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Thread: HP limits of Stock 2.5" exhaust system and Spool time for 770r turbos?

  1. #1
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    HP limits of Stock 2.5" exhaust system and Spool time for 770r turbos?

    doesn't anyone know the limits of our 2.5" system horsepower wise. I have read through the forum and saw that on the stock set up and up to around 550 you can just gut the pre-cats and call it a day. reason I'm after this information is because i'm working a long term engine build and I find it hard to swallow ~1500 for downpipes. the rest of the exhaust is not a problem as i have a local shop near me that does GREAT work...just trying to see if the 2.5 inch system is good around the 650-700 hp ranges.

    i'm in the beginning stages of my build and i'm not in a hurry so the more information i can gather upfront the better so when it comes time for exhaust i'll be prepared.

    so far i have ported and polished the heads/intake manifold/exhaust manifold and i have a tial 770r kit waiting for install (down the road).

    Also...

    I'm coming from the 1.8t and 2.7t platforms so i'm not do familiar with lag and spool times for these turbos on the 4.2 engines. on the 2.7t they hit hard around 4k rmps or alittle harder and carry through to alittle over 7k typically. Just wondering if anyone knows these states based on our engines as it should be much better since we flow more air and have more displacement.

    thanks!

    oh and yes 1st post, just been waiting for a good time to starting chatting haha

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    Do 2.7t 770rs bolt up to the RS6? Or, do they make a 770 kit for the RS6?

    Also, mind sharing what intake and exhaust manifolds you have?

    I would like to comment though, that anyone who has built heads and bigger turbo's that is in for a "long-term build," probably should invest in a quality exhaust front to back, regardless of the abilities of the stock system, to maximize the potential of your other investments. Also, your built heads are going to affect spool time, so even if you know someone else with the turbos on this car, the results aren't necessarily going to be a mirror image of yours. Spool time will also be affected by the exhaust you choose, your elevation, climate, and every other piece of your build. They should spool much sooner than on a 2.7t, but for the most accurate answer, try contacting EPL, or another retailer for Tial turbo's that may have installed and tuned them on an RS6.
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    Registered User Elevens's Avatar
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    I tell you one thing, I have Milltek Catless Race pipes on mine and the Turbo's spooled up noticeably faster than when stock. Also the Milltek system uses 2.75" pipes over the stock 2.5", probably because it's better Tuned to our motors..........................
    03 RS6, VIPER ECU, MTM TCU, Milltek Full Catless Non Res setup from Turbos to the boxes(ROAR'S), H&R Coilovers, Hotchkiss ARB's, 19x10's with 275-30-19 PSS's at each corner, Kenwood 9960 Head unit, V1 Radar Locator. 517 Trans Rebuild, ScrollProducts Turbo Rebuild.

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    Registered User JSRS6's Avatar
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    Elevens, I'm gonna have to take a trip to your neck of the woods soon and hear your exhaust.
    Avus RS 6, RNS-E/BT/RVC, Eurocharged/MTM, SuperSports, PSS9/Hotchkis, SS Lines/EBC Reds, FMU/BMC, Sportec vents, 007's, 9500ci, Black Optics/Headlights/Trim/Rims, CC; coming soon: stage 3 snow meth

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    Speaking of trips (thread jack), i pass through jax quite often headed to Orlando with the family. one of these days I'll make a few extra minutes to stop by and meet.
    03 RS6 :: 01 allroad

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    Registered User JSRS6's Avatar
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    Sounds like a plan!
    Avus RS 6, RNS-E/BT/RVC, Eurocharged/MTM, SuperSports, PSS9/Hotchkis, SS Lines/EBC Reds, FMU/BMC, Sportec vents, 007's, 9500ci, Black Optics/Headlights/Trim/Rims, CC; coming soon: stage 3 snow meth

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    I'll see if I can talk wifey and 3 kids into a stop soon.

    Back on topic... I think the 2.5" stock exhaust is nearly maxed out with the K04's. If you look at the 2.7t guys with 770's, quite a few have 3" exhaust, if not all. The interesting thing is I saw one 770 2.7t build with stock exhaust manifolds. I think this my be purposeful and help spool faster. Backpressure is important but it must be balanced with air volume. If 770's mate up to stock 2.7t exhaust manifolds then your stock RS6 manifolds should work as well. Go for larger downpipes if budget allows. Otherwise, keep 2.5" stock dowpipes and gut precats. That is common man's method of upgrade. Keep us posted on build. that will be a monster. I assume you are rebuilding internals also? I'm sure if you did a 2.7t with 700's you know the drill.
    03 RS6 :: 01 allroad

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    All good points...I always like to think out loud.

    I might try and have some dp's made at that price though especially if I can find full 3" of the sheft. Although who know they won't come for a bit.

    I plan to use the stock exhaust and intake manifolds. Port and polish intake and cleaned the exhaust ports up but they should both be good for this build. Also the 770's should bolt right to the exhaust manifolds if not I'll have a new flange welded on to fit. Very true about what I do making it very different for me with spool times. I will need to upgrade the fuel pump and injectors though.

    And yeah I'm going forged internals but I NEED to find a good machine shop since our cylinders are alusil and not sleeved or iron. Not many people deal with this...if anyone knows of a machine shop that works on these blocks give me a heads up please. I have been told no need to hone or refresh if the cylinder is in spec but I want to verify with a pro first!

    And not 700 of the 2.7t more in the 550-600 range.

    Thanks all and if you know a good shop please let me know for the block work.

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    I've been thinking of alternate turbos and downpipes as well.

    I've been discussing TiAl turbos with the designer of the 2.7T kit on and off for a few years (ironically, today as a matter of fact) and it will not be easy but it is possible, requiring some fabrication. As far as I know, the flanges on the 2.7T exhaust manifolds are identical to the 4.2 manifolds. I'd be grateful if someone could please confirm this, because if they are, then it should be possible to use the 034 or similar downpipes built for the 770s that are available in 3" diameter. The big fabrication issues then become the piping to/from the compressor.

    From the stock RS6 turbo standpoint, I was thinking that the RS6 turbo 2.7T downpipes just might work on the RS6. It might be throwing away a few hundred on the SSAC downpipes just to test the theory. Too bad I don't have any turbos to go with my engine that currently on the stand.

    Also keep in mind that my main focus is on an 01E outfitted RS6 which buys some room.

    Lastly, look up HT Motorsport for a consult on the Cosworth block and internals.
    2012 Q7 TDI S-Line - 2010 GTI - 2007 A3 3.2 S-Line - 2003 RS6
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    Quote Originally Posted by SteveKen View Post
    I've been thinking of alternate turbos and downpipes as well.

    I've been discussing TiAl turbos with the designer of the 2.7T kit on and off for a few years (ironically, today as a matter of fact) and it will not be easy but it is possible, requiring some fabrication. As far as I know, the flanges on the 2.7T exhaust manifolds are identical to the 4.2 manifolds. I'd be grateful if someone could please confirm this, because if they are, then it should be possible to use the 034 or similar downpipes built for the 770s that are available in 3" diameter. The big fabrication issues then become the piping to/from the compressor.

    From the stock RS6 turbo standpoint, I was thinking that the RS6 turbo 2.7T downpipes just might work on the RS6. It might be throwing away a few hundred on the SSAC downpipes just to test the theory. Too bad I don't have any turbos to go with my engine that currently on the stand.

    Also keep in mind that my main focus is on an 01E outfitted RS6 which buys some room.

    Lastly, look up HT Motorsport for a consult on the Cosworth block and internals.
    thanks for the tip I will give them a call...seems very hard to find anyone that knows about these blocks outside of the Porsche areana and they won't touch Audi blocks (at least in my area) for some reason.

    also i believe that the flanges on the manifold are the same as the 2.7t's just as you said, if for some reason they aren't (i don't have one anymore to test this) all that would be needed is to weld a new flange on the end that fits.

    I have been looking at the 034 3" rs6 turbo down pipes as well and at just under $1k they are a better deal and seem to be very well made too. I was also thinking that these would work on our aplications but i have no way to confirm this and through all my research over the last 6 months or so i haven't found anyone that has done it. Just a lot of "don't do that, don't do this, that doesn't make sense, waste of money, impossible, your better off just selling and buying X", all comments that i hate hearing. 034 also sells the rs6 turbo downpipe flanges for around $150 i believe if you choose to have some fabed up that is a good starting point.

    I managed to pick up a s6 4.2 bare block from a local salvage yard that i'm hanging onto incase i want to go 6spd since the 01E trans bolts right to that block.

    for the purposes of info sharing I believe that the 2.7t and the 4.2 in the A6/S6/RS6 all share the same connecting rods (154x21) i haven't phyiscally verified but they both do use the 154x21 rods. i don't have a spare 4.2 and 2.7t rod laying around or i would measure the crank opening and give a 100% on this.

    I do know that if you don't bore and sleeve the cylinders that you have to use customs pistons for the alusil walls, they have a coating on them that allows them to work properly with the aluminum/silicone wall surface.

  11. #11
    Registered User ttboost's Avatar
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    Based on what I have seen so far. I think the stock exhaust is plenty big for the stock engine and turbos. The biggest rectriction on this car is the turbine housing. Once the exhaust finally gets through that nightmare, it's free flowing...well it's as free flowing as the precat, cat, resonator and mufflers allow it to be.

    Tony might be a good resource for this as he has tuned many RS6's and now we have spent quite a little time with my 6 speed car.
    I have the 01E, stock turbos with upgraded wastegates (10psi cans) and 100% gutted custom made downpipes. All else is stock. I have noticed much quicker spool and power seems to carry out a little farther...not much more because of the turbine housings...but better. Car feels violently faster...we have picked up 50-70whp and over 100ftlbs so far and we are not done tuning yet.
    2013 Audi S8

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    all sounds very promising! thanks for all the info.

    also, Tony? new here remember haha...who is Tony?

    thanks again.

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    Registered User ttboost's Avatar
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    Tony Chick. Owner of EPL in Stratford, CT. Very reputable Porsche/Audi tuner.
    2013 Audi S8

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    Quote Originally Posted by SteveKen View Post

    Lastly, look up HT Motorsport for a consult on the Cosworth block and internals.
    Ditto. He and Marc Swanson at EFI Express are working on that right now so they know all about what needs to be done to the block.

  15. #15
    Registered User HT MOtorsport's Avatar
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    Quote Originally Posted by UrS6 View Post
    Ditto. He and Marc Swanson at EFI Express are working on that right now so they know all about what needs to be done to the block.

    Yup, We have a lot of experience in these motors, feel free to drop me an email haydn@motorsport-HT.com


    We recently finished up a monster build on the RS6 lump. Nickasil bores, custom pistons and rods, custom CNC heads, custom intakes, custom exhaust, dual Borg Warner EFR's etc etc. We made 1000+ Lbtq and 850hp. Note this motor is built as a DD not a HP big number lump, hence we can hit 35psi of boost by 3K rpm = 1000lbtq by 3K too.

    HP is limited by the stock cams, we are working on a custom cam setup for high boost.

    Here is a video from our dyno testing, this is close to the final tune but not quite as I didn't get good video of the last runs.


  16. #16
    Registered User HT MOtorsport's Avatar
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    Another video. Pump gas pull at 16psi boost, earlier in the testing.

    Note this motor has 16 injectors and we run pump gas on 8 and race gas on 8 and have the ECu blend between the two as boost rises past 20psi


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    Quote Originally Posted by ttboost View Post
    Tony Chick. Owner of EPL in Stratford, CT. Very reputable Porsche/Audi tuner.
    got ya thanks, very fimilar with EPL, i guess i just didn't put Tony and EPL together ha.

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    you know i've seen some of your work, just didn't know it was you guys.

    i will be emailing you shortly.

    great news on the spool time and 31PSI at 3k rpm is amazing!

    also i think i just feel in love with that motor ha.

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