davoaz

I have a stock 72 350 4bbl single exhaust.


My first performance upgrade I am thinking is going dual exhaust.


The cheaper option is convert the single exhaust to dual.


Other spend more go with headers. I plan on other mild mods in the future to try and get motor up to the 70 power torque range.


Questions are for the extra money to go headers would I see a good bang for the buck performance difference?


Also, since I'm at it what is the difference between long tube and shorty header?


Last, I hear sometimes there's fitment issues, what a good brand to that fits reasonably well?


Thanks

cutlassefi

When I bought my '72 it had single exhaust. The first 2 mods I did in succession were headers/dual exhaust and a rear gear change, with my eye on the same, further changes down the road. Each of those changes made a huge difference. I'd start there.
I have Dynomax headers, not fitment issues.

redoldsman

Shorty headers are not going to give you much of a power boost. Long tube headers will. I don't have either one on my 72 Cutlass. I just have duals with the stock manifolds and generic turbos. From what most folks say, long tube headers are a pain to install. Hooker seems to be one of the more popular brands. Keep in mind that you could put duals on with the manifolds and later change to headers. Very little would be lost that way. Are you going to buy one of the kits or take your car to a local muffler shop?

davoaz

Are you going to buy one of the kits or take your car to a local muffler shop?


Muffler shop. Definitely for the headers if I do those cause I'm sure they're rusted on good.

yankees

If u use the pypes down pipes, you will need to use an exhaust donut on the drivers side with stock manifolds

RandyS

x2 on what Joe said. What does rust have to do with your decision? Where are you locted? You're gonna pay a bundle to have a muffler shop install headers AND an exhaust system for you.

redoldsman

You could use the Thornton 350 JR manifolds. Here is the link.

http://thorntonmusclecars.com/produc...aust-manifolds

davoaz

What does rust have to do with your decision?
I'm worried about bolts being fused to the block and torqueing a bolt head off.


cut the metal bar out from between the tubes to stop warping.

Haven't heard about doing this before.


Those Thorntons looks interesting, How are they better than stock manifold?

oldcutlass

The Thorntons are in between a stock manifold and long tube headers in flow. very easy to install. Headers take a bit of finessing for the install depending on brand. I would install the manifolds or headers and then take it to the exhaust shop if going that route.

Each to their own on removing the flange material between the tubes, I've never had to do it on new ones. If it ain't broke... why fix it?

RandyS

The Thontons are much better than stock - they have divided center chambers which improves 'scavenging' and they have a larger inner diameter to improve flow. They are the way to go if you don't wish to do headers.

DoubleV

My 2 cents;

1) Dual exhaust will provide noticable gains over single exhaust.

2) Headers will not provide much gain over manifolds at your power level.

3) The Thornton manifolds are not very good as cast. Requires lots of porting to see any real gains IMO. For one the stock divider for one is a joke.

olds 307 and 403

Is 25 hp/tq worth it for long tube headers? Your call, stock manifolds blow. Shorty headers should be worth 20 hp/tq, again your call.

s i 442

Shorty headers are a waste of time and money.
A stock 1970 W-31 with a 325 horse engine uses the stock run of the mill factory exhaust manifolds, are you going to be anywhere near that really?

TripDeuces

Cutting the bar on Olds headers is going to leave you a bolt shy on the outside ports. How does that help leaking?

s i 442

You are absolutely right, the pic I posted is Chevrolet headers that I labeled "Oldsmobile headers" I put it the wrong file.
I am going to correct my mistake.

jensenracing77

x2

s i 442

I took a die grinder to the exit opening in my stock manifolds, about 2 inches up there is a ridge so I smoothed it all out.

olds 307 and 403

BTR gained 38 HP on a W30 build over W/Z manifolds. I say the tests done on a 300 HP 318 testing all the manifolds starting with terrible 318 manifolds. Then hi po manifolds, shorty and long tube headers, 11 to 25 hp/tq gained. I would believe 40 hp with ARH headers over non hi PO manifolds.

DoubleV

Had a detailed response that somehow got lost so here's the simplified version; magazine tests are mostly bogus and headers can make nice gains on the right build but do very little on mild/stock builds. In short, don't make your decisions based on anything in that 318 test. If you do you're going to be wondering where all the gains are when you install a set of headers on say a stock mid 70's 350...

davoaz

Provided the bottom end is good, long range plans would be mild cam, better intake and machine or replace the heads. If I have to go into the bottom end then maybe up the compression a little.

455man

Long tube headers are not that tough to install on a small block. Go for it.

joe_padavano

You might want to take another look at those manifolds. That center divider is only about an inch deep. They do not have the individual runners of the BBO W/Z manifolds. The improvement is optical only. There can't be a scavanging improvement if the entire manifold is the same open log manifold as stock.

rcrac3r

About the only thing to add to this would be you have to raise the engine to get the headers installed, plus some slight modifications to mounts, brake lines, etc. I just recently put Hedman headers on my '72 along with a dual exhaust kit from Magnaflow. Had to remove the heat shield from the left mount & trim the one corner of the right mount. The brake line that runs along the back of the front crossmember has to be rerouted a bit as well so it isn't so close to the headers once they are bolted up.

RandyS

Joe, I was just going by their description on the website:

Large 2 1/4" outlet on the driver side manifold (original stock manifold is 2")
No crossover pipe hole to plug on the passenger side
Divided center port design
Larger design for better air flow
Direct bolt on with no modifications needed

Is that bullshed?

joe_padavano

Let's just say that it's marketing at it's finest. I've held these manifolds in my hands. They are marginally larger than the stock manifolds and just about the same shape. Whether that translates to better flow is debatable until someone shows me back-to-back dyno or drag strip data. The SBO doesn't have the room for individual runner manifolds, which is why Olds never made them, not even for the W-31s. The Thorntons have a short divider between the two center ports that goes about 1" into the manifold and stops. One could even argue that this disrupts flow from the front (no. 1 and no. 2) cylinders, since that flow must move past this barn door. Again, having seen subsonic flow simulations, it's clear to me that the mods on these manifolds were done with exactly zero engineering. Subsonic flow does not follow what you would consider the expected pathways if you were eyeballing it. I'm still waiting for concrete test data. The fact that none has ever been produced should tell you something.

DoubleV

Well as I have mentioned before in the past, I had a back to back dyno comparrison between stock manifolds and PORTED Thorntons. Unfortunately, my dyno test is not technically 100% legit because when I tested the Thorntons I had a different exhaust system too. With that said though, the gains in the higher RPM's were pretty good ( 19-20 RWHP ) and I'm pretty sure not all of that was due to the exhaust ( though I suspect most was ). Until somebody does a legit back to back dyno test, this is the best info currently out there AFAIK.

These ported Thorntons are currently on my friends mild/street 440 diesel block build in an 83 Cutlass running 12 flats.

If all of this sounds like I'm a big supporter of the Thornton manifolds let me just say 'no', I am NOT a big supporter of these manifolds! If you port them, yes I believe there are some gains to be had. How much is debatable though. As cast, I wouldn't be suprised if they actually cost you hp....

joe_padavano

That's interesting info, and I also suspect most of the gain was the rest of the exhaust system. I am interested in the porting. Specifically, where did you port them? I'm assuming the work was done on the outlet end primarily, as there really isn't anything to port on the head side of those manifolds.

DoubleV

Initially, I started just cleaning up all the casting boogers which there was alot of. Then I realized the center divider looked like it was way too thick and needed to be thinned out or it would most likely hamper flow from the center cylinders. I further realized there was a crap ton of meat in the outlets which could be ground away too otherwise the so called 2.5" outlets would appear to flow no better than just having 2" outlets. I wasn't prepared or equiped to do all of this so I shipped them off to Greg Gessler who does alot of stock Buick iron stuff.

When I got them back from Greg, he smoothed out the casting boogers a bit better than I did. He 'hogged out' all the extra meat on the outlets. He narrowed the center divider and also carved out an arch on the bottom of it as he said without doing that the 2 forward cylinders would most likely flow worse. Greg did a nice professional job. When it was all said and done though, I had a bunch of money in a set of fricken exhaust manifolds! Overall, more money and work than what should be needed. I have no clue why the Thorntons are cast the way they are....

I wish I had pics of the manifolds and perhaps some day when my friend makes the switch to ARH I can snap a few for those who would like to see the work that was done.

One more thing too; the outlet on the drivers side manifold is angled slieghtly forward instead of strain down like the stockers. It's something most wouldn't notice but it IS there and IMO has no buisiness being like that.

Overall I feel the Thornton manifolds were/are a good idea that was poorly executed.

s i 442

Something I do with headers is, I always bolt them to the heads then add the exhaust that way nothing is pulling the header in an angle when bolting them down.
If I unhook the headers from the heads then they get new collector gaskets and get unhooked also.

davoaz

Anyone have any experience with flowmaster headers? ~ $200 cheaper then headman's. But would the install wish I spent the extra $200.