Karpellarpy

iTrader: (3)

I have an M6 street car with a ls2 402 and an sts kit that's in need of a new turbo. I've done a lot of research on turbo sizing, but haven't been able to figure out what turbo will work best. It seems like the turbo math for calculating the correct size would need to be scaled and tweaked to take into account for the turbo being mounted in the rear. Also, getting information on sizing the turbine side, especially on a rear mount, has been hard for me to come by. So I'm looking for turbo suggestions, and the reasoning (i.e. math or empirical evidence) behind your choice. I'm looking to make 700 rwhp max and since this is a manual street car, spool is really important. Useful motor specs: dart pro1 225 heads, TU2 236/236 .587/.587 112.5 cam. Thanks in advance for the help.

spaz1

iTrader: (9)

I was talking to forcedinductions and he suggested a tc76 or tc78. for my car and it is pretty much same engine you have - the dart heads. It would bolt right in place and they are about $1000.

Karpellarpy

iTrader: (3)

Yeah, I've looked at this turbo, but I've also heard some rear mount guys complaining about backpressure problems with it (96 a/r), and that peak power comes in early (4500 rpm) and then falls horribly (up to 250 hp) by redline. I'd like some data on how much the f1-68 turbine will flow compared to the old p-trim wheel, or some real world results with the tc76 before I went in that direction.

spaz1

iTrader: (9)

What have u heard about the 1.15 a/r units. This is brutal trying to ge proper info hey. I'd like to only have to do it once and be done with it.

Zombie

iTrader: (2)

Tough situation, big cubes + 6spd + rear mount.

If the comp side is too small, no top end. If the turbine wheel is too small, no top end. If the turbine is too big, lag.

The 78mm might get you to where you need, you'll just peak around mid 5000's and then be out of steam. A 408 really needs a 88mm if you want to rev it.

Your need to keep as much heat in the exhaust as possible. My exhaust is currently being redone to 2.5" Y pipe into a 3" I-pipe going under the axle (shorter run). Will be coated and wrapped. I'm interested to see how it affects spoolup.

spaz1

iTrader: (9)

Hey zombie I am gonna go auto now. What so you think of the tc78?

Karpellarpy

iTrader: (3)

I've been working at keeping the heat in. I'm running stock '02 manifolds, a bassani 2.5" ory into a 3" i-pipe (v-band) that has an ultraflow bullet in it. From the manifolds to the turbo is wrapped. Then to help with backpressure, I have a 4" exhaust from the turbo. I know the big cube, M6, rear mount is tough and that's why I'm asking for advice, and/or examples from people who have successfully done it.

stevegrizzle

look into the quick spool valve

Zombie

iTrader: (2)

Too small, go to an 88mm with a small hot side. Or see if you can get a quick spool valve. Auto + turbo =

Karpellarpy

iTrader: (3)

so since I'm an M6 maybe the TC78 will work correctly for my application?

stevegrizzle

It will spool fast but now make great peak power as stated

Karpellarpy

iTrader: (3)

what about a precision 76gts or a standard T76 or one of garrett's billet wheeled units, etc?

Karpellarpy

iTrader: (3)

no help? What about just turbine flow numbers to help with picking turbine side. I know the p-trim turbine is too small for my cubic inches ... how much does it flow? How much do the q-trim, s-trim, f1-68 trims flow (given the same a/r ... say .81 or .96)?

hawk584

iTrader: (1)

what are your goals

Karpellarpy

iTrader: (3)

my goals were specified in my original post. I'm looking for 700rwhp max with excellent spool since the car is a full-weight M6 street car. Would like to get the car capable of running 10s.

sujomatt

iTrader: (7)

700 should b easy with those cubes im planning an ST80 with a QS Valve on mine.. im doing a 370/same cam as u/rear mounted/1.25 a/r .. i am lookin for 750 minimum lol

Karpellarpy

iTrader: (3)

Ok, it looks like you're just following Zombie's build, so you're probably a stalled auto as well. How did you decide on that turbo and the a/r? You said you're looking for 750, which means that your turbo choice and combination is unproven at this point (no offense). I don't have a QS valve, and I'm not currently planning on using one. Also, that turbo is fairly large in physical size, too large I think for my daily driver (plus the expense and hassle of adding additional bracing and whatnot). What size/trim is the turbine on that turbo?

sujomatt

iTrader: (7)

Yes I decided on the turbo based on the way it moved out for zombie. As for trans - i have an M6, it is not my DD - just a weekend queen. Track sometimes for fun. i am running meth. decided on this for more room to grow - heads/trans, etc etc. 83mm turbine

i was recommended the TC78 as well btw lol

Karpellarpy

iTrader: (3)

Yeah, I guess I'm looking for a suggestion based on turbo specs (i.e. turbine ? will flow x amount, which equates to y hp with z backpressure, and compressor ? has a map that fits well with the flow requirements of a 402) or based on a working setup that's close to mine (4xx cubes, M6, rear mount). The only close example I've found is a 76gts with a .81 a/r on a 422ci making 760+. Basically, I'm not looking for suggestions without some proof to back it up, or said another way, I'm looking for ls1 *tech*, not ls1 popular internet parts.

eviltwin_1987

iTrader: (18)

People here are try to help you and your not listening. Like stated before a tc78 will hit your goal but will choke you out up top. Your asking for two things when you can only really have one and then getting mad when people tell you that. With your 6speed you need to make a decision, faster spool and not great top end or slower spool and great top end. There isn't a magical turbo that does everything.