[jtodd]

I have read many posts on the benefit of exhaust scavenging. What would the benefit of additional scavenging by non-traditional means? My thought is to assist exhaust flow by means of some type of vacuum, perhaps by way of a venturi. Is there much 'there' there, or is that going to an extreme to find little benefit.

Jeff

 

[nobody]

I'd like to answer your question but in all honesty I've been thinking about kinda tha same issue. I undestand the idea of the harmonics and it's effect on scavaging but what does a turbo do to this? figured why not ask all the questions at once. Bob are you around?

 

[Paul]

Jeff

Disclaimer: This following is not an end all explanation... just trying to relay a few concepts.

Exhaust scavenging can be a good thing. However, its effects only happen under a fairly narrow set of circumstances. There are essentially two mechanisms/therories of scavenging: Inertial and Acoustic/Wave. Each type is similar but different. Inertial scavenging happens as the physical gas pressure wave travels down the primary tube, there is a physical low pressure area behind it that can be used to pull the next pressure wave along. These pressure waves travel at speeds of around 300 Feet per Second. Acoustic or wave tuning is similar in that high and low pressure waves travel/bounce back and forth from the exhaust valve to the collector. But the laws that govern their movement is different than inertial waves. These are sound energy waves and travel at speeds between Mach.5 and 1.0.

Now there are two areas one can influence with scavenging: Reduction of pumping losses and increased cylinder filling. The reduction of HP consumed by forcing the exhaust out of the cylinder is pumping losses. Reducing "back pressure" of the exhaust reduces pumping losses. Having the low pressure wave arrive back at the exhaust valve when the intake valve is still open helps improve cylinder filling which helps get volummetric efficiency over 100%

For more information go to www.headerdesign.com

AT their web site you will read that there is little to be gained by improving the exhaust system flow if the exhaust valve is already flowing greater than ~80% of the intake. Since, on the stock Opel head, the Exhaust practically out flows the intake, there is not "a lot" of room for improvement, but there is some improvement to be had. That's why the sprint manifold is used with such great success.

HTH

 

[73Manta72gt]

Is the "sprint" mainifold just a 1975 model manifold or is it something different?..if it is diferent how does it compare to the 75?

Thanks

 

[GTJIM (R.I.P.)]

Is the "sprint" mainifold just a 1975 model manifold or is it something different?..if it is diferent how does it compare to the 75?

Thanks

The "Sprint" exhaust manifold was used with the 1975 Fuel Injection motors and it has no 'heat riser' for the carb intake manifold like the earlier exhaust manifold has. Later, European, fuel injection motors have a similar manifold with a larger outlet flange. There is also a more swept back version which can be seen in the pics attached to a couple of "Nobody's" recent posts.

Called the "Sprint" exhaust manifold because it was originally used on the 1968 Opel Kadette Rallye Sprint motors to increase power.

 

[nobody]

to explain a bit more there are really 3 sprint or non heat riser versions available. The 1.9 is the most saught after since it uses the existing collector flange and was used primarily on the 75 EFI models. Next is the 2.0 sprint and it was not used in US models but can be had but uses a larger flange to the collector. Then there is the 2.4 that is even bigger yet and has yet another collector flange. Each one is bigger than the other and allow very free flow compared to a stock exhaust. Just as an example the 2.4 is around 1 11/16th on the output side. The effects on scavaging for each model is a very undefined area and intake and valve sizing has a big effect on each one.
JM2CW

 

[tekenaar]

1.9/2.0 sprints compared

to explain a bit more there are really 3 sprint or non heat riser versions available. The 1.9 is the most saught after since it uses the existing collector flange and was used primarily on the 75 EFI models. Next is the 2.0 sprint and it was not used in US models but can be had but uses a larger flange to the collector. Then there is the 2.4 that is even bigger yet and has yet another collector flange. Each one is bigger than the other and allow very free flow compared to a stock exhaust. Just as an example the 2.4 is around 1 11/16th on the output side. The effects on scavaging for each model is a very undefined area and intake and valve sizing has a big effect on each one.
JM2CW

If you look at both the 1.9 and 2.0 Sprint manifolds side by side, ports, as cast, are all the same size (big surprise to me the first time I compared the two!) and the ONLY real difference is the exhaust flange size, which is ~1/2" wider.

 

[jeff denton]

Just for fun take a tubular header and an air hose with the blow nozzle and shoot a blast down through the exhaust port of one cylinder and at the same time feel the suction created at another cylinder's port.
See how headers work?
Try it on a stock manifold, try it on a Sprint manifold. I wish I had either to experiment with. Is a suction created or not?
I think naturally aspirated engines need all the help they can get in the scavenging department, and headers seem to be the simplest, most time-honored modification to the exhaust system.
Of course there's a lot more to it than that, but it's a basic start.

 

[GTJIM (R.I.P.)]

"Tri - Y"

The standard Opel CIH exhaust manifold is already far better than most other four cylinder motors exhaust manifolds since cylinder #1 & #4 are paired and so are cylinders #2 & #3 with the continuing pipes also seperated below the manifold. This effectively creates a "Tri-Y" exhaust header system which is usually considered as superior in smoothness and wide power band than the "racing" four into one header. The "Sprint" manifold's major advantage is the removal of the 'stove' for the intake manifold which allows the intake mixture to reach the cylinders at a considerably lower temperature - and thus more dense. Just maybe the centre #2 & #3 gas routing is also superior too due the the deletion of the "stove" area.

 

[jeff denton]

Very interesting. How well does the tri Y compare to a header during long periods (15 minute) flat out wide open throttle runs?
I'm into the dense air intake theory. So much that I removed all evidence of there ever being a stove under the intake. And thermal wrapped the headers and head pipe and muffler and tail pipe ( our exhaust system is inside the car, could be called a "passenger seat warmer") Also added some neat (expensive) thermal blanketing between the header and intake. Plus some heat shields above and below the wedge-shaped spacer/adapter that puts a Holley 350 on the engine. Not to mention 4 inch ducting from the grille up to a 4" turbo blower (marine stuff) that blows at the manifold area.
Does this really work, or just baffle the competition? I don't know...

 

[GTJIM (R.I.P.)]

Very interesting. How well does the tri Y compare to a header during long periods (15 minute) flat out wide open throttle runs?

Nowhere near as good! As the four-in-to-one equal lenght header can be specifically turned for "flat out" revs and will give better power near that rev range. The Tri-Y set up is less critical in tuning and more 'street-friendly' especially at lower, variable rpms. Indeed the intial cast manifold will tune for one rev range and the two follow-on down pipes are a different length that "tunes" them for another rev range. All nice and "soggy" for the street with a less peaky power band - just right for my Automatic gearbox GT !

 

[RallyBob]

Very interesting. How well does the tri Y compare to a header during long periods (15 minute) flat out wide open throttle runs?
I'm into the dense air intake theory. So much that I removed all evidence of there ever being a stove under the intake. And thermal wrapped the headers and head pipe and muffler and tail pipe ( our exhaust system is inside the car, could be called a "passenger seat warmer") Also added some neat (expensive) thermal blanketing between the header and intake. Plus some heat shields above and below the wedge-shaped spacer/adapter that puts a Holley 350 on the engine. Not to mention 4 inch ducting from the grille up to a 4" turbo blower (marine stuff) that blows at the manifold area.
Does this really work, or just baffle the competition? I don't know...

All good work Jeff, and well worth it on an Opel. Especially on a restart after an on-track accident, when the engine has been idling and there's a ton of heat-soak.