Hmm...throttle in front of turbo?

beepbeep · 07-28-2002, 04:04 PM

Question is mildly off topic ...altough principle is generic and valid (?) for any turbocharged engine

Now to the question...

Take a look at this turbo-era F1 engine:

http://www.san-tec.de/m-power/mpower4.jpg

What startled me is a presence of throttle in front of compressor. I wonder if this throttle is in some way synchronized with eventual second throttle in the intake?? I mean, this way you wouldn't need any dump valve....when intake-throttle shuts down, the one in front of turbo shuts too, making it hard for turbo to build up exessive pressure in the intercooler (which would happends if dump valve wasn't present)

Engine was pretty potent lump, doing over 1000 hp in qualifying trim...not bad from a 1.5L four banger, eh?

P.S. Engine is for sale, btw.

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=1752656897)

rattlsnak · rattlsnak's Garage

Actually 90% of all turbo engines are this way, including Porsches.. like 944's etc. Most have other piping where the actual throttle valve is further upstream, but is still ahead of the turbo. The 930 differs, but it does have the CIS sensor plate before it. The newer turbos, 3.6 etc, are like the photo. The wastegate is still needed because it needs to bleed off pressure to keep from overboosting just like any other turbo. The dump valve is older technology that ended when the C2Turbos came out.

beepbeep · 07-29-2002, 12:22 AM

Errr...no offence, but i don't think you understand my question.

Dump valve and wastegate are different things.

This engine has a wastegate, every turbocharged engine ha a wastegate. If you take a look at the picture one more time you can see biggish wastegate connected to headers, and blowing out trough smaller pipe. That is not the issue.

The issue is "why does it have throtle before turbo". No other engine has it that way. Not even your C2Tubo....take a look underneath the lid and you'll see that throttle is on your intake and that your car indeed has both wastegate and dump-valve.(but dump valves is redesigned compared to 930's)

Dump-valve , or recirculating dump valve that is used on most engines , is there to relieve pressure-shock when throttle shuts and turbo is still spinning , pumping air into closed throttle and intercooler assembly.

Cheers!

rfng · 02:09 AM

I don't know if there was a second throttle body, but in the old days, there were two different types of turbo engine, blow through or suck through.

With the main difference is the power delivery from what I understood. A blow through system has a tendency to be a more violent power band either on or off, while the suck through system delivered a more linear power band, closer to a normally aspirated powerplant.

bell · bell's Garage

my early T-1 turbo dodgo omni originally had a setup like you describe. the intake tract was this sequence.......air filter, throttle body, turbo, then into the head. dodge guys refer to this as a "suck through" setup since the air gets sucked through the throttle body. the downfall with this setup is to be able to intercool you need to change manifolds and electronics (intake charge will be a higher temp going through the throttle body).

however.....the bmw engine is a "blow through" setup, there is a vital piece missin, the intake tube from the turbo to the intake, this is a standard turbo setup with an external wastegate.

beepbeep · 07-29-2002, 09:11 AM

Quote:

the bmw engine is a "blow through" setup, there is a vital piece missin, the intake tube from the turbo to the intake, this is a standard turbo setup with an external wastegate.

Yeah, that piece is missing but there is still a throttle in the front of turbo...and wastegate don't have anything to do with this , all turbocharged engines have wastegate..."blow"-trough or "suck"-trough

RarlyL8 · RarlyL8's Garage

You seem to be having a bit of a problem getting folks to understand your question.

Simply put, with everything else the same, what difference would it make having the throttle positioned before the turbo vs after?

I'm not as knowledgeable on turbos as you, but I would think that chopping the fuel on a setup running the throttle before the turbo would cause surging and lag. Of course both of these situations can be eliminated with bipass valves.

Probably a more important effect would involve the throttles placement further away from the intake valves. This alone would induce lag and hinder overal responsiveness of the engine.

carnut169 · carnut169's Garage

I don't know the answer to your question, but wouldn't that be fun in a 2002!

beepbeep · 07-29-2002, 11:28 AM

Hmm...im really startled by this approach. Let's not forget that these engines used up to 5 bar boost, which probably surfaced some completly new problems (how good is dump-valve operating at 5-bar boost?)

Hmm...it might be so easy that they just used "suck-trough" approach beacuse of some reason and just didn't use dump valve at all! :-)

there are many ways to skin a cat ...

Guess only way is to ask someone in BMW engine department... Anyone knows Paul Rosche's e-mail adress??

WydRyd · 07-29-2002, 09:29 PM

They put it in front of the compressor to eliminate backward surging.

Imagine, on a 930 running 0.8bar, then the throttle plate closes - it will create a reverse boost spike/surge of approx 1.6bar!

Imagine on an F1 engine that runs 4.0-5.0bar! The surge would be so great (x2), so they use these to eliminate surges.

P.S: talk about POOR throttle response tho

beepbeep · 07-30-2002, 02:03 AM

Quote:

Imagine on an F1 engine that runs 4.0-5.0bar! The surge would be so great (x2), so they use these to eliminate surges

Yepp, but that's why we have dump-vavles (not to mix with wastegate) Hmm...why didn't they use them like all other people?? Boost was maybe so high that dump valves couldn't relieve pressure quick enough??

bell · bell's Garage

Quote:

Originally posted by beepbeep

Yeah, that piece is missing but there is still a throttle in the front of turbo...and wastegate don't have anything to do with this , all turbocharged engines have wastegate..."blow"-trough or "suck"-trough

where do you see the second intake, i see the one on the turbo, where is the other? i know the wastegates are on every turbo being i've owned and built 4 of them, do you have any more pics of this engine? it's kind of hard to tell you what were looking at when we can only see half of the setup. (the intake manifold is on the other side)