Comments by "Thump Er the Sweaty Fat Guy" (@SweatyFatGuy) on "driving 4 answers"
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Thank you for making this video, I have been trying to avoid making it myself because its a lot of work at a desk rather than in the shop. Now I can simply share your video so people can grasp the concept and understand what is going on. Its very informative, even its geared more towards the tiny Euro/Asian engines and pump gas, and in that area its spot on. Well done video.
My thing is ethanol, which is quite different from gasoline, and different though more similar to methanol. When you go with ethanol you can increase the static compression ratio dramatically, 13:1 and 20psi with iron heads is very easily achieved and does not hurt parts. Ethanol also provides more exhaust volume, cools the intake charge, and resists detonation/ping/knock as it only likes to light with a spark rather than heat and pressure.
I have found that by increasing the SCR from pump gas friendly 8:1 to a race gas only 13:1 but running ethanol (E85 to E100) you pick up mileage, and above 12:1 to 13:1 in some engines, you get better mileage on ethanol than on gasoline. Heating the fuel and the incoming air to ensure instant vaporization of ethanol increases efficiency as well, without much loss in power if any. It does preclude using pump gasoline in that engine. With boost you will need to add even more ethanol, because you are adding O2 along with the fuel as ethanol has O2 in it already, which is the real reason it needs to run richer than gasoline, not so much BTU content. BTU is a measurement of heating value, how long it takes a given fuel to heat one pound of water on degree. It says nothing about how much power, knock resistance, intake air cooling, latent heat of vaporization, or anything else a fuel has. Besides, gasoline engines are lucky to reach 20% efficiency, wasting more than 80% of the energy in gasoline as heat. Ethanol easily hits 40% efficiency, only creating 60% waste heat, and you can utilize that heat to make it run better rather than having to shed it so the engine doesn't rattle itself to death or destroy bearing surfaces.
Of course, if you run low compression engines on ethanol you will end up using a lot more fuel to make the same power, because you are not working the fuel hard enough so to speak. Handicapping an engine to run gasoline means it will not do nearly as well on ethanol.
Then you get into methanol and everything changes again. You can run a lot more compression with boost than you can on ethanol, and vastly more than on gasoline. Methanol is also the highly corrosive fuel, ethanol is not anywhere near as bad, and most vehicles will have zero problems on ethanol provided you get the engine warm enough to boil condensation out of the crankcase. Water condenses inside every engine during the heat cycle, and gasoline wastes so much energy as heat that its not a problem boiling that water out. Ethanol and especially methanol, run much cooler so getting the oil hot enough can be a problem, which is why those fuels tend to milk the oil.
With gasoline you have to run low compression, retard the timing, and run it as cool as possible or it will rattle itself to death, particularly on boost. With alcohol fuels you want the heat in the engine, running it cold hurts both performance and mileage, and yes you want mileage in a race engine because efficiency is power. The more efficient your engine is at making torque, the faster your vehicle will be.
Ethanol takes a different sort of thought process to tune it well, methanol is different yet again from ethanol. What works on gasoline will work with alcohol fuels, but you will not get the power out of it you could be getting. Tuning gasoline the way you tune ethanol will also cost power. Gasoline you lean it out to make more power, with ethanol you add fuel and go richer to make more power. If you pull fuel from it, you are leaving power untapped. Alcohol fuels make more power because they do two things, they have their own O2 in them, and they cool the intake charge making it more dense. It also vaporizes very easily compared to gasoline, and a vapor has vastly more surface area for combustion than atomization does, you pick up power and efficiency by getting the fuel to vaporize before it is ignited in the cylinder.
Rather than going with what most people claim about ethanol, I suggest you try it out, throw fuel at it while running it over 200F for coolant temp, and see how it responds, particularly with high compression and boost.
If you can't run ethanol in your high performance vehicle due to your government regulations or something, I feel sorry for you. It is the way to power and drivability. The best part is you can make ethanol yourself and run your vehicles on it like I do rather than buy it from someone. Ya know, like if for some reason we no longer have gasoline being brought to the gas stations, or you want to drive for a lot less cash... Some governments will get very unhappy if you produce your own vodka fuel so you have to watch out for that.
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Not all muscle car engines are big bore short stroke. I give you Pontiac as an example. People often assume Pontiac engines are low power, in reality they are low RPM. They make their power in a different RPM range than other V8s of similar displacement. Its that whole tq vs hp thing, and to me hp is simply tq over time.
For something not related to bore/stroke... The 400 Pontiac and sbc 400 share bore and stroke, 4.12" bore, 3.75" stroke, but they make very different power, because of something you alluded to, port length and diameter. the Pontiac 400 will make more torque everywhere in the RPM range that the chevy, under 6500rpm. Over 6500 the larger and shorter runners make the sbc an RPM engine.
The Pontiac has a 2.11" intake, and 1.77" or after 1972 1.66" exhaust valve. The sbc in stock form had 1.96" intakes and even smaller exhaust (with the largest intake valves being 2.02"), which is due in part to the 23 degree valve angle, while the Pontiac has a 14 degree angle (much like the 12 degree LS engines). The difference in runner length, and the valve angles that allow different sized valves make the two same size engines behave very differently. While you are lucky to get 450ftlbs anywhere in the rpm range from a small chevy, the Pontiac does it easily and a 400 with slightly more airflow can make 500ftlbs around/between 3500-5000rpm.
Sure the sbc can make more peak hp, but its sucking wind until it gets over 6000rpm and never achieves the torque of the Pontiac in its entire rev range.
So lets got big bore/short stroke vs long stroke/small bore with similar displacement engines. The 455 Pontiac with 4.15" bore 4.21" stroke and the 454 chevy with 4.25" bore and 4" stroke. The chevy has larger runners and canted valves which makes for low velocity at low RPM. To match a 455 the chevy needs its displacement increased to 572ci and then its still kinda lacking to a regular D port 455, not even a round port like the HO/SD/RA II/RA IV engines. It is incredibly easy to produce 500ftlbs with factory iron heads, intake, and a factory cam from 1967-1972 with a 455. Yes the 454 is capable of more hp, that just means it is making more torque above 5252 rpm, which means they need more gear and stall to run well.
Every Pontiac from the 287 way back in the 1950s to the 455 that ended production in 1976, and the 400 that went until 1978, had the same runner length. In 1967 the change from 24 degree valve inclination was made to 14 degrees, and along with that came the 2.11" intake valves that even fit in the 350's 3.875" bore which shares the 3.75" crank of the 400. They all have 6.625" connecting rods as well as all the heads being the same bore space and bolt layout, so you can bolt any head to any block, though valve sizes and reliefs can cause problems with early engines.
That makes Pontiacs unique in that they can show the differences in stroke while using the exact same heads, intake, and camshafts. Have to also realize something else, Pontiac tended to under rate their engines, they usually made a lot more torque than they are said to make in stock form. The factory claimed numbers are misleading, its best to look at the dyno graphs to see the curves.
The intake ports are actually 'too small' for Pontiac 400s and 455s, but they were designed to produce prodigious grunt, and they do that VERY well. What happens when you increase the port size with a Pontiac engine? It simply makes more torque everywhere in the RPM range. Factory cfm in D port heads is around 195 to 210cfm around .500" lift. That limits RPM greatly on a 400, 428, or 455. The 428 shares the 4.12" bore of the 400 with a 4" stroke, since I did not mention it earlier.
For instance, I have a set of ported aluminum heads for my Pontiacs that flow 330cfm at .550 lift. While running a 272/278 at .050" lift duration solid roller with a 110 degree LSA, with right at 10:1 compression on a 4.18" bore, 4.25" stroke in a 400 block (you can go to 4.5" cranks easily with Pontiac) and a Victor single plane intake, the resulting 467ci engine produced 522ftlbs at the rear tires, way down at 3000rpm... while being down a cylinder and having four other bent valves. It was still making 500rwtq at 5000rpm while 'hurt.' (someone decided to dump gravel down the carb).
With the increase from 200cfm to 330 the torque and HP it made went up substantially. Peak hp once it was repaired was a bit over 700hp at 6200rpm and the torque was over 650ftlbs from 2800rpm to 4500. That much torque will move heavy stuff real easy, or light stuff VERY fast.
Where most people go wrong with a Pontiac is putting deep gears, like 4.10-5.13 behind them, and 4500 stall converters. They are wasting all that torque the engine is making between idle and 4500rpm when they do that. You have to increase the airflow over 330cfm to get more than 7000rpm out of it. I run 3.08 to 3.50 gears with 2400 or so stall converters behind my 400 and larger engines. I want to keep it in the 2500 to 5500rpm range as long as possible, because that is where its making its power.
The engine I just built is 4.35" bore and 4.25" stroke which comes out to 505ci, and currently it has those 330cfm heads on it with a slightly larger solid roller cam than my 467. The 505 has a 3.50 gear behind it right now, but I might go 3.00 when I put the roots supercharger (6-71) on it in the spring. That combination should be good for around 1000ftlbs around 4500rpm with 7psi.
Compare dyno sheets from 455s and 454s with similar sized cams and compression with garden variety heads like D port Pontiac and oval port chevy, then you will see how much difference there is in the two because of runner length, valve angle, and chamber shape. If you like peak hp the chevy will win. If you realize torque is what moves things, the Pontiac will stomp on the chevy and have its way with its significant other after defiling the chevy corpse... all while pushing highway gears.
Yeah my idea of 'big torque' is somewhat different than someone who lives in Europe where a 4.0L is considered a big engine. Anything under 6.6L is what I consider small. Which 400hp engine is going to be faster? The that makes 400hp@7500rpm or the 400hp@4500rpm?
I'll take my under square Pontiacs with long runners and big valves for my daily drivers.. like the 65 GTO that runs mid to low 11s in the quarter mile and gets 17mpg because it has 3.08 gears, no overdrive and runs on E85 or E100.
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Finally someone else realized that HP is TQ over time. RPM is revolutions per minute, that is a measurement in time.
This video is very simplistic and blunt, which is ok for a YT video as its real easy to get off in the weeds with this sort of subject. Make traction a non issue and TQ wins. I have to admit getting my engines to hook is the challenge, and then getting them to not lift the nose off the ground is the next challenge once the tires hook.
Gear ratio is VERY important as is the torque curve of an engine when it comes to acceleration. Other large factors include mass, drag, etc. The engine design matters a great deal as well, because good luck getting a Honda 4 to make 1000ftlbs at 2000rpm. Can they handle over 70psi?
Lets make it easier to understand and make them both 500hp engines, but one makes that power at 5252 and the other at 10,000rpm. The 5252rpm engine is making 500ftlbs, and its going to be making 500ftlbs below that point as well due tot he nature of how torque is produced. The 10,000rpm engine is only making 265ftlbs, so it will need lots of gear to get anywhere.
I tend to build large engines, 455+ cube Pontiacs, which due to their long runner high velocity port design create copious torque between idle and 6000rpm. 500ftlbs is about where they start out with iron heads, and that is 500ftlbs from 2000 to 4000rpm. Some heads carry it a bit farther, enlarging the ports on a Pontiac simply nets you more torque everywhere, there is no hole in power created by the port being too big. The velocity of the port from venturi to the piston at BDC is high because of the length, shape, and size, so these engines fill the cylinders VERY well under 6500rpm. Yes, its apples to walnuts to compare it to a smaller engine, but bear with me.
A smaller engine, like a short runner length 1.8L Honda, making 500hp at 10krpm is going to have very meager torque through its entire RPM range and never come close to the torque produced by the Pontiac, even with the V8 at idle its making more torque than the Honda ever does. However, using gear ratios, and we are talking DEEP gears in the 5:1 range, can get the tiny engine through the RPM range much quicker thus mostly ignoring the lackluster torque production under 7500rpm. It lives at high RPM, and waddles around down low like a drunken water buffalo.
If the vehicles weigh the same, the torque engine is going to stomp the RPM engine because it doesn't need as much gear ratio, and the longer it stays in each gear the more time the engine has to accelerate the mass in that gear. After 60 feet or so, the deep gear isn't helping you much. If you ride in one of my 3.08 geared vehicles you will see the difference in acceleration with something that has 4.10. Its a big difference. The 3.08 with 500ftlbs pushing it for longer will put bus lengths on the 4.10 geared engine, not because it doesn't shift, but because the longer lever (after the fulcrum) lets you do more work and move it farther when you have the power to lift it. A 3:1 ratio requires more force to move the same mass than a 4:1 ratio does, as the shorter lever allows less force to move the same mass, but not as far.
Tiny high RPM engines require very light vehicles, but if you match the weights and maximize the gear ratios for the torque curve, the engine with more torque is going to accelerate faster.
My Pontiacs with iron heads are RPM limited, they simply do not want to pull after 6000rpm. I shift them at 5800 so the transmission makes the gear change right at 6000. Thats the trade off with long high velocity runners, you limit RPM, but maximize torque. If I run a 4.10 behind my 455 it slows down and is no longer accelerating past 800ft or so. The 1/8, 330, and even the 60ft will be slower with a 4.10 gear than a 2.73 to 3.55 gear behind my engines. More gear is not better in this instance, and a 4.88 will make it even slower, its moving the engine through the RPM range too fast and isn't using the force available for as long as it could be.
Its similar to supercharging a smaller engine, you don't need much gear with a roots blower, because it will be making high torque right off idle. Thats why TF dragsters and Funny cars are limited to a 3.2 gear, its an attempt to limit the top speed so its survivable in a wreck. Those engines are a wonderful example of how both torque and horsepower interact, but are far removed from normal vehicles because of the immense power they crate on nitromethane. Spooling a turbo at the line does the same thing, it increases torque at the launch RPM and all through the run, so they need less gear.
If you are trying to move a heavy vehicle, like a 4000lb muscle car, you want thick torque everywhere in the RPM range of the engine. If you have a 1500lb car you can match the performance of that 4k vehicle with a fraction of the power. Thats like freakin duh, right? Thats why the tiny engine cars can weigh a lot less than large cube vehicles in events like domestic vs import. you have to handicap the bigger engines because they have so much more potential and can make vastly more torque.
What are the drawbacks to high RPM? Wear on the engine, dropped valves, broken valve springs, rods deciding they want to be lawn ornaments freed from the confines of the block and their connection to crankshafts and pistons... things go boom with more RPM because of the forces involved. Piston speed, centrifugal force, the pistons changing directions at TDC and BDC, all are trying to rip the engine apart. Thats why I kinda like the big engine that makes tons of power under 6000rpm, because it will last longer since its not flinging pistons and rods around at astronomical speeds. My engines last decades of racing with minimal maintenance, how often does a 1.8L Honda need rebuilt if its making 700hp at the crank?
Racing is racing, going fast is cool no matter how you do it. I have my preference, you have yours. Who is faster depends on lots of variables, same as who spends more to go that fast. We put limits on vehicles so your 13 second Civic doesn't have to go heads up against my 11 second GTO (or the 8 second LeMans), except in brackets where you get a head start. Who can make more power and get it to the ground within a certain displacement range is the question they use in land speed racing. Its super easy to go fast with big cubes, its more difficult and thus more expensive to do it with fewer cubes, and you need a lot more RPM to do it.
Its fun to think about the 500 or 1000hp low vs high rpm engine, but in drag racing more torque is going to make you faster, because you are accelerating a mass from a dead stop. So I would advise you to build as much torque as you possibly can at the RPM your engine is capable of producing it, and let HP do its own thing.
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