Tubocharger, meets Venturi ???

[turbo2omni]

My goal is to build a High street tired 12'sec car and get somewhere in the nieghborhood of 40 mpg. and don't doubt me the last project was a 86 GLH Dodge Omni. ran 13.4 all day long and averaged 35 mpg. oh yeah and the whole car was put together with junkyard parts for less than 1000 US dollars.

The current project car is a 1985 Shelby Charger running a 2.5 turbo engine.

The ??? I have is why have I never seen a venturi setup on the exhuast side of things. The thought (may be way off base but.....) is to take a "ram air" style duct from the front of the car and run this ducting towards the rear of the car. At some point along this path the exhuast system would "T" into this pipe, so that given enough air volume and speed a suction would be created on the exhuast system.

The problem I am trying to overcome is that a large turbine side A/R is laggy and has some effect on the fuel economy. and using a stock .48 A/R leads to 45+ psi of pressure in the exhuast manifold, in my particular set up. So in theroy if a "large" enough suction could be created I could get by with a smaller turbine A/R and trick it into thinking it was bigger than it is.

??How am I wrong ????

Or how fast would I have to go for this to work

 

[patprimmer]

I don't think you can build a system big enough to cope with the volume of exhaust gass you would need to evacuate

Regards
pat

 

[turbo2omni]

That seems to be the most given reponse. So if that is true (I'll have to do some numbers later and find out a good estimate of what volume and air speed is in my exhuast pipe)

So if it won't create a 5 hp increase anywhere in my powerband, then what about just cruising down the highway at 70mph. at 2500 rpm with the throttle just barely open there isn't that much air in the exhuast system. I am struggling to figure out if I could create a pull on the exhuast system would it be a benefit to my fuel economy, by removing some of the resitance found between the exhuast valve and end of pipe. (understandin' that some level of resistance still has to be there)

 

[stevo440]

The 45+psi you are talkin about is between the exhaust manifold and turbo. The idea you are suggesting would only be able to connect to the after the turbo exhaust side where the pressure is created by the cat(if your usin one) and muffler (if your usin one) and pipe dia ofcourse. The only way to lower the 45+psi is to play with dif. turbos like you said bigger but more efficient, ball bearings, talk to the Turbo manufacterers maybe they can help you find one that will get you close to what you need. To lower backpressure in the after turbo side well bigger is better on that subject. A specially designed downpipe will help alittle also. Your biggest gain will be from workin with the computer program (chip)for the 40 mpg if you have the capabillity, fuel and timing under cruise conditions. I drive a Turbo Buick and have the ability to play with the chip programming and there is a special section for cruise mode fuel and timing. Also a wideband O2 sensor would help out with mpg control.

Good Luck
Steve

 

[Docengineheat]

1. If you have a pressure of 45 psi in your exhaust manifold, you have something really, really wrong with your turbocharger. In a well designed turbocharger system the exhaust manifold pressure will be less than the intake manifold pressure.

2. There have been a number of devices such as you propose that have been patented. One is US patent 4313523, issued in 1982. You can see this patent by going to the Patent office website --

http://164.195.100.11/netahtml/srchnum.htm

and typing in the patent number.

None of these devices work, for the same reason that "ram-air" doesn't significantly boost intake manifold pressure. At 60 mph, "ram air" will increase manifold pressur by a whole 0.062 psi. If you want to get a 7 psi boost from ram air, you'll need to be cruising at about 600 mph.

 

[turbo2omni]

Yes I can play around the computer, fuel and spark curves ect. That is just icing on the cake here.

and 45psi exhuast manifold pressure isn't all that extrodinary. my set up is a 2.5 liter SOHC engine with a t3 garret turbo .42 a/r commpressor and .48 a/r turbine. with a little touch up to the wheels. At 20 psi of intake manifold pressure the exhuast pressure gets up there pretty fast. Yes I know that boost level is way at the top of the efficiency level of commpressor map but.. hey it still made the car faster. I have the time slips to prove it.


Corky Bell recomends a 2:1 exhuast to intake manifold pressure in order reduce lag not give up HP.


I was reading 45psi in the exhuast @ around 15-16 psi. in order to make a 2400 lb dodge omni run 13.4 on a slippery track/ with street tires it took 19-20 psi. With more traction that would have been a easy high twelve. My trap speeds were in well past 105mph. Everything that bolted directly to that engine was 100% stock. (head, shortblock,intake and exhuast manifolds, turbo, throttle body ect.)


What got me started on the kick was I was looking at a large truck pipe and got to think'n. I know that there are not to many thing a guy can think of that are new and just going to work outstanding on the internal combustion engine. After all the engineers that have been going after 'em for the last oh 100 years, a good ole boy like me ain't going to just strike gold. but... every little bit counts in a low buck, high performance machine.

I have been lookin' at pic's off GT and indy cars. if I don't see anything there I'll give up this thought.

oh and thanks for the patent #. what do ya know someone beat me to my idea almost to the "T".