Whew. Let's see, 10,000 miles per year, most spent at redline should last me till I expire. Or replace it with a rumoured flat plane crank GT350. I'm good.
Thanks for the great posts Red. Both interesting and enlightening (for me at least).Thanks J.
I did not come up w/ 8500 rpm -- others did. I feel it to be an unrealistic level, and did a little coding and web searching to back that up.
I'd like to add one or two interesting tidbits (interesting to me anyway).
If one wants 8500 rpm from the basic Coyote/Road Runner architecture, the stroke has to be decreased. The engine from the factory actually carries a pretty large 'arm' at 92.7 mm (3.650") for 'only' 302 cid displacement, imo. Deciding to limit the mean piston speed to 24.0 m/s gives a stroke of 84.7 mm. If we want to keep the same pin height (stroke/2 + rod length), the rod needs to be lengthened from 150.7 mm to 154.7 mm. Keeping the same pin height means you can use the same compression height for the pistons and, importantly, the same deck height for the block -- i.e. one 'could' reuse the same block and pistons, saving costs. More on this in a bit. Keeping the bore unchanged at 92.2 mm gives the following specs:
rpm: 8500
bore: 92.2 mm
stroke: 84.7 mm
rod length: 154.7 mm
displacement: 4,524 cc (276 cid)
rod/stroke: 1.826
mean piston speed: 24.0 m/s
max piston speed: 39.09 m/s
peak acceleration: 4,361 g's
Achievable numbers, though still a highly stressed engine -- no way around it at these rpm levels. The Road Runner (RR) is already a highly stressed engine, and everyone involved w/ its design and manufacture deserves much respect.
Anyway, first consideration has to be getting the above conceptual engine to live well past warranty period. To reduce loads/stresses, perhaps titanium or Carillo/Crower steel rods and perhaps titanium intake valves will be needed. RR already comes w/ forged pistons, but I'd have to think this conceptual engine would need new lighter weight forgings to withstand the significantly higher peak acceleration (4361 vs 3815). Definitely some very high quality valve springs. The crank will be stronger due to the shorter arm (assuming bearing diameters are unchanged - a big assumption, and other things being the same), so that's one thing in this engine's favor.
Consider next what it'll take to get the torque and power desired. Let's say 525 HP @ 8000 rpm is desired. As mentioned above, we can easily back out the torque required at that rpm: ~345 ft-lbf. For comparison, the Road Runner makes ~ 311 ft-lb at 7000 rpm (this conceptual engine needs to breathe, to say the least!). Backing out the brake mean effective presure (BMEP), I get ~190 psi. That is a very stout number, imo, but not unreachable. The RR (311 ft-lbf @ 7500) has a BMEP 155 psi. The 458 Italia, with 562 HP @ 9000 rpm has a BMEP of 183 psi. If you run the numbers for NASCAR and F1 mills, you get 215 - 225 BMEP. I don't know how reasonable, or unreasonable, it is to get 190 psi BMEP out of a street engine, special edition or not. Hard to raise the compression much w/o getting into radical cams. DI could really help here. The RR heads are really good, but they may need revision for this level of performance, I don't know. Another thing working in our favor will be reduced windage losses due to the shorter stroke. A dry sump could go a long way on this engine (plus an extra stage to put the case under a 'vacuum' would definitely help). My guess would be 20 horse for the dry sump.
But, if we're willing to move the 525 HP up to 8500 rpm, then the torque (at 8500 rpm) falls to ~324 ft-lbf, and BMEP (at 8500) falls to 177 psi. Will likely be an even more high-strung engine, but perhaps a more realistic design.
Finally, after all this typing (), I still have to think that Ford could enlist the Aluminator (for N/A applications, not the S/C version) as the "Voodoo" engine. Slightly larger bore (94.1 mm) would give 5.2 liters (rounded to nearest tenth of a liter). Block has 100 mm bore centers, so there'd be 5.9 mm left between head gasket bores at narrowest point. Again, kind of on the limit (of blowing head gaskets), but I imagine that could be handled. It's otherwise a proven unit making 500 HP and carrying a 2 yr/24,000 mile warranty. Increasing the warranty period to 5/50 (or whatever it is) may require some concessions in HP/torque.
Of course, if the "Voodoo" is available in only non-street legal cars (CJ, 302S, 302R), then all bets are off.
Many thanks Red. Your detail and analasys is greatly appreciated. It does have six bolt mains (hopefully not "balsawood"), and notwithstanding the long stroke, I can confidently get back on the loud pedal with my usual enthusiasm!Folks, I didn't mean to alarm people over the durability of their own engine(s). Sorry about that -- absolutely unintended. Regardless of manufacturer, I'm sure there's a large safety factor built into the determination of redline. They have to do this for warranty reasons, risk mitigation, safety, and just engineering sense. Don't worry!
Steve, your 5.4 @ 6200 rpm:
bore: 90.2 mm
stroke: 105.8 mm
rod: 169.1 mm
displacement: 5,408.5 cc (330.0 cid)
rod/stroke: 1.60
mean piston speed: 21.87 m/s
max piston speed: 36.00 m/s
peak acceleration: 2,987 g's
max piston speed occurs at 74.00 degrees before and after TDC
Those numbers are much 'milder' than most of the other engines posted previously. Of course, materials and component design must be able to handle the loads created by the above speeds and accelerations. For example, a far-fetched one meant to prove a point, we wouldn't expect a 5.4 with balsa wood connecting rods to survive a single revolution, right?
I'm sure your engine will be fine (at least the reciprocating assembly) for as long as you own it -- assuming proper maintenance, of course.
If it helps to allay anyone's fears about their engine, here's the little relation for mean piston speed:
mean piston speed = 2 x stroke x rpm
for example, an engine with 3 inch stroke at 6,000 rpm has a mean piston speed of: 2 x 3" x 6,000 rpm = 36,000 inches per minute. These units (inches/minute) are not commonly used, but feet per minute (ft/min) is. Divide inches/min by 12 to convert to feet/minute. For this example, the result is 3,000 ft/min, which is a very safe speed. If you wish to convert ft/min to meters/second, divide by 196.85 -- giving 15.24 m/s for this example.
Hope that helps.
Thanks Falc'man, although its only the 260.
Build it. I'll buy it.To finish a conceptual exercise, I slightly modified the previously defined concept to the following:
bore: 94.0 mm
stroke: 81.7 mm
rod length: 156.2 mm
rod/stroke: 1.91
displacement: 4,535.8 cc (276 cid)
rpm: 8500
mean piston speed: 23.15 m/s
max piston speed: 37.59 m/s
peak accel: 4,166 g's
max piston speed occurs at 76.20 degrees before and after TDC
So, same pin height and same displacement (essentially) as before with an overbore of 1.8 mm (~0.071"), which would hopefully work fine w/ the existing 100 mm bore center block.
But this 'design' has lowered piston speeds and accels. The mean speed is essentially equal to that of the current Roadrunner @ 7500 rpm, the max piston speed is actually lower than that of the Roadrunner, but peak accel is roughly 7.9% higher.
Is it reasonable to think the above could make 525 horse @ 8500 rpm? That means the engine would have to produce 324.4 ft-lbf at that rpm, for a BMEP of 177 psi -- which is significantly lower than that of the previous concept. If you run the numbers on the Aluminator, you see it produces a BMEP of 175 psi. So, the actual levels are close, but the conceptual engine has to make the number @ 8500 rpm, instead of 7500 rpm, which is more difficult. But, at least it's feasible.
Let's look at required volumetric efficiency (VE%) and brake specific fuel consumption (BFSC) to see if anything there says "BS". Running the numbers for some of the engines listed previously, I find:
Roadrunner: VE% = 1.8448 * BFSC
Aluminator: VE% = 2.0775 * BFSC
Ferrari 458: VE% = 2.1448 * BFSC
Honda F20C: VE% = 2.2155 * BFSC
NASCAR 358 CID V8: VE% = 2.3369 * BFSC
Porsche GT3: VE% = 2.3370 * BFSC
F1 2.4L V8: VE% = 2.5028 * BFSC
NHRA PS 498 CID V8: VE% = 2.6889 * BFSC
Conceptual 4.5L V8: VE% = 2.1060 * BFSC
Since I don't know either quantity for any engine, I can't go any farther than the above relations between the two. The greater the BFSC coefficient (i.e. 1.8448 for the Roadrunner), the more highly tuned the engine, and the more difficult it is to attain. The conceptual engine falls between that for the Aluminator and the Ferrari 458. So, this too is feasible.
Finally, the relatively large rod to stroke ratio (1.91) helps to reduce the secondary imbalance (the shaking force that will want to shake the engine side-to-side) -- meaning a flat crank version of this engine would be more likely than for the previous concept engine.
And that concludes my little game.
