3" Exhaust L28E N/A

[S130Z]

Well I have been considering re-doing my exhaust lately. Right now my exhaust comes out right after the cat and I like the tone of it. The only thing I dont like is the fact that it is directly under me and it kinda gets annoying. I am planning on swapping to a mn47 head with a mild street cam. What my main concern is about how a 3" strait pipe setup would sound on an N/A motor.

 

Or if I went with a pacesetter header and 2.5" strait pipe all the way back, but.... I'm kinda tight on money so that might have to wait for another time.

[stprasinz]

I think in general the 3" would let out more noise but more of a grumbbly lous, as to where the 2.5 would rasp alot more and sound higher compression so to speak...

[essdeezee]

On my l24, I have a 6-2 header to y pipe, to 2.5" straight pipe, with 2 ~90* mandrel bends, to a dynomax superturbo. Down low, it sounds raspy, and builds nicely with rpm. No fart-cannish sounds.

 

If I were to re-do it, I would consider adding a resonator to the transmission tunnel area to try to cut down on the 500 rpm band in which it gets nasty resonance. However, from what I've read, it is not likely to reduce it enough to make it worthwhile.

 

From 2500-3000 rpm, it is droney. However, there is a simple and cheap solution. Never drop below 3k rpm

 

 

As far as performance goes, from my reading of others' experience, 2"-21/4" is more than sufficient for an l24, and 2 1/4" to 2 1/2" is sufficient for an NA l28 application. Forced induction setups stand to benefit from exhausts larger than 2 1/2".

 

 

As far as headers go, time has shown that their performance gains are nonexistent on street-ish setups. On some setups, they can shave weight, but they do raise underhood temps significantly in many cases.

 

So, imo, go 2 1/2" to a muffler. It's cheaper than headers, street legal, and streetable, cause straight pipes are damn loud.

[palauoriginal]

...straight pipes are damn loud.

 

true facts. not worth it imo

it gets annoying real fast.

[PalmettoZ]

Well I have been considering re-doing my exhaust lately. Right now my exhaust comes out right after the cat and I like the tone of it. The only thing I dont like is the fact that it is directly under me and it kinda gets annoying. I am planning on swapping to a mn47 head with a mild street cam. What my main concern is about how a 3" strait pipe setup would sound on an N/A motor.

 

Or if I went with a pacesetter header and 2.5" strait pipe all the way back, but.... I'm kinda tight on money so that might have to wait for another time.

 

I have a 2.5" exhaust with a magnaflow muffler on it on my 75 280Z if you would like to hear it run. I just bought a new header and exhaust system off of E bay so if you want you can have all the old exhaust except for the new muffler. You can get the same stainless steel muffler that I got from Pepboy's. Has a great tone to it.

 

Scott

[Over the Top]

i've run about 10 different exhaust setups on my 280zx..

the most interesting one was i think a long tube header w/ 2.25 inch piping and a streetable quite muffler.. electronic exhaust cutout right after the header.

start doing freeway pulls and open the cutout in mid gear... teaches you a lot about how these motors pull when you loose back pressure.

[SHADY280]

i have the msa 2.5" setup and 321 header, it really pulls harder when you take the muffler off, but they always tell me to put it back on at auto-x. im over the db level from 50 ft facing the other way!!! i like the system with the turbo muffler, but it really holds the engine back. think i may switch to flowmaster when this one wears out. 3" really would boom and make tons of noise, really its too much unless your race application or turbo

[LeX]

very true. the 3" booms like a mother. When i had it on my N/A with headers and a resonator, it was great for scaring people in parking decks

[ozconnection]

 

As far as headers go, time has shown that their performance gains are nonexistent on street-ish setups. On some setups, they can shave weight, but they do raise underhood temps significantly in many cases.

 

 

What do you mean by "streetish" setups?

 

I can't agree with this part of your response. The rest of it was on the money though.

 

I spent some money a while ago and 'improved' the exhaust system on my L28. Stock N42 head and compression, bottom end, automatic trans with just an MSD and 280ZX ignition upgrade and an Arizona Manifold and a 4bbl Holley. Then I put the exhaust on last. Did dyno figures before and after the change. WOW, big difference to the curves, the exhaust ended up being a set of non tuned length headers and a 2.5 inch single pipe with two 2.5 inch mufflers to keep it 'quiet'. The graph below is of this setup.

 

However, my next system will be a twice pipes setup. I've had a look at the 'science' behind this sort of thing. It seems to be able to offer the best in terms of power and torque production by the way this setup works with the exhaust pulses and resonant tuning. This won't happen unless you have headers.

 

The big single system will reduce backpressure, that why some guys here have said that they felt the motor run heaps better with a change in muffler or no muffler at all. But to get the full advantage of low backpressure and resonant exhaust extraction you need to be running the twin system.

[essdeezee]

I guess I should've been a bit more clear about what I posited.

 

On a street-ish setup= stock compression, near-stock cam, stock-ish induction and fueling.

 

Here's what I mean. The exhaust manifold (or header) is not the restriction to flow in the system. A street-ish setup does not produce enough flow to out-flow the capability of the stock manifold. As long as it is not the restriction to flow, you will see little improvement in power.

 

In your case, you replaced the entire exhaust system from the head back. The performance gains that you have seen are most likely attributable to the reduction of exhaust backpressure that was created by the exhaust itself, rather than the manifold.

 

If only we could go back and install the 2 1/2" pipe on the stock exhaust manifold and check numbers...

[ozconnection]

Very few factory exhaust manifolds are what I would call 'performance items', especially those that were penned 30+ years ago. The way they merge the exhaust gasses together indicates that performance wasn't a high design priority and to be able to improve on this design wouldn't be hard.

 

You've made an interesting point about testing the stock exhaust manifold. I think this is where the definitions become blurred. I agree that a totally stock engine may not flow more exhaust than the manifold can handle but add a cam or do some other flow enhancing mod and at what point will it be realised that the stock exhaust manifold isn't up to the task?? How would you know? Would you bother to drill and tap the manifold and attach a pressure guage to it to see how much backpressure pressure there was? There's always a 'weak link' somewhere in the system and what I'm saying is the sooner you get rid of it, the better. You'd be potentially limiting the performance gained by those mods until the manifold was replaced by a header. It wouldn't be hard to 'run out of flow' with the stock item.....I'd say lose it now!

[kiwi303]

Theres also an upper limit on the size of the pipe that makes sense...

 

 

 

not making a dig at you guys I just had this thread open when OI found that pic, so copied it in as (sorta) relevant (ish)

[Tony D]

Theres also an upper limit on the size of the pipe that makes sense...

 

Twin 2.5" flows like a single 4....or thereabouts, it's in the archives.

[johnc]

Very few factory exhaust manifolds are what I would call 'performance items', especially those that were penned 30+ years ago. The way they merge the exhaust gasses together indicates that performance wasn't a high design priority and to be able to improve on this design wouldn't be hard.

 

A number of Datsun racers here in the US have actually tested the factory exhaust manifolds on the L24/26/28 and they are very good. They are generally better then most header designs (excluding the Nissan Motorsport and the Stahl) for engines that are running less then 280 duration cams and/or have no headwork.

[ozconnection]

A number of Datsun racers here in the US have actually tested the factory exhaust manifolds on the L24/26/28 and they are very good. They are generally better then most header designs (excluding the Nissan Motorsport and the Stahl) for engines that are running less then 280 duration cams and/or have no headwork.

 

That's very interesting...I wouldn't have thought that be the case at all. I'm certain that the companies that produced most of the 'other' headers wouldn't like to read things like this. I know I don't as I'm one of those smo's that bought one!

 

Is there any dyno proof to back up these claims? It's not that I don't believe you, but I do rely on certain 'proof' if that be the case.

 

I have read in Bell's book "Four Stroke Performance Tuning" and others that its a waste of time to run a camshaft with more than 240 degrees duration with an exhaust manifold. A six cylinder engine fires every 120 degrees, so if one were to group the cylinders together in such a way, you could avoid the pressurisation of an adjoining cylinder during the blowdown period. If done this way you could in fact cause a negative pressure in the pipe, 'extracting' the residual cylinder exhaust gas from out of the cylinder. So strong is this effect, it can literally suck some of the intake charge straight out of the cylinder during the overlap period!

 

I really need to see those dyno tests......

[MJLamberson]

It makes since to me, smaller NA engines need decent back pressure.

[ozconnection]

It makes since to me, smaller NA engines need decent back pressure.

 

What do you mean? Please explain.

[johnc]

Is there any dyno proof to back up these claims? It's not that I don't believe you, but I do rely on certain 'proof' if that be the case.

 

The tests were done, at least the one I witnessed, back in the mid 1990s as part of a tuning effort for L6 engine running in SCCA's ITS class. The person that did the testing I witnessed was Javier at JG Engine Dynamics (now JG Edelbrock). Keith Thomas, Chet Whittle, and Jim Thompson (of Sunbelt Racing Engines) did their own series of tests in early part of this century and came to similar conclusions. The Stahl and the Nissan Motorsports headers did show a horsepower advantage over the stock exhaust manifold and all other aftermarket headers.

 

FYI... the headers helped blueprinted "stock" L6 2.4L engines that made from 185 to 205 horsepower on certified engine dynos.

[MJLamberson]

What do you mean? Please explain.

 

To be honest Im not sure how it works. BUT, I have seen and felt an engine loose torque from a larger exhaust... maybe somebody who understands back pressure can chime in?

[johnc]

Backpressure has been discussed ad nauseam on this site and many others. Search is your friend.