We had the roadster on a dyno one time – not interested in the numbers – just checking to see what spark advance put up the best numbers. And rechecking. Found the answer. Found out it was real loud, too. www.youtube.com/watch?v=nNoVYDO8_xg
What people should know is......... the HP graph and Torque graph on dyno charts should cross over at exactly 5252 RPM for all Engines. [ this goes back to James Watt's original calculation for HP] If they don't crossover the dyno chart is bulls**t. The greatest loss in driveline can be the tyres.........good traction, which is actually friction! needs hp to overcome this [a trade off] Aerodynamic downforce is the same, it needs hp to overcome the drag it creates.
Was it a chassis Dyno? Most of them have in there set up a calculated number for aero drag. Typically they come from a chart and are added to rear wheel HP. Most of the charts only go back 25/30 years. So if your car needs 50 HP to push it through the air at 50 mph, this value probably was not included in you run. I did my 56 Plymouth 230 with dual carbs, milled head, about 3500 miles after it was rebuilt. Chrysler rated the engine at 125 HP at 3600 rpm at the flywheel. When I did my stint I limited the rpm to 3300 which worked out to 62 mph over the road. We used the aero drag number from a late 80's Dodge Caravan. The resulting number was 127 HP at the wheels. So if typical drive train losses are 20%, my modifications gained that loss back, assuming the aero figure was close. A 20% gain over factory on a non turbo/blower motor is pretty damn good in most books. Torque gets you moving, HP keeps you moving. I have done a couple of unscientific 30 to 50 runs in top gear (1 to 1, with 4.11 rear) on level roads. My set up does that right around 7 seconds. Not record breaking, but good enough to keep up with traffic in most real circumstances. Be interesting to compare results by folks here to see what the real world comes up with.
The other thing to remember is horse power is a calculated number, we can measure torque (rotational force) horsepower is calculated from that. Sent from my iPhone using H.A.M.B.
Unfortunately the "Urban Myth" is wrong. Torque is how hard you lean against the wall [the higher up you lean, the more torque is applied to the foundations] Horsepower is how fast you push the wall over [horsepower requires movement ,or distance over time] Technically both are calculated AND both are also measured. The fixed factor is the leverage of the engine brake, and the variables [measured] are the force applied and the RPM's [Time] ------------------------------------------------------------------------------------------------------------------------ I've also had the discussion [dispute] over diesel horsepower vs gasoline horsepower A diesel getting 200hp @1500rpm is making 700 Ft/lbs A gasoline engine getting 200hp @ 7500rpm is making 140 Ft/lbs Now if you geared the gasoline engine down 5 x so the output shaft speed of both engines were the same, the Horsepower and Torque would equalize. The 200hp @ 7500rpm which is 140 Ft/lbs would multiply to 700 Ft/lbs but the output speed is lowered to 1500 RPM.
Lol,,,that is quite a dispute,,or discussion as you say. The Diesel engine has a stroke the length of the gas engines connecting rod. The gas engine has a stroke that would compare to the diesels rod journal diameter. The diesel has about 18 to 1 compression,,,or better. The gas would not be able to spin over at that compression. Diesel have some serious power stored inside its fuel. It just has to be brought out. It reacts in a somewhat similar fashion to nitromethane. Nitro loves a load,,,the harder you hit it,,the harder it reacts. Tommy
I was lined up next to you on saturday, we didnt make a run together. I liked your car. I got to make a run in my buddys channeled 32. My first time to trog. The whole event was amazing! We were taking off in 2nd, never shifted.
In my experience 75hp at the wheels equals 100hp at the flywheel (give or take one or two hp). "Your experience may vary"
Haha! The "expert" I was dealing with made the statement that "Diesel HP was different to Gasoline HP" If he said the behavior of a diesel engine was different to a gasoline engine ,it might have had some merit. Both forms of engines are an inefficient waste of BTU's I did a similar Math equation to basically prove output was output. And with the correct mechanical leverage ,both engines could do the same work. The holy grail of efficency is 100 ft/lbs per litre for naturally aspirated engines. Usually for 4 valves per cylinder A 3litre V10 Renault F1 [around 1995] would turn 14000RPM. 300 Ft/lbs @ 14000 = 799HP [Renaults were rated at 800HP] But Nascar 2 valve engines are up there at approx 85 Ft/lbs Litre [usually higher but volumetric efficiency drops off at higher RPM] 5.8 litre x 85 Ft/lbs =493 Ft/lbs x 9000RPM = 845HP
A stock flathead rates maximum horsepower at approx.. 3800 rpm. With the performance add-ons you have done the maximum horsepower should be achieved at more than 3800. I would guess around 4200 rpm. I have a similar setup in my pickup ( avatar picture). dual 94s, Isky cam, high compression heads, headers it pulls strong through 4000 rpm. If I was racing it, I would shift it somewhere between 4000 and 4500 rpm. If your curve ( horsepower or torque?) falls off after 3000, then I think something is not in sync.
That is what I was wondering about. Even with the inefficient flathead design, 3000 rpm for peak Hp seemed low. And yes, normally, I thought it was common practice to shift slightly higher than peak Hp rpm, to allow for rpm drop during time it took for shifting.
Well... You want to drive at a rpm where you have the most hp. You need to rev past max hp in one gear until hp has dropped so much so you have the same hp at the much lower rpm you get to on the next gear. Then you use the gear that keeps the rpm where you have the most available hp all the time - rev till the hp has dropped so far, so you end up on a so high rpm in the next gear so hp has increased to the same level. Sometimes not a good strategy with a motor that has a low red line rpm, a wide gear ratio gear box may very well force you to go far above the red line before you have reached the "optimal" gear change rpm. And even if you don't have that particular issue it quickly becomes obvious that changing gear ratios and number of gears can do more for performance than some fairly serious tuning - it doesn't matter how much peak power the engine produces, if you spend most of the time at other rpms where it has far less power.
What kind of fuel do those F1 guys run ? It has always amazed me about the high rpm that F1 has. However,,,short stroke,,small bore. Equals high rpm needed for power. They are very impressive,,and the drivers must have nerves of steel Just kidding about the fuel. I already know. Tommy
I think this is a digression from what the OP was looking for, but interesting discussion anyway, at least to me. This reminds me of a lot of talk regarding guitar amplifiers, with some folks saying Tube watts are louder than solid state watts, haha! Watts are watts, it doesn't matter the technology used to make them; and horsepower & torque are horsepower & torque, it doesn't matter the technology used to make them.... In reality, it's mostly about how the engines are designed to operate, the state of tune. Diesel engines tend to use an under-square design and gasoline engines tend to be over-square. These are not hard & fast rules, just generalities. Older gas engines also tended to be under-square with similar power & torque characteristics. And some modern diesel engines are over-square designs that have similar power & torque characteristics as gasoline engines. But most heavy duty diesel engines used in commercial trucking or earth moving equipment, or marine or power generation, etc tend to be under-square designs with long strokes, and as Desoto291Hemi put it far higher compression ratios. They operate at far lower engine speeds (lower RPM's), and have seriously high torque numbers and the curve has a very steep increase from just off idle to max torque at very low rpm's, and the curve remains flat until the engine runs out of breath and the torque drops off rapidly. I've heard people say that the combustion event in a diesel engine is much longer than in a gasoline engine, that the expansion of the combustion follows the piston farther down in the cylinder than in a gasoline engine. I'm not sure that is correct, but it is the common wisdom out there, and is repeated often. I'll go with it until I hear otherwise. But heavy duty diesel engines have what is know as "torque rise", that is as rpm's drop off under load, like when a truck it's a hill or a tractor that is plowing hits a tough spot of ground, the torque increases, it doesn't drop off with engine speed, so the engine settles in to a speed range where it works best under the conditions, and the truck maintains speed up the hill. Without that torque rise the truck would continue losing speed as it keeps downshifting trying to keep the rpm's up. You could put a big block gas engine that makes twice the horsepower as a diesel engine pulling the same load, but as the rpm's drop off, and so does the power & torque, the driver will have to keep grabbing gears until he finally find one the engine can pull the load with; meanwhile with the diesel engine, because of the torque rise, the driver may have to drop a couple of gear ranges, but he will maintain greater speed. Try getting a 1200 horsepower big block gas engine to pull an 80,000# load over a hill. Good luck with that. One more consideration is fuel economy. The biggest operating cost for a trucker is fuel costs. A high speed, high horsepower engine burns a lot of fuel to create those big HP numbers; a low speed high torque engine produces the same amount of work on far less fuel consumption.
Also consider that while the dyno info will show you where HP drops off and suggest where shift points should be, you shouldn't forget that the transmission ratio of 2nd gear vs 3rd gear effectively increases the available engine torque delivered to the rear wheels in 2nd gear. If you do the math, you will find that you may want to run a little further into that HP drop-off curve before shifting into 3rd.
We can theorize all we want, but a quick experiment (trying different shift points) will be how you figure out how to go faster.
If you are concerned that your engine should be making more power, consider spending some time dyno tuning it. If your air/fuel ratio is off and your timing curve is off, you could be losing 50% of your potential HP.
Maybe this should be a new thread but I'll ask here since a search didn't yield anything. Does anyone know of a dyno tuning garage with experience tuning flatheads in Pennsylvania or Maryland?
...........You might consider adding your general location to your profile page. There might even be someone nearby with the skills that you need and can help out.
As do all torque converters, unless they are badly designed. As indeed does any kind of gearing. That's the obvious rationale behind automatics generally having one gear fewer than equivalent manual gearboxes: the torque converter is an effective extra gear.
There are three major ways of measuring the power of an engine, in our arena. Dynometer, drag strip time slip and “ butt-o-meter”! Obviously the first two are more accurate. The Dyno is the most accurate, as it has less variables. Easier to tune, that is changing things to improve power, than at the strip. But the strip is were it’s at! But they’re a lot of variables at the strip that can cause misleading results.Such as, tire spin, shift rpm differential, temperatures of the transmission/ rear end and tires, etc.. These can lead to confusion of the changes made on the engine. Both ways have their merit and down falls. They are what they are! Now.... the “ butt-o-meter........well???lol Bones
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