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Old 07-31-2022, 03:32 PM
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Default Forged 3.25” main 4.00” stroke crankshaft options

Years ago there were a few different manufacturers offering 3.25” main 4.00” stroke crankshafts (All Pontiac/BOP/Scat, Ohio, Eagle, Star, etc.). Does anyone have experience with any of them in a higher horsepower application 1100hp - 1400hp? Any oiling mods to get it to live?

I’m gathering parts for my twin turbo build. My IA2 block is one of the few 3.25” main versions they made. I currently have an Ohio forged 4.21” stroke crank in my engine. The plan is to reduce the stroke to 4.00”. If I have to start over with a 3.00” main IA2 I will, but I’d really prefer not to due to cost and long wait times for parts. It would probably add two years to the project which I don’t want. I want to be up and running with turbos next year.

I had one of the early AP Scat 3” x 4.25” cranks in my 505 build and it rang like a bell and was damn near perfect out of the box. Ideally I’d prefer to find one of these early AP forgings in a 3.25” x 4.00” version (I think they made them).

Butler sells a 3.25” x 4.00” version made by RPM out of Southern California. I think Ace at PPR used a lot of their stuff. Does anyone here have experience with these? Ace has moved on from Pontiacs.
https://butlerperformance.com/i-2445...tegory:1234872

A Kellog SD 990 4.00” crank would be a nice option as well assuming I can find one. Plus find one that hasn’t been turned down to 3.00” mains yet. I do like the idea of using a high quality factory forging.

Suggestions?

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Old 07-31-2022, 05:11 PM
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I can not comment directly about the forged cranks you are considering. But I assume the larger question you are asking is how to achieve longevity with this set-up and high HP. You didn't specify the target RPM for your build. That will make a big difference with the large diameter crank. I also don't know if the forgings you are considering are cross drilled. I would think a cross drilled crank with the large mains could be an issue as the RPM's approach and exceed 7000 RPM's. A priority, straight shot oiling system in the crank would be better IMO. Others will probably not agree with me but I would limit the oil to the valve train with some lifter bore restrictors to force more oil to the mains. I would run at least .0035 and probably .004 main clearance, and I would run high oil pressure. An 80 lb. Melling pump would be the minimum pump I would consider. This is the recipe that worked for us at 1000 HP on a stock block 455 before switching to the IA stuff. That was on a stock N crankshaft I prepped. Yiikes! Never broke one. Magged it twice a year.

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Old 07-31-2022, 06:34 PM
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Agree with Mike. And to emphasize, RPM is your enemy with the 3.25" main due to the high tangential speed generating lots of heat. Since you're going twin turbo, the mindset of the package should be moderate RPM and let higher boost do the work for you.

Eric

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Old 08-01-2022, 01:41 AM
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Quote:
Originally Posted by mgarblik View Post
I can not comment directly about the forged cranks you are considering. But I assume the larger question you are asking is how to achieve longevity with this set-up and high HP. You didn't specify the target RPM for your build. That will make a big difference with the large diameter crank. I also don't know if the forgings you are considering are cross drilled. I would think a cross drilled crank with the large mains could be an issue as the RPM's approach and exceed 7000 RPM's. A priority, straight shot oiling system in the crank would be better IMO. Others will probably not agree with me but I would limit the oil to the valve train with some lifter bore restrictors to force more oil to the mains. I would run at least .0035 and probably .004 main clearance, and I would run high oil pressure. An 80 lb. Melling pump would be the minimum pump I would consider. This is the recipe that worked for us at 1000 HP on a stock block 455 before switching to the IA stuff. That was on a stock N crankshaft I prepped. Yiikes! Never broke one. Magged it twice a year.
Quote:
Originally Posted by Elarson View Post
Agree with Mike. And to emphasize, RPM is your enemy with the 3.25" main due to the high tangential speed generating lots of heat. Since you're going twin turbo, the mindset of the package should be moderate RPM and let higher boost do the work for you.

Eric
Thanks for the input guys. I had a great talk with Marty Palbykin yesterday and his concerns were with the 3.25” mains as well (size, oiling, rpm capability, plus durability). Super nice guy and such a wealth of knowledge and experience. He gave me a lot to think about.

I’m not trying to set the world on fire here so maybe if I limit rpm to the 6400-6500 range it will live??? The turbos will make the power, I just need it to stay together.

In a perfect world I’d start over with a 3” (or smaller) main block, but like I said in my first post I really don’t want to be down for 2 years to get a new shortblock together.

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Old 08-01-2022, 06:00 AM
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How are you planing to get to 1100 to 1400 hp, with NOS?

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Old 08-01-2022, 06:50 AM
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I'd feel like anything under 7000 rpm should be fine for drag racing or street use. Sustained RPM (like a boat or Nascar) would create lots of heat and demand lower rpm.

As Mike recommended, lifter bore restrictors, a little bit looser main clearance and stay away from the 20w-50 goop. You need plenty of oil FLOW thru the mains to flush away heat.

Eric

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Old 08-01-2022, 10:24 AM
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If your 4.21" stroke crank is Pontiac rod journals. Have you though about de-stroking your crank by reducing the rod journal size?

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Old 08-01-2022, 01:07 PM
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Quote:
Originally Posted by 25stevem View Post
How are you planing to get to 1100 to 1400 hp, with NOS?
Twin turbos. I need to call the turbo guy later this week but I’d guess twins in the 72mm - 78mm range.

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Old 08-01-2022, 01:29 PM
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Why not just run the 4.21 Ohio?

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Old 08-01-2022, 01:32 PM
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Quote:
Originally Posted by Elarson View Post
I'd feel like anything under 7000 rpm should be fine for drag racing or street use. Sustained RPM (like a boat or Nascar) would create lots of heat and demand lower rpm.

As Mike recommended, lifter bore restrictors, a little bit looser main clearance and stay away from the 20w-50 goop. You need plenty of oil FLOW thru the mains to flush away heat.

Eric
I’ll definitely check into it.

Spotts built my current engine and it runs like a champ. According to my build sheet the mains are currently at .0025. I’ll have to check with him to see what oiling changes have been made and what could possibly be done in the future.

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Old 08-01-2022, 01:41 PM
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Quote:
Originally Posted by Stan Weiss View Post
If your 4.21" stroke crank is Pontiac rod journals. Have you though about de-stroking your crank by reducing the rod journal size?

Stan
It is a Pontiac rod journal. I thought you could only change the stroke like .04 either way? I haven’t really looked into it

Quote:
Originally Posted by firechicken View Post
Why not just run the 4.21 Ohio?
I want to take off as much stress as I can so it lives a long happy life. The extra stroke isn’t needed.

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Old 08-01-2022, 04:24 PM
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Whelp it appears finding a 3.25” main 4.00” stroke forged crank is going to be more challenging than I anticipated. Butlers is out, KRE is out, RPM said the foundry that did the 4” stroke crank forging in China shut down during the pandemic and will not be reopening. I also called Ohio crankshafts, they don’t have them and don’t plan on making any.

While halfway through this post I called Scat and they don’t have any 3.25” x 4.00” in stock but said they can make one. It is considered a custom forging and is more money but at least it’s not a $5000 billet. Straight shot oiling and a 1500hp rating. 6-8 weeks lead time. This I was great news

I’m going to search around for a while and see what pops up for sale but I imagine the Scat custom forging will be my option.

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Old 08-01-2022, 04:49 PM
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You and I both have what the other wants. You have the 3.25 main aftermarket block that I've long searched for and I have the fresh .10/.10 990 crank that you really need.

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Old 08-01-2022, 08:13 PM
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Quote:
Originally Posted by Johnny406 View Post
You and I both have what the other wants. You have the 3.25 main aftermarket block that I've long searched for and I have the fresh .10/.10 990 crank that you really need.
You guys should trade

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Old 08-01-2022, 10:35 PM
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Quote:
Originally Posted by Johnny406 View Post
You and I both have what the other wants. You have the 3.25 main aftermarket block that I've long searched for and I have the fresh .10/.10 990 crank that you really need.
We may be talking about that soon

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You guys should trade

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Old 08-02-2022, 02:09 AM
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I sold a RPM 3.25 x 4" 4340 crank awhile back. Kinda doubt he would want to sell it but there are a few around.

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Old 08-12-2022, 12:53 PM
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I contacted Molnar again and received some good news. They advised that they have the capability to do a 3.25" main 4.00" stroke forged crankshaft. He said they require a minimum order of 5 crankshafts at a time for them to be machined.

Obviously I would be in for one. Does anyone else here have interest in a 3.25" main 4.00" stroke forging with 2.20 journals? If so, please let me know. We need 5 orders to make it happen

I also contacted Butler's to see if they were interested since their source for 3.25" main 4.00 stroke forgings from RPM have dried up. Waiting to hear back

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Old 08-15-2022, 01:39 PM
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I just received confirmation from Molnar. They are moving forward with building them.

3.25” main 4.00” stroke 2.20” bbc rod journal
Straight shot oiling
https://molnarrods.com/pontiac-400-crankshaft

I just called and placed my deposit. If you want one of these now is the time

Per Molnar:

“Since these are a special run and not currently a stocking item, we are requiring a non refundable $150 deposit to hold your order.
The reason for the non refundable part is there are often people who want the parts until they arrive then back out leaving a bunch of parts without orders. We currently have enough orders to go to production and will be starting them very soon. To place your order, please call us at 1-616-940-4640.”

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Old 08-15-2022, 03:50 PM
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Great Job James!!

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Old 09-27-2022, 08:14 PM
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Default 4.00 3.25 main Ohio crank

Did they make them. Interested

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