Main caps
#2768778
04/27/20 05:12 PM
04/27/20 05:12 PM
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Joined: Feb 2016
Posts: 55 CT
roadrunner2
OP
member
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OP
member
Joined: Feb 2016
Posts: 55
CT
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I’m in the process of building my first all out race engine and am looking for the advantages and disadvantages of running aluminum caps. This is for a stroker big block. Thanks.
1968 Road Runner 383 727 3.91 8 3/4 3520 with driver 11.04 @ 124.26 with 1.67 60’ Done on G70-14 redlines thru factory manifolds New quickest ever 383 build in FAST. 10:1 451” replaced with 14:1 499”.
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Re: Main caps
[Re: roadrunner2]
#2768801
04/27/20 05:47 PM
04/27/20 05:47 PM
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Joined: Oct 2006
Posts: 1,264 New York, USA
Chargerfan68
pro stock
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pro stock
Joined: Oct 2006
Posts: 1,264
New York, USA
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If this is a stock block Rb, i would definitely run the BRC cap and girdle kit. This is an all out race motor and the caps will help and the girdle should help strengthen the lower main area that is prone to cracking Even on a low deck 400, i am using the cap and girdle system for my all out race motor. I try to overbuild as I def don’t want to drive over the crank and/or oil down my slicks on a pass.
1.50 60Ft. , 10.75@ 127MPH Hauling 3900 LBS.
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Re: Main caps
[Re: roadrunner2]
#2768875
04/27/20 09:27 PM
04/27/20 09:27 PM
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Joined: Feb 2005
Posts: 20,174 PA.
pittsburghracer
"Little"John
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"Little"John
Joined: Feb 2005
Posts: 20,174
PA.
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I’m in the process of building my first all out race engine and am looking for the advantages and disadvantages of running aluminum caps. This is for a stroker big block. Thanks. Aluminum main caps are a very nice upgrade. Don’t buy into everything you hear on the web.
1970 Duster Edelbrock headed 408 5.984@112.52 422 Indy headed small block 5.982@112.56 mph 9.42@138.27
Livin and lovin life one day at a time
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Re: Main caps
[Re: pittsburghracer]
#2768900
04/27/20 10:35 PM
04/27/20 10:35 PM
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Joined: Aug 2003
Posts: 43,185 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,185
Bend,OR USA
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I’m in the process of building my first all out race engine and am looking for the advantages and disadvantages of running aluminum caps. This is for a stroker big block. Thanks. Aluminum main caps are a very nice upgrade. Don’t buy into everything you hear on the web. Mopar BB, RB and B,mopars V8 have a very strong design that really is a lot stronger than blocks like the early hemi and current LA type SB with two bolt mains. I'm assuming the 440 blocks had the main webbing thin down for costs and maybe weight saving, hence the tendency to crack the main webs between the bottom of the cylinders down into the main cap webbing The 400 blocks are a better choice to build due to them having thicker main webbing than the 440 blocks and the 383 blocks also. As far as adding a main girdle take a very close look at all of the them and then see if you can see where they add material or strength into the main webbing I have used the Mopar brand of Ductile iron main caps when they still sold and stock them, they are not available anymore so I use aluminum main caps instead now to help keep the stock cast iron block from cracking under drag racing conditions. EDITED: Do NOT use steel main caps, they will hasten the block cracking There are a lot of people believe if they have a certain race part in their motor and it hasn't broke yet they assume it is the best part like that so it must be good
Last edited by Cab_Burge; 04/28/20 01:50 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Main caps
[Re: Cab_Burge]
#2769002
04/28/20 09:06 AM
04/28/20 09:06 AM
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Joined: Jan 2003
Posts: 10,022 MN
JERICOGTX
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,022
MN
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I wouldn't build a Stock block, 600+hp engine without aluminum main caps. I've never had a oil pressure issue, and the caps are 5lbs lighter that stock caps.
69 GTX
68 Road Runner
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Re: Main caps
[Re: roadrunner2]
#2769014
04/28/20 09:43 AM
04/28/20 09:43 AM
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Joined: Nov 2015
Posts: 876 Missouri
jwb123
super stock
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super stock
Joined: Nov 2015
Posts: 876
Missouri
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This is what Herb McCandless told me many years ago, if you build a maximum effort big block Chrysler and want it to hold together, either use aluminum rods or aluminum main caps, to help dampen the internal harmonics to keep it together. I have built several with both combinations, only one that broke was an aluminum rod engine, that by my mistake, I did not replace the rods when they were over time to do so. I have never ran a girdle with aluminum main caps, seems like they would work against each other. Have built a couple with steel caps, and girdle, with aluminum rods. My experience with block failures that I have seen are in the number 2 main area, either the cap breaks, or the area between the main and cam bearing above the number 2 main cracks. I had one engine around 700HP level that I used the four bolt main conversion, water jackets had block filler, and a girdle, with aluminum rods, ran for several seasons. Started losing some ET, did a leak check and it was terrible, took the engine apart, the cylinders had barrel shaped and pushed so hard against the filler that it had hairline cracks between the freeze plugs on the outside of the block. That engine was bored .055 over, and I never had it sonic checked. But again it had around 600 runs on it. I look at it this way the original 440 block was engineered for what 400HP? When you bump an engine up to 750 HP or 800 HP , you are doubling the rated capacity of the block, the foundation of the entire engine. I finally learned and just purchased an aftermarket block, best decision I ever made. I know there was a shortage for a while, but I see several companies are now making and selling blocks again. With the machining cost of prepping a stock block, aftermarket caps, girdle, etc. then compare to the cost of the aftermarket block. Then realize that even if it holds together, when it comes time to freshen, will the block be a throw away?
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