Matt M

In our quest for more power out of our 08 SS/T, we decided to try swapping to a larger TB. I didn't expect huge gains based on past experience with forced induction TB sizing, but I was hoping to see a 2-3 HP gain. The TB we chose for the upgrade was the 2.4 LE5 TB. I don't remember the exact sizes right now, but the LE5 TB is 4 or 5 mm larger than the LNF TB. Here is a pic for comparison:

We machined an inatke to match the LE5 TB.

Current setup on my SS/T includes:
ZZP airbox mod on factory airbox
AEM intake tube
Stock turbo
ZZP upper charge tube
Stock intercooler and lower charge tube
ZZP ported head
ZZP offroad downpipe
ZZP custom catback
ZZP tune

When dyno testing new parts on the LNF, we use an external boost controller to keep the PCM from altering the boost level and skewing the results. After several dyno pulls in the 335-336 whp range using the stock TB, I swapped in the new intake manifold and LE5 TB. The swap was very easy and the car idles smooth and has throttle response not much different than before. Unfortunately, the dyno results were not at all what I was expecting. After 3 pulls, the best number it put down was 323 whp. There are no vacuum/boost leaks. The MAF readings decreased in correlation to the HP loss. Here is the graph:

While I realize that over-sizing the TB does not offer HP gains in many situations, this is the first time that I have witnessed a significant loss in HP from a swap of this type. I am going to look into this a little further tomorrow. I'm hoping that for some odd reason, the 2.4 TB only opens half way with the same signal that opens the LNF TB 100%. However, I'm not holding my breath, as that seems like a long-shot.

marcusicp

Maybe try swapping over everything from the LNF TB to the 2.4 TB?

mkriebs

Interesting idea. Definitely staying tuned for more info...

I would imagine more airflow would be a good thing, lol. Hope it gets panned out. Have you thought of trying this on the big turbo balt?

Mazdaboi318

400 tq?

Matt M

The highest it put down so far was 411 ft lbs.

Mazdaboi318

VERY impressive man... wow. i had no idea....

BIGTAG

thats sweet hopefully as soon as you guys get the head up forsale im gonna be on it like flys on ****

mkriebs

Wait... you are pushing 411 ft lbs from the stock turbo?!?!!?!!??!?!?

Holy smokes.

Mazdaboi318

I appreciate what you guys are doing Matt btw....

marcusicp

x 2!

mkriebs

x3!!!!!!!!!!!

ralliartist

tq falls off rediculously fast.

steddy2112

iTrader: (1)

I have never seen a dynograph where peak HP is made at like...early as fack

And that is the tune making it spike up and fall so much

boostking

looks like the torque is just a boost spike. I am going to go ahead and assume the maps are clamped and your spiking the turbo in to the upper 20's to get that torque. yes/no?

OneCOLDBIZL272

iTrader: (2)

yeah it possible my 09ss/tc is 316hp394.6lbs tqr
all that done to mine is 3" custom intake, 2.5"custom hardened charge pipes hot/cold sides, BIGGER intercooler,3" custom downpipe, solid trans mounts, solid upper motor mount. Custom tune 23lbs of boost.

Terminator2

larger TB will never work properly because the ECM calculates the pressure drop over the diameter of the TB. Changing the diameter skews the readings the ECM gets and it looses power as you all saw. BTF stated this fact a few months ago in a thread about ported throttle bodies and such.

And no one believes that I am pushing 345 whp 375 wtrq. Glad there are others with similar numbers, and more torque too.

Matt M

Most people think that tunes are making the boost spike on these cars, which is not what happens. The actual problem is that exhaust pressures get too high for the wastegate to control boost consistently. Exhaust just pushes past the gate and boost falls off. If you roll up to 5000 RPM real slow and then go WOT, the peak HP number is 10-15 WHP higher.

Having said that, yes boost is over 25psi at the start of the pull, and down to about 17 by the end of the pull.

The PCM does in fact compare the pressure readings, but what are you claiming to be the reason for the HP loss? Are you saying that the ECM closes the throttle until the pressure drop is where it would like? And if so, why would there be a loss of power instead of the same power?

revhigh18

how hard was it to get the head off for porting lol

PimpLay2

i might have to drive to MI to get my head ported

Terminator2

That was about 70 mph in third gear which is over 4K rpms. Right where my torque peaks too. Most peoples pulls start at 2-3K not 4k.

You got it. Because the diameter is changed you are in effect fooling the ECM into thinking it has reached it target pressure drop when it has not. I think the bigger throttle body is tricking the ECM into thinking it has reached the point sooner so less power. IIRC it is kinda like the DALs when you mod it reaches the target airload sooner with less boost pressure needed. The air velocity is decreased compared to the stock opening because of the larger surface area an that is skewing readings. I wish I knew more. I would contact Baldturbofreak if you want to know more. He knows what happens exactly when you change the diameter of the throttle body on the LNF.

It is a pain.You have to remove the valvecover, cam chains, cams, manifold for the turbo, turbo itself, etc. It is a big job unless, and you are a master mechanic I would not attempt it.

1badBlueberrySC

THAT WAS NOT THE STOCK TURBO! CHeck their other thread people... this turbo runs out of breath well before 400ft/lbs

mkriebs

To quote the OP:

1badBlueberrySC

THey are yankin' someone's ding dong... in their other thread...

411ft/lbs was on an upgraded turbo!

mkriebs

Thats what I thought... but it also turned much more HP than 323 to the wheels. I asked in my first post, and didnt get an answer.

1badBlueberrySC

The turbo cannot support 411ft/lbs...

Just ask Terminator pretty much has max'd it out... at 350whp and 375wtq

I smell somethin.......