hey all... I posted a message a while ago about help on a starting problem. then i figured out the search system. derr. . sorry about that. anyways, got an 89 crx si, all stock.. that i bought for cheap and am turning into strictly an off-road modified-class SCCA solo car. I'm looking for ideas on an exhaust system. emphasis on cheapness and performance... surely i can come up with something inexpensive and powerful if i don't give a crap about cats and emissions and such... ? i was thinking some mandrel bent 2" pipe coming back to a glass pack or something, exiting on the side. but then again i'm not a normal honda owner... haha. anyways, ANY thoughts?? i have no idea what type of back pressure i need to maintain in order to actually have a performance increase. thanks!

jon

 

yeah u need that back pressaure for low end on that stock motor.

 

right. i'm definitely going for low-end power here... its been my experience with racing other cars in these events that i don't often get out of 2nd gear. building the car for this is really a challenge... it seems most parts are oriented towards that high end...

 

Get a nice 4-2-1 header, go straight out of the header to a straight pipe with a short glass pack on it. Have about 4 inches of piping coming out of the glass pack with a bend to position the exit of the exhaust gasses down. I would draw a pic if this PC had paint on it

You want as little bends as possible, but you want to have the right size piping, I am not sure if you should go with 2 or 2 1/4.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by EF8VTEC &raquo;</TD></TR><TR><TD CLASS="quote">yeah u need that back pressaure for low end on that stock motor. </TD></TR></TABLE>

Backpressure makes little difference, exhaust velocity is the important part. The idea that backpressure creates the low end torque is a myth. Think of it this way, in a 3" exhaust on a stock motor, there is going to be more space per length of tube than there is in a 2" tube, therefore more exhaust is allowed to sit and not be pushed out, also the same reason that on a full race system a large side exit tube would be best - because the exhaust is not allowed to sit in the tube for any period of time.

See - https://honda-tech.com/zerothread?id=409404

My best suggestion on an exhaust for you would be a ceramic/heat tape coated (optional but the WRC cars use it) short exhaust with a side exit on the front bumper and an aluminum skid plate under the front bumper, both for aerodynamics and to protect the exhaust. This wouldn't be too cheap but you could have it custom built into the header to make it one piece, just make sure it is braced properly.

 

Open header. Get it ceramic coated and heatwrap to increase temp. to incrase velocity of the gases...

Blaze

 

so, some pretty good stuff here... i'm actually a mechanical engineering student, fresh out of fluid mechanics and internal combustion engines, haha... so i'm familiar with velocity being the key here. I also understand all the simple losses in velocity of an exhaust gas travelling through a pipe system (welds, surfaces, bends, etc). keeping in mind that this is a budget minded car, and there won't be any expensive mods to the stock D16 motor, does anybody have any experience with the correct size tubing to go with here? I here a consensus on spending the money for a nice 4-2-1 header... 2inch pipe afterwards? 2.25in?

tanx, jon

 

Here is one option. I had a 2.5" exhaust made for my CRX. Used a 2.5" Dynomax resonator, mandrel bent piping and a turndown just before the passanget LCA. Only cost $80 at a local shop.

 

mmm that looks pretty nice. you've got the idea with only 80 bucks... haha. any noticable effects?

 

Yes, very big difference in power. I had the stock pee-shooter exhaust on before and like you can guess, it was restricting some power. I never dynoed the car before this exhaust, but with it on and few other mods, it made 121whp/113wtq on a couple baseline runs. My car is prepped for SCCA/WCHC competition and there are few thoughts on what diameter exhaust to run. Most people I have spoken with that have cars like mine run between 2-2.5" exhausts. Some of them feel that with the 2" they get the correct amount of back pressure for the motor setup they have, while alot feel that a 2.5" straight pipe all the way back works the best. Either way, you will see a big difference in the power of the car. And remember that some tracks in your area may have sound restrictions, so you have to take that into account as well. My setup, according to others who have had the same setup tested should be in the low 90db range.