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iTrader: (3)

Hey everyone, well i need to take my car up to the fabricator either in may or june and i am debating about needing to change the downpipes. Here are my plans: run 2.5" downpipes with cutouts on the ends when i need big power i will open the cutouts and for normal driving i will have a truel dual setup that goes over the axle. Will 2.5" dowpipes be as much of a restriction that some make it out to be? The only real option i have is to go from 2.5" to 3" pipe. I can't be at 3" from the flange because i do not think i will have enough room while retaining a good flow angle on the downpipe and keeping the clearances safe. Each turbo will possibly be producing 625 hp max (i would pretty much need that to reach my 1000 rwhp goal). To me it might not even be worth it to get the downpipes modded to expand to 3" unless that will hurt me so much in making the power i want (given everything else is up to the task of making the power i want). I will still run the cutouts if i get the downpipes expanded but i honestly would prefer to leave them alone. BTW this is a CAS designed kit that i am modifying.


Greg

smokinHawk

iTrader: (48)

one 3.5" pipe has 9.62 sq in which where id beleive a minimum sized exhaust for that level (being single exhaust)
though people have made 1000rwhp out of a 3" downpipe, which has 7.07 sq in

two 2.5" have a total of 9.82 sq in (4.91 si each) so you should be good to go.
id still flare out the exhaust to 3" if you can bigger is always better in this case. And cut outs will help also if your trying to squeeze out every bit you can

Dustin Mustangs

From a strictly text book standpoint, two pipes that add up to the same cross-sectional area of a single larger one will not flow as well as well as the single. Frictional losses will be higher for the duals due to a larger "wetted perimeter", although not actually wet in this scenario. How much this will have an effect on flow numbers depends on a lot of things, the two main ones being the equivalent roughness of the inside of the pipes and the medium you are trying to flow. In this case it's most likely very marginal.

smokinHawk

iTrader: (48)

yes thats true, but those are minimal loses.
the extra area the two 2.5" pipes have can make up for it.

Louis

iTrader: (7)

3" will spool quicker than a 2.5 if that is an issue for the setup.

JZ 97 SS 1500

iTrader: (2)

The bigger the downpipe the quicker the spool (less backpressure/resistance to turbine flow)

Boostaholic

iTrader: (4)

I'm running twin 3in down pipes on mine.

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iTrader: (3)

Well of course i want the most efficient setup as possible but if 2.5" exhuast will cause my turbos to spool 50 rpm higher as compared to 3" then why should i bother? If 2.5" will restrict me from making big power up top like in the 800-1000 rwhp range then yeah it would be a good idea to make it 3" so i have the option of one day running that much power. I am running t3/t4's with a stage V p trim exhaust wheel and a .63 A/R housing. Would the housing and the wheel keep me from meeting goals rather than the downpipe? If my turbos aren't even going to be able to flow freely enough to make the power i want then why should i bother making some big mods to the downpipes? I know this is a tough question to answer but if anyone is familiar with the .63 housing might know the limitations.


Greg

JZ 97 SS 1500

iTrader: (2)

2.5's are fine for 1000rwhp

eviltwins

50 RPM's? Try like 300-500 RPM's. 2.5" is too small for trying to put twin T3 housing turbos on a large motor, and making 500 RWHP out of them. On 300 WHP single turbo cars 25 WHP is not uncommon by going from a 2.5" to a 3" downpipe. Do 3", it's worth it.

osuhunter07

iTrader: (10)

I am currently buying a CAS kit tomorrow the check hits the mail, is there enough room to take the down pipe to 3 inches? Havn't even got my kit yet, but quicker spool= more fun

smokinHawk

iTrader: (48)

with ONE 2.5" it would be way to small, but remember he is going to be using TWO.
two will be ok, the two will have more area then one 3.5"

69firebird

iTrader: (14)

yeah there is, however it is a 2.5" pipe that goes from turbo about half way down the firewall, and then flares out to 3"

its not 3" all the way, and i honestly dont think 3" would even fit all the way down

youre going to love the CAS kit though, its a really well engineered kit

eviltwins

I was talking about a single 2.5" downpipe on a car with one T3 turbine. 25 WHP on a 300 WHP car is a lot. 1000 WHP from a 347+ inch motor pushing through twin T3 turbines is a lot more exhaust and backpressure than 300 WHP from a grand total of 100 cubic inches pushing through a single T3 exhaust housing. On his setup I don't think it's a strech to say 80-90 RWHP at the 1000 RWHP level going from 2.5" to 3" downpipes.

disassembled

iTrader: (3)

I am probably going to expand the downpipes to 3" so i don't wind up shooting myself in the foot when i try to go for some big power and have to make it bigger anyway. Thanks for the words. If there's anymore opinions or any cases of people making similar with similar turbos + downpipes please speak up I am just trying to do this right the first time and only doing what is necessary as i would like to not waste any more money.



Greg

Louis

iTrader: (7)

I feel that backpressue preturbine will be your enemy once you start to crank the boost up. T3s are teeny for this goal.

JZ 97 SS 1500

iTrader: (2)

He's going to use T3's??? I guess I overlooked that...

disassembled

iTrader: (3)

T3 t4 hybrids are all i can fit(this a CAS kit that places the turbos next to the block). John Craig at Limit Engineering thinks these turbos will be good for 625 hp each. Like i asked earlier, should i not even worry about making the downpipes 3" if my turbine housings are going to be the majority of the problem?


Greg

Jammer

iTrader: (1)

With the cas kits, tony flared some kits to 3" to make up for the waste gas re-entering the system. If you vent to atmosphere, or run the waste gates their own pipe, you will effectively be similar to one og the 3" CAs kit designs.

qqwqeqwrqwqtq

I think that log manifolds and t3/t4's will hold you back long before 2.5in downpipes will.

That, and the exducer bore is no bigger than 2.5, so I don't think 3in downpipes would be worth the trouble with those turbos.


I honestly don't think you will come close to 1k rwhp with that setup. Those turbos may be capable of 600+hp each on a small displacement 4 valve/4cyl that is running 30+lbs of boost, but not likely on a large displacement V8.