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Old 03-01-2020, 01:56 PM   #21
Ggmac
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Default Re: 3.75 versus 4 inch crank

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Think you missed on that one! Tubman is in the overbore it camp.
Yes I did . Still agree with the bore vs stroke $ .
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Old 03-01-2020, 04:35 PM   #22
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Default Re: 3.75 versus 4 inch crank

I'm not worried about rebuilding it. I'm 75 and may not ever get another car built to use it in and I'll definitely never wear it out. I like Ron's suggestion of an 1/8th overbore as it appears I will have to buy pistons anyway? We'll see
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Old 03-01-2020, 08:32 PM   #23
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Default Re: 3.75 versus 4 inch crank

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I'm not worried about rebuilding it. I'm 75 and may not ever get another car built to use it in and I'll definitely never wear it out. I like Ron's suggestion of an 1/8th overbore as it appears I will have to buy pistons anyway? We'll see
Sometimes I have no idea of what goes on with this ste.
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Old 03-01-2020, 08:38 PM   #24
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Default Re: 3.75 versus 4 inch crank

Boring it out max can have an effect with heat for casual driving too. Do the crank and save another bore for your grandkids. or not and do both.


You could keep the bore lite and compression down and throw a blower on it.

Last edited by Tinker; 03-01-2020 at 08:55 PM.
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Old 03-01-2020, 09:15 PM   #25
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Default Re: 3.75 versus 4 inch crank

I repeat : 3 5/16" is NOT "boring it out to the max". If your 1/8" overbore has an overheating problem, there is something else wrong.
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Old 03-01-2020, 09:25 PM   #26
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Default Re: 3.75 versus 4 inch crank

I am still learning,,but from what I have read,,,1/8 is not the max .
Do whatever makes you feel good,,,but it should have plenty left after 1/8 inch if you go that route .

Tommy
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Old 03-01-2020, 09:34 PM   #27
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Default Re: 3.75 versus 4 inch crank

No matter the bore. a 4" crank is always better.


You'd probably be happy with a .040 over, a cam, and some 8/1 heads also.


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Old 03-01-2020, 10:24 PM   #28
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Default Re: 3.75 versus 4 inch crank

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I am still learning,,but from what I have read,,,1/8 is not the max .
Do whatever makes you feel good,,,but it should have plenty left after 1/8 inch if you go that route .

Tommy

.125 is close. Not much wiggle room really. Not plenty... could run into issues. Maybe depending on the cylinders. A 4" crank will always be better.

Last edited by Tinker; 03-01-2020 at 10:30 PM.
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Old 03-01-2020, 11:37 PM   #29
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Default Re: 3.75 versus 4 inch crank

All other things being equal, a shorter stroke is always better. Just about every automotive engine made currently is "oversquare" (bore larger than stroke). There has to be a reason for this. Piston speed comes to mind.

In practice, the difference in power would be undetectable; the difference in cost is not.
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Old 03-01-2020, 11:40 PM   #30
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Default Re: 3.75 versus 4 inch crank

We are talking flatheads, they don't do high rpms. Merc motors? 8k? no way. If you have a 70s hemi would you say more stroke is bad? Just asking... Cost??? Stroker motor?


I still think if you bore a motor out the only way to get more is from the crank. Only so far to go.


Topend engine is good too. Compression, cam, turbos, superchargers. No substitute for displacement.


Is it really that much more on a good block to do a bore over a crank? maybe so... I'm asking. I know you know your stuff. Yes having to rework the crank is added, but you have to anyway?

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Old 03-02-2020, 12:48 AM   #31
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Default Re: 3.75 versus 4 inch crank

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19Fordy: Any arm longer than 4 inches requires relieving the block for clearance according to the Tardel book.
Depends somewhat on the rods used and the block.
I have done quite a few engines with 4.25 stroke and never had to clear anything
for the lower end with 21A rods. The rods cleared by at least a quarter inch.
Did one engine with 4.438 stroke and Cat rods. NO grinding or clearing.
These were all 8ba blocks.
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Old 03-02-2020, 01:09 AM   #32
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Default Re: 3.75 versus 4 inch crank

"We are talking flatheads, they don't do high rpms. Merc motors? 8k? no way."

Actually, ALL DAY if need be, twice a lap. We usually gear for about 7200 though. Max power is around 6600 to 6900 depending on the cam.
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Old 03-02-2020, 01:21 AM   #33
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Default Re: 3.75 versus 4 inch crank

Still not 8k. Don't need it. Just cause you can don't mean ya should. Certainly if you are cruising you won't get there.

Very very impressive that you can Pete. Next level stuff.


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Last edited by Tinker; 03-02-2020 at 01:32 AM.
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Old 03-02-2020, 01:37 AM   #34
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Default Re: 3.75 versus 4 inch crank

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Still not 8k. Don't need it. Just cause you can don't mean ya should. Certainly if you are cruising you won't get there.

Still very impressive Pete.


.
Please RE-READ!!! I said 8K ALL DAY.

As far as cruising, tell me you haven't met someone that wanted to try you at a stoplight when you were lazy crusin'. lol
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Old 03-02-2020, 01:45 AM   #35
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Default Re: 3.75 versus 4 inch crank

Haha no, I'm a lazy cruiser. I had the better car still. Quite impressive man.
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Old 03-02-2020, 01:50 AM   #36
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Default Re: 3.75 versus 4 inch crank

I would like to build up a block some day for my 36 coupe. I've collected a few goodies over the years.


You guys with tire burners... god love ya.

Last edited by Tinker; 03-02-2020 at 01:57 AM.
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Old 03-02-2020, 02:05 AM   #37
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Default Re: 3.75 versus 4 inch crank

Why do i get the feeling Pete´s cruise engine would beat most racers around here..
I would love to have someone like Pete around my neighbourhood...to learn from and get me right back on the ground whenever i think i managed to build something fast...lol
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Old 03-02-2020, 02:07 AM   #38
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Default Re: 3.75 versus 4 inch crank

You got that right Murre.
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Old 03-02-2020, 02:28 AM   #39
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Default Re: 3.75 versus 4 inch crank

next level flatheaders
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