C5AE rods

pmuller9

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The 6.385” BBC small journal connecting rod can be used for the 300 six.
There are two available at reasonable cost.
Molnar CH6385NTB8-A and the Compstar CSB6385DS3B4AH

They are BBC small journal (2.100") rods 6.385" long.
Big end width is the same as the 300 rod at .992"
They would require custom forged pistons

[image]https://www.dropbox.com/s/dwdhm0yxuqrs57q/molnar-rod-side%201.jpg?raw=1[/image]
[image]https://www.dropbox.com/s/xcoizohhszoez5x/Compstar%20rod%20resized.JPG?raw=1[/image]
 

Max_Effort

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Tom Molnar has forgings and will make the rod. It was an order of seven sets to get good pricing.
He said the slant six rod was the same way, starting with a group of hardcore slant six drag racers, then just enough demand to put them In the catalog. He doesn’t sell a lot of them, but they do sell. The Chevy six is a more popular application.

I’ve had billet rods made from 4340 bar stock. They are CNC machined, but there are plenty of other steps to make the rod besides machining it to shape.

This is one of the rods I had made by Murphy’s Motor service. I think I paid $1600 for six rods in 2007.

1948AC99-448C-4410-9305-74841C510B0F.jpeg

They start from this

D4EC054A-282C-472B-9275-2C885FBA5284.jpeg
 

sandboxer

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Now that’s inspirational. I’ve heard of guys making their own bits and pieces, and I belong to those that wish they could make everything.

I like the look of that rod.
 

pmuller9

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I almost forgot an option for the 240 six.
Molnar makes a 7.130" long billet rod for the Chevy 292 six that will fit the 240 crank.
The 240 crank journals are turned down to 2.100" and the journals are widened .035" so a generous radius can be formed for extra crank strength.
https://www.12bolt.com/store/p32/292_Bi ... olnar.html


Combine those rods with a custom forged flat top piston that has a 1.28" CD and a total piston and pin weight under 600 grams for a screaming six.
 

Mdixon300f100

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So I’ve been running some numbers with the Wallace racing calculators, and found something interesting. The engine parameters calculator puts the redline rpm for the factory 240 rod length over 11k rpm. Is that what you meant by the only thing limiting you is the valve springs? Is that possible with worked over C5AE rods? Valvetrain aside, is the rotating assembly really THAT strong?
 

pmuller9

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Yes, but you want to include all of the valve train as the limiting rpm factor followed by port flow just in case someone wants to get picky about the statement.
Bruce used the worked over C5AE rod in the Prep H race car 300 six at 6800 rpm.
He broke Ford forged steel cranks often in the Pinto until he destroked from 3.98" to 3.75"
The 240 crank with only a 3.18" stroke is much stronger and has less destructive harmonics than the 300 crank.

The other weak link is the cast iron main caps that can crack when the 300 crank is wiggling around at high rpm.
Much less of a problem with the 240 crank

It is very important to reduce piston weight which also part of the equation.
 

THE FRENCHTOWN FLYER

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Mdixon300f100":5aq93bt6 said:
So I’ve been running some numbers with the Wallace racing calculators, and found something interesting. The engine parameters calculator puts the redline rpm for the factory 240 rod length over 11k rpm. Is that what you meant by the only thing limiting you is the valve springs? Is that possible with worked over C5AE rods? Valvetrain aside, is the rotating assembly really THAT strong?
Having the potential for a rod/piston to rev to 11K is way overkill vis-a-vis the rest of the rotating parts and pretty much a waste of resources. Friends of mine rev their crossflow well into the 9000+ range and trust me, every piece of that valvetrain has been evaluated on a Spintron (valvetrain dyno) and drastically redesigned. For example, the roller camshaft alone has to be moved over, with bigger journals and more journals added and revisions to the front drive. The gears (now belt), lifters, pushrods, rockers, rocker stands, valves, springs, keepers, retainers, etc. are all custom. I joke with them saying "I was going to buy a short block like that but I bought an airplane instead".

And don't even get me started on modifications to the block.

P.S. They use FORGED cranks exclusively.
 

Mdixon300f100

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THE FRENCHTOWN FLYER":bviefpt5 said:
Mdixon300f100":bviefpt5 said:
So I’ve been running some numbers with the Wallace racing calculators, and found something interesting. The engine parameters calculator puts the redline rpm for the factory 240 rod length over 11k rpm. Is that what you meant by the only thing limiting you is the valve springs? Is that possible with worked over C5AE rods? Valvetrain aside, is the rotating assembly really THAT strong?
Having the potential for a rod/piston to rev to 11K is way overkill vis-a-vis the rest of the rotating parts and pretty much a waste of resources. Friends of mine rev their crossflow well into the 9000+ range and trust me, every piece of that valvetrain has been evaluated on a Spintron (valvetrain dyno) and drastically redesigned. For example, the roller camshaft alone has to be moved over, with bigger journals and more journals added and revisions to the front drive. The gears (now belt), lifters, pushrods, rockers, rocker stands, valves, springs, keepers, retainers, etc. are all custom. I joke with them saying "I was going to buy a short block like that but I bought an airplane instead".

And don't even get me started on modifications to the block.

P.S. They use FORGED cranks exclusively.

I wasn’t looking at anything that extreme, I also wasn’t aware it was feasible in stock geometry.

So I was wondering what the displacement change does for VE in regard to the cylinder head flow. I understand it moves the powerban up the rpm range about 1k, but what about VE at lower rpm? Is there significant change in port velocity that hinders low (say 2500) rpm operation? I hear a lot of ratings in hp/ci, but is there a direct relationship between hp/ci/rpm and VE?
 

pmuller9

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Mdixon300f100":3q9k8pfa said:
So I was wondering what the displacement change does for VE in regard to the cylinder head flow. I understand it moves the powerban up the rpm range about 1k, but what about VE at lower rpm? Is there significant change in port velocity that hinders low (say 2500) rpm operation? I hear a lot of ratings in hp/ci, but is there a direct relationship between hp/ci/rpm and VE?
In general decreasing the displacement only, leaving all else as is, the smaller displacement engine will have to go to a higher rpm to create the same port flow and VE so the power band moves upward.
However looking at the 300 six we see that the port is undersized for the displacement as shown by the increase in torque off idle as the valve duration increases.
That makes it possible for the 240 to have a low rpm crossover point where it has a slightly better VE than the 300 but the 300 will have more torque over the entire rpm range simply from the fact that it has 25% more displacement than the 240.

When the intake system allows port reversion at lower rpm so there is a well defined power band (instead of flat torque curve), reducing displacement significantly reduces the low rpm VE and torque and while the power band moves upward it also becomes shorter.

One of my customers back in the late 1970s wanted more torque for his 1974 Z1 Kawasaki.
So we had his engine cases sleeved from 66mm to 76mm changing the engine displacement from 903cc to 1197cc.
We kept the stock cam and 28mm carbs and no port work to the head. The engine already had headers.
The 903 normally starts pulling hard at 5000 rpm and you shift at 8000 rpm.
When we finished there wasn't any power band to speak of, just a flat torque curve that would lift the front end off the pavement in first gear from 2500 rpm like it was a dirt bike.

In 1980 I did another 1197cc engine in a 1975 Z1 with a fully ported big valve head, "Hot" street cam, larger carbs and headers.
Now the engine started pulling at 4000 rpm and another hard pull at 7000 rpm, shift at 9500 rpm.
The owner only weighed 135 lbs. and he would run the 1/4 in 10.2 sec in full street trim including turn signals.
He promptly set out to annihilate the new Suzuki 1100 owners that were just hitting the road.

Excuse me for reminiscing the good old days.
 

pmuller9

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A 60mm TP38 turbo would make good power with a 240 to 6500 rpm but there are a few things that would help get boost early.
What A/R turbine housing does the turbocharger have?
What transmission?
 

MechRick

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One of those big two valve Kawasakis with an open megaphone header has to be the best sounding four in existence. Nothing like it...
 

pmuller9

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MechRick":2k4yez8b said:
One of those big two valve Kawasakis with an open megaphone header has to be the best sounding four in existence. Nothing like it...
Amen!
 

Mdixon300f100

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pmuller9":1ka7384k said:
A 60mm TP38 turbo would make good power with a 240 to 6500 rpm but there are a few things that would help get boost early.
What A/R turbine housing does the turbocharger have?
What transmission?

It’s the stock 1.15ar turbine housing. It has a wicked wheel compressor blade. I’m going to have to upgrade the transmission, right now it the T170 3+od. 2.75 rear. I’d like to start with a simple exhaust manifold, make a collector off the efi manifolds to the twin scroll flange to help spool.
 

pmuller9

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A 1.15 A/R turbine housing is on the large side for a 240 six as far as low rpm response. Good for making high rpm power.
I wouldn't expect the engine to start pulling hard till 3000+ rpm.

A 300 would have a much better low rpm response but you would not run it much past 5500 rpm.
It depends on what you want.
 

Mdixon300f100

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pmuller9":7pfzk3me said:
A 1.15 A/R turbine housing is on the large side for a 240 six as far as low rpm response. Good for making high rpm power.
I wouldn't expect the engine to start pulling hard till 3000+ rpm.

A 300 would have a much better low rpm response but you would not run it much past 5500 rpm.
It depends on what you want.

There are smaller turbine housings available, but I think spooling around 3500rpm should work for me. I’d like to change to a wide ratio 4 speed trans and keep the high gear rear end to utilize the rpm as well.
 

pmuller9

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If it all works for you then you have a good start.
Hoping your other block is good.
This will be a fun project. I don't remember anyone else posting a turbo 240 build.
 

pmuller9

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sandboxer":3sk6ytka said:
I’m assuming that a C6AE is still in the category of desirable?
Yes it is still in the category of desirable if you change the C6AE to C5AE. :lol:

Beams polished, rods shot peened and resized with ARP bolts
 

sandboxer

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Too funny:)
The engine block is a C6AE, which I believe is a 1966 block...
So therefore...
I’m about to travel a great distance to buy it so I’d better be sure
 

pmuller9

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Too funny indeed! I figured we were still discussing connecting rods.
Yes any 240/300 block will work as long as there is little wear and it's not cracked.

What is the block history?
 
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