Connecting rod dilema.

48Austin

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Now that I have decided to go aluminum. There is one problem. Size. Aluminum is physically bigger than steel. I remember back in the '70's we had to grind the blocks in Pontiacs just to fit them in with stock strokes. Would like to do a stroker, but if that is not possible with aluminum rods so be it. Would like to go with BBC rods. But machine work may cost more than going with Cad specific. Since most of you guy seem to be machinists, I thought you may have some answers.
 

El Diablo

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I haven't measured the "girth" of any aluminum connecting rods but if you go with a bb Chrysler rod, would the decreased rod angle buy you any clearance?
 

48Austin

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This is the reason I am asking. If I go with a stroker my rod angle would be more. I'm thinnin'.
"I'll do the Thinnin' around here Baba looey"
 

8ad-f85

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A Mopar or BBC rod can leave more room for the cam than the Cad specific H beams when the rod bolts are closer together.
Modern alums are not as bulky and often have more room around the hinge area of the rod than even OEM's (where the big end transitions to the beam).
The old Hemi top fuel rods are beefy-wide for sure, might be more suited to 472 crank to keep from bashing the cam.
Don't assume plenty of room until you get some rods to stack up and compare, they aren't universal by brand or engine family.
Very rough quick check is to add 1/2 stroke plus 1/2 journal including the outer edge of the rod shoulder.
A set of 2.5" journal K1's need some love with a grinder on a 4.3 stroke as opposed to a BBC I beam having more room @ 4.5" stroke.
If you think about it, the outer edge of the journal swings not more than the stock stroke, with the rod bolt itself closer to the centerline of the journal.

Too much worry about rod angle without enough consideration to skirt length and pin height/ring package.
4.75 stroke BBC's @10.200" don't leave much for rod length and there's been many done that survive 7500 rpm just fine.
Those are under 1.4 stroke/rod length ratio. Pics in the coming weeks to illustrate.

Get estimates on machine work before you pull the trigger, stroking itself isn't always that much more.
The cost difference of rods (in steel) can pay for the stroking and then some.
Make sure your oil holes won't move too far. Not all cranks are the same.
 

8ad-f85

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Found some helpful notes...
Rod bolt center to center distance (appx)
K1 2.5" Cad rod 3.250"
BBC Eagle SIR 2.950" (also several other BBC types)
426 alum hemi 3.150" (3 or 4 different ones)
There's .150" more room for swing with BBC (1/2 stroke) but always mock up your particular parts.
 

48Austin

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A Mopar or BBC rod can leave more room for the cam than the Cad specific H beams when the rod bolts are closer together.
Modern alums are not as bulky and often have more room around the hinge area of the rod than even OEM's (where the big end transitions to the beam).
The old Hemi top fuel rods are beefy-wide for sure, might be more suited to 472 crank to keep from bashing the cam.
Don't assume plenty of room until you get some rods to stack up and compare, they aren't universal by brand or engine family.
Very rough quick check is to add 1/2 stroke plus 1/2 journal including the outer edge of the rod shoulder.
A set of 2.5" journal K1's need some love with a grinder on a 4.3 stroke as opposed to a BBC I beam having more room @ 4.5" stroke.
If you think about it, the outer edge of the journal swings not more than the stock stroke, with the rod bolt itself closer to the centerline of the journal.

Too much worry about rod angle without enough consideration to skirt length and pin height/ring package.
4.75 stroke BBC's @10.200" don't leave much for rod length and there's been many done that survive 7500 rpm just fine.
Those are under 1.4 stroke/rod length ratio. Pics in the coming weeks to illustrate.

Get estimates on machine work before you pull the trigger, stroking itself isn't always that much more.
The cost difference of rods (in steel) can pay for the stroking and then some.
Make sure your oil holes won't move too far. Not all cranks are the same.
I beam or H beam are out of the question, unless they are Carillo. ALL the forgings are from China, including Venollia. Under $500 a set? Say what?
Found some helpful notes...
Rod bolt center to center distance (appx)
K1 2.5" Cad rod 3.250"
BBC Eagle SIR 2.950" (also several other BBC types)
426 alum hemi 3.150" (3 or 4 different ones)
There's .150" more room for swing with BBC (1/2 stroke) but always mock up your particular parts.
? Every thread I have looked at is saying 6.85, 6.90 up to 7.1. So what's the deal?
 

El Diablo

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If I went with aluminum connecting rods on anything, I would choose BMR.

For good steel rods, I like Oliver, but they are pricy.

I didn't know Venolia was made in China?
 

8ad-f85

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Practical off the shelf piston compression heights between 1.4 and 1.7 leave the rods in those lengths as you push past 4.5 stroke. Taller than 1.8 tends to get real heavy.

Scary thing about US forgings and supplied steel is that it still might not be US bar stock these days.
I don't know what the current levels of US steel production are or how much of what is out there.
I can say that when I was involved in manufacturing, even a fairly large OEM might not be able to insist upon the origin of their stock. Smaller Co's might have better luck with that.
My experience around 2005-2006 was that appx. 50% of the US steel supply house inventory of bar stock came from China.
[We had to track heat #'s and adjust our programming to manufacture OEM parts from raw bar stock, such as 4340? pre-hard. Analysis of test samples showed differences in the alloy enough to affect the process from feeds-speeds/DOC through the heat treating, even though the alloy meets the 'recipe' specs.
One of the main differences was that the US stuff was on the softer end of the scale and more uniform through it's section, whereas the Chinese stuff had more instances of hard spots, inclusions and 'banding'.
US material was more predictable to manufacture from.
The parts end up within manufacturing specs in the end, so I don't have a huge problem with the alloy type itself...the risks and problems I see are more machining and assembly problems than material ones. A lower cost product might skip some of the care involved, leading to a higher percentage of failures and more need for the assembler to inspect things.
We saw a handful of warranted failures out of millions of parts, and it's likely because the batches were mixed together by the time they got to heat treating.]
 

48Austin

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If I went with aluminum connecting rods on anything, I would choose BMR.

For good steel rods, I like Oliver, but they are pricy.

I didn't know Venolia was made in China?
When you see prices under $500, you know they are from china.
 

8ad-f85

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That's market demographics and production run sizes.
Regardless of what cost they could be made for, why would any established company lower the price for the entire market and undermine their bread and butter? (not defending them, BTW)
Small run, niche and outsourced stuff isn't making anyone rich, regardless of origin.
They cost what they cost to fill a need.
My point was that even USA made premium stuff still might be Chinese steel, regardless of what they claim.
I don't think the various industries recognize any wrong-doing there, it can't be helped.
It would probably take global-political level effort to make things change.
The hot rod niche market is small for anyone having the capability to make things in-house when there's other industries willing to pay for the entire production run.
It's really tough to warehouse a couple year's supply of (???) and hope to sell it down, just to free up that cash to do another production run.

If a Pontiac H beam and a BBC could come from the same exact forging, explain the huge price difference..and don't say quantity because it's literally just a number in the machine programming theoretically intended to switch over in the same time period as one part's equivalent cycle time.
What might appear as greed could be simply anticipating how long it takes to sell the run coupled with the fact that Pontiac owners don't have many choices.
 

El Diablo

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Do you guys remember about 20 or so years back when Summit Racing exposed some of the ugly truths about the auto hobby aftermarket? Companies like Holley and Comp Cams raised their suggested retail prices 10-20% almost overnight to reflect a "better quality " part. Summit said that since this was only a suggestion, that they would not raise their prices. It was a battle between the manufacturers and the retail giant. When the manufacturers threatened to not only stop selling to Summit but to take legal action as well for divulging "trade secrets", then Summit raised their prices. For a while, they were giving an equal discount on these certain items but eventually caved to the all mighty dollar.

I bet this has a lot to do as well with the price of rods.
 

8ad-f85

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Same thing in other industries...Best Buy and Onkyo with their famous 'price fixing' lawsuit.

In the grand scheme of an engine build with high buck parts and a normal guy budget, it wouldn't be unreasonable to purchase a bargain set of rods for measurement or slip fit a donor into the assembly to see the swing around the cam tunnel.
That way you can see the effect of the rod beam's width and how the shoulder and bolt placement varies.
It's straightforward to visually compare the differences, even with just a caliper.
Your unused parts could be resold.
 

48Austin

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Everybody is talking steel. I'm talking aluminum. I know steel is smaller, but aluminum is lighter. Which makes the rotating mass lighter.
 

El Diablo

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Bill Miller would be the only aluminum rods I would consider due to their strength and ability to hold up to daily driver builds.
Now will they fit your application? You are probably in uncharted waters with that one. But a little clearancing probably wouldn't hurt too much.
 

8ad-f85

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Aluminum rod enthusiasts seem to suggest that for street use, many of the modern generations of forged rods would hold up fine long term.
One thing we haven't explored is if this build is ragged-edge output/rpm or modest rpm?
There aren't many (good quality) rocker arm body failures due to metal fatigue until something goes very wrong.
Maybe for very good reason, BME might be the only one advertising the life of their rods in street-bound apps.
Like anything else that survives...if it isn't even going to come close to fatigue limits, is the material an issue?
I can't imagine air compressor and Briggs engines having very high tech alloy and process to their rods.
 

48Austin

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I have looked at the BME web site. Things look very in order. But I also looked into R&R Racing Products. Originally started in the Shitcago area. Custom built rod for about 1200. Seems reasonable to me.
 

48Austin

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Aluminum rod enthusiasts seem to suggest that for street use, many of the modern generations of forged rods would hold up fine long term.
One thing we haven't explored is if this build is ragged-edge output/rpm or modest rpm?
There aren't many (good quality) rocker arm body failures due to metal fatigue until something goes very wrong.
Maybe for very good reason, BME might be the only one advertising the life of their rods in street-bound apps.
Like anything else that survives...if it isn't even going to come close to fatigue limits, is the material an issue?
I can't imagine air compressor and Briggs engines having very high tech alloy and process to their rods.
Ragged! But in a 2000 lb. car. So I figure 4:10 gear tops. With an auto of course, or things could get silly REAL quick!
 
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