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Billet compressor wheel equipped Subaru twin scroll turbos review

Fitment of BRD Big MAF rescale and dyno time 

As stated previously due to me running the standard size MAF pipe and running a certain amount of boost on the LM450 Billet, I was getting really close to the edge of the MAF limit. Not really prudent to do this as falling off the edge of max MAF voltage can cause "bang bang" time.

The reason for this next level of modification was to provide more headroom for the MAF on the OEM ECU (don't forget.... no aftermarket ECU yet running speed density), ultimately making it all well within spec and safe.

Since the replacement of the MAF pipe required a new air filter element, it was going to be interesting to see if a change in filter made any difference to the airflow (and ultimately power).

The third part of the equation was to see if using the dyno could leak out any more power by virtue of being able to try different maps, with the ease of comparing the outputs on the dyno.

Tracktive Solutions (Richard Bulmer) were taking charge of the mapping again and I would be using their Rototest HUB Dyno.

I have used their dyno extensively before with my previous Spec C.

Since this is another different type of dyno (this measures power at the wheel HUB's) I won't be using straight output's from this dyno for a true comparison.... but more on that further on.

As suggested previously we wanted to get a "as is" figure, make all the changes and then get another figure to see any differences.

Prior to any changes, the car was put on the dyno and the car achieved 364.76bhp @ the HUBS (two runs were done with virtually the same figures)...

Richard uses a 18% transmission loss calculation to revert his HUB figures back to an estimated flywheel figure. This would equate to 444bhp at the flywheel. Extremely close to that of the flywheel figure measured on Surrey Rolling Road Dyno Dynamics RR. This is just for information and is irrelevant really. Let's just stick with what was measured at the HUBS.

Richard then set about removing the current filter and fitting the new set-up.

Unfortunately because of the size of the air filter element and the Hybrid Intercooler pipework, Richard needed to reduce the length of the silicon elbow (between the filter and turbo inlet pipe). This enabled the filter to sit lower so the bonnet could be closed.

So with the filter in place Richard set about rescaling the current MAF voltage curve, to take account of the new MAF pipe. 

You really can't run these cars on larger MAF pipes without having them remapped. As soon as the car was fired up on idle it was running lean!! Basically with a larger pipe diameter the ECU thinks it has less air than it actually has. If the ECU thinks it has less air, it will add less fuel.... hence why it can run lean if there is actually more air.

After the initial rescale Richard ran the car and power was immediately up from the initial runs!

After a few more tweaks we had hit 394.42bhp @ the HUBS, but this was running a tad too much ignition and running a tad too lean. It was doing well, but not something Richard was happy to leave. In another comparison (and it is only that - a comparison) my old Spec C made 395bhp @ the HUBS in low boost mode and at that level of tune it made 480bhp @ the flywheel on Zen's dyno. Again using Richard's estimate calculation, that hub figure would equate to 481bhp at the fly. Richard did say that if I wanted a bragging figure... that was surely going to be it!!

Anyway.... with some more map alterations (for Richard to be happy) the end result on the dyno was 384.87bhp @ the HUBS.

The main objective had been reached..... the MAF voltage was well in check now and gave me a fair bit of headroom. Richard did say "you should be OK to go for a LM600 now!". 

Let's look at the "before" figure and what we ended up with "after":

364.76bhp @ HUBS before
384.87bhp @ HUBS after

That is an increase of 5.5% in power.

I would estimate a flywheel figure of around 464bhp on a Dyno Dynamics RR, taking the % increase and applying that to my previous SRR DD figures (440bhp + 5.5% = 464bhp). Richard's own calculations estimate it to be 469bhp @ the flywheel based on his HUB figures.

The car was then taken out on the road. Fuelling was checked with slightly more added in part of the map and a touch of ignition was taken out around 6k rpm. So the final figures may of reduced slightly.

I would of thought it was now well over 450bhp in any case (or should that be any dyno)!

There has been a measurable increase and I asked Richard what it would of been to allow that..... without hesitation he said it was the changes to the inlet, as in bigger and better filter. He said he didn't really make a massive change to the mapping side, but he has seen time and time again, how much difference a bigger filter can make to airflow and ultimate power (to be fair we saw this on my previous Spec C as well).

So… job done and another Litchfield / Turbo Dynamics turbo that has done what I was told it would do. It was certainly interesting to see what changes the inlet made to the power as well..... This has been very positive.