Need some Help A/R Hot side sizing - Turbo Updated on Page 2
 

I'm looking at turbochargers at On3 Performance for a single turbo setup for a 5.3L with a rebuilt bottom end [stock], LQ9 cam (got it free and won't be buying another cam), and 317 heads milled 0.15" (also free and no I'm not buying anymore heads). This is a budget build. I have had some recommendations to use a 70mm from On3 for quicker spooling, and exhaust A/R of 0.96. This seems reasonable for a 5.3L, but given my compression is only going to be 8.6:1, is this too large? Should I be running a smaller A/R like 0.68?

The car this motor is going into is only going to weight 2700 lbs at the most. Boosting to an intercooled 15 psi, but 11 psi for break-in, if that matters.

Is the 0.96 A/R correct for my application? Target - 475-480 RWHP.

Lastly, is 2.25" hotside piping off each bank too big? Should I go 2" till the 3" merge?

Do not run a .68 a/r on a single set up!

Okay sounds good. 0.96 A/R it is. Now what exhaust piping size? 2" to 3" or 2.25" to 3" merged?

Either will be fine, the 2" might help a little better with spooling

Lmao spooling won't be a issue with a 5.3 and 65mm turbine wheel:jest: I run on3 70 as well but twins , spooling still no issue. On3 70 single is wayyyy to small unless you're looking for 550ish before 5krpms

Manual or auto? 8.6:1 5.3 and a .96 is going to lag on a manual.

Manual transmission. So a .96 is too much lag? 70mm too small? It's a swapped 944, that is light and retains the short factory gearing. All I want is around 475rwhp. 500 is fine with me too. Nothing too outlandish.

I'm also limited to space and this 70mm is the perfect size for my build. On3 says this turbo is also good to 680 HP but I doubt that.

.96 at is fine. You won't have any lag issues with that little 70mm. For your build I think that turbo will work great.

You pretty much will have to try to NOT make 500whp. Any of the setups will do it. In my opinion why not size the turbo slightly smaller so it's more fun and lights off quicker. Sure less room to grow in the future but a) turbos are cheap now and b) your goal is way less than what the setup is capable of. You can make 500w with a larger AR at lower boost and be laggier or make 500w with a smaller AR and have boost faster and with a manual faster is more fun.

So what AR should I use then? On3's 0.68 in the 70mm is too small. They don't sell a 0.81 either, but I have seen this AR in a T72 sold by CXRacing.

So even at 11psi intercooled I'm still going to make 500+ whp?? WOW.

Why I didn't jump on the force-fed band wagon years ago... I don't know.

I believe a buddy had the CX Racing T72 with the .81 A/R and it lit off quick. I would probably go that route. I didn't see the entire setup if you listed it or not, but 11PSI is almost double atmosphere so if you can make 250w N/A you'll be close to 500w@11 psi. The more power you can make NA the easier it is to make more power boosted.

DDNSpider, here's my engine setup - most parts I have already:

LM4 5.3
- Bottom end rebuilt to stock specs
- LQ9 Cam
- 317 heads milled 0.015"
- 1.8 Elgin Roller Rockers
- LS6 Valve Springs
- LS2 timing cover with AN10 oil drain fitting welded for turbo
- Melling High Volume Pump #10295
- LS2 timing gear set from Cloyes
- Microsquirt LS kit
- Siemens DEKA 80LB Injectors

Currently my unknown list for what to use:
- Pushrod length
- Timing Chain


I haven't bought the car yet, but it's going into a Porsche 944. Looking for a clunker where I can rip all the fenders, bumpers and doors off to replace with fiberglass and make it anorexic to the tune of 2650-2750 lbs.

Sounds like a sweet project. I would go the T72 .81 route. Like I said turbo's are cheap and it'll light off real quick.

You don't need to overthink this. I have a 5.3 with an MPT70 on it. I have ran the .68 and .96 housings with different cams, hotsides and transmissions. I have data logged lots of track and street passes. You will have a hard time seeing the difference in spool time between the two housings on this small turbo. My latest combo is a 5.3, ls6 cam with a 4l80 with a stock converter. I see full boost at 2700 or so with a 2" crossover into a full 3" exhaust. I maxed this turbo out at 13-14lbs on my old L33 setup so you should be okay with 15 on yours.
P.S.- I made just over 500rwhp at 9.5lbs through a th400 so you will make 480 pretty easy.

Thanks! Found a spot below the passenger popup headlight that will keep the turbo out of the engine bay for the most part in order to keep the temps down.

I was recently made aware of Hooker Headers new turbo manifolds. The passenger side manifold will work on my application, but their driver side won't. That is easily solved with a Trailblazer SS driver side that hugs the engine better. I will run the merge pipe behind the oil pan and around to the Hooker side to join the pipes.

EDIT:

I am completely indecisive now about either an On3 70mm or a CX T72 for my application. I like the fact the CX is water cooled, which will keep temperatures down on a road course (this is a time trial and HPDE car until I'm familiarized enough to enter full blown competition). However, the On3 price is very attractive, but only oil-cooled.

Anyone know of a remote oil filter mount that has a feed to a turbo? The swap pan I'm picking up does not have the fitting that most GM pans have above the filter you can tap into for fresh oil.

I'd just drill a hole in the filter adapter on the pressure side and thread it for a -4 to NPT fitting..

you can tap any remote filter housing for an oil feed.

I've decided to go with the CX Racing T72 water-cooled turbo with a 0.81 A/R. In addition, I've decided to incorporate the following in my build:

- 44mm On3 Wastegate and recirculate into main exhaust exit
- CX Racing 23.5x7x2.5 Intercooler
- Oil Cooler Line Fitting Kit For Mazda RX7 AN10 Fittings #OC-13B-RX7FB-KIT
- Derale 35709 remote mount - it has 2 exit ports and I can use one for the temp sender.
- Vibrant AN10 Tee after oil cooler for feed to turbo (reduced to AN4).
- ICT Billet LS Gen 4 Twin Turbo Oil Drain Return - Front Timing Chain Cover -10AN
- Use the water pump's heater lines to cool down the turbo.
- Screw the 11 pound spring. 15 psi all the way baby.
- Tune, Tune, and Tune. :D

Nice choice on the turbo. Any reason in particular you want to recirculate the wastegate?