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Old 12-18-2005, 11:53 AM
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400 SBC main cap strength question

I know adding splayed caps is the best way to do this, but would strapping the stock caps all the way through increase the strength by any significant amount?

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Old 12-18-2005, 12:23 PM
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Quote:
Originally Posted by flyin99
I know adding splayed caps is the best way to do this, but would strapping the stock caps all the way through increase the strength by any significant amount?
Explain strapping the caps, please.

Just use the Moroso splayed cap kit. It takes half as much machine shop labor to install it as some other kits.
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Old 12-18-2005, 02:15 PM
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Strapping the caps, is when you mill down the main cap flat and then install a billet steel flat pc. of stock that is used to strengthen the main cap.
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Old 12-18-2005, 02:28 PM
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This is the system i used on my 377 drag motor so i know it works for 520.hp and about 8000 rpm.on a 2 bolt main block.
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Old 12-18-2005, 04:08 PM
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Quote:
Originally Posted by flyin99
Strapping the caps, is when you mill down the main cap flat and then install a billet steel flat pc. of stock that is used to strengthen the main cap.
What advantage does strapping have?
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Old 12-18-2005, 04:20 PM
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I think it runs under the assumption that it wont let the cap move away from the block. I have difficulty understanding what stops the "strap" from applying to much pressure to the cap. They are dissimilar materials and shapes so expansion and contraction will occur at separate rates. Further, the straps do nothing to address the concerns of cap walk if they are not connected like a girdle.

My biggest concern on a small block would be cap walk and splayed gear on a two bolt would be best as suggested earlier. In addition, the force trying hammer the crank out of the bottom of the block has more of an effect of closing the cap at the parting surface. This can be demonstrated by taking your caps and wailing on them with a ballpeen hammer on the center of the inside of the cap. Eventually, you end up with a closed or broken cap.
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Old 12-18-2005, 05:45 PM
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OK, I have installed a bunch of Moroso splayed caps but never straps.

Moroso is a much better kit than anything else we tried. Much less time to install.

I'd say the straps are not worth the trouble.
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Old 12-18-2005, 05:49 PM
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Yeah I'd agree with that.
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Old 12-18-2005, 08:37 PM
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Typicily you would only strap the rear main. I've never seen or heard of strapping all caps.

Strapping is a process designed to help the rear main gain strenght without fully machining a billet cap to fit that block. To get the registers correct you would spend twice the amount of time maching the rear as you would aligning the other four. Ever notice a rear main isn't included with a a splayed cap kit?
What happens if your making enough power to destroy the rear main cap?
You can cut the cap .500 for a drysump or .600 for a wet sump and gain roughly twice it's normal strenght. Wet sumps are drilled for a oil pump provisions.

These pictures are courtesy of CNC Blocks a their state of the art 40,000 sq ft facility.

http://i7.photobucket.com/albums/y27...ockwork004.jpg

http://i7.photobucket.com/albums/y27...YEDCAPS020.jpg
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Old 12-18-2005, 08:57 PM
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Quote:
Originally Posted by johnsongrass1
Typicily you would only strap the rear main. I've never seen or heard of strapping all caps.

Strapping is a process designed to help the rear main gain strenght without fully machining a billet cap to fit that block. To get the registers correct you would spend twice the amount of time maching the rear as you would aligning the other four. Ever notice a rear main isn't included with a a splayed cap kit?
What happens if your making enough power to destroy the rear main cap?
You can cut the cap .500 for a drysump or .600 for a wet sump and gain roughly twice it's normal strenght. Wet sumps are drilled for a oil pump provisions.

These pictures are courtesy of CNC Blocks a their state of the art 40,000 sq ft facility.

http://i7.photobucket.com/albums/y27...ockwork004.jpg

http://i7.photobucket.com/albums/y27...YEDCAPS020.jpg
Thanks for the info............CNC blocks was the ones telling me about strapping all of the caps..........we have done it at our machine shop for years, with no problems, but I'm just curious about where the HP limit determines changing from stock caps w/straps, to going full splayed etc..............I appreciate the input
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Old 12-19-2005, 07:45 AM
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Always splay over 500 actual hp. Not a gestimate. Strap the rear main when you do.

475hp in a circle track engine asks for a splayed cap. Strap the rear.

550hp or better needs a aftermarket block IMO. I tend to over build. I don't like my engines blowing up.
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Old 12-19-2005, 08:17 AM
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A few years ago Hot Rod magazine made 400 hp on a junk yard 350 short block pulled from a '75 Impala. They used the Vortex heads and a Comp cam IIRC. The short block held up just fine to the many dyno pulls as well. As a general opinion, I think we tend to listen to salesmen too much in believing stock parts are junk.
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Old 12-19-2005, 06:23 PM
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usually with the sprayed caps you only do the center caps which means you still have to do something with the front cap and the rear cap. These are the ones that most guys cut and put a brace on.The front cap on a 400 block is the weak link.They like to crack in the center at over 500 hp. Not a good thing.when you cut and brace the caps you have to use some good high strength metal for your braces.I don't feel the rear cap is as big a problem as the rest of the caps. But they build a brace for that to.This set up should work to 600 hp on a normal aspirated motor with a little commonsense.Any thing more than that or if you just want to feel safe go aftermarket block. The reason i braced all but the rear cap on my block was more a test on my theory than anything else and as i said i know it works on 520 hp and 7600 t0 8000 rpm tested at the tune of about 300 10. sec runs.
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Old 12-19-2005, 07:22 PM
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The external balance of the 400 is not a desirable thing. Change to internal balance and relieve stress on the front main.
A drag application needs much less durability than road race or circle track engines which operate not only on acceleration, but also deceleration and over continuous periods of time.
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