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#1
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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?
Im 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 Id really prefer not to due to cost and long wait times for parts. It would probably add two years to the project which I dont 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 Id 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 hasnt 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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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
#2
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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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#3
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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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"Everybody has a plan until they get punched in the mouth" noted philosopher Mike Tyson Life begins at the end of your comfort zone. The mind, once stretched by a new idea, never returns to its original dimensions. |
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#4
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Quote:
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Im 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 Id start over with a 3 (or smaller) main block, but like I said in my first post I really dont want to be down for 2 years to get a new shortblock together.
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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
#5
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How are you planing to get to 1100 to 1400 hp, with NOS?
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I do stuff for reasons. |
#6
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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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"Everybody has a plan until they get punched in the mouth" noted philosopher Mike Tyson Life begins at the end of your comfort zone. The mind, once stretched by a new idea, never returns to its original dimensions. |
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#7
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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?
Stan
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
#8
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Twin turbos. I need to call the turbo guy later this week but Id guess twins in the 72mm - 78mm range.
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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
#9
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Why not just run the 4.21 Ohio?
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#10
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Quote:
Spotts built my current engine and it runs like a champ. According to my build sheet the mains are currently at .0025. Ill have to check with him to see what oiling changes have been made and what could possibly be done in the future.
__________________
James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
The Following User Says Thank You to R 70 Judge For This Useful Post: | ||
#11
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Quote:
I want to take off as much stress as I can so it lives a long happy life. The extra stroke isnt needed.
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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
#12
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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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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
#13
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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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Johnny US Army Retired 1978 T/A 463 Pontiac, KRE 74cc 292CFM D-ports, Lunati VooDoo, V-max lifters, TKII, ATM 850 E85 carb, TCI TH-350 race tranny, 3600 converter 3.73 12 bolt 11.63@116.68mph 1981 T/A 4-speed 406 Pontiac, Merrick ported 6X heads, Comp 270S cam, Crosswind intake 750 Street Demon, 3.42 30 spline Eaton posi street car. 1980 Formula 350 Pontiac back burner project 1972 LeMans 350 Pontiac |
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#14
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You guys should trade
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#15
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Quote:
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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
#16
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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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#17
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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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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ |
#18
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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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James 1970 Trans Am Spotts Built 484" IA2, Highports, EFI Northwind Terminator X sequential EFI fabrication and suspension by https://www.funkhouserracecars.com/ Last edited by R 70 Judge; 08-15-2022 at 01:55 PM. |
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#19
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Great Job James!!
__________________
Johnny US Army Retired 1978 T/A 463 Pontiac, KRE 74cc 292CFM D-ports, Lunati VooDoo, V-max lifters, TKII, ATM 850 E85 carb, TCI TH-350 race tranny, 3600 converter 3.73 12 bolt 11.63@116.68mph 1981 T/A 4-speed 406 Pontiac, Merrick ported 6X heads, Comp 270S cam, Crosswind intake 750 Street Demon, 3.42 30 spline Eaton posi street car. 1980 Formula 350 Pontiac back burner project 1972 LeMans 350 Pontiac |
#20
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4.00 3.25 main Ohio crank
Did they make them. Interested
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