1970Olds442

Hello! I have a Main Cap question. I am slowly (and I mean slowly) working on an Olds 496 build. I have a 1974 455 block I’m working with. I’m putting a lot of decent, if not nice parts on this motor (could be better/could be worse). I have ported Edelbrock heads/intake, Holley Ultra HP 850 Carb, MSD ignition, American Racing Headers, Eagle 4.500 crankshaft and Eagle H-Beam rods with L19 bolts, etc.…

I recently purchased a Rocket Racing chrome moley full main girdle to support the bottom end. I planned on getting billet aluminum Main Caps to replace the cast iron originals. I was talking to a friend and he asked why I would go with Aluminum vs Steel. He said (in his opinion) that steel caps would be better than aluminum. His thoughts were that aluminum caps would dissipate heat better over a short period of time (drag racing) but steel would be better/stronger for everything else. He said something about the aluminum caps expanding, which would cause problems with a full girdle. I’m not an engine builder, so I don’t pretend to know about all this stuff. My buddy is a dirt track/circle track racer. I figured I would ask the Olds experts. Would you recommend aluminum caps or a billet steel? And, if billet steel, who sells them?

I am building my Olds 442 to be 50/50 street & track. No long highway trips. All street driving will be city (small town)/secondary highway driving at best. The rest will be at the race track (St Louis Gateway - ¼ mile) that is about 15 minutes frommy house.

Thanks for your time

Ray

joe_padavano

Steel inherently has three times the stiffness of aluminum. Most aluminum blocks use steel caps. Aluminum caps negate the whole point of a girdle. Frankly, even the stock caps would be a better choice in my opinion. The problem with the Olds bottom end isn't strength of the caps, it's stiffness. As the caps deflect, you lose the oil film on the bearings, leading to bearing failure.

cutlassefi

How much power do you expect to make?
I made 600+ with stock caps and a J&S 5 main halo. Crank was internally balanced and hardened though. I would recommend at least doing it internal as well.

OLDSter Ralph

Whats the advantage of balancing internally ? Who is qualified to harden a 455 crank ?
Ralph

cutlassefi

On an external balance, even though you’re actually bringing it INTO balance with the external weights, that adds to twisting and flex. The closer to the center you can bring the weight the better, ie fully counterweighted cranks.
Ohio crank did the crank on this build. They did a good job but I’m not sure the hardening was necessary. Throughout multiple dyno pulls, oil pressure remained consistent.

69455

The alum caps are thicker than stock.
This is suppose to eliminate the flexing and or squirm.(ARP bolts also)
They are also suppose to help with harmonics.


These caps need to be line bored with the block.
To use a girdle you would need to machine down the height
which would defeat the design I believe.


I am running Alum caps, 500 + engine hp w/ 125 shot Nos
3 years of beating on it , no issues.

joe_padavano

Thicker alone does not necessarily help. Stiffness depends both on the material properties and the overall dimensions. Aluminum is inherently one third the stiffness of iron or steel for the same cross section. Bending stiffness of a beam depends on the thickness and the CUBE of the depth. The result is that for bending in the direction away from the block (where primary loads would be on a crank due to the downward force of the piston) an aluminum part would need to be THREE TIMES the thickness of a steel part to provide the same bending stiffness. It would need to have about 1.4 timed the depth to have the same stiffness. Obviously this is a simplistic analysis, and bending loads are present in multiple directions, but you get the idea.

The ARP studs are STRONGER than stock bolts. They are not STIFFER, however. The studs will stretch the same number of micro-inches per inch for a given load as the stock bolts. The only difference is that the stock bolts will break first if you continue to load them.

The more important issue in an engine is fatigue loading. This is called the S-N curve for the material. The endurance limit is the number of cycles a metallic part can sustain before the part sees a fatigue failure. Steel actually work hardens and eventually bottoms out on the S-N curve. Aluminum continues to lose strength with cyclical loading.



This is why aluminum con rods need to be checked and replaced periodically. Sorry, but as a structural engineer I can see no reason to use aluminum main caps (or girdles).

69455

Joe,

Being a structural engineer
I assume you know Steel & Alum come in several grades, tensiles and yields.

The caps are made 7075 T73 heat treated alum.
and much stronger than cast iron.
They are also taller (thicker) in the direction of crank force than cast iron.

Hands down better than stock cast.

This is for caps not rods.

To each there own.
Good luck.

joe_padavano

Being a structural engineer, I also know not to confuse STRENGTH with STIFFNESS. (This is like people who confuse a "quick" car with a "fast" car - drag cars are quick, land speed racers are fast)

Heat treating aluminum (or steel, or most metals) improves STRENGTH. It has zero effect on STIFFNESS. 7075-T73 has virtually the same modulus (the inherent stiffness properties) as does dead soft aluminum. Main caps don't usually fail due to a strength issue, they fail due to either fatigue loading or deflections. The deflections are what cause bearings to go bad, as this lets the oil film leak out and thus wipes bearings. And obviously we are talking about main caps. My con rod comment was an example of how aluminum engine parts require more frequent inspection and replacement due to fatigue loading.

jensenracing77

I am NOT a structural engineer so my opinion don't really matter here but... I did not know and can't understand why they made main caps out of aluminum. If they need to be better then make them out of steal to the specs of those aluminum ones. In this area of the engine are they really that concerned with saving 4 or 5 lbs.

joe_padavano

My point exactly. Weight different in this area is unimportant. Protecting the main bearings under load is the priority. Frankly, aluminum main caps (and girdles) must be designed by people who do NOT understand engineering or materials properties. From a production standpoint, it's much easier and less expensive to machine aluminum caps, thus more profitable. I just don't see how they are any better than the factory. Note that aluminum motors (like LS motors) use steel caps.

The bottom line is that there is a lot of "conventional wisdom" that isn't very wise. One of the classics for me was the use of those stupid straps across the factory main caps. Sorry, but structurally that's just worthless.



If the straps were actually added parent metal on the main caps, that would be beneficial, but separate straps like this with clearance holes to the bolts don't pick up any load at all, and the stiffness increase is barely measurable.

OLDSter Ralph

Jensen, I totally agree.

Bernhard

I agree with Joe in theory!
But their have been many that have used aluminum main caps with out failure.
This topic has been discussed on ROP you might want to look it up for more feedback on the subject.

joe_padavano

How many have used stock main caps without a failure also?

This is like the deer whistle argument. The fact that you haven't hit a deer isn't proof that they work.

Bernhard

The one racer running aluminum 4 bolt main caps by Dave Smith is close to the top of NA Oldsmobile fastest list.
One respected engine builder said that the way the aluminum absorbs force was one reason they were using aluminum caps.


Joe I don't disagree with you on the rigidity that a steal cap offers.
I do not know how many are running cast caps with success.

joe_padavano

Whoever said this is not an engineer. Ironically, iron and steel have higher damping than aluminum. Of course, in both cases, the damping of the metal is negligible. When we need a material that damps out unwanted vibrations in aerospace applications, we often use magnesium. As an example, most fixtures for mounting a spacecraft to a vibration table are made from mag to avoid introducing any "ringing" into the test from the fixturing.

As I've noted previously, the most important aspect here is keeping the main bearings round to protect the oil film. Once the caps deflect, bearings loose shape and the hydrostatic film goes away, followed by the crank. If you are talking about a race engine that gets torn down and inspected (and bearings replaced) frequently, then this may be a non-issue. If you want the motor to last any length of time, I'd pick the more rigid material.

ELY442

Is magnesium or titanium a good idea for main caps?

joe_padavano

How much money have you got?

w-30dreamin

This has been some very interesting reading,thank you.

1970Olds442

I’m definitely not an engineer so I wouldn’t think to argue with you Joe and what you say does make sense. I love the whole deer whistle thing!

So, that said, do we Olds guys have a hole in the market? I mean, I know we inherently have a hole in the market just because it’s Oldsmobile and we don’t have a big aftermarket presence. But, the only main caps I know of are the original iron caps that are all 40+ years old or billet aluminum caps. It would seem that if someone developed a billet steel main cap with the same dimensions as the billet aluminum ones, they would be able to corner the market.

cutlassefi

Both Rocket Racing and Dick Miller offer steel caps.
But the concern is the spreading of the block between the main saddles and the pan rails. Billet caps of any sort won’t help that. That’s why many opt for the halo, or even a full pan rail girdle, right or wrong.

1970Olds442

Yea Cutlassefi, I see what your saying, thanks! I cannot find them on Rocket Racing, but I'm in contact with Dick Miller. It looks like his are 1045 medium carbon steel.

So, if this is the case, would a good combination be the Rocket Racing chrome moly full main girdle, Dick Miller 1045 steel main caps with ARP studs? To me, this sounds likea pretty solid bottom end, but I’m no expert by any stretch.

Bernhard

There are many suppliers of billet steel main caps.
Most that are making serious power are going with the new Rocket racing big block or Nascar or DX block small block.

Bernhard

Joe what are your thoughts on the Halo?

Bernhard

What brand of oil pump is that?

1970Olds442

Bernhard, I agree, I would love to have one of those Rocket Racing blocks! But, they cost $5000.

I got a 455 block for $700 that was vatted, bored and honed .060 over and decked. I purchased a Rocket Racing full main girdle for $1000 (with oil pan studs and RR 2 piece timing chain cover) and can get the steel main caps with ARP main studs from Dick Miller for about $500.

So, basically $2200 vs $5000. And of course, I purchased the block long before the new Rocket Racing block came out. While I fully admit that the new RR block is the superior option, and something I may pursue in the distant future, the girdle and caps are what I'm looking at right now. Had I known 2 years ago, when I bought the 455 block (and I wish I did!) that Rocket Racing was going to come out with this new block, I may have went in a different direction.

OLDSter Ralph

It has been a spirited and interesting thread. It has also been a very informative thread. I think my choice would be steel main caps.

cutlassefi

What is your anticipated power level?

joe_padavano

^^^THIS!

Again, this is a stiffness design problem, not a strength problem. Since the space is limited, steel would be the correct design choice. The real trick is retrofitting some sort of support (girdle, or whatever) that actually carries load. The amount of deflection we're talking about is very small, and any clearance in the bolt holes means that the fasteners just move in the holes before the girdle becomes useful. Match drilled, press fit pins or a similar fastening feature would be required for the added system to actually be useful. We deal with design problems like this in the aerospace world all the time, only there weight does matter.

Bernhard

If you look at all the aftermarket girdles only one is tied to the caps.
All other girdles use clamping force to aide bottom end support.
So is the stiff crank and light rotating assembly the reason these engines live?


What effect does stroke and road length have on forces being applied to the block.
The reason I ask is because the the early 425/400 have shorter stroke and longer rods.
I was wondering if this lessons the load compaired to the later 455/400
longer stroke and shorter rod engines?

madmax442

I know BTR offers Billet Steal caps! I have a set of used BTR steel caps I’ll use for a future build. I probably should have had a set installed on the build Mark did for me but we shall see if anything happens in the future!

TripDeuces

Pro-Gram Engineering used to make Olds main caps also. Not sure if they do anymore. Here a link with some tech info. http://www.pro-gram.com/tech.html

joe_padavano

The problem with that data is that they don't list modulus of elasticity, which is the relative stiffness of the material. Ferrous metals (iron and steel) have a modulus around 0.3 x 10^7 psi. Aluminum alloys run around 0.1 x 10^7 psi. Note that modulus is unchanged by heat treat, so while 7075 may be as strong as mild steel, it is still only 1/3 the stiffness and thus will deflect more under load. This can cause bearing deformation, which leads to the oil film being lost, which leads to wiped bearings. Of course, that link DOES point out the fact that CTE of aluminum is greater than that of steel or iron, so in addition to the deflection under load, you also have the thermal expansion causing looser bearing clearances at temperature.

Here is a mildly technical discussion of strength vs. stiffness vs. hardness of metals.

TripDeuces

I know my information was lacking and wasn't meant to show anything but support for your information Joe. I didn't mention it but you pointed it out that the expansion rate is huge for aluminum compared to steels, cast or otherwise.
Bearing clearances would be my concern also.

fleming442

I'd put the money toward internal balance.

Bernhard

How about a 455 crank with center weights made from a quality forging?
Light pistons and aftermarket rods. Stock caps with studs???