goose2w1

Well I have been e-mailing a bunch of info and questions to Nathan at MPI about what set of twins would be right for me. He suggested the Stocker/S00 or a 62/71/13 and a GT42. I am pretty much sold on the Stocker/S400, but I am curious about option #2. I figure it would be more expensive, but I am wondering if I should consider it or not. Current/future mods are in sig and I will be adding studs and springs too. I didn't want to bother Nathan anymore so I thought I would ask here.

soulezoo

Well the s400 and the GT4202r flow right about the same quantity of air. Difference is the 4202 will spool much faster. In fact, it will spool right along with your secondary and may be fully spooled before your secondary! The drawback is that turbo will be two to three times the price of the s400.

Stainless

In this case why isn't the GT42 used as the "ultimate" single? Other than the price tag.....

Hintz

Can you run a GT42 w/ the stock turbo?

soulezoo

Well first, we are talking about it being a primary in twins which ends up being "different" than using as a single. You are only asking the turbo to spool to around 30psi as a low pressure turbo. While I know of no one that uses it as a single, I imagine that properly configured it would spool much like a silver bullet or A5K. But I am only guessing here without first hand experience.

I find in my twinset that the lower turbo is often at or over the 30psi mark already before I reach full boost...

soulezoo

I don't see why not... again, I know of no one who has tried.

cquestad

A GT42 is on the bottom of Mark K's aka bigman twins...with a 62/65/14. WORKS GREAT for a sub 700 hp truck.

dodgezilla04

i have the gt42 as the bottom and a t58 as the top. it is one of nathans earlier sets. and they spool LIKE NOW!!!!.

JCLeary

I asked Nathan the same thing. Response:

I have built kits for the stock turbo and a GT42 before but it hasn't worked out all that well. The turbine side is just too restrictive between the two. Mostly it is the stock turbo causing the problem. You can get away with it by using a S400 but not the GT42. So there are two combo's I'd consider, one is a Garrett stage 2 or 3 Dodge turbo and a BB GT42 or a modified stock turbo and a GT42. The modified stock turbo gives you a bigger turbine wheel to help the back pressure. You get basically the same thing in the Garrett. The only other option I would possibly consider is a S300G (Basically a BD super B) with a GT42. Any of those combo's will get you into the 650hp range and possibly 700.

I've run the stock/S400 combo with a external wastegate and it doesn't help enough to justify the expense because I can get enough wastegate flow out of the stock wastegate now. The problem is the drive pressures when you combine 2 really small turbine wheels together. It's some what the same with the BD towing twins. The other problem with those is the big turbo is just way too small to make a significant improvement over the top turbo by itself.

metal_miner

Nathan upgraded my BD twin turbo set to a Super B (57/65/14) over a GT4202. They spool ridiculously fast.

Details here:

https://www.dieseltruckresource.com/...d.php?t=186665

The Super B is kind of like a newer (+04.5) stock turbo on the compressor side, but has a bigger exhaust side than stock.

Oh yeah... the GT4202 is also internally wastegated to give even more adjustability than just by having the top turbo wastegated. This means I can run a tighter exhaust side to get even quicker spool.

Still need to dyno though...

wap

So the 4202 wont move enough are to hang with an S480 then?

O.T

Julius I'm dying to hear some numbers...come on

bigman

I have a 62-65-14 over a gt4202 on my auto and i run a stocker over a gt 4202 on my 6 speed. They both are amazingly quick to spool. Zero egt issues and very drivable. If you tow alot and want to be around 550 go the stocker as your primary, if you want to play alittle more go with a 62-65-14 over a gt4202. Both will amaze you.

soulezoo

The 4202 is roughly the same lbs/min as a s400. The gt4508 is roughly the same Lbs/min as a s480.

jaredb900rr

What elevation are you at in southern NM? Elevation plays a HUGE factor in how fast turbos spool up. I have a 62/71/13SS over an S474. It is a tad laggy here in Utah at 4000 feet elevation, but I've never really thought of it as an issue. UNTIL, I went to the California coast a few weeks ago. I was able to punch it from a stop and it was instant-spool! Completely changed the truck!

I'm considering dropping to a 65mm wheel on my top turbo to quicken spoolup here in Utah.