drjimmy

I sold my Vortech and now I'm looking to build a low boost (7psi) twin turbo system. The engine is a carbed 400sbc. I used turbo calc to help me size the turbos and it told me that a pair of T3's would do the job. They seem small to me. Any recomendations on size?

mn_vette

a set of large T3's will do the job if you are sticking with low boost. But if you are ever planning on running anything higher I would suggest a set of T4's or just go with a single.

A nice set of 60-1 turbines with either T3 or T4 housings would do you just fine. T4's for sure if you are planning on going for max horsepower. But it would be nice for packaging if you can get the T3's with built in wastegates.

lcvette

Garrett GT35R's on a 400CID build would be pretty great. get the .82 AR housings out back. these are ball bearing units and will spool very quickly.

A more cost conservative unit would be a set of Precision Turbo & Engine 6262 Billet turbochargers, these are less expensive and offered in journal bearing form to help save some money.

Hope this helps!

Chris

502SCS

MN .. do you have some details about your car
I am thinking of a twin turbo build for my 96 LT4 Coupe
I would love to do the project but finding very little info
Thanks

Orr89rocz

Got twin 60mm T4 flange units on my 401 small block chevy. Works good. My lowest boost is 10 psi and its an animal on that level. Turbos are perfect for that size. Ran 10.3's at 135mph on 10 psi with no launch whatsoever. 14psi it runs 9.8's at 141

If 7psi is your max, T3 60-1's will do ok. Cant go wrong with a T4 flange 58-60mm unit tho. With smaller housing on the turbine side, they spool very quick

502SCS

THank you for that info !!

I have been looking for header choices and t-4 flange seems the most popular.

Engine management mods?

drjimmy

Thanks for all the advice everyone. The more I look at my engine bay, the more sense it makes for me to go to a big single turbo and put it on the passenger side seeing as how I removed my AC.

Brand-X

New to the turbo side of this forum.... I was looking at the Garrett site and based upon the math on their page, a 400 cid making +1k whp, you would need a pair of GT40s (94mm, 52 trim, .72 ar), does that sound right? Also, from my read of their tech, it sound like you want to be in the upper right portion of the map at peak rpm so you can be i the middle of the map at peak torque...can anyone shed some light on this and can you describe your ar and trim sizing process?
thx
CT

lcvette

twin GT40's are either going to be the GT4088 which has a 63mm compressor wheel and the GT40 turbine or the GT4094 which has a 68mm Compressor wheel and the same GT40 turbine wheel. the GT4088 can put down around 700rwhp while the GT4094 can support almost 775rwhp. in order to run these units the car would need a very broad RPM band to take advantage of the flow capabilities.

The GT3582R units would be capable of over 1krwhp with a much broader torque curve and would come online alot sooner. and you wouldn't need to spin the engine to the moon. packaging the GT3582R's would be considerably easier as the GT40 family is much larger physically.

regarding the compressor maps, when you start climbing upwards you are getting into a much higher pressure ratio.. the taller the map the more capable of a unit it is for a smaller displacement high boost requirement motor ~30+psi, it means it will remain in its efficiency islands at elevated pressures better. If you review the turbotech 103 section you will see where a GT3071R turbo on a 2.0L plotted turning both 5000 and 7200rpm by the red dots. if you consider halfway between the two RPM point will be where most V8 motors fall in their max RPM range. take into consideration that plot is done at a PSIG pressure of 26.4psi. lower boost pressures will plot the dot in more favorable areas at higher RPM's.

below that is plotted the GT35R, this shows the higher mass flow capacity for that compressor wheel. if these units are used as a pair (twins)the flow capacity of the turbine increases to accomodate the 400cid's motor, the compressor wheel is capable at max of 60lbs/min of mass air flow. the basic quick rule of thumb is if you have adequate turbine (hot side) flow, you can effectively multiply the massflow of the compressor wheel at its highest point time 10, and this is what the turbo is capable of producing powerwise. Using this quick calculation you can estimate the rwhp as such: (60lbs/min) x (10) = 600rwhp

I have had several opportunities to test this calculation and it is accurate to around +/-10%, I know for a fact that the GT3582R can support right around 600rwhp at 7000rpm on a 3.8L engine. this was tapped out full steam nothing left in it.

I would put these on that 400cid motor all day long and providing the motor can handle it, you could easily make 1000rwhp with supporting mods and an efficiently designed turbo system.

Chris

Orr89rocz

Sorry i didnt see sooner

I'm running stock 91-92 speed density 730 ecm using modified GMC syclone/typhoon code known as code 59, or $59 which is the bin code mask. its a 3 bar map sensor based batch fire system. WOrks good so far. Factory GMC syclone code is actually called $58 but its been modified by a group of guys and this version is called $59. Its improved as alot of ppl had problems controlling motors on $58

yeah either would work fine for 1000whp depending on the rpm range of the motor but a 35R will also make that power.

35's are a good flowing 61mm compressor wheel. I got 60mm old school wheel design master powers on mine and I think they are good to over 800whp for the pair easily. A modern 61mm will outflow them and could easily make 1000whp

I wouldnt go any lower than that. 35R is minimum I'd say.