Justinvd

1988 4runner 22R-E

I was just wondering if you need a certain amount of back pressure for your engine to run properly, i have always heard lot of talk about this but have no real proof. My exhaust is straight to some sort of muffler put on by a local exhaust shop then out. I wanted to make it sounds a bit better.Any tips on exhaust set ups would be awsome too. There are no air care regulations here so i dont have any cats either.

Ganoid

Back pressure = bad
Velocity = Good

read and learn...
Exhaust theory

James Dean

An engine needs some back pressure. Unless you have alot done to your motor (high compression pistons, larger cam, ported and polished heads, etc.) you don't want to go much bigger or much more free flow than it came with. If you put a large pipe and/or too big of a muffler you will lose all of your low end torque. Why does Nascar, IRL and pro modified that have 800-1200 hps motors only run 3"-4" exhaust? Maybe they haven't met any of the techs in the article listed above that say "you can't get an exhaust pipe that's too big". Maybe the millions of dollars they've spent in R&D was wasted.

I'm not saying factory setups came be a little restrictive, but don't put 3" or 4" open exhaust on your 4 cylinder. All that will accomplish is let everyone know your coming, and slowly.

InternetRoadkill

Depends on the cam grind.

SEAIRESCUE

EFI systems will compensate for changes. Carbs do too but not as good. Less restriction = more power. A restrictive intake side and a open exhaust side equals very little improvement but a lot more noise. Efficiency is the name of the game and a less restrictive exhaust is a step in that direction. Why do race cars and dragsters have no mufflers/air cleaners? Most improvements start with a low restriction muffler and junking the stock air filter arrangement for a low restriction cone air filter. What cha waiting for?

Luvmeye22re

A while back I had a 4runner that I put a K&N filtercharger, NWOR header, freeflow cat, and 2.25 exhaust on. The extra flow in intake and exhaust helped immensely. As to what is too big I don't know from experience but I don't think you would want more than 2.5" on a 22re or 3" on a 3.0 as I have read that engines in stock form prefer some back pressure, not much but some.

CoedNaked

Can someone define "back pressure" ??

thook

The exhaust valve opens and the piston pushes exhaust out through the manifold/header/piping. The resistance that exhaust meets on it's way out is creates a pressure the piston must push against to expel the exhaust. Backpressure.

Targetnut

Ideally you would want 0 backpressure. It'll never happen. if you remove your exhaust manifold you will actually increase the back pressure. In a properly designed exhaust syatem the velocity off the exhaust actually creates a negative pressure wave (scavenging) that helps to clear the remaining exhaust from the combustion chamber just as the piston is nearing TDC (and it's slowest velocity)

Headers are the best at this, and the timing of the negative pressure wave is related to the dimensions of the header. So the size of the exhaust is related to the engine speed that you want to achieve the maximum scavenging. Fat exhaust=high rpm, skinny exhaust= low rpm

People will tell you that that you need backpressure because they do not understand how this works and someone they know has but too large an exhaust on their vehicle and feel that they lost power because it does not perform well in the rpm range they normally operate usually low to mid rpms for a street vehicle.

CoedNaked

I'm sorry, it's not I don't know what back pressure is, but I honestly think a lot of people use the term back pressure incorrectly or post about it but don't understand it. It seems just like more vehicle related jargon to me the way it gets used on here sometimes.

thook

Oh....okay.