Exhaust options?

[Sveneng]

What options are available for the C70 T5?

I've seen the Jetex system but I don't like the tailpipe, I like the oval look that comes as standard. I am only considering something as the tailpipe on my exhaust is really marked, I've looked at the replacement exhaust trims that are for sale on ebay, are they any good? I'm not necessarily after extra performance so even a good looking backbox would suit my needs.

I'm sorry it such a general question but when I look at performance retailers' websites they don't seem to list options for the C70.

Thanks for looking and any advice you can offer,

Sveneng

[DuncVolvoTurbo]

From what you are saying, you might as well just get a replacement tail pipe from your Volvo dealer, or forum member RUFE. Seems pointless buying a whole exhaust or even back box if it is just the end that bothers you.

[Sveneng]

Fair point!

I was fairly surprised that the car wasn't catered for by the majority of exhaust manufacturers.

Sveneng

[dionbullock]

TBH - i woldnt trust the cheaper tailpipes on asle on ebay etc - my friend boutght one a while back, it said full stainless steel on the box/package. it ha rusted and pitted after about a month. i suppose its a case of you get what you pay for???

[Alan M]

Some stainless goes rusty, especially if its a cheap grade.

[dionbullock]

perhaps you should get a custom made exhaust? plenty of tailpipe options for you then :) depends how much cash you want to splash out tho - some can be expensive. theres a fella up by mine who does them, £280 he charges for a turbo back (with decat) system. had it on my 99 v70. sounded awsom, but at a price of course.

but perhaps you can get a custom made tailpipe made from high quality s/steel. wont rust for ya then.

[pangster]

I liked the oval tailipe as well and wanted a Milltek although they stopped making them for the C70 - so I opted for a custom made exhaust:

http://www.paullynch.pwp.blueyonder.co.uk/exhaust3.JPG

http://www.paullynch.pwp.blueyonder.co.uk/exhaust5.JPG

:)

[Sveneng]

Pangster,

that looks great, is it much louder than the standard exhaust? I like the fact that the C70 is quiet, I think my days of loud boomy exhausts are over (still sound great though, just wouldn't want to live with one on a day to day basis)!

Sveneng

[pangster]

Pangster,

that looks great, is it much louder than the standard exhaust? I like the fact that the C70 is quiet, I think my days of loud boomy exhausts are over (still sound great though, just wouldn't want to live with one on a day to day basis)!

Sveneng

Its a fair bit louder than stock - but that's how i wanted it (as free flowing as possible).. i guess thats the benefit of going custom.. I went for 2.5 inch mandrel bent piping with one straight through box.. it could have been much quieter (i.e. comparable with stock) if i had went for 2 muffled silencers.

[siamblue]

Some stainless goes rusty, especially if its a cheap grade.

Or if like Mitsy you get a mate to MIG 304 st/st :rotfl:

Its ok just lag it no one will see the rust then :lol:

[Liddo]

Im getting a full stainless steel cat back 2.5" system fitted on Monday by Blumeflame Performance in Skelmersdale, near me. Its costing £375 fitted, and will HOPEFULLY soundc and look like Pangsters ;)

I'll post up a video of it next week :D

[Alan M]

Or if like Mitsy you get a mate to MIG 304 st/st :rotfl:

Its ok just lag it no one will see the rust then :lol:

:hilarious:hilarious:hilarious:hilarious

[OogieBoogie]

Mine is also oval - don't have a better picture to hand I'm afraid. I'll find out what it is and re-post. Sounds awesome, more engine than drone. Not quiet.

Looked up the invoice and I'm afraid it's of no help - simply says stainless steel with oval pipe.

http://i236.photobucket.com/albums/ff1/RachandIan/General/2007-01-28VolvoC70004rs640np.jpg

[Liddo]

My new exhaust has been delayed, thanks to the fitter having tonsilitus :(
Will update after the 15th ;)

[siamblue]

I have just worked out the cost of my 3" exhaust in st/st 304,

total cost £255 plus welding,

But i am going to run the 3" upto the rear axle to keep costs down,
so it will be £155 plus the welding,

Gary

[kyebosh]

Not sure of the cost of this!!

[thebadger]

TBH - i woldnt trust the cheaper tailpipes on asle on ebay etc - my friend boutght one a while back, it said full stainless steel on the box/package. it ha rusted and pitted after about a month. i suppose its a case of you get what you pay for???

All stainless will show signs of pitting (given time) and surface discolouration (rust look).

My Ferrita pipe had quite a bit of surface junk, wet & dry pad (fine), 5 mins & it looked brand new again!

Also recall that a hot exhast sprayed with mud/dirt will dry out & stick like it was welded on! It looks pitted, but might not be!

Remember, clean the car after you've finished playing (hard) with it!

[t5 pete]

where about are you from theres a place in sheffield that does a 3" cat back system for £300

[t5 pete]

Also i forgot to add ive had myne for 3 years all i do is clean the tail pipe and back box once a week the polish it with chrome cleaner and its liikes as good as it did the day it was fitted

[Sveneng]

I'm just being a bit of a perfectionist. I bought the car 3 months ago from a dealer and it's in great condition but the previous owner has obviously been frequenting the car wash on a regular basis and it looks like the exhaust has never been cleaned. As a result I am having trouble removing all of the carbon that is on it. After a good session with wire wool and Megs metal polish it is looking much better but there are still few parts of the tail pipe that are caked in carbon.

If the exhaust ends up needing to be replaced due to failing an MOT or developing a fault then I would go for a full stainless steel option of some kind but in the mean time I think I will stick with whats on it.

Sveneng

[Jaseb77]

here's a piccies of my C70, when I had a twin tailpipe rear box, it was specific for the C70 as it was cut on the diagonal to match the tapering rear bumper, until someone bump it in a car park and broke it !!.

So now have a Jetex S/S cat back system, with 2.5" round, doesn't look as good though, and too long, sounds better though

http://i106.photobucket.com/albums/m242/jasec70/IMGP1243.gif
Twin tail pipe

Jetex too long for tapered bumper, needs shortened
http://i106.photobucket.com/albums/m242/jasec70/Photo-0001.jpg

[Alan M]

You could shorten the section after the rear box for the tailpipe then have it welded to suit.

[Terminator]

I'm just being a bit of a perfectionist. I bought the car 3 months ago from a dealer and it's in great condition but the previous owner has obviously been frequenting the car wash on a regular basis and it looks like the exhaust has never been cleaned. As a result I am having trouble removing all of the carbon that is on it. After a good session with wire wool and Megs metal polish it is looking much better but there are still few parts of the tail pipe that are caked in carbon.

If the exhaust ends up needing to be replaced due to failing an MOT or developing a fault then I would go for a full stainless steel option of some kind but in the mean time I think I will stick with whats on it.

Sveneng

Try brake cleaner as its very good at removing carbon deposits.

[pangster]

if you are looking for a new exhaust then one of the common questions that comes up is what size to go for (2.5 inch v 3 inch diameter). As far as I'm aware every off the shelf exhaust available for the Volvo C70 is 2.5 inch in diameter - which means that if you do want to go 3 inch or over or want one built to your specifications then the only option you have will be custom.

I found this article written by Jay Kavanaugh a turbo systems engineer from Garret explained the differences and pro's and con's quite well:



N/A CARS: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.

TURBO CARS: You throw all the above out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.

Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.

Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”

"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.

A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.

If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.

Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.

Also, the temperature of the exhaust coming out of a cat is higher than the inlet temperature, due to the exothermic oxidation of unburned hydrocarbons in the cat. So the total heat loss (and density increase) of the gases as it travels down the exhaust is not as prominent as it seems.

Another thing to keep in mind is that cylinder scavenging takes place where the flows from separate cylinders merge (i.e. in the collector). There is no such thing as cylinder scavenging downstream of the turbine, and hence, no reason to desire high exhaust velocity here. You will only introduce unwanted backpressure.

Other things you can do (in addition to choosing an appropriate diameter) to minimize exhaust backpressure in a turboback exhaust are: avoid crush-bent tubes (use mandrel bends); avoid tight-radius turns (keep it as straight as possible); avoid step changes in diameter; avoid "cheated" radii (cuts that are non-perpendicular); use a high flow cat; use a straight-thru perforated core muffler... etc.”

"Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.

There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.

As for primary lengths on turbo headers, it is advantageous to use equal-length primaries to time the arrival of the pulses at the turbine equally and to keep cylinder reversion balanced across all cylinders. This will improve boost response and the engine's VE. Equal-length is often difficult to achieve due to tight packaging, fabrication difficulty, and the desire to have runners of the shortest possible length.”

"Here's a worked example (simplified) of how larger exhausts help turbo cars:

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure

so here, the turbine contributed 19.6 psig of backpressure to the total.

Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

As you can see, the backpressure penalty of running a too-small exhaust (like 2.5" for 350 hp) will vary depending on the match. At a given power level, a smaller turbo will generally be operating at a higher turbine pressure ratio and so will actually make the engine more sensitive to the backpressure downstream of the turbine than a larger turbine/turbo would.

HTH