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10-31-2018, 12:37 PM | #1 |
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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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10-31-2018, 01:01 PM | #2 |
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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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10-31-2018, 01:10 PM | #3 |
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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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10-31-2018, 01:11 PM | #4 |
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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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10-31-2018, 02:19 PM | #5 | |
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Re: Flathead Overbore/Size Feedback
Quote:
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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10-31-2018, 02:30 PM | #6 |
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Re: Flathead Overbore/Size Feedback
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10-31-2018, 02:31 PM | #7 |
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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. |
10-31-2018, 03:24 PM | #8 | |
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Re: Flathead Overbore/Size Feedback
Quote:
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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10-31-2018, 03:26 PM | #9 | |
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Re: Flathead Overbore/Size Feedback
Quote:
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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10-31-2018, 05:41 PM | #10 |
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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. |
10-31-2018, 06:31 PM | #11 |
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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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10-31-2018, 07:13 PM | #12 |
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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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10-31-2018, 07:21 PM | #13 |
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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 ..... |
10-31-2018, 07:35 PM | #14 |
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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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10-31-2018, 07:58 PM | #15 |
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Re: Flathead Overbore/Size Feedback
Not sure I understand the bore size concerns, a good block can always be sleeved.
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10-31-2018, 08:13 PM | #16 |
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Re: Flathead Overbore/Size Feedback
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10-31-2018, 08:35 PM | #17 |
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Re: Flathead Overbore/Size Feedback
Speed/performance cost.
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10-31-2018, 08:54 PM | #18 |
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Re: Flathead Overbore/Size Feedback
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10-31-2018, 10:35 PM | #19 | |
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Re: Flathead Overbore/Size Feedback
Quote:
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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11-01-2018, 12:14 AM | #20 |
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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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11-01-2018, 12:47 AM | #21 |
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Re: Flathead Overbore/Size Feedback
My current flathead is 3.345 X 4.125. Ross pistons with Metric ring pack
Previous flathead engine was 3.330 X 4.125. Egge pistons with standard rings Both engines were sonic tested Last edited by Kahuna; 11-01-2018 at 10:53 AM. |
11-01-2018, 05:48 AM | #22 |
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Re: Flathead Overbore/Size Feedback
One of my current engines broke a piston pin retainer while I was flogging it on the dyno. The tiny little broken piece got jammed on the side of the piston and created a perfect groove in the cylinder bore. I was VERY happy I had only bored to +.060 during the original build so I could clean it up at +.125.
The power value difference between +.060 and other sizes will never be noticed on the street. In fact there is usually more potential in professional, time consuming, tuning than the favored overbore. |
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11-01-2018, 12:35 PM | #23 |
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Re: Flathead Overbore/Size Feedback
Question.... Can Scat cranks and rods be used with smaller than .125" pistons? For example can a scat crank and rods be used with Ross .060" pistons? or better yet can a Scat Crank and Rods be used with Egge or anyother cast piston?
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11-01-2018, 01:35 PM | #24 | |||
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Re: Flathead Overbore/Size Feedback
Quote:
Quote:
Quote:
Today we are working on a 3.385" (finished) bore/metric ring pack on a "59" block with a 4.250" arm which will and up being a 306" unit! Thanks, Gary in N.Y. P.S. I will have more info about this post in the coming days concerning the o'bore sizes we will be putting on the shelf. Some of the o'sizes we are considering today will be .070", .080", .100", and we always have the .125" on hand. All of these will be Ross pistons for the 4.250" stroke only since the general consensus here appears to be all about the most "cubic-inches". To me it seems just more appealing to have .080" or .100" over with a 4.250" arm, either will still yield over a 280" build!
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11-01-2018, 02:11 PM | #25 |
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Re: Flathead Overbore/Size Feedback
The advice from the machine shop I used (J & M Machine) was to go just enough to clean it up and preserve the 59A-B casting for the future. Ended up at .040 over, 3.225. Seemed to be a hard piston to find in stock for the 4" stroke though.
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11-02-2018, 11:00 AM | #26 |
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Re: Flathead Overbore/Size Feedback
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11-21-2018, 09:45 AM | #27 |
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Re: Flathead Overbore/Size Feedback
I brought this back up to let everyone here know what we decided to do about the piston sizes to put into inventory!
We chose to go with .070" and .080" overs, this will allow many blocks to be finished to an "in-between" size so to speak. Not to have to initially go to the popular .125" over. We will also still stay with this combo however, the 3.312" (bore) x 4.250" (stroke), Eagle cranks, Scat h-beam rods, and Ross pistons! Thanks, Gary in N.Y. P.S. These will ALL be Ross (forged) pistons and have only the "metric" ring packs, 1.5, 1.5, 3.0. They will also be for various stroke combinations, mostly the OEM 4.000" and the also popular 4.250". There will be a "handful" for the not-as-popular 4.125".
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11-21-2018, 12:11 PM | #28 | |
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Re: Flathead Overbore/Size Feedback
Quote:
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11-21-2018, 12:38 PM | #29 | |
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Re: Flathead Overbore/Size Feedback
Quote:
These pistons will work with all the factory components if that's what the customer decides. They will go with a 4.000" conventional Merc crank or an "up-stroked" one as well, same with the OEM 8BA style conn rods, doesn't matter, they'll work here also!! Thanks, Gary in N.Y. P.S. What we're trying to accomplish is "saving' the blocks for future builds w/o any hassles (sleeves, etc). If you "wear-out" (highly unlikely) an .080" o/b you still have the .125" over option open to you? We can also generally go anywhere between the .080" and the .125" if necessary, as long as the rings are available?
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11-24-2018, 10:46 AM | #30 |
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Re: Flathead Overbore/Size Feedback
Hey Gary - a bit late to this party . . . but here are my thoughts. I have used the 3 5/16 bore (3.3125) for most everything that I've built - and in a good block, I can get a few more over-bores at that size (so I've not worried about it). With that said, if you can get good 1.5, 1.5, 3.0 mm ring packs at smaller bores - why not go to .080 or .100 for most situations? The last few cubic inches will not make any difference for about 99.9 % of the folks who want a "hot" flathead. Hell - most are more concerned with how it sounds and how it looks - versus how it actually performs. I've sonic tested quite a few blocks and when you get out to 3 3/8 bore, then I tend to see cylinder wall thicknesses in the .090 to .110 range. Obviously it depends on the individual casting, amount of rust over the years, core locations, etc.. I see no real reason to bore the crap out of a good block these days . . . unless you're going to Bonneville . . .
I'm not a big fan of putting 8 sleeves in a block that was previously bored to 3 3/8 - to get it back to 3 3/8. It tends to get quite expensive and also a lot of structural strength was removed (bored out of it for the sleeve thickness). This is more of a concern for high-end race engines - which is about the only place you see it. Not as much of a concern for NA engines, more of a concern for supercharged engines where sealing the deck surface is already hard (because the decks are thin). Also, most race engines are relieved - so the transfer areas are already thin . . . so sometimes issues are caused in these areas as well. Last edited by Bored&Stroked; 11-24-2018 at 10:55 AM. |
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