Cam upgrade 741 or 651
#12
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Joined: Jul 2004
Posts: 11,332
Likes: 73
From: chicago

Not sure I would do more cam at this point. I'd slap a larger blower like a 420 b&m, slow the blower down, and maybe run it to 6lbs of boost. Probably pick up a bit of power, and the blower will live longer.
I'd imagine on that setup, the 250 blower at 5lbs intercooled, is probably overdriven quite a bit. Guessing you are still running the 250 blower overdriven quite a bit based on those massive torque numbers from 3000rpm and up.
Last edited by MILD THUNDER; 12-31-2011 at 08:09 AM.
#14
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Joined: Jul 2004
Posts: 11,332
Likes: 73
From: chicago
The 741 is 114lsa cam, where i think the 731 is 112lsa. The 114 might make a little more cylinder pressure. I suppose if the engine is torn down already, go for it. I assumed it was together already.
Im sure the 741 will keep pulling past 6000. Use some good lifters and maybe some stud girdles! Keep us posted on the results!
#16
139741 grind is the cam I'll try then . I wanted to try a dual carb set up this time ... hoping for better distribution of fuel. The 250 single set up have a tendency to leanout the forward cylinders . B&M had a plate that move the carb about 1.5 inches forward to correct the problem. I found a set of new /old stock dual quad adapters from Holley so why not give it a try.
The reason for the bore to 4.310 is a cylinder with some pitting that I couldn't hone out last June when I repaired the port engine ( head gasket ... burn't #6 pistion ) to save the boating season I decided to run it as is . It ran fine but was pushing oil out the dip stick after a hard run . After 4 seasons on these short blocks its time to freshen them up .
Always looking for more ... Thanks for the help everyone !
The reason for the bore to 4.310 is a cylinder with some pitting that I couldn't hone out last June when I repaired the port engine ( head gasket ... burn't #6 pistion ) to save the boating season I decided to run it as is . It ran fine but was pushing oil out the dip stick after a hard run . After 4 seasons on these short blocks its time to freshen them up .
Always looking for more ... Thanks for the help everyone !
#17
The 525EFI cam is 741 that is ground on a 114 lob sep instead of the standard 112 lob sep.
http://www.summitracing.com/parts/CRN-168741/
http://www.summitracing.com/parts/CRN-168741/
Last edited by Griff; 12-31-2011 at 11:36 AM.
#18
139741 grind is the cam I'll try then . I wanted to try a dual carb set up this time ... hoping for better distribution of fuel. The 250 single set up have a tendency to leanout the forward cylinders . B&M had a plate that move the carb about 1.5 inches forward to correct the problem. I found a set of new /old stock dual quad adapters from Holley so why not give it a try.
The reason for the bore to 4.310 is a cylinder with some pitting that I couldn't hone out last June when I repaired the port engine ( head gasket ... burn't #6 pistion ) to save the boating season I decided to run it as is . It ran fine but was pushing oil out the dip stick after a hard run . After 4 seasons on these short blocks its time to freshen them up .
Always looking for more ... Thanks for the help everyone !
The reason for the bore to 4.310 is a cylinder with some pitting that I couldn't hone out last June when I repaired the port engine ( head gasket ... burn't #6 pistion ) to save the boating season I decided to run it as is . It ran fine but was pushing oil out the dip stick after a hard run . After 4 seasons on these short blocks its time to freshen them up .
Always looking for more ... Thanks for the help everyone !
#19
#20
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Joined: Oct 2007
Posts: 8,439
Likes: 93
From: yorkville,il
with his current cyl heads,i agree,the 741 would be better,but if he goes with a better set of heads,even though the motor is small,the 651 will make more hp,but at a higher rpm,and when he gets ready to go with a bigger blower[as everyone who has a b&m eventually does]he will see even more gain.




