Does a Rear Mount Turbo have a Lot of Lag? Remote Mount Turbo Benefits and Drawbacks Explained
803,584
Published 2024-01-07
Patreon: www.patreon.com/d4a
Become a member: youtube.com/channel/UCwosUnVH6AINmxtqkNJ3Fbg/join
In today’s video we will discuss rear mount / remote mount turbo setups, so engine in the front turbo in the back. We will analyze their benefits, their drawbacks, we will see if they are actually a stupid idea and along the way we will hopefully learn some important lessons and bust some turbocharging myths.
So let’s start by answering the most obvious question…why would someone want to mount a turbocharger far away from the engine? Usually the primary motivator for a remote mount turbo is space. Sometimes it is very difficult to find space for a turbocharger in the engine bay of a car that came naturally aspirated from the factory. And even when you can find the space you might require a one-off complex custom exhaust manifold if you’re working with a platform that doesn’t have sufficient aftermarket support or if you’re doing an engine swap. If you don’t have the fabrication equipment and skills such an exhaust manifold can become a very expensive item on your parts list.
And even if you find the space for the turbo the location might be less than ideal and require complex routing of the intake piping and exhaust downpiping which may negatively impact performance. On top fo this a turbocharger is a major source of heat and the space you find for it may negatively impact the components around the turbo leading to a reduced lifespan of these components.
A remote mount turbo is sort of a path of least resistance towards solving these problems. There almost always plenty of space somewhere along the underside of the car, even more so at the back so finding space for one or even two turbos here is not an issue. A remote turbo is also a one stone two birds affair because it eliminates heat problems. By locating the turbo away from the engine bay we save the engine from the added heat and we also help the turbo itself to run cooler. Companies and individuals who specialize in remote mount setups and have completed such projects usually report turbine side or hot side temperatures of the turbo to be lower by around 300 degrees celsius.
This is a pretty significant difference in temperature which helps the turbo last longer and makes cooling the turbo less important. In other words it becomes feasible to run a turbo that isn’t water cooled, instead it can be oil cooled only. This reduces cost and simplifies install. Of course, you can still definitely run a water-cooled turbo in a remote mount setup, there is no harm in even better turbo cooling.
But it gets even better. The remote location of the turbo doesn’t just save the engine bay from the added heat, it actually positively impacts performance. If a turbo runs cooler than it doesn’t heat the intake air as much. On top of this we have as much as a car’s length of intake piping that’s exposed to fresh air passing along it which means that the intake air gets cooled even more before it gets to the engine. Cooler air is denser and denser air means that we can stuff in more air mass into the same volume which means more power.
Now this cooling effect isn’t as significant as that of an intercooler so ditching the intercooler isn’t a smart idea in my opinion, instead this is added cooling simply further improves performance and helps prevent knock which means that, all else being equal, we can potentially run a higher compression ratio in the engine than with a turbo mounted near the engine.
So, it costs less because you don’t need a fancy exhaust manifold, it reduces heat and it improves performance. As you might be guessing things can’t be all good, there must be downsides.
The biggest downside of a rear mount turbo setup is that it allegedly leads to massive amounts of turbo lag. And apparently this occurs because now the turbo has to pressurize an entire car’s length of piping. This requires time and we experience this time delay as turbo lag or reduced responsiveness of the engine, in other words a car with a rear mounted turbo will feel lethargic and sluggish due to the crazy lag.
This is simply not true and I believe that this idea that a rear mounted turbo creates massive lag comes from a mis-understanding of how a turbo actually works and how it increases engine performance.
A special thank you to my patrons:
Daniel
Pepe
Brian Alvarez
Peter Della Flora
Dave Westwood
Joe C
Zwoa Meda Beda
Toma Marini
Cole Philips
00:00 Benefits
04:38 Turbo Lag
12:29 Boost Threshold
17:22 Oil return, noise, damage
#d4a #boostschool
All Comments (21)
-
Become a Tuning Pro: hpcdmy.co/dr4a Support the channel by shopping through this link: amzn.to/3RIqU0u Patreon: www.patreon.com/d4a Note: Cylinder surface formula is not the right one for the example as it places to much importance on cylinder bases which are not important in the case of a long pipe. However, the statement is still correct and a larger diameter exponentially increases heat loss since it lowers gas velocity. More time in the pipe is more time to pass heat. Become a member: youtube.com/channel/UCwosUnVH6AINmxtqkNJ3Fbg/join
-
There are no solutions, only compromises...
-
Very well said! What's most impressive about your videos is I don't think you're even referencing a script for most sections. You do a brilliant job outlining the subject matter clearly and concisely but unlike so many creators, you obviously know your stuff inside and out. It's that undeniable passion that makes you such a great educator. I always learn something I didn't expect from your content. Creators like yourself are becoming more and more of a rare breed and I genuinely respect your efforts. Keep killing it man.
-
Mechanical Engineer here - what he says @13mins into the video is crucial. Thermal energy is the source energy. The ''hot side'' of the turbo is just a gas turbine and the simplest form in thermodynamics to relate the work done (Wout) by a gas turbine is Qin = Qout + Wout.... Qin - thermal energy IN, Qout - thermal energy OUT, Wout - Work produced. This is the basic thermodynamic law of any heat engine and this will make it easier to understand the basics on how a gas turbine or engine work from a scientific perspective. So when you relocate a turbo to the rear, there is heat loss in the exhuast gas, therefore your Qin becomes less, resulting in your work produced by the turbine being less which is not good. The turbine side of a turbo is designed as a adiabatic system meaning they try to make it as insulated as possible because any heat loss is just a loss in potential energy - therefore turbos are manufactured very robust. Obviosuly there are China turbos too which dont comply to this but every big turbo manufacturer designs there turbos to run at very high temps so a drop in turbine temp is again not really a win w.r.t turbo life span. (This is why modern car engine designers put the turbo as close as possible to the exhuast manifold). Now this issue of charge air being too hot can very easily be solved by selecting the correct intercooler, but I also know space is usually a problem - a short fat intercooler is not as effecienct as a large thin one. If you want to learn the in depth science of intercoolers, go look at Gale Bank's videos on intercooling, he explains it very simple and easy. Remember folks, chase efficiency, not power. Power is a by-product of eficiency. If you build an efficient, well designed engine, it will produce more power at less stress levels.
-
So glad to see the steady growth in viewership of this channel over the last year or so. This video is pretty damn niche, even among auto engineering videos, and yet it has almost 200k views in just two days. Love to see that because it's very well deserved. It also shows me that there's still a few knowledge-seekers left in our increasingly vain, self-obsessed world
-
Decades ago I had a C4 Corvette ZR1 that was modified with a remote mount turbo. Yes it had noticeable boost lag, as you will undoubtedly have with an 83mm turbo, but the remote mount I think contributed to a more subtitle boost ramp. Also, the added air volume meant that the turbo was far less interrupted by momentary throttle cuts as the transmission shifted. All in all, it was a 9 second car every day of the week, and breaking 200 on a one mile was easy.
-
Fun fact. The WW2 era P47 Thunderbolt had a turbocharger located in the rear of the fuselage, well back from the 2,800 ci. (45 litre!!!) twin row 18 cylinder radial.
-
16:40 Small correction: the 2pi*r^2 term of the surface area formula represents the two circles at the ends of a cylinder. In the case of an tube like an exhaust pipe these are absent, therefore A=2pi*rh (hence a 10% increase in r will increase surface area by 10%, etc)
-
Great explanation. I worked at STS back in the day and i dont know how many times ive explained the remote turbo lag myth to people. The best argument was just giving them a ride - the average car guy could not tell the difference from a remote mount vs under hood mount system (other than the exhaust note of course).
-
one extra thing to consider: all the infrastructure (piping for oil, air and exhaust gas) is going to add more weight to the vehicle, which does effect performance, but you are also lowering the cars centre of mass since you're installing it all way down low so it might also have benefits.
-
Perfect video. It is frustrating how many people look individually at pressure and flow but it is prevalent throughout the engineering world! A pressure washer with 2,000 psi is not more powerful than a get engine with 700psi discharge pressure (50:1 EPR) You describe things so clearly, please keep it up. Another fantastic video. Clear and concise with common sense easily relatable concepts. 👌
-
This guy is an absolutely brilliant communicator
-
Your videos are always so informative. I learned a lot with this one. While I've never really thought about this kind of setup, I definitely went straight to "oh man that's gotta increase the lag" and now I know how that is wrong frameset, and the "heat energy" vs. kinetic explanation was great. Thank you again all around. Great work!
-
Nicely explained! I appreciate the distinction between Turbo Lag and Boost Threshold. So many car enthusiasts equate the two terms, but as you said, they are not the same!
-
A video on the pros and cons of a hot-v configuration would be a nice counterpoint to this.
-
Congratulations on 1M subscribers man. Absolutely colossal achievement. I've always believed you would be huge, but this is wild! So well deserved.
-
This guy is so much better than engineering explained
-
I've played with remote mount turbos through the years. They are surprisingly effective, the thing I found mostly different was that it has similar gains to a log manifold even with tuned header(s). This makes sense because you are using a much higher amount of built up static pressure for the turbine as opposed to the individual exhaust pulses of pressure - so even tuned headers are working against a much higher base pressure. It is sort of the extreme opposite of cleanly delivering the pulses and eliminating the base pressure buildup like you get when dividing an exhaust between multiple turbo scrolls.
-
The house of cards in my head with the name "Turbo" has just crumbled. I have learnt something again and D4A has corrected my half-knowledge. Greetings Lucas
-
Very well done mate. What a fantastic video. So much information crammed into it (which was all relevent to the subject) but more to the point, this was for the first time in a long time where i havent found myself getting easily distracted or catching myself bailing out after 10-15 minutes because of the lack of interesting content or poor delivery of it. In fact I think this is the first time ive bothered to comment on any video in all the years of watching youtube, so thats speaking volumes right there. This is how you're meant to get people to like and subscribe, not by begging them to. I've not seen any of your other videos but you've already got my sub mate. Plus on top of all that, Im gonna bet that English most likely isnt your native language, and you still delivered it clearly and I never missed a trick. Honestly you killed it guys. Bloody good on ya. Very good form.
