Parts Compatibility

[Randalla]

I'm cobbling together an exhaust system for my 620 with an L18 motor. I have an A87 head and N23 exhaust manifold. I think both are square port, but need to know for sure if they are compatible on my truck. If so, I'm in need of a short section of a down pipe with flange to connect between the exhaust manifold and the exhaust pipe going to the muffler. I only need maybe 10" worth. Thoughts?

[datzenmike]

Only the '78 and up L20Bs had the round exhaust port W58 heads. W58 head with steel liners...

 

 

 Your head and exhaust are square although the square port exhaust manifold will also fit the W58 head.

 

Good luck finding a two into one down pipe. They are a few years short of 50 years old. Mklotz70 had a bunch of flanges water jet cut out years ago. One of those and some inch and a half pipe and a welder you could make one. You have the manifold to trace the shape out with.

 

I found a never used thrown out 240sx down pipe and removed the heat shields....

 

Cut the flange off. Slit the pipes and closed the gap to narrow to 1.5"? Put the flange on.

 

 

 

Put in car and lined the pipes up to clear and tacked in place. (realistically, about 4 times to get right) Removed and welded them permanent.

 

 

Later removed for O² sensor. Home made gasket and SS studs.

 

 

You may have to do something similar.

[Randalla]

Excellent information Mike, thanks! Wondering if buying a new or used header with 4 into 1 collector might be easier way to go, though most likely more expensive. 

[datzenmike]

Have to say this. That manifold is already paid for, will never rust out like a header, it already fits tight and does not come loose or leak like a header, it's quieter than a header, requires no maintenance like a header, radiates less heat and works just as well. Better actually. Four into one is ok at extreme high RPMs where the four into two is better for low and mid range power and torque. That manifold was new in '74 or earlier so is 48 years old at the least. Now imagine that header in 48 months.

 

 

There is one thing better about a header. It's lighter.

 

[Randalla]

Sold me on using the cast iron manifold vs. header. Just need to figure out how to mate it up with exhaust pipe.

 

[datzenmike]

 

You need to get or cut a down pipe flange and get a shop to make something like this.....

 

 

On 10/19/2018 at 4:31 AM, Charlie69 said:

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

 

I had to make my own for L20B 710.

[Randalla]

I lucked out this week finding a nice stock exhaust manifold, that I refinished, and a solid down pipe to mate it with the exhaust piping to the rear. Hope to get this installed in the next week. Both were sourced locally here in AZ.

[banzai510(hainz)]

use antiseize on those those bolts.  all mine broke when I took them off.

[datzenmike]

I heated and removed the original studs and replaced them with stainless steel. SS is not as strong  as steel but the heat doesn't accelerate the rusting and they unbolt much easier. I also got a set of the bronze? or copper alloy?? nuts from a later Z24. They look kind of brass colored when scratched. Maybe they are SS which turns yellowish when heated above 600F. If not get SS nuts also.

[Randalla]

Good tips for sure. When I got the manifold, one of the three holes had a broken off stud in it that I had to extract. I then chased the threads on all three holes so they're ready for new bolts.

[datzenmike]

Mine all three were nubs. Heated to yellow hot and vice grips turned them out. You can see the discoloration.

 

 

The nuts I used came off a Nissan and they are longer than most. Look like these... notice the brassy color.

 

[yenpit]

On 12/10/2022 at 9:53 PM, Randalla said:

I lucked out this week finding a nice stock exhaust manifold, that I refinished, and a solid down pipe to mate it with the exhaust piping to the rear. Hope to get this installed in the next week. Both were sourced locally here in AZ.

 

The exhaust manifold will bolt right up.  The downpipe looks to me like a 68-73 510 (which has some value to a 510 guy!) & my understanding of the 521/620 trucks is that the downpipe has a "squiggle" heading down stream to clear the truck torsion bars............I've heard the 510 downpipe does not fit the truck chassis 😑

[Randalla]

Yenpit, you were right about the downpipe coming from a 510, and not fitting a 620 with torsion bars. My local muffler shop had to do some cutting and welding to make everything fit and clear the bar. I also discovered the intake manifold and new exhaust manifold had to be clearanced quite a bit (1/4") in order to allow the intake manifold to seal to the side of the head. Fortunately, there was plenty of material to work with. All good now.   

[yenpit]

On 1/4/2023 at 10:00 AM, Randalla said:

Yenpit, you were right about the downpipe coming from a 510, and not fitting a 620 with torsion bars. My local muffler shop had to do some cutting and welding to make everything fit and clear the bar. I also discovered the intake manifold and new exhaust manifold had to be clearanced quite a bit (1/4") in order to allow the intake manifold to seal to the side of the head. Fortunately, there was plenty of material to work with. All good now.   

 

Yeah, I thought I had read that the truck downpipe was different!

 

Curious what intake needed to be clearanced?  What is the OEM casting # on top of the rear runner OR is it an aftermarket intake?