Modification plan for a non-charged H6/3.0R

[dr20t]

On an n/a car, the factory cats are alot better than aftermarket, especially in a Japanese car.

Never replace a factory cat on an na car with a 'high flow' one

These are usually Chinese or Taiwanese rubbish. The Japanese cats are actually filled with titanium and are better at heat dissipation and burn that aftermarket wank ones

The fact is in an n/a car, you want to have a small amount of restriction to assist with the scavenging effect. The best form of this restriction should be the factory cat not the pipes themselves. Therefore upgrade all other pipes but keep the stock cats

My theory is this: larger from engine to front half of exhaust, gradually getting smaller to a higj flow rear muffler(s)

In my n/a celica (gen3 jdm 3sge motor which made 176hp atw naturally aspirated), I had factory larger diameter 4-2-1 headers, into a 2.25" mid to the cat then 2" from cat back to a single cannon (yes rice I know it was back in the day)

Initially the exhaust place upsold me to a high flow cat, but I noticed a good solid low end torque difference with the factory cat back in place. It also removed the buzziness I used to get which toyota 4 bangers with aftermarket exhaust were renowned for.

Mick

[SegR]

Interesting; prior to this discussion I hadn't seen any proponents of keeping the stock cats.

Any point changing the centre pipe then?

[dr20t]

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

[HoFF]

Some headers, catback, stock cats fine for NA

Get yourself a mad tuner and tune the hell out of it

I have given some thought to the intake (CAI) for a long time but not sure if gains can be made there, the factory system allows for a reasonably decent air charge in stock form

So do your Raptor headers bolt straight up to the existing cats?

[Brunsy3.0]

ima keep an eye on this as like most H6 owners plan to do similar (also on the grapevine I have heard x-force MIGHT be making an aftermarket header for the H6)

[Tradewind]

Some headers, catback, stock cats fine for NA

Get yourself a mad tuner and tune the hell out of it

I have given some thought to the intake (CAI) for a long time but not sure if gains can be made there, the factory system allows for a reasonably decent air charge in stock form

So do your Raptor headers bolt straight up to the existing cats?

No header system can bolt up to the existing cats, because there simply is no bolted flange at the cat. Raptor supplies weld on flanges, every customer takes their headers and their car to an exhaust shop and has the fitted. This ensures the headers are properly fitted to the vehicle.

[Tradewind]

ima keep an eye on this as like most H6 owners plan to do similar (also on the grapevine I have heard x-force MIGHT be making an aftermarket header for the H6)

I talked with XFORCE about it directly - they have zero interest in the H6, I was hoping they WOULD do them but nope - they couldn't have cared less. Whats more unless they direct copy my product or K2 its quite likely the results wont be there either , I made and tested a few versions before I found the combo that produced the right kind of gains without low speed losses

Raptor NEEDED to produce headers so the supercharger kits could be effective to their fullest extent, otherwise I wouldn't have bothered at all - which would have left the K2 option only. Raptor couldn't rely on its customers paying out $2000 + for a header/cat set to get full performance from their SC system. Incidentally the K2s cost Australians about 20% less at least of late ........... if I got my sums right

[Brunsy3.0]

true, my sources must be a little of their head

with the headers I have gotten wind they basically increase performance over a certain rev band? as I have no personal knowledge of this it would be good to get some clarity of it, as I am nearly talked out of getting headers at this point

[Tradewind]

My findings on the matter

See chart - XRT tuning assisted with the research by analyzing the data Raptor logged, I also made certain the car FELT better across the range. Some of the first versions of the header added top end power but made the car un-driveable at low speeds due to massive torque loss, going too far the other way, no room for the enormous high end airflow this motor is capable of. The balance is critical

As you can see the difference in the power at 7300rpm even with stock cats - this proves well enough changing cats on NA would be useless to do. Its just 110kw stock and around 137kw with the headers, you cannot expect any gain larger than that on an NA 3.0 liter, even I was shocked - you get those kinds of gains on a V8 5.0 liter - if you are lucky, to see it on a 3.0 was amazing. Of course you can see the torque curve is very enhanced, more torque everywhere in the working rpm range

If you have seen the stock header you will know without any further query that there has to be room for improvement

[SegR]

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

Is that likely to have any effect on the third cat or does it just mean emissions won't be reduced by as much?

[Brunsy3.0]

is it better to leave the cats stock to add some restriction to the exhaust or is it beneficial to have free'er flowing cats even around 200cel?

if new cats don't give any more kw can it make the lower rev band more driveable? I find 1st is the worst at low speed it it very very jerky (this is what I dislike the most)

[dr20t]

I can't see the cats being a cause of the jerkiness you describe

Personal opinion (which seems to be somewhat supported by data trade wind posted above) is that "high flow cats" are a gimmick on mildy modified n/a cars..

[kleinerbastler]

My 2 cents, first i have done the exhaust system and cats (200 cells) - driving was a lot better. But to change header system was the best thing - with the tuning from Ed it was amazing what kind of power this engine has. Free exhaust, less power to work against the pressure - but a bit of exhaust pressure you will need.



The times are meassured at same place and 3th gear.

[Robbks]

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

[SubMeister]

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?