Hypathetical Exhaust question (purely out of curiousity)

[PHam92]

I know that too much back pressure is a bad thing, and too little is also bad. And I know each car has that magical balance between the two. So my hypethetical (spelling) question is how much back pressure is needed in the svx. For example (and I am never going to do this) if you were to run straing pipes from the cat, too little back pressure? Or is the svx relatively unafected? I know, its a strange question, but for some reason i like to know things like this. It also seems the popular pipe diameter is 2.5 for this car, was this arrived apon after trial and error or is it all that fits or just what is normally used?

(I am glad to see no 4" exhausts with garbage cans for tips, I get enough of those with the civics, del sols, etc.)

Thanks
Paul Hampton
92 svx LS-L 106k

[cocacola08]

As much as the computer seems to control everything, I'd think that running straight pipes might be too little back pressure, MAYBE the cat might cause enough but I have no idea

Any thoughts Eddy, or anyone else?

[nvrmore100]

Are we talking straight pipes with no muffler? If so that would definately cause too little pressure. However, it is all dependant on the size of your pipes. 2.5" seems a little large to me, however this is a fairly large displacement engine as well. I guess I'm just use to 4 bangers. I personally would go with a 2 1/4", with a somewhat restrictive muffler (not completely straight through). This will give the high end power you want, without taking out the low end torque at the same time.

Ryan

[eddycat2000]

Originally posted by cocacola08

Any thoughts Eddy, or anyone else?

Wrong person to ask Coke. I don't believe in screwing with perfection. I'm a purist all the way. Take a good long look at the mod mania thread and all the headaches those guys go through when lowering or modifying this or that...it ain't worth the trouble, the car was built as a touring coupe, not a drag racer. That's why I don't generally post in mod mania...it's people that have way too much money, or way too much time, that are trying to make a racer out of a heavy, comfortable cruising car. It can be done, but one fella is just about ready to sell his because of his modifications, not me my friend, it's all stock, up to and including rotors, plugs, switches, and anything else anyone has tried to mod.

If ya ever need to know how I fix a Subaru problem though, I'd be tickled to answer yer question!:D

[svxter]

Originally posted by nvrmore100
Are we talking straight pipes with no muffler? If so that would definately cause too little pressure. However, it is all dependant on the size of your pipes. 2.5" seems a little large to me, however this is a fairly large displacement engine as well. I guess I'm just use to 4 bangers. I personally would go with a 2 1/4", with a somewhat restrictive muffler (not completely straight through). This will give the high end power you want, without taking out the low end torque at the same time.

Ryan

I'm fairly confident that the diameter is 2 1/4 inches.

[cocacola08]

Originally posted by eddycat2000

If ya ever need to know how I fix a Subaru problem though, I'd be tickled to answer yer question!:D

I knew you don't do mods, but I thought maybe you'd be able to answer the tech side of that question. My fault.. I sorry:o

[oab_au]

The only engine that needs back pressure is a two stroke fitted with an expansion chamber.
No modern four stroke needs or uses back pressure. Defined as a residual positive pressure in the engine pipe. The only positive pressure used, is sound or pressure waves that are produced in a resonate tuned length system that most modern designs use. The SVX uses a resonate system without back pressure.
Before you all light up the flame sticks, a quite exhaust does not always mean backpressure, it can also show that the sound energy has been fully used up in producing power, the rest is fully expanded in the huge rear muffler.
I don't know where the idea of an engine needing back pressure started, but its all crap.
Hope this helps.
Harvey. :)

[Chris]

Originally posted by eddycat2000


the car was built as a touring coupe, not a drag racer. That's why I don't generally post in mod mania...it's people that have way too much money, or way too much time, that are trying to make a racer out of a heavy, comfortable cruising car. It can be done,

Just on a side note: This is my second straight year racing my car at Firebird Raceway. I have won a 1st place trophy, I enjoy doing so, I dont think I have damaged the car in any way (hope hope hope), and other than a drop in K&N, I am bone stock! 150K miles and still pulling strong. Honestly, as much as I want to mod the car, it takes me where I need to go, when I need to, and still runs the 1/4 mile VERY consistantly. I am afraid that if I do mod the car I will have nothing but two years of beta testing the bugs out of it. :)

I know its not designed as a racer, but I have fun at the track with it anyways! Nothing like watching that 13 second Mustang getting loaded back in the trailer after going first round with me. Also nothing quite like wathing the anger build in the eyes of some ricer 13 second Civic that just broke out trying to bracket race my 16 second SVX. I have fun!

Chris

[cdigerlando]

I would like to point out that after I had all of that tranny work done, the SVX turned over on the first try. Couldn't help but get wheel, even though I was not trying. Although are mods have bugs, most of them are being very easily worked out, and the SVX is responding well. I love my flat 6!

As for the suspension, it is uncomfortable, but the car pulls Gs like crazy.

The reason I am modding the SVX is I think the engine has the most bang for the buck than any commercially available. The only engine that I thing is engineered better is the 3.6 911 ruf.

Although I have done the turbo, I would love to see how an NA project turns out. I doubt it would be dissapointing. Should not even need to get into the bottom end.

[cocacola08]

Originally posted by oab_au
The only engine that needs back pressure is a two stroke fitted with an expansion chamber.
No modern four stroke needs or uses back pressure. Defined as a residual positive pressure in the engine pipe. The only positive pressure used, is sound or pressure waves that are produced in a resonate tuned length system that most modern designs use. The SVX uses a resonate system without back pressure.
Before you all light up the flame sticks, a quite exhaust does not always mean backpressure, it can also show that the sound energy has been fully used up in producing power, the rest is fully expanded in the huge rear muffler.
I don't know where the idea of an engine needing back pressure started, but its all crap.
Hope this helps.
Harvey. :)

Well now don't I feel dumb.....again.:(

[newsvx]

Thought I would add my two cents, if I may.

I normally am not a person that modifies for the sake of modifying. I figure auto manufacturing engineers a lot smarter than me worked the details out better than I ever could on my own (I'm not an engineer, but I enjoy tinkering). But of course, they compromise ride for handling and the like. The SVX is truly a touring automobile, and a damn fine one at that. Weight partly makes it so, but that same weight hampers performance - there's that compromise again. While the SVX is not "slow", it certainly could never be called "fast". I would love to have another 100 HP - even 50 more would be welcome! And it is extremely quiet - another excellent touring attribute.

Now, what have I modified on two "family SVX's (a FWD '94 L and a '97 Lsi). I have a K&N filters - not that it provides a performance increase, but because it is a better filter. Removed the very heavy rear muffler (I bet it weighs 50 lbs) and added a small muffler just after the resonator. On the '94 FWD, a Borla one inlet and two outlets small muffler with pipes to the original exhaust tips. Whereas the original muff;er is ultra quiet, this set up has a robust (but not loud) sound to it. On the '97 with the AWD there was no room just after the resonator for a Borla like muffler, so we put a "Bullet Turbo" (sort of like the old glass packs from the old day, except one can't see all the way through because of the baffles). Then 2 1/4 pipes with new tips to the back from a "Y" fitting behind the Bullet muffler. Now this is significantly louder that the '94, but not overly so. At low RPM (below 4K) it is very throaty, actually getting quieter as the RPM's go up. As you have probably guessed, I like to hear my cars running. That's all the mods done to the cars, and I suspect all that will be done.

As for racing, the SVX is, I think, very under rated. We don't drag race the car, we autocross and put it on tracks like Summit Point, West Virginia (a great 2 mile course with 10 turns). At Summit, the SVX handles really quite well, bone stock, and with a good run out of Turn 10, it will make 115 - 120 MPH at the end of the 1/2 mile straight before having to brake (wonderful brakes!) to about 50 MPH for the Turn 1 hairpin turn. This a fun car! As for autocross, my two sons and I (my oldest drove my '97 with me) took 1,2,3 in G stock at this past Sunday's autocross. My oldest beat me by 4/10 of a second and I beat my youngest by only 3/10 of a second. We run racing tires too - the Kumho, Victoracer V700. Fortunately, the WRX's were on street tires, otherwise they would have kicked our butts -very fast cars, and this year run SCCA G Stock. SCCA wised up and next year the WRX will be in F Stock with the Firebirds and Mustangs where they will kick THEIR butts!

I apologize for the length of this, but the SVX is just so much fun. And its capabilities FAR exceed my abilities behind the wheel!
Harry
newsvx

[cdigerlando]

Hey Harry

Good to hear from you again. I hope that all is well with you and your family. Your exhaust modifications sound really well thought out. Have not got out to the track yet but I am hoping to in Late Fall. Still have a few things to finish.

Chuck

[newsvx]

hey, Chuck.

I see your postings from time to time. But I find I have less time available to check the web site, etc. It's terrible to HAVE to work, isn't it. Give me until 2003, and I'll be retiring - the second time!

Yep, kinda learned on the '94 SVX FWD with the Borla. It's actually a lot quieter than I would have expected. I tried the '97 with NO muffler - just straight pipes from the resonator - and it sounded great! Except one would be deaf after 300 mile or less. It would have been hard to take for long periods of time. The Bullet Turbo muffler tones it about right. It feels stronger too, but I suspect it is mostly in my mind.

Good to hear from you. Get your SVX to the track. You'll enjoy it. Interestingly, my oldest son (you know, the one that had to beat his old man at autocross - in my own car!) made an interesting comment. He said,"You know that car HANDLES very well. He has been driving a '96 Firebird Formula since it was new and has instructed at Summitt Point at Club events and at autocross. Now that bird is a fast car - about 140 MPH at the end of the 1/2 mile straight at Summitt. And itself handles really well, especially for a rear drive car. We might convert the boy yet!

Keep'm rolling, Chuck, and keep the shinny side UP!

Harry
newsvx