SR20 HP plateau

[Greymedic88]

I have a technical riddle I know someone has the answer to.

The riddle is two different S14s with very different set ups are peaking at about the same power, each peaking around 330whp.

S14 #1 has a high port red top with 720cc injectors, Walbro 255lph fuel pump, GT2871R turbo, metal head gasket, Profec B, AFCII, Apex intake, Z33 MAF, custom FMIC set up (spearco core), Greddy Type S BOV, underdrive pulleys, Greddy intake plenum, Koyo radiator, electric fan, stage 3 clutch, full exhaust/tube headers. This set up peaked at 333 whp on the Dynojet at 21psi. Engine was running very rich at peak boost initially (10.5) prior to tune. Increasing the boost actually dropped power on subsequent runs (no further than 21psi). Power seems very low for this set up, especially at 21psi boost.

S14 #2 has an S15 motor, stock 480cc injectors, Walbro 255lph fuel pump, stock GT28 turbo, stock S15 MAF, HKS intake, cometic head gasket/ARP studs, rebuilt valve train/RAS (cam spec, valve spring spec unknown), Profec E-01, E-manage, Greddy V-spec FMIC, HKS SSQV BOV, Koyo radiator, FAL 210 fans, underdrive pulleys, tube headers, Greddy outlet, HKS downpipe, Apex GT exhaust, Blitz active clutch, stock plenum. After tuning, this set up pulled 323whp on the Dynojet at 14psi. Increasing boost resulted in a drop in power although theoretically, the T28 shouldn't reach max flow until 18psi. Injectors were running at about 90% according to the E-01.

So the question is why are these two set ups unable to push beyond the 330whp mark? What is the weak link in each set up?

I suspect in #1, the BOV may not be holding boost properly in addition to a problem with the intercooler piping (FMIC intake coupler popped off during the final pull at peak boost). The problem shouldn't be related to fuel delivery or the turbo with the 720cc/GT2871R.

My guess for #2 is the 480cc injectors, but according to the E-01, they're not maxing out. The E-01 is using the Greddy MAPS to compensate for the stock MAFS, but I suspect this could be another possible bottleneck. Beyond that, the stock turbo is the other natural bottleneck, but even though power is peaking at 14psi, technically, it shouldn't max out until around 18psi.

So... Anyone have the answer?

[Nismo_Freak]

S14 #1 - BOV is leaking, Type S are notorious for it. Remove the BOV and build a block off plate, redyno.

S14 #2 - Injectors and MAF are topped out.

On the top S14, check the voltage on the fuel pump under WOT. 21 PSI requires a good amount of fuel pressure and the pump may not supply it if it's only getting 10 volts. Hardwire if you are getting less than 12 volts.