muster up. And I wanted that quick-change in the back! I have liked them from the time I first knew what a car was and I still do. I have the time and the money!!

Last edited by JSeery; 10-31-2018 at 02:28 PM.
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Old 10-31-2018, 02:30 PM   #6
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Default Re: Flathead Overbore/Size Feedback

I don't know if its possible, or honestly how much work would be involved, a lot im guessing. But at some point do you just overbore the crap out of it and stick in a sleeve? or doesn't it work that way? sorry in advance, not trying to derail the original post.
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Old 10-31-2018, 02:31 PM   #7
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Default Re: Flathead Overbore/Size Feedback

Let me throw this out there: Assume you go out to .125 and use a metric ring pack and hone with a torque plate. Use quality oil and a filter, etc.

All the best machine work and you need to rebore many years down the road. Assuming the walls don't lose thickness do to rust, etc. is there a next "common" piston size between .125" v. 3/8ths?

By "common" I mean one that is not custom build.
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Old 10-31-2018, 03:24 PM   #8
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Default Re: Flathead Overbore/Size Feedback

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Originally Posted by Tim Ayers View Post
Let me throw this out there: Assume you go out to .125 and use a metric ring pack and hone with a torque plate. Use quality oil and a filter, etc.

All the best machine work and you need to rebore many years down the road. Assuming the walls don't lose thickness do to rust, etc. is there a next "common" piston size between .125" v. 3/8ths?

By "common" I mean one that is not custom build.
You can get pistons in any size you need. You most likely will not be fooling with a flathead in the first place if cost is a parameter.
Just as a side note, an all out flathead circle track engine will cost within a 10% of a 410 World of Outlaws sprint car engine and only make a third of the hp.

Most 8ba blocks will go 3/8 on the first bore and have plenty left for 2 .010 over rebuilds.
That is probably 200K miles on the street or 6 seasons of vintage racing.

In the olde dayz, there was too much variation in engine size rules at different tracks to keep pistons in stock. It only took 3 days to get them on order anyway.
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Old 10-31-2018, 03:26 PM   #9
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Default Re: Flathead Overbore/Size Feedback

Quote:
Originally Posted by Tim Ayers View Post
Let me throw this out there: Assume you go out to .125 and use a metric ring pack and hone with a torque plate. Use quality oil and a filter, etc.

All the best machine work and you need to rebore many years down the road. Assuming the walls don't lose thickness do to rust, etc. is there a next "common" piston size between .125" v. 3/8ths?

By "common" I mean one that is not custom build.
Realistically in our world I doubt anyone would wear out any bore size. The amount of miles it would take to wear out a block is beyond what any of us will do. Heck even my high mileage cross country drives and decades of use the bores in my block are still fine. The use of modern low tension rings which have been available for a long time helps greatly as well.

Tim to answer your question no common size is available between the two diameters you listed however Im sure Egge machines piston sets in say 3- 5/15 plus .020 oversize would not be a lot of money compared to their standard size 3-5/16 pistons.
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Old 10-31-2018, 05:41 PM   #10
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Default Re: Flathead Overbore/Size Feedback

When I built my 258' (3 5/16" bore by 3 3/4" stroke), the machinist said it would go 3 3/8" easy. I had already made a smokin' hot deal on a set of .125 pistons, so I went with that. Even though the block sonic tested OK, when he did the overbore, he hit a casting flaw in one of the cylinders. He said it would run OK as is, but for the extra $75, I had that cylinder sleeved.

I have a 255' Merc in my '51 Ford coupe, and with the additional displacement, a set of heads, a Rochester 2GV, and a decent ignition, the car is a pleasure to drive. I can keep up to traffic with no problems, and the car will cruise at 75. With the stock engine, the car was a bit of a slug.

I will also agree with "Pete"; with he way these cars are used, there is more than enough cylinder wall left for a couple of hones and new rings. How many miles does that amount to given modern oils and all? I'll let the museum curator in 2311 worry about the third overhaul.
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Old 10-31-2018, 06:31 PM   #11
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Default Re: Flathead Overbore/Size Feedback

GOSFAST

I know that Ross will make custom piston sizes but can you get the metric rings to go with the custom pistons of various sizes as you described?
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Old 10-31-2018, 07:13 PM   #12
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Default Re: Flathead Overbore/Size Feedback

I have a perfect 59AB block, a 4" merc crank, and a set of used 3 5/16 pistons that look pretty good. Thinking of glass blasting the used pistons to build this motor. I used some used 1959 Oldsmobile pistons a long time ago in a Model B block and they worked fantastic.
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Old 10-31-2018, 07:21 PM   #13
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Default Re: Flathead Overbore/Size Feedback

I have a French block that I know will be able to go with .125 over pistons, 4" crank, L100 cam. I will check but I am sure there will be more overbore room for the next guy
... I have three engines to build using my roadster as a test mule. Hopefully my grandson will get hooked on this stuff and he, will have plenty of spares to with it - 4 engines, 2 rebuilt 5-speeds, another open drive 36 rear, replacement brakes, etc, etc. We've got some work to do together so he will know what to do when I'm gone .....
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Old 10-31-2018, 07:35 PM   #14
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Default Re: Flathead Overbore/Size Feedback

With good blocks getting as hard to find as they are, there was no way in hell I was going to bore a NOS 59 series block. Why take life out of something for (if you are honest) a small amount of gain? I put a 4" crank, Ross 3 3/16 pistons with the skinny rings mild cam and 4bbl Holley in it and it performs fine. The engine in my avatar roadster is much higher performance (and $) but unless I really jump on it, it is not going to be that much different. I am more into keeping these things around then ultra max hp. But, to each his own.
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Old 10-31-2018, 07:58 PM   #15
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Default Re: Flathead Overbore/Size Feedback

Not sure I understand the bore size concerns, a good block can always be sleeved.
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Old 10-31-2018, 08:13 PM   #16
Tim Ayers
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Default Re: Flathead Overbore/Size Feedback

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Not sure I understand the bore size concerns, a good block can always be sleeved.
I guess so, but at an added cost of $600 if we use the $75 per hole for a sleeve.
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Old 10-31-2018, 08:35 PM   #17
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Default Re: Flathead Overbore/Size Feedback

Speed/performance cost.
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Old 10-31-2018, 08:54 PM   #18
Tim Ayers
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Default Re: Flathead Overbore/Size Feedback

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Speed/performance cost.
I guess, but it would nice to put that $600 to something you could see and find a block that doesn't need sleeves. After 3 3/8ths, you may not too much of a choice I guess...
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Old 10-31-2018, 10:35 PM   #19
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Default Re: Flathead Overbore/Size Feedback

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Originally Posted by deuce_roadster View Post
With good blocks getting as hard to find as they are, there was no way in hell I was going to bore a NOS 59 series block. Why take life out of something for (if you are honest) a small amount of gain? I put a 4" crank, Ross 3 3/16 pistons with the skinny rings mild cam and 4bbl Holley in it and it performs fine. The engine in my avatar roadster is much higher performance (and $) but unless I really jump on it, it is not going to be that much different. I am more into keeping these things around then ultra max hp. But, to each his own.

Deuce, we both live in rural Washington state. We don't have Bonneville salt flats, Race of gentlemen or Muroc dry lake beds. Fun to go up hills without downshifting, but I am with you. Lets save those holes just in case someone actually cares in the future. Still, I'm not holding my breath, but......
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Old 11-01-2018, 12:14 AM   #20
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Default Re: Flathead Overbore/Size Feedback

I'm going .100 over on a 21 stud '37, just to leave .020-.025 for another bore if it's ever needed. Took me 5 blocks to find a good one.
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