Time to go Stage II!

[Alky V6]

A few other CART Champ examples of well known, highly tuned turbocharged engines and the exhaust systems that were developed for them.

Chev pushrod V-8 3.4 L, 720hp at 8600rpm. 425cc cyl capacity. 8 primary pipes 14in x 1.75in dia. 2 secondary pipes 36in x 2.5in dia.

Cosworth DFX V-8 2.65 L, 820hp at 10,700rpm. 331cc cyl capacity. 8 primary pipes 24in x 2in dia. 2 secondary pipes 29in x 2.5in dia.

Drake DT-160 V-8 2.65 L, 795hp at 9200rpm. 331cc cyl capacity. 8 primary pipes 27in x 1.75in dia. 2 secondary pipes 30in x 2.5in dia.

Due to restrictions that were placed on the teams in this class of racing, turbo specs, boost and fuel loads were tightly regulated, the exhaust system became the major component that the teams focused on in attempts to gain a power advantage.
Interesting that log manifolds were not found to be the best solution in any of these cases.

 

[Dusty Bradford]

The question would be how much power??

If Nascar teams are willing to spend $$$ supporting a full time engine building and dyno shop to make 5hp a year....what is considered beneficial for an F1 or Cart team? NHRA pro-stock falls into this same category.

10hp to them may be astronomical gains.

 

[Alky V6]

The question would be how much power??

If Nascar teams are willing to spend $$$ supporting a full time engine building and dyno shop to make 5hp a year....what is considered beneficial for an F1 or Cart team? NHRA pro-stock falls into this same category.

10hp to them may be astronomical gains.

That's a good question.
With an exhaust system where a fair attempt has already been made to tune it to the engine, a change in pipe diameter or primary/secondary section lengths might make small 5-10 hp gains.
What kind of gains can be had with a tuned system comparing it to a circumstance where the old system it would be replacing was simply put together for packaging and low cost reasons with absolutely no consideration to properly match piping diameters and lengths to the needs of the engine combination and hp target? Just 5 hp?

 

[Alky V6]

I'm going to run some sims comparing more simpler exhaust systems to the one I've come up with for the Stage II config. Does anyone have any specs they'd like me to try? I'll post the comparisons of the outputs.
The first setup I'm going to try will be 1.75 primary, short, with 2.25 collector, long length.

 

[Dusty Bradford]

99% of the turbo headers built all use a primary slightly larger than the exhaust port on the head. If 1 7/8 is slightly larger than your port, use that for the sim. As for the length. The collector is usually placed somewhere out of the way but is never much further forward than the front of the valvecover. So on the pass side #2 will be very short, #4 will be slightly longer than #2 and #6 will be slightly longer than #4.

 

[Dusty Bradford]

Here's an example of the downswept I built for my big block.

 

[Alky V6]

99% of the turbo headers built all use a primary slightly larger than the exhaust port on the head. If 1 7/8 is slightly larger than your port, use that for the sim. As for the length. The collector is usually placed somewhere out of the way but is never much further forward than the front of the valvecover. So on the pass side #2 will be very short, #4 will be slightly longer than #2 and #6 will be slightly longer than #4.

The sim won't do separate primary lengths. In that situation, I would need an average length number to use.
If one wanted to see what sort of hp difference one cylinder is making compared to another cylinder that is running a different length primary, one could run a number of complete sim runs using the different primary lengths and compare the outputs.

I agree with using a primary that is larger than the port size. Some have eluded that they'd like to use a smaller tubing size, so I thought I'd try that out first. 1.75 would just match my exhaust port size.

 

[Alky V6]

Here is the comparison between the specs I've come up with to use and a simpler, smaller system.
The primaries are 1.75in dia 12in length. Secondary pipe is 2.25in 26in length.
The comparison point is at 7000rpm. A 128hp difference at 7000rpm.

 

[Dusty Bradford]

At this point I'd say the sim is smoking crack. Obviously it's effecting something else in all these calcs that is straying the results.

 

[Alky V6]

Here's a comparison run that is comparing different primary lengths using the same collector length and diameter for all runs.
At 7000rpm: 7in 1,245hp; 12in 1,243hp; 17in 1,148hp.
Notice the 7 and 12in pipes are close in output, but the 17in is really straying from the shorter pipes.
About a 100hp difference in overall output. If one engine were using similar unequal length primaries, there would be about a 16hp difference between the high and low outputting cylinders. Up to a 6-7 percent variance in cylinder to cylinder output.

 

[Alky V6]

At this point I'd say the sim is smoking crack. Obviously it's effecting something else in all these calcs that is straying the results.

Does it really sound that far off? Trying to push 1500hp out of 6 cylinders through 1.75" primaries?
I think you're not realizing how sensitive my build may be to exhaust back pressure. Any type of exhaust back pressure. Whether the back pressure is a result of a small turbine side, or a small exhaust system.
My engine specs are assuming I will have an unordinarily low exhaust back pressure to boost pressure ratio. Anything that upsets that balance is going to have a large affect on output.

 

[Dusty Bradford]

Did you increase it to 2" to see what happened?

 

[Alky V6]

Did you increase it to 2" to see what happened?

What I'll do is run a comparison calc with a range of primary diameters from 1.75" to 2" at .125" increments. Comparison calcs are a good way to visualize trends.

 

[Dusty Bradford]

I see something now. I said 1 7/8. You used 1 3/4 or 1.750. I'm sure 1.875 is what most of the headers would be made of for a stage 2 head.

 

[Alky V6]

Here's a comparison of the simple system with varying primary IDs starting at 1.75 and ending with 2.0".
You can see from this comparison that the engine combination is favoring the larger primary ID. Completely understandable considering a target hp level of 1500hp.
A difference of about 29hp at 7,000rpm between the 1 7/8" and the 2" primary IDs. I wouldn't even consider the 1 3/4".

 

[Alky V6]

I see something now. I said 1 7/8. You used 1 3/4 or 1.750. I'm sure 1.875 is what most of the headers would be made of for a stage 2 head.

Yes. I would consider a primary ID of 1 7/8" as the smallest for a Stage II head. The optimum diameter will vary with the target hp level. The more hp, the more exhaust gases that need to be handled. The more exhaust gases that need to be handled, the larger the tubing will need to be.

 

[Dusty Bradford]

That looks more reasonable.

 

[turbofabricator]

Or.......................You can just turn the boost up. I like that you are trying someting different. Keep at it. You might find a few horsepower and if you are fabbing your own headers, no down side 'cept for a few bucks in material. What did Duttweiler do on Gallina's car? I personally don't know. I've only seen it once up close and can't remember. (hell I can't remember what I had for lunch) Donnie you will analyize this to death, I'm sure, then half way through your fabrication you'll "learn" something else. And have to start over. Even if it makes a WHOLE 25 HP gain.......Just turn the dang boost up. Boost covers ALOT of issues. Sooner or later you have to get the car down the track.
My offer still stands.......You buy the material, and I'll make a set of caveman schedule 40 headers and then swap 'em and see what happens. I personally don't know WHAT will happen, and am willing to help with fabbing 'em to see what if any difference they make. We BOTH will learn something. I've got StageII heads and block ready to start making caveman headers. (on center or off center)
But I really want to see what you have up your sleeve. I am always looking to learn something. The more I think I know....The dumber I feel.

 

[Alky V6]

Ken, there's something you're not catching onto. The amount of boost I can get out of this particular turbo using this new engine configuration will depend completely on the header design. I can't simply 'turn up the boost'.
The intake manifold boost climb rate will be very closely tied to the engine rpm climb rate. Just like the sim graphs I posted show. Little changes in the header design will affect this close rpm/boost relationship. Go back to the sim graphs I posted (post #228) and notice how the boost level ramps up with rpm. That is strictly due to the relationship of the size of the hot side of the turbo and the amount of exhaust energy the engine is creating. I am not controlling that boost rise rate in the sim. I simply have a max boost limit of 43 psi entered in the sim. I saw the same sort of tight relationship between the hot side of this turbo and the Stage I configuration.
If I get the exhaust header design right, the boost will ramp up along with rpm in a manner where cylinder pressure (MEP) limits will be on the edge (notice in post #228 that the BMEP is practically flat lined) right up through the rpm climb, and the boost level should top off at my max boost target just before or right at peak hp rpm, around 8250-8500rpm. That should also be very close to the point where the fueling capacity will max out. The closer I match the exhaust system to the needs of the engine/turbine combination, the sooner in the rpm band max boost will be obtained. If I'm off on the exhaust system, the max boost target may not be obtained and peak power will suffer for it. Playing around with the exhaust system specs has shown me this.
This should all happen with the wastegate clamped down tight throughout the complete rpm/boost rise. No wastegate control will be needed to dump excess exhaust energy to prevent the chance of overboosting. The turbine side and the engine will be a perfect match.
When the turbine side and the engine is this closely matched, the exhaust system becomes the component that will make or break the combination. The system could be too big, or too small and affect the engine rpm climb rate / boost climb rate relationship.
The exhaust system becomes an important tuning tool in two different ways. First, to affect the best VE for the engine, an engine configured to take advantage of crossover flow, and second to provide the turbine with the correct balance of exhaust flow velocity and exhaust system restriction.

 

[Alky V6]

Why some of you may not understand this concept is because everyone will simply throw a small turbine wheel and housing onto their combination to make sure the turbocharger has the capacity to overboost. Then, will employ the wastegate to dump excess hot side energy to control the boost climb rate in relation to the rpm climb rate.
This is the sort of turbine sizing strategy that saddles you with higher exhaust back pressure to intake boost pressure ratios, which create limits on the engine.
The smaller turbine wheel/housing combinations that allow this sort of strategy are generally less efficient than the larger turbine assemblies. The search for spool up quality is what pushes everyone to the smaller, less efficient turbines.