How big is your pipe ;)

[r0p0doe]

Just like the title says  :rofl: no but seriously how big is it???

 

OK enough with all that, I'm going to get my exhaust done on my car tomorrow and the muffler guy suggested I go down to 2in to get a lil more bottom end instead of 2 1/4 I'm running right now. I have an LZ22 runnig a shorty header from top end performance with compression around 9.84 - 10.48 so it's a bit peppy and it's 2 1/4 cus that's what the po had it at, should I take the advice of the muffle man or stick with the current size. Also curios as to what you guy are running and why, thanks in advance for your replies :thumbup: 

 

EDIT: It's straight pipe with a resinator no muffler, he said going down to 2in will give me a lil more bottom end since im not running a muffler. Would you guys keep it 2 1/4 and throw a muff on or keep it straight at 2in?

[freetheoranges]

I'd have to grab the tape measure

 

Big enuf to get that shot outta here

[MicroMachinery]

Not technically a pipe, but..

 

[datrod]

I think I would get a second opinion from another muff shop. Muff's like big pipe...LOL

 

I ran 2 1/4 on my L20B and the LZ23 I had, It worked for me. But I don't build exhaust systems for a living so what do I know.

[Son_of_a_Datsun_Guy]

I'm running 2.5" on my 2.1 liter L series (it's a franken build out of a Z22, but it was destroked in order to get more compression). That's with a set of SUs and -- currently at least -- a stock exhaust manifold. I've got a header that I'm redoing for the car right now, then it's going to a friend to get dyno tuned. 

 

It's loud. Like, really loud. But I really don't think I'm losing anything on either end of the RPM range with it, at least nothing noticeable. 

[shacks510]

2" is fine.

[]2eDeYe]

Once my brother had big exhaust put on his Mazda 2600 truck for some reason. He lost a bunch of power, being that we were cheap we stuck a reducer on the end and got most of the power back. :lol: 

 

 

There is a way to calculate pipe size for optimal back pressure, I do not know that calculation. :)

[r0p0doe]

I think I would get a second opinion from another muff shop. Muff's like big pipe...LOL

 

I ran 2 1/4 on my L20B and the LZ23 I had, It worked for me. But I don't build exhaust systems for a living so what do I know.

I'll ask around for another credible place the first place I went to did a shit job

 

I'm running 2.5" on my 2.1 liter L series (it's a franken build out of a Z22, but it was destroked in order to get more compression). That's with a set of SUs and -- currently at least -- a stock exhaust manifold. I've got a header that I'm redoing for the car right now, then it's going to a friend to get dyno tuned. 

 

It's loud. Like, really loud. But I really don't think I'm losing anything on either end of the RPM range with it, at least nothing noticeable. 

Thanks for the response

[Ranman72]

short header will give you more bottom end a long header will give you more top end 

same with pipe size larger will give you more top end  BUT you can be to large and lose power 

Rebello suggested I replace my tired exhaust with 2 1/4 instead of the 2 inch when I get it re done 

I have a 2150 long rod motor 

[shacks510]

"Just go back to stock"

 

Then you'll win the local elementary schools annual pea shooting contest :D

[datzenmike]

You want the smallest pipe that will give the fastest gas speed but still not be restrictive. The problem is an engine operates over a wide RPM range AND medium to full throttle. A 2 1/2" is probably fine above 6k at full throttle but again who drives at this intensity? Where do you drive the most? Probably under 4K 99.999% of the time with occasional blasts. So it would make the most sense to run a 2" pipe or 1 7/8" and gain or retain your mid range.

 

The ideal pipe would expand in size to match the volume going through it.

 

 

Ztrain has a 2.2? with (I forget the head) small ports and valves. You would think it would be choked but it has insane torque numbers at mid range and up. It's not a high revver but it must pull like hell. Ask him to post his dyno sheet again. See what exhaust pipe he's running also.

[Busta Nut]

I got 2 1/2" all the way back to a 2 chamber flowmaster......loud as fuck!!

 

Love it though......

 

I did it cuz I knew I was gonna go bigger with the engine....

 

L20 punched out to 2.2.....mild cam....closed chamber head....shorty header.....lightened flywheel.....dual webers....

 

 

Cuz racecar..................

 

 

 

 

I have not played around with exhaust systems enough to know if I l gain power with going smaller......just don't want to....

 

..........becuz I've never heard anyone say this.......vv

 

 

2" is fine.

 

 

:rofl:

[Son_of_a_Datsun_Guy]

You want the smallest pipe that will give the fastest gas speed but still not be restrictive. The problem is an engine operates over a wide RPM range AND medium to full throttle. A 2 1/2" is probably fine above 6k at full throttle but again who drives at this intensity? Where do you drive the most? Probably under 4K 99.999% of the time with occasional blasts. So it would make the most sense to run a 2" pipe or 1 7/8" and gain or retain your mid range.

 

The ideal pipe would expand in size to match the volume going through it.

 

 

I drive like that  :rofl: . I mean, I don't speed ridiculously, but second and third gear go a long way for having fun within the speed limit. 

 

I forgot to mention that I have a Magnaflow pre silencer AND a Borla muffler (can't remember if it's a turbo style or standard off the top of my head). I suspect that the biggest difference you see when you change pipe size is the back pressure, and having two muffling appliances along the way may be keeping my back pressure numbers similar to someone with a 2 1/4" exhaust and a solo muffler. 

[DanielC]

I have 521, with pretty stock L-16.   The old exhaust pipe was pretty much stock sized, and I replaced it with a 2" OD pipe.  Exhaust pipe is commonly measured by outside diameter, and the pipes on the muffler are measured by ID, so a 2" pipe fits into a 2" muffler.

See this thread:

http://community.ratsun.net/topic/61167-how-i-replaced-a-521-exhaust-system/?hl=exhaust

 

I do not believe the mantra that a little back pressure is good for low end torque.   Exhaust systems are way more complicated than that. 

Consider this.  The engine is running, and a cylinder is on the power stroke.  Sometime before BDC, the exhaust valve starts to open.  there is still fairly high pressure in the cylinder, and as the exhaust valve cracks open, a sonic high pressure pulse starts down the exhaust manifold, toward the exhaust pipe.  Not a lot of flow, but a high pressure pulse, travelling at the speed of sound, in hot exhaust gas.  As the exhaust valve opens farther, more exhaust flow.  High pressure gas in the cylinder moves to low pressure in the exhaust pipe.  The gas flows faster, and faster, but is limited by the speed of sound.  By this time the piston is coming up on the exhaust stroke, and the exhaust instead of being pulled by the speed of the gas flow, gets pushed by a rising piston.   And here is where it gets weird.  The piston can easily move faster than the speed of sound, for a brief part of the exhaust stroke, and because the exhaust gas is limited to the speed of sound, it can get compressed again.  This creates another shock wave, or sonic pulse down the pipe.

More weirdness.  If the exhaust pipe is open, or get a bigger cross section, the positive pressure exhaust pulse can get reflected back up the pipe, or manifold as a negative pulse.  If this negative pulse is timed right, it can arrive back at the exhaust valve just as the cylinder can use a little extra help in scavenging exhaust gasses out of the cylinder.

 

All that is just a small bit of exhaust pipe theory.   And I will tell you there is way more that I do not know than what I do.

 

Remember everything on an engine affects everything else.  Change the exhaust system, and the carburettor tuning may be affected.  I honestly believe that if the engine is optimally tuned with a smaller pipe, you can replace the exhaust system with a larger diameter exhaust system you will have more power, without losing lower end torque, if the engine is optimally tuned again.

 

Back to the 521 exhaust system I replaced.  The small pipe keep the exhaust gas speed fast theory tells me I should have kept the smaller pipe.  I do keep track of my gas mileage, almost every fill up.  It varies, depending on the season, and type of driving I do. 

After I changed to a 2" od system, on a stock L-16, in a 521, almost every tank of gas was better mileage than the best mileage reading I got before I changed the exhaust system.

 

My L-16 was happier with a 2" pipe.  I am pretty sure your LZ-22 will be happier with a bigger pipe than that.

But a bigger pipe will be harder to fit under your car.  That means the muffler shop will have to work harder, or longer.  That cuts into their flat rate.  That might be the real reason they are suggesting a smaller pipe.

[KoHeartsGPA]

I have 2" with a 25" glass pack by the driveline and a shorty magnaflo at the tail, she does ok at low rpm, however on the freeway when I'm at 3600 and punch it she puts your head against the headrest and it fucking goes, rpms go up very quickly, it's FUN, scares the shit out of my uncle :lol:

[Busta Nut]

I must say I have a lot of low end torque.......

 

........probably moar than the upper end.......

............carb jetting also plays a factor in this though.....like what was stated earlier....

[KoHeartsGPA]

I must say I have a lot of low end torque.......

 

........probably moar than the upper end.......

............carb jetting also plays a factor in this though.....like what was stated earlier....

For sure, I've got a "small" 48mm single side draft mikuni, I'm still playing around with the jetting.

[r0p0doe]

Thanks guys I really appreciate the input  :thumbup: When I put the new header on I noticed an increase in response and take off and over all performance. Was a slight increase in top end but not too drastic, idle did change significantly tho like I figured it would. I think I will end up sticking with the 2 1/4 because the motor already has nice compression and I don't want to mess it up by dropping down a 1/4. Once my exhaust is done I'm going to get my carbs tuned and hope to gain a bit of top end, I'm going to go today after work and give him more details about my motor and then see what he says about pipe size but I'm pretty sure I'll keep it at what I have...

[GoGoGo]

I have a full 2" exhaust for a medium-build L20b and it works great. Based on your higher compression motor and larger displacement I think it 2.25" is going to be perfect. IMHO a 2.5" is really only necessary when you start pushing 180hp+ in a L-series and are really driving the piss out of the car, i.e. racing. 

[Burabuda]

2200cc=134cid