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Why do only Mopars experience "cap walk"???
#13679
12/13/04 12:47 PM
12/13/04 12:47 PM
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Joined: May 2003
Posts: 1,118
Central Missouri - USA
Ramcharger
OP
super gas
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OP
super gas
Joined: May 2003
Posts: 1,118
Central Missouri - USA
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I have been watching the “Low-Deck Super Block” thread with great interest. It is an interesting proposition. The suggestions for a new and improved race block are very creative. But I do have a question. Why are big block Mopars plagued with cap walk and Chevys are not? Does the Mopar block simply lack the sufficient clamping force capabilities that the 4 bolt Chevy main caps have to prevent cap movement? Cap walk seems to be an ever-growing problem that more and more racers are experiencing. What is the actual cause of cap walk? I know that things such as detonation contribute to the result (damage), but exactly why is it happening?
Last edited by Ramcharger; 12/13/04 01:47 PM.
'64 Dodge 440 2 dr. sedan - 440/pushbutton 727 (in the body shop)
'99 Dodge 2500 Quad Cab Long bed 4WD - CTD 5 spd. 3.54
'89 Dodge 150 4x4 - 5.9 TBI/727 35x12.50's and 8" lift
'14 Dodge Dart Limited 2.4/6-speed A/T
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Re: Why do Mopars experience "cap walk"???
[Re: Ramcharger]
#13680
12/13/04 01:37 PM
12/13/04 01:37 PM
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Joined: Jan 2003
Posts: 1,361
Wild West
M_D
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,361
Wild West
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My opinion is that a pair of 1/2" bolts don't have enough clamping force for the higher loads. The stock blocks also don't have any too much material in the main webbing either. The cross bolts help, but I think a splayed 4 bolt holds the cap and block together best.
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Re: Why do only Mopars experience "cap walk"???
[Re: Ramcharger]
#13682
12/13/04 02:43 PM
12/13/04 02:43 PM
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Joined: Feb 2003
Posts: 2,928
A tad North of Indy
Blown71X
super gas
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super gas
Joined: Feb 2003
Posts: 2,928
A tad North of Indy
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Don`t assume that Chevy`s or Fords are immune from this either, I was up close and personal with a carillo crank and rodded, billet 4 bolt cap (not splayed) 14:1 355" small block that routinely sees 8000 rpm, a while back, that if you were to take a picture of the mating surfaces only, you would swear it was a BB mopar
I absolutely agree with MD and andy also that it is a combination of issues, Bolt clamp force, Block flex, etc...As Andy said..it really is amazing that they take what they do, considering the crudeness (is that a word ?) by todays standards on how they were designed.
Rick
Blown71X V2.0 under construction
71 Cuda 383 4-SPD (maybe for sale)
2010 Challenger B5 Classic
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Re: Why do only Mopars experience "cap walk"???
[Re: Ramcharger]
#13683
12/13/04 03:11 PM
12/13/04 03:11 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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4 bolt mains don't mean anything unless they are splayed and doweled. thats the only way to keep them from moving around. the BBC merlin blocks with ductile iron caps without dowels have cap walk too. as i said before, splayed and doweled is the way to go. we routinely see merlin and dart blocks holding up to 1800-2200 HP without cap walk. don't you wish a mopar block would do that.
if it's worth doing it's worth doing right. don't skimp like MP did and have a heavy iron block that still has issues. it would be a waste of time and money in the investment and the same for the end user IMO.
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Re: Why do only Mopars experience "cap walk"???
#13684
12/13/04 03:46 PM
12/13/04 03:46 PM
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Joined: Jan 2003
Posts: 2,915
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,915
A shed in England
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Sorry to butt in on this thread, but I was dissapointed to hear that the mega block has issues too. Would a block girdle help on this block too?. I'm almost in the process of obtaining parts for a 572ci motor and was hoping for 850+ Hp. As far as I can tell I've had no problems with my 528ci making around 730 hp on a good day, but I hear thats approaching the limit before cap walk becomes a problem.
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Post deleted by Defbob
[Re: Tig]
#13685
12/13/04 04:07 PM
12/13/04 04:07 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Re: Why do only Mopars experience "cap walk"???
#13686
12/13/04 04:17 PM
12/13/04 04:17 PM
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Joined: Nov 2003
Posts: 2,503
Illinois
CRE2004
super gas
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super gas
Joined: Nov 2003
Posts: 2,503
Illinois
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Quote:
4 bolt mains don't mean anything unless they are splayed and doweled. thats the only way to keep them from moving around. the BBC merlin blocks with ductile iron caps without dowels have cap walk too. as i said before, splayed and doweled is the way to go. we routinely see merlin and dart blocks holding up to 1800-2200 HP without cap walk. don't you wish a mopar block would do that.
if it's worth doing it's worth doing right. don't skimp like MP did and have a heavy iron block that still has issues. it would be a waste of time and money in the investment and the same for the end user IMO.
You hit the nail on the head with the 'doing it right' statement!
I agree that the splayed bolts help keep the caps from moving as do the dowels, but from what I've seen, they are only keeping the bottom of the cap from moving and transferring metal, the rest of the cap is still having to deal with the harmonics which is why it's no surprise that I feel a girdle(in conjuction with whatever main cap you choose) is the only way to fully stabilize the bottom end on a BBM. The aluminum caps seem to dampen the frequency a little better than steel and iron, and are softer giving little or no signs of transfer, but I'm not a fan of aluminum caps on multi climate street cars. JMHO..
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Re: Why do only Mopars experience "cap walk"???
[Re: CRE2004]
#13687
12/13/04 04:35 PM
12/13/04 04:35 PM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 12,675
Columbia, CT
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Yeah, all makes can experience it..Many small block chevies I've seen have caps that fit loose, even the 4 bolt mains..I'm talking stock blocks here...But, the chevy design has a greater footprint on the parting lines, and I think this adds to the fastener's holding ability. A big block mopar has less area there, and it adds stability, even with the 2 bolts. I would be interested to see what some "out of the box" thinkers can come up with...Perhaps eliminating some pan bolts and adding material to the cap areas, and splaying the second set of bolts like the 6 bolt version posted in the other thread..I think 6 is overkill if the cross sections and caps are enlarged a bit. Also loose the "hollow" between the cap and block skirt, use that for more contact area between the cap and main web. 
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: Why do only Mopars experience "cap walk"???
[Re: Ramcharger]
#13689
12/13/04 05:13 PM
12/13/04 05:13 PM
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Joined: Nov 2003
Posts: 2,503
Illinois
CRE2004
super gas
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super gas
Joined: Nov 2003
Posts: 2,503
Illinois
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Quote:
And how about CRE's idea of the girdle. Would it be possible to incorporate some preload against the mains when installing a girdle? I know that it wouldn't be much, but, would it be enough to make a difference?
If you run a heavy girdle like what Best Machine posted, a little preload on the cap could be achieved. However, I feel that the reason for the cap walk/bounce is that the cap is trying to go oval and is flexing in a circular manner consistant with crankshaft rotation. If you can stop the begining of the movement by bracing the cap sideways against the block, it helps disipate the harmonics into the block and prevents the flexing cycle from even beginnning. The preload might help some on the 850+ hp applications, but it's the unification of the entire bottom end that's critical. Take a look here and try to envision what I'm saying...
My stud girdle page...
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Re: Why do only Mopars experience "cap walk"???
#13690
12/13/04 05:13 PM
12/13/04 05:13 PM
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Joined: Nov 2003
Posts: 1,664
North Sweden
RT540
top fuel
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top fuel
Joined: Nov 2003
Posts: 1,664
North Sweden
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Quote:
What if you take a Megablock, and add dowels to the caps and use tight fitting shoulder bolts instead of the standard cross bolts? Would this help with cap bounce?
You just described exactly what have been done to my block. It still got some cap walk it´s not much but it´s there. Why when only having 810hp ?? with 35° timing and flat tops with 13:1 and C12 fuel I shouldn´t have detonations, but........
Heres a pict. of the cross bolt.
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Re: Why do only Mopars experience "cap walk"???
[Re: Ramcharger]
#13691
12/13/04 05:17 PM
12/13/04 05:17 PM
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Joined: Nov 2003
Posts: 1,664
North Sweden
RT540
top fuel
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top fuel
Joined: Nov 2003
Posts: 1,664
North Sweden
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Quote:
Doweling seems like it might solve some of the issues but is there enough material/room to install dowels in a Mopar?
Yes, look at the att. picture, sorry for the bad quality of the pict. it´s an old one as I don´t have a cap off right know.
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Re: Why do only Mopars experience "cap walk"???
[Re: CRE2004]
#13693
12/13/04 06:23 PM
12/13/04 06:23 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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CRE2004, i think you might be missing my point, not sure. you won't have the harmonics if the caps aren't moving. no need for the girdle in that case. i've never put a girdle on a BBC 1800HP motor and i've not seen any problems with blocks breaking or caps walking with the 4 bolt splayed and doweled billit caps. the fact is that it works.
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Re: Why do only Mopars experience "cap walk"???
[Re: CRE2004]
#13694
12/13/04 08:01 PM
12/13/04 08:01 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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CRE, your system looks good , too me. How is different(if any) from the the one Dvorack has been offering?
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Re: Why do only Mopars experience "cap walk"???
#13695
12/14/04 01:11 AM
12/14/04 01:11 AM
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Joined: Nov 2003
Posts: 2,503
Illinois
CRE2004
super gas
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super gas
Joined: Nov 2003
Posts: 2,503
Illinois
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Quote:
CRE2004, i think you might be missing my point, not sure. you won't have the harmonics if the caps aren't moving. no need for the girdle in that case. i've never put a girdle on a BBC 1800HP motor and i've not seen any problems with blocks breaking or caps walking with the 4 bolt splayed and doweled billit caps. the fact is that it works.
I got your point, I was just thinking one thing and typing another. I agree with you on doweled, splayed, billet 4 bolt caps, no doubt. What I was thinking of is doweled two bolt Mopar main caps. You can pin down the bottom of the cap and hold it steady, but the harmonic is still present and the cap will still flex and move as it forms and egg shape and the shape changes as the crank rotates. The two bolt BBM main cap design is far from ideal, and as pointed out above, would greatly benefit from a cap with side contact to the block like a hemi cross bolt. The function of the cross bolts and the girdle are similar. I know you'll have to try one successfully before your convinced... 
Mike
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Re: Why do only Mopars experience "cap walk"???
#13696
12/14/04 01:32 AM
12/14/04 01:32 AM
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Joined: Nov 2003
Posts: 2,503
Illinois
CRE2004
super gas
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super gas
Joined: Nov 2003
Posts: 2,503
Illinois
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Quote:
CRE, your system looks good , too me. How is different(if any) from the the one Dvorack has been offering?
Dan's system (pictured below) is a four bolt main cap conversion requiring some fairly involved machining. Our girdle is a true bolt on piece that augments the two bolt cap setup and ties them into the block sides boxing in the entire lower end. The end results of both methods are similar, just different ways of getting there.
He lists his setup as withstanding 1500hp and I'm not in a position to doubt him. The most power put to one of our girdles so far is a 935hp dragster running stock 400 main caps. It broke two cranks the season before the girdle and ran all last season with no issues after the girdle installation. It's not the end all be all of mopar bottom ends, it's just our solution to a pesky problem.
Dan's 4-bolt conversion...
Our main stud girdle
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Re: Why do only Mopars experience "cap walk"???
[Re: CRE2004]
#13697
12/14/04 01:50 AM
12/14/04 01:50 AM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Hey CRE, here's a question for ya. Will having the block absorbing the harmonics using a girdle make a stock RB block last to higher HP levels before braking in the main webs? Is it the harmonics that are a major contributor in RB blocks failing in the web area?
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