Ok I know this probably sounds retarded, but why hasn't anyone put a TB before the turbo? I'm sure there is a good reason out there somewhere, but I have no idea what it would be.

 

im sure that the lack of air will likely kill a turbo like surging will kill it.

 

no....why would you want to do that?

Can you explain what you are thinking about/what benefit a TB would have there?

 

It has been done before. As with anything there are advantages and disadvantages to every setup. This is no exception. A disadvantage of this is that the farther away from the engine the throttlebody is, the worse the throttle response. However we have seen carbs before turbos and obviously superchargers. The longer your intercooler piping (if you have one), the farther away from your engine the throttle plate gets and the more of a delay you have in throttle response. Remember that after a throttle plate the pressure is much lower than in front of it. This means there is less air in the system after the throttle plate and hence a vacuum. The farther away from the engine the tb is, the more area has to be filled back up with air which slows down response. Just think about longer piping in regards to turbo lag. Similar phenomenon.

Having a throttle body before a turbo does away with the need for a blow off valve. A bov is designed to relieve the high pressure after a turbo that backs up when a throttle plate closes off suddenly after it. With a throttle plate before the turbo you are merely cutting off the air supply to the turbo and nothing backs up after it.

If you have a system that has no intercooler or a small one with minimal piping distance, a tb in front of the turbo may work just fine. It's been done before on many occasions. Everything is a tradeoff though so weigh the pros and cons of each before you decide to go this route.

 

So this would be only good for possibly a drag car perhaps where you just mash the throttle constantly?
I just figured it would provide perhaps better airflow, i never really thought about throttle response though.

 

You are most likely not going to get into a situation where you will ever consider a throttle plate before a turbo. There's really no reason to anymore but it can be done. If this were an engine that didn't rely on throttle response such as a stationary power generator, it wouldn't really matter much. There are people that look back to WWII to the P51 Mustang and point out that it had a rear mounted turbo and a long induction system but then conveniently forget that they usually ran them at a pretty constant rpm. I'd just leave a conventional setup with the tb after the intercooler as normal if I were you. There is more than one way to do everything though.

 

Not so much. I've owned a couple diesels that loved to stall the turbo under drop throttle situations and they don't have a throttle body in sight.

 

we were just looking at pics of the bmw turbo F1 engines last night, and they seem to have a throttle body mounted on the turbo AND throttles on the engines....

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

http://www.gurneyflap.com/bmwturbof1engine.html

 

Oh, that's good stuff!

 

First of all diesels don't have throttlebodies so there is nothing to stop flow to them. With a throttlebody in front of the turbo, when you suddenly close the throttle, you are basically free spinning the turbo for a moment in a vacuum. This doesn't really take any energy and the turbo is no longer moving any air. It can't move what isn't there. Spinning in a vacuum is easier than spinning in a pressurized environment. I suspect the diesel issues you had were not what you think they were.

 

I only see 1 throttlebody. I see a mechanical linkage going from the tb to the mechanical fuel injection on the intake runners though.

 

Good point. Hadn't thought of that.




It's surge. Happens a lot on Cummins engines with big turbos. Broken shafts are common on the small shaft HX40s. BD sells a kit that's adapted a Tial BOV to be electrically actuated by a throttle switch and the vacuum pump.

 

werd^^^

i have heavy fueling 12 valve, and i grenaded the stock HX35 letting off the throttle instantly under full load at 40psi. ......... tis to say it didnt sound healthy

 

Did you have an exhaust brake? I could see this happening then as you are suddenly shutting down air from leaving the engine which will in turn back up to the turbo. It's basically a throttlebody in the exhaust which is still after the turbo. I could see a need for a blow off valve then. If this is without an exhaust brake then it is just interesting and I'll have to study that one for a bit.

 

With the turbo under hard spool and the engine revs are cut, the air will be backed up from the engine to the still spooled turbo..... it can be seen as a small spike on a boost guage

Stalling is very prominent on the stock HX35 because of the large comp. wheel to the small turbine wheel ratio

enhanced also because of the higher pressure ratios involved as well

 

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

 

No exhaust brake. It's never made sense to me either. Without a throttle plate in the system you'd think it couldn't surge. But they do. Sorry to have brought it up. After you pointed out how the pre-turbo TB actually worked the diesel part is now OT.

 

So, what if you mounted 2 throttle bodies, one in the normal position off of the IM and the second TB just ahead of the turbo? The 2 TBs would have to be linked, and I could imagine that a properly programmed e-TB could probably be used to prevent surge without a WG while minimizing the lag associated with having the TB ahead of the turbo. Perhaps it could be programmed to stay open at all times except when manifold pressure spikes suddenly, as associated with surge, or even just when the driver lets off the throttle suddenly. Perhaps I am overengineering an unnecessary solution for a problem that has already been solved with existing techinques, but hey, that's what I do.

 

Putting a throttle body before the turbo is a bad idea. It would destroy your turbo in a heartbeat.

 

yeah that makes sense

 

rice racing knows a lot about them, other than that, info seems kinda hard to find

 

please explain why you think it will distroy the turbo.

i really do not like the idea just because you are sacrificing throttle response along with some other things, in most situations, for the lack of a BOV, which just doesnt make sense to me. hell you dont technically need a bov and some people think they are useless but that is a whole other argument.

 

lol just use a BOV and one, or more, after-turbo TB(s)!!! your idea is cool, crazy and completely useless , but i like it.

 

lol, thanks! If I had the interest in the schooling required, I would love to be an automotive engineer. That way, I could get a job with an automaker or tuning shop and get to fiddle around with these ideas I get. Personally, I do like having a BOV myself (I mean, c'mon, when you hear that pssssh, you look around for the ricer who actually graduated beyond the fart-can, springs, and ugly wheels), but I was just trying to add to the original poster's idea.

 

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.