geeteego

iTrader: (1)

OK, short story:

STS, 76GTS intercooled turbo, 364ci iron block with stg 3 ported heads, fairly stout reverse-split cam, Vic Jr/Sheetmetal upper, 90mm ported TB.

OEM STS hotside:
Manifolds
2.5" JBA catless mids
2.5 and a ?2" y-pipe into a single 2.5" pipe back to the turbo.

I know the LT debate has been beaten to death, and this is NOT about that, but at my CI displacement and potential exhaust flow into the compressor vs the output side, am I creating a restriction by this weenie-size piping? I never realized the driver's side of the Y pipe was 2" OD.

I am seeing poor low-end #'s on the 0-3k rpm side, where a better-flowing exhaust would be incredibly helpful, and I think there's some peak power to be had as well.

Thanks!
-Ronnie

koolaid_kid

iTrader: (21)

I don't know about the hp. ratings, but you should wrap the exhaust either way. It really helps keep the heat in the exhaust, which increases power and spin up time to the rear mount turbo.

smoke20

iTrader: (2)

i know there have been numerous threads about LTs and how much heat they lose. but i believe that due to their flow rates the HP gains might offset that. with that said your not going to know until you make the swap and check your track times. im currently running a Bassani Y-pipe 2.5" which then dumps into a Borla 3" cat back - welded to the turbo flange. stock manifolds and heat wrapped from manifolds to the turbo.

your really not going to be able to answer the question until you make the switch and see how your #s turn out. good luck.

Zombie

iTrader: (2)

Nope, doesn't work, tried it, so did one of my friends. Sucked HARD.


Geeteego, as for the stock exhaust setup, I went from 3" unisulated to 2.5 insulated and have gone much much faster. The turbo is a cork in the exhaust. If the turbo is only capable of flowing 700 HP worth of exhaust out of it, adding a 4" exhaust setup before it won't help. The turbo is almost always your limiting factor in producing HP.

I'm flowing at least 850 HP worth of exhaust through my 2.5" setup.

ddnspider

iTrader: (26)

totally overkill for a setup like yours and could possibly be why your lowend is so soft.the OEM STS hotside is saving you.besides running piping all the way to the rear of the car and then back up to the intake youre also slowing the velocity of said air with that intake setup.smaller pipe=more velocity=better lowend and starts to choke up top.id put money if you swapped to an ls6 and a stock ported TB your lowend improved......which ive got,wanna trade

geeteego

iTrader: (1)

Oddly enough, it feels like it's being held back. Previously, with the box-stock LS1, LS6 intake and 78mm TB, it made over 600 to the wheels, proving your theory on flow capability...but even then, the torque curve was more Supra than V8 turbo. I figured with 18 extra cubes coming from a forged assembly, it would flatten out the curve somewhat, but same deal.

Zombie, that GTS76 should be able to handle waaay over 700whp, which is where the car theoretically should be.

Zombie

iTrader: (2)

Poor low end response is the almost always the result of lag. The trick to reducing lag is keeping the heat in. Is your exhaust setup fully insulated? If it is and you are still having isues, then you need to examine the entire exhaust system for leaks as well as the intake side. What a/r is your turbine housing? Spool can be improved some by tuning, but the biggest improvement is by keeping all the heat in the exhaust.

The other big thing that improved my spool response was converting to an automatic. Putting the turbo far away from it's energy source has it's limitations and you have to be willing to work within those limitations if you want it to work well. The automatic allows you to load the engine harder sooner and get into a higher rpm faster due to converter slip, all of which improve spool dramatically.

ddnspider

iTrader: (26)

id wrap the entire exhaust and try swapping back to a stock intake setup.whats your downpipe setup consist of,just a dump?thats the same turbo i have in my 383 front mount setup.i run an ls6 intake and a ported stock TB and my boost threshold is ~2700rpms depending on what gear.also what are u running for the inlet on the turbo?

geeteego

iTrader: (1)

I'll be wrapping the entire exhaust this coming weekend. It's a .91 A/R, so it should be on the quicker side spooling.

No auto for me...until it becomes a drag queen, I like rowing. (I'm actually more of a roadracer, anyhow.)

I'm keeping the intake for now. My other option is running a little gas to "encourage" quicker spool times.

ddnspider

iTrader: (26)

i dont recall there being a .91 A/R for a T76GTS,i thought there was a .96 and a .8x.im with you on the no auto swap.but running gas is just a bandaid for a problem,not a solution

geeteego

iTrader: (1)

This is where it gets a little weird. Mind you, I know nothing about turbos. I just knew it was a 76mm.

Guy that sold me the turbo says it's a GTS. I hear it's a GT76 from other sources. I can't see the backhousing, so I can't tell the A/R for myself. I've heard .91 and .96...

I have some pics on the home computer of the actual unit.

ddnspider

iTrader: (26)

.96 sounds right.and if so thats the LARGER of the housings not the smaller