Flathead Bore Size ?
 

This is for a street rod,34 coupe, flathead 8BA bore size favorite !

Re: Flathead Bore Size ?
 

+.030, .060, .080 or .125. Just wherever it will clean up.

Re: Flathead Bore Size ?
 

It is determined more by block condition then your wishes/favorite size.

Re: Flathead Bore Size ?
 

If you want to bore one from standard all the way out to max, you will lose a lot of potential use of the block. If you are already at 3 5/16" then that is a good size for a hot rod. A person can go to sleeves though and use larger if you have a mind to. It just depends on how much you want to spend and how long you want it to last.

Re: Flathead Bore Size ?
 

I did my first a 3 5/16 (276 with a Merc crank) and it worked well. I just bought another set of 3 5/16 pistons (this time for a stock stroke). Pistons, rings, and pins were $100, which is a heck of a lot less than a merc crank (if you can find one) for a comparable increase in displacement.

Re: Flathead Bore Size ?
 

I'am at 3-5/16 with my build and one four inch merc. crank. 276 inch ?? at my age (82) I saved some for the next build ....?? and here I sit with two more complete engines with 59 on the bell ... I just like saving some for the next build or the next guy, and a JWL says just what it take to clean it up ?? Yes the grandkids will have a big yard sale someday ??......OLD.....BILL:cool:

Re: Flathead Bore Size ?
 

255 is stock with a 4 inch crank.

Re: Flathead Bore Size ?
 

Well I have a 51 merc eng(255 stock for now)for my Av8.May go a bit over in the future.

Re: Flathead Bore Size ?
 

I agree with JWL.

Re: Flathead Bore Size ?
 

I like 276, 1/8'' bore. If you wear that bore out they make ,030 over 3-5/16 and probably .040 and .060 Walt

Re: Flathead Bore Size ?
 

Tubman, where did you get 3-5/16 pistons and rings for $100.00 Walt

Re: Flathead Bore Size ?
 

Egge makes light 3 ring piston in 3 5/16, + .020 and .030. With the thin Metric rings. Saved a 276 with the .020" and rings from a Volvo truck. I now have a 280 (279.4) Milled EAB heads 8.2CR and a stock EAB cam. Talk about torque??? I think even JWL would like it.

Re: Flathead Bore Size ?
 

I've got a 265 by my calculations, I just think, why bore it bigger than you have to, after all they aren't making them anymore.

Re: Flathead Bore Size ?
 

Speedway's garage sale section. About a year ago thay had a lot of piston sets (some were advertized as being made by Offenhauser) on closeout. I posted it here and on the H.A.M.B. The pistons came in a "plain brown wrapper", so they may be Chinese. but I took a chance on them. They look real nice and I went over them with a mic and all appears well. We shall see.

(Edit : Just for kicks, I checked the Garage Sale page again; there are still a few sets of pistons, but the prices I paid are long gone,)

Re: Flathead Bore Size ?
 

That's what I have too.

Re: Flathead Bore Size ?
 

Speedway had some hypereutectic flathead pistons for a while that were cast for them. They must not have sold too well but I haven't really heard anything about how they worked out. It would be interesting to know. I always wondered why the piston makers didn't go that route. The expansion factors for those pistons allow for a tighter bore clearance than with forged ones. The cost might be prohibitive in a niche market. How strong they are would be the big question for me.

Re: Flathead Bore Size ?
 

Flathead bores are tougher than some of you give them credit for … part of the reason there still here.
The truth is you’d have a hard time wearing one to the point of needing a rebore in the time any of you have left.

Bore it out all the way ... you cant take it with ya

Re: Flathead Bore Size ?
 

The main question was WHAT IS YOUR FAVORITE BORE SIZE FOR A STREET ROD ...

Re: Flathead Bore Size ?
 

Hey Calkid; looks like you got your answer 3-5/16...276, hands down, or 75 per/cent .........not good enough for you, :confused:?? all this talk about it, make me want to do it again, all I need is someone to make the "HOLE"
And find me a pieeeekup 39 or 40 I'll do it........OLD.....BILL:cool:

Re: Flathead Bore Size ?
 

3 3/8

Re: Flathead Bore Size ?
 

265 (+60). Cleaned up at that and leaves some for later.

Re: Flathead Bore Size ?
 

I'd probably go for +.080 unless I was building for performance. It's a decent overbore over stock, would clean up most bores (except maybe a +.060) and is the biggest size you can use with stock rather than big bore gaskets.

You've still got +.100, +.125 left to go after that, but as said, that option would probably be a consideration for someone else.

Mart.

Re: Flathead Bore Size ?
 

Me too! Coupled with a 4 1/8 Stroker . Love it

Re: Flathead Bore Size ?
 

Thats what I am running right now

Re: Flathead Bore Size ?
 

For most flathead REBUILDS (meaning after hot rodding) the block will clean at .010 or .020 at the most so I go big the first time.
The customer is always more pleased with the hp a 315 ci engine puts out than one under 280 ci.
A big bore can be left with .020 and get 2 sometimes 3 rebuilds with nothing but honing. I have found that 3 3/8+.030 is a safe bore with many 8ba blocks.
I always sonic check them to be sure.

Unless they are racing, most people could never wear out 3 flathead rebuilds.
I tell the customer, they are paying for the engine so THEY should enjoy it to the maximum and don't worry about the next owner.
Going conservative is like putting seat covers on a new car so the next owner can enjoy the new seats.

Re: Flathead Bore Size ?
 

Re: Flathead Bore Size ?
 

times 2 Pete. Walt

Re: Flathead Bore Size ?
 

I guess it is good to be in America where opinions can be expressed no matter the quality of content.

Re: Flathead Bore Size ?
 

We run a 99 engine in vintage competition with a 3 5/16 bore. Seems to have been the preferred performance capacity bore out here in NZ for many years.Cheers.

Re: Flathead Bore Size ?
 

How did that 3 5/16 bore with the stock stroke turned out ?
Cam ? Ive been thinking abiut doing that using an L100 on my 8BA

Re: Flathead Bore Size ?
 

See for yourself : https://www.youtube.com/watch?v=deAgpVmvjhU.

I find the MAX-1 to be a little mild, although the engine runs fine. I would seriously consider the L100.

Re: Flathead Bore Size ?
 

Sorry, duplicate post.

Re: Flathead Bore Size ?
 

Thanks tube

You kept it single carb ? How does it feel driving it though ?
How about compression drop because of the over bore without stroking ?

I got myself an L100 already and I dont think I will be able to use a Merc crank

Re: Flathead Bore Size ?
 

The single carb was for the initial start only; it now has a Navarro Universal dual (like a super with exhaust heat). You will notice the Edmunds heads; they were individually fitted to this engine to optimize quench and compression. After initial run-in, the engine had 150-155 lbs compression on all cylinders.

Unfortunately, advancing age has caught up with me, and progress on the car this is going in has come to almost a complete stop. Spending 6-7 months a year in Florida away from my shop doesn't help either. When I get back this spring I'm going to try to finish the rear suspension and get to final assembly.

Re: Flathead Bore Size ?
 

Sound really good. Hope you can finish the car soon

I just found out there are Ross specific pistons for 3" 5/16
Bore and 3.75 stroke :D

Re: Flathead Bore Size ?
 

On this one, I used pistons from Speedway Motors I got from their "Garage Sale" section about 10 years ago. Less than $100 for pistons, rings, and pins. I was a little leery about them at that price, but bought them anyway. I took them to my engine builder, and he checked them out and said they were fine. They were 4 ring pistons (an extra oil ring at the bottom of the piston), but after several discussions with the gurus here and on the H.A.M.B., decided to run them without the bottom ring. That meant I had to have the rotating assembly balanced, but you should do that anyway. Although it has minimum hours, the engine started immediately the first time and it runs, well you can see for yourself. After replacing the Speedway oil pump with a used genuine Ford pump with a new relief spring, oil pressure is factory spec (25 psi hot idle and 57 psi hot at 2000 rpm). The compression and vacuum numbers are where they should be and I am completely satisfied with the build.

In my opinion, a 258" engine like this is actually superior to a stock bore and stroke Mercury as it has 3 more cubic inches, and lower piston speed (which is always good). If I ever decide to rebuild the 255 merc in my '51, you can bet it'll get 1/8" over pistons, even if it doesn't need them.

Re: Flathead Bore Size ?
 

I agree. I never bore more than is needed to clean up the cylinder walls.

Re: Flathead Bore Size ?
 

Sure, but Seth, Aren;t you still in your twenties? :)

For us 70+ characters, I say

" Gimme one two five on the overbore,
Then stomp the ol' go-pedal hard to the floor.
Might not win the race
But you'll never lose face
And you'll bury that dude with your Roar."

Go big or go home. And Seth, I once felt as you do, but I have ten good blocks, and see many more coming into the stream. Don't make me write a poem about ' The block hoarder, who had a disorder.'....

Re: Flathead Bore Size ?
 

Another thing. The way we use and maintain these engines means that they would probably get rebuilt as soon as they started to blow a puff of smoke or lose a little compression. This can be solved with a hone and a new set of rings. That means another rebuild or two before another bore job is needed. Experience with my car tells me that they will go 75-80 thousand miles before they need any work if maintained properly. That's a lot of miles on one bore job.

Having replaced a tired engine with a healthy one, I know it really increases your enjoyment in a car.

Re: Flathead Bore Size ?
 

Ive always thought the 0.125 overbore went hand in hand with a Merc crank swap. Specially when using a performance cam like the L100 due to the low end drop, etc.