Need Opinions... Exhaust From 1.25" to 2"-2.5"

[SCT]

So I was thinking of making the entire exhaust system diameter bigger. I think it's 1.25" OEM, planning on maybe going up to 2" or 2.5" at most. I like the deep sound from it anyways, I may also not be putting on a muffler/ resonator (I like the natural sounds). I don't have either on now.

I'm sure the bigger diameter will improve performance since it'll breathe better. And the concept of a smaller diameter able to move more exhaust out than a larger diameter, I don't believe that. That's like saying if I blew up an air tank, the air will escape slower compared to opening a little built-in valve. From start to end, you're still moving the same amount.

This is all in the planning stage for when I get a loaded silvertop.

[bigbret]

Do it go 2.5 and then don't look back. Then you will need to start adding more fuel and air into your engine maybe their is boost in your future.

[mtl5240]

Originally Posted by SCT

So I was thinking of making the entire exhaust system diameter bigger. I think it's 1.25" OEM, planning on maybe going up to 2" or 2.5" at most. I like the deep sound from it anyways, I may also not be putting on a muffler/ resonator (I like the natural sounds). I don't have either on now.

I'm sure the bigger diameter will improve performance since it'll breathe better. And the concept of a smaller diameter able to move more exhaust out than a larger diameter, I don't believe that. That's like saying if I blew up an air tank, the air will escape slower compared to opening a little built-in valve. From start to end, you're still moving the same amount.

This is all in the planning stage for when I get a loaded silvertop.

do it and do it straight pipe with a cat and it should add 12 too 25 horse power and add a coult air in take you will fall in love with it

[eage8]

I'd go 2", 2.25" max. I'd also put a resonator and a muffler on it or it'll sound horrible.

and also, bigger isn't always better. It has to do with fluid dynamics and exhaust pulses. basically if the velocity is great enough it'll create a vacuum which will actually pull more exhaust out of the cylinder causing more fresh air to go in.

But allowing it to breath is also beneficial, it's a fine line that you have to walk. I think 2" is probably a good bet. that's what my HKS cat-back is.

disclaimer: all this stuff goes out the window if you have a turbo though, the turbo spool time gain is far more beneficial. As big as you can fit is normally just right in that case

[SCT]

Originally Posted by eage8

I'd go 2", 2.25" max. I'd also put a resonator and a muffler on it or it'll sound horrible.

and also, bigger isn't always better. It has to do with fluid dynamics and exhaust pulses. basically if the velocity is great enough it'll create a vacuum which will actually pull more exhaust out of the cylinder causing more fresh air to go in.

But allowing it to breath is also beneficial, it's a fine line that you have to walk. I think 2" is probably a good bet. that's what my HKS cat-back is.

disclaimer: all this stuff goes out the window if you have a turbo though, the turbo spool time gain is far more beneficial. As big as you can fit is normally just right in that case

That's why I said "loaded silvertop". Hopefully I'll be able to get a lot of stuff done to it so I can get a nice turbo even though I don't plan on racing; All for show and bragging rights, maybe racing but that's not my intention. There's a place in Glenn Dale, MD; Paradise Racing. They specialize in Toyotas, especially the AE86 and stuff. They actually drag them too.

[RogueMoog]

Not to be a typical noob who doesn't do his homework (or to derail the topic in some way), but I was wondering if there are aftermarket (DC Sports, Skunk2, etc) exhaust manifold options for the 4A-FE engine? Was thinking about giving my All-Trac wagon a little help.

[bcp477]

The stock exhaust tubing diameter is 1.75" OD / 1.625" ID. As for gas flow and power, etc. there WILL be a difference.... and it has to do with the volumetric efficiency and total pumping volume of the engine. What it comes down to, in practical terms is, IF the engine is basically stock as regards hp output.....then increasing exhaust diameter will certainly increase overall hp, but at the cost of low and mid-range torque. Exhaust systems are designed based on lots of factors, but engine displacement and pumping volume is the main one. IF the engine in question is modified (higher compression ration, wilder cams, etc. etc.....and thus significantly more hp than stock).....then a larger dia. exhaust will certainly help throughout the rpm range. In that case, the stock dia. exhaust would be "holding the engine back", so to speak. But, as I said, if you increase the exhaust dia. on a stock output engine, you will gain really ONLY at the top end....and lose everywhere else.

Going from a 1.75" dia. exhaust to a 2" dia. one is an increase of about 31 %.....2.25" dia. is an increase of about 65 %......and 2.50" dia. is an increase of a whopping 204 % - if all other things are equal. What this means is that, in order for the tractilbility of the engine to remain the same at all rev ranges, the engine output (and torque, as well), would need to be increased by about the same proportion. If you simply bolt on a 2.50" dia. exhaust, especially one with few or no restrictions, such as a muffler or resonator, all you will do is completely GUT the powerband below probably 5000 rpm (but get a strong increase above that). 2.50" is thus RIDICULOUS for that engine.....2.25" is not that much better. If I were you, I would NOT consider going larger than 2" in OD.....otherwise, you'll lose any drivability the engine might have, especially if the car is ever driven on the street. Again, that is assuming that the engine is basically stock in output. You may not believe it, but those are the FACTS. If you can't accept basic engineering facts such as these....well, you can find out for yourself... and then you'll see.

An excellent historic example of this sort of thing was the type of exhaust used on WWII piston powered fighter planes. Running a "stub exhaust" on each cylinder such as that made for a LOT more top end power....which was exactly right for the fighting conditions under which the engines were used. However, they ALL ran very poorly at low and mid rpms....sputtered and coughed incessantly....and were difficult to keep running at all at "idle" speed (they stalled ALOT, if kept running like that for any length of time). Once opened up, they ran beautifully. It is the same for every engine. This example is an extreme one, of course....but it illustrates my point well, I think.

In fact, I have been dealing with this issue in the last few days myself, as regards my AE92 sedan with fairly stock 4AFE engine. I have decided to stay with the 1.75" OD exhaust, keep the cat and resonator, but go with a low restriction muffler with a 2.125" ID inlet (2.25" OD). This will keep streetability pretty intact, but still give a nice sound and a bit more hp at the top end. Since the car will only be driven on the street, this makes sense.

[REN69]

tops 2" max or you'll start losing power unless you're turbocharged... you'll loose a lot of bottom end but top end will light up a little bit.

[Createdtoburn]

+1 to BCP and REN.

[Kiwi-Corolla]

2.25" (OD) is a good size (depending on the engine of course). I recently bought a 2.25" straight through exhaust for my 5A-FE, haven't got around to putting it on yet. You'll definitely see noticeable gains, especially when paired with the stock 4AGE front pipe and headers. As others have said, it'll be loud as hell without any form of muffler on it. At least chuck one resonator in to dampen things down a bit.

[SCT]

I drove an SCCA Cobalt that maybe had 2.5" or 3" exhaust. No cat, muffler, just all pipe. I had to do a check on it, so I "had" to take it for a test drive. OMFG I fell in love with the sound. Floored the pedal in 1st and 2nd gear and ride the 2nd gear at a high rpm and boy the gunshots and caboom and what not...

I like the sound of race cars, all pipe.

Depending on how loud it'll get, I may throw on a resonator. Or maybe a bypass valve, so I can switch the exhaust to go through a resonator or bypass it, depending on how I feel or if I see a cop or something.

[REN69]

Cobalts have a bigger motor though... more displacement, power and torque.

[SCT]

Yea, I think they're 2.2 liters (it was the ecotech motor, non-supercharged).

[ae92raybrig]

You will lose low end torque because there is such a thing as too big with NA engines. Why dont you get the ST first and then upgrade the exhaust?

The car will be a handful to drive in stop and go driving with an oversized pipe. You wont like it.

[REN69]

you think the ST would be better with bigger exhausts? I doubt it.