Has anyone, had HP or TQ losses, that can be definately linked to an exhaust that is to large...

SO, here is an example... You had 300 rear wheel HP, with 425 FTlbs Of Tq, with 2 inch exhaust, then you went to 3 or 3 1/2 and you lost both.

I am looking for facts... Not I heard billybob down the corner, losta tun when he put them thar stacks on, and he has 1 million miles on her...LOL.

I would like input, for gas, but diesel will do, with engine mods linked to this.

I can say, I run as big of exhaust as I can fit..3 or 3 1/2 couple guys run 4 inch tubes behind a 302 or a 4.6, with only gains...

Lets hear it...

 

Ok, an exhaust system work on principles of induction. Exhaust like all gases, has mass. If it has mass, it also has inertia. Inertia is the principle where objects in motion tend to stay in motion. It exhaust is moving inside an enclosed tube in a pulse, it will act as a pressure wave. It will also leave a relative vacuum in its wake. This effect helps remove as much residual exhaust gas from the cylinders as possible. The more exhaust you get out of the cylinder, the more fuel and air mixture can enter the cylinder during the intake stroke.

The challenging thing is that these conditions are in constant change. The engine doesn't run at a constant RPM. At high RPM, larger volumes of gases will flow through the system, and if the tube is too small, it may resist the flow of gases through it. At low RPM, the exhaust moves slower, at if the pipe is too large, the exhaust may not have enough inertia to remove all the exhaust from the cylinder. Both conditions rob potential power, but the later is more destructive, because you spend at least 60% of your time under 2500 RPM under normal driving conditions.

This tradeoff has always existed and always will. The question you have to ask is what kind of driving will these vehicle be used for. If it is going to the track and doing quarter mile runs, you want to produce as much peak HP as possible, and it doesn't matter what part of the powerband that power is produced in. But if the truck is going to drive on the street, and tow, and do the common and heavy work, it must perform its best at low RPM.

Very often people feel the power gains at that higher RPM, and realize they gained power at the peak output. The deeper sound reinforces the effect. But if the gas mileage has dropped off, this is a sure indicator that the engine has lost efficiency at low RPMs.

The example you gave above is an extreme one. Going from 2" to 3" or larger is very extreme change. The 3" exhaust flows well over double the 2" pipe. If you did not at least double your power output, your pipe is way too large. After all, if you more that double the volume of airflow, the power should increase very dramatically right?

A 2 1/2 exhaust pipe will flow 521 cubic feet of air per minute. A 302 running at theoretically perfect conditions with 100% volumetric efficiency will only flow 480 cubic feet per minute @ 5500 RPM. So 2 1/2" is more than adequate. However, no engine runs at 100% volumetric efficiency. You are lucky to get even 90% under ideal conditions. So the real world draws down the actual airflow. Realistically, a highly modified 302 might get you a peak of 360 CFM. 2 1/4" pipe would work well for that.

Have you ever dyno tested any of your vehicles. Were other power inducing modifications performed at the same time as the exhaust upgrades? I'm not looking to say you are wrong, I would agree that a 2" single system would bog down a 302, anything larger will show an increase in power. But you don't need to go all the way to 3" or beyond. If I had a 302, I would run 2 1/2". Same with a 4.6L. On a 5.4L, I would find it hard to call between 2 1/2" and 3". On a 5.8L, 2 1/2" definitely. And with a V10 or 460, 3" definitely.

 

Are you talking about single or dual? Is a single 3" enough for a 460?

 

All of my info, is Dyno based.... or dragstrip based info... or truck pull... It is fact,

dual 3 inch exhaust for a 460 or any bigblock, is the minnimum,when it comes to performance.... Maybe 3 inch for a small block, but like I said, 3 1/2 or 4 for a big block for sure... Based on numbers, from either dyno, or real world tests/results. I try to put as big of pipe I can, when trying to get performance...or increas in performance.

I guess what I am trying to do, is lay the false info to rest, that small tubes are needed to build HP or TQ... It is very much the oposite...

That is why I am asking for fact...as stated in the opening article, I am trying to stay away from the guys that want to hang in a crowd, for the feeling of belonging, or what ever there purpose is...

 

Are you just talking about racing ??? Or some guy that has a 300 6cly they tow & haul with . Dual 3 1/2 exhaust on a 6 cly . Just want to know what your talking about ... Lew

 

I am talking about anybody wanting to upgrade ther exhaust, For what ever there reason may be... Low end tq??? whatever.

example:
The guy that bought a truck, the exhaust fell off, and put a new one, that may have been smaller, and noticed poor drivavbility, or went bigger, and noticed better drivability. Or the Pulling truck, or the street car/truck, or vise a versa...

This is a general question, and has been put out other places, with pretty much seeing the same input across the board...

 

Ok . The exhaust systems on a full race car & street driven car are going to be different . This is just my opinion from owning & working on 302 mustangs & trucks & talking with people at the mustang shops where i get parts . I am not a exhaust expert . On a street driven car opening up the exhaust is one of the best ways to increase performance IMO . Also on a street car or truck i dont go to big right off the headers to keep some scavenging efect , this will help TQ in the lower rpm where in a street car it helps with drivabilaty . On a full race car this isnt needed . So on a 302 mustang i think its good to keep the scavenging efect with no back pressure . Example .. 2 1-2 pipe off the headers to a X or H pipe (X pipe better for high rpm motors ) . After the X or H pipe step up to 3 in to the mufflers then go to 3 1/2 mufflers with turn downs . This is very similar to the exhaust i use on my 302HO truck & it works good for me . It being a truck (3800 # ) auto with stock 2000 stall converter i need to try to keep some good low end to help off the line . So this works good for my setup . But if your motor is set up for hi RPM & use a manule or auto with hi stall converter your exhaust my be differant.... Lew

 

I am hopeing for real world test results, not opinions on what wortks in an application...Thats all.

One of the biggest improvements in the over all performance of a SBF is letting it breath... Headers, intake exhaust. The one other item, that everyone forgets is that darn nuckle Ford put in the exhaust port, to meet emissions ect...

People also port an polish heads, open up runners, 3 angle valve grinds, blueprint. and use tubes, collectors that is best to there advantage... Most collectors are at least 3 inch or bigger... I never saw a 2 inch collector on a V8 or 6... Many things, but I am looking for real world info. Supporting, small tubes, and there benefit...

Honestly, There is no real benefit. as reasons stated above But was hopeing for a good reason...

I want to figure out why, all these years people have used free flowing exhaust, when the back pressure, or resistance of the exhaust is what buiilds torque??? All the money wasted on engineering exhaust sytems, and the improvment of catalytic converters, when the ones first installed in 1976, The ones that robbed all the horse power, where actually not doin that at all.

Diesels are going threw that today infact...

 

My opinion is NO! dual 3 inch perahaps....

 

.... I guess your looking for dyno results ?? I can just tell you evertime i open up the exhaust on a sbf there is a huge improvment in performance , i never run cats . I think your getting back pressure mixed up with scavenging . You don't want or need any back pressure , the scavenging efect just helps pull the exhaust out of the clyinders better at low rpm , this helping with low rpm TQ , sorry i don't know how to explane it any better.... Lew

 

large exhaust tubes.
<HR style="BACKGROUND-COLOR: #d1d1e1; COLOR: #d1d1e1" SIZE=1 itxtvisited="1"><!-- / icon and title --><!-- message --><!-- BEGIN TEMPLATE: ad_showthread_firstpost_start --><!-- END TEMPLATE: ad_showthread_firstpost_start -->Has anyone, had HP or TQ losses, that can be definately linked to an exhaust that is to large...

SO, here is an example... You had 300 rear wheel HP, with 425 FTlbs Of Tq, with 2 inch exhaust, then you went to 3 or 3 1/2 and you lost both.

I am looking for facts... Not I heard billybob down the corner, losta tun when he put them thar stacks on, and he has 1 million miles on her...LOL.

I would like input, for gas, but diesel will do, with engine mods linked to this.

I can say, I run as big of exhaust as I can fit..3 or 3 1/2 couple guys run 4 inch tubes behind a 302 or a 4.6, with only gains...

Lets hear it...
<!-- / message --><!-- BEGIN TEMPLATE: ad_showthread_firstpost_sig --><!-- END TEMPLATE: ad_showthread_firstpost_sig --><!-- sig -->__________________

 

I don't have dyno results to back it up, but I do have experience. On my current vehicle, I opened up the system from 2" (the converters and everything are 2.25" stock, but neck down to a 2" system at the rear flange), to 2 1/4". I wanted to run just 2 1/4" but the shop that did the work said the bends in the pipe would restrict the flow and went with a 2 1/2" tailpipe. I drove the vehicle for 2 1/2 years this way. I recently had the entire catback redone, also in 2 1/4", but this time had the tailpipe redone in 2 1/4" the way I thought it should have been done.

Did I gain torque. Absolutely. Way quicker off the line. I do a lot of towing, and if I loose torque, the PCM will unlock the torque converter clutch, which causes more heat, forcing me to downshift. With the smaller tailpipe, I can hold the higher gears longer. the trick is to have the right sized pipe for the job.

 

I recommend changing that idea. Forget about back pressure, and start thinking about velocity. You should concentrate on maximizing velocity. When you do that everything else will take care of itself and you will have the optimum system for a particular application or setup.

Often times a properly sized and designed catalytic converter will give a little increase in performance because it raises the temperature of the exhaust gases. A hotter gas travels faster than a cooler one. Again, the performance increase is based on velocity not back pressure.

 

So would you say a larger tube would be beneficial, to HP/TQ gains??? or Smaller tube. Give some examples say 460 + 2 1/2inch tube or 302 = 2 inch tube, or would you agree that 3 inch, and let it flow, or as you stated, it will tke care of itself... Elaberate a little if you dont mind.

 

Yes I have.. both the 5.0 and 5.8 motors that have been in my truck produced less low rpm TQ with a larger exhaust system. I wouldn't go as far as calling either of them too small or too large because they were both better than stock but the big system is still only a 3" single with a 2.5" Y build from mendrel bent tubing VS the smaller system that was built with compression bent tubing. The larger system does makes more peak HP but the smaller system was a better match in my opinion because it produced a broader powerband.