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CIS turbo-THROTTLE BEFORE OR AFTER?
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BIMMERBOY  
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PostPosted: Wed Aug 22, 2001 6:31 am    Post subject: Reply with quote

Please help me with my BMW/VW/PORSCHE monster
it's a BMW motor with an aftermarket turbo.Ect..Ect.. ect.. My question is this: I am using the Bosch CIS system from a 928 v8 with two injectors per cylinder(where would you ever get injectors that flowed enough for 2>1 per cylinder? volvo racing maby)The fuel distributor has the throttle mounted before the metering plate. This makes intake vaccume and the pressure in the turbo the same. That would eliminate the need for a BOV. Would the constant vaccume on the turbo reduce the spool up time or have any other benifits? Why use throttle before/after. I hope you porsche people can help me with this simple/complex question.

PS the tranny is porsche too.
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Rick MacLaren  
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PostPosted: Wed Aug 22, 2001 10:24 pm    Post subject: Reply with quote

Have you considered Chevy injectors?
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Rick MacLaren  
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PostPosted: Wed Aug 22, 2001 10:25 pm    Post subject: Reply with quote

...just yankin' yer chain...heh heh.
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Rick MacLaren  
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PostPosted: Wed Aug 22, 2001 10:30 pm    Post subject: Reply with quote

Say, just a question...when you eat your food, do you, like, take a fork and smush it into your mashed potatos and mix it all around with your roast beef and veggies until the whole thing looks like a big potato beef veggie soup?



I'm killing myself here!
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924RACR  



Joined: 29 Jul 2001
Posts: 8063
Location: Royal Oak, MI, USA

PostPosted: Thu Aug 23, 2001 12:02 am    Post subject: Reply with quote

Rick, you're such a tool...

I'm a little unclear on the BOV function, is it the same purpose as a CBV? If so, I don't think the throttle placement would prevent the need for a CBV/BOV...

Your best bet is to get a copy of Corky Bell's book Maximum Boost... check out our link (above) to the 924.org Tech Section, and look under the Turbo section, there's a pic of the book cover and a link to the publisher... it's an excellent book on designing your own turbo... I used to have a copy, gave it away to a friend with a 951, then got my own turbo... LOL

_________________
Vaughan Scott
Webmeister
'79 924 #77 ITB racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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BIMMERBOY  
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PostPosted: Thu Aug 23, 2001 3:21 am    Post subject: Reply with quote

Actually, when I eat I tend to keep things very seperate. In this case however it has been a question of what was the most economical(read cheapest) way to get proformence. A BOV equalizes pressure before and behind the impeller preventing the impeller from making 140psi between it and the throttle. I am no expert but it seems like having the whole system under vaccume would allow the impeller/rotor to operate more efficinetly i.e. at a higher rpm more of the time thus reducing spool. There would be no way for the turbo to build damaging boost. One major problem i see with the idea, seeing as the intake system will be custom made is that piping,turbo,intercooler,metering plate and tubing will have to deal with high vaccume and high pressure. Got some real advice there Rick? I would like full porsche but that wouldn't be much of a sleeper would it.
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Rick MacLaren  
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PostPosted: Thu Aug 23, 2001 4:02 am    Post subject: Reply with quote

I respect that you're building the system piece by piece and learning about the engineering needed to make the thing sing.

I am very surprised that you don't smush up your food into a soup and then eat it all. I had you pinned as a guy that would sprinkle crushed Oreo cookies on ham.

Caveat 1: My approach would be completely different. I'd try to 'imitate' what has been done before and only get creative on small, doable pieces. It looks like you're trying to do one heck of a large refit of your system, and frankly I tend to avoid reinventing the wheel whenever possible. I'm not being critical, I'm just saying that unless you're an automotive engineer or nearly one, it's a tough discipline to learn. And since we might not have the same strategy, I don't know how helpful I can be on tactics.

Caveat 2: I'm not sure exactly what you are asking...maybe you can put it into one question for us.

Here is what I can say, for what it's worth:

If the problem is only high vaccuum and high pressure, then I'd pull an intake system off a Grand National and cut and paste to make it fit - or rebuild from scratch using materials that can handle the pressure. That's a no brainer. Increase in pressures calls for increase in material strength. Simple.

I think a blow off valve is the only thing that's gonna give you the right pressure balance before and after the turbo - it's there to reduce spool up time. But I do not believe it does it through vaccuum, rather, I think it does so by equalizing the pressure, not by making it a vaccuum.

Throttle placement should be after the turbo, as I understand the system, because ONLY the throttle can control pressure at the valves, and if it were located before the turbo then the pressure in the system wouldn't hurt the intake per se, but it might mess up the air pressure balances needed between the plenum and the valves during times just before and after the throttle opens and closes.

As I said, if you can sort of just focus the question a tad I can try to narrow down something more concrete. As far as the turbo goes, and intake, and body shell, two questions apply: What have you got? And what do you want?

It sounds like you're doing a big overhaul here. Good luck with it!

_________________
1980 Porsche 931 C2H5OH/H2O injected 15 PSI
1979 Porsche 924

[ This Message was edited by: Rick MacLaren on 2001-08-23 04:10 ]
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BIMMERBOY  
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PostPosted: Thu Aug 23, 2001 4:52 am    Post subject: Reply with quote

OK,OK. LET ME DRAW THE SYSTEM

====
XXXX <----- air filter
=||=
||
[/]# <------ Throttle Body
||
/__~~} <--------- CIS meter
/VV
|| /-------Intercooler
\ V __
\ _____/TTTTTTTT____/ \
/^/N____HHHHHHHHH _____/Uu <-- Int. Man.
{ O / ZZZZZZZZ/ ^ ^^^
_/ <-
_____Turbo --normal TB place




As you can see the TB is before the rest of the system, as on a 928. The intercooler, you may note is from a 944, is in the middle. The system would not require a BOV because there is no way to build boost in front of the turbo, any boost would be "eaten" by the engine. When you closed the throttle the whole system would experience vaccume. The turbo would be more "efficient" because the impeller would have less resistance; it would spin in 1/5 atmosphere. Problems that seem clear to me:
1)How would the CIS be affected.
2)How will this affect the behavior of the maifold/resonance.
3)Will I have to fix intake leaks all the time because my homemade intake piping connections will work themselves loose.

Remember this was Dr. Porsche's idea not mine. The 928 v8 came stock this way in 78. Obviously the volume of air in the system will kill my throttle response, but it's a giant turbo anyway throttle response is going to be shoddy!
Damn that's a neat drawing. You should tell people to look at it as it illustrates the question at hand.
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BIMMERBOY  
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PostPosted: Thu Aug 23, 2001 4:53 am    Post subject: Reply with quote

Ouch! it got messed up! let me put that up again!
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BIMMERBOY  
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PostPosted: Thu Aug 23, 2001 4:57 am    Post subject: Reply with quote


====
XXXX <----- air filter
||==
||
[/]#<------ Throttle Body
|
/__~~}<--------- CIS meter
/VV
| / /-------Intercooler
\ V __
\ _____/TTTTTTTT____/ \
/^/N____HHHHHHHHH _____/Uu <-- Int. Man.
{ O / ZZZZZZZZ/ ^ ^^^
_/ <-
......._____Turbo --normal TB place
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BIMMERBOY  
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PostPosted: Thu Aug 23, 2001 4:59 am    Post subject: Reply with quote

well darn. Anyway. It is all there

Filter
TB (new placement)
CIS
TURBO
INTERCOOLER
(normal place for TB)
MANIFOLD
ENGINE
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Rick MacLaren  
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PostPosted: Thu Aug 23, 2001 5:19 am    Post subject: Reply with quote

The first two diagrams show the intercooler before the turbo, and the third diagram shows the turbo before the intercooler. Which is it? A turbo burns hot...so after you cool the air with the intercooler you're gonna heat it up with the turbo? Maybe that won't matter much. But I'd think it'd be more sensible to have the intercooler after the turbo, again, in keeping with not reinventing the wheel.

Porsche used this exact system with the turbo and all? Wow.

_________________
1980 Porsche 931 C2H5OH/H2O injected 15 PSI
1979 Porsche 924

[ This Message was edited by: Rick MacLaren on 2001-08-23 04:21 ]
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BIMMERBOY  
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PostPosted: Thu Aug 23, 2001 6:12 am    Post subject: Reply with quote

Ok ok. The 928(noturbo)v8 bosch CIS had the TB before the metering plate of the CIS. All other CIS cars I have seen had the TB after on the manifold. Race cars that i have heard of with large turbos have two throttles one before the turbo and one on the manifold. Either in progressive with the manifold throttle opening first then the preturbo or with one of the two servo controled. This was done to control boost surging during throttle closure in those 2liter 1500HP kinetic fireballs(with every hour my research progresses!).
I could try to make my own progressive double throttle setup , but a simpler system appeals. The book you mentioned is on my reading list, excelent and universally praised. I need a CIS expert!

Rick- You mention that you are using liquid dihidrogen monoxide injection. Do you inject it preturbo, pre intercooler, or on the TB? How much more boost can you run with it? Using alcohol? I would like a way to get into the higher boost (around 28 psi) without 106 octane fuel (applied CR 13.5/1) Any ideas?
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larso  
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PostPosted: Thu Aug 23, 2001 6:45 am    Post subject: Reply with quote

The turbo cars are different.

On a 924 the throttle can be anywhere, there's probably some gains with having the TB out near the front of the intake system before the throttle body, and probably some gains with having it after the CIS, i would think that there is more low end power with the TB further away.
BUT getting on topic, you have a turbo car here, very different.

The throttle body after the turbo ans CIS is whats going to work.
Having the throttle after the turbo allows you to build up more boost for throttle response when u aren't at WOT.
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BIMMERBOY  
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PostPosted: Thu Aug 23, 2001 8:22 am    Post subject: Reply with quote

That makes some sense, to press the point however, this is a garrett t04 S trim designed to produce 36psi at 6000 rpms (on a 1. It is the largest turbo i have ever seen outside the hood of a sixteen wheeler. Anything that can reduce the transient response time (i.e. higher turbine revs @ rpm) is very desireable. I have driven similar engines and found that upwards of two seconds of spool time is required at WOT to come to full boost from idleing turbine revs.
The idea of keeping both throttles in place in a progressive setup is gaining my interest. The cables would be tricky but a setup where both open simultaniously but the throttle on the intake opens twice as fast giving WOT at part throttle on the first intake that would resolve issues with the intake flow/resonance. It might also give that slight boost-punch at part throttle that you were talking about.
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