Piston speed

[allrightmike]

  Do the old rules about critical piston speed still apply? Seems I recall John Kasse running something like a 4.750 stroke in a four cam ford in the EMC and it really liked to rev. Piston speed at a given rpm must be very high with that much stroke. Yes,no?
Mike.

[machoneman]

https://www.racepagesdigital.com/piston-speed-an-intense-look-at-mean-piston-speed-inertia-and-controlling-the-massive-destructive-forces-at-work-inside-your-engine/

With Kaase.....no rules apply!

[FERoadster]

Jim Wiltrout and I had this discussion a week ago about why did Ford use larger connecting rod bolts in 427"s and SCJ's. Does the  larger hole in the cap reduce it's overall capacity or does the larger bolt size make up for the difference. This question came up on the FEForum regarding C3 vs C7 large bolt rod differences so I took detailed pictures and the seem identical, This question seems timely. Jim's thoughts were use stronger bolts like ARP's and have the cap as strong as possible.

Here are a few pictures comparing C3 and C7 rods. C7's on top or to the right in some photos.

Richard >>> FERoadster

[Falcon67]

I would say "yes" because the physics don't change.  Mass and acceleration are still factors.  What has changed is the quality of the components IMHO, so that current good quality parts can sustain higher speeds without failure.   

[frnkeore]

The real proof would be in the failure rate.

Ford did the same thing with the 271 HP 289 but, went a a full 1/16" increase in rod bolt size.

The weak point, will be in the counter bore area, on the rod cap. Measure the thickness, from the c'bore, to the parting line and see if there is a radius at the edge of the c'bore.

[machoneman]

Interesting too is Ford's failed experiment with the very high rpm Tunnel Port 302, the predecessor to the Cleveland-headed Windsor block, otherwise known as the Boss 302.  At the time, race teams were losing engines left and right since the TP head had zero bottom end and poor mid-range too. Hence, sustained rpms killed the engines.

I do wonder though if this was due to weak rods (kinda' doubtful I always thought) or the fact that the Boss engine was waiting in the wings and was a better choice.

[gt350hr]

    Bob,
   The 302 Tunnel port used ''Indy" rods which were designed for 500 miles continuous operation at 8,000 rpm with a 2.87 stroke. These rods were ridiculously heavy and used a 7/16ths  bolt and nut arrangement. I have a good amount of experience with these engines as I ran several over the years. The reported bottom end failures were often cause by valves hitting the pistons but there was also a harmonic issue with the over 750 gram rod causing an rpm related "shake" in the engine at an rpm where it ran for long periods. I ran my last Tunnel port ( stroked to 331) with equally heavy Carrillo rods to 8,000+ without issue. The difference "to me" was the titanium valves roller cam and monster valve springs. That short block has Vic Jr heads on it now and is still going strong.
   Randy

[gt350hr]

  Chris is right the physics still apply Mean piston speed is still regulated by stroke and rpm. Connecting rods by design tend to "pinch" at the mating area of the rod and cap as inertia increases. Larger diameter bolts and increased "mating area" along with higher clamping force reduce this natural tendency. Lighter reciprocating parts also help. If the stroke and rpm used is less than the rod is capable on handling , all is good and parts live.

     The piston acceleration off of and back onto TDC is greatly affected by rod length. This "changeable" acceleration ( unlike the "fixed" max piston speed generated by stroke and rpm) can be useful in changing engine performance . Cylinder head airflow characteristics come into play and can be enhanced by altering rod lengths. Using the "longest rod possible" isn't always the best choice.
    Randy

[frnkeore]

I have saved factory Ford stuff for over 56 years and I have part numbers for four 427 rods between '63 and '68. All with 13/32 bolts by the torque specs.

1. C3AZ-6200-C, Presumably the initial LR 4v & 8V

2. C3AZ-6200-F, listed as a Reinforced Cap, 4V & 8V

3. C5AZ-6200-D, a class "C" part, meaning it came out of the National Parts Depot in Livonia, MI.

4. C5AZ-6200-J, same class and rod but, a heavier cap.

I don't have any specs for the 302 TP rods but, I do for the Boss 302. They used the basic 289 rod length of 5.150, with a part number of C9ZZ-6200-B, with 3/8 bolts, 2 7/64 long.

Around 1970, I was at H&M's shop in Long Beach and saw a whole box full of 4 cam, Indy rods ($10 ea), they where 5.315 long, as I remember, so if you were to use those, you would have to have a piston with a C/H of 1.375, with .016 deck clearance.

Before the TP and Boss, the 271 HP rods, where running at least 7500 RPM, in TransAm racing. Hell, I shifted mine at 7000+ many, many times. I had 3 of them, all early 5 bolt blocks.

[machoneman]

    Bob,
   The 302 Tunnel port used ''Indy" rods which were designed for 500 miles continuous operation at 8,000 rpm with a 2.87 stroke. These rods were ridiculously heavy and used a 7/16ths  bolt and nut arrangement. I have a good amount of experience with these engines as I ran several over the years. The reported bottom end failures were often cause by valves hitting the pistons but there was also a harmonic issue with the over 750 gram rod causing an rpm related "shake" in the engine at an rpm where it ran for long periods. I ran my last Tunnel port ( stroked to 331) with equally heavy Carrillo rods to 8,000+ without issue. The difference "to me" was the titanium valves roller cam and monster valve springs. That short block has Vic Jr heads on it now and is still going strong.
   Randy

Thanks and good to know. Interesting on what actually occurred as I had long doubted that Ford would have used 'weak' rods. Sounds too that unlike the GT-40 engine programs (hours/days of dyno run time simulating the 24 Hours of LeMans) they didn't run the same durability tests on the T-Port engines.

[gt350hr]

  Frank you are right about the HiPo rod being good. Shelby's engine shop found that a switch to the "406-427LR" rod bolt in the HiPo rod was a plus. Only the "team" engines got them as it was hush hush. "Ford" engineers on the other hand went straight to the special Indy rod after they failed HiPo rods and a modified version with a "football " headed bolt ( sound familiar?)which were so well polished the looked like chrome . It is interesting that the bearing shell was also thicker to reduce reformation under load. The initial rods had 3/8ths bolts and those were quickly changed to 7/16ths. these were indeed 5.315 and had a .912 pin for injected alcohol and .975 for the turbo engines. The originals used a special "splined" nut that required a special socket for use with the "flat " splines. Ford eventually offered a replacement "conventional" 12 point nut in '70 under a DOZX part number. Too much ''small block talk"  on the FE forum.

    The "LeMans rod" as it became known was initially done as an SK version for use in the 427 SOHC.  the initial rods were close to the nut and bolt rods and modified to go to a capscrew bolt only. Ford had MANY revisions to the initial rod which was forged at Vulcan Forge. In my SK log book there are at least 12 revisions and on major bolt study with SPS Manufacturing regarding bolts and thread types. While the LeMans rod worked , the stock car boys lobbied to get a better rod which led to the Nascar rod/crank and SPS bolt. Again while heavy , they did the job. They were designed for 500 miles @ 7,400 , and did that.
    The CJ employed the LR rod design as Ford engineers had rpm concerns with the 3.98 stroke. The SCJ package added a sorely needed oil cooler because of the higher oil temps seen with the 3.91 and 4.30 axle ratios. The rods were deemed necessary by the engineers that felt the nut and bolt rod would fail under those conditions. In the end it was the rod bolts that was the demon with the LeMans rod.
    Randy