Visiting small block guy, need advice on turbo sizing.

[Jester90RS]

You guys have been great help with my turbo related questions in the past, so I thought I'd ask this one.

my motor has a twin turbo setup I fabbed...but I'm thinking I didn't make the turbos big enough. I kinda knew that going in, but they're what I had. I have 3 good turbos in the existing size, so I'm think I can get away alot cheaper by just getting one more from a junkyard, rather than 2 new suitibly larger ones. I've already worked out all the packaging and fabrication details, and I'm sure I can do it without too much trouble. I'm a pretty skilled wrencher and fabricator, but how to work out quad turbo sizing is beyond my experience.

So, my question is how would 4 standard Garret T3's, .43/.48 AR, work on a 350 ci small block with good heads, a 234/244 cam, and 8.5:1 CR with a 6500rpm shiftpoint. Would it not actually see boost before 6000 or so, or would it actually be useable?

 

[JDEstill]

How much boost do you want to run?
Will you be intercooled or not?
Any idea of the max lb/min or cfm your turbos are rated for?

John

 

[Reggie West]

From what I have seen with V8s and turbos, your A/R sizes are way too small. You will spin them up really fast and they will not flow well on the top end.

If it were me, I would stick with two turbos and change the existing ones you have. Something along the lines of two 60-1s would work pretty well and buy the .81 exhaust housings for them.

V8s seem to be able to spin turbos pretty fast without the lag problems we see with V6s. I am sure it has a lot to do with two more cylinders.

The lower CR you are using will mean you make more boost and run 10 to 12 psi through the motor. You will make max torque I am guessing by 4800 rpm maybe sooner. I dont know if your shift point will be as high as 6500.

I would post this question on the LS1.com board as well. They have a Forced Induction section there and those guys have more experience than I do.

Good luck

 

[Jester90RS]

Originally posted by Reggie West
From what I have seen with V8s and turbos, your A/R sizes are way too small. You will spin them up really fast and they will not flow well on the top end.

Yeah..I think so too. Thats exactly why I'm asking this question And I may end up just staying with twins and going larger....but I think this is worth considering for a few reasons, including cost effectiveness believe it or not.

To answer the other guy.....I have no idea. I'm gonna start with 10-12 psi and go up from there as much as fuel delivery/availability will allow. i'm not sure where I'll hit the limit.

It will not be intercooled, but it will be alchohol injected. I would like to run a water to air cooler, but as of yet, I havn't figured out a way to physically fit it. If I ever do, that will change.

I don't know what those turbos are rated at either, but I'll see if I can find a flowmap to post up. Should be really easy.....40 trim T3's are a dime a dozen.

 

[Reggie West]

The better question is what kind of car is this going in?

Are we talking a LS1 motor or SBC or 4.6 Ford?

From the way you are talking injectors and fuel pumps will be a major concern as well...

 

[Jester90RS]

It's a SBC. And yeah....things like that will be a concern, but that stuff I don't need to ask about.

 

[Jester90RS]

Here, I was able to find a compressor map for it. Altho I'm still not really sure how to translate this data into something useful.

edit: damn bad link

 

[Jester90RS]

 

[Jester90RS]

btt

 

[Reggie West]

Get some twin 60s and you will be amazed........


For a management system look at AEM, it does a LOT of stuff for a very good price.


Look at what LS1 motorsports is doing with one turbo. It is impressive.

http://www.ls1motorsports.com/

 

[jastrckl]

you might want to look into clipping your turbines or switching to a higher a/r housing, if you don't want to spend the money on new turbos. a set of bigger turbos would be better if you could afford it though.

 

[Jester90RS]

Look guys, don't take this the wrong way, I appreciate y'all taking the time to reply and trying to help, but thats not what I asked. I know what twin 60's would do, who makes a good managment system, and what Ls1s can do with one.

What I wanna know is how 4 40 trim T3's would perform on my motor. Would the boost lag till too high an RPM to be useable..or not?

 

[WIKEDV6]

Dude, you want to put 4 turbos on? is it on a 90 RS? man that is lot of plumbing. I have a SBC 355cid w/ twin turbo setup. I used two Turbonetics 60-1 Hifi turbos with .59 a/r. I also have good converter 3200 stall and a trans brake. 20+ psi no problems. for fuel management I have DFI and 55lbs injectors.I haven't had the car to track yet, I am still getting all the bugs out of it. What is you goal?, It depends on what time you want to run. You can go with a single t88 turbo w/.96 a/r and run in the 10's. I belive if you go to the third genaration F body site, Guido is running that with 5psi and pulled a 10 sec run. check it out. http://www.thirdgen.org/techbb2/showthread.php?s=&threadid=142807I I think 4 turbo's will complicate things. just my .O2.

Good luck

Prasad

 

[JDEstill]

Jester -
to answer the question you asked...

350 cid, 6500 rpm, yada yada yada

Four of your T3s are good for about 80 lb/min, absolute max. With no intercooling, no water injection, at 6500 rpm, they ought to be able to provide boost up to the low 20's, ~20-24 psi.

With water/alky injection and no intercooler, I think they can get you up to 16-17 psi.

With a good intercooler, 13-14 psi will be their limit.

That's assuming they work right, that you manage to get all the plumbing issues worked out.

You are right in thinking that two of these turbos are too small. They are so undersized I don't think two of them will flow enough to make ANY boost on a 350.

It seems to me that you'll be way ahead of the game to ditch these things. The headaches involved in trying to make 4 of these things fit just doesn't seem worth the relatively low cost of getting 2 turbos that fit your needs a lot better. As has been mentioned before, twin 60-1's will take you to 25 psi intercooled easily, you'd be SO much better off starting with two of those. Even two stock GN turbos are only a little less capable than 4 of those T3s, and you should be able to find a pair of those pretty inexpensively.

John

 

[Reggie West]

Agreed.....

 

[Jester90RS]

Originally posted by JDEstill
Jester -
to answer the question you asked...

350 cid, 6500 rpm, yada yada yada

Four of your T3s are good for about 80 lb/min, absolute max. With no intercooling, no water injection, at 6500 rpm, they ought to be able to provide boost up to the low 20's, ~20-24 psi.

Even two stock GN turbos are only a little less capable than 4 of those T3s, and you should be able to find a pair of those pretty inexpensively.

John

Thanks man, thats exactly what I needed to know.

I honestly still havn't decided which route I wanna go, but at least now I have a better idea what it is I'm debating between.