As the title says, im trying to figure what to do here is the story,

first off here is the setup:

Junkyard 5.3L
317 heads
GM MLS HG
ARP Head Studs
Lunati Gold Dual Springs
Comp Cromoly 7.4" pushrods
LS7 lifters
Comp Cam 235/239 .621/.625 114+4 LSA (9* advance overlap)
GSP T76 (exact copy to On3 T76)
Tial MVS
Ebay 3" intercooler
3" exhaust/DP

This in a 240sx chassis.

Set up was running fine and dandy on 7 psi but just felt dum slow, so I put a boost controller on it and I could not for the life of it get more then 10psi out of it.

On 10 psi it was ok, but still I could not increase boost, checked all pipes by doing a leak test and nothing, everything was solid. I was mind boggled to where I disconnected the vaccum source to the wastegate and capped off the vaccum line. Then came 14-15 psi and it was a freakin rocket, the car became alive and felt so good but I was puzzled to why the wastegate had be shut and the most I could get was 15psi.

I left it like that (Dumbass decision) keep in mind its not a DD the car came once every week if that. 2nd time I ran it I notice that after 6100-6200 rpm the car would nose over and it would get worse as the higher the RPM. I know it wasnt the cam or valve springs.

I spoke to couple ppl they said converter for sure (b&m holeshot), so I had a JW converter that I was going to swap in, in the meantime I started shooting coolant out the radiator and it resulted to a rod knock.

Heres where I found out the where my truck manifolds meet the crossover pipe the gasket (rtv high temp) burned itself out so that 2 leaks before the turbo.

After doing extensive searching I came to a conclusion that my heads lifted because the turbo was too small. T4 .81 A/R Turbine wheel 72.78mm Inducer/ 64.2mm exducer.

Her's where im stuck, HOW the hell did everyone else with on3 t76 on 5.3 not have this problem? Im swapping the shortblock to a 4.8 but im being told by ppl that my turbo will still choke and still lift heads because not just the housing but the turbine wheel size, well then shouldnt we have a bunch of 5.3's with lifted heads that ran t76's??



Sry for the book I just typed but I searched and searched and im getting soo many different scenarios its giving me a headache. please HELP!

 

I dunno man but that cam is huge for a 5.3.

 

I've been told that by ppl but the worse it could do is shift my powerband wayyyy up top but I had no topend, the car pulled crazy hard and right around 6k is where it would go downhill.

 

A properly sized cam will have less tendency to build excess back pressure and worse, heat.

 

probably too much cam for turbine, but there still seems to be other issues, perhaps bad bearing in the turbo? are you sure it didn't over heat it? I don't think you were making enough power to lift the heads unless you you had a ton of timing in it.

 

I have a 5.3 with 317 heads, LS6 cam and intake, arp studs, yada yada. Running a Turbonetics GTK1000 which is a 76mm turbo with a 68mm exhaust wheel, anti-surge ported compressor cover with dbb chra. Most know on a v8 application the 68 mm exhaust wheel is done at around 5800-6k.

My power levels off from 5-6k where I shift. Running it over that would cause serious backpressure issues as I am running 14-15 psi. With the smaller wheels you have to shift early. Sounds you like you should have went with at least a 75mm exhaust wheel and a minimum .96 a/r if you planned on running above 6k.

 

21.5* I know thats high but I had no knock at all so I thought for low compression its ok.





Wow, I did not know that. This explains alot because whenever in gear under boost right around 6k rpm COOLANT started shooting out the radiator overflow tank onto the windsheild, this is when I suspected head lift.

I think theres only two solution to this either add another one of these 76mm or switch over to a borg warner s475.

 

why don't you connect a pressure gauge to the manifold (pre-turbo) and check the pressure .This will solve your problem checking not guessing.

 

What backpressure should one see between the manifold and the turbo?
Sub'd for info.

 

I dont mind doing that but after big reg said 68mm turbine is known to fall at 6k and mine is 64mm!! Then at this point I dont wanna even put it back on because I plan to port the heads and add edelbrock xt w/92mm TB but no point unless I figure this backside situation.

Im torn between just adding another turbo because my buddy has a new one identical to mine or just slap a S475.

 

I would say 2:1 so if you see 14 psi at intake manifold the you should see 28 psi on the exhaust side.

 

Your cam is made to spin to 8k rpm and the turbo to 6k rpm. Just a wrong combination.

 

would you s475 or add another t76?

 

I told you to get a new cam like. 8 Months ago lol

 

even if I put a stock ls1 cam in my motor Ill still have backpressure. Spoke with forced induction and that's what he told me, its not the cam its your turbine wheel.

 

The Borg Warner units work great and are cheap, just physically huge. I have been debating a billet S475 or Turbonetics billet 7675. I don't know if I can fit the Borg unit without moving **** around as im already close to the abs system.

If you don't have space constraints, I would do a S475 with the 83mm turbine wheel and 1.0 a/r exhaust side. That will pull right through 7k and beyond.

 

whats the most you can sqeeze out of them? whp wise?

I would like atleast 800 to 850whp.

 

Double post from phone

 

It might but the S480 might do it easier. If you are looking for just peak power too, get the 92mm exhaust wheel.

 

@OP......amazing build and sorry to hear about the issues.

Very glad I stumbled onto this thread because I am buildings something similar (240sx with a turbo 5.3) and was wondering what turbo would be adequate for this type of build. I am def sub'ed for more information. The BW turbos are awesome, great for the price, sound awesome (not important but a cool little perk to me), but they have a larger footprint then most turbos especially with their racecovers.

OP since you have your turbo setup pretty much where I am installing mine you may run into fitment issues with a S475. You may need to modify your plumbing to move the turbo location further towards the passenger headlight to accommodate the size. If you google 93 Nissan 240sx LS1/T56 Backhalf you will see where someone with an S13 had to mount their turbo to accommodate a large sized unit.