Modification plan for a non-charged H6/3.0R

[dr20t]

I'd get rid of the cat in the headers but keep the mid cat with new piping

Problem with doing this is you need to reloacte the rear (post-cat) o2 sensors.
that's gonna need wiring extensions

Hmmm didnt think of this as I don't own a h6

Surely wouldn't be too hard to do with some shielded wire?

[kleinerbastler]

@submeister
Yes, the most important thing for the design of the original headers was the emission level, not the economy. Small pipes mean more heat at the cats (less cooling during expansion of the gases) and higher gas flow, so the cats will work faster after starting the engine - important for the latest emission levels. The double wall isolation have the effect, that not to much heat will be "eat" from the headermaterial self (best way to isolate with low mass of material) - more heat at the cats too. The economy is better with big pipes - less resistance to overcome. With bigger headers you will have a significant improvement of economy - about 10%, but ....

[Tradewind]

Tim, thanks for posting your findings as well as that chart and pic, some really useful info there. Some good gains on stock cats!

What are your thoughts on why Subaru went for such a restrictive header design to begin with given the H6's considerable air volume throughput at higher revs? Do you reckon it was done to get better fuel economy and/or lower emissions?

Also, I note in your cutaway that the 3 into 1 collector is double walled. Are your headers single or double walled? And if single, does that have any impact on NVH and heat radiation?

Sub

You have guessed correctly on every point about the factory manifolds

The Raptor header is very conventional - single wall, definitely would run a cooler and have slightly more NVH - however you will have to be extremely good to pick the NVH difference! The stock design is 100% first about emission management on cold start

[SubMeister]

@Tradewind

Through thoughtful design, the graphs suggests headers let you have your cake and eat it too re power/torque gains on low end and high end.

Does the same apply to fuel use? On the one hand, fuel use should go up to match higher air flow. But Kleinerbastler makes some interesting points about fuel use being less due to less resistance. What's been your customer experience to date?

This would be a point to consider in any H6 mod plan...though obviously we need to set aside the right foot getting heavier because the engine likes rev more!

[Robbks]

Does the same apply to fuel use? On the one hand, fuel use should go up to match higher air flow. But Kleinerbastler makes some interesting points about fuel use being less due to less resistance. What's been your customer experience to date?

remember that those power runs are performed under WOT conditions,
something you only do for about 1% of the time with a road car.

If you make it easier to get the gasses out of the engine (which the charts prove) then air also goes in easier
thus you have much lower "pumping losses" and you will get better economy when in "cruising" conditions as a result.

[kmac]

Tim, thanks for posting your findings as well as that chart and pic, some really useful info there. Some good gains on stock cats!

What are your thoughts on why Subaru went for such a restrictive header design to begin with given the H6's considerable air volume throughput at higher revs? Do you reckon it was done to get better fuel economy and/or lower emissions?

Also, I note in your cutaway that the 3 into 1 collector is double walled. Are your headers single or double walled? And if single, does that have any impact on NVH and heat radiation?

Sub

You have guessed correctly on every point about the factory manifolds

The Raptor header is very conventional - single wall, definitely would run a cooler and have slightly more NVH - however you will have to be extremely good to pick the NVH difference! The stock design is 100% first about emission management on cold start

Would it be worth wrapping the headers? Metal covers would also be required for protection. Presumably this would take care of both the NVH and cold start emissions.

[Robbks]

header wrap and then some VHT paint to seal them would be sufficient for protection and noise reduction while aiding the transfer of heat to the cats for emissions,
but wouldn't have any real performance benefits as far keeping the gasses hot to spool turbo's like you would find in turbo applications.
It may assist in maintaining higher gas velocity though, Tim should be able to advise any further benefits

[Tradewind]

This for someone

viewtopic.php?f=65&t=17262&p=312649#p312649

[SubMeister]

3.0 litre V6 + Supercharger + Tune = 450hp V8

http://www.youtube.com/watch?v=2KfMY96v_Gc

Bring it