Turbo size advice for 408
 

I am in the process of putting a 408 into a '03 Silverado RCSB and need help picking a turbo. The engine has a 8.7cr, p&p 6.0 heads and a 224/231 .595 LSA 114 cam. The turbo kit is a rear mount STS that came with a Garrett GT70.

How much boost, and RPM are you wanting to run? I would go on the smaller side being in the rear. I would think the 70 would work ok for low boost, and a 76 should support moderate boost.

15lbs max. As far as RPM I don't know but definitely not more than 7K. I just want to be in the low 11's.

I have a PT76 with a .96 a/r housing on my 408 and I'm pretty happy with it. It build full boost by about 2700 or so, and I can get 1 or 2 psi while cruising in 4th at about 2200 or so. 76 would probably be a good size to go with if you play with the a/r a little bit. 70 might be a little better though for building boost quickly. I know those rear mount kits take longer to spool up. Once it's spooled though, it won't make much of a difference.

Get a GT-76/PT-76 and go with a A/R housing that's bigger than .70 but smaller than .96. Not even sure what's between the two! :jest:
I have a rear mount 76 with a .68 A/R on a 6L and the turbo size is on the limit of being to big but the A/R chokes down at higher RPM, so I figure the 76 will work well for you but get a bigger A/R

I spun my GT70 .96 A/R to 15psi, but it was pretty inefficient there... I set my plug wires on fire :)

You definitely want at least a .96 A/R with the exhaust pulse from the 408 -- maybe bigger unless you want maggie like insta-boost and are willing to sacrifice going higher than 15psi.

Personally, I'd just cut to the chase and put an 88 on there :devil:

(There's a .81 housing, I believe, you will want more for the 408)

OK so a Garrett GTS-76 or a Turbonetics TC76 with a .96 A/R is the ticket for 12-15lbs on the 408? I should have ordered the STS kit with the 76 to start with. Now I have to sell the GT70 and buy a 76.

s85 with a 1.1 housing :eyes:

I agree with two of ya'll. An S85 or bigger is what I'd go with. A 408 should have an 88mm turbo or bigger if you use a standard turbo. A T76 is more of a turbo for a 6.0L.

An STS GT70 will do 12psi all day long. You can get to 14psi if you take some steps (run headers and ! cats to help with the pressure) but may take a lag hit (I ran a set of bassani middies for a while with no big increase in lag and no big heat/pressure problems).

It's great for almost immediate boost... Not so great for huge top end power (even at 14 psi) I believe I gave up around 50-60 rwhp with the 70 at 14psi compared to Parish's 76 at 14psi (front mount) -- it was around 100, but I was awd on a mustang and he was 2wd on a jet, so...

Upgrading your kit to a bigger turbo is more than just buying the turbo. You'll need a new flange to step up, and a new #1 pipe. If you don't already have the big oil pump, you'll need that too.

If you keep the GT70 (or anything but the monster S85 with a 1.1 lol), you need a reverse split cam. Your back pressure will be too much for a forward split with that much overlap. Again, if you are not looking for all-out numbers...

If you haven't installed anything yet, contact STS directly to see if you can swap the turbo. There will be an upgrade fee, but it's cheaper than buying a new turbo and selling your 70.

I am very happy with my PT76 on my 408. I think anything bigger would be too big for a street driven truck.

I think the Garrett GTS-76 or Turbonetics TC-76 is what I will be going with since the truck will be run 80% street 20% track.

As for the cam I have no idea what the numbers mean but they are in the first post. It is supposed to be a turbo cam.:confused:

Now I need to start a post for some fuel system help.



Edit: What A/R should I go with if using the 76 in rear mount form?

I love how my truck drives on the street. It is mild as can be when crusing, but once I step on it its lights out and the tires are up in smoke. I guess it is all in what you are looking for.

That's exactly how I would describe mine. I guess I'd have to go for a ride in yours before I could judge.

A 76 should spool up real quick on a 408, but with anything other than low boost you'll work out of the turbo's efficiency range pretty quick.

A TC76 would be the quickest spooling of the bunch and still support pretty big power. Above that then you might want to think about the ST series units instead of making a jump to the full on S-series unit.

I think the S85 would be great if it were a front mount but a 76 would work better being that it will be a remote/rear mount.

What about an S78?

You could always do an ST78 or ST80. They are T4 flange units and will spool quicker then the larger turbined S-series and SX-series.

Yeah, but would an S78 have much spool time issue on a 6.7L? Just asking, not knocking what you're saying. You're Jose' correct?

Cam = 224/231 .595 LSA 114 cam

What do the numbers mean. It is supposed to be a turbo cam. http://i47.photobucket.com/albums/f1...LLR/idunno.gif

What A/R should I go with if using the 76 in rear mount form? I am going to go with the 76.

I like the LSA at 114, but I'd reverse that duration. I'd have to agree with Berzerker on the A/R.

Im running a T76/.96AR front mount on a 6.0l. It is a bit laggy for me, but Im at 7000' elevation. It spools really slow compaired to the T66/.81AR I had. If you mat it from a dig it will take 3-4 seconds to come on. On a 408 at low elevation it would be fine. If you are going to run 13-15psi I would go with the T76/.96AR. Under 12psi you might get away with a .81AR. Im afraid anything smaller will choke you up top, and bigger will be kinda laggy. Just my .02$.

I have bulit quite a few 408's with rear mount's . at 12lbs of boost with a T76/.96 your boarder line in the eff zone of this turbo and with out meth you'll see some high IAT's over 5300 rpm . An 88mm or a GT4202r [ thats whats on my 403 in my tbss ] will be in a very happy place on a 408 . as for spool time CAM is such a big factor . I have had very good result's with the LPE GT-7 cam it idles like stock and combined with my 3200 vig I have zero lag and have some traction issues with AWD . With a T70/.96 it made 580hp and 650 tq to all four tires on a mustang dyno at 9.5 psi . I will dyno new GT4202r this weeka nd post the results.
See video here .
http://www.youtube.com/watch?v=y1RwJCvKACE

Just watched your video's...that's some pretty impressive stuff man!! :thumb:
What else have you built?

My shop will be on here soon as a vendor. We have built a lot of trucks TBSS's , SRT10's, Fullsize GM's . yeh the video is at 5.5 psi total and me leaving at 1psi . I have left from a stop at 6psi but it's not very good for my tires ....LOL

No but it's good for entertainment and promotional vids! Lets see some 5psi AWD launches! :nod:

i am interested in how diferent cams would effect spool time. can you share any back to back cam swaps and how they efected hp and spool time?

On my 403 I have swapped between Stock ls2 cam [ 01 zo6] an 02-04 Zo6 cam , and LPE GT7 . I have done this on 4 different C-5's with rear mount's and one C6 with a rear mount what I have found is the longer the exhaust duration is the faster the turbo will spool at least 400-500 rpm sooner on my LPE gt 7 then the 02 ZO6 cam . Peak hp and Tq are 3% higher with the GT7 cam and hit sooner. This seems to work better on remote mount .

nice info. any comparisons on front mount cam swaps?

we did a swap from a stock 5.3 cam to an 01 z06 cam and gained 100rwhp at the same boost level. no spool time info though since we have a 5000+rpm stall. we got such killer results we had to ask ourselfs how much a 02+ cam would help or an aftermarket grind.

might have to do some serious cam swap dyno thrashing on our next project.

I run a 1.30 A/R on-center hot sided T76 on my tow rig (very mild 393). It's an old turbo and crotchety compared to the GTS-series stuff. It's making somewhere around 850 crank hp based on weight and ET. I leave at about 4 psi and see about 18 psi peak. Friend of mine is making about 1200 crank hp on a tangential housing small frame T88 on a 408.

I'm personally not a big fan of a T70 because of the peak efficiency pressure ratio, though I understand that the Holset T70 has a different map than that Garret T70.

I personally think the optimum turbo for a fairly large displacement gas motor with moderate power goals is a .96 A/R GTS or GTSH series 76 because it will move a lot of air at relatively low pressure ratios.

I'm building a front mount kit for the GMT900's and will test the cams out , the gains you got are great are you using a 5.3 with 243 heads or 5.3 heads ?

I would put an S400 on your 408. THis is a great turbo and is only $585. I can't post the link though because Majestic Turbo isn't a sponsor here.

it was a completely stock 5.3 with just valve springs, then the cam swap.

spoiling is greatly effected by one thing on a camshaft. And its easy to play with spooltime and tricks to make it come on later or sooner. But there is a cost to everything of course.

R