12valve vs. common rail power questions

[Forrest Nearing]

HP is a function of quite a bit more than RPM.

not really... the only measurement of "work" we really use is torque... horsepower is simply an equation of torque at speed...



there's a reason indy cars get 1000hp out of a 1. 5 liter engine... RPM!

 

[Tomeygun]

What can I say, I wish I had 12v in my truck... (Love that sound)



I equate this comparison to the Hemi engine - All these years of HP technology advancements, and what does the Top-Fuel dragsters use?

Old-school HEMIs - It has NEVER been topped

 

[bmoeller]

but still like to know why pump went down with a fass system on the truck from day 1 of upgrading performance?

Just a guess here, high rail pressure? CP3 Pump was working too hard.

 

[BigGunZ]

horsepower is a function of rpm... the p7100 trucks can turn 5000-6000rpm and put out more fuel...
the p7100 at this time is capable of more power than the HPCR...
it also is capable of more torque

Actually, according to physics, Power, defined as a time rate of doing work, is quite simply a function of Torque and RPM. The dyno measures the torque or twist of the output shaft and the RPM and from that it calculates the power. The equation is HP = (Torque in ft-lbs * RPM) / 5250

So you guys believe that the phenomenon we now know as horsepower, would not exist if James Watt hadn't assigned a math formula to it? Interesting.

I'm not arguing or disputing the math used to compute HP, but to imply that an engines ability to produce it is solely RPM dependent is flat wrong. We're not talking about math here. We're talking about engines, which reminds me... I need to finish transplanting that S2000 engine into my Ram. After all... it spins to 8k rpms... get ready to be owned:-laf

 

[BigGunZ]

My guess as to why the CP3 won't make RPM is that the frequency demanded of the injectors (up to three events for one 'fire') is probably a factor. You only have so many milliseconds to get the various jobs done, and given response-time capability of the injectors (open, close, and fuel-flow) there ceases to be sufficient time to get it all done above a certain RPM...

Unless, of course, you reduce the number of events to ONE.

Sounds like we need to apply some talent to this job. :-laf

Mark

This makes more sense than anything I've heard. All things being equal, a 24 valve engine should be physically able to spin faster than a 12 valve engine. This is one area where I have to hand it to Chevy... . I can plug a laptop into the OBDII port on my Vette, and change anything in the PCM that I want. Hopefully someone will develope a similar program for the CTD one day.

 

[CJEliassen]

Horsepower is a combination or Torque and RPM. If you increase torque at a given RPM, you increase HP. If you increase RPM and maintain torque, you increase HP. The problem is that as you increase RPM, torque will start to decrease, and it will decrease rapidly at a point. That is why you see best HP numbers often below redline. The engine may produce 300HP at 4500RPM, but the redline is 5000RPM. After 4500RPM, the engine isn't getting enough air to continue the same amount of torque output and HP drops.



So, why do they allow an engine to rev past peak torque? Well, even though your acceleration starts to decrease after peak HP, taking the RPM right up to redline will mean that when you shift to a higher gear, you will have a higher RPM and be producing more HP than if you shift at peak HP.

 

[AMassaro]

Old timers always told me "torque is what moves you, but they advertise horsepower. " I think most people misunderstand that horsepower is a derivitive of torque. It has to do with timing and rpm's. Look at "typical" gasser hp/trq curves plotted on a graph. Almost always, torque starts off higher, gets flat then drops off. Horsepower starts low, rises and peaks at or around redline. And they always cross at 5250rpm's.

So I can't see how anyone can claim this one can make more horsepower but less torque. If you're dealing with similar engines, timing and rpms being similar, torque and horsepower would have to follow. I know different cams change timing events. And I'm sure that 24valves should, in theory, flow much better than 12.

So what I can gather, in the future, 24valve common rail CTD's are gonna be making big time power. Instead of doing it with a plate or a shim, we're gonna have to do it with a keyboard. It's all good. I love this stuff Oo.

Tony

CJ - we must've been typing on the same wavelength at the same time...

 

[CJEliassen]

Tony,



Two engines that produce exactly the same amount of torque can produce vastly different amounts of horsepower. If peak torque of an engine is at say 1500RPM, and another engine has peak torque at 3500RPM, the engine that has peak torque at 3500RPM is going to have significantly higher horsepower even though the same peak torque is acheived.

 

[Forrest Nearing]

So you guys believe that the phenomenon we now know as horsepower, would not exist if James Watt hadn't assigned a math formula to it? Interesting.



I'm not arguing or disputing the math used to compute HP, but to imply that an engines ability to produce it is solely RPM dependent is flat wrong. We're not talking about math here. We're talking about engines, which reminds me... I need to finish transplanting that S2000 engine into my Ram. After all... it spins to 8k rpms... get ready to be owned:-laf

the S2000 doesn't make any torque... it also doesn't make any horsepower! :-laf



let's compare apples to apples here and just talk about 5. 9 Cummins since that's what we all have in our trucks...



someone was talking about "two kinds of power"... I'm assuming he was talking about torque and horsepower...



TECHNICALLY torque is the only thing we measure, but in reality horsepower is all we should give a crud about... these things are always going to make more torque than we need. Horsepower is what gets you to the finish line the fastest or gets the sled across the 300' mark.



so dealing with the same displacement, similar cylinder head flow, and similar boost, the higher you spin the thing, the more power you're gonna make...

 

[BigGunZ]

someone was talking about "two kinds of power"... I'm assuming he was talking about torque and horsepower...

TECHNICALLY torque is the only thing we measure, but in reality horsepower is all we should give a crud about... these things are always going to make more torque than we need. Horsepower is what gets you to the finish line the fastest or gets the sled across the 300' mark.

so dealing with the same displacement, similar cylinder head flow, and similar boost, the higher you spin the thing, the more power you're gonna make...

That was me and I was referring to 2 ways of expressing power (actually there are more than 2)

 

[Forrest Nearing]

you talking metric?

 

[AMassaro]

CJ, I'm in total agreement with what you said. But if were talking about the same displacement, with the same redline, which can mean camshafts of similar lift and duration, all things being equal, things are going to be close. If you have two 350cubic inch engines with the same camshafts, timing set the same, similar intakes, etc. You are going to produce "close" to the same hp/trq curves. The only variations would be the efficiency of the heads, engine temp, ect. This holds true for our CTD's with 12 or 24valve heads.



btw- this argument has been going on forever. Ask 20 different high performance engine builders what they shoot for -high hp or high trq- and you going to get many different opinions as to what is best. Some guys like thumping big blocks with lots of low end grunt to win drag racing and some like high spinning small blocks.

 

[BigGunZ]

you talking metric?

Watts and BTU's are used in certain circles depending on the application. They're all units of measurement for power.

 

[Forrest Nearing]

CJ, I'm in total agreement with what you said. But if were talking about the same displacement, with the same redline, which can mean camshafts of similar lift and duration, all things being equal, things are going to be close. If you have two 350cubic inch engines with the same camshafts, timing set the same, similar intakes, etc. You are going to produce "close" to the same hp/trq curves. The only variations would be the efficiency of the heads, engine temp, ect. This holds true for our CTD's with 12 or 24valve heads.

this is true... and the 24v trucks breathe a little better... BUT, p7100's will allow turning more RPM, and unlike gas engines, diesel engines can continue to make more power in richer A:F ratios, so the pump that puts out the most fuel wins!

 

[BigGunZ]

the S2000 doesn't make any torque... it also doesn't make any horsepower! :-laf

He He... don't say that around an S2000 owner. I think my power window motor makes about as much torque as one of those things:-laf

 

[Forrest Nearing]

they are pretty nifty little cars... something like 240hp out of a 2. 0l engine? but like 120ftlbs or something?



and I think they'll turn 10k, won't they?



you're not going to catch me in one, but they're not the worst car ever made

 

[BigGunZ]

they are pretty nifty little cars... something like 240hp out of a 2. 0l engine? but like 120ftlbs or something?

and I think they'll turn 10k, won't they?

you're not going to catch me in one, but they're not the worst car ever made

Considering that they're a Honda, they're probably great cars as their quality has always been outstanding. Not sure about the red line but they can sure hum... I know it's at least 8k but it could be more.

 

[Bob4x4]

It's not alway hp or torque that wins... ... ... . my 350 hp 05 was running rings around a 500+hp 01 truck at Glamis this wk-end. Thanks KORE Oo.



Bob

 

[Hohn]

Guys, HP and torque are not an either-or pair. They are different ways of expressing the same thing.

HP is simply the rate of tq appication. Therfore, hp is a function of BOTH tq and RPM.

You can use gearing to change the ratio of one to the other, but hp will always be constant.

So it doesn't matter if one engine makes 300hp @ 8K rpm, and the other makes it at 2K rpm. Yes, the 2K rpm engine makes a lot more tq. But the 8K rpm engine could be made to have JUST AS MUCH tq using gear multiplication.

RPM matters. The higher you can rev an engine, the more air and fuel it can process (and combust) per min. Therefore, it can make more power (remember, power is related to TIME).

Just about every racing form involves higher RPM to get more HP. More rpm, more fuel/air used, more power. Then you just gear the car to take advantage of the higher RPM range.

Some people think that tq is all that matters. This is wrong. Different engines optimized in identical cars would illustrate this:

Car A: makes 500lb-ft from 1000-3000 rpm. It has 2:1 axle ratio to match the low RPM range.

Car B: makes 500lb-ft from 5000-7000 rpm. It has a 4:1 axle ratio to better match the higher RPM range.

Now you can see how the higher RPM is important. The formula tells us that Car A produces an average of 190. 4 HP in its low RPM range. Car B meanwhile makes 571 avg HP within its rpm range!

Now, which is faster??

The racing value of Low-rpm tq is only that you have to have it to accelerate the car to where your high-rpm tq is being made. A high-revving, high HP engine is only valuable to you when you can operate it within its power range. Unless you drop the clutch at 6K rpm, it takes time to accelerate up to that high rpm--- and that's time you don't have if you are racing.

So it's not just how much tq/hp you have, it's HOW SOON you can access that power in a racing environment that often proves decisive.



All this just to say that for the forseeable future, the P-pump will remain King. It possess BOTH the elements required for big power: RPM capability and FUELING (which makes tq).

Until they can get a dual CP3 setup to run at 5500 rpm, the P-pump is safe.