No the title isn’t a shot at the car — I’m finding it to be a great car and the motor is turning out to be pretty solid. There’s just one thing that’s quite annoying — Honda gimped the potential of the motor with the fuel system. The D/I fuel pump is pegged out very easily once you turn the power up, which in fact leaves you literally scraping the bottom of the barrel to make a clean power curve as you’re riding a very fine line with the fuel system.
This turns out to be even more true once we put on the PRL Motorsports Intercooler on the car and found out it improves cooling efficiency to a point we were making the power we had before while running less boost. Of course we wanted to make more power and run more boost — which proved futile given the limitations we kept hitting in the fuel system.
The car is 100% OEM aside from the PRL Intercooler and we used E35 blend fuel for this test (as we wanted to see how much more we could push the motor).
So what did the results look like? We were able to make a clean power curve and pick up more power before the fuel system maxed out — and make roughly the same top end with less boost.
Well here’s why — in our MoTeC programming we’ve added code that estimates how much injection time you have left before your spark event. You need a certain amount of time left over for a clean mix in the combustion chamber before the fuel is ignited. Do not leave enough time for this to happen the engine doesn’t make power or even worse — misfires. It appears that on this motor we want at least 1.5ms of “Injection Time Remaining” to get a complete mix.
But as fuel demand on the D/I pump goes up it skips a beat and we see a large fuel pressure drop — from a target of 22.5MPa to 16.6MPa (a 6MPa or almost 900psi drop in fuel pressure). As a result of the pressure drop the injector pulse width has to increase and now we’re running out of injection time!
Really Push It
How bad does it get if you REALLY push the D/I fuel system? Well take a look at this. Wow it’s just a roller coaster ride after 5500 rpm — we were making over 390whp and would of made well over 400whp if we had the fuel…
You can see how tapped out the D/I fuel system was on this 29psi pull as we dropped 8MPa of fuel pressure.
Injection time remaining was super low… and the motor even misfired at 6600 rpm.
So Did the Intercooler Help?
Absolutely. Here’s some useful data from actual hard acceleration runs on the stock intercooler and with the PRL intercooler. You should note — we actually used a bit less boost on the stock intercooler runs and the stock intercooler had colder ambient temperatures versus when we ran the PRL intercooler test. However the stock intercooler still heat soaked rapidly. For comparison are runs at WOT from 1st to 3rd gear.
First on the left is the stock intercooler. Note the following — “Airbox Temperature” is the temperature sensor in the intake BEFORE the turbo and the “Inlet Air Temperature” is the temperature sensor in the intake manifold. The sensor in the intake manifold tends to heat soak at idle/low air volume conditions (not much fresh air flowing through the intake manifold).
On the right is the run w/ the PRL intercooler. You can note that with the stock intercooler the Inlet temperature never touches the airbox temperature and in fact starts to climb almost immediately after dropping. With the PRL intercooler the aircharge is rapidly cooled and comes down to match the temperature at the airbox — and stays steady all the way through 3rd gear and would *maybe* start to slowly climb in 4th gear.
Clearly the intercooler upgrade is worth it — especially for our road course folks.
After having the car for a while and getting more comfortable with the clutch — I wanted to see if it would hold a bit more torque. I brought in 23-24psi earlier in the powerband, held 24psi through the top end — and made ~390hp and just a hair shy of ~400tq.
Is there more potential there? I believe so — I think we can probably make 450wtq quite easily — if we had reliable fueling. We had a 6MPa pressure drop and the fuel pressure just did not look that great.
Yes — this is E35 fuel (we had made 360whp on 92 previously), but there will be comparable gains from this intercooler on pump gas as well. The E35 actually doesn’t bring up fuel demand *that* much over pump gas (which is E10 to begin with) — it’s about 10% more fuel. So what’s that tell us? Where the hard limit is for fuel volume with this D/I fuel system.
How much can we do on just pump gas? Maybe 400whp before we need to do secondary injection. Maybe less, maybe more. We’ll find out once we have a the PRL downpipe on the VitR!
The other option is to use a race gas that reduces fuel system demand over pump gas….