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General Info on SR20DE Exhaust Systems

Written by Merlin Johnson

Between James and I we have tried other mufflers (Flowmaster, Walker Dynomax, a generic turbo) and they all suck. They are too loud, "drone" on the freeway and are just obnoxious, I drive 50-80 miles a day to work and he drives about 120 miles, so we couldn't stand the cheaper mufflers after a few months. When we went to the Stillen and Borla we both felt a very nice improvement in low end torque and upper end pull over the other mufflers.

Lately James took out the resonator, the car got a little louder, but he didn't really notice any improvement. He has since replaced the resonator with a 12" dynomax glass pack, it's as quiet as mine now, and isnt "blatty" when the system is cold.

(5/15/95) Speaking of bigger diameter pipes, since putting on the HotShot headers I am going to try and make the pipes 2 1/4" all the way back. The headers have changed the exhaust note and is slightly annoying to me. I will try and go with a 12" middle muffler and am thinking about a Sebring muffler as I heard they were quiet.

(6/1/95) I have had a chance to do some back to back comparisons with the Borla muffler and the prototype that HotShot Systems is putting together. Right now I am using the stock middle pipe with middle muffler, with the HSS muffler at 2" diameter with a 3" tip (which looks pretty cool). At first this system seemed pretty loud, but there was a leak at the connection between the muffler and the middle pipe. Even so on the drive home from HSS the setup felt great, good low end with lots of top (my car has JW ECU, JW POP,Exhaust,HSS Headers). Until I could find a gasket, I switched back to the Borla. I had the Borla back on for a few days, I lost the bottom I had felt and that nice surge at 5000rpm. I would think that the borla would flow more, but it has that stupid restrictor. I found a Nissan gasket and switched back...very cool, good bottom end, and the top came back. I am ditching the Borla. The HSS is finally letting the headers do their job of giving you more bottom end, which is what tri-y headers are supposed to do anyway. James drove my car with this setup and he liked it alot, he has a stage IV Stillen setup (stillen exhaust,stillen hi-flow,JW ECU,ported TB/MAF) and he definitely thinks my car has more pull on the top and bottom.


A few days ago Hotshot Systems fitted the prototype exhaust system onto my car....feels good. It is 2 1/4" all around, NOW the engine is breathing. The blatty resonance at 4k rpm went away, there is a little more noise or drone below 4k rpm, bottom end feels about the same. Top end from 5k up is great, it has built upon what was there before. Clark from JWT hooked up the Consult computer and he took air flow and other readings to compare against the last test. We have not had a chance to thoroughly compare the results but peak hp has moved is now a little under 6.7k rpm.

(12/27/95) I have finally had some extra time to go out and test exhausts some more. I got a back pressure gauge and did some measuring on various systems.

Cat=Catalytic Converter
No Cat=2.25" test pipe
2.25" mid=2.25" mandrel bent middle pipe with 14" glasspack
Stock=Original Equipment Nissan SE-R muffler at 1 7/8" diameter
2.25" ex=2.25" mandrel bent generic Turbo muffler with 3" rolled tip (I thought it was a Walker Dynomax, but it's not).
TLTM= To Low To Measure
FL=Fixed Leak
This test was done a 92 SE-R with Hotshot Headers, JWT Street Cams, JWT Intake, and JWT ECU with cam program.

Please take into account that I am giving general descriptions of how the car felt with different combinations. If it was strong enough to make a difference I commented on it. Also take into account that I am flowing more air than a mildly modded SR20DE, so I may be getting more back pressure than a car with a Stillen Exhaust/JWT ECU/Intake simply because I am sucking more air in to begin with. Just use your head, you should be able to see some trends here.

Cat/2.25" mid/Stock
Car very quiet, good bottom end, throttle response felt "blunt" at higher speeds, took longer to wind up.
Cat/2.25"/2.25" ex
Car louder, drone at 70 mph, no loss of bottom end as I had thought before, a little better throttle response although not much better than before.
Light Throttle 5th Gear 2 psi .5 to 1 psi
WOT 1st/2nd Gear 6.5 to 7 psi @ 7900 rpm 5 to 6 psi @ 7900 rpm
Prolonged 3rd/4th 8 psi @ 7900 rpm 8 psi @ 7900 rpm
No Cat/2.25" mid/Stock
I found out the system was leaking big time after the test. With the leak, the car was still loud, but not annoying like with the 2.25 turbo muffler. When I went back and fixed the leak things changed a little, it was very quiet at part throttle, but I still got a resonance or buzz at WOT around 4500rpm then went away. The car still feels peppier than before, throttle response not as "urgent" as with the bigger and much louder exhaust.
No Cat/2.25"/2.25" ex
The system was leaking a little. There was very good throttle response. Rpms wound up quickly, especially after 6800rpm. The car was loud, lots of drone, had a trumpet like resonance around 5k rpm, just a loud and obnoxious car in general. I am guessing I gained about 5-7 hp here, it make a big difference. This is not a car you would want to drive for any amount of time with this setup.
Light Throttle 5th Gear TLTM
FL=.5 to 1 psi
WOT 1st/2nd Gear 5 psi @ 7900 rpm
FL=6.5 psi @ 7900
4.5 @ 7900 rpm
WOT 3rd 3 psi @ 5500 rpm
FL=4.25 psi @ 5500 rpm
3 psi @ 5500 rpm
Prolonged 3rd/4th 5.75 psi @ 7900 rpm
FL=7.25 psi @ 7900 rpm
5.75 psi @ 7900 rpm
5th gear at 70 MPH WOT 1 psi  
No Cat/2" Trust/2" Trust
Louder than the OE muffler, much better sounding and quieter than the turbo style muffler. Least restrictive of all the systems tested so far. This system is quieter than the Cat/2.25" mid/2.25" ex setup I previously had and flows MUCH better. Good positive engagement of gears whether upshifting or downshifting, the car seems to "chomp at the bit" more.
OE Cat/2" Trust/2" Trust"
A bit quieter than before. I can feel no real loss at the top with the cat back in. Bottom end feels about the same. Leave your cat in.
Light Throttle 5th Gear TLTM TLTM
WOT 1st/2nd Gear 3.5 psi @ 7900 rpm 3.5 psi@7800 rpm
WOT 3rd 2 psi @ 5500 rpm Forgot to measure
Prolonged 3rd/4th 3.5 psi @ 7900 rpm 3.5-3.75psi@7900rpm
5th gear at 70 MPH WOT TLTM 1 psi

Of course removing the cat is illegal on the street and will produce a resonance at particular rpms, even with an otherwise completely stock exhaust system. With all the exhausts I have gone through I can probably pick out what someone has put on their SR20DE just by listening to the exhaust through the RPM band :)

The OE muffler is of excellent design, of course it produces back pressure to reduce noise, but only above where non cammed SR20DEs poop out, or after 6500rpm. With or without a cat the stock muffler is producing results close to the turbo muffler, but MUCH quieter. The OE muffler seems to start increasing back pressure at about 5500 rpm on up. Nissan did their homework in designing that muffler, the back pressure buildup corresponds very nicely with the stock engine performance characteristics. A stock SR20DE starts to choke after 6500rpm, the OE muffler ramps up 1 or 2 psi till about 6500rpm where it sharply increases to its maximum.

The OE cat is of good design and is huge for a 4 cyl, the inlet and outlet diameter is 2.5", with the inside growing to 3". Aftermarket cats might get to about 3", but you would have to have a 3" exhaust to make it work, which would lead to a very loud SR20DE, and I dot think you will gain that much. Either leave the stock one alone, or take it out for use on the track.

(4/24/96) Hmmm, I have done some more testing with the OE cat back in place with the Trust, I think I am incorrect about the BP increase. With only .25 more at WOT on prolonged runs the OE cat seems fine even with various mods like cams and headers.

Turbo style mufflers bite the big one, for the SR20DE you will gain nothing but noise by going to that type of muffler. You will only reduce back pressure about 1 psi way at the top and hold off gaining back pressure a little at the bottom in return for a shitty sounding exhaust.

I installed a Trust cat back 2" exhaust system on the car and gave it my run in with the BP gauge, it so far seems to be the less restrictive of systems I have tested. Noise is very acceptable, even without the cat. I am amazed, a livable, highly flowing system that doesn't sound gross. The design is a straight through type, with a mid muffler. The mid muffler has evenly spaced rings through the center with lots of holes, the tip is cut at an angle which I would suppose helps in tuning the sound. The back muffler itself is large and heavy, not sure what stuffing they are using. I will put the cat back on and test some more. It should be a very quiet system.

I am almost to a final suggestion for an exhaust system. Either a Trust or HKS (I need to get ahold of one for sure) or a 2" cat back, mandrel bent system with a Walker Dynomax Ultraflow or Sebring of some good size with at least a 14" or larger glasspack. I am not sure if there are other things available for that mid muffler, and I would be interested in getting ahold of some different types.