Regarding Rod Length in 300

[twocron]

FTF; The late Kay Sissel(& I think Ak Miller) seemed to think the 240 rod (6.795") was a good option for the 300. The Piston compression height would be in the 1.170-1.185 range. Too much crowding of ring package with this short of a C/H? Also am wondering if destoking forged steel crank to 3.75" range (w/ welded throws) would help (288")rpm survival ??

[StrangeRanger]

At one time Clifford sold pistons with a 1.1719' CH for a 300 with 240 rods. No idea if they still do or not.

[russk]

Twocron:

My son is building up a 408" SBC for his '67 Chevelle (he's also an inline fan so I'm not too hard on him) and the particular combination uses a 3.75" Lunati crank and 6.0" rods. Given the SBC's deck height (9.025" typical), the stroke, and the relatively long rod, the Lunati flat top pistons have the pin location go partially through the oil ring land with the compression height of 1.150" to arrive at a zero deck. The ring set has a "support" included that bridges the exposed portion of the pin bore and that apparently does the job to keep the oil ring set working properly. I suspect a similar setup can, and would be used with the compression heights you are talking about when using the longer 240" rods with the 300" crank.

I used the following formula to get the compression height:

zero deck compression height = (block deck height - (stroke / 2) - rod center to center length)
( 9.025 - (3.750 / 2) - 6.000)
( 9.025 - 1.875 - 6.000) gives 1.150"

Russ

[worken2much]

I think there is a Keith Black 351 Hyperutectic stroker piston that will work. I'm away from my notes but the pin dia, bore diameter and compression height would work with the early 240 rods with a .912 wrist pin diameter and 300 crank. From memory, the compression height is something like 1.12 or 1.14? I just can't recall. Anyway, if you find a website that has the K-B hyper piston dimensions, (maybe KB-276?) it won't take long to figure it out. I think my next motor is going to be built this way. The last 300 I built had what I thought was lot of rotating friction. I'm sure the steep rod angle, which side loads the pistons heavily contributes to this.

Worken2much

[THE FRENCHTOWN FLYER]

I use the 240 rod length and a skinny, state-of-the-art ring pack. Modern ring packs are much thinner so it is possible to jam it all in there safely.

[russk]

'Flyer:

Just curious:

Over in the Chevy [!] camp when building up a race 292 (or greater), there is a problem with clearing current aluminum rods as they rotate past the cam. I believe most of the 292s have traditionally used the "small" Superod aluminum rods. But like your X-flow head, those are mighty rare these days. Does the 300" (or greater) Ford have a similar problem with aluminum rods clearing the cam? I know you were using BME rods at one point; would that be your current choice for a 300" build?

By the way, as I work out the 30-thousand foot view of a 240+ race motor, I'll have a qustion or two about the rotating assembly combination I'd like to run past you. Given a compact ring package, relatively short stroke of the 240, and the 10.000" tall deck, I'm thinking some fairly long rods (7+ inches center to center) would be indicated giving something above a 2:1 rod/stroke ratio. I'm assuming that would be a good thing?

Russ

[MaxRat]

unless you are racing the thing I wouldnt use a longer rod...

the longer the rod the slower the piston speed off its centers....when you have this you need a bigger flowing head to make use of it...

shorter rods have a faster piston speed off its center and can more utilize a smaller flowing head...

the 300 already has a restrictive head...adding rod lenght would be a minimal effect kind of thing...unless you plan on massively hogging out the head for flow...

personally for a stock headed app with a port job and good flowing valves I would be inclined to use shorter rods than factory to increase the piston speeds and more utilize the smaller head...then you can put the cam where you want it and rpm would be less of an issue....

of coarse I would have the crank massively lightened and rods too and use super light weight pistons to get the rate up...

[CNC-Dude]

'Flyer:

Just curious:

Over in the Chevy [!] camp when building up a race 292 (or greater), there is a problem with clearing current aluminum rods as they rotate past the cam. I believe most of the 292s have traditionally used the "small" Superod aluminum rods. But like your X-flow head, those are mighty rare these days. Does the 300" (or greater) Ford have a similar problem with aluminum rods clearing the cam? I know you were using BME rods at one point; would that be your current choice for a 300" build?

By the way, as I work out the 30-thousand foot view of a 240+ race motor, I'll have a qustion or two about the rotating assembly combination I'd like to run past you. Given a compact ring package, relatively short stroke of the 240, and the 10.000" tall deck, I'm thinking some fairly long rods (7+ inches center to center) would be indicated giving something above a 2:1 rod/stroke ratio. I'm assuming that would be a good thing?

Russ

Russ, the main thing that gets the 292 into trouble is the stroke. Even with the Superods, you still have to notch the camshaft in several places, meaning you usually can't use aluminum rods in a 292 except with a roller cam, because you severely weaken a flat tappet cam by doing this. The Ford 300 has a much shorter stroke than the 292, and the cam/crank centerline is also farther apart on a 300 than the 292, so you typically don't have the clearance issues on the Fords as the Chevies. Also, to add to what Maxrat said, the shorter rods will also provide more torque than the longer rods. Unless you are looking to spin the engine into the twilight zone, super long rods give up more than they will gain. You just have to determine the type of operating range the engine will be used for. And just to show that you can't always count on formulas to use as a guide to build an engine with. I built a SBF nitrous engine that competed in the NMCA very competitively that had a 4.250" stroke and had a 6.100" rod in it....the rod/stroke ratio was 1.47! I still have people tell me today, there is no way that will work. But it ran 8.68 in the quarter in a 3200 lb. Mustang back in the late 1990's, with very little maintenance for the whole season, and the driver finished 11th in points in a class with 198 other drivers....

[MaxRat]

thats because Smokey Yunik always toted you needed a 2:1 rod ratio according to stroke...but that was because the DZ 302 made for the Camaro for Trans Am worked very well...Even though racing has been going since the day the wheel was invented things are still to be learned....

Lately I pick the head and then build the engine around the head...I pick rod length according to head flow...and actually I think torque comes from a longer rod...but we can agree to disagree if you like...

as much as the greats were there is so much more to learn...I dont think we will ever understand it all...

but even that sbf proved rod ratio not 2:1 still makes optimum power...I think it is more of getting the combo right...making the heads match the rods and compression from there...

on my 340 I used a small journal 283 rod and kept the length the same at 5.7 but then I switched from a 210cc head to a cnc AFR 195cc head and picked up 100+hp for 708hp at 7800rpm-8200rpm pretty sweet for me...

[THE FRENCHTOWN FLYER]

When using a (relatively thick) aluminum rod in a 300 you must:

a) notch the bottom of each cylinder where it protrudes past the cooling jacket - not much - about 3/8 x 1"

b) remove the mechalical fuel pump eccentric lobe from the camshaft or it will crash into the side of the rod (been there).

Superod no longer makes rods. Bill Miller and Howards rods are made from heavy forgings that are overkill.
I just this year switched to steel rods as it was getting to be a hassle getting a good aluminum rod. No decrease in performance with steel. Why? They're smaller and slice thru the oily mess in the crankcase easy, and you can run tighter squish and therefore more compression with steel rods.

RE ROD LENGTH: I remember reading a paper about a Bonneville LSR car that was running a very small SBC V8(220 ci?). They used as short a rod as was possible because the head, which flows enough to support a 350ish V8 displacement, was very "lazy" in the overlap cycle causing the scavenging gasses to slow down too much to run efficiently. In using the shortest rod possible they could maintain a higher piston velocity as the piston approached TDC, thereby insuring efficient scavenging.


Isn't this the exact opposite condition of our 300s? We have an oversize displacement vis-a-vis the relatively poor flowing ports, which would seem to dictate that as the stroke increases the rod length and L/R ratio should also increase to allow the head flow more time to "catch up" by slowing the piston earlier in the cycle. Or so it would seem to me.

P.S. I have nothing but the greatest of respect for anybody who ever got a 292 Chevy to run decent. After reading Leo Santucci's book about all the hoops one must jump thru to make it happen I would have given up on them long ago. Us 300 gearheads must realize how relatively easy it is to make the 300 run and live. Anytime you get discouraged about trying to run a 300 read Leo's book. Very enlightening.

[CNC-Dude]

P.S. I have nothing but the greatest of respect for anybody who ever got a 292 Chevy to run decent. After reading Leo Santucci's book about all the hoops one must jump thru to make it happen I would have given up on them long ago. Us 300 gearheads must realize how relatively easy it is to make the 300 run and live. Anytime you get discouraged about trying to run a 300 read Leo's book. Very enlightening.

Leo definately took the long way around to make his engine combo. He has asked me to consult with him on his newest book, and to review his first one for accuracy. The stock siamese port head when ported is much better than the Frankenstein head he created to replace it with, but he just wanted to be different. It is totally unecessary to go to that extreme to make one of them go fast. I think he was just trying to mimick the efforts of some of the early Ford 6 racers that took the 4 BBL. Cleveland heads and welded them together for the 300's.

As for the rod length issue, this is one of those topics that is always debated. It has been thoroughly tested by many engine builders and cam companies to help determine the relevance to it. Ed Iskenderian has a page on Isky's website detailing his findings in this matter, after an exhaustive dyno session where they tested (4) different rod lengths in a SBC engine. He concluded, that he saw no more than a 5-7 HP gain from the shortest to the longest rod they tested. Buddy Morrison of Reher-Morrison fame, also tested in many of their companies Pro Stock engines the same theory, and used rod lengths that increased a total of over 1/2" in .050" increments(thats 10 different rod lengths), and concluded his findings with this statement, "The connecting rod only connects the crank to the piston, nothing more". So, be that as it may, many builders use longer rods for different reasons, mostly to help use a more commonly available piston in some cases without having to go custom. Plus, you can get a lighter piston usually, when it has a shorter compression height as well. And in the Ford 300, it greatly helps with the cylinder loading because of the poor rod/stroke ratio, so there are advantages, even if they might not always yield more HP.

[StrangeRanger]

Just my $.02:

Within the range of performance that 99+% of the people on this board are concerned with there is probably no advantage or disadvantage whatsoever to any length of rod. However, if you have to replace your conn rods during a rebuild, the 240 rod swap is probably worth doing simply to reduce the side loading on the pistons. The 300 is known for throwing skirts and I am convinced that this is at least partly due to the side thrust from the stock short rods. But I've been wrong before...

[CNC-Dude]

Strangeranger, I think this is an istance that would be very condusive to going to a longer rod. I totally agree with this scenario....

[russk]

Guys:

For the second time in just a couple of days, I seem to have lost a post to the "ether". Don't exactly know why but I assume I did something wrong. Hmmmm . . .

In any event, it's like being back in school attending one of those very rare classes you really enjoy every day, soaking up the subject matter like a sponge. I really appreciate all the good information you all have to offer, even when sometimes there are opposing views on a particular topic.

As I posted ealier, my interest at this point is in a class-limited (260ci max) drag race motor. Given the 240/300 tall block (at 10.000"), the 240's relatively short stroke (at 3.130" if I recall correctly), and a modern light weight piston package, you pretty much end up with a long rod (something at or just above 7.0") by necessity. If that reduces the cylinder side loading and gives a few extra HP in the deal, that would seem to be a good thing all 'round. Besides, as one of the earlier posts said, you gotta connect the piston to the crank . . .

'Flyer (and others): I was particularly interested in your choice to switch away from aluminum rods in favor of steel. I was going to ask about the [aluminum] rod stretch issue but steel makes that moot. Curious what your thoughts are about selecting a good steel rod? I-beam vs. H-beam? Material? Forgings vs. billet?

Russ

[THE FRENCHTOWN FLYER]

'Flyer (and others): I was particularly interested in your choice to switch away from aluminum rods in favor of steel. I was going to ask about the [aluminum] rod stretch issue but steel makes that moot. Curious what your thoughts are about selecting a good steel rod? I-beam vs. H-beam? Material? Forgings vs. billet?

Russ

I am using Oliver rods, basically their small block V8 forging I-beam style. Before switching I talked with others who use them and the consensus is that they are indestructible regardless of the number of cycles on them - something you cant get with aluminum or titanium rods. The I- vs H- thing can probably be debated to eternity like rod length.
I like forgings because the grain structure has a chance to align with the axis of the part. Most car and motorcycle manufacturers are now using powdered metal technology in their new engines as it saves material and money. They are very robust parts in most cases. I think that, like hypereutectic pistons, they don't get much respect from the performance crowd.

[MaxRat]

I think Powdered Metal rods would get more looks if it wasnt called what it is...when people think Powdered Metal they think like what it says...compressed powdered metal...like making a cast and pouring sand it in...most minds think powdered metal is more brittle...but if the OEMs use it...it has to be OK..? no?

[THE FRENCHTOWN FLYER]

Yes I think it could have been marketed better. Maybe WE should start a contest to name them.

My attempt: Thermal-Forged

[StrangeRanger]

A truly "sintillating" contest

[Thad]

How about - The latest, greatest, newest metalurgic technology developed with laser science in the presence of turbo titanium fumes resulting in the "Nova rod" they won't go broke.

[StrangeRanger]

It's sort of like convincing people who don't understand the process that investment casting yields a high precision, high strength alloy part. "It's just a lousy casting" is the invariable response. My take is that forgings are still probably better than sintered rods simply because of the work-hardened surfaces. What happens when you prep a set of sintered rods? There's no rough spots to polish and no kerfs to remove so there's precious little prep work required. Does the sintered metal respond to shot peening like a forging does?

[THE FRENCHTOWN FLYER]

How about - The latest, greatest, newest metalurgic technology developed with laser science in the presence of turbo titanium fumes resulting in the "Nova rod" they won't go broke.

In the past my wife and I used to muse over the latest marketing gimmicks used in advertising. For a while every car had "radial tuned" suspension (WTF?), every cutting or bearing device was "teflon coated" and every soap product was "lemon scented".

So I wish to modify my nomination to Teflon coated, lemon scented, radial tuned Thermal Forgings.