Background:
The previous posts discussing the Shuenk IS48 turbocharger focused on efforts to push the compressor into surge and exploring the maximum boost pressure that the turbo can produce.
With those complete, I’m turning to see what a ‘reasonable‘ maximum power output for my setup is. While pushing to achieve high boost at both low and high RPMs can be viewed as a step toward making high power, this next revision focuses on a balanced approach and consideration of diminishing returns.
Power Tune:
The current fuel is 93 octane gasoline blended with ethanol to achieve a 50% ethanol content. This is intentionally kept lower than full E85, which is why I describe the effort as one that seeks the maximum ‘reasonable‘ power.
Additionally, I have a requirement to maintain OEM knock safety levels and will not adjust the air-to-fuel ratio (AFR) to make it leaner.
I decided to revert to an earlier, lower boost tune, since the higher boost pressure tune was showing diminishing returns in power output.
Russell Road and Racing provided me with a tune update based on this lower boost profile that increased ignition timing by a couple of degrees.
The conditions when I logged the car were just over 83 degrees Fahrenheit.
The ignition timing and AFR with this tune are shown below.
Knock sensor activity remains below the threshold where ignition timing retard would occur.
The boost pressure and wastegate duty cycle are shown next.
The estimated power and torque calculated using Virtual Dyno are shown below:
The peak values are:
| Peak WHP | Peak WTQ |
|---|---|
| 446 | 434 |
These estimates are higher than those of the previous tunes, but my assessment, along with that of Russel Road and Racing, is that we are getting minimal improvement from the changes made to the tune.
If we were trying to achieve the maximum power possible, a higher boost tune could be used, likely with a degree or two more of timing and a leaner air-to-fuel ratio. Additionally, as mentioned at the outset, a higher percentage of ethanol could be utilized.
I would estimate that we could achieve over 450 whp, but the increase would be of little practical use compared to the car’s current capabilities.
Cool Weather – 500 WHP?
It would be interesting to see how this setup performs in cooler weather. A day in the 50s would be a 30-degree drop in intake air temperature from the 83F outside temperature I was logging in.
To illustrate the significant effect cooler weather can have, I made a comparison of the wastegate duty cycle on a cooler day (48°F) and a warmer day (85°F) when using the Mabotech M520 turbo.
In some areas, the turbocharger wastegate duty cycle (WGDC) decreased by 20% and was 10% lower when the pull was ended.
A similar change to the WGDC was shown in the post where I compared the catted versus catless downpipe, although the effect was less dramatic, with a maximum 10% change in WGDC.
That post showed that the 10% reduction of WGDC immediately led to an 11 whp increase of peak HP, and once the tune was adjusted for the lower WGDC, approximately 45 whp were gained.
Those results suggest that the current setup on the GTI, if tuned in cooler weather, might approach 500 whp under more favorable temperature conditions.
Or, maybe not; I’ll have to wait and see if I still have the current setup on the car in 6 months to find out.
Conclusions:
The Shuenk IS48 turbocharger was tuned for maximum ‘reasonable‘ power with the GTIs current hardware and fueling. Using Virtual Dyno to estimate the peak power and torque, figures of 446 wheel horsepower and 434 ft-lbs of torque were calculated.
Next:
The Shuenk IS48 is designed as a direct replacement for an IHI IS38 or aftermarket IS38+. The IS48 replaces the IS38+, which Shuenk previously sold, as it is no longer offered following the release of the IS48.
As a direct replacement, the Shuenk IS48 should work seamlessly with off-the-shelf (OTS) IS38 tunes, or custom IS38 tunes. I have a Eurodyne Powertap cable and flashing software which will allow me to utilize the Eurodyne OTS IS38 tune, with a slight modification.
The GTI currently operates with an RS3 low-pressure fuel pump (LPFP), and the Eurodyne software will need to be adjusted to work with this fuel pump. I will be working with Eurodyne dealer Mabotech to adjust the IS38 tune, and then will evaluate the IS48 using this Eurodyne IS38 tune.