Ford Mustang Forums banner

What crank/rods for a 6800-7000 rpm 331

9K views 35 replies 11 participants last post by  Mark O'Neal 
#1 ·
I have a Mexican 302 block and I'd like to build a N/A 11.5-1 331. With the cam and heads I have I figure we will shift at 6800-7000. The two choices I was looking at was a Scat 9000 cast steel crank (28 oz balance) and Scat 4340 I beam rods or a Callies Internal balance 4340 forged crank and Scat H-beams. I guess I wasn't sure what the safe limits were with the 9000 series crank and I-beams. HP should be around 500 at the crank. Let me know what I need to use and still be safe at those rpms. Thanks!
 
#3 ·
The callies compstar is way overpriced nowadays and almost always needs mallory metal to balance which equals a very expensive import crank. The crank market has consolidated dramatically. k1, rpm, liberty, ohio crank, lunati voo doo, and now eagle are all the same cranks, different prices and cardboard boxes. Yet these are the best cranks hands down in the category. Eagle and rpm are 2.123 rod journal, everyone else is 2.100, so plan accordingly.
 
#9 ·
All BS aside I'm not sure personally I'm looking at it from a Balancing perspective. As has been stated the Callies will be off unless you spend good money to have them Balanced. And Im not sure your budget but Callies aren't cheap so I thought $1800 maybe close to that price and RPM is good out of the box.

You want to make 500hp on a block rated for 500hp It better be very well balanced.

Woody also sell this but for your app he may say it needs to be balanced (I'm not sure) if not at least you can trust the parts and no its safe.

http://fordstrokers.com/stroker-kits/302-stroker-kits/331-347-Scat-Rotating-Assembly

Why doesn't Woody sell a ton of options My Guess Quality control. Took me longer to type but sounds right lol
 
#8 ·
The cast crank is just not a very good quality unit alot of times, I send back plenty of them. They are hit or miss, sometimes the finish and sizing is god awful and as a retail person you cant pay to fix it, because then you have a very expensive cast Chinese crank. Once you balance it, you own it as well.

If you want a crank that is always accurate and finished excellent then the light grey internal is what you want.

Ofcourse the cast will work as well. Pick quality or cheap, in this instance.
 
#10 ·
This is just my option after doing a bunch of homework before buying my 363ci.

I knew I was going to build a 347 in a stock block so I was learning about that at the same time. It looks like the RPM is a safe bet on balance the one I post. And at the end of the day whats $500 to keep from destroying all of it in a stock block and I'm just going to be turning 5500rpms you are wanting to go 7000rpms.
 
#11 ·
All cranks needs balancing, scat cast is 28oz, light grey are internal, no mallory metal required. Callies compstar is a 50% chance it needs mallory metal installed which can add a fair amount to the cost of balancing. If it's a money thing, I get it. If the cost difference between the cast and interal is not a factor, its really of no discussion
 
#14 ·
the question isn't its capability its the longevity. Sure a scat crank can handle more than that hell I've pushed over 900rwhp through a cast scat crank on a 408 stroker before but sub 6k rpms. But the issue lies in the rpm's. If you plan on spinning over 7k then your best bet is to do as woody said and go with the internally balanced crank.
 
#20 ·
No, because noone has ever wanted that or asked for it. Today, to do that you have to use an rpm crank or an eagle because all the other internal cranks are 2.100 and scat doesnt make a 5.400 2.100 I beam rod. RPM has been out of these cranks for a LONG time, he may have a 3.250 but definitely doesnt have or had any 3.400 cranks for a long time.
 
#22 ·
Its not confusing. The only internal balance ready cranks, which means balancing by simply removing weight with a 2.123 rod journal, is eagle and rpm. All the other internal ready cranks such as k1, liberty, ohio crank, molnar, lunati voo doo are all 2.100 and scat doesnt make a 2.100 I beam that you want to use. So you only have 2 crank choices with that rod.

I dont use much rpm stuff anymore as he never has any stock anymore, but all the cranks above are the same as rpm, they come from the same factory. So I use any of the above because they have them in stock and ohio is alot closer to chicago than california.
 
#25 ·
I was just trying to find the best way to go, not the lightest, cheapest, heaviest or most expensive. One of those "What would you do questions I guess" for a N/A 6500-7000 shift point Mexican block bottom end. Thanks
 
#30 ·
You had all the good parts, held them a long time, and you sold them cheap. Now you want to make power with a mexican block, which in my experience are inferior. I had one crack at about 500 crank HP. Their claim of being stronger is an internet myth.

Build a motor and run it, spend your time in the car (instead of on the internet). Have Jim build it for you, it will last and its not expensive. Things are cheap for a reason.
 
#34 ·
Things happened and we needed to sell the parts. We'd like to build something but not put $10,000 in the engine. We just want a healthy N/A street/strip project. All I heard on the internet is you need a pre-81 block because the roller 5.0 blocks are junk, so now I get a older block and all I hear is the older blocks are junk too. The car is a beautiful 27,000 original mile 85GT that already runs 11's with it's 34 year old stock shortblock on motor. All it has is a HCI and never even had the oil pan off of it. So it's too nice to turn into a race track only car. We just want to pull the original engine out and keep it and drop in something a little faster.
 

Attachments

  • Like
Reactions: thadude
#32 ·
I am putting together a 3.250 with an RPM forged crank that I had cut down to 2.00 on the rods (Mark sourced the crank for me many months ago). Using an eagle H beam rod (not sure if they are around anymore at that size). Looking to spin it 7500. SHP block, of course.....
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top