In theory you want your turbos to be big enough to support your final HP number, but not much larger. Trouble is everyone "wants 600hp instant spool but want to grow into 1200rwhp when I turn it up" without replacing the turbos and thats just not going to happen like that.

 

Yep run in to this often.

 

I do not know the exact specs on those turbos...but most likely the turbine housing was too small to flow the exhaust volume of the 6.0 over 5,000 rpm. And at the same time built TQ very quickly and very early. The smaller exhaust volume of the 4.8 allowed the turbos to keep flowing and increasing rpm and thus HP.

It probably had nothing at all to do with boost or the compressor side.

 

I would have to be a very small exhaust side to choke a 3.0L engine.

 

Hmmmm. True.....What else might cause a larger engine to make massive TQ earlier and make less peak HP and level off at 5K? Cam?

EDIT:
Just saw this on that thread about his twin gt35 2500 truck:

its a t4, 4 inch inlet, 2.5 outlet
61mm,

.68 AR 3 inch Vband downpipe

So the turbine housing does not SEEM to be too small.....if those specs are ACTUALLY what he received...

 

This is what i was getting at with my last question.
if you wanted 600hp that would mean that if you run twins then 300hp each side?

the spec of the turbo

Turbine .68 A/R
Compressor Wheel 61.3 /82 mm
Turbine Wheel 62 /67.8 mm

im confused on how half an lq4= 3.0L cant push a 61/62 turbo to high numbers when back in my supra days(granted it was I6 3.0) we were pushing single 61mm to 500whp


the cam was the other thing that might have caused an issue but he switch it out before addressing anything.

 

What was the peak torque number with the supra and what RPM did it make peak torque?

 

The final hp is 700whp. if I decided i wanted more later on i have no problem switching them to a pair of 70mm or 76mm(they are cheap enough)


and as it stand the options im considering are all in the same price range.
I want as close as you can get to "instant spool" which is why im really considering using twin gt35. id like to stay below 20psi mainly because im planning on 91octain and methanol. (maybe even a 87oct + meth, because im going to be taking this to trips and some station only have 87 octain)


if the gt35 is too small then 67mm twins is next but looking at the specs the 70mm is not that far off. Im thinking a .68 70mm would probably spool close if not faster than the twin 67mm due to AR?
downside= I was reading that twin 70mm is way too much of a turbo for my goal


GT35 twins
Compressor .70 A/R
Turbine .68 A/R
Compressor Wheel 61.3 /82 mm
Turbine Wheel 62 /67.8 mm

vs

t67 twins
Compressor 67mm Wheel Compressor
Turbine P Trim .81 A/R Turbine
Turbine Wheel 74.1mm/64.6mm



the next in line is 70mm twins

Compressor Wheel 70mm .70 a/r
Exducer- 94mm

Inducer- 64.5mm
Available in 2 A/R sizes - .68 or 1.0(would go with .68)

 

I dont recall actual numbers but somewhere in 370-390ish. but above 5krpm
turbo lag is the main reason i switch to turbo v8

 

i had those turbos on my 4.8. i think my thread on ls1tech is what got you thinking about this.
those turbines are really small and the housings are .68
with a small cam it probably wouldnt be too bad on a 6.0 but you definitely wont be able to spin it up or make a lot of boost. but the power would be there.