intercooler tank design question

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Post by dwilliams »

ptuomov wrote: Tue May 21, 2019 1:22 pm There was a long thread on a related topic where people answered many of my questions:

viewtopic.php?t=39841
Interesting. That one didn't pop up when I searched. Speedtalk's search usually works better than that...
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Re: intercooler tank design question

Post by j-c-c »

ptuomov wrote: Wed May 22, 2019 10:59 am
LoganD wrote: Wed May 22, 2019 9:49 am Have you actually measured the boost response? I suspect this is the placebo effect, increasing volume is a direct boost response loss. The turbocharger has a set mass flow rate relative to wheel speed, you aren't affecting the exhaust pressure drop across the turbine because the intercooler piping doesn't affect the exhaust, and you're increasing the volume that needs to pressurized. Now, if you're installing a higher flowing exhaust system post-turbine along with these larger intercooler pipes then I believe it, but it's the exhaust that's helping response not the induction piping.

You can improve boost response by increasing the radius of the bends in the induction system or reducing the number of bends, but increasing the diameter will definitely make response worse. If you've got 80mm intercooler piping and you increase that to 90mm, you've increased the intercooler piping internal area by over 26%. That's huge. You should be very, very careful about increasing piping size.
Not rigorously, so it could be just that the bigger pipes make it sound louder and by human perception louder means faster!

I don't even have a rigorous definition boost response. What I mean by boost response is that if I'm leaving a stop light how quickly can I get to 60 mph or if I'm cruising at 60 mph how quickly can I get to 90 mph without downshifting.

If you put a straw between the compressor outlet and the intake valve, I believe that by my definition "boost response" is bad. The car might never make it to 60mph! Making the straw larger makes boost response better, again by my definition.

Now, the question is how big is too big. If a five-liter motor displaces about (say 100% VE) 2.5L per revolution, at 1500 rpm it displaces 10x that per second. Make the pipe shorter, sure, it's better. How about for diameter, what's the optimal diameter?
I would think in this context "boost response" would be better indicated by time it takes to go from say 60 to 70, or zero to say 20, which in a road car is really considered "throttle response"?
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Post by dwilliams »

volodkovich wrote: Tue May 21, 2019 5:16 pmI've done CFD on standard style aftermarket IC end tanks and they are indeed horrible. I suspect they reason they work is because the extra mass of core conducts heat away from the cores that are actually passing the air.
My cynical theory is that the engines in those vehicles don't actually *need* an intercooler as such to meet their required performance, so the OEM is just sticking in the cheapest intercooler-like object that will fit, because "everybody knows" you have to have an intercooler.
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Re: intercooler tank design question

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j-c-c wrote: Wed May 22, 2019 2:21 pm
ptuomov wrote: Wed May 22, 2019 10:59 am
LoganD wrote: Wed May 22, 2019 9:49 am Have you actually measured the boost response? I suspect this is the placebo effect, increasing volume is a direct boost response loss. The turbocharger has a set mass flow rate relative to wheel speed, you aren't affecting the exhaust pressure drop across the turbine because the intercooler piping doesn't affect the exhaust, and you're increasing the volume that needs to pressurized. Now, if you're installing a higher flowing exhaust system post-turbine along with these larger intercooler pipes then I believe it, but it's the exhaust that's helping response not the induction piping.

You can improve boost response by increasing the radius of the bends in the induction system or reducing the number of bends, but increasing the diameter will definitely make response worse. If you've got 80mm intercooler piping and you increase that to 90mm, you've increased the intercooler piping internal area by over 26%. That's huge. You should be very, very careful about increasing piping size.
Not rigorously, so it could be just that the bigger pipes make it sound louder and by human perception louder means faster!

I don't even have a rigorous definition boost response. What I mean by boost response is that if I'm leaving a stop light how quickly can I get to 60 mph or if I'm cruising at 60 mph how quickly can I get to 90 mph without downshifting.

If you put a straw between the compressor outlet and the intake valve, I believe that by my definition "boost response" is bad. The car might never make it to 60mph! Making the straw larger makes boost response better, again by my definition.

Now, the question is how big is too big. If a five-liter motor displaces about (say 100% VE) 2.5L per revolution, at 1500 rpm it displaces 10x that per second. Make the pipe shorter, sure, it's better. How about for diameter, what's the optimal diameter?
I would think in this context "boost response" would be better indicated by time it takes to go from say 60 to 70, or zero to say 20, which in a road car is really considered "throttle response"?
Yes. The driver doesn't care about how fast the turbine is spinning, driver just cares about how quickly (and consistently) the car can accelerate from any initial conditions.
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Re: intercooler tank design question

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LoganD wrote: Wed May 22, 2019 12:53 pm As long as you are keeping the velocity in the intercooler piping at a reasonable level you will not have large pressure loss in the system. For example, a common goal for a complete compressor outlet to intake valve system would be 15 kPa on an OEM project. The charge air cooler would be 6-8 kPa of that depending on the design. Changing to larger piping post compressor might get you from 15 kPa pressure drop down to 13 kPa pressure drop. That is not even remotely worth a 5% reduction in boost response, particularly if you have some surge margin in your compressor. The entire turbo system becomes MORE efficient if you can run with less exhaust flow going through the wastegate, so if you have surge margin you simply up the pre-charge air cooler boost level (2 kPa increase is nothing anyway) to achieve the same boost level in the manifold. This closing of the wastegate actually helps turbine response.
I wouldn't go as far as saying that the system is more efficient if I run the turbine wastegate closed. Suppose I replace the boost pipe with a straw. Now, the compressor works hard and the energy turns to heat in the restrictive boost pipe. How is that more efficient than a free-flowing system that has already met the boost target at the intake valve and thus has opened the wastegate? It's not.

A lot of people here at Speedtalk are chasing two things. First, coolest possible charge in the intake manifold. Second, best possible pressure ratio between intake manifold and exhaust manifold. I'm not saying that those two things are be-all end-all, just explaining where people are coming from. Although maybe you already know the speedtalk.com turbo writers anyway.
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Re: intercooler tank design question

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Modern turbocharged OEM engines are much less "laggy" almost entirely because the engineers worked hard to reduce intake system volume. Turbine efficiency and design helps, but the volume reduction compared with something 25 years ago is the biggest gain in terms of reducing "lag".
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Re: intercooler tank design question

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ptuomov wrote: Wed May 22, 2019 3:11 pm
LoganD wrote: Wed May 22, 2019 12:53 pm As long as you are keeping the velocity in the intercooler piping at a reasonable level you will not have large pressure loss in the system. For example, a common goal for a complete compressor outlet to intake valve system would be 15 kPa on an OEM project. The charge air cooler would be 6-8 kPa of that depending on the design. Changing to larger piping post compressor might get you from 15 kPa pressure drop down to 13 kPa pressure drop. That is not even remotely worth a 5% reduction in boost response, particularly if you have some surge margin in your compressor. The entire turbo system becomes MORE efficient if you can run with less exhaust flow going through the wastegate, so if you have surge margin you simply up the pre-charge air cooler boost level (2 kPa increase is nothing anyway) to achieve the same boost level in the manifold. This closing of the wastegate actually helps turbine response.
I wouldn't go as far as saying that the system is more efficient if I run the turbine wastegate closed. Suppose I replace the boost pipe with a straw. Now, the compressor works hard and the energy turns to heat in the restrictive boost pipe. How is that more efficient than a free-flowing system that has already met the boost target at the intake valve and thus has opened the wastegate? It's not.

A lot of people here at Speedtalk are chasing two things. First, coolest possible charge in the intake manifold. Second, best possible pressure ratio between intake manifold and exhaust manifold. I'm not saying that those two things are be-all end-all, just explaining where people are coming from. Although maybe you already know the speedtalk.com turbo writers anyway.
Well certainly you aren't going to be foolish and put tiny intercooler piping on an engine, but just going for the biggest thing you can stuff in there is bad engineering. You can graph inlet system pressure drop/velocity profile vs. flow orifice diameter and there is a point of diminishing returns like anything else.

From a driving experience standpoint, having a small intake system volume makes the engine feel so much better in transients. Who wants an engine that doesn't reach full boost till 4000 RPM and redlines at 7000? A 3000 RPM powerband sucks.
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Re: intercooler tank design question

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LoganD wrote: Wed May 22, 2019 3:18 pmFrom a driving experience standpoint, having a small intake system volume makes the engine feel so much better in transients. Who wants an engine that doesn't reach full boost till 4000 RPM and redlines at 7000? A 3000 RPM powerband sucks.
Opinions vary. My perspective is that biggest pipes that fit inside the engine bay (2x2.5" mostly) worked well with a 5.0L 32V twin turbo engine in a sports car. The powerband is very wide if you judge it from the torque curve (like humans typically do).
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Re: intercooler tank design question

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LoganD wrote: Wed May 22, 2019 3:14 pm Modern turbocharged OEM engines are much less "laggy" almost entirely because the engineers worked hard to reduce intake system volume. Turbine efficiency and design helps, but the volume reduction compared with something 25 years ago is the biggest gain in terms of reducing "lag".
My recollection is that BMW M5 went in the opposite direction on the intake side with their technical update. The TU engine has everything a little bigger on the intake side, I think. In an interview, the designer said they made the gains by "dethrottling" everything on the intake side.
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Re: intercooler tank design question

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ptuomov wrote: Wed May 22, 2019 3:57 pm
LoganD wrote: Wed May 22, 2019 3:18 pmFrom a driving experience standpoint, having a small intake system volume makes the engine feel so much better in transients. Who wants an engine that doesn't reach full boost till 4000 RPM and redlines at 7000? A 3000 RPM powerband sucks.
Opinions vary. My perspective is that biggest pipes that fit inside the engine bay (2x2.5" mostly) worked well with a 5.0L 32V twin turbo engine in a sports car. The powerband is very wide if you judge it from the torque curve (like humans typically do).
Why would literally every OEM be designing their turbo engines with small inlet volumes if it didn't work? Drive a turbocharged car from 1995 and drive one from 2019 and you tell me which has better "throttle response". Most of that improvement is due to intake volume reductions.

This is very, very simple volume flow stuff.
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Re: intercooler tank design question

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LoganD wrote: Thu May 23, 2019 10:13 amWhy would literally every OEM be designing their turbo engines with small inlet volumes if it didn't work? Drive a turbocharged car from 1995 and drive one from 2019 and you tell me which has better "throttle response". Most of that improvement is due to intake volume reductions.

This is very, very simple volume flow stuff.
" Drive a turbocharged car from 1995 and drive one from 2019... Most of that improvement is due to intake volume reductions."

Why would you say or believe that? It's an absurd statement, in my opinion.
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Re: intercooler tank design question

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Here's Porsche 944 Turbo engine from the 1980's:
engine2.jpg
Here's the new BMW turbo:
5410.jpg
Yes, the throttle response is hugely better for the new BMW engine. But eyeball the volume between the compressor outlet and the intake. I can assure you that the throttle response did not come from reducing that volume. Claiming that it did is absurd.
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Re: intercooler tank design question

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ptuomov wrote: Thu May 23, 2019 11:16 am Here's Porsche 944 Turbo engine from the 1980's:

engine2.jpg

Here's the new BMW turbo:

5410.jpg

Yes, the throttle response is hugely better for the new BMW engine. But eyeball the volume between the compressor outlet and the intake. I can assure you that the throttle response did not come from reducing that volume. Claiming that it did is absurd.
Oh yes, compare two engines from different companies that have completely different architecture. That's the way to disprove my point!

Look at the size of that Porsche intake manifold. I'd bet money that the BMW engine has less total inlet volume post compressor than that Porsche engine. Tell me again, how many OEM quality turbocharger setups have you designed? If you've done any at all, then we can take this discussion offline and I'd like to know how you got any engineering leads to sign off on your "bigger is better" philosophy. I've designed engines that make over 30 bar BMEP on pump fuel and generate 180+ bhp/l, I know how turbocharger systems are designed these days.
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Re: intercooler tank design question

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LoganD wrote: Thu May 23, 2019 1:31 pm
ptuomov wrote: Thu May 23, 2019 11:16 am Here's Porsche 944 Turbo engine from the 1980's:

engine2.jpg

Here's the new BMW turbo:

5410.jpg

Yes, the throttle response is hugely better for the new BMW engine. But eyeball the volume between the compressor outlet and the intake. I can assure you that the throttle response did not come from reducing that volume. Claiming that it did is absurd.
Oh yes, compare two engines from different companies that have completely different architecture. That's the way to disprove my point!

Look at the size of that Porsche intake manifold. I'd bet money that the BMW engine has less total inlet volume post compressor than that Porsche engine. Tell me again, how many OEM quality turbocharger setups have you designed? If you've done any at all, then we can take this discussion offline and I'd like to know how you got any engineering leads to sign off on your "bigger is better" philosophy. I've designed engines that make over 30 bar BMEP on pump fuel and generate 180+ bhp/l, I know how turbocharger systems are designed these days.
I have given somewhat serious design help on one turbocharger system, and that most certainly wasn't a car factory system. My lack of professional experience and your argumentum ab auctoritate don't however change the fact that your claim is absurd. The absurd part of your claim is not that the car factory professional design engineers try to keep the boost pipe volume to minimum at a given pressure loss, that is all true. The absurd part is where you claim that the improvements in response have come from the reduction of intake volume.

You seem to be upset enough now that you're misrepresenting my position, or perhaps I didn't communicate my position clearly enough. I think that given the typical space constraints under the hood, the optimum design is often the largest diameter (and, of course, shortest) pipes that fit. It's not the unconstrained optimum that "bigger is better", it's however in my opinion the constrained optimum in many cases.

You note that the intake manifold of the 1980's Porsche looks different from the modern day BMW, which is true. The intake manifolds of turbo cars have changed pretty dramatically over the years, but I believe think that those changes were not primarily motivated by reducing volume (although less volume is of course better, holding everything else constant). They were primarily motivated by the intake manifold resonance tuning no longer being required. In the new cars, the turbocharger produces boost at such a low rpm that it's better to simply make a short-runner intake manifold that gives a very flat torque curve.
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Re: intercooler tank design question

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ptuomov wrote: Thu May 23, 2019 2:00 pm
LoganD wrote: Thu May 23, 2019 1:31 pm
ptuomov wrote: Thu May 23, 2019 11:16 am Here's Porsche 944 Turbo engine from the 1980's:

engine2.jpg

Here's the new BMW turbo:

5410.jpg

Yes, the throttle response is hugely better for the new BMW engine. But eyeball the volume between the compressor outlet and the intake. I can assure you that the throttle response did not come from reducing that volume. Claiming that it did is absurd.
Oh yes, compare two engines from different companies that have completely different architecture. That's the way to disprove my point!

Look at the size of that Porsche intake manifold. I'd bet money that the BMW engine has less total inlet volume post compressor than that Porsche engine. Tell me again, how many OEM quality turbocharger setups have you designed? If you've done any at all, then we can take this discussion offline and I'd like to know how you got any engineering leads to sign off on your "bigger is better" philosophy. I've designed engines that make over 30 bar BMEP on pump fuel and generate 180+ bhp/l, I know how turbocharger systems are designed these days.
I have given somewhat serious design help on one turbocharger system, and that most certainly wasn't a car factory system. My lack of professional experience and your argumentum ab auctoritate don't however change the fact that your claim is absurd. The absurd part of your claim is not that the car factory professional design engineers try to keep the boost pipe volume to minimum at a given pressure loss, that is all true. The absurd part is where you claim that the improvements in response have come from the reduction of intake volume.

You seem to be upset enough now that you're misrepresenting my position, or perhaps I didn't communicate my position clearly enough. I think that given the typical space constraints under the hood, the optimum design is often the largest diameter (and, of course, shortest) pipes that fit. It's not the unconstrained optimum that "bigger is better", it's however in my opinion the constrained optimum in many cases.

You note that the intake manifold of the 1980's Porsche looks different from the modern day BMW, which is true. The intake manifolds of turbo cars have changed pretty dramatically over the years, but I believe think that those changes were not primarily motivated by reducing volume (although less volume is of course better, holding everything else constant). They were primarily motivated by the intake manifold resonance tuning no longer being required. In the new cars, the turbocharger produces boost at such a low rpm that it's better to simply make a short-runner intake manifold that gives a very flat torque curve.
I have literally never put the largest diameter compressor outlet tubing I could fit on an engine design. As I said before, you model the entire package in CFD and as long as you are getting down to the 10-15 kPa pressure drop level for the post-compressor system, you don't make the tubing any bigger. If your tubing is substantially larger than the compressor outlet ID it's not doing much. Turbocharger compressor outlet diameters aren't that big.

Intake manifold resonance tuning is still very desirable, they simply don't do it so that they can make the volume smaller. If it was just a resonance tuning issue, they wouldn't make the plenums so small as well. As I've designed several OEM intake manifolds using the most advanced technology available, I'm informed enough to make that statement.

If you are so wise and know where the improvements in turbocharger response have come from in say....the last 10-15 years, where have they come from?
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