Ditching the idea of twins and looking at single turbo now. No way to run down pipe on driver side… ugh.

So looking at T76 single on pass side with a 3" down pipe, then I will make my own 3" mandrel cutback with a 3"x18" muffler with a single 3" exit on the driver side rear bumper. (should make it really quiet and fun on the street )

Motor is stock 1999 LM7 5.3LS with 150K, I pulled the valve covers and motor looked pretty clean.

Motor mods:
Already got brand new GM LS6 valve springs to put in.
Have new Fbody oil pan, pickup, windage tray, dipstick on the way
Stock truck accessories, new 130amp alt and gear reduction starter
Stock truck intake, EGR and purge blocked. Looking into plugging rear brake booster vacuum port and inserting IAT sensor in intake, 2 bar MAP sensor
Stock ECM, de-pinned and modded OEM to standalone harness, HPT tuners
adjustable setback motor mounts, solid motor mounts to racecraft moly Kmember.
Rest of motor is going to be all stock! Looking for 8-10psi boost

Turbo specs:
Compressor Inlet 4"
Compressor Outlet 2.5"
Bearing Ceramic Ball Bearing on Compressor Side Compressor
Cooling Oil + Water
Oil Cooling Fitting 1/8" NPT Feeding. M8 x1.25 Return Flange Mounting Screws
Water Cooling Fitting M16 Threaded
Flange Standard T4
HP Rating 500-700 HP
Internal Wastegate None
Compressor 76mm Wheel Compressor
Turbine P Trim .96 A/R Turbine
Compressor Wheel 102.4mm/76.7mm
Turbine Wheel 74.1mm/64.6mm
Hot Side 3" V-band

Exhaust will be a 3" down pipe snaked all the way out the back to a 3" cutback style with single exit on the driver side. I honestly thought that 3" cutback is only good for 450 fwhp but the turbo only has a 3" Vband. Maybe it won't matter? Otherwise 3" to 4" Vband adapter and 4" downppipe with a 4" cutback (going to be super annoying to fab since I run dual 3" now. But if you guys think 3" won't be enough then I have no choice.

What do you guys think about the setup? turbo okay? Looking for boost early in the RPMS like maybe by 3k? I have a 2004R with 2400 stall billet converter and 3.55 rear gears. I currently cruise at 2000 rpms on the highway at 80mph with the converter locked with a 28" tall tire. Which is nice bc I would be out of boost at 2K for cruising and downshift and boost starts!

Help me pick out the turbo!

 

Look at a gt45 or the 7675 from vs racing

Run larger exhaust, 3.5 ideal. Ok to have 3" for a foot or two but should neck it up to 3.5-4" for 550-650 whp else you may start to have backpressure concerns

A single ptrim 64/74 turbine like you list in the op, is too small. Its been used as a twin turbo and a 5.3 will spool two of them very well with right tune and mild cam. As a single its gonna be way fast to spool but choke out early. Wont make the hp

Else run a turbonetics tc76. Its got a larger 68mm turbine wheel but it flows alot more for its size due to design. .96 ar. Its same size as the one you list but makes 550-650 in those motors as a single

Anothet good option is borg warner s366 for 550-600$

 

Thanks Orr.

Can you specify some specs I can look for? It gets confusing when you see the HP rating of 500-800hp from the orignal t76 turbo and then like a borg warner turbo rated to 320-800hp but the t76 is too small. I get the wheel size and A/R but I don't know the range I should be looking at.

Here is a borg warner (one you pointed out) but has .91 A/R

Turbo Part Number: 177275

Comp. Wheel OD: 3.60
Comp. Wheel Inducer Diameter: 2.60(in.) 66(mm)
Turbine Wheel OD: 3.14(in.) 80(mm)
Turbine Wheel Exducer: 2.89(in.) 73(mm)
Turbine A/R: .91
Cartridge Assembly: 176646
Service Kit: 318393


This one uses a 4"Vband exhaust. With my original turbo I was thinking of running the 3" back to the trans pan where I have the fram knotched for 3" tubing and then run a 4" catback to help with the backpressure. Which would mean there was 4-5ft of 3" tubing which is probably too much.

 

I found the exhaust routing to be the toughest part of a single. Snaking 3+ by the transmission, crossmember, without screwing up ground clearance is an epic battle.

-- Joe

 

I looked at the Denmah gt45 special but cant find any specs.

Here are 2 other turbos from VS racing that might fit the bill.

New released VSRacing 77/83 turbo. This has turbo is the ability to meet the demands for larger cubic inch motors. With 76.7mm Compressor mated to 83mm Turbine wheel in T4 .96ar open housing. 4" discharge turbine 3" compressor outlet

VSracing 78/75 78mm compressor 75mm turbine .96ar T4

 

You go down factory exh routing. Stay away from trans area

You have to mount turbo in a way that allows downpipe to go on passenger side down by heater box. Tighter primary bend off cyl 8 to give more room. Ac delete box likely necessary

You can run 3.5-4" thru there.

 

Yea thats where I'm at. 3" down to the trans pan/trans cross member and then 4" back would be easiest. I knotched my stock subframe by the trans for dual 3" so I could run a 3" through it just like I have and wouldn't hang lower than the trans pan. then increase from 3 - 4" after that if need be.

 

I run 3.5" all the way back, About 1 foot of 4" off the turbo. Keeps the factory routing as well.

Jay

 

Most of the time its the turbine wheel that limits the power. One wheel diameter is expected to run in a large range of motor sizes. Thats why they can make 300-800 hp. Cubes and rpm sets the boost pressure desired to make a hp value. Required boost pressure sets turbine/compressor wheel speed. At given speed compressor wheel size needs to be large enough to pass the flow
76mm of good design should make a 800-1000 hp motor. It passes enough air mass to produce that power. But it takes power to turn compressor. Turbine wheel design needs to be large enough to turn the compressor at required speed. It also has to bypass the exhaust mass produced. Too small a turbine wheel wont drive a compressor hard enough or pass enough flow. Flow backs up and pressure rises preturbine. This is hard on the motor. Pumping losses etc

Depends on design but ideally you want turbine near same size as compressor or even slightly larger

Those china p trim 64/74 mm turbines are good for 60-70 mm compressors. Its a mismatch starting at 70 and way off at 76mm. Thats why that turbo may only make 500-600 hp on a typical v8.

Bigger motors use less boost to make same power as small motor. This means less turbine speed so less flow can be passed. Small cube motor requires high boost and high turbine speeds and can pass more flow. Result is more hp less back-pressure.
Thats why my buddies honda race car makes 1000 whp on a single billet 67 mm and my 400" v8 would need 2 of them to do the same.

 

The 7875 vs is what i was refering to not 7675. Thats a good turbo for a single mild 5.3

 

Understood, thanks for taking the time to explain. I like the 7875... looks like a keeper. But I'm assuming its a cheap chinese version? and I cant find the specs of the outlet Size and if its a Vband.

 

Thats exactly how I want to run mine. But my headers are forward and up so they come out higher than yours (basically right next to the valve cover and the oil fill on the pass side.

Side note... what throttle cable are you running?

 

I can't, I have subframes that are not meant for factory exhaust routing.

-- Joe

 

What subframes dont work with stock exhaust?? 95% of cars have stock type exhaust routings

 

I also can't run factory exhaust routing. I have 2 sets of SFC but mine are all homemade. I run 2"x2" square steel through floor SFC which blocks the factory exhaust routing completely. Then I added in 1x1.5" perimeter style SFC that tie the outer rocker to the OEM front and rear Sub frames as well as the through floor SFC.

Hence why I knotched the stock subframe right before the trans crossmember for the dual 3" exhaust.

 

I have no idea why you would do a subframe connector and not beable to run a factory exhaust lol. Theres no room under trans!
This is why i run spohns

 

I should add I run the Jegster subframe connectors which add nice clearance for exhaust. with forward upright facing headers you will have a tough time running a 3.5-4" unless you get a tubular K-member.

Im using a 4th gen throttle cable and bent the stock pedal arm a tad to make up for the slack in the cable

Jay

 

BMR.

And it's WELL welded in place.

I thought about cutting it up but I got pissed off and shut the shop door. That was a month or so ago.

When I had the blower and 2.5" duals it fit beside the transmission.

With the single 3" it's almost impossible. I got it somewhat mocked up but it cooks everything around it.

-- Joe

 

True dual 3" on sides of tranny with stock subframe knotched works like a charm. Then I dont have that giant U shaped out of the way exhaust running to the outside edge of the car just to run back to the tunnel lol.

I have never liked anything that has come from Spohn. I sold everything I ever bought from him and never ran any of it.

 

I like how mine fit. Single bar forward along rocker panel and then tiny bar across to trans subframe. High enoigh that its over the exhaust

 

can you PM me a link to pics ?

-- Joe

 

I dont have any but view their website

http://www.spohn.net/shop/1982-1992-....html?expand=1

 

I ended up calling VS Racing and spoke with someone.

Said that on my 5.3 with 8-10psi he recommends the Gt45 standard, should be good for 650 wheel HP maxed out. Should start to build boost around 3200rpms and full boost by 3800rpms. It uses 3.5" Downpipe Vband so I could run 3.5" and step it up to 4" farther down at the trans pan and run a 4" catback with 4" ultraflow muffler.

 

I wanted to run 4" on mine but just stuck with the 3". I am running about 3-4 ft of exhaust that dumps under the car at the transmission. I will be changing that when I go with a bigger turbo. Now I am running a 70.

 

Yes, I do run a tubular Kmember, racecraft Moly kmember and I run solid mounts so no flex pipe till i get down to the trans tunnel.