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Old 12-23-08, 07:05AM   #1
ORBIT 4-SP
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Default 4.5 Stroke Factory Block

I am interested in anyone that has direct experience with installin 4.5 crank in a factory block.Your results,longevity,rpm,etc.I realize alot of opinions on this,but i am looking for people who have done it or personally know someone who has.
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Old 12-23-08, 07:34PM   #2
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I second this request. I have in my possession the 4.5" crank, rods and pistons with Kauffman high ports, solid rollers, to go with this. I am almost ready to start the machining and preparation work on a four bolt 3.25 main block. I have gotten some mixed information regarding reliability and have requested Pontiacdudes input without a response so far. If someone has direct experiences please share that here with us in what they are, what was done and the end results. Personally I do not want to build this if it's just a time bomb waiting to go off having reliability issues.
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Old 12-23-08, 11:21PM   #3
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I've never done it...I doubt they'd be any reliability issues. As far as putting it in a stock block the only thing that I know of that might have to be done is grinding the block to make sure the counter weights clear the block.

You do have to know most of the reliability issues would come in the HP and rpm level you plan on taking the motor to...stock blocks usually don't last long with making over 650 hp at 7000-7500 rpms. The bigger the stroke the lower you would want to keep the rpms. A 550 hp stock block would probably live a long life around 6200 rpms...but a 650-700 hp one at 6500-7000 rpms would probably last about 75 runs maybe more who really knows..with that kind of stroke.
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Old 12-23-08, 11:41PM   #4
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Gach: Horsepower and reliability are my questions. I thought I would be around 650, 700 at the most. Using Jim Hands formula on head flow put me at over 700. Higher than where I thought I would be. I should be around 62 for redline, but I could be off. I remember hearing about the blocks that split in half from excessive HP. I have considered a main girdle, but cannot find one for Pontiac. So I am considering making my own. Ford and Chevy have used them for years and anything that would make the block stronger to survive I would consider. I know they are primarily for bearing stability, but they should give reinforcement to the block making all the caps locked in one place, preventing movement and giving the block some rigidity.
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Old 12-24-08, 12:10AM   #5
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It also depends on which block your using too. The 455 blocks are thin
around the #4 mains..were the bore meets the main that the cap bolts to. That's usually were it splits up to the cam bore. The 400 blocks are stronger in that area, but not by much. Cast cranks don't help because
the flex...so going with a steel crank will help allot. There's no grantee
here but if you can keep it around 6200 rpms..with a real light assembly
aluminum rods...light pistons and lighten the crank by cutting the counter
weights..getting the crank down to 65 lbs..steel 4 bolt caps with studs,I think at 6200 rpms you'll be good.
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Old 12-24-08, 01:10AM   #6
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I have two blocks a 69 428, factory four bolts and a 70 455 block. Initially I was going to pull the 428 apart and install my stroker kit which is all forged with 6.8 Chevy rods. The crank is not light, it must weigh 80 lbs but it is forged. All this weight is being a major concern. I suppose getting it turned could work but I would need to talk to a machinist and see if getting it down to 65 lbs is possible? I do not want to run aluminum rods as this is going to be for the street with occasional strip and I would like to make it where it will last and not have to worry about the rods getting brittle. But with reliability an issue perhaps I should reconsider?
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Old 12-24-08, 01:13AM   #7
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WD: I agree and I had questions about what you were running and how hard in the hopes that I could learn without repeating the mistakes. What RPM's were you turning? What was your power level?
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Old 12-24-08, 01:42AM   #8
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Default Stock Block

It will be an eventual grenade.
If you build it that big the temptation to "throw a kit on it" will come next.

Why put all that money in good parts ,machine work and time into a weak piece block that has been demonstrated to eventually fail at power levels above 650.That is why the new stuff is out there.
Do the math on the cost of all the other pieces and work it will take to stuff it all into a stock block.
The cost savings on the stock block is a false economy even if you have a garage full of them.

35 years ago if you were making 500+ horsepower you were shitting in tall cotton.
Now everyone wants 700 to 1000 horsepower to push their 1 - 3/4 ton"street sleds" down the track or they aren't happy.
The technology is there to support it now but one could also take a lot of weight out of the car and do more with less.
Single or twin turbo on a 400 or 455 would get you there too and without a monster rotating assembly.
Just another way to go.

Leave the 28year+++++old blocks to the restorers and "low power" racers.
Oil downs are now a delay of game penalty.
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Old 12-24-08, 10:22AM   #9
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I have always heard that Aluminum rods in a street motor would last as long as the motor...Only racing it with big power and RPM will shorten their life.

I heard this from a engine builder who builds KB & Brad Hemi's He said it was a myth that the aluminum rods wouldn't hold up....Of course the aluminum rods he was talking about were Brooks brand and made for 3,000+ horsepower.

A buddy of mine built a 65' Tempest that had a 484" Pontiac that ran 9's with Aluminum rods and as far as I know they were the same rods in the car when he sold it....With MANY seasons on them.
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Old 12-24-08, 11:12AM   #10
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That big stroke and 6.8 rods results in a piston pin height that tends to rock the piston enough to bring on scuffing and early wear. A 6.5- 6.625 rod will be fine. (shorter rods are usually lighter and offset any piston weight gain) Keep the revs down. Some turbo Pontiac combos making 800 plus hp and living fine. They are using cast cranks(good rods) studded 2 bolt mains and keeping the revs down. RPM is what stresses the block the most.

BTW the cost of fabbing and fitting and reinforcing a stock block rapidly approaches cost of of an IA2 block and there is no assurance your modded stock block will live like the IA2 does. Think twice before risking expensive internal parts to a weak block. At some point your power "fix" habit will need stronger dose and you will eventually need that IA2 block.
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Old 12-24-08, 11:15AM   #11
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FWIW,Piston speed at 6000rpm will be higher with a 4.50 than with a 4.25 stroke,creating more stress on a factory block.
Bigger 3.25 mains have a higher bearing speed and creates more heat.also less material in the block.
Lighter weight parts help,but the longer stroke will pull the block apart if you want any RPM out of it. splayed caps would be better than straight,they tie into the sides of the block pulling it together. Like Sprint said,it will be a grenade. When it comes to Bore size and stroke,where is the point of diminishing returns.
The 326 built with the 4.5 stroke was a bad idea(one of the TV shows,don't remember which one)

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Old 12-24-08, 07:36PM   #12
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Since the question was asked of THOSE WHO HAVE DONE IT I figured I would tell you my experience. I ran a 4.5" MT cast crank with 6.7" steel rods and custom CP pistons. This was with 3.0" mains and 2.5" rod journals. I can't remember the exact #'s, but with factory Dports that flow about equal to an untouched Edelbrock head, it made about 650TQ@ 4100rpm & 625HP @ 5900rpm. I didn't rev it much past 6100rpm. I would have tried more put it stopped pulling. Upon disassembly the valve springs had gone from 185lbs to 130lbs in less than 15 runs. The best it ran at 3500lb race weight at a Density Altitude of 6500plus was 11.36 @114mph. I ended up putting a 6" hole in the side of the block. I cannot say with 100% certainty, but it appears the problem was caused when I had the block decked and did not recheck piston to head clearance. Upon disassembly all the pistons showed very light marks where they had touched the heads. This very well could have caused oiling problems for the rod bearings that seized. I like my new combo better with the 4.35" stroke and much larger bore as it revs easier and the heads flow better with the larger bore. Plus it has run 10.68 @ 125mph and has stayed together.It dyno'd at 675HP and 624TQ. I still have the damaged 4.5" crank if anyone is interested, though even if repaired, I would only use it as a killer street engine and keep the rpm below 6000rpm, maybe even 5800rpm. It would be very cool motivating a big ole Cat or Bonnie! Better assembly should help yours to live, but there is still quite a bit of side loading on the cylinder walls.

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Old 12-24-08, 09:43PM   #13
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Quote:
Originally Posted by g_man View Post
I have two blocks a 69 428, factory four bolts and a 70 455 block. Initially I was going to pull the 428 apart and install my stroker kit which is all forged with 6.8 Chevy rods. The crank is not light, it must weigh 80 lbs but it is forged. All this weight is being a major concern. I suppose getting it turned could work but I would need to talk to a machinist and see if getting it down to 65 lbs is possible? I do not want to run aluminum rods as this is going to be for the street with occasional strip and I would like to make it where it will last and not have to worry about the rods getting brittle. But with reliability an issue perhaps I should reconsider?
Use BME Rods Thats The Key to Having a Stock block live LIGHT ROTATOR!, Trust me they last 100,000 miles of street/strip use, My STREET/Strip 535 is going with BME 6.7 396 series rods They are Forged Alum and Do not act the same as cast billit, Also 6.7 rod length is a Good length, Also I got my Light Weight 65lb 4.50 Stroke Crank from All Pontiac FWIW
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Old 12-25-08, 04:18AM   #14
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Heck My paps ran a USED 396 series 6.335 long set in his 1600+hp 540 Chubby Blown Alky motor for almost 3 seasons at 8500rpm before losing two pistons, Rods are still good and measure in spec and He will still run em, He Broke many rods before the BME's, Brooks,C&A,and Venolia's Big Heavy POS's! They usually would pull the caps off at the Big end on Shut down
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Old 12-25-08, 07:56AM   #15
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464GP69, What rods do you guys like? Is the Brooks 88 series any good?
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