Honestly it sounds a little questionable. A few horsepower difference one way or the other is expected however about a 10% difference is too significant. There is probably some other reason for the difference likely it is dyno operator and/or dyno calibration... or possibly just the engine being more broken in and/or ecu figuring things out.

Because a fuel pump and fuel rail really don't make any difference in how rich the engine is running (unless your original pump was defective). The plugs can sometimes add a but of power but usually when the old ones are overdue for a change (which shouldn't have been the case at 2600 miles). So reality is you shouldn't have seen much change.

 

(unless your original pump was defective)

I completely agree. I was shocked when I saw the gains. I was thinking the same thing maybe something up with the dyno, however after replacing the pump I did notice an improvement on the street. And yes my original pump did fail at the track, it quit pumping enough fuel once it reached 4000 RPM so I had to drive home at a lower RPM. Who knows, the factory pump could have been not performing well for awhile, however the base HP pull calcualtes to 193HP which is right on the money.

Next trip to the dyno should confirm that the numbers are accurate for this latest run. I may stop down and have Phil do a run too and take a look at his shop.

 

Agree with comment above . There is not that much horsepower to gain without fiddling with the tune.

 

Power gained by replacing fuel rail and fuel pump? Bwahahahahaha!!!!!!!!!!!!!!!!!!!!!!!!

 

are all the dyno pulls performed on the same dyno?

 

Dates and mileage posted above.

 

163 to 166 rear wheel hp is the "accepted" stock HP figure, after your engine is broke in. This allows for a more realistic 12 percent transmission loss. Your original dyno values were a bit low, but then, your engine and transmission was not fully broke in yet and may have had more friction losses. As others have said: the dyno, temp that day, humidity that day, tire type and pressure that day.. make a difference.

 

I added a note that on the last run stickier rear Toyo tires were added too, but I would not think this would make any difference on the dyno.

 

Ya, there's just no way those mods would make that kind of change on an otherwise "normal" running car.

Perhaps she was running ultra lean on the base with the failing pump, etc, and that was costing power. Hard telling without data...

As for tires, they can absolutely make a difference on a chassis dyno-- particularly on low hp cars like a NA elise... Tire pressure and sidewall deflection can impact results quite a good bit.

Always monitor AFR when doing pulls and always make a point to keep as many potential variables the same... even climate conditions, as SAE corrections are not "all that"...

I'd love to play with your car, but my dyno won't be relevant data either, as no two dynos should really be compared to each other. Especially if you were on an inertia dyno (dyno jet), as mine is eddy, so the way it loads the motor is different and the power will subsequently be slightly different too...

When I'm doing tunes, I just keep the car on the rollers. The conditions are then as controlled as can be. We data log as many parameters as possible. Spark, AFR, MAF, engine harmonics, etc... When we're doing mods and trying to examine the benefit of the mods, we try to do them within a week of each other and ofcourse we're using the same dyno and same calibration. Sometimes, we'll do the more minor mods right on the dyno. You get the idea--- it's good practice to control as many variables as possible and collect as much data as possible so that you can more accurately conclude that the mod did what you thought it would do and if the motor output was more or less than the previous, WHY that was... If the delta output doesn't make sense, there's probably good reason for it...

Cheers,

Phil

 

Phil, what dyno do you have?

 

I'd be interested to see the dyno graphs and air/fuel traces. I agree that there is a strong chance that the dyno is responsible for the difference. The fuel rail should not make a measurable difference at stock power level. It's possible that the fuel pump did make some difference since the 255 pump does raise fuel pressure slightly because of the construction of the stock fuel pressure regulator. As flow increases the regulated pressure rises a bit. It's not a big difference but if your car was running too lean before then the extra fuel could cause some improvement.

Does it feel faster?

 

Yeah it felt better with the entirely new fuel system. I will try to post the A/F numbers later. One note, the dyno guy just stuck the A/F sensor at the output of the exhaust pipes. I was sort of sitting on a 2x4 base, not directly connected to the pipes, so each run on a different day, the sensor could have been positioned a couple inches differently, not sure how much that would affect the dyno's A/F sensor too. I dont have any A/F gauge in the car yet.

 

His current power figures are for a healthy engine; I suspect he is fine, but it doesn't hurt to keep an eye on it.

 

Just throwing this out there;

Cup Airbox
BWR Decat
VF muffler
VF tune

=186 WHP

My base run on the dyno before tune was in the mid 170s.

 

Much more reasonable than the OP's numbers considering you have a tune as well.

 

don't forget the NOS stickers, they're worth 5 HP (each)!