Why do you need backpressure again?My dad still insists that larger pipe is higher power. Then he
>>28211424Then he went to get some milk and never returned?
https://www.youtube.com/watch?v=DvMBbojZpIINo.
>>28211424sorry to hear that your dad suddenly started doing dumbbell dance.but yeah backpressure somehow helps with low end torque and acceleration
Backpressure is total bullshit.I think the idea was a juvenile misinterpretation of wind tunnel design where a smaller section flows faster.
>>28211424oh my god, your dad saw candlejacki send my condo
>>28211424it doesnt matter
Now first of all I know absolutely nothing about cars or anything else, but exhaust gasses are a fluid and they are pushed out of the pipe by the exhaust cycle, in theory wouldn't backpressure cause a bottle neck of sorts as it basically just restricts the free flow of the fluid?In theory it also could encourage scavenging which is beneficial in a 2 stroke and in theory that's how 2 smoke expansion chambers/resonators work, but shouldn't be in a 4 stroke that is tuned correctly and not dumping unburnt fuel into the exhaust.Then there was some shit I remember seeing about exhaust pulses or something that help push the fumes out, but I can't remember that shit, basically you need some sort of pipe to properly push the gasses out of the head, that's about it.Straight pipes shouldn't hurt performance.
>>28211424He probably thinks that due to restrictive manifolds in gas crisis era classics. Bigger pipe does indeed make number go up to a point.
>>28211424Backpressure is bad. Too big of a pipe is also bad.What you do is optimize pipe length and diameter for resonant scavenging in a certain RPM range. Smaller pipe means better scavenging at low RPM, but more restriction as RPM increases so ultimately limits top-end power.
>>28211474Because "back pressure" is an incorrect term that we got stuck with because boomers.If you look at something like a p51 mustang, the exhaust is just a foot of pipe to prevent a burnt valve (that too is misleading - a burnt valve is one that has been cracked, can happen from the shock of cold air hitting a hot valve- like when an engine is shut off and the valve is exposed directly to cold air- a hot exhaust pipe prevents that).
Then he WHAT
>>28211424You don't need backpressure you need velocity.
>>28211554A whole Coke bottle.
>this thread
>>28211569but low backpressure means low velocity. High volume doesn't mean high velocity
>>28211554Then he?..
>>28211424Bernoulli's Principle of fluid/gas flow dynamics and scavaging. Learn it.
>>28211450Should have sent him your condom much much earl
how truthful is this video? https://www.youtube.com/watch?v=vA-Z3ncTdUY
>>28211474>Then there was some shit I remember seeing about exhaust pulses or something that help push the fumes out, but I can't remember that shit, basically you need some sort of pipe to properly push the gasses out of the head, that's about it.scavenging, it's incredibly minimal gains but it matters for race cars. basically if your pipes are in a certain way, you can have the exhaust from one cylinder create a low pressure in the incoming exhaust from another, which will help it go out faster. (it's literally the opposite of "backpressure"
>>28211634Tri Y's
>>28211554He accidentally the whole car
Doesn't matter. Exhaust has been decoded to the point that even the stock exhaust you get on any decently performing car is going to maximize power. You can spend $10k on intake, headers, and headerback exhaust and maybe get a 5% increase.
>>28211650Gains arent "incredibly minimal" from scavenging. Even in a streetcar, the difference between proper length longtubes and shorties is about 20whp.
>>28211537P51 mustangs were just big engine and supercharger to win the war and they did, they weren't race engines optimised to squeeze every drop of power out of them, I'm sure they were probably "underperforming" a bit for reliability.But yeah it doesn't matter THAT mich what kind of pipe you have>>28211650>>28211684Isn't that more about redoing the whole manifold and header from the head, not just the pipe from the end of the manifold to the back of your car?
>>28211639Haha I'm glad this meme is still alive, never change 4chan, never ch
Tuning is a compromise. When you tune your induction (exhaust scavenging is just the last stage of the intake induction process) for high range you're losing low range.It's fine and dandy if you don't give a shit about drivability/its a track car, but there's a reason most factory vehicles have 95-100% of torque from about 1/3rd to 2/3rds the rpm range. Drivability/average system efficiency compromise
>>282116505-10% gains are not minimal. Especially because headers and an x pipe are quite cheap
>>28211424As long as you're not running into stagnant airflow, bigger pipe = more-er faster-er
>>28211639>>28211703You dumb niggers can't even candlejack correc
what's more important is runner volume and flow.
>>28211424you want FLOW and VELOCITYToo much exhaust diameter hampers scavenging by reducing velocity. If the velocity, flow and RPM all align correctly, ALL of the exhaust gas will be sucked out of the cylinder, leaving a vacuum that allows more air-fuel mix to take its place. No velocity means the cylinder still has >10psi of exhaust gas in it by the time the valve closes, leaving little room for new air-fuel mix.Too little exhaust diameter reduces flow by providing resistance to flow, causing less exhaust to make it out of the cylinders before the exhaust valve closes.
>>28211797So theoretically, is this why swapping out the manifold for headers or changing mufflers/cats while keeping the pipe diameter increases horsepower? Less restriction = more velocity?
>>28211810Headers are changing the scavenging effect timing significantly, or should be at least, to make a noticeable increase in the peak torque rpm range.Changing your cats and muffler for high flow passthroughs might give 5 entire HP on a 500hp v8. It's not just not worth the money, it's a gain that won't make any difference to your speed.
>>28211424Did candlejack get this an
>>28211933who are you talking a
shut the fuck
Cursed thre
>>28211634This.There's no such thing as ((((back pressure)))) only resistance to flow.
>>28211424>Then heWhat? What did he do? Don't leave us hanging
The cam timing is tuned to the factories quiet and restrictive exhaust. Put on a set of top fuel headers, with no back pressure, and it won't run right.
>>28211424Nope. Common misconception. You want the least amount of backpressure possible, BUT the vehicle didn't come that way and the intake and fuel mapping aren't set up for it. Neither is the cam. You can't just put in a free-flowing exhaust and expect it to run right.
>>28211627Depends on the rpm
>>28212344What are your goals?
>>28211673>You can spend $10k on intake, headers, and headerback exhaust and maybe get a 5% increase.Bullshit. Untuned longtube headers show a 30hp/50ft-lb ish increase or more in the output of almost any modern v8 throughout the entire powerband, evn on cars with a tubular shorty manifold like the 6.1/6.4 hemi.Stop being retarded.
>>28211684This anon gets it.
>>28212317You have no idea what you are talking about.
>>28212459>5%
Back pressure is what makes the car go forward dum dum it pushes out the back for a reason
>>28211554looks like OP...couldn't handle the pressure.
>>28211424It's only kind of good in a two stroke, but not constant back pressure like your boomer dad might be thinking, instead a timed pulse of back pressure to help keep more of the combustion mixture in the cylinder where it can actually be used is beneficial, that's what an expansion chamber does.
>>28211450/co/ 2010 sends its regards
Instead of thinking of it as "back pressure" look at it as pulse timing for optimal torque at a certain RPM range and engine load.If you're building/modifying a car for racing you want your peak torque as high in the RPMs as you can get at WOT. For your daily driver you want a system that gives you 90+% scavenging efficiency at 2000-4000 rpm at part throttle.Cars from the factory give up 5-10% power at the peak range for that 2000rpm cruise.
>>28211810Headers are more involved as >>28211932 said, you're close enough to the engine where timing the individual pulses starts to matter. But yeah, nice stainless steel tubes will flow better than an equivalent-length cast manifold.
>>28212573I'm too dru k to explain ex h aust but I'll cone back to.orow
>>28211449This I've never found back pressure to be beneficial
>>28212573It's good in NA engines too, you just have to time the pulse to suck the gasses out of the cylinder and suck in the mixture. Not too sure abt forced induction tho
>>28212565>5%lol. 5% =/= 7 to 10% througbout the entire powerband.
>>28211424my ass thought that was a motorbike...
>>28212671>nice stainless steel tubes will flow better than an equivalent-length cast manifold.But at what cost.Modern exhaust manifolds flow about the same as shorty headers and any power increases can be explained by dyno error, there is no benefit to them except for boosted applications. Longtubes on the otherhand are worth the cost and provide a measurable and noticable increase.
>>28212681>This I've never found back pressure to be beneficialIt can help build low rpm torque in certain high HP or high RPM NA applications.For instance, a "bolt-ons" d16/d17 will run faster with a 2" exhaust system than a 3" system.
>>28211424Did he die?
>>28213024and what did your vagina think it is?
>>28213022Except your numbers are embellished
>>28213481>Except your numbers are embellishedlols, you can gain 5% of a heavily modified motor, even more on a stock motor, and even more from a boosted motor,. Both of these are showing dyno info for cheap off the shelf stuff with oversized tubing:https://youtu.be/SzxHG3Ma4r8?t=188https://www.mopardiy.com/gen-iii-hemi-headers-shootout-finding-the-perfect-header-for-your-hemi/Properly tuned longtubes on any v8+ engine with ported heads and freeflowing intake are a 40hp/50ft-lb gain across the entire powerband.This isn't even a debate and has been known since the 60s.
>>28211537>If you look at something like a p51 mustang, the exhaust is just a foot of pipeThose are also designed to point back into the airstream and add a bit of extra thrust
>>28211449>>28212681It helps with 2 smokesMight help build mid range torque if you have a huge cam or something
>>28211537>If you look at something like a p51 mustang, the exhaust is just a foot of pipeThose are also designed to point back into the airstream for extra scavenging
>>28212573No exhaust pressure is "constant", it always comes back in pulses.
>>28211673And modern cars never make concessions for anything other than performance.You truly are not as smart as you think.
>>28212464No, you have no idea what im talking about.
>>28215308No one's putting aftermarket exhaust on a minivan
>>28215370hold up did somebody say something about minivans?
>>28213026>Modern exhaust manifolds flow about the same as shorty headersThe power benefit is noticable when you're putting them on some 80s POS with cast pig-iron log manifolds. If we're talking "modern", yeah a lot of modern cars do use well-designed tubular manifolds that don't leave much power on the table.
>>28211424>Why do you need backpressure again?for cold starts
Look at any race car. Do they give a fuck about back pressure?