ok, ive been reading around and researching a bit and i need just alittle more clearification.
If this gets read and more info placed into it, a sticky should be created one way or another.
Ive been reading Zombies Saga and ZL1killers threads over and over (great reads by the way and love the pictures that go with em) and have learned tons. Still want to know alittle more about different sized turbos and their effects of power, spool, reliablility, and overall differences.

Ok i know the STS starter turbo is tiny and chokes the engine off and limits the engines overall power. so i wont ask for the 60mm turbos. I want to know about the 70s and up.
Im about to decided on which size to go with but everytime i finally pick one, i read somthing else that says a different size would be better. also not just size but what about the turbine AR sizing? like .81-1.0 AR's. I know with a divided and a spool valve things change so add that info too please.

Now mind you im on a stock block with no plans of chanign internals anytime soon. mine is a stock 98 Ls1 with a few bolton mods. unfortunatly i put LT headers on it before i and alot of other people knew better about LTheaders and rear turbos. i stil have my stock manis but really dont want to put them back on. but for now thats how they gotta stay until i get back to the states. ill wrap em up reall good and deal with the laggyness until i get my stock back on. They are OBX headers so they arnt the huge kooks that alot of people wasted $1000 on. if anything mine internally are small then those but not by much they still are good LT headers.

anyway, i want to know what turbo for a STOCK 1998 346.5CU 5.7L LS1 with 60LB injectors and a Racetronics fullpump and a good tune would best be suited for. i have a 3200 stall on a stock A4 with 2.73 gears, frost tuned and with currently 301 RWHP (bad gas and its an Auto lol)

these are the typical canidates that ive been reading about that i would like to know what they would do differently between eachother. I know the typical journol and Ball bearing spool explaination so i dont want that right now. i know a Ball bearing turbo will spool faster then a journal bearing. I also know about the oil less turbos with their fancy stuff. lets keep this simple.

Looking for info as if all these are typical T series turbos with journal bearings and no billet fancy metals or spool devices. for now lol

All with T4 inlets mind you
T67 with .81 / .84 / .96 / 1.0 AR's (small side i know but info please)

T70 with .81 / .84 / .96 / 1.0 AR's

T72 with .81 / .84 / .96 / 1.0 AR's

T76 with .81 / .84 / .96 / 1.0 AR's

T88 with .81 / .84 / .96 / 1.0 AR's (big, i know but info please)

yes im a bit of a noob and yes ive been reading and researching. i want ONE thread that narrows it all down a bit when it comes to REAR Mounted Turbos.

 

I have been looking into doing a rearmount with my car as well but the one thing that I have noticed is that the oiling system is the biggest headache and causes the most problems. I plan on saving up for an oil less turbo to keep it simple, don't have to worry about a oil pump failure or anything like that.

 

wow at 66 view already lol didnt think people would have seen this yet.

oiling is an issue but not too worried about it as long as a quality pump and a way to watch it are in place. I was considering a stand alone system but gonna go with Zombies advise and just keep it simple for now.

 

Honestly, I think you are comparing too many apples to oranges. All of those turbos have their pros and cons. You already know that without a spool valve, second wastegate, and twinscroll turbo that a smaller single scroll turbo will spool faster but choke up top, and a larger turbo will spool slower but give more power. Everything totally depends on your goals. IMHO I would keep the LT's but just exhaust wrap them and the entire exhaust all the way back to the turbo. Also get a turbo blanket to keep your spool times low. Good to go.

 

i was gonna wrap em up real good from front to back and leave them in for awhile.

i do know that the smaller the quicker and the larger the slower spooling BUT with T70-T76 how much difference is there bwtween them. thats where im getting at.

I myself am aiming at roughly 550ish with 10PSI as my max boost level... for now. I drive high speed with my 2.72 gears and 3200 stall. Im not a hole shot drag person. more of a down the back stretch surge person. I also perfer road racing. to put it plainly. I want usable broad torque curve with alittle more up top for high speed runs as appose to peak horsepower numbers. i drive my car. its not a trailor queen.

so again i want to know the general differences between these and what will they could do for me and what have they done for others.

 

I too have been researching the **** out of this and frankly at times literally losing sleep over this. I intend to buy a comp oil-less so it is not crazy to lose sleep over spending that kind of money on the wrong turbo. I have very similar goals for my current setup. I am being told by the comp turbo guys that their version of the 67mm with a .81 AR will easily suit my needs and give me a little headroom. They claim that their setup will outflow your normal 70mm. With what research I have been doing for 550 RWHP they are likely correct. Plus that turbo should spool like nobody's business. What I have noticed is that all of these guys throwing watermelon size turbos on are doing it for drag racing, and top HP numbers. Drag cars can afford some slow spool. There are many ways to minimize it or use it to your advantage when drag racing. Your daily driver\road race car not necessarily. If you run a turbo that is too small the major downside is that you likely will be shifting before red line. IMHO this isn't that big of a deal on a street car. The more I have been paying attention to my driving habits I realize that it is a rare day indeed when I have my car over 5k. So in order for me to get maximum fun out of my turbo setup I am going to want to build it to spool as soon as possible. In the end I believe that i have come to the conclusion (subject to change tomorrow of course) that I should probably trust the turbo experts to picking the turbo for my goals. I have also decided that I can't exactly size this turbo for the next motor with high HP goals and expect to be satisfied with its performance on my current setup.

I know that is a very long winded answer to not have said anything but I have to agree that there are too many variables at play to be able to give any definitive on what those turbos can do. How many bends and the sizing of both your hot and cold side can have drastic effects on how each performs.

I know that many of the things I have said here are debatable and I am not interested in debating them. my disclaimer is as follow.

**This post written by another poor schlum that is trying to figure out what the hell he is doing with FI as well**

 

my friend has a 2010 silverado. 4.8l stock motor with a zr1 cam and springs, we have the turbo under the truck, first it was a mpt76 with the 1.00 AR

now its a gt45 with the 1.05 AR divided, its lit at 4k and its a ******* beast.

it makes 605rwhp on 17lbs and it goes like stink, if you have a manual trans its going to be shitty, but an automatic with long gears is going to love life, you can drag the brakes or just light it, and youll have more power than you can use.

anything between 80-100AR t4 will work great, just throw on something cheap and see how you like it if you dont wanna blow big money on a oil less turbo, buy a 300 dollar gt45 and run some oil lines and a pump, should be easy with the money you save

 

The key things to making the rear mount reliable are the oiling system and the PCV system. Make sure these two areas are solid, and the rest will be much easier.

For a street car, the smaller turbo you can get away with the better. I wouldn't go larger than 70 or 72 myself unless you have big plans in the future. If you go too big, it will be laggy as f. I ran their larger 67mm on my stock motor and it was just fine. When I added a larger cam, the 67 ran out of steam up top.

Get rid of your headers. Period. The car will be better overall with the stock manifolds. Headers will leak over time, are laggy, and don't help at all.

To be honest, if you drive the car alot I would avoid the rear mount completely. Too many things that can go wrong and leave you stranded/broke/frustrated. I ran a rear mount for almost 5 years, "improved" everything I could with the kit and it still wasn't that great of an experience.

 

Figured id chime in Hear,i have a home built rearmount and I used zombies and zl1killas experiences. I went with a on3 t76 and I do like it and it makes good power and spools decently,however lately I have been contemplating going to something in the t67 to t70 verity. I had certin expectations when I built my set up. I also thought my car was going to have major traction issues on street tires.but it does not,infact it feels quite tame and sometimes I honestly think im driving a stock fbody. It does make good power for what it is some where in the upper 400s. But I think the car would be more responsive and fun with a smaller turbo. Im probly going to try something smaller soon to see if it does what I want. As far as the oiling stuff it is a major pain to set up but if you use a good pump everything should be reliable.luckily for you your a a4 with high gears so that should make a worthy difference just by loading the turbo.if I cant get mine to react much better I think ill end up doing the same thing as pingking and build my osn version of the ptk kit using manifolds.

 

I debated a ton on what to do for my application as well. I'm running a C5 so space was my limiting factor as well as the heat issues that arise with the Corvette. I decided to go with a T76 with a .81 AR for a couple of reasons. (car is a 6-speed)

I DD my car and want to maintain driveability and not KILL the drivetrain components. I am going to do an LS7 clutch, Aluminum flywheel, and Tick master & slave to assure my clutch will handle the 500-550 rwhp I am looking for. Other than that, I do not have any immediate plans or the money to do a significant tranny or rearend upgrade. With the T76, it should still have a decent spool with the .81 AR but will not spool so fast that I am either spinning the hell out of my tires and/or putting a huge torque load on my drivetrain. I do quite a bit of roll racing so I feel this will allow me to start from a roll that is just below my max spool so I can catch traction and load the tires before the turbo hits peak boost. Mind you, this is ALL speculation LOL, but it makes sense in my head at least. I feel like it will keep my car a perfect DD and a BEAST above 3500-3700 RPM

 

ive been noticing that alot of people are actualy down sizing their Turbone housing a bit (ie .96 to .81) for spooling reasons, especialy with the T76 sizes, are these turbos possibly too big for a stock LS1 with a rear turbo setup? with a built engine with more cubes and higher airflow bigger turbos can be fed better but with a stock LS1 whats the deal?

 

I thought the on3 t76 I have would spool faster than it does due to the small exhaust wheel.but I also have the 1.0 ar exhaust housing. The car spools decent dont get me wrong but not as fast as id like. I may try a smaller ar ratio first tho. Problem for me is my last turbo car was a front mount 5.0 with a 62.1 turbo and boost hit hard. Everyone whos ridden in my car says its fast as hell but to me its lacking. Heres a vid of some wot runs on the street.
https://www.youtube.com/watch?v=k4D6...e_gdata_player

 

huh. seems like i might want to go with a .81 for starters. makes me glad i didnt already order the T76 with 1.0 ar from them. I had already asked them about that and for 25 bucks extra they where gonna puy the 1.0 ar on there for me. and with a .96 not being that much smaller, im starting to thing for a starter turbo .81 would be a better option. but what about the compressor side?

how about i narrow the question down a bit to this then for now. leaving the tougher questions up top to those that have used those in series and can tell me first hand knowlege.

whats the difference between the T70, T72, and T76 with a .81 AR? All things being equal of course and "in a perfect world" lol
(you know, stock manifolds, wrapped up exhaust, no leaks, good oil pump, good PCV system, great conservitive tune, 60# injectors, a single ractronics pump with wiring harness, 550ish horsepower goal, 10psi max boost, 3200 stall, 2.73 gears and a stock LS1) i think ive covered most of the variables)

 

I'm running an On3 76mm BB (rear mount) w/ .96 AR. It does take a bit to get it spooling, but when it kicks in... it's nice!

I just wrapped my exhaust (last night), I can already feel the difference. I also ordered a .81 housing ($85) and will be putting that on here soon.. Will let you know how it helps or not.

 

I would go with a comp oilless turbo,seems like life would be easier

 

What BOV, sounds cool.

 

I agree but can totally understand why people don't they are a little cost prohibitive. If you were going to buy a high dollar billet, ball bearing, super duper double nutted turbo in the first place then the cost difference is negligible could be about the same as the proper oil pump. But for the on3 crowd the juice isn't worth the squeeze.

I intend to go the comp turbo route so I am actually pushing my project back due to lack of funds but I am a huge fan of their spooling characteristics. The only thing that is throwing me for a loop is because they supposedly outflow the competition, out spool the competition and comp doesn't release compressor maps. I am not sure which turbo is best paired to my application.

 

nogo the bov is the fleabay 50mm emusa on. I like it but when I have extra money im going to step up to a turbosmart.

Hrhohio yeah definitely let us know on your results im very interested. I wanted to originally run a comp turbo but the price was pretty steep for what I was quoted,but at some point I probly will upgrade to one

 

HRHohio, does wrapping the exhaust really make that big of a difference on a rear mount turbo? I been debating this for my s10 and I have the same turbo you do but I just dont want to pay $100 to wrap my piping for nothing.

 

OMG YES. I couldn't believe how much it helps. Without the wrap (as early as 2 weeks ago at the track), I couldn't even get above 0.5 psi of boost while foot braking on the line. Would get to about 1.5 psi at the top of 1st, then 3 psi at the top of 2nd. (Street driving). On Dyno, starting in 3rd at 2800 rpm, it would build boost up to 10, but that was at the top end of 3rd.

Finished the wrap last night and took it out for a spin. Got 3psi with wheels spinning free in 1st. Boost spools up so much faster in ALL gears now.

With the rear mount, the way my coldpipe is run, it's so close to the catalytic converter (driver side) and y pipe that the heat was transferring to the coldpipe. It was heating the air as it went through. The coldpipe was literally too hot to touch for more than 1-2 secs (180* +). I wrapped the whole y pipe and I pipe to the hump over the axle (left that section open still), AND wrapped the whole coldpipe from same spot to the K-Member. Seriously... what a difference in spool up.

Still not completely happy with time to reach full boost, so will be putting on the .81 housing here in the next week or two. Gotta get time.

Stangtrader - Will let you (and all) know what it does by switching the housings. Gut feeling is that it will spool up so much faster, and won't hurt top end. (fingers crossed).