Hi guys, I have a few questions if you don't mind. I'm a noob when it comes to exhausts and many of the members here seem more knowledgeable than asking some mechanics around.

I have a Top Speed Pro-1 Exhaust. Everything is stock down to the mid-pipe, so stock headers, cats, & y-pipe. So everything down to there is 2.5 inches or less. The mid-pipe that connects to the y-pipe is 3 inches and that branches off into two, still 3 inches, into the mufflers (cans), which are 4 inch at the tip. The silencers fit into the cans and blocks off most of the hole leaves a hole of 2 inches in diameter.

When I shift into 1st and 2nd, the car feels to be slow and it just doesn't feel like it wants to accelerate. The car also responds very slowly when I tape the throttle. It seems to accelerate slower in all gears, especially in the lower RPMs.

So, given the exhaust with the above description, do you think I've lost power? When I take the silencer out, it's loud as hell and it feels like my car isn't as fast. When the silencers are in, they kinda sorta feel a bit faster than when the silencers out. Would you guys mind explaining what exactly is going on?

Thanks,
Chris


P.S. I tried searching but I couldn't find anything and after a while the search feature died on me and keeps giving me page errors.

 

Loss of power where?

Any exhaust mod will alter the torque and horsepower curves. In other words you might drop 5 pounds of torque at 3,000rpm and pickup 5 pounds at redline. Add headers and the curves change. Add high flow catalytic converters or test pipes and the result will be different.

 

What's happening in my specific case is that my car feels like it's just not wanting to move as fast. It feels lazy in lower RPMs up to around 4K. From there, it sounds pretty damn good, but I still don't feel an increase in acceleration when compared to stock exhausts.

Could it be the 3" piping in the midpipe and to the 4" cans? What about the silencers? Do they usually cause loss in power or increase or neither?

 

exhausts, esp. 3'' on a stock engine, will make you loose a **** load of down-low tq and give you gains up top

hence why I did headers+hfcs - absolutely NO power loss anywhere in the band, gains everywhere and a kick-*** sound ^_^

 

Hmm.. so you're saying because I'm NA, I just lost a sh1tload(?!?!?!?!) of torque in the lower RPMs? The gains on top, are they more of tq gains or hp gains? Is it enough to overbalance the loss in the lower RPM range?

The fact that my new exhaust is causing my car to run slower is pissing me off. And I'm going to a drag strip this Friday. I was gonna try to improve my time, but it looks like I'm just gonna have to try to match my previous time. Gay...

I can't do headers nor the high flow cats, because my exhaust is loud as hell already.


Can anybody answer the silencer question? Does it cause more loss in power or increase and why? Is it better to leave them in (thus having 3" piping and 2" tips) or take them out (3" piping and 4" tips) for maximum performance?

 

Man, I'm in the same boat as you. I have Top Speed exhaust, 5/16" plemum spacer and AEM CAI. My best time ran at SA Raceway was 14.3 @ 98mph. I did run it on 19" aftermarket wheels....I hope that made a full second difference....lol. I really expected to be high 13's.

 

Like what davidv said, you just altered the hp and torque curves. What your experiencing is loss in low end torque, which is expected when going up in piping size. Even going to 2.5in. true dual will yield the same result,but if you are able to run pre and post dyno numbers, comparing stock to your current setup, it would be obvious that you lose hp and torque in the early rpms, but should gain alot of area in the higher rpms. Theres a bunch of thermal dynamics, and other techno-babble that explains this but that just the gist of things.

 

its called a loss of back pressure. the stock exhaust was made to flow through the 2.5 inch piping. now after the y-pipe, the exhaust gases are forced to go through the 3inch piping which means the gases are more free flowing meaning less back pressure. that is why you feel the sluggishness down low. but you should have gained some up top because of the increased amount of exhaust gases as rpm goes up. that is why when u do alot of breathing mods and ur A/F ratio gets thrown off, u need a good ecu tune to keep things intact.

do a few more mods and get a tune. then u will get a more consistent power curve and also get some of the low end grunt back

 

I remember reading somewhere that any CAI combined with a plenum spacer do not yield much gain due to an increase in turbulence in the manifold (something like that). Also theres many factors in your E.T. so i wouldn't hang on to the numbers just yet. Traction, temp, humidity, you yourself as a driver (not trying to imply improper driving techniques), increased rotational mass, our spastic ECU's, blah blah blah....

 

Wow, thanks guy. That helps a lot. I understand a bit more now. So is there a way to prevent this or am I stuck with low end sluggishness?

Also, does NOBODY know anything about using silencers (whether they increase or decrease power and what effects it has)?????

 

I don't think that the changes you've made should have resulted in a power loss so dramatic that you can feel it all the way across the RPM range in every gear! Even if this exhaust did cost you some power, it should only be 5-10 horsepower... barely enough to register on the butt-dyno.

I would check to make sure you haven't caused some other issue, O2 sensors or something like that. As others have said, you might have shifted your power band around a little, but it shouldn't cause a dramatic drop across the entire RPM range like you're describing!

-E

 

put it this way...anything that makes your exhaust quieter will result in more restriction, which in turn can result in a loss of power....thats why silencers suck.

 

-EL - I can definitely feel loss of power in 1st and 2nd in the lower RPMs. The other gears feel slower also, in the lower RPMs, but not as dramatic as 1st and 2nd.

zdrift78 - Yes, that's what I figured, but could you explain it in a more technical term and perhaps give reasoning behind as to why it results in even less power (other than just restriction)?

 

But he's seeing the opposite... better performance with the silencers IN than OUT. Also, while backpressure in general is bad, it doesn't always mean bigger exhaust=better. One thing that is important with exhaust is to maintain the velocity of the exhaust gasses to improve scavenging.

Here is a brief discussion on the subject:

http://www.miata.net/garage/KnowYourCar/S4_Back.html

-E

 

i agree -EL ...kinda weird how he says its faster with the silencers in.....strange....but like someone said above, i dont think it should have caused such a dramatic loss in power...i believe something else is at fault...

 

You might want to reset your ECU to feel the power again. Do a search on this "hope the search engine is working" and you might find something interesting. Good Luck

 

With the silencers out, it does feel slower in the lower RPMs than when the silencers are in. I haven't had the chance to stay in the higher RPMs much as my exhausts are very very loud. I'm going to a drag strip tomorrow to see how much of a difference my exhausts made on my car, with and without the silencers. If my best time tomorrow doesn't at least match the best time with stock exhausts, they're coming off.