Single Turbo RX-7's Questions about all aspects of single turbo setups.

Throttle body before turbo?

Old 01-26-07, 04:42 PM
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Well, we can agree to disagree, because I do not see any performance benefit of having a throttle body before your turbo. You will get the best modulation when the throttle body is closest to the engine, and putting a throttle body in front of the compressor inlet will cause you to fail a turbo for a couple reasons among many. You will cause a large vacuum resulting in probably compressor fin failure, due to the fins wanting to be pulling away from the turbo, and you will cause a huge vacuum underneath the compressor wheel, causing oil to be pulled out from the center housing. I would like to see some proof of F1 engines using a throttle body before the turbo, and why they do it.

Originally Posted by rotarygod
Installing a turbo after a throttlebody is no worse for it than installing a turbo after a carb and we know that's been done on countless ocassions. The issues they had were with certain turbo seals which weren't designed to have gasoline fow through them.

Having a throttle plate close off before a turbo doesn't cause a turbo to surge. Surge is when you have a turbo that is trying to supply more air than can be ingested after it. It's flow rate is too great for the application required of it. When you close off the supply of air to the turbo, it isn't surging as there is no air (very little) for it to move and the amount that can be taken after it at this point is definitely greater than what it is flowing. Spinning a turbo in a vacuum isn't going to hurt it and it is slowing down anyways since airflow to the engine has decreased. I'm sure the old F1 engines used the turbo after the throttlebody or packaging reasons. Those engines revved up over 11,000 rpm back then and those cars generally have a high, narrow powerband so due to high intake air velocity in the system at high rpms, throttle response was probably a moot point for them. If a throttlebody before a turbo led to a turbo's premature death, you'd think such an advanced racing series such as F1 wouldn't have used them.
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Old 01-26-07, 05:29 PM
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Originally Posted by CarbonR1
Well, we can agree to disagree, because I do not see any performance benefit of having a throttle body before your turbo. You will get the best modulation when the throttle body is closest to the engine, and putting a throttle body in front of the compressor inlet will cause you to fail a turbo for a couple reasons among many. You will cause a large vacuum resulting in probably compressor fin failure, due to the fins wanting to be pulling away from the turbo, and you will cause a huge vacuum underneath the compressor wheel, causing oil to be pulled out from the center housing. I would like to see some proof of F1 engines using a throttle body before the turbo, and why they do it.

http://www.gurneyflap.com/Resources/DSC06079.jpg

if you look at the pic i posted on the frist page, thats a throttle body on the front of the turbo.

reliability might not be important for the F1 guys, the cars dont have to go very far (relatively) and when the throttle is open most of the time....
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Old 01-26-07, 05:32 PM
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If you follow the progression of the engines on that site it appears that the TB before the turbo was an early idea. Both BMW and Ferrari used it. Ferrari later switched to TBs after the turbo.

We're talking 1980s technology here. Is it possible the TBs were placed before the turbo to specifically combat surge before the BOV was invented? The BOV came along as a direct result of wanting to place the TBs after the turbo?

Also, one of the most interesting things I got from that site was one of the manufacturers specifying their fuel as 80% tolulene! Wonder what the octane rating of that stuff is?
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Old 01-26-07, 05:49 PM
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What are we agreeing to disagree on? I've never said I see a performance benefit from using one before the turbo. I have merely answered the original question. Can you have a throttlebody before a turbo? Yes you can! That's an answer completely devoid of opinion as to whether I personally would or not.

Your logic for compressor failure sounds suspect to me. You say that you think vacuum will cause oil to leak. Yes this can happen if you don't use a carbon seal on the compressor. If you have a dynamic seal, it will not work! Diesel turbos do have a carbon seal! A throttle plate before a turbo has been done before. Lots of times! Tons of times! It was probably the first way a turbo was ever used! Think draw through carbs. There are no records of turbine blades flying off as a result. You can get a turbo built with seals anticipating such a usage.

If you think a small turbo can spin at well over 100,000 rpm and be fine and yet decreasing the pressure due to a closed throttle plate while a turbo is spooling down will cause it to self destruct, I'd sure like to see some proof of this. It's not going to happen.

You want to see proof F1 used them? Did you not see the link on the first page. There's a picture of one right there!!!

Here's a link to installing a carbon seal on a turbo. Please note the terminology that say "draw through". That is any instance where the carb or throttle plate is before the turbo. Most draw through setups were carburated but that is really nothing more than a throttlebody that also has a mechanical fuel metering device built into it. The vacuum loads would be the same.

http://www.smbaker.com/rail/ihirhb5.html
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Old 01-26-07, 05:52 PM
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Originally Posted by Hyper4mance2k
900bhp @3.8 bar in 1987 on a 4 banger. Awesome! I wish I was old enough to fully appreciate the turbo days of F1
A 1.5 liter 4 banger at that! After seeing that, a 400 hp Evo or even a built Honda engine of larger displacement with half of that power suddenly sounds trivial!
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Old 01-27-07, 02:35 AM
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The BMW engines ran a BOV

with the throttle body before the turbo

Honda who dominated F1 in 86, 87, and 88 ran a V6 1.5L twin turbo that made 650bhp @12,500 rpm on 2.5 bar. Honda ran the TB after the turbos. To answer that other question toulene is 110 octane if I remember correctly.

Last edited by Hyper4mance2k; 01-27-07 at 02:47 AM.
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Old 01-28-07, 09:43 PM
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That looks like a pop off valve which protects from overboost situations.
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Old 01-29-07, 01:11 AM
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Originally Posted by rotarygod
That looks like a pop off valve which protects from overboost situations.
You are correct that is a "pop off" valve and not a blow off. F1 never used a blowoff valve. Here is another example of a draw through. And the other picture is a 13b Street ported with twin T04 turbo's and with throttle bodies before the turbos 32 psi boost and about 900+bhp Methanol Mechanical Injection.
Attached Thumbnails Throttle body before turbo?-f-12%2520308%2520engine.jpg   Throttle body before turbo?-grantwilliams.jpg  
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Old 01-29-07, 01:15 AM
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Yea I think you're right. after looking at the other pictures that vaccume line doesn't look like it's clearly going to it.
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Old 01-29-07, 09:31 PM
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The Cosworth V8 single turbo engines used in CART use the same setup , a throttle body before the turbo and "normal" throttles on the motor , I have a book with an article that states that the before turbo TB is used for BOOST CONTROL ! , because the motors rev soo high and flow soo much air it is somewhat difficult to control the boost levels in the conventional way , hence the Tb and the pop off valve .
As for surge it is a phenomenon that can occur with all centrifugal compressors , it is the REVERSAL OF FLOW through the compressor ! I am a senior production supervisor on a 1500MTpd methanol producing facility , we utalize multiple giant sized compressors , with multiple stages (impellers) to get the process gas flowing through the plant .On each machine there is a valve called an ANTISURGE valve that is used to route some of the compressors discharge flow back to its suction in order to maintain the MINIMUM flow requirement of each machine , these valves are electronically controlled , when you think about it a BOV IS actually a miniture antisurge valve , they open to maintain the compressors forward flow by routing its discharge back to its suction ......the atmosphere .
If you completely close off the suction to ANY compressor it will surge ! , when you do so the volume of air that it has just compressed and pushed down the intake pipe , will now be at a higher pressure than the vacuum in the compressors suction , so it will reverse its flow and head back to it as we know , "nature abhores a vacuum" when it gets to the suction the pressure there will now be higher than the discharge of the compressor and flow reversal will happen again ! these oscillations occur multiple times per second ! every time it happens the compressor is loaded and unloaded ,eventually causing failure in the form of broken shafts , failed thrust bearings (as the thrust load increases to a rew times more than normal )and damaged wheels.
Most before compressor TB's WILL have a "minimum Stop" position that is physcically set via an adjustable screw (or something of the sort) , this opening will be enough to supply the turbo with enough air to eliminate or minimize the occurance of an extreme vaccum condition at its suction when the TB is "closed".
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Old 01-30-07, 01:32 PM
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Good stuff!
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Old 01-31-07, 12:36 AM
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Originally Posted by Marcel Burkett
The Cosworth V8 single turbo engines used in CART use the same setup , a throttle body before the turbo and "normal" throttles on the motor , I have a book with an article that states that the before turbo TB is used for BOOST CONTROL ! , because the motors rev soo high and flow soo much air it is somewhat difficult to control the boost levels in the conventional way , hence the Tb and the pop off valve .
As for surge it is a phenomenon that can occur with all centrifugal compressors , it is the REVERSAL OF FLOW through the compressor ! I am a senior production supervisor on a 1500MTpd methanol producing facility , we utalize multiple giant sized compressors , with multiple stages (impellers) to get the process gas flowing through the plant .On each machine there is a valve called an ANTISURGE valve that is used to route some of the compressors discharge flow back to its suction in order to maintain the MINIMUM flow requirement of each machine , these valves are electronically controlled , when you think about it a BOV IS actually a miniture antisurge valve , they open to maintain the compressors forward flow by routing its discharge back to its suction ......the atmosphere .
If you completely close off the suction to ANY compressor it will surge ! , when you do so the volume of air that it has just compressed and pushed down the intake pipe , will now be at a higher pressure than the vacuum in the compressors suction , so it will reverse its flow and head back to it as we know , "nature abhores a vacuum" when it gets to the suction the pressure there will now be higher than the discharge of the compressor and flow reversal will happen again ! these oscillations occur multiple times per second ! every time it happens the compressor is loaded and unloaded ,eventually causing failure in the form of broken shafts , failed thrust bearings (as the thrust load increases to a rew times more than normal )and damaged wheels.
Most before compressor TB's WILL have a "minimum Stop" position that is physcically set via an adjustable screw (or something of the sort) , this opening will be enough to supply the turbo with enough air to eliminate or minimize the occurance of an extreme vaccum condition at its suction when the TB is "closed".
Good info. Never thought about it all that way before.
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Old 01-31-07, 09:33 AM
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So, my overly complicated twin eTB idea can be made to work, it just would be unnecessary in the face of modern technology and relatively low air flow levels (compared to F1 engines of the 80's).
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Old 07-05-15, 03:02 PM
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That anti-lag pre-turbo butterfly in the picture above is called DPV (Dispositif Pre*rotation Variable - Variable Pre-rotation Device) and was devised and used first by the French guy Jean-Pierre Boudy in the early 80-ies.
The real throttle bodies are after the turbo.

Here:
Quote:
This was first used at the Monaco GP in 1982, and developments of the same system are still used in Formula One. But because Boudy defected to Peugeot with his ideas, the 205T16 was the first turbocharged rally car to use his system (The T16 being out before the final evolution R5 Turbo – The Maxi 5 Turbo). Which Renault calls DPV, or Dispositif Pre*rotation Variable (Variable Pre-rotation Device).

"At the very beginning we had made the decision to use it on the Group B R5 Turbo. It's not really necessary for road cars and a little expensive for them, but it's not so complicated". It may not be "so complicated" but the DPV system is an 'extremely effective way of ensuring near-instantaneous throttle response from a competition turbocharged engine’. The system provides for variable air areas and direction angles at the intake to the compressor wheel in advance of the rotation period during which the compressor turbine will require those conditions.

It's not a by-pass system, it's essentially a multi-variable nozzle arrangement which is mechanically linked to the throttle and which changes the direction and area of air which hits the compressor wheel according to throttle position. The rate of change of air flow area and direction is not exactly linear, but it's progressive and always increasing toward full flow at maximum compressor wheel speed.

This irregular mid-compressor-speed flow, which constantly changes the way the air hits the compressor vanes in the mid-range, improves the compressor's efficiency under part-load, because it is arranged so that the turbine will idle at a higher speed than it would given a fixed intake air direction and area. And of course, the higher the compressor idle speed, the shorter the time it will take to reach its important operating RPM. Result: less lag.

The DPV is inoperative at each end of the turbine's speed range. Under pedal-to-the metal full boost conditions it has no effect because there's regular full flow to the compressor, and with the throttle closed the DPV is shut down as well. But it is not just retained inertia and completely eradicated turbocharger lag which form the real benefit of the DPV system, because there's another major advantage in that as a result of there being no by-pass or blow-off to atmosphere, and because it's an internal function to the turbocharging system, there is no pressure wastage in the all*important part-load condition (ie. The blades don't stall during gear changes, or on/off throttle movements).


And here is Boudy's patent. You can see the diagram inside how the pre-turbo anti-lag device is linked to the post turbo throttle bodies:

Device for regulating the air supply of an internal combustion engine
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Old 08-24-15, 05:57 PM
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Never did I think I would log back on and find an 8 year old post was brought back, and actually have good information in it.
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Old 08-24-15, 06:43 PM
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If you are wondering how/why they manage this bit-
"which changes the direction and area of air which hits the compressor wheel according to throttle position"

It is to pre-swirl the inlet air to aid in compressor efficiency.

https://www.rx7club.com/single-turbo...26%25-1062575/

The device looks like the unison ring, foils and actuator on a Ford 6.0 variable turbine exhaust side in its most complex/effective form or a slanted throttle body blade in its simplest form.

Some of the pre-swirl effect (without the variable volume component) can be had with just a bend right at the turbo inlet if you are wondering why so many OEMs seem to do that.
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