I am relatively knowledgable in the basics of turbo systems, however, i did have a questions regarding the power produced by different turbo sizes. For instance, i am aware that 7lbs of boost from a t-25 produces less power than 7lbs from say a t-3. Now quite evidently, the increase in power is rooted in the fact that the t-3 is larger, but how does this translate to more power from your motor? Additionally, we seem to relate engine limitations when it comes to turbocharging by boost pressure (i.e. you shouldn't run more than 7lbs on stock internals for very long , etc). Why is it that 7lbs from a t-25, while making less power than 7lbs from a t-3, would have the same impact in terms of engine wear. Thanks in advance

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mafioso102 &raquo;</TD></TR><TR><TD CLASS="quote">i am aware that 7lbs of boost from a t-25 produces less power than 7lbs from say a t-3.</TD></TR></TABLE>

I really wish people would stop making silly blanket statements like this. While this may be true for *peak* hp, it may not be true for *useable* hp.

First, saying "a t-3" is like saying "a Ford". Which Ford? An Escort or an Excursion? They're not the same. T-3s go from pretty small, like a .48/.42, up to a Super 60 or a 60-1, so if you say "a t-3" be sure to say which one you mean. If you choose a t-3 that is only efficient at high boost pressures, then it is going to suck at 7psi no matter what the flow rate is.

Second, at a certain point the two turbos will be equal. Because the t-3s efficiency island is centered at a higher flow rate than the t-25, at any flow rate above that point the t-3 will be better. At any flow rate below that point the t-25 will be better. Of course this also depends on where their efficiency islands are located with respect to pressure ratios. Some turbos are only good at high pressure ratios and some are only good at low pressure ratios.

Finally, choosing the right turbo means picking one where at YOUR boost pressure and YOUR max flow rate at redline, you are just leaving the fat middle part of the efficiency island for BOTH THE COMPRESSOR AND THE TURBINE FLOW MAPS. A lot of people on this board seem to forget that a turbo has an exhaust half too and they only look at the compressor side.

 

A T25 will make more torque than a T04E at the same boost level. If you get into the forumula you'll see why.

 

P V = n R T
This will explain why a t25 will not produce as much power as a t3 for example. Plug and chug in some numbers... keep in mind the temps the t25 develops are much higher then the t3 will produce.

HP = Torque * RPM / 5,252

See if you can somewhat relate this with your turbo... You can see from the horsepower equation that high RPM values favor horsepower. If you take an engine with a certain torque and run it at very high revs, it can generate lots of horsepower even though its torque hasn't changed at all. A racing engine can produce relatively low torque, but because it can rev so high it gets a great horsepower rating. A big diesel has huge torque, but "gets no respect" in terms of horsepower because it cannot ever get above 2,000 RPM. This "makes sense" -- if two engines produce the same torque, the one that can do it more times per minute does more work and therefore has more power.

Does that make a little bit of sense? Maybe not... I'm not too articulate at 2am when I'm in the middle of fluid dynamics homework. Anyways, take the equation and plug and chug in some numbers and relate them to RPM's that the turbo's spin.

I know this is a little bit vague but read this for all the info you'll ever need:

https://honda-tech.com/zero...age=1

https://honda-tech.com/zerothread?id=710270

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Arturbo &raquo;</TD></TR><TR><TD CLASS="quote">A T25 will make more torque than a T04E at the same boost level. If you get into the forumula you'll see why.</TD></TR></TABLE>

I would REALLY like to see that formula! You don't need to explain it to me, but be sure to define *exactly* what all of the variables and symbols are.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GudeH23a &raquo;</TD></TR><TR><TD CLASS="quote">P V = n R T
This will explain why a t25 will not produce as much power as a t3 for example.</TD></TR></TABLE>

It...um...I'm not even sure where to begin with such a dumb statement! Unless one of the turbos has made a pact with Mother Nature and can sidestep the laws of physics, then this ideal gas law applies equally to both of them.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GudeH23a &raquo;</TD></TR><TR><TD CLASS="quote"> keep in mind the temps the t25 develops are much higher then the t3 will produce.</TD></TR></TABLE>

This statement is 100% completely meaningless unless you state WHICH T-25, WHICH T-3, AND AT WHAT BOOST PRESSURE AND FLOW RATE!!! At some boost pressures and flow rates the T-25 is better, meaning it is more efficient and blows cooler air, and at other boost pressures and flow rates the T-3 is better. If you had read my first post this would have been obvious, which is why it pisses me off so much when people keep repeating these same stupid meaningless statements over and over and over...


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GudeH23a &raquo;</TD></TR><TR><TD CLASS="quote">HP = Torque * RPM / 5,252

See if you can somewhat relate this with your turbo... You can see from the horsepower equation that high RPM values favor horsepower.</TD></TR></TABLE>

Again, I'm almost speechless! Of course hp favors high rpm, any child knows that. It is a time dependent function of the work being done. And this only applies if the torque is constant, which it isn't.

Get this through your heads people. You can't talk about what turbo is better IF YOU DON'T SAY AT WHAT FLOW RATE AND BOOST PRESSURE! Is a T-25 too small for a fully built B18C1? Yes. Are *some* T-3s too big for a stock D15 or D16? Yes. BE SPECIFIC!

signed, the Bigger Isn't Always Better H-T Rebel

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tjbizzo &raquo;</TD></TR><TR><TD CLASS="quote">I really wish people would stop making silly blanket statements like this. While this may be true for *peak* hp, it may not be true for *useable* hp.

First, saying "a t-3" is like saying "a Ford". Which Ford? An Escort or an Excursion? They're not the same. T-3s go from pretty small, like a .48/.42, up to a Super 60 or a 60-1, so if you say "a t-3" be sure to say which one you mean. If you choose a t-3 that is only efficient at high boost pressures, then it is going to suck at 7psi no matter what the flow rate is.

Second, at a certain point the two turbos will be equal. Because the t-3s efficiency island is centered at a higher flow rate than the t-25, at any flow rate above that point the t-3 will be better. At any flow rate below that point the t-25 will be better. Of course this also depends on where their efficiency islands are located with respect to pressure ratios. Some turbos are only good at high pressure ratios and some are only good at low pressure ratios.

Finally, choosing the right turbo means picking one where at YOUR boost pressure and YOUR max flow rate at redline, you are just leaving the fat middle part of the efficiency island for BOTH THE COMPRESSOR AND THE TURBINE FLOW MAPS. A lot of people on this board seem to forget that a turbo has an exhaust half too and they only look at the compressor side. </TD></TR></TABLE>

thanks,it makes sense and i guess i should have been more speific concerning what sizes i was refering to.