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Header and exhaust pipe sizing.


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Hello, so to go with my 2 different builds im trying to figure out if there is a happy medium for exhaust sizing.

 

Im doing a L18 (1854cc with new pistons next year) dual 40mm solex carbs, a87 peanut with 44mm and 38mm valves, big ish cam (dont know the specs)

 

And

 

Future build is a z20 long rod with the parts above. I do realize these have different block heights.

 

I have a good friend that does beautiful custom exhaust, chassis, cage and suspension work. He is a real artist when it comes to tig welding. So Im going to have him make me a stainless header and exhaust. For what hes going to charge me I cant say no.

 

Reading through my how to modify your datsun book and reading other material along with seeing what works on other platforms. Im trying to figure out my proper pipe sizing.

 

My original thought was

4-2-1 header

1-5/8 primary

Unsure on secondary diameter 

total length of 32-34in for the runners

2-1/4 collector

2-1/4 exhaust.

 

Now im thinking 

4-1 header

1-1/2 primary stepped to 1-5/8

32-34in primary length

2-1/4 collector

stepped exhaust being 2-1/4 then after the axle stepping to 2-1/2.

 

I "feel" like this might be the better setup/compromise for the 2 engines

 

Im just trying to figure out my best route for a street car that needs some midrange tq but also doesnt fall on its face when reving it out. I know the L18 and Z20 have different powerbands.

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Don't throw away your cast iron header. Save it.

 

You're not going to see much improvement as the stock exhaust is 4 into 2 into1 to begin with and not at all restrictive. You may gain a bit and even more as the engine becomes more modified. I wouldn't go 4 into 1, but that's me. If possibly going to an L20B or LZ something allow for the header to rise another 3/4" and still clear the floor.

 

 

The exhaust valve is 1.49".  How far around the square exhaust opening is it on the head? If 4.7" then a 1.5" pipe is perfect circumference and just needs to be squared up. There would be a step or lip if the pipe was larger than the port. I suppose you could port match it. IIRC a (slightly) smaller diameter favors low speed torque while maximum diameter favors extreme high RPM.

 

As hot exhaust cools quickly after leaving the head it contracts and takes up less room so going to a larger pipe after the axle is almost backwards. On a stock L20B I would run a 2" exhaust. What's the stock 510 exhaust pipe? 1 3/4"???? 1 7/8"

 

diameter/cross section

1.75"....... 2.4 sq in

1.875"..... 2.75 sq in*

2.0"......... 3.14 sq in

2.125"..... 3.54 sq in

2.25"....... 3.97 sq in.... doubling a pipe diameter increases the cross sectional area by 4 times not double, so a small diameter increase make a really large increase in flow.

 

If the stock 510 exhaust pipe is 1 7/8" (1.875") then going to a 2 1/4" (2.25") is a whopping 44% increase, or enough for a 2592cc engine over an L18. A bit ambitious for an L18 but plenty of head room for a future 2 liter engine. I wouldn't go higher.

 

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Solid logic, good point about the exhaust valve size and its correlation to pipe diameter. Looking at the nismo comp header had me second guessing my original tri y plans.

 

2.25in exhaust it is.

 

I wouldnt throw the header away anyway. I havent seen any badging or engraving but when I bought the car I was told it was a Hooker header. It is cast and and a 4-2-1 and 2 piece just like the factory.

 

So perhaps doing the tri y with 1.5 primary 1.75 or 1-7/8 secondary to a 2.25 collector would be the best for bet my application.

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Mike, I know your numbers are based on math, and math is a good tool for reasoning, but the fact is, the L motors respond well to a good header and a 2" to 2.5" exhaust. Even the blueprinted stock L16 ITC engines that I was building back in the '90s made more power with a 2.5" exhaust. Every Datsun engine expert recommends at least a 2.25" exhaust for performance. It is known.

 

If you're going to build the 2.0L, start off on the right foot with the proper exhaust. You've got the header specs nailed down, but you may consider a 4-2-1 collector instead. It will be harder to fit under the car, but they do fit. We used to use the Flowmaster D-port collector. I don't believe they come in stainless though. The 4-1 header is good for a higher RPM range, and totally suitable for the 2.0L also, but maybe step down into a reverse cone collector. I think the reverse cone collector for a 2.5" exhaust would neck down to 2" and then right up to 2.5".

 

Stepping the exhaust, I tried that recently on my 3RZ swapped '83 Toyota and it did not work out that well. Of course that's an apples to oranges comparison. I have built V8 exhaust systems that dump into a 3.5" section of tube, then into the muffler, and then 3" out all the way back, but again, apples and oranges.

 

If you go with a 2.5" system, from the collector back, you won't be disappointed.

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33 minutes ago, Stoffregen Motorsports said:

Mike, I know your numbers are based on math, and math is a good tool for reasoning, but the fact is, the L motors respond well to a good header and a 2" to 2.5" exhaust. Even the blueprinted stock L16 ITC engines that I was building back in the '90s made more power with a 2.5" exhaust. Every Datsun engine expert recommends at least a 2.25" exhaust for performance. It is known.

 

If you're going to build the 2.0L, start off on the right foot with the proper exhaust. You've got the header specs nailed down, but you may consider a 4-2-1 collector instead. It will be harder to fit under the car, but they do fit. We used to use the Flowmaster D-port collector. I don't believe they come in stainless though. The 4-1 header is good for a higher RPM range, and totally suitable for the 2.0L also, but maybe step down into a reverse cone collector. I think the reverse cone collector for a 2.5" exhaust would neck down to 2" and then right up to 2.5".

 

Stepping the exhaust, I tried that recently on my 3RZ swapped '83 Toyota and it did not work out that well. Of course that's an apples to oranges comparison. I have built V8 exhaust systems that dump into a 3.5" section of tube, then into the muffler, and then 3" out all the way back, but again, apples and oranges.

 

If you go with a 2.5" system, from the collector back, you won't be disappointed.

Would the 2.5in exhaust show a loss of tq in the low to mid range on the L18?

Ill be running the L18 bored to 87mm 10-10.25:1ish cr for 1-2 years.

 

Right now my exhaust tapers from 2in at the collector to 2.5in at the muffler. I dont remember if there was a felt difference good or bad when I did that. The car was pretty much strait piped when I bought it so I was looking to bring the noise down so I immediately put a magnaflow straight through muffler and resonator in.

 

For the collector my buddy showed me that he makes his own

Screenshot-2021-03-13-10-59-50-1.png

Here is a pair he just built for a blown big block.

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Those collectors are nice, but the transition is rather quick. More length in the taper I think is beneficial.

 

A stock L18 might show diminished lower end torque with the 2.5", so that's where the 4-2-1 comes into play. Your L18 is not stock though. If you've got enough cam for the 10:1, the 4-1 with the 2.5" would be ideal, not too big.

 

The reverse cone helps scavenge, so it is likely only felt at higher RPMs.

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20 hours ago, gumby510 said:

 

 

Im just trying to figure out my best route for a street car that needs some midrange tq but also doesnt fall on its face when reving it out. I know the L18 and Z20 have different powerbands.

 

2 hours ago, Stoffregen Motorsports said:

Mike, I know your numbers are based on math, and math is a good tool for reasoning, but the fact is, the L motors respond well to a good header and a 2" to 2.5" exhaust

 

 

 

Was erring on the side of caution and favoring his mid range over all out high revving HP. Z Train posted a dyno sheet for an engine he had. The A87 head had the smaller intake ports than the L20B heads and the mid range torque numbers were crazy high. Apples and oranges... I know but less that huge pipes favor higher gas speeds and improve volumetric efficiency but not always good for extreme high revving.

 

What we need is a VEA (variable exhaust aperture) a pipe that expands as the revs go up keeping the exhaust speed always at optimal.

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1 hour ago, Stoffregen Motorsports said:

Those collectors are nice, but the transition is rather quick. More length in the taper I think is beneficial.

 

A stock L18 might show diminished lower end torque with the 2.5", so that's where the 4-2-1 comes into play. Your L18 is not stock though. If you've got enough cam for the 10:1, the 4-1 with the 2.5" would be ideal, not too big.

 

The reverse cone helps scavenge, so it is likely only felt at higher RPMs.

So you think to keep the mid range tq acceptable do a 4-2-1 but use a 2.5in collector and 2.5in exhaust, not doing something like 2.5in collector then a reverse cone to 2.25in to the axle then bumping back up to 2.5in? Only reason I keep bringing up stepped exhaust is because I did that on my na s2000 which that had favorable results (stepped tri y header with 2.5in collector to stepped cat delete 2.5-2.75in and 2.75in exhaust.)

 

Sense I dont have the cam specs here is a video of it idling at 900rpm. This is with the 2-2.5 tapered exhaust.

https://youtube.com/shorts/Z7wRyNl8oxw

 

 

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21 hours ago, datzenmike said:

Was erring on the side of caution and favoring his mid range over all out high revving HP. Z Train posted a dyno sheet for an engine he had. The A87 head had the smaller intake ports than the L20B heads and the mid range torque numbers were crazy high. Apples and oranges... I know but less that huge pipes favor higher gas speeds and improve volumetric efficiency but not always good for extreme high revving.

 

What we need is a VEA (variable exhaust aperture) a pipe that expands as the revs go up keeping the exhaust speed always at optimal.

 

20 hours ago, gumby510 said:

So you think to keep the mid range tq acceptable do a 4-2-1 but use a 2.5in collector and 2.5in exhaust, not doing something like 2.5in collector then a reverse cone to 2.25in to the axle then bumping back up to 2.5in? Only reason I keep bringing up stepped exhaust is because I did that on my na s2000 which that had favorable results (stepped tri y header with 2.5in collector to stepped cat delete 2.5-2.75in and 2.75in exhaust.)

 

Sense I dont have the cam specs here is a video of it idling at 900rpm. This is with the 2-2.5 tapered exhaust.

https://youtube.com/shorts/Z7wRyNl8oxw

 

 

I believe both of you are correct. This could be tuned with stepped tubing (after the header collector). I only know what I know, but if one was to spend some time testing these ideas, I am sure some power is on the table.

 

Though this article does not do a great job explaining the ins and outs of the collector transition, it does show different styles. The longer style transition is the one I prefer, but I have yet to play with the megaphone style. - https://burnsstainless.com/blogs/articles-1/merge-collectors

 

I also feel like building one exhaust suited for both engines means projecting into the future. What are your future needs? If you don't want to build the exhaust twice, I would go with the 4-1, mid length transition merge collector and a 2.5" tailpipe. The muffler should be at the end of the exhaust, near the rear bumper.

 

I'd love to see what you come up with.

Edited by Stoffregen Motorsports
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21 hours ago, Stoffregen Motorsports said:

 

I believe both of you are correct. This could be tuned with stepped tubing (after the header collector). I only know what I know, but if one was to spend some time testing these ideas, I am sure some power is on the table.

 

Though this article does not do a great job explaining the ins and outs of the collector transition, it does show different styles. The longer style transition is the one I prefer, but I have yet to play with the megaphone style. - https://burnsstainless.com/blogs/articles-1/merge-collectors

 

I also feel like building one exhaust suited for both engines means projecting into the future. What are your future needs? If you don't want to build the exhaust twice, I would go with the 4-1, mid length transition merge collector and a 2.5" tailpipe. The muffler should be at the end of the exhaust, near the rear bumper.

 

I'd love to see what you come up with.

I dont want to build the header twice, Id be ok with doing the exhaust twice.

 

I have read that article a few times. Between the short, long and megaphone I was favoring the long.

 

Im very intrigued by the nismo japan factory race header. Tri y, stepped primarys

20210314-204153-1.jpg

 

So id maybe skip the stepped primary but do something similar to this. I do like the idea of a long transition reverse cone collector, maybe trying something like you recommend as in 2.5in to 2in then back to 2.5in for the exhaust. Or I might try 2.5in collector with the reverse cone down to 2in then back up to 2.25in to the axle then 2.5in for the axle back. I can have v-band clamps installed in a few places so I could swap out pipes.

 

Im going to do a little more research on other similar displacement engines and see what they do for piping size tri y lengths (4ag, b18, beams motor and a few other) I know thats apples to oranges. Still keep the 32-34in pipe length but make the collector transition a bit longer than normal. 

 

Here is what my s2000 header is.

Our Ballade Sports Exhaust Manifold features 5 step piping size with each step helping in anti-reversion, and also backing up of exhaust flow. Weighing at 12lbs less than stock (OEM is 25lbs), the primary runners are 1.75 inch, to 1.875 inch, to 2.00 inch, to 2.25 inch, to 2.5 inch merge collector. Stepping the header pipe size helps direct flow and increase scavenging, thus allowing for a faster exit. The S2000 firing order is cyl 1-3-4-2, therefore our runner design is sequential, creating a venturi effect. This application fits standard factory catalytic converter location. Wheel horsepower gains are approximately 10whp mid-range dependent on application setup

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I got rid of the stock 4 into 1 log manifold that is co-joined to allow exhaust heat to warm the intake under the carburetor. I put an earlier L16 4 into 2 manifold on and (insane though the idea is) fitted a 240sx KA down pipe to the manifold. The down pipe continues the 2 pipe down and under the car before merging into one where the stock L16 joins immediately below the manifold. From exhaust valve to final merge is well over 30+ inches with 1/4 and 2/3 pipes the longest. 

 

Does it make any power/torque? Beats me but the stock manifold is horrible to look at and this separates the exhaust pulses the longest. Does not run worse that's for sure, and appears to be a better exit from the head and gradual merge. Often it's a lot of small improvements that on their own that are modest increases, but added together make for a combined definite difference. I did this to be sure there was minimum resistance in the exhaust before adding R-1 motorcycle carburetors.

 

'75-'77 L20B co-joined 4 into 1 manifold.

fId8YzE.jpg

 

L16 and modified 240sx down pipe.

mdH9tOQ.jpg

 

mRhIAwH.jpg

 

 

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  • 2 weeks later...

2.25 -2.5 is good. The stock manifold is better than one of those shorty headers so stay away from those. 
 

the bigger the pipe the louder it will be as well no matter what muffler is on it. 

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On 3/25/2021 at 10:04 AM, scooter said:

2.25 -2.5 is good. The stock manifold is better than one of those shorty headers so stay away from those. 
 

the bigger the pipe the louder it will be as well no matter what muffler is on it. 

There is no intention on running one of the ebay headers. It looks like I have a factory L16 4-2-1.

Im going to have a custom header made.

 

I think after I tune my sidedrafts ill dyno the car as is. Then with exhaust and after that with the custom manifold.

 

So taking what worked for my s2000. Ill go with a 4-2-1 sequential paired. Ill step the primary from 1.5 to 1-5/8 then after the first merger 1-3/4 or 1-7/8  to 2in a burns long transition 2-2.5 collector then a short reverse taper to 2.25in probably being closer to the 34in length runners. to the 2.25in exhaust which will taper to 2.5in after the axle. It will be all v-bands so if I decide to change things out it will be simple. For the dyno ill have a 2.25in silencer to put in the muffler to see if there is any difference in output.

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On 3/15/2021 at 3:02 PM, banzai510(hainz) said:

Baz in Austriaila said it good for 140-150 with the cast iron stock manifold and I believe him

 

 

Before and after would be great. But not an open header. I'm guessing that the stock is sufficient for the majority of driving and what gains you might get from a made header are less than you expect and at high RPMs. A before with the down draft and after with the side drafts would be instructional.

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2 hours ago, datzenmike said:

 

Before and after would be great. But not an open header. I'm guessing that the stock is sufficient for the majority of driving and what gains you might get from a made header are less than you expect and at high RPMs. A before with the down draft and after with the side drafts would be instructional.

I agree, no open header. I also agree that the stock L16 4-2-1 for everyday driving is probably more then fine.

My weber downdraft is currently on my wifes car. I dont really want to put it back on but that would be better for doing a base line.

 

Power wise im not expecting to much. 10hp and tq would be great in the mid but I think ill be lucky to see that.

 

Ive come to grip that it is more money than its worth.

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This is a very interesting thread. I’d like to do something similar but making it myself. 
 

Fortunately I’ve got plenty of time to kick this around, since I’ll be painting my truck this spring.  I’m interested to see what you come up with.

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  • 2 weeks later...

So is the consensus for a built L20b a 2 or 2 1/2” exhaust from the collector back (using stock exhaust manifold)??

Edited by d.p
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The stock cast manifold is 1.5" X 2 correct? That 1.5" X 2 pipes is the same as a 2 1/8" single pipe. 

 

As the exhaust is largest in volume as it exits the combustion chamber and it shrinks in volume as it sheds heat, then the pipe could reduce in diameter (slightly)  as you get farther from the head not get larger. A 2" would be sufficient. A 2.5" pipe is 56% larger than a 2" pipe. The answer is 2.5" because it's obviously... bigger. And as everyone knows, other than vaginas, bigger is always better. 

 

 

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