I did a dyno day last Friday with my car. Setup is an internally stock S5 motor, stock manifolds, stock porting, stock airbox, and all emissions intact. Only mods are a ******shack header, two catalytic converters, a pre-silencer after the cats and a single Dynomax muffler.

Car made 156rwhp peak on a dynojet with a pretty broad spread of torque, but there is a dip in the middle of the powerband. Thoughts on what is causing that?

I spent about an hour and a half on the dyno playing with varying AFRs, leading timing advance, split, and trigger points for VDI. What I learned is varying the AFR between 12.5:1 and 13.5:1 made no measurable difference in power anywhere in the rev range. The car likes a good amount of leading advance up top and less split (more trailing advance relative to leading) made more power in the midrange.

I'm scheduling another session in a few weeks to try a couple more things, and I'm open to suggestions.

Thanks,

JV

 

i dont know much about s5 n/a's but i guess they are 6ports? the dip you are seeing on your torque curve is the transition, your first stage is running out of breath and when your additional ports are opening your torque begins to climb again.. i guess you can tweek the transition a bit since they probably are controlled by vacuum..

maybe i should read more about s5 n/a's before commenting... if someone feels they want to correct me pls do!

 

5th/6th ports are set to open at 3800 RPM. I was in the car during the pulls so I can't verify that they opened at that RPM, but that's what they were set to.

Also I didn't change the setpoint at all during any of these pulls, so why would the baseline run (in red) have it at a different RPM?

 

5th/6th ports are set to open at 3800 RPM. I was in the car during the pulls so I can't verify that they opened at that RPM, but that's what they were set to.

Also I didn't change the setpoint at all during any of these pulls, so why would the baseline run (in red) have it at a different RPM?

 

i have a feeling its something weird like header length or something.

however since you can, maybe you should try a run with the 6 port and vdi OFF and then try with them ON at a really low rpm, so its on at idle or something.

 

My first thought was the header as well, but if it was a resonance point it would be constant. It moved up 500 RPM.

I didn't make any changes to the VDI, 5/6 port engagement or secondary injector staging between the two curves I posted. All I was changing was fueling and timing.

It makes me think the VDI actuator or barrel was sticking. I did a run with the VDI engagement point moved down from 5,250 RPM to 4,500 RPM to see what happened and the dip got worse. For some stupid reason I didn't do the same test with the VDI engagement point moved up to 6,000 or something.

Your test is a good idea. I was running out of time on the dyno so I didn't do it. I'll schedule some more time in a few weeks and see what happens. Maybe I'll try a cone filter as well. My gut says the stock airbox is more than sufficient for a stock port motor breathing through cats, but I could be wrong.

 

Looks like the 6 ports are sticking. I did some logging of airflow and there's a dip that moves around between 4800 and 6000 RPM. gusfd3s gets the win.

I removed the actuators and the front aux port is sticky to move. Keep in mind this motor was completely rebuilt and cleaned of carbon and grime only 2500 miles ago.

I wired them open and re-logged airflow... no more variable dip in airflow.

I'm wondering if my air pump isn't putting out enough pressure as well. Ugh. Annoying problem.

 

Are you trying to keep this car quiet and stock, or make more then stock hp level?

I say the airbox is inadequate for the car even with stock exhaust and stock ecu.
You're tuning with an Rtek7 right? would you setup a log of the pressure sensor, and place it at different vacuum sources down the intake path and to the air filter.

i wonder an alternate way of opening them has much effect. there always seems to be a bit of a dip on the 6port 13bs.

 

I say you're right. I did a couple logs with no airbox (no filter... eek) and saw more airflow across the board.

Again I'm sort of concerned the air pump (with 180,000 miles) may just not be up to the task anymore. Need to run some tests on it. Unfortunately I need to keep the stock airpump for my racing class.

 

And to answer your question, I want to make as much power as possible. I have an RTek2.1 in the car. Have to keep the cats and the AFM.

 

if you don't have to keep the stock airbox, 3inch full intake into fender mounted cone filter, and ducting from were the stock fog light is. i've had this on an s5
n/a that felt like an s4 turbo. best Intake mod i've personally done. you could even use the factory hose to the afm from the manifold, just replace from to the filter.

is your exhaust as unrestrictive as your class will allow?

As for the 5th/6th(aux) ports. i've been wanting try out a cable driven mechanical device to turn them open after about 1/2 throttle. you could possibly use parts of a space throttle body.

 

No way to legally run the intake tube like you're suggesting. I can't remove the washer bottle, so that hole is a no-go. I don't have a battery on the driver's side, so I could run a long tube over the radiator shroud and to the passenger's side fender hole, but I think it's only 2" or maybe 2.5" in diameter. I'm considering that route, though.

The exhaust is a stepped header to two 3" cats to 3" piping all the way back.

Actuating the aux ports in a non-stock way would not be legal.

 

story of my life! last time it took 3 hours to strap the car down and figure out we didn't have the cable to tune the ecu!

 

what about using the other washer bottle( the bottle for the headlight washer equipt. ) for the windsheild wipers to free up the space for an airfilter?

 

I can't legally relocate the washer bottle.

 

it's not exactly relocating, there are two factory washer bottle in the front. one for the windsheild one for the headlight washers..
i assume you're not using a 10th AE so you don't have washers for the headlights.. but you could put the FACTORY washbottle in The factory location for the headlight washer. technically it could be illegal because you'll be route the lines for the stock box to another location, but it would still be all stock?

how would they know the difference?

 

I posted this in the 2nd gen section, but just to close the loop on this thread, I'm posting the Cliff notes here.

I logged airflow (as measured by the stock AFM) using the RTek that I run as my ECU. I noticed a big dip in airflow centered around where I saw the dip in torque on the dyno.

Thinking this had to do with the VDI or aux ports, I ran a bunch of tests by manually wiring both systems open and closed and wasn't able to correllate the aux ports or VDI operation to the dip in torque. This led me to believe it was some sort of disagreement between my header primary length or an intake tuning phenomenon.

I removed the factory air box and ran the AFM open-air (no filter) and saw an improvement in airflow. To take it a step further, I installed a custom aluminum, 3.5" intake tube from the AFM to the throttle body, with a large cone filter on the end. Summary is that I was able to smooth out the dip significantly by eliminating the airbox, and improve things more by swapping out the stock rubber intake tube with the smooth-bore, larger diameter piece.

Hopefully I can get back to the dyno and verify that this translates to an increase in power.

In the airflow vs. RPM plot below, yellow is stock configuration (as the car ran on the dyno), blue is with the airbox and filter removed, and maroon is the new configuration with the cone filter and high-flow intake tube.

 

interesting how rough the blue line is....

 

Agreed. The inside of the factory air box has a crude air horn where the AFM attaches. Without the air box, the flow of air entering the AFM is probably not laminar. Additionally, the AFM wasn't terribly well secured for my quick test runs and the spring inside is very soft. So there was probably some vibration put onto that measurement.

With the AFM well mounted and the cone filter / high flow tube attached, it smoothed out greatly (red curve).

 

yeah i see, i think this is a good thing. its interesting that the red trace outflows the stocker ALL the time.

i take it you're allowed to have an intake?

 

Intake from the "engine inlet" (AKA throttle body inlet) and back (away from the engine) is free, with the restriction that factory sensors must remain in place, i.e. stock air flow meter.

I was shocked to see that red curve also. Never would have guessed that with a stock port motor the factory bellows tube is a restriction.

 

yeah its like 4"!

 

It's actually less than 3!

 

You ever heard of the Variable Fresh Air Duct on the Rx-8? It changes the length of the intake pipe using a vacuum actuator. It's pretty sweet. It's also one of the reasons why putting an intake on an Rx-8 basically gets you no power.

 

interesting.... having seen some flow numbers for various stock bits over the years, it almost seems like the 12A carb outflows the later EFI intakes....