lsjeep52

Hey guys, looking to buy a cheap On3 70mm .68ar turbo for my 4.8. I was hopeing someone could chime in and let me know if thats a good size for a fast spool up with 2in hotside? I need it to spool fast as my converter is 1800 lockup and its in a 4x4 buggy. Dont need no more than 500-550rwhp. Thanks!

98Camarod

iTrader: (43)

Are you going to run a cam? A .69 a/r is probably not your best option. My first turbo setup I had a single 70mm on my 5.7, it had a .96 a/r and was making 10 lbs at 3500rpm. At that time, that is all I ran. It ran 7.0 at 100ish mph and weight 3800lbs. That should be right where you want to be power wise.

lsjeep52

I plan on running a mild cam, prob a BTR stg2 truck. My jeep weighs almost 5000lbs lol. I want something small to spool fast.

lsjeep52

Specs are 212/218 .553/.553 113+2


Thats off of btr. I figured thats plenty of lift for an 1800 stall

JosephIV

iTrader: (14)

If it were me I would be looking at a VS Racing 78/75 in .96 A/R or the ON3 version. You're going to want to carry power throughout the RPM range and I'm doubtful that you'll have problems spooling a turbo this size with your nearly 300 cubic inch engine. If you're still worried you can look at the VS Racing 76/65 also in .96. None of the turbos that I mentioned should cost more than $450.

If you get a 78/75 in .96 you can hold onto it and swap it onto a 5.3 or 6.0 build down the line. It may not be ideal on a 6.0 but the 70mm in .68 wouldn't be feasible and you'd be looking to sell it IMO.

lsjeep52

Maybe im not undertsanding ar.....i thought a .68 would spool faster than a .96?

Forcefed86

iTrader: (4)

I think the .68 is the way to go for what you want. A 70mm on3 with the .68 housing will spoolup much faster than any of the other turbos mentioned above. 500ish HP is doable with that small of a housing. Just remember, lots of power down low tends to bend rods. I wouldn't want 600ft lb at 2200 rpm personally.

lsjeep52

No, by no means im only looking for 500-550 rwhp and 450tq

JosephIV

iTrader: (14)

It will. But you seem to be hung up on a spool time that may only be different by hundreds of RPM's or a bit more when the real question is IMO, "What is the best sized turbo for my application and budget that will make GOOD power throughout the useable RPM range of my engine?"

Why try to spool super fast and hit a brick wall (boost maxed out at a lower RPM, engine not making any more power) with the small A/R when you can spool quick enough and make power throughout the RPM range with the larger A/R?

You have a V8 that can make over 300 HP with a cam and valvesprings. It wants the bigger A/R and will spool a 7065, 7868, or even 7875 just fine in .96 A/R. It's all just my opinion but there is a distinct lack of people putting the smaller A/R turbo on their 4.8's or 5.3's. There might be something to that.

svslow

A Borg Warner S366 would also work pretty well. Good turbo, and they are cheap.

lsjeep52

Well id rather hit a brick wall with my first cheap turbo, rather than be stuck with a turbo that doesnt spool till 2200. Id like my turbo to spool at 1200-1600. Like i said, i dont need more than 500-550 hp this go around. My 4l60 is built, but it still is only a 4l60

JosephIV

iTrader: (14)

Are you talking about an Off Road rig that will be crawling around in low range? At any rate, I'd call or e-mail someone who builds / sells turbos and tell them you're goal as we're all guessing at this time what you're trying to do with it.

If you're street driving and towing you may want something different than if you drag race and may want something entirely different if you're crawling around rocks on 40" Boggers.

lsjeep52

I will be crawling around but it still is my dd. Im only runnning 37in with 4.88 gears. Currently when im on the highway cuisin at 75mph im at 2250rpm with my 4l60

Forcefed86

iTrader: (4)

“FourG63 97GST” has a precision .96 T4 67/75 on a factory LS1. Said it was super responsive. Started making boost around 1800rpms. Targeted boost of 7psi by 2800. 400ftlbs @2500, 500-590ftlbs from 3500-6500rpms. He turned it up to 12lbs on the street. Might still be a little much for a 4.8.

I can tell you from experience that a 4.8 is a gutless turd with a 1.10AR T4 S475 below 4000RPM. My converter was tight, but not 1800RPM tight. I could make about a pound of boost on the trans brake @2800. That’s with a smaller 212/212 @ 112 cam. Wanting instant spool on an 1800rpm stall isn’t happening with a 78/75 or any of the larger AR housing turbos mentioned IMO.

You’ll have to give up top end charge for low end grunt or vise-versa. Even a 66mm compressor should hit your goals on a 4.8. Larger you go on the compressor the slower it will spool.

The S366 is an awesome unit, but you’ll pay $580 for a legit one these days. The new S366 clones are $375. Not too much more than an on3 unit, might be worth a shot.

http://www.ebay.com/itm/Brand-New-Af...BWGMKe&vxp=mtr

lsjeep52

That still has an AR of .91. Can someone explain what im missing? Some say a 70mm .68ar will spool fast, but others say 66mm .91ar is good. I dont think im understanding the housing size versus the AR rating.

Forcefed86

iTrader: (4)

There’s more to a turbos “spool” behavior than the AR housing. You are correct though. In general the smaller the housing the quicker the initial spool time. But You also have to factor in the compressor/exh wheel sizes and designs. A large exh. wheel mated to a smaller comp. wheel will spool more quickly. So if you have a 78/75 in a .96/T4 and a 67/75 in a .96/T4, the 67/75 will spool much faster.

Think of it as a leverage thing. When exhaust hits the tip of the turbine wheel, a larger wheel will have more leverage (extract more energy from exh) to drive the compressor. Smaller you go on the compressor, the less energy is required to drive it. So ideally you’d go with the smallest most efficient compressor as possible that still meets your goals. Then mate it to the largest housing/exh wheel possible that still meets your spool-up/power goals.

Then you have to look at the major/minor diameters of each wheel. A 66mm-minor, 80mm-major comp wheel will move much less air than a 66/91 comp wheel.

These are an S366’s specs.

In general the china cheapie turbos are using old technology compressor/turbine castings and flow much less than a “new” Borg unit or similar race turbos of the same or smaller size. The S366 has a better wheel design on both the compressor and turbine and will most likely out flow the On3 76/65 turbo because of it. It will also spool more quickly and limit the overall power less due to less backpressure.

lsjeep52

This is the turbo im looking at from On3
Cold Side

Compressor Wheel 61mm
.70 a/r
4” Inlet and 2.5” Compressor Outlet
Inducer- 70mm
Exducer- 99mm
Exhaust Side

Exhaust Housing T-4 Flange
.68 / .81 / or .96 ar Exhaust Housing
3.0″ Vband outlet
Inducer- 74.5mm
Exducer- 65mm

Forcefed86

iTrader: (4)

Can’t have a cheap china turbo that makes boost lightning fast and performs up top as well. So it’s all a matter of what you’re willing to sacrifice for the level of performance you want. I’m all for cheapie china turbos with cheap LS builds. What is your budget?

Generally you want an exh wheel that is the same size or larger than the compressor wheel. So the ON3 70 won’t be an ideal turbo in that respect. They are also using old wheel tech. You can drop the housing size to make up for this to a point, but as mentioned you sacrifice top end as the back pressure rises. A .68 housing will limit you but it will also help that gutless 4.8 make power down low. The .81AR housing sounds like a good compromise between the two. I’d give it a shot if you’re set on the ON3 stuff.

lsjeep52

Maybe a Precision 5976E MFS? I want something that will survive lol. This is the specs from precision.
MFS (Machined From Solid) 59mm inducer compressor wheel
• "E" compressor cover 3.0" inlet/2.0" outlet
• 64.56mm exducer turbine wheel
• Turbine housing option:
T4 on center .69ar

lsjeep52

So i want a smaller exduser and a biger inducer for a fast spool?