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Low end vs Top end Hrspwr (back pressure) autocross-RS*R
I have some questions:
From what i know, the dc header primary tubes are similar in size to the oem header except that they have smoother bends.
Why do most people opt for the larger diameter header as opposed to the smaller diameter piping of say a DC header? Is it because they are trying to increase top end horsepower? Gaining a few hp in the top end doesn't really make sense considering the capability of our d17s. Thus, I would think that our little d17 Civics should be modified more simply and more emphasis should be placed on the suspension aspects. Wouldn't it be better to be have more low end torque if our cars are autocrossing and spending most of the time in first and second gears?
So, then on to my question....
I have a HP racing header and "high flow" cat with an RS*R ex mag cat back. My low end torque is pitiful and i want to change that. I have come to the realization that our cars are slow and that adding top end hp by increasing the pipe diameter is pointless unless i boost which i don't want to do.
So, considering the exhaust i currently have, how can i increase torque? Could i replace the "see-through" high-flow cat with a cat that is more restrictive?
Or replace the header with a dc header that has smaller piping that could increase back pressure?
Lastly, in theory, let's say that I did either of the changes listed above and kept the RS*R (which i plan to do), do you think that there will be a significant increase in back pressure despite the size of the RS*R pipe from the highflow cat?
Thanks for your help, I'm not sure what to do.
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Adding low end is not easy. You really can't do much with just bolt ons. You need to open the motor up and change things like the cam profile to really make a difference. The 1 or 2 HP difference and its assocated change in torque doesn't matter. Just build the car so you don't have to slow down.
Adding low end is not easy. You really can't do much with just bolt ons. You need to open the motor up and change things like the cam profile to really make a difference. The 1 or 2 HP difference and its assocated change in torque doesn't matter. Just build the car so you don't have to slow down.
Ok, but is it not true that by relieving back pressure in order to gain top end hp our motors lose some torque?
And, from what you're saying, i can conclude that replacing my header or cat won't make a significant difference in torque or hp, correct?
I plan on getting smaller rims and stickies for the track sometime in the future. The smaller tires and wheels would help all around but i like the 'bling' when daily driving.
You pull back pressure, you will lose some low end. But the amount we're talking about here is probably not enough that you're even going to notice it. Its really just not worth throwing parts around left and right until you gain 3 HP. Its more money than its worth. Changing the cat didn't cause you to lose so much power you don't have any low end anymore. Larger header runners done right should probably have helped, but I'm sure they're not done right. The exhaust... well, you won't do better than the RSR as far as a street exhaust for midrange unless you use smaller piping. But honestly, I wouldn't worry about it. Keep your foot on the gas, keep the revs up and drive with both feet.
to answer your question about top end vs low end, not everyone mods their cars for racing. some people just want better performance from their daily driver. if you mod for low end, you might end up w/ a very jumpy car at the start, which isnt very fun in traffic or anything like that. but adding high end hp helps with passing on the highway or accelerating at the on-ramp faster.
Autocross: Because Life is more fun on three wheels......
"I know Solo only comes one minute at a time, but what an intense, non-stop, fast-forward car control exercise minute it is. Sure, the velocity is higher in road racing, but inside the car it is slow-motion in comparison. In Solo, the turns come like machine-gun rounds. "
Randy Pobst
to answer your question about top end vs low end, not everyone mods their cars for racing. some people just want better performance from their daily driver. if you mod for low end, you might end up w/ a very jumpy car at the start, which isnt very fun in traffic or anything like that. but adding high end hp helps with passing on the highway or accelerating at the on-ramp faster.
not everyone does auto-x.
PS - also, get lighter wheels. LOL
I'm not sure how you answered my question. I realize that most people don't mod their cars for racing. I, however, am trying to find a balance that will consolidate both aspects of moding for street and track. I have to consider a number of variables such as daily driving comfort vs performance and cost per mod. Switching out internals and such isn't cost effective for the engines we have.
My question really stemmed from the fact that I had thought that my car had better acceleration and lower end power before i switched to a full cat back. My low end was good when i only added the hp race header and cat while keeping the resonator and having a magnaflow muffler.
Unless i get smaller piping from the cat i feel that i won't get there, but this is why i had posted looking for other options such as a smaller header tubes or by creating more back pressure.
The wheels are daily driven, i need to change them if i want to increase the accel at the track, that's a given, i know. thanks.
Most people dont know what that means.... and it also explanes your brake issues....
It doesn't explain my brake issues..... there was only 1 corner out of 14 where you could LFB. The rest of them are pretty much "Oh shit! There's a corner, I better hit the brakes!". 90 to 50 as fast as you can is not nice to brakes.
If you want your low end back, throw the OEM parts back on. Its that simple. You sound just like me two years ago. Now I can hear myself think and the car can get out of its own way in city driving.
i have i/e/h/downpipe i took out header and cat boyyy the revs take longer to go up but low end got much much better. id rather keep it other way because i always rev high
im going turbo real soon so the bolt-ons will be off
90 to 50 as fast as you can is not nice to brakes.
acctualy its better than a slow steady brake, 1 hard shot, then take your foot off the brake, that way if it overheats it can cool down faster and doesnt warp the disc. just thought id add that in
Low end vs Top end Hrspwr (back pressure) autocross-RS*R 
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