aluminum main caps

Posted By: Deepockets

aluminum main caps - 12/15/12 03:19 PM

when i talked to me local machine shop about useing the aluminum mains, he did'nt suguest them. i see that there's a lot of people swear by them on the big blocks. what are the reasons?

Posted By: 70dusterjohn

Re: aluminum main caps - 12/15/12 03:23 PM

On big inch high HP motors it will cushion the crack so to speak! Kinda the same idea behind using alum rods! Plus it may help stop the stock block from splitting!

Posted By: Deepockets

Re: aluminum main caps - 12/15/12 03:51 PM

so this is done for mopars only? makes me wonder why don't aluminum after market blocks come them instead of steel?

Posted By: 440Jim

Re: aluminum main caps - 12/15/12 04:01 PM

It has to do with the poor (low strength) factory Mopar wedge big block design. If a block is designed for the high loads, it doesn't need them.

Posted By: Mopar_Rich

Re: aluminum main caps - 12/15/12 05:45 PM

The oil pressure changes a lot with aluminum caps too. Not a major problem with aluminum rods because they are the last in the oil sequence, but mains need to maintain their clearance. Also, it's much harder to line hone with aluminum caps on an iron block since the caps cut quicker. You can make anything work but is it worth the effort? Most machinists would stay with what they know.

Posted By: mopar dave

Re: aluminum main caps - 12/15/12 05:58 PM

I have heard somewhere that the mopar blocks were strong block as they have a high nickel content? How are the chevy guys getting away with 1200 hp with factory big blocks? I will be using aluminum main caps on my big block build.

Posted By: Performance Only

Re: aluminum main caps - 12/15/12 06:03 PM

Quote:

The oil pressure changes a lot with aluminum caps too. Not a major problem with aluminum rods because they are the last in the oil sequence, but mains need to maintain their clearance. Also, it's much harder to line hone with aluminum caps on an iron block since the caps cut quicker. You can make anything work but is it worth the effort? Most machinists would stay with what they know.

Rich, That's the first time i've heard anyone say anything about fluctuating oil pressure when using aluminum caps. I've installed close to a hundred sets over the years and have never had such an issue.
I always align bore the block when installing any cap conversion whether it's steel or aluminum. IMO that's the proper way to do it. some shops will bore the mains to within .001 and hone the rest, which is okay as well.
I believe the aluminum caps help dampen harmonics to some degree. In any case, I think it's been a time tested upgrade to help our stock block combo's live a bit longer when pushed beyond their normal limits.

Posted By: Jeremiah

Re: aluminum main caps - 12/15/12 06:47 PM

For comparo below we have the SDC/BCR caps on the let and the 440 source caps on the right:

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Posted By: Stanton

Re: aluminum main caps - 12/15/12 07:08 PM

Quote:

when i talked to me local machine shop about useing the aluminum mains, he did'nt suguest them.

Either he's a Chevy guy or he doesn't think your power level warrants them.

Posted By: BradH

Re: aluminum main caps - 12/15/12 07:21 PM

Quote:

Quote:

when i talked to me local machine shop about useing the aluminum mains, he did'nt suguest them.

Either he's a Chevy guy or he doesn't think your power level warrants them.

Or he's a Mopar guy who doesn't believe in using aluminum main caps, regardless of the power level. I know of a couple of Mopar engine builders with that opinion.

Posted By: Mopar_Rich

Re: aluminum main caps - 12/15/12 07:22 PM

Quote:

Rich, That's the first time i've heard anyone say anything about fluctuating oil pressure when using aluminum caps. I've installed close to a hundred sets over the years and have never had such an issue.
I always align bore the block when installing any cap conversion whether it's steel or aluminum. IMO that's the proper way to do it. some shops will bore the mains to within .001 and hone the rest, which is okay as well.
I believe the aluminum caps help dampen harmonics to some degree. In any case, I think it's been a time tested upgrade to help our stock block combo's live a bit longer when pushed beyond their normal limits.

Well, I guess because you are doing things right by setting the bearing clearances accordingly. The oil pressure change is from the extra expansion of aluminum in a hot engine. It doesn't really hurt anything because it's only noticeable at idle on a hot engine. As we all know if the pressure comes right up with RPM we're good to go. There's no question they help absorb shock as do aluminum rods.

Posted By: CompWedgeEngines

Re: aluminum main caps - 12/15/12 08:56 PM

I happen to be one of the builders that likes them, uses them, and has what I would consider great success with them. As Rich says, there are some things to be aware of, and machining them can be scary to the guys that dont understand them, but when done properly, I believe they serve a great purpose.A good friend of mine thought I was nuts the first time we spoke of them,and he couldnt for the life of him understand WHY? Yes, he builds a lot of Chevys ( you simplycant compare a Dart Big M block to a stock block Mopar)...lol....but once he saw them in cars running 1200 passes, he became a believer. Its all in the proper machining, set up, timing, and bearing clearances.....carry on....

Posted By: JCFcuda

Re: aluminum main caps - 12/16/12 05:19 AM

I have them on my 500 Rb . Ive never seen any oil pressure issues.
wouldn't Alu expand in all directions so how would it increase bearing clearance?

Oil pressure was great until I peeled a crane rocker off my head not so good then and then ran it all the way back to the trailer duh

.

Jim

Posted By: dvw

Re: aluminum main caps - 12/16/12 11:23 AM

For what it's Worth the only set I ever ran did have slightly less oil pressure at Idle when hot. This was using the same main clearance .003" as I use with steel caps.
Doug

Posted By: Jerry

Re: aluminum main caps - 12/16/12 02:32 PM

absolutely nothing wrong wit aluminum main caps, as long as they are align honed prior to use you should be fine. we also offer girdle caps which are beefier than the stock replacement style caps. see the pic in my signature. if your building for 700hp+ i definitely suggest using the girdle, ours is 1/2" thick.

Posted By: mopardamo

Re: aluminum main caps - 12/16/12 04:27 PM

JCFcuda,
A chunk of any metal with a hole in it when heated will cause the hole to enlarge and increase the clearance. Thus the loss of oil pressure when the pump cannot keep enough flow like at idle. When half that chunk of metal is AL then the hole becomes even larger due to heat.

Damon

Posted By: Cab_Burge

Re: aluminum main caps - 12/16/12 06:06 PM

Quote:

JCFcuda,
A chunk of any metal with a hole in it when heated will cause the hole to enlarge and increase the clearance. Thus the loss of oil pressure when the pump cannot keep enough flow like at idle. When half that chunk of metal is AL then the hole becomes even larger due to heat.

Damon

Half gets bigger than the other half, the bottm half

I have used the Mopar Ductile iron with really good results

To bad there not avalaible anymore

Now, how to decide between steel and aluminum caps

Probally aluminum

Posted By: dannysbee

Re: aluminum main caps - 12/16/12 06:48 PM

I think there is a place for both doctile iron and aluminum. The mixture of unlike metals does not concern me too much as that will always be the case with a aluminum block. Milodon has doctile iron caps available.

Posted By: Jeremiah

Re: aluminum main caps - 12/16/12 07:00 PM

You naysayers will still be on here talking about expansion rates when I am riding around town giving people lessons on how to spell the word "C H A R G E R" with my aluminum main capped 511 MW victor motor.

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Posted By: mopardamo

Re: aluminum main caps - 12/17/12 01:34 AM

I don't know about naysayers. If I would of stuck with an iron block I would of had AL caps for sure.

Posted By: cudasteve68

Re: aluminum main caps - 12/18/12 11:36 PM

Quote:

For what it's Worth the only set I ever ran did have slightly less oil pressure at Idle when hot. This was using the same main clearance .003" as I use with steel caps.
Doug

I have noticed the same issue in the late rounds, however you will notice a drop no matter what caps you use. I have found two answers to this problem, and they both work GREAT!!!!

1) Ride the Harley on race day & leave the Racecar in garage.
2) Become a first round runner up like me.

Both keep oil temps down & pressure up!!!