I would think the bigger ones shift the spool up up 500rpm or so. They are not hugely bigger. 50 pounds per minute versus 60 or 65 they say on the aps website under the specs. They use 3 inch inlet on the bigger ones.
They will pull better up top for sure and better if you go up to bigger engine in the future. But as said not convinced that the smaller ones totally die off higher up even on 402 or 408. Jm ran 9s at like 12 psi on his 402 at near 140mph . Thats faster than I need to go but whatever some guys are trying for 8s or 160mph or something crazy crazy.
Remember on track you need medicals and full cages and all that for over 9.99 and think 135 mph?
Course 9 second street car is already crazy enough for most sane people even us old die hard speedfreaks.

Still if you plan on bigger engine in the future then get the bigger kit. If you want a bit more power even off spray and really doubt another 500 rpm in spool will be that noticeable and it might help traction then go for the bigger kit. As said try to find the aps graph of their forged up 346 with similar mods to you and me. pretty sure that graph was strong to 6500 or so.

 

i here the bigger turbos are better than the base ones that come with the kit
im thinking of trying to get those new centers that we talk about in Louis@LGM post some time ago
but spool time is great

 

I went to the APS site and looked at the dyno graph for the standard kit on a stock 346. It made 502rwhp up to about 6,100rpm. That is the only dyno for a 346 I could find on the site though. If you can find the graph for the built 346, pleas post a link.

http://www.airpowersystems.com/fbody/tt.htm

 

https://ls1tech.com/forums/8080509-post121.html




If I remember correctly, the graph below is where APS messed with the impeller or something





Oh, and supposedly all of this is possible with the original inlet ducts

 

Yeah the second one was the tweaked wheels . not sure how they kep their ducts open
maybe ran no ducts on the dyno? Or maybe the ducts don't suck shut until after several heat cycles on the street.

I have seen some other high hp graphs here one on gto. I am waiting for some high boost dynos on the standards on 402 or 408 . Maybe I will be one of those dynos this coming season. Sounds like easy to stent the original inlets with 3 inch oval two inch or so sections as read about on here recently. Might be worth trying that before buying the upgraded ones.

 

How hard is it to actually do internal changes and tweaks on the turbos themselves, such as the springs and impeller upgrades? I'm trying to get as close to that 830rwhp mark without breaking the bank.

 

You can get different wheels and stuff and turbos are simple things to take apart but pretty sure problem is things have to be properly balanced when reassembled by a pro shop to be reliable.
This could be why some of the standard turbos had problems. They could be using knock offs by accident maybe ,as at least one guy had his duds taken apart and parts were missing or poor quality. And there are knock off mits out there.

So really options are to buy the upgraded kit now from APS or used if you find one or possibly let LG upgrade the turbos thru Forced performance which don't think will do it directly.

They are some drop in housings for sale on ebay that are supposedly improvement. I might get those not sure yet. They are literally drop in.

You should be able to get to around that 800 and change rwhp with the standards. You have spray if you come up a bit short. If you for sure want that number no spray then go to the bigger ones or upgrade the standards later if you fall short. Expect it to cost a good bit to upgrade. Think LG said 1000 per turbo to upgrade them not sure if that was with old cores on exchange or what exactly. And aps wants 2500 to sell the upgraded ones later.

 

If I get the drop-in upgraded wheel kit off ebay, that should get me to around 800rwhp off spray I would think. If you know the link to that ebay kit, post it up. I don't even know where to begin to search for something like that. I could just take it to a good turbo shop somewhere in the area here and let them install and balance the new wheel upgrade before I get the kit put in. I really don't want to have to pull these turbos back out anytime soon once they are in. I would rather go ahead and do it right the first time. If I find that all this is too much trouble and that buying that used standard kit is more trouble than it's worth, then I'll just go back to my original plans to get an F1 Procharger from EPP.

 

This is similar but they are not currently listing the correct water cooled housing right now.

http://cgi.ebay.com/ebaymotors/Turbo...Q5fAccessories


It is tdo6 h water cooled 20g this one shown is oil cooled center housing. You could run just oil cooled but think its still best to run both oil and water cooling.

these are plug and play into the aps compressor and inlet housings. Price is reasonable and they say they have been high speed balanced. I may get these not sure yet.
It is for sure a pain to take on and off the aps turbos if they have a problem. As far as i can see you have to drop the kmember to get them out. Unless some other aps guys have removed theirs without taking off the k member somehow. They pretty much have to come out the bottom.

 

Was still going to say that there have been quite a few bad f body turbos but didn't find anyone on the gto or c5 boards saying they had bad ones. They are identical turbos.
So not sure what is up with that. You might have problems with the them and you might not. The upgraded kit might be fine too. Mits 20g are normally very reliable.
I have lots of experience with mits turbos in my talons although those were 14b's still basically same thing.
I have seen mits turbos go for over 100,000 miles many times. As for procharger have been in a d1sc procharged ls1 and a p1sc procharged lt1. The procharger was interesting but does not compare to a twin turbo in area under the curve and efficiency.It can give similar peak numbers for hp not sure about tq. The power can be a bit more controllable on the centrificals due to the way they build more and more boost with rpm. At the track they can turn similar numbers to turbos. On the street again though the area under the curve shows up more often. Especially when you go up thru the gears and can't gear down to bring up rpm. Manual turbo cars though will need two step and maybe antilag to help get decent boost off the line.

They are both fun toys I might procharge my 96z28 at some point in the future. Have enough turbo toys right now.

 

I just think that dropping off power before 5,500rpm is ridiculous. If this internal upgrade really is a cost effective way to bring that power band up past 6,000rpm, then I'll stick with the turbos. I have about 3 weeks or so to decide since he said he would hold onto the kit for me for that long since he will be going out of town on a big trip.

 

MY99TAWS6, you said something earlier about getting the manifolds ceramic coated before I install them. This sounds expensive, is it really worth it?

 

There are several things that might make them drop off power at 5500 I would not blame the turbos so quickly for that. especially on a 346. The aps graphs hold the power quite well past 5500 although the one with bigger wheels does look of course stronger up there than the standard wheels.

Things that might make power fall off up top are weak or insufficient valve springs..inadequate fueling maybe, as said not sure how high you can go on the 7.5 standard gate springs might need to swap them for higher base ones. And we have seen problems on the aps with the standard inlet pipes collapsing before they starting selliing those upgraded ones. Possible even boost leaks could be one cause. Boost leaks are common on boosted cars and can be hard to find sometime.

The turbos might run out of steam on a bigger motor top end. Thats why I want to see more 402 ,408 high boost dyno runs with upgraded or stented inlets. Or no inlets on the dyno.

And not sure the effect of cam choice on top end power but sure it has some. I wish could give you more observations from my car but its still away for winter for another couple months.

Ceramic coating would keep heat down some more .It can still get pretty hot.There are heat shields supplied for the exhaust manifolds and starter but still coating would look nice and help things out so you could maybe not run those razor sharp shields..
I went to Granatelli high temp wires after cooking an accel 9000 wire.

I would also consider coating the hot side of the turbos as well.

 

I think I'll give LG a call and see what they say about upgrading the turbos. I have no idea where I would go around here to have stuff coated and no base for what is a good price either.

 

Its not esential to coat that stuff just nice to do. I didn't and if have them off might do it . Have to send them off to city about 500 miles away. No one does it here either. The manifolds will get a bit rusty if you don't coat them.I sprayed them with high heat paint and baked them in oven..wife is still mad..stupid idea use old oven in garage or something!! LOL never again..paint is staying on so so on the manifolds didn't paint the turbo exhaust housings.

 

What did it do to the oven? LOL

 

thats funny i have been looking in to coatings for the DIY guys like us. it looks easy they even have coatings for piston you can do at home i think this is the same place that shops get there coatings from

 

on that coating the place was call tech line coatings
i talk to louis@LGM he was a great help im waiting on more info from him

 

I looked at the coating, it seems like a pretty easy do-it-yourself kind of thing. I think I will probably order some if I get this turbo kit. Too bad the turbo coating doesn't come in red though.

 

Call Jet-hot and talk to them. they can coat it in Red for you if you want. i had them do mine in black and it was well worth it. brings the engine compartment temps down a little which the way everything is crammed in there, has to be worth something. cost me like $140 or something to that effect to get em done. turn around time was less than a week.

my car pulls strong to about 5700-6000 before it tappers off which i expected since im running a 402. eventually i may swap them out for something else but for right now since i dont race on a reguler basis i may just leave it the way it is.