SOHC and DOHC exhaust manifold

[Bearded1mx3]

I will be doing a DOHC swap but I have to wait til I have a place to do it so I'm trying to do what upgrades I can in the mean time. I'm curious if the exhaust manifolds are the same. I want to get a set of obx headers. Just curious if they will bolt to both sohc and dohc.

[Saturn Night]

They will not. The SOHC intake/exhaust ports are different dimensions than the DOHC.

www.car-part.com for the DOHC manifold

1991-1992 Saturn S-Series DOHC used a 4-2-1/Y-Pipe(also known as a balance pipe for the out-of-sequence #2 cylinder scavenging) from the FACTORY.

Walker makes the replacement Y-pipe and gasket.

The OBX header is prone to cracking the welds, and the factory header flows almost identical to the OBX. Only difference is the OBX has a collector and the factory header has the balance pipe.

[Bearded1mx3]

Oh I didn't know that about the obx....I thought it was pretty well I'm already in the process of "mathing" up a custom intake manifold so may was well do the same for a header...I was thinking of getting a honda 4-2-1 and modifying it for my sohc for the time being. I have a dc honda header laying round

[OldNuc]

Originally Posted by Saturn Night

The OBX header is prone to cracking the welds, .

That is pure BS. If you do not install something correctly do not blame the product for your sloth.

[Saturn Night]

Originally Posted by OldNuc

That is pure BS. If you do not install something correctly do not blame the product for your sloth.

http://www.google.com/search?q=do+ob...27.zSGBvgEdU3I

A simple Google search of OBX headers will reveal MULTIPLE online forums with complaints about cracks in the welded seams, and them being the weak point of the exhaust systems from OBX.

I have the 1991-1992 DOHC/Y-Pipe, and my Walker balance pipe has the same issue with the welds rusting out first. The header is fine. Been on the car almpst 2 years, and I have a lifetime warranty on the Y-Pipe.

When the Y-pipe finally cracks, it will do so at the welds. This is simple physics, as welds leave the surface of the metal porous and ruins the galvanized coating used to prevent corrosion.

[Saturn Night]

Originally Posted by Bearded1mx3

Oh I didn't know that about the obx....I thought it was pretty well I'm already in the process of "mathing" up a custom intake manifold so may was well do the same for a header...I was thinking of getting a honda 4-2-1 and modifying it for my sohc for the time being. I have a dc honda header laying round

The Honda header may not work, as your bolt pattern may be different and the gasket for exhaust manifolds is supposed to match the manifold, not the cylinder head.

Most exhaust systems are precisely machined, for the specific engine they go with. My 1992 Camaro 3.1L V6, for example, didn't even have manifold gaskets. The manifolds were precision machined for the head, to make a gasket-less seal.

You will want to be very thorough, when swapping a Honda engine manifold onto your SOHC Saturn engine, before doing it.

Changing the exhaust flow characteristics can disrupt the intake/exhaust balance % of the engine, and burning valves can happen on any engine with improperly setup exhaust systems.

[Bearded1mx3]

I did know that I thought more air out would be compensated by the ECU with more air in. And as far as bolt pattern goes. I'm cutting the honda flange off and getting a flange lasered to match the sohc gasket. Then bend tack and weld. The spacing should be too bad.

[alordofchaos]

Originally Posted by Saturn Night

http://www.google.com/search?q=do+ob...27.zSGBvgEdU3I

A simple Google search of OBX headers will reveal MULTIPLE online forums with complaints about cracks in the welded seams,

Because if it's on the internet, it must be true?

All that shows is that people on other car forums may have installed the OBX incorrectly as well (though I am sure they would all deny it).

I have no opinion or experience with OBX, just pointing out "I found it on the internet so it must be true" is not a game-winning strategy At best, it's selective - people love to complain on the internet when things break, but more rarely post on things that worked fine; and for OBX to stay in business, it's likely at least some of their products are workable.

A simple google search also shows that Reptilians disguised as humans are secretly running all the governments on Earth.
https://www.google.com/search?ei=1Go....0.swBNCAcWAx4

[Saturn Night]

Ok.

Then we'll go with price:

OBX Header for a DOHC: $200-$300

https://www.ebay.com/bhp/saturn-sc2-header

And now for the 1991-1992 DOHC factory "manifold":

$25-$115 and you can likely get the factory Y-Pipe on some of those, as some yards cut off exhaust pipes and others do not.

Seems to me the factory manifold is still the better choice....

[fetchitfido]

The OBX doesn't have the downpipe brace like the factory one so of course it's going to crack. The factory one cracks too when you don't use the lower brace.

[OldNuc]

delete

[OldNuc]

Making the proper lower support is not a particularly difficult task and as has been pointed out anyone doing this should know it must have a lower support. When they crack or the flex joint fails 999 times out of 1000 it is an installation error.

I have been running one for years and it is not cracked. Install is not a 15 minute job either and there is no muffler shop that will do the job correctly unless you stand over them and supervise.

I have previously posted exactly what has to be done to install a custom exhaust.

[Saturn Night]

Originally Posted by fetchitfido

The OBX doesn't have the downpipe brace like the factory one so of course it's going to crack. The factory one cracks too when you don't use the lower brace.

Been driving for almost 2 years, without the lower brace that mounts it to the oil pan.

[Saturn Night]

Originally Posted by Bearded1mx3

I did know that I thought more air out would be compensated by the ECU with more air in. And as far as bolt pattern goes. I'm cutting the honda flange off and getting a flange lasered to match the sohc gasket. Then bend tack and weld. The spacing should be too bad.

With smaller displacement engines, a free-flowing exhaust system is great for improving performance(as with any engine). TOO MUCH CFM of exhaust gases is what burns valves out quicker.

It has to do with physics. As the cam lobe opens and closes the valve, it is on a spring. Dynamically, the valve actually bounces a few micrometers during its closing. With more exhaust out, in the same amount of time(as camshaft duration remains the same), yes you get more intake air into the engine. Valves are a "wear 'n' tear" item inside the engine.

This is known as "scavenging", because the intake valve begins opening just before the piston reaches TDC, on naturally-aspirated engines.

What this also does is allow more air and fuel into the engine on your intake stroke. This increases power, has more fuel to burn, which means more heat energy produced and higher combustion temperatures, which will burn out your valves quicker.

A leaky exhaust is one of the main reasons the DOHC will burn the #3 cylinder exhaust valves, if the owner doesn't repair the exhaust system.