help pick twin turbos

[aaronr]

Motor: LS1 with 317 heads and triple 12 cam.
I building an twin turbo set-up for my 67 chevy truck and need a little help picking some turbos. I'm looking for a turbo that will spool quick. The first choice turbo would work but afraid the big A/R housing is going to hurt spooling. The second choice is bigger turbo over all but if I go with the .68 A/R would hurt me up top. if go with .81 house should spool ok. The last turbo is the best choice but out of budget. What do you guys think.

Here are the two turbos picked so far.

1. BorgWarner Airwerks S200SX-56, with 1.22 A/R Twin Scroll Turbine Housing
Compressor: 56mm inducer / 69.6mm exducer,
Turbine: 69.6mm inducer / 61.5mm exducer.

2. Magnum Performance 60-1 / P-Trim .68A/R or .81 A/R


Dream turbo but budget can't take it.
Borg Warner Air Werks S200-56 / S256 Turbo .86 A/R
::Compressor:: (cold side)
- Wheel: 56mm Inducer / 80mm Exducer
::Turbine:: (hot side)
- Wheel: 74.1mm Inducer / 65mm Exducer

Thanks
Guys

[George C]

spooling is not just from the actual turbo but size of primaries going to the turbo. You need to have everything mapped out before picking the correct turbos but yes those little 60s will work on a Ls1 even with a .68 ar

[lilblu]

I was asking the same questions, when I went twins. Have a 408 stroker with twin 70's an spools really quick an haven't ran out of top end pull yet. An that's from 60 to 160 mph. But don't think I would go to much smaller than 70mm.

[George C]

Gotta take into account exhaust wheel size as that's the factor here.

[jansen]

spooling is not just from the actual turbo but size of primaries going to the turbo.

. George I've read where you've mentioned this several times and have noticed on a lot of the new nelson performance builds that everyone is using large primaries. Please correct me if I'm wrong because I'm just trying to comprehend it. At first glance one might think that smaller primaries would be less space that would have to be filled with exhaust and would make it spool faster but it would also be restrictive. With The larger primaries the engine would be less restricted but since the primaries would already be full of exhaust it wouldn't slow down the spool time very much. I guess an example would be a 100 gallon air compressor blowing air out of a 3/8 inch hole with the hole being the turbo housing. Hope I didn't cause mass confusion. I'm just trying to understand it.

[George C]

Large primaries slow the gases down before collector losing velocity. Smaller or stepped primaries keep velocity up pre turbine and helping spool.

Doing a stepped setup like this will allow you to run a larger ar and not effect spool as a larger primary with larger ar would. Its basic thermodynamics.

Pick up corky bells maximum boost and you'll see the theory's backing this.

Your restriction isn't the motor its the turbine and its ar .

By setting this up correctly you'll see a difference in back half mph

[jansen]

Cool thanks for the info I'll definitely be checking it out!

[aaronr]

Running log manifolds

[farmtruc]

Pick up corky bells maximum boost and you'll see the theory's backing this.

By know means do i wanna get in a debate on size, logs, headers, primary size, etc, but basically, most of the theories in most books are thrown out the door in the real world at our level.
All the thermodynamics and theories on this subject are for another level.

Case and point, and STS rear mount turbo system isn't supposed to work according to Corky, lol.

Some of the ugliest kits out there are producing good results.

I went from stock manifolds to full length headers, NO GAIN!

Just isn't worth it to get into details on what works and doesn't work.

- in conclusion, if you just build a good kit that seems to flow well, it's gonna work and flow well.
just be sure to pick a turbo big enough not to choke it down, hence Quik's comments regarding exhaust housing size.
all of us guys are going to slightly bigger turbos than the map suggests, so take that into consideration.
there are too many variables that play are part in choosing a turbo, the map is a great starting point but it seems we all change out turbos eventually.



just my two cents on it,

don't over think it.

[George C]

agreed in many cases you can shit on a stick and call it a turbo kit and it will work but you can also agree that mapping everything out to the T will perform....To many the extra effort into the full monte isnt worth it

ive personally seen spool differences in doing the stepped headers going large to small pre collector vs when dealing with a large primary setup. HP on dyno was the same, difference was close to 400 rpms eariler spool in the graph, a better graph down low, and few more mph out the back door vs other but in cases where WOT is all that matters and you have plenty of time to sit and spool on line then the Mapped out setup wont be for that person


as for the manifolds, thats a point as well since theyre ID isnt consistant thruout the primary and are along the lines of a stepped setup which help nicely but are ugly lol