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Datsun 620 ultimate SS exhaust


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#21 Beastlikethat1

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Posted 12 January 2018 - 07:38 PM


I can't remember what the stock L20B pipe diameter is, may be 2" but there's no mention of cams, head work and induction. That said I doubt it will flow as much as a 3.5 liter engine. The cross section of a 1 7/8" pipe is 2.75 square inches. If you go to a 2.5" pipe the cross sectional area jumps to 4.9 square inches. Now that's an increase in area of 77% so if a 1/78 pipe works well enough for a 2 liter engine a 2.5" pipe will support a 3.55 liter engine.


Mike, as working at an exhaust shop for 4 years I can agree with you on this. We are one of few shops who only do SS and bend manderal in house. We gurantee 3" manderal tubing for up to 600hp so it would depend on the numbers we are talking, but yes 2.5" should be enough for a 3.5L engine that's NA. Many engines up to 5L even use 2.5in tubing, really the displacement doesn't mean much as far as tubing size is concerned. Just HP and Torque. Or if turbo charged.

#22 datzenmike

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Posted 12 January 2018 - 08:05 PM

Yeah, just saying that if 1 7/8" for L20B then 2.5" would be roughly able to support 3.55 liters. Naturally the factory will run the smallest they can get away with to keep noise and costs down and still have 'good enough' performance. Doubling a pipe diameter increases the cross section by 4 times so a little change makes a large difference. A turbo 2 liter could definitely produce the exhaust of an engine twice the displacement... and more.  


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#23 Stoffregen Motorsports

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Posted 13 January 2018 - 09:42 AM

If 1 7/8 pipe will flow an L20B then a 2.5 pipe will flow 77% more air or a stock 3.5 liter.  

 

 

 
I can't remember what the stock L20B pipe diameter is, may be 2" but there's no mention of cams, head work and induction. That said I doubt it will flow as much as a 3.5 liter engine. The cross section of a 1 7/8" pipe is 2.75 square inches. If you go to a 2.5" pipe the cross sectional area jumps to 4.9 square inches. Now that's an increase in area of 77% so if a 1/78 pipe works well enough for a 2 liter engine a 2.5" pipe will support a 3.55 liter engine.

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.



#24 datzenmike

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Posted 13 January 2018 - 11:03 AM

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.   


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#25 5t341tH

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Posted 13 January 2018 - 11:33 AM

Where’d you get that sexy flange

#26 Str8jacket

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Posted 13 January 2018 - 12:43 PM

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?

#27 flatcat19

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Posted 13 January 2018 - 05:51 PM

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?

You can't hang if your nuts haven't dropped...it's physics


#28 distributorguy

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Posted 13 January 2018 - 06:13 PM

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.  



#29 Str8jacket

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Posted 13 January 2018 - 08:46 PM

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.

#30 Stoffregen Motorsports

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Posted 15 January 2018 - 12:05 PM

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.



#31 banzai510(hainz)

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Posted 15 January 2018 - 12:31 PM

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


Throw on some Weber sidedrafts, Rising Sun hood.... call it good

#32 datzenmike

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Posted 15 January 2018 - 05:48 PM

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.


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