OK, I have seen quite a few dyno charts here where people have ran open header vs. with an exhaust, etc. The dyno charts have clearly shown gains running open header.

I know alot of people are running 2 1/2 piping or close to that. My question is, who is running 3" diameter piping? Wouldn't bigger definately be better? Seeing that the ability to breathe better with no exhaust has given gains, wouldn't 3" piping give gains over 2 1/2"?

I have heard of a few NA guys running 3" Thermal exhaust systems. Does anyone have any dyno comparisons on this? Or some insight on the truth of whether or not bigger is better?

Thanks,
Miguel

 

I know bigger diameter is better for your top end power but you might loose torque. A lil of back pressure is good to keep the torque up.
There is an optimal exhaust diameter for our NA engines, being moded, looks like it is around 2.5" for better results. Torque is important too. If you only care about top hp, I guess it is ok to run 3" in a highly moded engine.

 

I used to think the same thing about "needing" back pressure and losing torque but, from what I have seen on dyno charts, it seems that is a myth. There have been some recent charts here showing only gains in both torque and HP throughout the whole graph when running open header. This is what brings me to the question at hand.

Anyone have those dyno charts?

I'm gonna search for em..

Thanks for the input.

Miguel

 

Well, I guess that noise control also comes to play.
Anyway, if you're a hardcore hp fan, who cares about noise?(read: not street applied).

 

the search function using an archive section option is your friend...it has been covered already....

3 in. is too big for N/A according to most people and yet Tony the Tiger runs it just fine on his little wagon. The consensus though is 2.5 in. i the way to go. Even Jeff in that old "is 3 in. too big?" thread stated that a crush bent 2.5 in. is good...well at least better than your standard 60mm exhaust everyone sells.

 

Many Japanese full race exhaust systems go with 2.25" and under ID. The Amuse R1 for example is 50mm, which is roughly 2", although the R1 is pretty much a straight pipe design.

There remains a lot to be said for the actual exhaust flow characteristics of an exhaust, not just it's diameter. Personally, driving cars that have switched to and from 2-2.25" and 2.5" exhausts, I do find that the smaller ID are smoother and more responsive. On the other hand, the larger ID does provide better high end (obviously). When we dyno'ed the car with the Spoon shortblock, the car was running a 50mm exhaust and the dyno results would indicate that the smaller ID wasn't holding back the engine. (larger ID proponents will suggest a 2.5" exhaust would have netted a bit more power though, but at what effect on the rest of the powerband? only testing will tell!)

 

I did search... Didn't find what I wanted so I posted. Problem with that? Too bad. I can't stand the whiney "do a search people". If you haven't already noticed the search function here at H-T is less than acurate if it even works at all. Also, I am not asking if 2 1/2" is good, I am asking if 3" performs better.

BTW: 90% of what is on this site has already been covered.

Miguel

 

Thanks for the info Spikey

Miguel

 

 

Why not slap on a T1 exhaust on there and see if it makes any additional power. I'm sure there's on in the AJR shop ready for use.


[Modified by CPR, 9:51 PM 9/2/2002]

 

I think this is the part most people leave out when they compare tests of catbacks.. throttle response.... it is critical for roadracing and I think it seems that a not-too-big catback will offer more feedback and response without giving up too much power. Also there have been many people I trust that say there is no reason you will lose power with a 3" setup on a NA motor... I have 2.5" and it screams, feels great too, I am not going back to 2.25", so there

LOL