Piston & connecting rods

clintonvillian

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I saw on another site that the 300 came with forged rods, and those would be better for a boosted build over the longer 240 rods.

Is there any truth to that? Are there any part numbers available for those rods?
 

pmuller9

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All 240/300 rods are forged.
The problem with the 240 rod on a 300 crank is there is very little room under the piston head for a deep dish since the top of the connecting rod is so high in the piston.

The 1965 to 1968 300 rods without the spit holes and .912" pins have a forging number of C5TE
 

clintonvillian

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So strength wise the same?

I had assumed the longer rod ratio would deliver better results. Below is a topic, as well as a quote, do you guys feel this is accurate?

Lazy JW":1cadx2vv said:
Fordman75":1cadx2vv said:
..... And it will never see any use above 5,000 rpms.....

This is the key. Longer rods don't provide their advantage at lower speeds, and 5000 rpm really isn't all that fast in the modern world.

What you truly need in a 7000 lb vehicle is low-end torque, and that[highlight=yellow]long rod will hurt the low-end torque[/highlight]. The short rod gives the piston a quicker yank downward on the intake stroke; this improves cylinder filling.

On the power stroke the short rod moves the piston away from TDC sooner too; this[highlight=yellow]improves detonation resistance[/highlight], which you will want in the forced induction mode.

I wouldn't even contemplate a 240 rod unless top rpm were desired.
Joe



https://fordsix.com/viewtopic.php?t=54824
 

THE FRENCHTOWN FLYER

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clintonvillian":gs5i3nml said:
I saw on another site that the 300 came with forged rods, and those would be better for a boosted build over the longer 240 rods.

Is there any truth to that? Are there any part numbers available for those rods?
ALL 300 rods and ALL 240 rods are forged.
 

pmuller9

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clintonvillian":1g53l03u said:
So strength wise the same?

I had assumed the longer rod ratio would deliver better results. Below is a topic, as well as a quote, do you guys feel this is accurate
The main reason for going to the 240 rod on a 300 crank is for the 30% reduction in piston and pin weight.
The reduction in piston side loading would be another reason.
The stock piston skirt travels 1.1" below the bottom of the cylinder while the 240 rod piston stays within the cylinder.

The problem with the 240 rod piston is the CD is only 1.200" and doesn't leave much room over the top of the connecting rod for a deep dish required for low compression boosted application.
 

clintonvillian

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THE FRENCHTOWN FLYER":2us4iqut said:
clintonvillian":2us4iqut said:
I saw on another site that the 300 came with forged rods, and those would be better for a boosted build over the longer 240 rods.

Is there any truth to that? Are there any part numbers available for those rods?
ALL 300 rods and ALL 240 rods are forged.

FTF, ever had one fail?

What's the comfortable power level with them?
 

xctasy

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THE FRENCHTOWN FLYER":saqxw3eu said:
Shorter rods were once the rage in drag racing for an application where the cubic inch displacement was reduced by de-stroking, to make a class requirement for a specific cubic inch-to-weight.

This was done in an effort to enhance the flow in the overlap phase, where port and valve sizes were very large in comparison to the (reduced) cylinder displacement, leading to lazy flow characteristics during overlap.

The situation in our 300 six is quite the opposite - we have a relatively large cylinder to fill and purge with a relatively small set of ports so there is really no advantage to keeping the shorter rod.

Once again I would like to paraphrase one of my engine building heroes Buddy Morrison of Reher Morrison fame, " If I were to list the most important factors in the construction of a race engine rod length would rank about number 50."

For me its like the 7 th thing.

Behind
1.carbon fibre pushrods (Noise, Vibration and Harshness Removal helping valve control and durability)
2. independent runner intakes,
3. Fuel standoff space and dual port broad band intake shrouding
4. Noise, Vibration and Harshness control by Critical Frequency Mass adjustment (removing counterweights or adding them, depending on the measured merits)
5. Port size reduction to a Pipe Max minimum and then bulstering peak combination flow
6. The use of the ITB Italian Aero engine Weber ITB chart.This is to optimize the rpms per horsepower ideal as per example Formula one Repco Brahbam 2.5 liter engines designer Phil Irving, and eg 2 A. Graham Bell on the advantages on the 906 headed L31 Vortech over the best LS1s,

Eg 3 Larry Perkins Holden V8 Supercars sublime idling 8.9 inch deck 305 Holden over the technically better 9.0 inch deck 302 SBC in 1995.

All of this is just debatable but definately provable positives that are cumulative low hanging fruit.

Its cheaper to ger Mahale 1.169 inch Compression Depth 347 4.030" with a cheap strong Mopar or 240 6.800" forged rod.

All seven are Win Wins on an air limited engine.

Id add each of these up together.

Bill in Indy did a 3 page Engine analyser free ask and answer session. The 300 gets an extra 5% power boost for every 10% improvement in L/ R ratio. Absolutely, because its air flow limited.
 

xctasy

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See six pages of what works with the big six. Post responses to #16, #39 and #48 were epic proof of David Vizard, Stan Weiss and Burrel carb and rpm power and torque response to those items 1 to 7.


viewtopic.php?f=2&t=42347&p=312589&hilit=Bill+in+Indy#p312589

viewtopic.php?f=1&t=77066&p=593102&hilit=Bill+in+Indy#p593102

xctasy":7wpify5s said:
Bill in indy, you are surely the man! That is an exceptional program.

167@3500 rpm 299ft/lbs@2000 rpm vs.

194@4000 rpm 309ft/lbs@2000 rpm

Pulse tuning in a 300 yields perhaps 16% more power over the better 4-bbl set-ups, perhaps 4% more torque.

If the 'port on port' carb sizing is too small for the combination, a 16% smaller engine will yield a lot more power!


Taken the other way, the best carburation is likely to yeild well over 16% more power, and a good increase in torque.

To corroborate, back in 1971 Chrysler Australia put out a triple carbed 265 cube I6 engine with a mild 260 degre cam, split exhast. They put out 248 hp gross at 4800 rpm. Allowing for the the conversion from gross to the net flywheel figures, thats the similar to the 208@4500 torque 278 @3000 ft/lbs you have there.

Thankyou for the effort involved. ;)
 

THE FRENCHTOWN FLYER

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clintonvillian":3qalqg7b said:
FTF, ever had one fail?

What's the comfortable power level with them?
clintonvillan, I have never had a stock connecting rod fail, largely in part because if I build a serious race engine (400 - 500 hp) I go with custom pistons (Diamond) and connecting rods (Oliver). I continue to use stock rods for engines with less power output with no issues (<250 hp).

I did fail one engine with an aftermarket rod (Superod) and it was totally my fault for neglecting to change out the aluminum rods after the recommended finite life span was exceeded. At the time I was preoccupied with other projects - building another race car - and exceeded the number of runs on them by a bunch. Broke in two, kicked it out a prized SVO block, and learned a valuable lesson.

IIRC the factor of safety for a stock 300 rod is 2.6. That is probably at 4600 rpm. So you engineering types out there can reverse engineer those numbers to arrive at a FS at whatever rpm. As far as my own anecdotal experience I have been using stock rods in my NA RPU drag truck and I limit its rpm to 5500. I'm guessing its putting 220 hp at the rear wheels.

Aside from the cracking piston skirts, I would say the weakest link in a stock engine is the puny 5/16" pushrods. I upgrade to 3/8".
Not the stock rods.
 

guhfluh

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clintonvillian":28jo1x4q said:
THE FRENCHTOWN FLYER":28jo1x4q said:
clintonvillian":28jo1x4q said:
I saw on another site that the 300 came with forged rods, and those would be better for a boosted build over the longer 240 rods.

Is there any truth to that? Are there any part numbers available for those rods?
ALL 300 rods and ALL 240 rods are forged.

FTF, ever had one fail?

What's the comfortable power level with them?
There has been an example on this site of a 240 rod failure in a high torque turbo application.

What would be a good tell is a picture and measurement comparison of a 240 and a 300 rod side by side showing the difference in beam strengths. I have seen one picture posted on this site before, but I cannot find it.
 

pmuller9

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Here is the 240 rod failure in a turbo 240 engine.
viewtopic.php?f=2&t=80597

We figure the beam failure happened because the rods had not been checked for defects (cracks) and should also have had the forging lines removed then shot peened and resized with ARP bolts.

The other failure mode is big end break at the spit hole due to rpm above 5500.
Here is that example.

Broken%20Spit%20Hole%202.jpg


FTF has the best advice in that you don't push the limits of the stock rod if you want to minimize the chance of failure and go to an aftermarket rod instead.

The "off the shelf" solution to a heavy boosted 300 six is the BBC small journal rod which is a little longer than the stock rod and has the same big end width.
https://www.summitracing.com/parts/cpi-b6385ds3b4ah
 
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clintonvillian

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THE FRENCHTOWN FLYER":hj5w1gp7 said:
clintonvillian":hj5w1gp7 said:
I saw on another site that the 300 came with forged rods, and those would be better for a boosted build over the longer 240 rods.

Is there any truth to that? Are there any part numbers available for those rods?
ALL 300 rods and ALL 240 rods are forged.


Don't the later model 4.9L have some kind of weird alloy rod?
 

THE FRENCHTOWN FLYER

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You may be thinking of the 4.6 Modular V8 which has powdered metal technology. That type of rod has a very good reputation and is being widely used in the industry today. Due to its homogeneous nature and consistently uniform qualities, not to mention the low cost of production, they have a very good reputation.

I do not believe the 4.9 ever switched to PM rods, at least not on my watch.
My experience is that rods usually fail in tension - that is, stretch, not column buckling (compression) or bending. Having said that I do not feel a boosted engine is significantly harder on rods. The rod will fail when the crank is pulling it downward trying to stretch it apart, not when increased gas pressure on the piston is trying to cause it to buckle. Higher RPMs greatly increase this type of loading on the rod. Often a rod will fail on a coast-down period when the throttle is closed but the engine is spinning at maximum RPM.

Of course if by some reason you starve the journal of oil all bets are off.
 

xctasy

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Thats right, no Powdered metal rods on Fords Big Six or the small six. A point of not is that all 1976 to 1980 US 250s, all 1978 to 1983 US 200s, they reverted to cast iron el cheapo rods. 87 to 99 hp, 155 to 185 lb-ft emgines dont really need them.Although Pontiac had cast iron rods in Big blocks.for.years.

The Australian 4 liter 243 cube DOHC Barra got the same kind of six inch rods theTaurus HSO 2.5 liter got in 1986. A rod 120 thou longer than the historically strong C9 forged steel 1969 to 1975 250 six rod, traditionally okay to 360 hp with a TO3 60 Garret and 12 pounds of boost. When the 4.0 turbo charged in 2002 with just 6 psi of boost and 320 hp, it suffered terriably with bending failures. The Australian engine was boost modulated to 332 lb-ft uniform from 1500 to 4000 rpm. Due to the wastegate over boosting at low rpm, the early GT35-82 equiped 4 liter Barra Turbo Fords bent a few conrods that had never had problems or service history matters before. Same with the OHC 2300 Carb turbo..No history of con rod failures untill the 1979 to 1982 US and Canada Turbo engines. Same 6 pound boost happening early, with a big T03-60 turbo. Even Turbo MG Metros with the same TO3-60 turbo took out the odd crankshaft at just 100 hp, up 40 hp from stock.
 

guhfluh

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THE FRENCHTOWN FLYER":lurbvhwv said:
My experience is that rods usually fail in tension - that is, stretch, not column buckling (compression) or bending. Having said that I do not feel a boosted engine is significantly harder on rods. The rod will fail when the crank is pulling it downward trying to stretch it apart, not when increased gas pressure on the piston is trying to cause it to buckle. Higher RPMs greatly increase this type of loading on the rod. Often a rod will fail on a coast-down period when the throttle is closed but the engine is spinning at maximum RPM.

Of course if by some reason you starve the journal of oil all bets are off.
Failing in the beam from RPM or in the big end? I have seen many beam failures from turbo applications when pushing the compressive limits of the rods and especially when riding that limit and the tune isn't spot on. Just a touch of detonation when at the limit is all it takes to bend the rod, then depending how badly bent and engine details depends on the following carnage. Then there's the bending and failure from way too much boost, torque and peak cyl pressure at low RPM even when the fuel octane is plenty enough to prevent any detonation and tune is spot on. The big end failures I've always attributed to RPM and stretch, unless it's obvious rod bolt or bearing failure first.

Having said that, I'd say it's not fair to assume the turbo 240 rod failure was purely from an inclusion in the beam material, when the owner admitted to subjecting it to 20+psi and detonation at well over 500 wheel torque. There is also quite a bit of piston to counterweight clearance in a 240 to allow for a bent rod to run unnoticed for a while and experience cyclic fatigue.

I would still like to see a side by side comparison picture of a 240 and 300 rod added to this thread. Beam thickness measurements would also be benefitial I'd think.
 

sixtseventwo4d

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THE FRENCHTOWN FLYER":3koz7mr7 said:
I wonder why I haven't heard of rod beam bending failures in 12,000 hp Top Fuel motors?


Would those have aluminum rods? And replaced after every-so-many rebuild/runs?
 

THE FRENCHTOWN FLYER

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I know the crankshafts are good for about 550 revolutions at WOT. Total. And when removed the journals are blackened.
 

pmuller9

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clintonvillian":2pgqa5n3 said:
Other than turning down the Crank to 2.100, are there any other modifications necessary for the compstar rods?
Since it is a V8 rod the one side of the big end has a larger bevel than the other.
You can bevel the one side so it matches or check the clearance against the radius at the crank journals.
The last set used here had enough clearance with the rod as is.

Other than that they are good to go.
 
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