Car Makes Less Boost and Power WITHOUT Air Filter (EFR9180)
 

Hi Guys,

I dyno'd my car last night for the first time and say some interesting results.
Ultimately, the car made 538whp at 25.5psi on a Dynopack dyno.
The car is an '88 TII with:

• Large street port 13BT
• 93oct and water injection.
• EFR9180 IWG w/ Turblown IWG manifold and Turbosmart dual-port actuator.
• Large water-to-air intercooler
• Megasquirt MS3X ECU
• 4" Downpipe, 60mm cutout, 3" Racing Beat dual exhaust

I was kind of hoping that the car would make more power than it did on 25psi so, with some free time left on the dyno, we decided to poke around and see if there was anything holding it back.


I have a large 5" inlet, 8" long air filter that looks like it should flow well, but we removed it to see if it'd make a difference.
Between the filter and turbo, there is a 60* aluminum 4" elbow and a 45* silicone coupler. For testing, I removed the coupler and filter only, leaving the elbow.

What we saw is that without the filter, the car made 4 PSI LESS boost and about 60hp less as well. All at the same boost control duty cycle.

We repeated this with and without twice and saw the same results.

Dyno sheet below. Purple is WHP, Yellow is WTQ, and Orange is PSI Boost






https://cimg2.ibsrv.net/gimg/www.rx7...079faf84b.jpeg


https://cimg7.ibsrv.net/gimg/www.rx7...62d1cfc122.jpg

Interesting. Perhaps the filter creates some sort of swirl turbulence that promotes flow.
BTW did you replace the filter and re-dyno to see if the power went back up?

Maybe its just because its drawing hotter air off the radiator? The only way to loose 4 psi would be because the air density is so much lower I would think. What were the AITs between each run with and without the air filter where the boost pressure is the same( up to 5k rpms it appears).

I have done this test on multiple cars, and its usually the opposite( like a 6rwhp gain over a very large filter above 20-25 psi).

Do you have the boost controller duty cycle lower in the low rpms? It looks like its only making 18.5 psi by 4k rpms? My FC with a large streetport makes 31psi here.

Have you tried running an open downpipe vs that WG bleed on your exhaust( I imagine a WG would not flow anywhere near the same as an exhaust cut out). For those not aware he is using a 60mm wastegate as an exhaust cut out on his downpipe.
That might help your top end. ( what was the difference between open and closed on that anyhow?)

Congrats on not popping the engine :)

I turned boost control off for both of those runs. Just the 14psi (lol) spring in the Turbosmart actuator. Funny enough, IATs were almost exactly the same. Without the filter, peak IATs were 90*F at redline. I only labeled the data log without the filter, so I'm not 100% sure which was the back-to-back with the filter, but IATs were within 5*F for sure.

One thing worth mentioning, I believe the airfilter has a plastic radius in the base that could be acting like a velocity stack or doing weird stuff with turbulence?

My other though was that maybe the bypass valve is doing something weird.

There is definitely a lot to be gained tuning the low end of the boost map. I still have boost come in a little slower since I haven't been able to get closed-loop tuned. My biggest issue is that if I get open loop to spool fast in the lower gears, I get surge in higher gears. No a huge deal, but I've actually had it surge with the cruise control set going up steep hills lol. Closed loop is high on my list of things to iron out.

Probably the shape of the inlet opening without the filter was killing flow.

On a turbo civic on the dyno we picked up 30hp on a ~200hp civic by putting my air filter/v-stack on the turbo instead of just the 3" tube that was on the turbo before.

30hp gain on a 200hp car from just changing the shape of the opening on the inlet pipe.

On my own FC we did a test with and without the air filter (but kept the velocity stack) and it made the same power either way, but 2psi less boost without the filter.

It was 3" dia 45 deg pipe to 3" to 6" velocity stack to 6" inlet 12" long filter.

But... on my friends ~100hp na civic there was no power difference no matter what we did to the intake inlet. Engine did not need more inlet flow, the restriction to flow was elsewhere.

Anyways, velocity stacks.... they work!

+1 i dynoed a 71 Mercedes 300SEL 3.5 once, and removing the air cleaner lost 3-4 hp. the air cleaner was just a typical V8 style, but it did have a nice inlet.

Even though I love the racing beat exhaust, I lost 20+ whp switching from an Apexi N1 that I thought was too loud. Exhaust restriction is probably also a factor.

I have this installed in the downpipe. The filter test was done with the cutout open. It's an ebay 60mm wastegate, but with it on, I picked up 60whp at 2psi more boost. Definitely contributed to boost creep, but all the high boost tuning was done with it open. Most I made with it shut was I think 460whp on 21psi. Definitely seems like the exhaust is a choke, but I didn't change the exhaust when i did the filter test...




https://cimg2.ibsrv.net/gimg/www.rx7...56c3f38774.jpg

There are multiple factors here.

The size and shape of the cone filter can act as a velocity stack to improve airflow. The bend in the inlet pipe is a source of restriction. Both can affect the tendency of the engine to compressor surge. The surge line on the compressor map is not generated on a firing engine with a realistic compressor inlet. They are done with burners shooting hot gas into the turbo. That's one of the reasons why compressor and turbine maps have their flaws. Besides the inlet shape, There's also the difference in compressor inlet temperatures that could result from having or not having the filter, as has already been pointed out.

The problem here is that you don't have a compressor speed sensor and you don't have a pressure sensor in the inlet pipe. If you are really curious, you need to install a 1 bar MAP sensor into the inlet pipe of the compressor and measure the pressure drop. That's the bare minimum to understand this.

Ideally you would compressor speed sensor, compressor inlet pressure, compressor outlet pressure (all 3 needed to compare to compressor map and have correct pressure ratio), and then backpressure measurement at the inlet (both scrolls) and outlet of the turbine. That is what I use to evaluate intake and exhaust design when I am working with an engine dyno.

how's the exhaust reducedfrom 4 inch to 3inch? is it at the flange or in the pipe?
Meaning the gas is not hitting a flat wall

It's a conical reducer. One on the turbo to go 3-4" and one at the midpipe around the shifter from 4-3".