L20b exhaust manifold questions

[Grimlid]

Hey Guys,

 so just setting up to swap an l20b into my 510. I'm aways off and still have to get my transplant rebuilt but I want all my goodies ready to go in advance....

The l20 I bought came without an exhaust manifold. My understanding is that the height of the new motor may pose a few issues with the exhaust manifold.

 Does anyone know if the 510 stock exhaust manifold will bolt up to an l20 ?(I assume no but I dont have access to measure the motor itself) likely a dumb question but not the first one i've asked.

 Does anyone have an opinion on headers or stock manifold. I read a few negative reviews on l20b stock exhaust manifold but no real reasons or data (just they suck was what I read).

 Will there be any issues with the height of a stock l20b manifold bolting up in the 510 engine compartment ? I heard there may be....

Any feedback appreciated thanks

[iceman510]

A few things to watch for.  The L16 manifold will readily fit the L20B cylinder, presuming that it is a rectangular port head.  Datzenmike will likely chime in and say it will fit a round port head as well, which it will bolt up, but not the best combination.

 

Given the L20B block is taller, the manifold will end higher above the exhaust collector pipe, and connecting them may lead that exhaust pipe to hit the front floor/lower firewall.

 

Also due to the height, you may have contact with the hood from either the valve cover, or air cleaner.  You did not mention what air cleaner assy or carb you plan to run.

 

These all generally can be worked around with modifications, as thousands have done over the years.

[datzenmike]

There are two L16/18 exhaust manifolds, you want the earlier ones that separate 1 and 4 from 2 and 3 into the twin down pipe where they merge into one.

 

Good one on the left........................................................................... not so good one on the right

 

They will fit on all heads even the '78-'80 W58 round exhaust port ones. All L20B exhausts just dump into a single pipe, the '75-'77 being the worst in my opinion as the exhaust is bolted to the underside of the intake to warm it, but more likely just baking it. If you go to a header on the '75-'77 L20Bs you have to find some way to seal the hole in the bottom of the intake. I had a '78-'80 intake so I just swapped it.

 

Nissan spent a lot of money engineering their 4 into 1 'cast iron header'. Might as well take advantage of it of just keep it.

 

 

Headers... almost never fit without some 'adjustments', dump more heat under the hood, louder, because of flange thickness differences the bolts can't tighten properly, cheap ones need maintenance to repair weld cracks from heat and or rust unless you get ceramic coated which last longer but $$$.

 

The stock 4 into 2 cast iron header works as good to about 150 hp before a bought header may start to lead. To take advantage of a bought header the engine should be modified. Stock manifolds have none of the disadvantages above, but the header is lighter. If you buy a header save your stock 4 into 2 iron manifold and what's left of your down pipe so you can switch back. It's an expensive experiment to find no gain on a stock engine. This is my experience  in the late '70s for a header on my 521. I was extremely underwhelmed and disappointed with no gain but I got to tighten the collector bolts and replace the gasket every three months. Unfortunately I threw the stock manifold away and couldn't go back.   

 

The L20B is only 2 cm taller, that's 3/4" so take a look under your feet where the exhaust is now and imagine. I don't remember anyone saying that it was impossible to fit L20Bs into 510s because of exhaust clearances. If there are, it must be easy to correct.

[Stoffregen Motorsports]

I always prefer a nice header over a cast iron manifold. They sound better, but yes, most headers you can buy absolutely suck and they do create more under hood heat. If building a header, use thick flanges and stainless. For collectors, I try to use v-band clamps where possible.

 

Troy Ermish sells a nice L20B header for a 510. They are nicely built, but they don't come with any kind of collector flange (because of how tight they are to the floor of the car). These will use a strap type clamp which is good at sealing the connection. He does get a bit of money for them. Over $700 for a mild steel ceramic coated header, and over $2k for a race stainless header. https://ermish-racing.com/exhaust-systems-mufflers-headers

 

Everyone else here is going to suggest a cast manifold for ease of fitment and less headache over the long term,