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Now that's a horny bastard.
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Oct 23, 2017 14:20
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mekilljoydammit posted:Out of curiosity, where did that terminology come from? I understand fully the concept but I've never heard that part of the equation referred to as anything other than Brake Mean Effective Pressure. I blame going to a German University. Most of the terminology for individual parts we learn in English automatically, but the scientific stuff is very colored by language.
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Oct 23, 2017 15:54
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Combat Theory posted:I blame going to a German University. Most of the terminology for individual parts we learn in English automatically, but the scientific stuff is very colored by language. That makes sense - I haven't delved into German language technical papers so haven't come across that.
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Oct 23, 2017 16:17
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So how do you add horsepower without adding torque? Like whats the most effective way to make that trade when rebuilding an engine?
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Oct 23, 2017 19:57
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RPM
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Oct 23, 2017 19:58
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Increase engine speed. However this means you have to make sure the maximum torque (middle pressure) can be achieved at higher engine speeds. So you have to proof the engine for higher speeds, which usually means first of all increasing spring rate of the valve Springs, especially because you now have to use wider camshaft angles to supplement enough air load at higher rpm, which means steeper ramps on the cams, which means you need more force to have the valve follow the cam at the same rpm already. Then you have to look at the plumbing. Can your cylinder head deliver enough air and exhaust flow at increased rpm? Can your intake and exhaust system too? You very likely will adjust intake and exhaust length to match the new rpm goal as well. Then check if the cooling system can get rid of the increased heat generation both engine internal as well as through the radiator. Then when you are done with the engine you ideally would look at final drive ratio if not individual gear ratios even to optimise the pulling force over speed with the new engine power curve.
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Oct 23, 2017 20:23
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DogonCrook posted:So how do you add horsepower without adding torque? Like whats the most effective way to make that trade when rebuilding an engine? Stick a rotary in.
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Oct 23, 2017 20:33
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DogonCrook posted:So how do you add horsepower without adding torque? Like whats the most effective way to make that trade when rebuilding an engine? BlackMK4 posted:RPM Short answer, that. Longer answer, at higher RPM you have less and less time to get air into the engine - double the RPM and the valve is open for half the time (measured in seconds not degrees). So to have more air flow in at higher RPM you increase how long the valves are open (cam duration) and ideally make it easier to flow in (ported head ports). But having the intake valve open longer means that at lower RPM your effective compression ratio is lower, so you up that. And intake manifold and exhaust manifolds are tuned (think pipe organ) for various speeds so you increase the pitch by shortening them. Things like that - that's the basic, it gets to all sorts of follow-on effects. *edit* Well, Combat Theory beat me to the punch. There's actually all sorts of really interesting details with cam lobe design that mean you may or may not need stiffer valve springs! But I'm pretty sure nobody wants to hear the calculus there. mekilljoydammit fucked around with this message at 20:51 on Oct 23, 2017 |
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Oct 23, 2017 20:46
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By the way the best aproach to rebuilding an engine with power in mind is to make sure it runs up to its original power in first place. Getting the whole engine back into ideal spec geometrically is much preferable to sticking a new intake on it while a cylinder blows half of its charge into the crank case. Also think about quality of life stuff. Hardened valve seats (for engines designed for leaded fuel), new or improved valve stem seals (driving a BMW with an M50 makes you aware that some companies take the 0.5 L oil per tank quite serious) and such.
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Oct 23, 2017 20:52
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I know the next answer I think. It's Boost. So this really high rpm spinning engine that has now got half the airflow, cram back in that missing half, and bam more HP. It doesn't always double up HP unless you are that Freiberger guy from youtube
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Oct 23, 2017 20:52
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Cop Porn Popper posted:Stick a rotary in. They allegedly make torque at like 1/3 of their redline. As long as you don't do what rotaries are designed to do, you'll get impressive torque for a 1.3L mekilljoydammit posted:Short answer, that. Longer answer, at higher RPM you have less and less time to get air into the engine - double the RPM and the valve is open for half the time (measured in seconds not degrees). So to have more air flow in at higher RPM you increase how long the valves are open (cam duration) and ideally make it easier to flow in (ported head ports). But having the intake valve open longer means that at lower RPM your effective compression ratio is lower, so you up that. And intake manifold and exhaust manifolds are tuned (think pipe organ) for various speeds so you increase the pitch by shortening them. So that's why big, low revving engines produce hilarious amounts of torque, despite producing low HP relative to their displacement. It makes perfect sense, and I knew that HP was a function of torque and RPM, but it never clicked in my mind that that was why engines built for torque didn't like to rev
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Oct 23, 2017 21:03
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Now we have beautiful things like variable valve timing, variable valve lift, variable geometry intake manifolds, direct injection, and turbos that spool very early but are still able to flow large amounts of air.
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Oct 23, 2017 21:20
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Sometimes these design choices are artificial, too. For instance, the old British taxation system for cars was based on bore size. So everyone built really undersquare engines.
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Oct 23, 2017 21:44
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aaaaaand all of these hideously complicated things are why electric vehicles are the future more torque: more 'lectricity more power: more 'lectricity and better bearings
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Oct 23, 2017 21:45
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The Door Frame posted:it never clicked in my mind that that was why engines built for torque didn't like to rev It's more accurate to say that "engines not built to rev don't like to rev." You can have tremendous torque in a high-revving engine that produces a ludicrous amount of horsepower, it's just super expensive
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Oct 23, 2017 21:47
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The Door Frame posted:So that's why big, low revving engines produce hilarious amounts of torque, despite producing low HP relative to their displacement. It makes perfect sense, and I knew that HP was a function of torque and RPM, but it never clicked in my mind that that was why engines built for torque didn't like to rev Yeah. I mean if you think about the side-effect of having the valve open longer (cam duration) ... at high RPM, the air (ideally) has enough inertia to keep going in despite that the piston is moving upwards now. At low RPM though, it just means you're pumping air back out. In the end, everything is about getting air in the cylinder, keeping it there, burning it efficiently, and getting the exhaust out. All the optimizations get to about what RPM it does those things well. Also loving LOL at electric cars... electric cars are easy as long as you're willing to put up with lovely ones and ignore where the electricity comes from.
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Oct 23, 2017 21:55
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Horrible HR failures: "What do you do when the mechanic who is working on this BMW decides to quit his job?"
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Oct 23, 2017 22:02
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Cry?
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Oct 23, 2017 22:07
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Bill the customer double.
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Oct 23, 2017 22:09
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Sagebrush posted:aaaaaand all of these hideously complicated things are why electric vehicles are the future Hahahahahaha No but just to open that can from my personal 2 cents of engineering standpoint. Electric cars and IC cars will likely coexist for the rest of our lifetime. IC for urban environments will shrink to a degree which is good because air quality in urban centers is absolutely poo poo, but electric will not replace medium (petrol) or long range (diesel) internal combustion Historically spoken utilization for engineering aproaches formed around the strengths of a concept and that natural balance is shaken by the introduction of new designs that still need to find a balance with the market. The lithium ion powered battery electric vehicle is a new large scale production addition to the market and is subject to hype as well as a not yet established niche, which is why everyone tries to label it as "IC killer" which it is not. The green party wishes so and the electric vehicle only manufacturers wish so but when you see how the batteries in a "long" range tesla are arranged you don't have to be an engineer to realise why lithium ion EVs will never replace IC for range driving.
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Oct 23, 2017 22:15
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InitialDave posted:Sometimes these design choices are artificial, too. For instance, the old British taxation system for cars was based on bore size. So everyone built really undersquare engines. That said those displacement-based laws have given us some very nice applications of forced induction.
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Oct 23, 2017 22:20
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wolrah posted:Or every country that taxes based on displacement as a lazy approximation for efficiency. Put a 13B-REW next to a LS1 and then try to defend a system that treats the V8 as an inefficient polluting monster by comparison. To be fair both engines from that example are absolute shite when it comes to efficiency or emissions One of them makes a hell of a racing engine tho 
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Oct 23, 2017 22:27
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 Interesting apparatus by the way. This is a 4 column hydro pulser that lets you simulate vertical movement both by frequency/amplitude and by track profile. We use it for comfort measurements and to experiment with the resonance frequencies of organs and body parts. I had to write several pages about the correlation between female (and male) boob size to comfort issues at resonance frequencies.
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Oct 23, 2017 22:34
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You should get someone to laser scan Sage Creek Road north of Scenic, SD and put cars through that. Worst washboards I have ever experienced. I mean there's no making that comfortable for a human, but maybe you could test the car rattling itself to pieces.
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Oct 23, 2017 22:40
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wolrah posted:Or every country that taxes based on displacement as a lazy approximation for efficiency. Put a 13B-REW next to a LS1 and then try to defend a system that treats the V8 as an inefficient polluting monster by comparison.
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Oct 23, 2017 22:43
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Some more impressions of this weeks see-through-engine  
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Oct 23, 2017 22:54
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Combat Theory posted:We use it for comfort measurements and to experiment with the resonance frequencies of organs and body parts. Well...don't keep it to yourself. What kind of boobs are best?
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Oct 23, 2017 23:14
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Combat Theory posted:To be fair both engines from that example are absolute shite when it comes to efficiency or emissions Have you performed harmonic testing on the valve springs?
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Oct 23, 2017 23:15
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C-Bangin' it 
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Combat Theory posted:
Oooh, shaker rig! That's coooooooool. I'm in the engine development side - small engine maker but automotive stuff recreationally. InitialDave posted:Ahaha, no, not displacement. That would be potentially sensible. Bore. It was a theory for a while that piston speed was a hard limit, so it was considered that the only displacement variable that mattered for power was bore. Funny reprecussions like that.
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Oct 23, 2017 23:15
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So on the torque thing my problem is i have a 72 318 with real low compression. With new heads intake exhaust manifolds i could easily get 250 to 300hp but then id have like 500 to 600lbft of torque and im trying to stay mostly stock because its just a cruiser but anything i add to hp side is just gonna poo poo out gobs of torque. I know the real answer is a 340 or 360 swap but its a survivor car and i cant bring myself to do it. Im gonna see what can be done with a tuned exhaust and cam but i was wondering if there is anything i can do geometry wise to effect that ratio. Its very airflow restricted so adding better flow is a must but then all im doing is uncorking a shitload more torque. It hits at like 1,000 rpm too so its pretty drat hard to get a fast shot of fuel in there to handle it. If anything funky at all is going on in the carb or it isnt perfect itll starve for a sec, not enough to missfire but you can feel the hiccup if you stab the throttle.
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Oct 23, 2017 23:37
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spog posted:Well...don't keep it to yourself. Well since constant Frequencies are rare in actual Driving conditions, we mostly found out that you get rash nipples from the seatbelt when you dont wear a shirt... and yes i wish that was a joke but its not. Also mekilljoydammit posted:
I was in Engine/Powertrain Development too, the shaker and some other Lab Stuff was just because my Degree is in Automotive Powertrain- and Suspension Development Colostomy Bag posted:Have you performed harmonic testing on the valve springs? Nothing past holding a Strobe Light on an LS3 on a Flow Bench with the Valve Covers removed... which does look particulary interresting (looks like spring is made from cheese under Strobe) but nothing scientific i remember from that time Combat Theory fucked around with this message at 23:42 on Oct 23, 2017 |
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Oct 23, 2017 23:38
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DogonCrook posted:So on the torque thing my problem is i have a 72 318 with real low compression. With new heads intake exhaust manifolds i could easily get 250 to 300hp but then id have like 500 to 600lbft of torque and im trying to stay mostly stock because its just a cruiser but anything i add to hp side is just gonna poo poo out gobs of torque. I know the real answer is a 340 or 360 swap but its a survivor car and i cant bring myself to do it. Im gonna see what can be done with a tuned exhaust and cam but i was wondering if there is anything i can do geometry wise to effect that ratio. Its very airflow restricted so adding better flow is a must but then all im doing is uncorking a shitload more torque. It hits at like 1,000 rpm too so its pretty drat hard to get a fast shot of fuel in there to handle it. If anything funky at all is going on in the carb or it isnt perfect itll starve for a sec, not enough to missfire but you can feel the hiccup if you stab the throttle. You're probably not going to be literally at 500ft/lbs of torque on a 318 because that's tricky - a lot of compression and good efficiency. The more cam you throw in the more it's going to shift the powerband to high RPM in short but also the more lumpy the idle and the less anything operating on vacuum works.
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Oct 23, 2017 23:51
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Oh they are. Typical malaise era dart runs one gear for drag racing applications. Im gonna have a lot one way or the other but its 160hp 267 lbft stock.
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Oct 23, 2017 23:54
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Sure, but you're going to reach a limit to how much torque you can make at a given displacement. Put it this way, 500ft/lbs of torque is a higher BSFC (torque per displacement, a measure of combustion efficiency) than NASCAR Cup engines, which are some of the most highly developed naturally aspirated pushrod engines in the world - NHRA Pro Stock eclipses them but they only have to do so for a few seconds at a time. In stock form the 318 doesn't breathe well but has a small cam... so yeah it's running out of breath at high RPM but it's doing well at low RPM. More compression and everything else will pick the torque up some yes, but you're not going to double it, just make it at higher RPM.
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Oct 24, 2017 00:05
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Guys and gals, forget the arguments...let's burn some gasoline and make power together. Life is too short.
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Oct 24, 2017 00:50
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Yeah if compression pushes it up the rpm range then im good. My main worry was unrestricting the airflow was just gonna make my fuel starvation issue worse.
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Oct 24, 2017 01:04
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Colostomy Bag posted:Guys and gals, forget the arguments...let's burn some gasoline and make power together. Life is too short. This is Kerosene, but i find the video calming in a sense. Must be fun to work with these huge Powerplants https://www.youtube.com/watch?v=VOeXKWRxaMc
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Oct 24, 2017 01:49
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I don't claim to know my way around standard domestic 4-barrels so I won't take a guess about tuning the things. Maybe I've been playing Automation a lot lately but it's not unrealistic to think about most of the basic variables as kind of tradeoffs. More cam duration starts shifting the torque peak (RPM it hits) upwards in the powerband but sometimes costs you magnitude of what the peak torque you're getting - head ports can be the same way, ignoring stuff where it's just plain better design. Single plane manifolds end up having more plenum volume and shorter runners so (usually) lean towards shifting torque peak higher than dual plane manifolds. Compression affects BMEP - all else being equal increasing compression will increase torque per displacement, up to the point where the engine is detonating.
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Oct 24, 2017 01:51
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Ok yeah a lot of people recommend the single plane and i wasnt really sure why since its street but i guess that makes sense in this case.
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Oct 24, 2017 02:45
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mekilljoydammit posted:BSFC (torque per displacement, a measure of combustion efficiency) Can you explain this? Because I've always heard of BMEP being torque per displacement, and BSFC being completely independent of displacement.
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Oct 24, 2017 03:52
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