Why does the torque vary so much?

I have noticed that when you have something ported and polished, the torque on this truck goes WAY DOWN...

I have a 6lb lower and I am making 545 RWTQ.. and thats at 12.5 psi...

people with ported heads and blowers, or even kenne bell cannot even come close to those torque numbers at the same boost level... so I am curious to know why you port something out.. the HP goes up some but the torque comes down... las ttime i checked the torque is what puts you in the seat.....


what am i missing?

 

Nope. It's always HP that moves the truck. Torque is a static measure. It takes torque times RPMs to actually move an object.

But to answer your question (sort of), you need to lay the charts side by side. Since HP is a mathematical calculation, you need to compare the charts at each RPM to be able to see where the HP is being made.

The "torque" (actually, low end HP) is usually not actually going down, it's being shifted higher up the RPM range. Since HP=TQ X RPMs/5250, moving the torque curve up means that, relative to peak torque (a static measure), the peak HP will grow proportionately more. So you don't actually lose torque so much as you gain power.

And even if you do lose a little peak torque, the engine is usually still stronger. For instance, 400 ft lbs at 10K RPMs is a buttload more powerful than 500 ft lbs at 5K RPMs - 761 vs. 476. Only slightly less twisting force (20%), but a lot more work (60%) is being accomplished per unit of time.

Or something.

[edit: despite the brillant analysis above , I realize on re-reading that I may not understand the question. Do you have some actual numbers to compare?]

 

not really any numbers....

I have a 6lb pulley running 12 or so psi, I came to 420/545

but there are guys with higher hp numbers with 6lb ported eatons, but like only 490RWTQ....

so, I guess the only number to really be looking at is the HP, when it comes to the power curve.....

 

http://vettenet.org/torquehp.html

 

I have read all of that before...
this is not a question on how torque is related to HP...

thats not my question... my question is.. "Why do you loose torque when you port if you don't increase the boost afterwards..."???

like I said.. take my torque numbers with a 6lb pulley at 12.5 psi... 545RWTQ...

now If i do nothing else and then port my blower... the torque will come down about 30-40torque counts... but the HP will increase 30-40 hp...

why is that?

so theoretically I should have less power pushing my into the seat after I port but thats not the case....

 

I'm not an engineer, but if memory serves me correctly, and based on the early 60's Chrysler 426 Wedge engineers tests on intake and head port designs for that motor, it was a matter of Velocity vs Volume. Air velocity had produced more torque with their "longer" Ram intakes and slightly smaller (but still large) valves whereas the larger ,shorter intakes and larger valves had produced more air volume and horsepower with a less torque curve across the powerband. I do believe that this can be somewhat related to S/C engines as well, though the supercharger itself would be a factor in the final equation. Just my 2 cents.

 

Sorry, I misunderstood the question. I agree with Mondo. As I see it opening the bottom of the blower reduces the velocity of the air which reduces torque. With no other changes in the system this would produce a torque loss across the entire RPM band. The reason you see a gain in torque on the top end is because of a cooler IAT2. The charge is cooler because you are taking advantage of more surface area of the I/C.

--Steele

 

Exactly.

Think of it like this, set a air compressor on 100psi and have it blow thru a straw at a beach ball, the ball goes flying away very quickly. Now do the exact same thru some 4inch tubing, the ball still moves but definately not with the same authority. If we think of our engines the same way a 2inch pipe connected to a 500 gallon air tank with another 2inch pipe outlet you get a certain pressure going out, but alter the exhaust to something larger say 8inch pipe and we lose power. My dad use to say think of horsepower as how fast you hit the wall, and torque as how far you carry the wall with you.

 

I think your asking 2 totally different questions and kinda mixing them together, hence confusing the questions and answers. For starters porting a SC DOES NOT lower your tq, (not unless U have a bad Apten or Steig) I've had 3 PE's and gained tq with ea, and U should too. Now if we R talking built motors w/ported heads, mani, and matched ported everything (like I have) again U DO NOT lose tq, (however U do lose boost). Actually U dont lose it U create a more efficient motor so it will show less.

 

Now to what Tim was saying, yes we need a certain amount of tq (especially cause we're heavy) but HP is def more important as he said. AND there is a point where too much tq will actually hurt et. Hence the reason JDM actually builds all their top motors with less tq than they did yrs ago...

 

so let me get this striaght...

when you port out a S/C you loose torque, but you gain more HP due to cooler air being blow in othe cylinders?

whic then allows you to turn up the boost some and get even more hp than before because of cooler air?

 

Translation into scientifically accurate statement (as I understand what Rob is saying):

"Hence the reason that JDM has shifted the torque curve higher on their top motors than they did years ago, so as to maximize the horsepower delivered across the entire power band."

There is a reason why F1 engines are approaching 20,000 RPMs. RPMs X twisting force = work = power

 

Are we talking HP and TQ with corrected numbers? I bet not

 

ok.. lets ask it this way...

in our Lightning....

would you rather have

500RWHP 650RWTQ .... or .... 550 RWHP 600RWTQ

???

 

was thinking the same thing. Curious about the following:
1. AFR
2. temp/humidity
3. kind of dyno used??
4. other mods aside from 6# lower

want to make it clear that I am NOT questioning your torque #s. I have read elsewhere that you have a Turbo F-150!!