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GT-R DUN, Son.
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Ok so lets say your turbo outlet to the DP is 3.5" and you got a DP that is 3.5 as well..and an exhaust thats 4" (HKS titanium)

So lets say now that we put a full 4 inch DP exhaust and it bolts up to the 3.5 turbo exhaust outlet. Your still bottlenecking at the exhaust outlet at 3.5" so doesn't it render the extra .5 inch moot? Obviously people don't think so....and I just wanted to know the argument for why I should go with a 4" DP when the DP I have is 3.5" and matches the exhaust outlet of the turbo...obviously having a 4" is just an overkill right? would the gains be worth the additional cost?
 

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Ok, ok, maybe 500rwhp!!!
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Hah! I too was just thinking about this, and it was just last night about my VS Ti and 3.5" dp (BL).

Currently, I have a 3" dp bolted to the VS Ti 3.75", and the VS Ti has a step down to 3" for the 3" downpipe.

Now, when I goto upgrade to the 3.5" dp, It'll be stepped down to 3", the back up to 3.75" on the VS Ti.




Brian
 

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brian, in regards to your 3.5 dp, i think what most people do is they basically just cut off that reducing section of the veilside and put a test pipe/dp extention to bolt it up to the veilside with some custom flange they make.

in terms of what use is it to have a bigger exhaust when your turbo outlet is only 3.5 inches. just because you can only squeeze it through that area in the beginning, doesnt mean that it doesnt want more area. ill try to explain:

think of pressurized air or water in a tight space...like a balloon, when you let go of the end, the air is going to flow through the small opening and out into the atmosphere...if you carried that same diameter opening on for 8 feet or so (like 1cm diameter) then it would take a long time for that balloon to deflate. however if you hooked up like a paper towel roll (or wrapping paper roll) to the end of that same balloon...even though it is coming through the same 1cm diameter opening at hte beginning. the balloon will still deflate MUCH faster due to the lack of backpressure in the 'piping' that is the wrapping paper roll.

now i HOPE that made some sence...as you can tell i was reaching for my example :D
 

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LYTLdiablo-
That's a really good example.

brianb-
Were are you getting the 3.5 inch downpipe from? I'm also looking for one, but I need it to fit the stock turbo manifold. Does yours go with the stock turbo?

Thanks
 

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The new #1 Hardtopper
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This was explained to me by one of the techs at Precision turbo.When the exhaust comes out of the turbo it is in a circular fashion much like a tornado.Its not until the tornado exits the velocity of the turbine housing that it begins to get wider.At this point the exhaust follows the walls of the exhaust pipe until it hits a bend which causes a disturbance in the tornado and causes turbulance.The larger the pipe,larger the tonado,the less turbulance,the less restriction.He went on to say that some of the techs are putting plates in the center of the downpipes at the exit of the turbo (creating to "half tubes") up to the first bend in order to break the tornado and make it use the whole pipe diameter at the bends but the results have been hard to measure. The best possible is to have no bends and keep the tornado going.

So in answer to your question REG,the exhaust is in a thin stream (tornado)when it exits the turbo anyways so increasing the diameter an inch or two later than the housing wont be an issue.
 

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Transition? We don't need no stinking transition!

I love my Burns Stainless transition. (3.5" full DP to 4" catback)



Btw, having Vbands throughout my exhaust system was worth the 90 bucks per piece. I hate dealing with exhaust bolts.
 
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Well how about a hole in the hood and a 4" turn up exhaust! Flames shooting out of the top of the hood....who hoo!
 

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Ok, ok, maybe 500rwhp!!!
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Parham said:
LYTLdiablo-
That's a really good example.

brianb-
Were are you getting the 3.5 inch downpipe from? I'm also looking for one, but I need it to fit the stock turbo manifold. Does yours go with the stock turbo?

Thanks
LYTLdiablo,

Understood.

Parham,

I have a Boost Logic turbo kit on the way (67GTQ), and opted for the 3.5" mp/dp.

Silvino,

Are there other transitions available? Say, if I hacked off the reduced flange, then used a straight 3.5" to 3.75" stainless pieces with clamps, think something like that would work?



Brian
 
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What would the benefit be with a 3.5" downpipe vs the standard 3" on a 71GTQ?
 

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how much power? lots of factors come into play there...in terms of what it would do...it will help spool and give you more power.
 

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Brian, they have various sizes but you'd probably use the same piece I did.

http://www.burnsstainless.com/Transitions/transitions.html

You'll end up doing something similar to what I did which is to cut the transition piece when it gets to 3.75". I used the 3.5" - > 4.5" transition piece and cut when the larger side was only 4" and welded on the 4" Vband flanges to each side (cut my HKS Ti too which is NOT titanium piping, just canister).

Link to vband flanges:
http://www.burnsstainless.com/Hardware/Clamps/clamps.html

I can see two possible problems you'll have and I'm not sure what to tell ya as an easy solution but you can ask around.
1) 3.75" isn't a standard vband flange but maybe someone else besides burns makes one.
2) If you have a true Titanium piping on that catback, I'm not sure if you can use the standard flange or must find a special Ti flange.

Sil

brianb said:
LYTLdiablo,

Understood.

Parham,

I have a Boost Logic turbo kit on the way (67GTQ), and opted for the 3.5" mp/dp.

Silvino,

Are there other transitions available? Say, if I hacked off the reduced flange, then used a straight 3.5" to 3.75" stainless pieces with clamps, think something like that would work?



Brian
 

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GT-R DUN, Son.
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Discussion Starter #12
hey great answers guys! Specially diabalos! I see the light!
However when exhaust cools it should contract but in any event its convinces me to do something about it! IN the process of having a buddy make a 4" DP to the hks tit exhaust for the greddy kit
 
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What kind of gains could you expect to see in spool and HP by going from a 3" to a 3.5" downpipe on a 71GTQ? I just want to know if it is worthwhile
 

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Burns made me a custom-sized long transition at essentially no extra charge. That way you take advantage of the long taper as opposed to chopping some of the transition length off. Like Silvino, I love the V-band system -- makes it a snap to remove any part of the exhaust.

I also built a down pipe that goes from the turbo to exit behind the passenger side front wheel -- no muffler, just 3.5" mandrel bent tubing. The turbine whistle with that thing is insane. There is so much turbine whistle that it is almost louder than the exhaust portion. :D

Steve Hayes

silvino said:
Brian, they have various sizes but you'd probably use the same piece I did.

http://www.burnsstainless.com/Transitions/transitions.html

You'll end up doing something similar to what I did which is to cut the transition piece when it gets to 3.75". I used the 3.5" - > 4.5" transition piece and cut when the larger side was only 4" and welded on the 4" Vband flanges to each side (cut my HKS Ti too which is NOT titanium piping, just canister).

Link to vband flanges:
http://www.burnsstainless.com/Hardware/Clamps/clamps.html

I can see two possible problems you'll have and I'm not sure what to tell ya as an easy solution but you can ask around.
1) 3.75" isn't a standard vband flange but maybe someone else besides burns makes one.
2) If you have a true Titanium piping on that catback, I'm not sure if you can use the standard flange or must find a special Ti flange.

Sil
 

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Steve, holy crap. tell me you have an vid clip or even a sound clip of the dp dump. i notice you live in florida, id love to stop by sometime and check out what you have done...i can just imagine how that sounds :eek: do you use that when you go to the track since its so easy to take off your exhaust due to the v band's?

Mark
 

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Boost Junkie said:
Burns made me a custom-sized long transition at essentially no extra charge. That way you take advantage of the long taper as opposed to chopping some of the transition length off. Like Silvino, I love the V-band system -- makes it a snap to remove any part of the exhaust.

I also built a down pipe that goes from the turbo to exit behind the passenger side front wheel -- no muffler, just 3.5" mandrel bent tubing. The turbine whistle with that thing is insane. There is so much turbine whistle that it is almost louder than the exhaust portion. :D

Steve Hayes
Steve, did you just fake an exhaust then out the back? Do you run the dump tube to the same spot?
 

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LYTLdiablo and Adrocktt,

Sorry for the delayed response. I've been in Vegas for about 10 days. :)

I only ran the dump DP for a couple days. It is so loud I'm afraid to go near cops with it, particularly with the outlet sticking out right behind the front wheel. If the dump were under the car I'd be less worried, but with it sticking out so menacingly behind the wheel, it is just begging for police attention. :(

I don't have a video or sound clip, but I'll try to make one next time I have the pipe installed. If someone wants to host a picture shoot me a message at [email protected] and I'll send a couple of photos of the dump DP on and off the car.

LYTL, I live in extreme NE Florida (Amelia Island). Let me know if you're ever up this way.

Next time I go to the dyno I'd like to dyno with the full exhaust and then also with the dump DP to see if there is any difference in power. As wrong as it sounds, seat-of-the-pants and traction/lack of traction says that the car doesn't make as much power with the dump as it does with the full exhaust. :confused: However, I really need to see that confirmed on the dyno to believe it.

Once the car is jacked up enough to get under it, removing my entire exhaust system (turbo back) is about a 5 minute job. V-bands are great. :)
 
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