Rear/Underside Mounted Turbo Setup.

91LX_5L said:

I thought of this a while back and now see that GreenMustangGt is doing it. Great idea bud glad to see someone stepped forward and started this project.

Anyways Im wondering what the downside to the rear mount turbo setup is. Do you not make as much power as a normal turbo running off the headers in the engine bay? What are some downfalls of this style of setup?

Anyone have any articles on it? There was one on a Fbody I saw in a magazine, wish I bought that mag.

Thanks

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Same here I was reading that a while back. It does seem like a good idea Just things you have to plan more about for our cars. But I th ink we could come up with a Kit with all of us people on the forum and our ideas we could put together one badass kit. I know It seems like a crazy idea but I honestly Think we could do it.

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some of the downsides of rear mounting a turbo are:

A turbo is very dependant on heat to help it spool fast. Alot of the heat is lost by the time the gasses reach the back of the car.

Plumbing is another huge concern. There is a lot of room for failure when you run pressure pipes the length of a car.

Oiling is also another problem. One must either run a oil drin and feed all the way from the motor (baaaadddd Idea)or run an independant lubrication system.

Longevity, Turbo's generally dont like water, or sudden temperature changes. The tolerances change when the turbo is quickly cooled (like by hitting a puddle)

security, It is much easier for someone to steal the turbo's off the car, if they are actually outside of the engine bay.

I have been building turbo cars, and boosted cars for years, and developed a personal relationship with some of the people at Turbonetics. We discussed the rear mount turbo kits, and we all were in agreance that though they do show gains, they are not efficient at all.

no one does rear turbo setups for our cars period... i think greenmustanggt is the first to try (as far as i know... haven't been on turbomustangs.com in a while)

Any rear mounted turbo is a waste of time. Aside from the very obvious oiling issues. The turbos are mounted below the oil pan. You not only have to feed them oil, but you have to suck the oil back out of them also.

Boost control will be hard also since the vacuum lines will collapse if they are going to be that long. You are going to need to have a vacuum block under the car.

Crash Gordon is absolutely correct. The turbos are going to spool like garbage if they are not getting heat, and they will not last as long when they can not be oiled as efficiently.

Extra plumbing is a terrible thing in a turbo setup. Assume that you have a twin setup and the turbos are 5 feet back from where they would have been in a conventional system that is 588 extra cubic inches of pipe that you now have to fill with air. Plus you need to have extra bracing to hold the turbos and piping which will add weight.

A single turbo is always a better idea because you have half the stuff to control and more efficient charge piping. However, a rear mounted setup is just asking to head aches. You are shooting yourself in the foot if you want to run rear mounted turbos. I am not sure why you would bother, it is not even cost effective. Just buy turbo manifolds and sell your headers. The price difference will be negligible. Before you turbo your car, you better break out that calculator. Corky Bell's book Maximum Boost should help you out.

http://www.amazon.com/exec/obidos/tg/detail/-/0837601606/103-7683990-5323814?v=glance

wow, you guys are feeding this guy with all sorts of screwed information, lol..


One question.. have any of the above poster's ACTUALLY done R&D on a rear mounted 5.0 setup FIRST HAND?

yes, but i haven't really expressed any opinions other than sts is the only company i've heard of to make remote mounted turbo systems, and even then, none have been for stangs

i do have problems with a few questions/concerns raised, but i'm just gonna head over to tm and figure it out


what do you think about greenmustang's progress and the whole basis of a remote mounted turbo for a stang oink?

OinkAodeOink said:

wow, you guys are feeding this guy with all sorts of screwed information, lol..

One question.. have any of the above poster's ACTUALLY done R&D on a rear mounted 5.0 setup FIRST HAND?

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Last time I checked the volume of a cylinder is pi*r^2*h. Assuming you use 2.5 inch intercooler piping and run that along the outside of he H pipe to the front of the engine, that is roughly 5 feet for each side. [3.14*1.5625*60 inches of pipe]*2 since there 2 pipes=588.75 cubic inches. This extra volume translates to pressure drop and a loss of velocity. Throttle response will suffer as a result of the extra volume.

Basic physics will tell you that heat will add velocity so mounting the turbos further away from the heads will reduce heat available to the turbos. Therefore inhibiting the ability to spool the turbos.

The oiling concerns are absolutely a fact. The drain on the turbos can not be gravity induced since the turbos are on the bottom of the car. You will need to suck the oil out as well as feed them.

External wastegates have a diaphragm that is most often vacuum operated although you can use pressure to actuate the wastegate like in Tials. You will not find the necessary vacuum/pressure source next to the gas tank. A good option is a vacuum block which I already mentioned.

The extra charge piping, bracing, and remote oiling system translates to weight which is the last thing you want to add to the car. Simplifying the system by mounting the turbos under the hood above the oil pan would reduce weight.

You might think that you are saving money by avoiding the purchase of turbo manifolds, but that initial cost incentive will be lost when you consider the price of AN lines, the remote reservoir, pumps, T-bolt clamps, miles of charge piping, and bracing required.

Actually this applies to all cars not just Mustangs, but any RESEARCH you do will tell you that it is not worth DEVELOPING a remote mounted turbo setup. I NEVER said that remote mounted setups can not work, they are just not worth the hassle since it is easier and cheaper to run turbos under the hood.

Really, the only advantage I can find in a remote system is relieving the under hood temperatures. Personally, I would rather spend less money while going faster with the turbo under the hood and just deal with the added heat compromise.

V8SHME8 said:

Last time I checked the volume of a cylinder is pi*r^2*h. Assuming you use 2.5 inch intercooler piping and run that along the outside of he H pipe to the front of the engine, that is roughly 5 feet for each side. [3.14*1.5625*60 inches of pipe]*2 since there 2 pipes=588.75 cubic inches. This extra volume translates to pressure drop and a loss of velocity. Throttle response will suffer as a result of the extra volume.

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couldn't you account for this by using a smaller diameter pipe?

V8SHME8 said:

Basic physics will tell you that heat will add velocity so mounting the turbos further away from the heads will reduce heat available to the turbos. Therefore inhibiting the ability to spool the turbos.

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how does heat spin the turbines? isn't it the exhaust pressure

V8SHME8 said:

The oiling concerns are absolutely a fact. The drain on the turbos can not be gravity induced since the turbos are on the bottom of the car. You will need to suck the oil out as well as feed them.

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well, like sts and greenmustang gt, they use separate pumps i believe

i mean, these are just opinions, i'm really not attacking... just information seeking


i see a TON of advantages: underhood temps, accessories, smog legality and ease of installation and removal.. i dunno, i'm sure there's more

or you could use a venturi system to keep the air moving at the right density all the way up to the intercooler. but i don't see why you would need an intercooler with that much plumbing.. Oh maybe to collect all the air befor releaing it to the intake side, LOL just very curious how it will work and maybe Greenmachine will prove us all wrong..

donjohn said:

couldn't you account for this by using a smaller diameter pipe?

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You could use a smaller pipe, but that is a band-aid for the problem. Using 2 inch piping will reduce the number to 288 cubic inches. I used 2.5 as an example because that is what I used for my charge piping and the great availability for mandrel bends. Keep in mind that this value is just the volume you need to fill before you can even begin to fill the standard charge piping that you still have under the hood. Flat out, mounting the turbos further away will result in pressure drop and loss of velocity because of the extra volume.

donjohn said:

how does heat spin the turbines? isn't it the exhaust pressure

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Hot air moves faster than cold air because the molecules are excited and have additional energy.

donjohn said:

well, like sts and greenmustang gt, they use separate pumps i believe

i mean, these are just opinions, i'm really not attacking... just information seeking

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That is the solution, but it you are adding complexity and the old addage keep it simple stupid always applies. The weight factor is a major concern as well.

donjohn said:

i see a TON of advantages: under hood temps, accessories, smog legality and ease of installation and removal.. i dunno, i'm sure there's more

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I am not sure how it is any less difficult to remove since you will have all the piping under the hood in addition to the miles of piping under the car. You have more clamps that will require servicing, and a remove reservoir and pumps to deal with. Mounting the turbos after the cats will not make the setup any more legal than mounting them under then hood and maintaining all the original smog equipment. You could easily design a setup that allows for all the accessories. Take a look at all the kits on turbomustangs.com and you will find some that maintain all the power accessories.

The point is that mounting the turbos way back there is not ideal. I would not spend my money for the extra hassle when I could do it the right way for probably less effort.

i have never been into forced induction, but aren't there guys running rear mounted intercoolers off of centrifigal s/c's? most of the ones i see are on drag cars where they don't really worry about throttle response, but just a thought.

Well, right off the bat what works for a drag car is not always what works for a street car as well you know. I assume you are refering to the liquid intercoolers that sit behind the dash.

There are a couple of issues when trying to compare the two setups in quesion. Drag guys never worry about throttle response because they are never faced with an off throttle situation. The actually do not have that much piping because they usually run a intake manifold that faces back so there is really not that much piping. Plus lag is not really an issue with superchargers. Those drag guys generally have larger motors also.

V8SHME8 said:

The point is that mounting the turbos way back there is not ideal. I would not spend my money for the extra hassle when I could do it the right way for probably less effort.

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You're thinking is alot different than many guys on here. Me for example .... if I knew it could be done .... I would not care about the extra hassle/effort, especially if I ended up spending less money that way. The "extra effort/hassle" you refer to is what gives me pride in my car during my downtime, lol. I like to reflect on all the challenges I've had .... it's makes the car more .... sentimental, if you will.

91LX_5L said:

I thought of this a while back and now see that GreenMustangGt is doing it. Great idea bud glad to see someone stepped forward and started this project.

Anyways Im wondering what the downside to the rear mount turbo setup is. Do you not make as much power as a normal turbo running off the headers in the engine bay? What are some downfalls of this style of setup?

Anyone have any articles on it? There was one on a Fbody I saw in a magazine, wish I bought that mag.

Thanks

Click to expand...

STS make that kit for the f-body.. I think its http://www.ststurbo.com/

I saw a LS1 trans am with a rear turbo kit and when it down shifted to 3 it got its ass did a little dance

wow, where do I begin??

I have been building and designing turbo systems professionally for many, many years.

Rear mounted turbo's are not any cheeper when done correctly than a proper turbo setup. Everyone keeps saying that if its cheeper they can live with the differences, well, fine then, I highly doubt that you will save more than a few hundred dollars

as for spooling, a turbo recieves most of its energy from heated exhaust, the hotter it is the faster it will spool (some extremes require exotic impellers, like inconel)

Now when it comes to underhood heat, that always is misunderstood. Turbo's often dont raise the underhood temperature much if they are designed correctly. Iron glows red hot at a very low temperature. If you had cast Iron manifolds on your car even without a turbo, under the same conditions that the turbo glows, your manifolds sans turbo's would glow as well. The turbo's dont have magic ovens in them that make more heat, they just use the existing heat to you advantage.

All turbo kits I have built and designed use turbo's with both liquid and oil cooled center sections. This, believe it or not will decrease the center sections temperature by an average amount of 200degrees.

I may ruffle a few feathers, but most of the turbo manufacturers, and builders in the industry have standing jokes about the rear setups.

I have been at dyno testing with a trans-am with a normal turbo kit, and a rear mounted kit, and if I remember correctly the rear mounted turbo ls1 made a little over 400whp, while the standard mounted turbo ls1 made hp numbers in the upper 500whp, These were both off of the same boost settings. Granted there are many other circumstances that could have played a role in this difference, and most likely comprised in the majority of the peak HP variance. When looking at the two cars, and when the power came on, it was incredibly obvious that the standard car spooled waaaaaaaaaaaayyyy sooner than the rear mounted car.

On the website where the car downshifts into third and the raear gets a littly squirelly, well of course, if he was in a higher gear he was able to build boost, and then downshift with that positive boost to his advantage. Any forced induction car could do that...

I am just stating my opinions based off of my own personal experiance. do not take what I have to say, and make your decision based solely off of that, but also do not look at price and base your decision solely off of that either. You bought a Mustang not a Geo Metro!!!!which was cheeper??

If you cant afford this hobby, I hear that model boats arent too expensive. haha j/k

Plain and simple.. Let the guy build it, if he is pleased with the results, then is that not a success? Sure the rear mounted setups are not optimal when compared to a standard single or twin setup, but they do make power.

That being said, the Kits I build are all standard 4-1 custom headers, with a crossover to merge into a single T4 flange. This has been proven to work, and work well, IMO. By no means am I doubting the builders idea, and plan.

I give people like him credit for ACTUALLY attempting this, insted of constantly debating over why it will not work , and how un efficient it is, lol