Air Filter size important on Turbo engine? Yes!
09-14-2013, 08:41 AM
#1
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Join Date: Dec 1999
Location: Upstate New York,USA
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Air Filter size important on Turbo engine? Yes!
Being between contracts (programmer) for the moment, I went out to address a situation with the air filter on my car.
Scenario: My latest hotside is tubular manifolds into a PT7675, 3” downpipe exiting to the passenger side of my 96 Z28, built by Jon(LT1boost.com). The configuration of my hotside leaves little room between the compressor housing and the frame rail. In haste to get it up and going, I got the shortest Spectre Air filter (4” to 5” installed?) and crammed it in there. Afterwards I got my 2 bar speed density tune AFR to mediate a 14.5 at both Idle and 75mph cruise.
Fast forward to yesterday when I decided (initially) to cast my own inlet tube using hardware cloth (essentially a sheet of wire mesh) and a fiberglass kit I bought at the local parts shop. I took an old Spectre air filter and cut off the filter portion, leaving only the metal base plate and its attendant rubber mounting flange. This would give me both the readymade seal onto the turbo compressor inlet and a flange to append the wire cloth. The intention was to cut a portion of the hardware cloth and shape it over the flange and trial fit it, modifying it until it would fit in the confines and be easily removed/installed. Afterwards, I would be able to mix my resin/catalyst and wrap the fiberglass cloth around the wire mesh to get the desired sealing and shape.
It was while I was under the front of the car, having removed the small Spectre filter and looking at the space available that I renewed my suspicion that my old ‘Cobra’ turbo inlet *might* fit in there and, with the proper 4” elbows/tubing, allow me to use my maxxy sized K&N airfilter. I fetched the cobra elbow and pushed it into place. After rotating it to a few angles and contemplating the consequential tubing routes, I settled on one that looked tight, but promising. I got out my array of 4” aluminum tubes/elbows (from Racepartsolutions.com) and my sawzall and, after some measuring, cut the tubes and mocked them up. Well, I’ll be. It all fits just fine and the filter is not in harm’s way. It actually gets some cool air too as it is in the passenger side front fender near the overflow bottle.
Since my last trip to the ¼” was disappointing in terms of MPH (126 whereas it had gone right near 130 with the old kit), I had been wondering where the performance loss might have been sourced. I found a couple of things suspicious. For one, the kit would get to 14 psi for a nanosecond, but then the wastegate (JGS) would open and the boost would stay at 12psi for the majority of the pass afterwards. Next, that tiny air filter. I had misgivings about its ability to pass enough air on a naturally aspirated 350, much less a 76mm turbo . I still have to work out what to do on the wastegate issues but here’s what I found immediately upon starting the car after the air filter change.
As mentioned above, my Speed density tunes AFR at idle and cruise with the small spectre was solid at 14.5 to 14.7. Now, with ONLY the filter change to the large K&N, the AFR was now 2 points higher (lean) across the board. Instead of Idle being 14.5, it was now 17.5. Cruise was the same, .. prior was 14.5 to 14.7, now 17.x to 18.x. Aha! That filter *had* been a restriction.
I got out my tuning software (Tunerpro) and set the injector constant down two notches, to richen up the fuel across the board, and took her for a test drive with datamaster. Hmm. Now it’s a tad rich, showing 13.x. I reset the injector constant back up by 1, load it and test drive. Perfect! Now if it will quit raining for a bit, I’ll take her out and see how she runs on a drag race style pass.
If you’re curious about the Cobra Turbo elbow inlet, I don’t know what to tell you. I found it online in 2007 or so and damned if I can find it anywhere. It’s perfect for tight confines where you need an immediate sharp 90 elbow. It’s made of a thick heavy rubber and has construction embedded in it so that it won’t collapse under high vacuum. I have a picture of it somewhere. I just have to find it. Now that the Elbow is on the car, I don’t want to have to pull it off just for a picture.
Scenario: My latest hotside is tubular manifolds into a PT7675, 3” downpipe exiting to the passenger side of my 96 Z28, built by Jon(LT1boost.com). The configuration of my hotside leaves little room between the compressor housing and the frame rail. In haste to get it up and going, I got the shortest Spectre Air filter (4” to 5” installed?) and crammed it in there. Afterwards I got my 2 bar speed density tune AFR to mediate a 14.5 at both Idle and 75mph cruise.
Fast forward to yesterday when I decided (initially) to cast my own inlet tube using hardware cloth (essentially a sheet of wire mesh) and a fiberglass kit I bought at the local parts shop. I took an old Spectre air filter and cut off the filter portion, leaving only the metal base plate and its attendant rubber mounting flange. This would give me both the readymade seal onto the turbo compressor inlet and a flange to append the wire cloth. The intention was to cut a portion of the hardware cloth and shape it over the flange and trial fit it, modifying it until it would fit in the confines and be easily removed/installed. Afterwards, I would be able to mix my resin/catalyst and wrap the fiberglass cloth around the wire mesh to get the desired sealing and shape.
It was while I was under the front of the car, having removed the small Spectre filter and looking at the space available that I renewed my suspicion that my old ‘Cobra’ turbo inlet *might* fit in there and, with the proper 4” elbows/tubing, allow me to use my maxxy sized K&N airfilter. I fetched the cobra elbow and pushed it into place. After rotating it to a few angles and contemplating the consequential tubing routes, I settled on one that looked tight, but promising. I got out my array of 4” aluminum tubes/elbows (from Racepartsolutions.com) and my sawzall and, after some measuring, cut the tubes and mocked them up. Well, I’ll be. It all fits just fine and the filter is not in harm’s way. It actually gets some cool air too as it is in the passenger side front fender near the overflow bottle.
Since my last trip to the ¼” was disappointing in terms of MPH (126 whereas it had gone right near 130 with the old kit), I had been wondering where the performance loss might have been sourced. I found a couple of things suspicious. For one, the kit would get to 14 psi for a nanosecond, but then the wastegate (JGS) would open and the boost would stay at 12psi for the majority of the pass afterwards. Next, that tiny air filter. I had misgivings about its ability to pass enough air on a naturally aspirated 350, much less a 76mm turbo . I still have to work out what to do on the wastegate issues but here’s what I found immediately upon starting the car after the air filter change.
As mentioned above, my Speed density tunes AFR at idle and cruise with the small spectre was solid at 14.5 to 14.7. Now, with ONLY the filter change to the large K&N, the AFR was now 2 points higher (lean) across the board. Instead of Idle being 14.5, it was now 17.5. Cruise was the same, .. prior was 14.5 to 14.7, now 17.x to 18.x. Aha! That filter *had* been a restriction.
I got out my tuning software (Tunerpro) and set the injector constant down two notches, to richen up the fuel across the board, and took her for a test drive with datamaster. Hmm. Now it’s a tad rich, showing 13.x. I reset the injector constant back up by 1, load it and test drive. Perfect! Now if it will quit raining for a bit, I’ll take her out and see how she runs on a drag race style pass.
If you’re curious about the Cobra Turbo elbow inlet, I don’t know what to tell you. I found it online in 2007 or so and damned if I can find it anywhere. It’s perfect for tight confines where you need an immediate sharp 90 elbow. It’s made of a thick heavy rubber and has construction embedded in it so that it won’t collapse under high vacuum. I have a picture of it somewhere. I just have to find it. Now that the Elbow is on the car, I don’t want to have to pull it off just for a picture.
09-14-2013, 10:19 PM
#2
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Join Date: Nov 2002
Location: Jacksonville
Posts: 4,784
Re: Air Filter size important on Turbo engine? Yes!
I had talked with Bob about using a Procharger truck inlet on my Vortech years ago but I never ended up going through with it. I was planning to cut it to fit with some couplers and other pipe but then I just had a local guy fab up a metal inlet tube.
ATI AIGI3I-015 Truck Inlet Hat
ATI AIGI3I-015 Truck Inlet Hat
11-13-2013, 06:12 PM
#3
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Join Date: Oct 2009
Location: Dallas, TX
Posts: 176
Re: Air Filter size important on Turbo engine? Yes!
Thanks for the info! I'm curious to see how much better it runs at the track. I have my setup apart right now, and an going to work on it this weekend if I don't head down to Austin for the F1 race. If I go by my shop, I'll snap picture of the Cobra elbow and post it. I bought it pet your recommendation for my Procharger,and it works great. It took some Googling, but I found it online. Cheers!
12-22-2013, 11:55 AM
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12-25-2013, 07:20 AM
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