Limited02
Explorer Addict
- Joined
- November 1, 2006
- Messages
- 3,568
- Reaction score
- 8
- City, State
- Gardner, KS
- Year, Model & Trim Level
- '02 Limited V8
I PM'd two people I knew of that tune A LOT of vehicles and have experience related to how exhaust size will affect power. The first response posted is a guy who tunes Mercede Benz and the likes. Second is a local tuner who turns out CRAZY work, check out the link. The word that's highlighted red was changed for content
I sent a link to both about this thread. Anyway, here is the question and the responses-
"Simple question. Is it possible to have to large and to free of flowing exhaust that will kill your lowend torque no matter how good of tune is done? I am referring from idle to 3000 rpm and the motor would be a 4.6 2V in an Explorer."
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#1
"Thanks for the kind words bro, we work hard and appreciate it!
Ok reading through the post, info posted in #19 was all correct.
Pretty much all info posted in #24 is INcorrect.
Here's the thing, I'm not sure if he's saying that in this particular case going larger with exhaust tubing (didn't see anything about header primary length/dia, or the collectors where 70-80% of all power is made from flange to tip) since the OEM manifolds/mids are somewhat restrictive (aka compensation)?
Anyway here's the rub. Yes you can very easily make an exhaust "too large". Choosing header primary dia, length, collector size, dia of mids, placement of X, etc etc all play important roles in maximizing gains from an aftermarket exhaust.
Case in point, going from a 1 7/8" primary to a 2" primary on a LS7 or even H/C LS7, you're going to lose 20-30 HP and TQ.
You do in fact need backpressure to make BOTH HP and TQ, why, because it increases velocity and again especially N/A velocity is KING. Modern higher static compression engines are no different. For example our C63 LTs have 1 7/8" primarys but the collector necks down to 2.25" (to build velocity), even though the full race catback is full 3" all the way back. M156s are 11.3:1, and yes I tried cutouts both on the dyno and the track (before we made our LTs just for the hell of it) with the OEM exhaust manifolds in place and the car lost a ****load of area under the curve--there was not a single data point that was higher.
Cutouts lose area under the curve (both HP and TQ) unless we're talking about a race motor with a very narrow powerband, a ****load of inches, and/or a superlight chassis. Usually it's all 3, and they run nitromethane--which negates this potential digression altogether.
Another example, about a year ago I was driving my Jeep otw to the gym and the rear section of my exhaust (Catless 1 7/8" LTs with full 3" system, so everything after the X pipe which is basically nearly straight tubing, resonators and mufflers/tips) literally detached from the X pipe (thankfully the hangers still held it in place). It was obviously audibly speaking immediately noticable however what really shocked me was how much of a pig it was at WOT even at 6000rpm+ (6.1 Hemi's have 10.4:1 static C/R. I TIG'd that stuff together about 20 minutes later.
If no one makes an upgraded exhaust for you, I would definitely (if you want max power/tq) remove all cats. The OEM system itself is restrictive enough to give you all the backpressure you need.
Hope that helps, the guy seems to have some exhaust knowledge but if what he were saying were true (yes engines are large airpumps, but they are complex air pumps) everyone would have an open intake manifold with 1" runners and 2-3" primarys. LOL.
TTYL "
MHP
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#2
There is such a thing as too big of exhaust. A naturally aspirated engine wants some back pressure in it. Its when you get into forced induction set ups that the engine doesn't need much back pressure at all. A 2v 4.6 doesn't need anything larger than 3" and most n/a 2v's will make great power through 2.5"
Jeremy from HOB
Buildup thread- http://www.svtperformance.com/forums/pics-videos-buffet-149/678085-hobs-1300hp-c6-z06.html
Video- http://houseofboost.com/z06_teaser/ Turn up the volume
CDW6212R- This is in NO WAY intended to slam you. I just wanted to make sure that that correct information is being posted in regards to exhaust size.
I sent a link to both about this thread. Anyway, here is the question and the responses-"Simple question. Is it possible to have to large and to free of flowing exhaust that will kill your lowend torque no matter how good of tune is done? I am referring from idle to 3000 rpm and the motor would be a 4.6 2V in an Explorer."
--------------------------------------------------------------------------------
#1
"Thanks for the kind words bro, we work hard and appreciate it!
Ok reading through the post, info posted in #19 was all correct.
Pretty much all info posted in #24 is INcorrect.
Here's the thing, I'm not sure if he's saying that in this particular case going larger with exhaust tubing (didn't see anything about header primary length/dia, or the collectors where 70-80% of all power is made from flange to tip) since the OEM manifolds/mids are somewhat restrictive (aka compensation)?
Anyway here's the rub. Yes you can very easily make an exhaust "too large". Choosing header primary dia, length, collector size, dia of mids, placement of X, etc etc all play important roles in maximizing gains from an aftermarket exhaust.
Case in point, going from a 1 7/8" primary to a 2" primary on a LS7 or even H/C LS7, you're going to lose 20-30 HP and TQ.
You do in fact need backpressure to make BOTH HP and TQ, why, because it increases velocity and again especially N/A velocity is KING. Modern higher static compression engines are no different. For example our C63 LTs have 1 7/8" primarys but the collector necks down to 2.25" (to build velocity), even though the full race catback is full 3" all the way back. M156s are 11.3:1, and yes I tried cutouts both on the dyno and the track (before we made our LTs just for the hell of it) with the OEM exhaust manifolds in place and the car lost a ****load of area under the curve--there was not a single data point that was higher.
Cutouts lose area under the curve (both HP and TQ) unless we're talking about a race motor with a very narrow powerband, a ****load of inches, and/or a superlight chassis. Usually it's all 3, and they run nitromethane--which negates this potential digression altogether.
Another example, about a year ago I was driving my Jeep otw to the gym and the rear section of my exhaust (Catless 1 7/8" LTs with full 3" system, so everything after the X pipe which is basically nearly straight tubing, resonators and mufflers/tips) literally detached from the X pipe (thankfully the hangers still held it in place). It was obviously audibly speaking immediately noticable however what really shocked me was how much of a pig it was at WOT even at 6000rpm+ (6.1 Hemi's have 10.4:1 static C/R. I TIG'd that stuff together about 20 minutes later.
If no one makes an upgraded exhaust for you, I would definitely (if you want max power/tq) remove all cats. The OEM system itself is restrictive enough to give you all the backpressure you need.
Hope that helps, the guy seems to have some exhaust knowledge but if what he were saying were true (yes engines are large airpumps, but they are complex air pumps) everyone would have an open intake manifold with 1" runners and 2-3" primarys. LOL.
TTYL "
MHP
--------------------------------------------------------------------------------
#2
There is such a thing as too big of exhaust. A naturally aspirated engine wants some back pressure in it. Its when you get into forced induction set ups that the engine doesn't need much back pressure at all. A 2v 4.6 doesn't need anything larger than 3" and most n/a 2v's will make great power through 2.5"
Jeremy from HOB
Buildup thread- http://www.svtperformance.com/forums/pics-videos-buffet-149/678085-hobs-1300hp-c6-z06.html
Video- http://houseofboost.com/z06_teaser/ Turn up the volume
CDW6212R- This is in NO WAY intended to slam you. I just wanted to make sure that that correct information is being posted in regards to exhaust size.
that is the type of guy I like 
