3" Exhaust L28E N/A

[zclubhouse]

I ran a 3 inch straight pipe set up on my L28 (Dual SUs, hot street cam, 6-1 long tube headers,) and it was absurd. I recently switched to a 2.5" system and have the exhaust exiting before the drivers side rear wheel. It's still way to loud to be considered a daily driver, but my car is more of a dedicated loud toy anyways. Power response seems to be better than the 3" system, but I have no dyno results to back up that claim. Regardless, in my experience, any straight pipe system on a L6 is going to be foolish loud, but the 2.5" had more of a race motor sound and the 3" was so loud you could hardly make sense of it. Unless one was building a full on race car or going forced induction, I would echo the opinion of others on this board and stick to the 2.5".

[S130Z]

I have been doing alot of thinking about it lately and just ordered a st of pacesetters 6-2-1. I think I am gonna ditch the 2-1 pipe and run 2.5" twice pipes straight off the header with a glasspack on the end of each pipe.

[Daeron]

According to consensus, that is about the worst exhaust flow you could have. I have broken down "the twice pipes situation" plainly enough multiple times; if you run a search on the term "twice pipes" and insert my name, you should find one of the many conversations regarding how you should and should not set them up. The short version is that you NEED that Y pipe before you split the pipes in two for the run back. TonyD has shared a great deal of firsthand information as well; most of my knowledge is regurgitated from research here and elsewhere.

[S130Z]

Wow, that is kind of interesting. Im going to read up on that. When you think about it, it really sounds like it would flow better then cramming all the exaust flow back into 1 pipe rather than to split it up from the header.

[Daeron]

Heh, I am feeling a bit more verbose now than I was yesterday.. It has to do with exhaust pulse scavenging. Basically, each combustion wave helps pull the next wave along behind it. "Marrying" all six cylinders into one pipe establishes this scavenging as it should be; to leave both triplets of pipes "divorced" is to lose exhaust efficiency.

 

"Backpressure," while not exactly a myth, is something of a red herring, as long as it is not excessively high. It is NOT the pri mary parameter to analyze when designing and sizing your exhaust system.

[S130Z]

So it kinda acts like an expansion chamber on a 2 stroke engine. I knew the pulse had an effect for a 2 stroke engine but never really thought it was the same with a 4 stroke.

[ozconnection]

Heh, I am feeling a bit more verbose now than I was yesterday.. It has to do with exhaust pulse scavenging. Basically, each combustion wave helps pull the next wave along behind it. "Marrying" all six cylinders into one pipe establishes this scavenging as it should be; to leave both triplets of pipes "divorced" is to lose exhaust efficiency.

 

"Backpressure," while not exactly a myth, is something of a red herring, as long as it is not excessively high. It is NOT the pri mary parameter to analyze when designing and sizing your exhaust system.

 

Like you Shawn, I have read a few books on the topic too. The best book I have found on the topic is Smith and Morrisons book, 'Scientific design of exhaust and intake systems'.

 

The chapter on 'pressure phenomena' , 'Sud-division of manifolds' on page 101 says "There is absolutely no evidence to support this theory."

 

On the other point of backpressure, Bell's book 'Four-stroke performance tuning' suggests on page 157 in Chapter 5 'The exhaust system' that the lower the exhaust backpressure the less restriction, or pumping loss, the engine will see and the greater the potential for power production, combined with appropriately timed camshafts and well designed intake systems. Volumetric efficiencies greater than 100% are possible in some instances.

 

Neither book suggest that six cylinder engines with a firing order like ours are to merge into one pipe. They are to be split into two separate groups of three and remain that way.

 

There are two types of wave action taking place in the exhaust system. The exhaust travels throught the pipes between 200-300 ft/second. The other, more powerful and influential, are the pressure waves that move at 1500 to 1700ft/second. These later waves are the ones that help to evacuate the cylinders at overlap if setup correctly. They work particularly well in exhaust setups that are split into two groups, again due to cam timing and the firing order split by 120 degrees of crank rotation ie.(1,3,2 and 5,6,4).

 

I do think that Roberts' exhaust designed for the racing/hot street L powered Z cars are built that way for good reason with sound scientific research and evidence to back it up.

[Tony D]

"Backpressure," while not exactly a myth, is something of a red herring, as long as it is not excessively high. It is NOT the pri mary parameter to analyze when designing and sizing your exhaust system.

 

It is on a turbo, though... ZERO exhaust pressure downstream of the turbine is the ideal curcumstance.

 

On an N/A, the lowest you can get is the best, as long as you have a crossover pipe to equalize the pressure (or pulses, if you want--if this is required on the engine design you are making the exhaust system for) between the two pipes you can package equivalent cross section with lower groundclearance.

 

If you look to the Z432, which was a 2L engine that had the potential to rev to over 10K rpms in race trim, but which had to run the factory exhaust Nissan chose a twins system (twin 60mm pipes) with the resonator acting like the corssover pipe. The header on the Z432 (which was mirrored in the JDM for the L-Series) had divorced pipes at the collector, and all the way back. Any crossover was accomplished (I suppose) in the chambers of the premuffler, while the muffler out back was divorced chamber. I cut apart the muffler can once to rewrap the glassfibre and it was divorced chamber. The premuffler was not opened up, so it may be divorced there. I have said in the past it was crossing over in there in a common wrapped chamber...but that is my assumption.

 

When I cut my system apart to replicate it, I will get the information once and for all.

 

Some of the 'other' manufacturers sold the same system as Greddy/Trust and used twin glasspacks as premufflers, and the exact same can as I had out back so it may indeed be segregated all the way back as Oz Connection suggests!

[johnc]

Like you Shawn, I have read a few books on the topic too. The best book I have found on the topic is Smith and Morrisons book, 'Scientific design of exhaust and intake systems'. The chapter on 'pressure phenomena' , 'Sud-division of manifolds' on page 101 says "There is absolutely no evidence to support this theory."

 

I've also read Smith and Morrison's book and the last time it was updated was 1972. A LOT has happened in exhaust system technology in the last 36 years. Things like shallow merge collectors, commonly available thin wall 3" and larger tubing, CFD software, etc. Exhaust system science has moved on and Smith and Morrison's book is now really only appropriate for vintage folks.

 

A properly designed single exhaust will generally make more horsepower and toque over a wider rpm band then a dual exhaust on almost any engine type (including rotaries). TransAm race cars for years ran 180 degree headers that merged into a single 5" or 6" exhaust. These engines made 50+ more horsepower with an exhaust like that.

 

Dyno testing I witnessed in the mid 1990s and again in the early 2000s showed that a single 3" exhaust, properly designed, made significantly more horsepower and torque on 2.4L, 2.8L, and 3L Nissan L6 race engines over commonly available and/or highly optimized twice pipes. And another side benefit is that a single exhaust weighs less then a dual exhaust.

[Daeron]

I haven't read a single text on the subject; 99% of my learning either came from this forum or from links provided in this forum.

 

This subject is one where a lack of knowledge is very common; that being the case, I feel justified repeating what I have learned. I believe it was John Coffey or DragonFly and those dyno experiences I allowed myself to set my mind in stone about this subject; my understanding was that a true, fully split twice pipes setup (with no collector) had been proven less desirable than a system that unified.

 

Having no greater knowledge or experience myself.. I'm respectfully bowing out and reading the rest of this discussion.

[ozconnection]

I've also read Smith and Morrison's book and the last time it was updated was 1972. A LOT has happened in exhaust system technology in the last 36 years. Things like shallow merge collectors, commonly available thin wall 3" and larger tubing, CFD software, etc. Exhaust system science has moved on and Smith and Morrison's book is now really only appropriate for vintage folks.

 

Are there any books written (to your knowledge) that would be considered 'updates' to Smith and Morrisons' book? I wouldn't mind upating my library if one existed.

[johnc]

http://www.sae.org

 

Some examples:

 

http://www.sae.org/technical/papers/2008-01-1004

http://www.sae.org/technical/papers/2002-01-0059

 

You can even sign up for a seminar on how to design high performance exhaust systems:

 

http://www.sae.org/servlets/pdEvent?OBJECT_TYPE=PDEventInfo&PAGE=getPDEventInfo&EVT_NAME=C0235

[ozconnection]

Thank you very much John, Cheers mate!

[Tony D]

"SAE: Membership Has It's Privilidges"

 

LOL

[S130Z]

Has anyone ran or heard the Monza exhaust ran with the pacesetter header? I can't tell if the muffler is like a glasspack or not. I'm searching for a certain exhaust tone.

[S130Z]

So the time has come for me to install the header and get my exhaust show on the road. I am taking the header to a powder coating shop to get it ceramicoated. My only delema is that after I install the header I have to get the car to the only exhaust shop that is willing to do the exhaust with no cat. The place is 10 miles from my house and I think I might have to drive with an open header for about 15 minutes. It kinda sounds risky to me unless there is another solution. I know a guy that has a trailer but I have no truck to tow it with.

[S130Z]

My only delema is that after I install the header I have to get the car to the only exhaust shop that is willing to do the exhaust with no cat. The place is 10 miles from my house and I think I might have to drive with an open header for about 15 minutes. It kinda sounds risky to me unless there is another solution. I know a guy that has a trailer but I have no truck to tow it with.

 

Any Ideas?

[johnc]

Just drive it and keep the rpms low and don't give it too much throttle. If a cops stops you, tell him you're going to the muffler shop.

[S130Z]

I'll try to keep it down. I will probubly need to put an exhaust clamp on the collector just to be safe. I'll let every one know how it goes on monday and try to get a video clip up of the new setup.

[S130Z]

MSA sent me the wronge collector so it will probubly be another week before it goes on. At least it will give me time to get it coated.