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Old 12-30-18, 07:03PM   #1
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Question main bearing spacers???

I've been always wondering about this, esp since I only have a couple 455 blocks. Does someone make a spacer to use a 3 inch crank in a a 3.25 block? Who and where?

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Old 12-30-18, 07:57PM   #2
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I have to ask,why not just use a 3.25 crank?Unless you want less than 4in stroke its just a waist of money IMO.Kasse did this in a couple of his engine master pontiac build to use like 2 5/8 mains in a 3in main block.Not cheap and you need to over come the rear main seal issue.ANYTHING can be done,just numbers in a check book.Tom
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Old 01-09-19, 04:15PM   #3
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In the past from what I remember oil pressure or lack of high oil pressure at rpm starves the rods with the large journal cranks, where the smaller journal cranks tend to be more forgiving.

Whenever I built a small journal crank motor I never had issues getting good oil pressure and getting the motors to live but when it came to the big crank motors they lost pressure over time and the bearings always took a beating.
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Old 01-09-19, 11:50PM   #4
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Spin my large journal 455 Crank to 6500-7000 RPM and not had any problems since when i built it in 2010. Using a melling select oil pump.
Paying attention to small details during assembly goes along way.
You can shear a sheep many times, but you can only skin them once.
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Old 01-16-19, 06:29AM   #5
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Originally Posted by healthservices View Post
I've been always wondering about this, esp since I only have a couple 455 blocks. Does someone make a spacer to use a 3 inch crank in a a 3.25 block? Who and where?

it has been done before, but if you want the advantage of a smaller main journal, it's way easier to just cut down a 3.25" crank to 3" and drop it in a 400 block. or buy/have made a 3" main forged or cast crank the stroke of your choice, and drop it in a 400 block.

or if you already have a 3" main crank, why spacer it into a 455 ? just drop it into a 400. that's what I was gonna do with a complete 366 CID NASCAR Pontiac rotating assembly I had, crank-rods-pistons. but common sense prevailed, I thought hells bells, why give up 100 cubic inches just to run the 366 ? not a good idea in a heavy car. the 366 is gonna have less torque for sure. so I sold the 366 stuff.

these are the common sense decisions that must go through your head when you contemplate this stuff, otherwise you may end up wasting a lot of money and time, only to be disappointed.

another option is use a 1958 370 or 1956 347 Pontiac block and adapt it to your transmission, those have an even smaller main bearing journal. but now you're giving up cubic inches, and as the old saying goes, there's no substitute for cubic inches. why give it away for a smaller journal, it becomes counter productive.

most guys who go that route also use the shorter 4" stroke to gain more rpm through the traps, and reduce piston speed and internal friction- that's what Nunzi and Rudy Dreyfuss did with their RA V engines. they ran cut down 421SD forged cranks in a 400 block, max overbored for around 446 cid, with tunnel port heads and the factory Pontiac 2-4 open plenum tunnel ram intake. Rudy also high ported the exhaust ports, i.e. cut them off and straightened them.

having said all this, Steinbrick from Canada ran the same time as Rudy with a 60 over 455 with big journal crank, 8.30's- by using a higher end chassis.

so there you have it, which way do you want to knit the sweater, or skin the cat ?

at that level we're talking a lot of money, time, and work for every tenth or 2 improvement in e.t. IMHO if it's a street car with a license plate, just use the stock big journal crank in a big journal block. the speed limit is what, 65-70 mph ?? what good is the smaller journal on the street. I got a sheetload of speeding fines driving my 4 cylinder and V6 family cars with less than 200 HP. where we going here ? my V6 2001 Monte Carlo has 200 HP, a 140mph speedometer, and it will bury it on the interstate highway. the new Ford Focus is a 4 door, 4 cylinder with turbo, and it makes 350HP bone stock form. it would eat a Ram Air IV GTO or Trans Am for lunch. I got stopped twice and fined once going over the speed limit in a 25mph zone just idling through traffic down the street with my RA V 455 with my foot OFF the gas, and on the brakes- cuz I was going 37mph at like 2000 rpm.

there's no place to open up a street car anymore without getting pinched, so save the cut down journal, etc. for track only cars where it actually might matter, and the amount of gain will be small, a tenth or two in e.t. ?? when all is said and done. there was quite a few 8 second Pontiacs with ported iron heads and big journal Pontiac cast cranks out there. how bad can they be ?? do you even need a 455 with big heads ?? cuz the Super Stock GT Pontiacs are running deep into the 9's with only 400 engines and casting 6x and 4x heads, with 156cc intake ports, and 142cc exhaust ports, and 2.11/1.66 valves. I spoke with one of them yesterday, his 400 SS/GT Pontiac walks away from $35,000 high end small block Chevys at the end of the track- and he has cast iron D-port 4X heads unported, a Qjet, and Pontiac 400 block. he runs 9.80's and there are other Pontiac SS/GT cars faster still.

moral of the story, do you really want to spend time, money, effort with the crank journal issue- is it even worth it ? not really, for a street car.

now, if you are into LEARNING all you can about the mysteries of the internal combustion engine, and building a working database in your head as time goes on, that's another issue. then yes, it's worth it. cuz then you're gonna find out first hand, how much is to be gained. but it's going to cost you a lot of time and money. the old saying, the road of excess leads to the palace of wisdom.

just remember, on the street, there's no substitute for cubic inches- so run the biggest engine you can. the 455 fills that bill admirably.
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Old 04-20-19, 01:45AM   #6
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Step Away From The KOOL AID !
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Old 04-20-19, 04:20PM   #7
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IMO the IA2 and MR1 blocks that come with 3" mains and the 3.25 mains are a "free" option and they should all come with 3" mains and the "free" option to come with 2.75 BBC mains and the crank companies should offer the cranks for sale to the racers.
They are steel or billet steel so cutting them down to 2.75 and welding the thrust is no that big a deal.
And the blocks would be that much stronger too.

HO Racing did a 2x4 "326" back in the day. It was a 347 block out of a armored car car with a different crank. Not a real 326 as they were dogs,dogs dogs. And it had the tiny 2.5 mains. It revved 8300 no problem.
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