In Texas the law is that it must direct the exhaust away from the passenger compartment. As long as you don't have a camper (considered passenger compartment) I see no problems. Even if you do, your probably OK. I think the only thing they won't allow is a turn-down under the bed on trucks w/ campers. My Dakota passed several times w/ a turn-down exiting about a foot from the back of the cab (no camper).

 

low end will be gone, that is why it is called low end, it doesn't matter if it was moved to a different rpm, the fact of the matter is, the power that was there is mover so therefore, it is gone.(not low end anymore). you can't have more exhaust coming out then you have incoming air. you have to equal that out. that is what i am saying.

 

how does opening up the exhaust make you lose low end torque?

 

if you get too big of a pipe, that will allow the air to outflow the incoming air which is not good, this is not good for a stock sb, and moves the power up in the rpms. this is why when mustang guys whine after they come back from the muffler shop and ask why is it slower. you ask him, what size pipe and not to my suprize they arlways say 3 inch. but you are good to go since you probably are not thinking of doing 3 inch anyway, it is more expensive as well.

 

f100guy, i have seen a few trucks w/ small V8's get Gibson/flowmaster 3" exhausts and not lose any low end (atleast not from ~2k rpm up/as low as the dyno measured). Maybe 1-2 ft-lbs, but #'s can change that much from baseline to baseline. While peak TQ did move up a couple hundred RPM's they didn't lose any anywhere.

When the "cat-back" being too large will start to matter is when you start tuning the whole exhaust system (headers, high flow cat/no cat,y-pipe). As it stands most stock manifolds, y-pipes, and cats cause enough restriction/turbulence so as to make the cat-back being too large not much of an issue. It might not be ideal, but since nothing else is, it doesn't matter much. No, this doesn't mean that backpressure is a good thing .Though in this case it does create an odd benefit.

In rare cases you are correct even w/ fairly stock applications. In general, my experience has shown the opposite. I can't vouch for extreme low-end (below 2k rpm) w/ #'s, but driving impressions lead to the same conclusion as above. Even straight-piped after the cat(otherwise stock exhaust) my Dak sure spun the tires easier off the line, even at light throttle.

there's still much more info./many more variables than this, but I type very slowly, so...

 

i have a k&n fipk air filter w/ mass air. i plan to save up and get new headers, new high flow cats, new muffler (maybe flowmaster), and all new pipes. what would be better 2.5inch or 2.75 inch?

i do mostly highway driving but added acceleration comes in handy.

 

2.5 would do good. i also have driven a friends 95 ext. cab chevy truck with an auto,305 with just a 3 inch flow dumped. i don't know if it was just the crap 305 but i tried to peel out and it wouldn't even roll a pebble around and the accel was crap

 

2.5 would be excellent as long as it's mandrel bent. Any other modifications planned (cam, throttle body)?

 

I've ran 4 complete exhaust systems on the same 302 and know for a fact that to big of exhaust pipe = no low end torque. For duals on a stock 302 2 1/4 pipe is great, with a single setup 3 inch pipe is good for mid to upper power but the 2 1/2 single pipe makes more low end power. I know about exhaust velocity and back pressure but also know that the smaller pipes will help your low end torque to a degree.

 

Oh, I must admit that i don't have much experience on 2000-up model trucks. I've heard that the exhaust are getting better (especially manifolds), so my results may not apply. Also you are always going to be better off in the long run (if you end up doing a whole exhaust later instead of just cat-back, for instance) going w/ pipe sized matched to the motors needs. You won't gain anything extra by going too big, that's for sure. I just kinda felt like arguing .

95F150: one more before I go. You say the dual 2.25's are great yet a single 3" is too big? Dual 2.25's have almost an inch more area than a single 3", if I'm not mistaken. Please explain.

 

f100 is right. I put true dual 2 1/4" pipe on my f150 and I swear the torque is there. It's a small 302 you don't need anything any bigger. You gain low end tq with small pipes and well it doesn't sound unreasonable. It's stupid when people say "I've got 3" duals!" That to me sounds funny when people put that.

 

Moose94: Do you mean '95f150' instead of 'F100guy'? (only refering to 'F100' is kinda confusing)

If 'f100guy', then I'm sure he would disagree w/ DUAL 2.25"'s (seeing as how he states SINGLE 3" is too big-dual 2.25 would be WAY too big in his opinion). Right?

If you meant '95 F150' (the proponent of dual 2.25") then I would still like to know how SINGLE 3" isn't good for low-end, yet dual 2.25"s are. It just doesn't make sense. I'm sure it's just a typo or misunderstanding.

Dual 3" were mentioned (by 'f100guy') at one point, but that isn't the general topic and no one suggested it as an option. (including this just to help clear the air)

Not trying to continue the arguement, I just want to know where people stand. It doesn't make sense. Would someone please clear this up? I just need closure .

 

the title is HOW EXHAUST SETUPS AFFECT LOW END TORQUE. so there is no one asking which is best and what he wants, i was just saying 3 inch is way too big for astock or near stock 302. if it had a turbo then go with it but if not, stay away. i believe that 95f150, is on my side of this and as well as moose.

 

Hey tdister chill out, I was just posting my personal experience with many exhaust sytems both single and dual on the same truck. I never said 3" was "to big" I was just stating that it wasn't as torquey with the single 3" pipe as it was with the single 2 1/2" pipe.

 

I'M ONLY TRYING TO CLARIFY INFO

"For duals on a stock 302 2 1/4 pipe is great, with a single setup 3 inch pipe is good for mid to upper power..."-posted by you '95 f150'

It just seemed to me you were implying dual 2.25's (notice the word dual)were better for low end than a single 3". As I said, I just wanted you to clarify were you stood, because some posts didn't make sense(and still don't). You almost did. Thanks...

You stated something that not only doesn't make sense, but it went against my statements. I don't think it's too much to ask for someone to clarify in such a situation (something that has yet to be done). Is it? Feel free to drop it right here, I don't care. I'll just assume you make no sense, or I misunderstood your post.

f100guy: As I said, I'm done arguing, I was only using your name and statements for clarification purposes. I appologize for not making that clearer.

I'M ONLY TRYING TO CLARIFY INFO

Are my questions and intentions w/ this post clear? Jeez, I hope so...