Which exhaust manifold and downpipe do I need?

[damesta]

Quick question for those in the know. I have a 72 620 with an L20b and A87 head. It has some kind of super leaky long tube header with 2.5" exhaust piping that hangs way too low for a lowered truck....so I'm trying to go back to a cast oem manifold and a downpipe that will tuck up nicely and potentially finish it off with 2" pipe. Question is what year manifold/downpipe do I need? Ive found some 74/75 setups but have read mention that I should get a very early L16 set but I'm not sure what the difference is? Would a 510 set work or is the downpipe 620 specific? Any help is appreciated, couldn't find any answers searching.

[Draker]

The important part is if the head is round or square exhaust ports. Other factors include you probably don't want a manifold that connects to the intake to warm it up. Those are junk.

 

510 manifolds have a different output flange, where I think the 620's are a 3 bolt round flange. I'm sure Mike will be here soon with pictures to show the differences.

[G-Duax]

Sounds like the same POS header I have on my '73 620.

Mine had round ports, that someone ground on to work with a square port head.

I think it was for a 4WD truck, but what ever....

It hangs too low, and is a pain in the arse to work around, and can't be removed without lifting the engine up, and the trans can't be removed when it's in place.

 

Anyway, I bought one of the El-Cheapo 510 headers off eChinaBay,

(that used to be a $100 5-6 years ago, and now are nearly $280, which is a rip off for the quality)

and am reworking the collector to fit around the torsion bar.

Also added an o2 bung so I can monitor the fuel ratio, and an EGT bung.

Found a nice tapered exhaust adaptor to reduce the collector outlet to 2", to fit between the bell housing & torsion bar, where it will taper back out to 2.5" tail pipe after a foot or so.

Note that I heated, and reformed the transition from the 4 primary tubes to the collector outlet, to more mimic a true merge collector.

 

 

Top view

 

I may add a port at the end of the collector for a crank case vacuum generator.

Not as good as a vacuum pump, as they typically only pull a few inches of vacuum, but better than nothing.

 

Said chinaBay header:

El Cheapo eBay header (that isn't cheap any longer)

 

[banzai510(hainz)]

I believe they are made here by Trimill in California. I have one also and havent used it as I perfer the stock cast iron one. I also had it ceramic coated, otherwise they rot rust in about a month.

[wayno]

Just try to find an L16 exhaust manifold without the smog shit on it if you can and have the 2 into one piece made to fit the 2 inch exhaust you mentioned.

Otherwise try to find a slightly used shorty header, they are out there, but I am not sure about the area you live in.

[G-Duax]

2 hours ago, banzai510(hainz) said:

, otherwise they rot rust in about a month.

 

I keep hearing this, but fail to understand the issue.

The header on my truck was on it way before I bought it 14-15 years ago.

Maybe the climate ?

But even then, I had a VW bug back in the late '60s that I had installed a header on, and didn't have issues with that either.

[banzai510(hainz)]

issue is they will look like crap. As most Datsun kids will just run the cheap black paint in there and looks like shit in a few months as every non ceramic coatted one does.

These fit loose also.

[wayno]

They last longer than that Hainz, I usually got 2 to 4 years out of them cheap headers made in CA by Top End Performance before they needed repaired, and after being repaired I got another 2/3 years before replacing it with another one.

There are these better headers out there with this oval tag on them called Trimill that are way better quality, I have a Hooker header for the L block, and I also have a heavy Stainless Steel(??) one made out of a thicker metal.

But in the end the stock 521 cast iron exhaust manifold without the smog shit is the best bang for the buck, they last for a very long time and don't leak or make this leaking sound like a header does, I have this what I believe to be a 1980 720 header on my work truck that one can hear the exhaust coming out of the head, it is not an exhaust leak but it sounds like one at lower RPMs.

So far they all look like crap to me after being on the vehicle for a while, although I have never mounted the heavy one I have that has not been used or at least it doesn't look like it has been used, I believe it is for an L16 510.

[datzenmike]

'70-'72 521

'68-'73 510

'73 620

 

These will all have the better 4 into 2 cast iron exhaust. Some later L18 engines had similar ones but there were also some that were not discrete 4 into 2.

 

 

You want the one on the left with 1 and 4 joined and 2/3 joined. The right one is a waste of time.

 

Some have air injection tubes some don't. Just remove them and put a pipe plug in or weld the holes up no big deal. Some later ones have fins on them for the warmed air for the ATC on the air filter.

 

 

The ONLY advantage to a tube header is a weight savings. Only a very modified engine will gain from tubular headers.

 

The L20B head sits 3/4" or 2cm higher than thew L16/18 so have a custom down pipe made or a stock one will sit higher by this amount and may hit the under side of the floor.

[Charlie69]

This is using the Mike Klotz flange design.

 

L engine flange and down pipe.  Down pipe outlet 2". Contact Martin Guerra at clevermartin01@gmail.com

 

 

 

 

 

[damesta]

13 hours ago, datzenmike said:

'70-'72 521

'68-'73 510

'73 620

 

These will all have the better 4 into 2 cast iron exhaust. Some later L18 engines had similar ones but there were also some that were not discrete 4 into 2.

 

 

You want the one on the left with 1 and 4 joined and 2/3 joined. The right one is a waste of time.

 

Some have air injection tubes some don't. Just remove them and put a pipe plug in or weld the holes up no big deal. Some later ones have fins on them for the warmed air for the ATC on the air filter.

 

 

The ONLY advantage to a tube header is a weight savings. Only a very modified engine will gain from tubular headers.

 

The L20B head sits 3/4" or 2cm higher than thew L16/18 so have a custom down pipe made or a stock one will sit higher by this amount and may hit the under side of the floor.

 

How bad is the one on the right? Like a complete waste of time don't buy it bad....or just not quite as good as the one on the left? Curious because I can get one locally cheap.

[Stoffregen Motorsports]

I may be mistaken, but I think the two pictured above are identical in shape, so if nothing else, you get the one on the right and install it until you can find the one on the left.

 

Am I right? They are the same shape, correct?

[datzenmike]

No where near the same. Inlets and outlets are the same but internally the left one pairs 1 and 4 cylinders together and out the closest of the two outlet openings. Cylinder 2 and 3 join and exit from the farther of the two outlet openings.

 

The right side one dumps 2 and 3 with 1 joining from the right side and 4 from the left. They appear to me to all be on the same plain.  I'll look for more pictures tonight that show the thing from another angle.

[banzai510(hainz)]

for a basic L motor I think they would be better than the ones with the airinjection ports. Dont pay more than 50$  25 is better as soem guys have stacks of these laying around.

 

That Y pipe is awesome!!!!!!!!!!!

[wayno]

In my opinion the one on the left is the best, but the one on the right is better than a Top End Performance shorty header.

[datzenmike]

 

EGR was on the '74 Datsuns so this is likely an L18 exhaust. Again the pipes do not appear to be paired, but mashed together. The only reason for the two pipe outlets is to match existing down pipes.

 

Compare to a 'good' one...

[Stoffregen Motorsports]

20 hours ago, datzenmike said:

No where near the same. Inlets and outlets are the same but internally the left one pairs 1 and 4 cylinders together and out the closest of the two outlet openings. Cylinder 2 and 3 join and exit from the farther of the two outlet openings.

 

The right side one dumps 2 and 3 with 1 joining from the right side and 4 from the left. They appear to me to all be on the same plain.  I'll look for more pictures tonight that show the thing from another angle.

What I meant was, are they interchangeable? If you had one installed, could you swap it out for the other without any modifications?

 

I think so, but don't recall. I never ran manifolds on my 510s. Always Nissan Motorsports headers.

[datzenmike]

I think they would be. The down pipe for a car might be bent differently than a truck because of the car steering and the truck torsion bars? The picture I posted may have introduced camera lens distortion. Perhaps they don't lie the same.

[gene knight]

Pm sent 

Edited November 3, 2018 by gene knight