I figured I'd bring this up since there is/was some confusion as to what the Borg Warner IHI RHC6 GM1-8 compares to when comparing any of them to a Garrett TO4B or TO4E.
The IHI RHC6 GM8 measures 2.756" major diameter and 1.968" minor diameter on the compressor wheel. There are NO minor diameters of TO4E that measure 1.968". The closest you would get would be the TO4E 40 trim which measures 1.870"...BUT..the major diameter is 2.950". A difference of a finger nail on each side...quite a difference in percentage and overall flow potential.
Now moving on to what is closest- The TO4B S which measures 2.750" major and 1.904" minor.
Here is the TO4B S which has a max choke flow of 37 lbs/min or roughly 17.7 m³/min which equates to roughly 625 CFM. Take the rules of 150 CFM per 100 hp and you'll see that the TO4B S is capable of enough flow for 300~500 hp. 300 hp comfortably, but 500 hp IS A STRETCH, especially on a small displacement engine. You'd likely see most of your hp taper off in the 350+ range
Now onto more facts courtesy of IHI. The closest current
compressor map that you'll find is located here:
But this is for the latest
series of IHI turbos which aren't ancient and weren't made in the 90's. The updated
(ie current) version of the RHC6 family
is the RHE
61 which is the same frame, same size, same everything except 2000'ish rather than 90'ish.
Note that the airflow rate for the RHE61 is 3.3 m³/min - 17.7m³/min or 116.5- 618 CFM. Now that we've gotten that
taken care of, we'll move onto the actual flow maps. Here is the entire updated
family of IHI turbos:
Note that the RHE61 barely passes the 20m³/min mark and that spooling the turbo that fast would be the equivalent of trying to boost a VJ11 to 30 psi. As said, the choke flow is 17.5 m³/min.
What does this all mean? Why and I posting pictures of turbos that aren't the turbo in question? Glad you asked.
Here is the archaic RHB3-RHC9 compressor maps:
The RHC6 family
tops out at 17.5 m³/min or 620 CFM.
All that and I haven't even gotten into how the GM8 is the worst out them all.
The GM8 has the wastegate flapper in the exhaust elbow (which can't be used) and in order to use it, you'd have to use an external wastegate and a block off plate for the wastegate hole.
The GM3 has the wastegate flapper integrated into the exhaust housing the same way the Vj11 does.
Anyways, here is the GM3 with integrated wastegate:
Now here's the GM8 with wastegate in the exhaust elbow that you can't use:
Unless you're going to put your exhaust out of the hood, make a manifold that has exhaust flow coming from underneath and the exhaust housing rotated, or a block-off plate and an external wastegate: