4G15 SOHC I4

     This page is for Mitsubishi's little engine that could, the 4G15.  The G15 is a SOHC inline four cylinder, that was destined to be turbocharged.  This page will focus mainly on turbocharging the 4G15, what is required, what is recommended, and what to expect as an outcome.  The info on this page comes from my personal trials with the engine, as well as specs that come from the OEM.  When done porperly you can achieve 200whp reliably, and over 400whp in full race applications from this little 1.5l.  As a background, my Mirage started life with a G15, which became boosted, and over a period of time, I pushed it to the max, eventually fining it's breaking point,

Here is an example of a turbocharged 4G15.  This was designed around a IHI RHB5-VJ11 journal bearing turbocharger.  This turbo is a small displacement ideal for engines up to 2.0l in size.  This setup spools lighning quick (2200rpm full spool), and pulls great through redline when coupled with the correct support components.

 







Seond shot of the turbo setup - As you can see the I/C piping is less than ideal, but was built out of convenience.  this caused minor heat soak issues at higher boost levels with repeated track abuse.  This combination was able to produce a 7.9sec 1/8th mile run at 91mph in a 2200lb 5th generation Mirage sedan. 

 Strapped to the Mustang 500 AWD the Mirage spun all four rollers (dragging the rear as a rollin road) to the tune of 152.4WHP and 114.3WTQ at only 7psi.  This was later street tuned with an AFC and driven daily at 12psi (15psi on weekends). 

The turbocharger is the backbone of a fast 4G15, so correct sizing is crucial.  More often than not, people chose a trubocharger much to large for the application.  This will cause extreme turbo lag (a delay in building up pressure in the intake manifold), and you will never feel the full potential power of the engine.  Being the G15 is so small, you can utilize a small turbocharger as well.  This is especially true on a road going car used for commuting on a daily basis. 

When building my first turbo 4G15 I used an IHI RHB5-VJ11 (the OE turbo on a turbo MX6).  This was due to availability, cost, and pure luck.  I did very little research before beginning that build, but with some luck on my side, it workied out fantastically.  This turbo reached full spool by 2700rpm (12psi) and began spooling by 1600-1800rpm.  this was with a DSM pocket cooler to chill the air charge.  Later with a small FMIC (front mount intercooler), it would reach full spool (as high as 17psi) by 3300rpm. 

For my second build I used a 50Trim T-3 Garrett turbocharger, which was very thought out and well planned to get the job done and do it right.  The smaller trim T-3 was still able to spool by 3500rpm (as high as 37psi), and would build some boost as low as 2000rpm.  This thing would pull like a freight train all the way to redline, and would scare litre bikes away on high boost levels.  On moderate boost this turbocharger was letting the little 4G15 make well over 200whp on e85.