Stock spec v times - Page 5

ProZach626 · #61 10-06-2005, 04:07 PM

keep in mind I said extended cab, because I know a non extended cab can take a 350z

nismo_pilot · #62 10-06-2005, 06:04 PM

lol i was going to say, i thought the SS silverado was built to contend with the lightnings and srt-10 ram, didnt think there was any competition there..........i DID beat a srt-10 at the track once, my 9.85 to his 9.97........he didnt know how to drive though.....hahaha

ProZach626 · #63 10-07-2005, 03:27 PM

!!!!!!!! DAMN WTF WERE YOU DRIVING? But I think the SS silverado runs a lower 14 in the 1/4.

nismo_pilot · #64 10-08-2005, 10:41 AM

lol my bad zach, that was in the 1/8th mile here at jax raceway park, i was driving the spec of course

leolo007 · #65 10-10-2005, 10:49 AM

Quote:

Originally Posted by slideways...

i have yet to see any proof that backpressure is needed at all for power...

http://www.supertrapp.com/technology/index.asp

I had a friend who was very serious about atucrossing and used a supertrapp muffler to tune his car at a dyno. He didnt just use the muffler, but when he had the car tuned to his liking, he would get a few extra ponies here and there by tuning the muffler.

Rowens V-Spec · #66 10-10-2005, 12:36 PM

Quote:

Originally Posted by leolo007

http://www.supertrapp.com/technology/index.asp

I had a friend who was very serious about atucrossing and used a supertrapp muffler to tune his car at a dyno. He didnt just use the muffler, but when he had the car tuned to his liking, he would get a few extra ponies here and there by tuning the muffler.

I'm not sure i completely understand the concept of the backpressure in this case, and how it will cause you any gains? Can someone explain that to me?

leolo007 · #67 10-10-2005, 02:56 PM

Quote:

Originally Posted by Rowens V-Spec

I'm not sure i completely understand the concept of the backpressure in this case, and how it will cause you any gains? Can someone explain that to me?

Honestly I dont even understand very well myself, it is actually more complicated than I care to understand. But I believe its something like this. suppose you have a mass of air coming out a 2.5inch pipe. and the same mass of air coming out of a 3.5" pipe. For the same rate of air, there will be more volume on the 3.5" but more speed on the 2.5" pipe. And at low rpm you want the air to move quicker than at higher rpm.... I dont know exactly, the first part is true about volume and speed, thats simple physics. the other part... Im not even sure if that is true but so Ive heard. maybe you should do a search to see if you find something. a have seen different explanations and they all make some sort of sense. I guess its actually a mistery and people make up their own conclusions

I have heard other explanations like if you have ever run in one of those bikes at the gym that you can adjust friction. you can pedal pretty fast with the right amount of friction, two much friction and you get tired, not enough friction and it just doesnt feel like your doing your best. I DONT KNOW!!! WHY DO YOU MAKE ME THINK ABOUT THIS!?!?

Rowens V-Spec · #68 10-10-2005, 07:16 PM

At high or low rpm the flow size is the same, but the backpressure is created if the outlet size is too small, and at higher rpms is trying to force the air out. That creates back pressure. What i"m not sure about is why you want back pressure. I guess i'm not to understanding of the optimum exaust size all together. I'm in a physics based engineering program, and have done some physics labwork on some of the issues. Like with that tornado thing.

Someone explain the reason why you want the backpressure please!!

Chiquae07 · #69 10-10-2005, 08:03 PM

cuz the backpressure will 'press' you 'back' into the lead.....i guess that wasn't a good explaination

nismo_pilot · #70 10-10-2005, 08:07 PM

you want backpressure because it forces your NA engine to work, turbo cars want no backpressure because they get enough of it from the turbines and anymore would create lag, but a NA car wants backpressure because it will keep the exhaust speed constant, if it free flows then the exhaust speed will vary, causing a change in vaccum in the exhaust tubing which will cause power to fluctuate, it does this due to wave scavenging, which is where a vaccum in the exhaust tubing pulls the exhaust out of the cylinders on their exhaust stroke, this frees up some of the enigines energy to make power in the combustion chamber and not have to spend it expelling exhaust gasses. so there you have it, backpressure will not create a huge difference but as a previous poster mentioned, it will help tune a few extra ponies out of an NA car.

JerodKing · #71 10-11-2005, 12:30 AM

Quote:

Originally Posted by nismo_pilot

you want backpressure because it forces your NA engine to work, turbo cars want no backpressure because they get enough of it from the turbines and anymore would create lag, but a NA car wants backpressure because it will keep the exhaust speed constant, if it free flows then the exhaust speed will vary, causing a change in vaccum in the exhaust tubing which will cause power to fluctuate, it does this due to wave scavenging, which is where a vaccum in the exhaust tubing pulls the exhaust out of the cylinders on their exhaust stroke, this frees up some of the enigines energy to make power in the combustion chamber and not have to spend it expelling exhaust gasses. so there you have it, backpressure will not create a huge difference but as a previous poster mentioned, it will help tune a few extra ponies out of an NA car.

Actually backpressure is always a bad thing. What you want is exhaust velocity. If you go too large on the exhaust, you exhaust velocity suffers. I would go find the physics formula for all this stuff, but I am lazy, and unless anyone contests me, I will not spend the time. But at low RPMS you are putting out less exhaust, that is why if you go with the max recommended size exhaust (lets say 2.5 inch on a Spec-V) you gain HP at high RPMs where the velocity is at its max, but lose a little bit of low RPM power.

fugiot · #72 10-11-2005, 12:36 AM

Plus, exhaust systems with no backpressure sound TERRIBLE. Just think of all those 1.5 liter Civics with 3.5" tubing. The air is practically falling out of the car making a farting noise.

slideways... · #73 10-11-2005, 03:33 AM

Quote:

Originally Posted by fugiot

Plus, exhaust systems with no backpressure sound TERRIBLE. Just think of all those 1.5 liter Civics with 3.5" tubing. The air is practically falling out of the car making a farting noise.

ahahahhaha

my new sig

nismo_pilot · #74 10-11-2005, 08:32 AM

rofl holy shite, beat me to it slideways

Rowens V-Spec · #75 10-11-2005, 09:44 AM

Quote:

Originally Posted by JerodKing

Actually backpressure is always a bad thing. What you want is exhaust velocity. If you go too large on the exhaust, you exhaust velocity suffers. I would go find the physics formula for all this stuff, but I am lazy, and unless anyone contests me, I will not spend the time. But at low RPMS you are putting out less exhaust, that is why if you go with the max recommended size exhaust (lets say 2.5 inch on a Spec-V) you gain HP at high RPMs where the velocity is at its max, but lose a little bit of low RPM power.

So the optimum exaust tubing is dependent on where you want your power curve? Like a smaller tube for more low rpm power, and bigger for higher rpm curve. So midrange will optimize high and low end power?

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