Dyno runs old and new

On the topic of redlines. I've always noticed a tendency for many owners of certain vehicles (e.g. Italian sports cars or Japanese 'hot sedans') to run around at extremely high RPM's - constantly "wringing the neck out of it", pushing redline all the time. Please note this is not directed at anyone and no intention to offend at all. While some engine setups may be focused toward top power at only the upper most range, I'm of the opinion (and that's all it is) that the reduced longevity of an engine brought on by that isn't worth the little bit of performance it offers. I currently have three X1/9 engines torn down that were the victims of such driving styles and the internal damage is horrendous. If the low power levels of certain engines just doesn't cut it, then I believe a powertrain swap may be a better answer than pushing the original one too far (referring only to street vehicles; track cars have rules and regulations and fall under a completely different situation). To be honest I didn't always think this way; when I was young things were a little different, but with experience I've learned better. So please realize this is nothing more than my personal view at this stage of life.
 
Dr.Jeff said:
I might have misread the data, but I believe his power band drops off above 6500 rpm, which could be a function of many design factors. So there's no need to shorten the engine's life by revving higher than that...especially with a boosted application where internal thermal loads skyrocket under those conditions. But that's only my assumption.
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Yes, the power drops off rapidly over 7500rpm. I haven't looked into what you'd need to do to prevent that, but I would imagine its to do with restrictions on breathing when you get up to those rpm. Apart from a bit of head work, the valves and inlet & exhaust manifold are standard. The extra expense of addressing that, as well as the associated turbo and fuelling modifications wouldn't be worth it for me.
Mike's correct that the forged internals give a potentially higher rpm than 7500, but if the engine can't efficiently make use of that then best be kinder to the engine keep the revs down
 
speedy fiat said:
I would imagine its to do with restrictions on breathing when you get up to those rpm
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That would be my guess, particularly with a boosted application. The higher the RPM the greater the charge pressure. Higher pressures create a lot of resistance and heat as a result. Therefore trying to run higher RPM's will only result in detonation and destruction. If your ECU has knock detection and protection built in then that might even be a further reason why the power reduces (as the ECU cuts back to stop the detonation). "More" isn't always better.
 
speedy fiat said:
Finally got a round to getting this info. I've three levels of boost, with the lowest one producing 166hp for 0.75 bar boost.
I dug out some old records of when I started this exercise six years ago to compare with the latest efforts. I fully admit that at the start there the enthusiasm was far higher that the knowledge and budget, hopefully I have these in balance now. People have sometimes said its a shame that Fiat didn't get more power as standard, but given the time and money this has taken I can fully appreciate why manufacturers keep things simple! Having said that its still cheap for the performance I've got
The standard is 115hp. In 2013 I wrung 147hp out of the engine in a very unsustainable way and today we are getting 207hp in a way that is, by general consent by knowledgeable people, sustainable within the caveats of serious engine tuning.

2013 - red line 6500rpm
3500rpm HP=100 Torque=150
5000rpm HP=140 Torque=145
6000rpm HP=147 Torque=120

2020 - red line 7500rpm
3500rpm HP=140 Torque=140
5000rpm HP=205 Torque=190
6000rpm HP=207 Torque=180
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Wow Speedy Fiat you sure have put a lot of work into the X. Wish I had your drive. Turbos do make things go and I commend you on the job you've done. I do have one question. The HP and Torque figures for the 2020 version seem to have a problem. As I'm sure you know that the HP and torque are always equal at 5250 RPM and below that RPM torque is always higher than the HP and above that RPM the HP is always higher than the torque. It's simply the math HP= torque x RPM/ 5250. The 3500 RPM and the 5000 RPM entries seem to be a bit off. At any rate it's got to be a goer, I'm jealous.
Charlie
 
I didn't know that about the 5250rpm figures. I went straight off and checked and they are just as you say! The torque and hp lines are near identical up to 3500rpm and then start to separate, very rapidly above 4000rpm (I'd post the read outs but the quality of the copy I have is poor). Well spotted regarding the 5000rpm figures, I have them the wrong way round
 
speedy fiat said:
The torque and hp lines are near identical up to 3500rpm and then start to separate, very rapidly above 4000rpm
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In my opinion that is nearly perfect, particularly for a street car (I realize yours is a track car, I'm only making a point). That low/mid range torque would offer excellent acceleration off the line, where more "grunt" is in demand. Then the HP will take over as the RPM's rise, where more "speed" is demanded. Shift gears and start that same cycle over again. Repeat the process until you reach your cruising velocity. Want to suddenly accelerate? Drop down a gear and do it over again. A well balanced power band of both torque and HP. That's one main advantage to building a turbo engine vs a high performance naturally aspirated engine; turbos provide more torque vs NA having less torque, yet both have relatively the same top end....a "best of both worlds" in my opinion.
 
NEG said:
Not bad an explanation

www.caranddriver.com

Horsepower vs. Torque: What's the Difference?

Torque and power are what engines produce when you turn the key and press the accelerator. But it's a lot more complicated than that. And which is better?
www.caranddriver.com www.caranddriver.com
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Well here it goes guys. Don't get mad at me, just trying to clarify. HP does nothing for acceleration, it's for selling cars and bragging rights, I use it myself. ALL the acceleration is determined by the torque. Torque is the ONLY thing that accelerates a body, in this case a car. This was determined in 1687 by Newton in the Principia and in 1688 the Royal Academy agreed with him and it's been that way ever since. Acceleration=Force/Mass. Torque is a force. HP is not a force it's a measure of work done by the force, it adds time and distance. The reason the engine keeps reving above the peak torque is because there is still torque above that point although less. The car will accelerate at the fastest rate at peak torque not peak HP. Just look at a dyno run and you will see the peak HP and the peak Torque usually at different RPM's. So will the car accelerate faster at peak HP or peak torque. Well it's the torque. One other thing for you guys that adjust your own Fuel injection systems you may notice that the highest fuel numbers for the injectors are at the maximum torque RPM, because that's where the engine in making the most energy. The fuel numbers actually reduce above that RPM but the engine is turning faster, more FI pulses, so it does get more fuel, add the time factor. I made a spread sheet for shift points at one time, maybe I can find it and attach the file, it is interesting how much torque there is in the lower gears especially with tires with a 24 inch or less diameter tire, tires taller than 24 inches reduce road torque and tires shorter than 24 inches increase road torque. And lastly and engine can never make as much HP as torque below 5250 RPM. In fact the HP will be considerably less than the torque the farther you go down from 5250 RPM, just use the formula HP= torque x RPM/5250. So is there any use for HP at all, well yes. If you know the torque and HP it can give you some idea of the RPM range of the engine. A motorcycle will have low torque numbers and high HP numbers and be a high rever and of coarse the opposite, high torque with low HP is a low RPM motor think Diesel. This is why turbos work so well, it actually acts like a displacement increasing device, and that's torque. Also the higher RPM for the torque, the lower gears you can use which even further multiplies the torque. HP is not multiplied by gears, torque is which explains why a car accelerates faster in first that fourth gear. So modifying the engine for more HP is actually modifying the engine to create more torque at a higher RPM. So it turns out HP is just a made up number, the designers of it could have used a different RPM for the math and the HP would be different IMO. Jees I hope you guys still love me LOL.

Charlie
 
All this torque vs power talk is doing my head in.
I thought power equates to top speed, since the engine can do more work at a faster rate, it brings the time factor into it. I can see why you say modifying an engine for more hp is actually modifying for more torque at higher revs, but it can also be for the same or even slightly less torque at higher revs, that will produce more power. It all depends on where the max power and/or torque is required. Like road racing v rallying v street driving. Racing generally requires power/torque at higher revs. The old 2.4 litre F1 engines only produced about 215 lbft of torque, but as they revved to 18,000rpm they produced over 700 hp, they didn't need high torque to go fast.
It is interesting to compare the Abarth 124 with the MX5 it is based on, essentially the same car except for the engine. The mx5 has more power at 181hp to the Abarths 170hp, the Abarth has much more torque at 184 lbft to the mx5 at only 151 lbft, yet it's the mx5 that has the faster acceleration times, eg. 0-100kph in 6.5s vs Abarth at 6.9s. Power beats torque in this case.
In the post above, what is so special about 24 inch diameter tyres?
 
GregS said:
All this torque vs power talk is doing my head in.
I thought power equates to top speed, since the engine can do more work at a faster rate, it brings the time factor into it. I can see why you say modifying an engine for more hp is actually modifying for more torque at higher revs, but it can also be for the same or even slightly less torque at higher revs, that will produce more power. It all depends on where the max power and/or torque is required. Like road racing v rallying v street driving. Racing generally requires power/torque at higher revs. The old 2.4 litre F1 engines only produced about 215 lbft of torque, but as they revved to 18,000rpm they produced over 700 hp, they didn't need high torque to go fast.
It is interesting to compare the Abarth 124 with the MX5 it is based on, essentially the same car except for the engine. The mx5 has more power at 181hp to the Abarths 170hp, the Abarth has much more torque at 184 lbft to the mx5 at only 151 lbft, yet it's the mx5 that has the faster acceleration times, eg. 0-100kph in 6.5s vs Abarth at 6.9s. Power beats torque in this case.
In the post above, what is so special about 24 inch diameter tyres?
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Some disjointed thoughts:
A 24"OD tire has a 12" radius from the axle to the pavement (technically). It relates directly to more or less Foot/Pounds at the wheel.
Overheard at the Bristol SCCA National Tour Autocross in part of a discussion about the 124 and the MX-5------"Looks like the Fiat is the way to go". Sorry, I didn't catch the rest of the conversation.
Last, I have 2 trucks; one is a '97 Suburban with a 7.4L engine, 290hp, 450 torque, 4 spd auto, 4.10 gears. The other is a 16 Yukon XL Denali, 6.2L, 420hp, 460 torque, 8 speed trans, 3.42 gears. 10ft/lbs difference but the '97 could never come close the '16s 6 second 0-60 time. (reported time, I wouldn't actually know how fast it is......)
 
Perhaps a bit of terminology/semantics confusion? Sort of the classical use of the terms in the scientific world of physics vs the automotive performance world? But as stated there is a difference between torque and horsepower, and they are often misunderstood by many car enthusiasts. Plus many other factors like gearing (including tire circumference), drivetrain losses, vehicle weight, aerodynamics, traction, etc, also come into play. So it is difficult to accurately compare 'apples to oranges'. However the automotive world often seems fixated solely on HP numbers unfortunately.
 
Guess I started it. The formula is simple Force and Mass are the things that create acceleration. The force for a car is the wheel force which is created by the engine torque, gearing, wheel diameter which is really gearing, Gene Cooley got it right with the 12 inch radius of the 24 inch tire as it relates to Foot pounds. There are also frictional drag losses but we don't know what they really are so forgive me the omission. Of course a more exact point is this is what would happen in a vacuum. No matter Dr. Jeff your right, the performance world does like the HP figures maybe because it's a carryover from the horse and buggy days, who knows. Ya GregS your right you can modify an engine to give more lower RPM torque or any RPM you like, my Motorhome is a good example of that, but that's not the normal direction but certainly true. I understand your point about the difference in acceleration of the two cars. I am not familiar with these cars but I suspect there are other differences such as tranny gearing diffy gearing tire size weight. That 18000 RPM motor has low torque and high HP, just think about the gearing for that thing. Gears multiply the torque and that's a big number with low gears, HP is not multiplied by gears. I'm not sure if when you say power you mean HP, if so only the available toque at any speed or RPM accelerates the car. The formula has no room for HP only torque and mass and yes in a vacuum but it's hard to breath there so I don't count that. One other thing GeneS Cooley, you can see that the 97 is a lower RPM motor and produces it's torque at a much lower RPM than the Denali which means there will be a gearing advantage, probably in the tranny, don't know about the tires or the weight, for the Denali which multiplies torque. It's all about the torque where the tire touches the road. Have some fun, take an X19 with say 90 FT LBS of engine torque max. Multiply that by the the first gear ratio in the tranny then multiply that by the ring and pinion gear ratio and lets assume you have a 24 inch tire. WHAT IS THE TORQUE TO THE GROUND, forget frictional loss.

Have a great days guys
Charlie
 
I think we may have high jacked the original post, but it is interesting.
I get the relationship between hp and torque and rpm, but I still believe that quoting hp is useful for comparing performance. For instance as a power to weight ratio such as hp/ton, because using hp it brings both torque and rpm into the equation, and power to weight ratio is a good indicator of acceleration capability. If you used torque to weight ratio it could give you a wrong indication of a cars acceleration capabilities, for instance with the F1 engine mentioned previously as an extreme example.
This discussion has caused me to rethink about driving on a race track for fastest times. If I change up so that the next higher gear is right at max torque rpm, that should give the maximum acceleration, rather than holding each gear to max power rpm, or redline. Something to think about.
 
GregS I made a spread sheet that gives you all that information as to when to shift gears and tried to attach it here but It's an XLS format and I can't attach it here. If you PM me with your e-mail I should be able to send it to you. You just fill in the blue colored cells and it figures everything out for you. It's really good and you'll like it.

Charlie
 
Thanks Charlie, that's great, I will send my email.
I have been researching it and have found a few differing views, even on technical sites. One promising method is with a graph plotting torque at the wheels to road speed, and to shift gear where the torque lines cross, trouble is with my engine the lines don't cross. I will be interested to see yours.
 
Dr.Jeff said:
I'm curious, does that have to do with the particular build of your engine (i.e. power band) and your specific gearing ratios?
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No Dr. Jeff. It relates to all engines. If you want a copy PM me with your e-mail address and I'll send you a copy and you can check it out. GregS it will work just fine for you engine. I sent you a copy.

Charlie
 
I always heard that hp is a measure of how fast you can produce torque. (No I can't explain that)

Another useless "fact"?--------- You can have all of the torque in the world, but unless you are actually moving something you are not doing any "work".

Now I have to head out and mow/move some grass with my 27hp mower, oops, sorry, 26hp mower after the government lawsuit.
 
Too funny Gene. Right HP is a measure of work done, torque is just the force that makes it happen . I don't have a lawn mower, fake grass these days, no work, LOL.

Charlie
 
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