Exhaust experimentation

[Fun and games]

I spoke to demand engineering and they highly recommended the x pipe over h pipe to keep the scavenging effect, I'm booked in Saturday, good luck with your tests, it'll be interesting to see what you find.

[coffey555]

For me the stock exhaust with valves open has to be one of the best sounding v8 engine notes around.

I think the trick will be to enhance the stock valve open volume like 15-20% but maintain that deep throaty tone and not get that raspy thing happening that most people end up with.

Keen to see how you go!

Pretty much what removing the centre res section and replacing with straight pipes gives you. Oh, and removing the vacuum hoses to keep the valves open all the time. With the valves still connected you don't get the lovely bassy note under load just above 1500rpm in the lower gears if I remember rightly. Been so long since I had them connected I forget when they operate.

[dougle_turbo]

Okay so I have now had the straight through central resonator done on the spare exhaust, and had it fitted yesterday. My Initial thoughts are that in S mode its an awesome sound, and that in non S mode its still 'neighbour acceptable'......other than a cold start which seems loud enough to wake the dead!. Inside the car I get a really nice tone around 2000rpm (valves open) and the car now has a nice understated lift off crackle and pop. In non S mode (valves closed) there really isn't a lot of difference, which I what I was hoping for.

The next stage is the X-pipe which is being fabricated this week and should be fitted on Sat. That gives me a week with the straight through pipe.

So to be clear the current setup on the car is the standard system with centre resonator removed and straight pipes fitted. Below are a couple of comparison videos, which unfortunately didn't come out quite as well as I hoped. It was so windy yesterday I had to film it in the garage.

Stock exhaust: First three revs valves closed, second three valves open.

https://youtu.be/EmugaxplGR0

Centre resonator delete, straight through: First three revs valves closed, then valves open.

https://youtu.be/UdA83PQQjjw

Thoughts?

[dougle_turbo]

P.s Apologies if any of you were in the Costco Sunbury car park this afternoon.....I couldn't help myself.

[docurley]

Lol, it sound like you need the cold start mapped out

[dougle_turbo]

Lol, it sound like you need the cold start mapped out

Definitely.....If I get some time I'm hoping to get the car to MRC for a carbon clean and a stage 2 map.

[Rs4.]

I always thought the straight pipe mod
Lost that v8 rumble sounds a bit raspy but I guess it sounds different when your on it .

[MikeFish]

Sounds very much like my car now. Except I disconnected the valves, it's not that noisy when open that I'd want to make it any quieter. I have no cold start though.
Im still dubious about the actual benefits of scavenging. My car recently dynod at MRC at 438ps. Only engine mods I can recall is MRC remap. Centre res delete is about noise and not power so my exhaust is the same configuration as factory ie no h or x pipe. I also have a revolution carbon air intake which according to most people causes a power loss but I have a bigger than normal cold air feed.
Edit just checked my signature, forgot about the pre cat delete.

[docurley]

From all accounts precats make a big difference.

[MikeFish]

Yes but my point being that I don't seem to be lacking any power by not having a x pipe.

[Dantheman84]

Lol, it sound like you need the cold start mapped out

I'm curious is to why you map out cold start is it just because it's loud or is there any other reason
Thanks

[dougle_turbo]

Sounds very much like my car now. Except I disconnected the valves, it's not that noisy when open that I'd want to make it any quieter. I have no cold start though.
Im still dubious about the actual benefits of scavenging. My car recently dynod at MRC at 438ps. Only engine mods I can recall is MRC remap. Centre res delete is about noise and not power so my exhaust is the same configuration as factory ie no h or x pipe. I also have a revolution carbon air intake which according to most people causes a power loss but I have a bigger than normal cold air feed.
Edit just checked my signature, forgot about the pre cat delete.

Thanks Mike,

I may disconnect the valves and see how it goes once the cold start has been mapped out. I like being able to quieten it off if I come home late.... I'm probably being to considerate a neighbour! As you have, I'm only doing this modification for the noise. If I luck into a few more HP then I'll take it, if not I don't mind I'm not sure I'd notice either way.

On paper scavenging should work well as the x/h pipe effectively doubles the cross-sectional area of the exhaust allowing to to flow faster. If the x pipe if placed at the correct distance from the manifold it should blend the exhaust pulses, which is why they tend to be quieter than an H or straight through. The h pipe doesn't blend the pulses and only allows the pressure to equalise (to an extent). If I had the time it would be great to tune a x pipe properly and compare it to a stock exhaust on a dyno. The other benefit of tuning/designing an exhaust properly is that drone can be if not eliminated, certainly moved along the rev range if required. Happily my straight through mod only really drones at 2000rpm and not a motorway speeds.

[maars]

Love this thread dougie!
Any chance of getting a rolling video of the straight pipe sound, through the gears?

[dougle_turbo]

Love this thread dougie!
Any chance of getting a rolling video of the straight pipe sound, through the gears?

Cheers mate,

My sound recording equipment is limited to an IPhone, but I'll see what I can do. I'll try and get something recorded before the x pipe goes on. It sounds great in the car.

[maars]

That would be great dougie.

Really keen to hear how those straight pipes sound through the rev range, right up to the limiter.

Any thoughts on how you position the x-pipe for maximum effect?