Datsun 620 ultimate SS exhaust

[Str8jacket]

Math doesn't change the fact that a stock blueprinted L16 with a DGV and a Nissan Motorsports header makes the most power (on a dyno) with a 2.5" exhaust.

 

Reasoning it to death won't change the truth. It just works with a larger pipe.

 

I use the L16 as an example, but the same can be applied to any L4. 2" is good, 2.25" is also good, and if you can handle the tad bit of extra noise, a 2.5" is the right choice for a spirited driver.

Do you have a pic of a motorsports header?

 

I dont really have a problem of the 2.5in exit, I just think an extra 15in-20in of the 1 3/4 would have worked better.

 

In other pics it appears to have twin mikunis and a cast exhaust mani.

 

If you rev the engine with out air cleaners on do you get a cloud of fuel standing off the stacks at a certain point in the rev range?

[flatcat19]

I think the real question for the OP is when is he gonna start selling down pipes for the rest of us L motor guys?

[distributorguy]

Look up PipeMax software for designing exhaust systems - as it calculates tubing size and length based on the exhaust port size in the head.  Its a crude program, but it kicks out some valuable dyno proven data.  

 

If anyone needs a header flange, I made a couple extras for the rectangular port L-series head.  Laser cut mild steel, oversized to push the tubing into the ports and be ample size.  

[Str8jacket]

Look up PipeMax software for designing exhaust systems - as it calculates tubing size and length based on the exhaust port size in the head. Its a crude program, but it kicks out some valuable dyno proven data.

Pipemax is what i used to size my headers, and the intake for that matter, plus he is about to release a new version hopefully by the end of the month.

[Stoffregen Motorsports]

And it works well with open exhaust also if reasoning it to death. But in the real world works just fine with a smaller pipe and there's been no mention of a header or even if the engine is modified. At some point the law of diminishing returns set in.   

Reasoning to death. That's exactly what you're doing.

 

I am saying that real experience shows that a 2.5" is not too large for an L4.

 

Don't keep throwing numbers out that confuse people. Let experience speak.

[banzai510(hainz)]

2.5 is too big for a L motor!!!!!!!!!!!!!! yep just like Stroff said

[datzenmike]

Math doesn't change the fact that a stock blueprinted L16 with a DGV and a Nissan Motorsports header makes the most power (on a dyno) with a 2.5" exhaust.

 

Reasoning it to death won't change the truth. It just works with a larger pipe.

 

I use the L16 as an example, but the same can be applied to any L4. 2" is good, 2.25" is also good, and if you can handle the tad bit of extra noise, a 2.5" is the right choice for a spirited driver.

 

Who said anything about DGV and Nissan Motorsport header???? There's been no mention of header, carb or even cam here only that it's an L16. Of course a larger pipe will make more but at some point the law of diminishing returns sets in, even more so on a stock engine. 

 

 

Reasoning to death. That's exactly what you're doing.

 

I am saying that real experience shows that a 2.5" is not too large for an L4.

 

Don't keep throwing numbers out that confuse people. Let experience speak.

 

You can run any pipe you like but it's more than you need is all.

 

Nothing confusing about math. Double the diameter of a pipe and you get 4 times the cross section. Work it out or ask someone. If you go from a 2" to a 4" pipe it's the same as running 4 X 2" pipes except 4 pipes would have more surface for exhaust rub against so a single 4" would flow better. A small change in pipe diameter makes a huge difference in flow.

[distributorguy]

A lot of things come into play.  Wall friction, heat loss, back pressure, overall tube length, etc...  In the end, experience and testing different systems on a dyno is what works.  The results are not always what you expect.  PipeMax taught me not to guess based on industry standards, but their numbers are assuming no internal turbulence is being caused by welds, joints, or kinks that potentially hinder flow.  Getting to play with a flowbench teaches you how important pie cuts can be - both to add "length" to an uneven set of header tubes, and how damaging they can be to flow when you need the most you can get.  

[Beastlikethat1]

Sorry for late reply but the flange was made by me, I plasma cut it out of steel and then drill pressed the holes out.

[2wheel-lee]

Though late in the discussion, I rerouted the exhaust on my stock '75 L20, and the stock exhaust was 1-3/4".

Since I got rid of the torsion bars, I routed it above all the cross members.  

 

I didn't go larger, because an SR20 will be going in later and all the cross members will be rebuilt to fit 2.5" piping. 

[5t341tH]

how is the radiant heat in the cabin with the piping above the crossmembers? I'd like more ground clearance especially now with the coilovers installed. I want to move it up!

[2wheel-lee]

I haven't really driven this truck much so I don't know how it is, but years ago I had the exhaust run above the cross members - even with torsion bars! - and I don't recall heat being an issue. 

 

If you did find it to be an issue, there are a lot of heat barrier products you could use. 

 

Wait...are you Ryan? If so, we've chatted a bit on facebook. I'm just up Beach Blvd from you. If you're going to be doing an SR20, you won't fit 2.5" piping above the stock cross member - well, not likely, even if you do cut off the torsion bar bolt tabs. It would be tight. When I do install mine, I will replace that cross member. 

[5t341tH]

Yepp it's me. I will measure how much space is above the cross member. I want a 2.5" pipe. I would also be willing to use oval piping