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Cam upgrade 741 or 651

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Old 12-31-2011 | 07:57 AM
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The 651 works well in a 540 blower motor. I think its a little big for a 496. The 741 ground on 114 lsa would be my choice.
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Old 12-31-2011 | 08:02 AM
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Originally Posted by Noise Pollution
Dyno Sheet for Bob's motor with blower. Sorry for the quality. Couldn't find originall sheet.
Peak torque - 773 @ 4500
Peak Hp - 785 @ 5800


That nice numbers for a 496 stroker with a 250 blower

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.
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Old 12-31-2011 | 08:54 AM
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Mild Thunder,
Right now its a 489, Bored .030 over. Bob is going .060 over which will make it a 496. I think thats his reason for the bigger cam.
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Old 12-31-2011 | 09:16 AM
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Originally Posted by Noise Pollution
Mild Thunder,
Right now its a 489, Bored .030 over. Bob is going .060 over which will make it a 496. I think thats his reason for the bigger cam.
I doubt the extra 7ci will matter much. If anything, maybe gain a tad of airflow from the larger bore unshrouding the valves a bit more.

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!
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Old 12-31-2011 | 09:17 AM
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...

Last edited by MILD THUNDER; 12-31-2011 at 09:18 AM. Reason: double post
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Old 12-31-2011 | 09:50 AM
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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 !
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Old 12-31-2011 | 11:34 AM
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Originally Posted by offshoredrillin
741 is the same cam in a 525 correct?
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/

Last edited by Griff; 12-31-2011 at 11:36 AM.
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Old 12-31-2011 | 01:20 PM
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Originally Posted by 737jetmech
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 !
Good choice on the 741, think about doing the 7/4 swap while at it. Also I liked Mike280s idea on the 1.8s for the exhaust valves. Add shaft mount rockers and you should get a nice pop.
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Old 12-31-2011 | 03:01 PM
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Originally Posted by blue thunder
Good choice on the 741, think about doing the 7/4 swap while at it. Also I liked Mike280s idea on the 1.8s for the exhaust valves. Add shaft mount rockers and you should get a nice pop.
Being that your my running buddy should I still be looking for a set of peanut ports ?
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Old 12-31-2011 | 04:03 PM
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Originally Posted by Griff
IMO, the 651 has way too much duration for a 496ci. You would have to spin it at least 6000rpms to make power. I think the 741 would be a better choice.
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.
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