Best Stock Exhaust Manifold

[Racer Z]

We have two stock engines, a 72 and a 73, both from a 240z. The 73 has a burned cam and the 72 seemed to work well and is claimed to have a "fresh" rebuild. (we will see about that later) There is a slight difference in the bolt on accessories like the carbs and exhaust manifold. We don't have the cash to just go buy "real" headers and other nice things. Both engines are complete from fan to clutch.

 

Does anybody know which of the two exhaust manifolds might actually be better? This is not going to be a Daily Driver, but a low-budget road-racer. I don't have the casting numbers available.

 

We have two sets of Round Tops and one set of Flat Tops. Word is that the Round Tops are better. Working with what we have is our plan for now.

 

Thanks, Racer Z

[hoov100]

try and find a used set of long tubes, they can be had on craigslist for less then $60, as for the carbs, its really up to you, but i have heard many different stories and experiences from old racers who some would say the flat tops can be tuned and modified to out perform the round tops, where others say the round tops are best, but in the end i said f*ck and went EFI..

[Daeron]

I have also heard that the flat top needles make good street/performance needles in a pair of round top SUs.

 

I doubt much difference will be had between the two stock exhaust manifolds TBH. If I were in your shoes, I would ignore the minimal advantage in flow that you MIGHT get from using one over the other, and go with the manifold that "fits" best.. look at airspace between exhaust and intake, heat shield options, cleanest look, etc. You are trying to decide which unwholesome looking apple to take a bite out of; I wouldn't worry about which one is granny smith and which is a macintosh, NEITHER is a red delicious.

[Racer Z]

In the end I did pick the one that fit the best, the 73. The other one has the exhaust flange in a different position and would require re-doing the collector and exhaust pipe.

 

I was able to weight them and the 72 is 15 pounds compared to the 73 at 25 pounds. Ouch. I think the 72 might actually flow better and my brother thinks the 73 will. In truth, the header is probably not the weakest link here, nor is the carburetter. The head or valves and cam are probably the deciding factor for flow on the stock motor.

 

I went to my Dads shop and filled in the EPA fresh air ports in the header. Took me about 4 hours to hog out the humps in the ports. Then i drilled out the passage and slipped a steel dowel in and braised it solid. After it cooled slowly I finished the port and polish job. Nothing fancy, just removed the worst of the hump. I took a gazillion pictures and will post a few later.

[Daeron]

If this is really a low budget road racer, you ought to find a way to make the 72 manifold work for you or get ahold of some headers on the cheap. Most of the headers on the used parts market (or the new parts market for that matter) are mass-produced items that aren't really any appreciable improvement over the stock exhaust manifold, as far as power production is concerned. That being the case, an old dinged up MSA header (for example only, standard MSA headers are a perfectly adequate piece but nothing to write home about) can probably be had for $50-100 locally, if you keep your eyes peeled. We've got one that (if we sold it) would go for $50 right now, but with four Z-cars to think about.. a spare header is always nice to have around. Besides, cross-country shipping would kill that right out.

 

My point is, keep your eyes peeled... 25 pounds is ALOT when you could slap a manifold that weighs more like 10 on there. Low budget road racers win through three ways: Superior piloting (that depends on you being good, and on your opponents being bad;) Superior L-gata knowledge and wisdom (thanks to my uncle and my dad there ) and LESS WEIGHT, better handling.

 

Chipping every bit of sound deadening off; removing the interior and zip tying your stock speedo up next to the used autometer tach you scored cheap, and finding an aluminum plate to attach all the other switches to; finding the lightest manifolds, radiator, alternator, wheels and tires (BIG one there,) etc to use; THESE things add up to one MAJOR checkmark you can frequently count on on your list of "Things To Do To Win."

 

Somehwere around here is a thread titled "280Z rat rod" or some such thing. I posted some pics of my Dad's Grey Ghost up there; IMHO, that baby was the ULTIMATE S30 budget road racer. So I am biased; shoot me!

[Tony D]

Egads, not a revisit of wether headers save weight over cast manifolds again!

[Daeron]

Egads, not a revisit of wether headers save weight over cast manifolds again!

 

??? no, he has two stock exhaust manifolds and was wondering which would be better for performance. Kind of a "pointless" question, but you can't blame him for not knowing there was no appreciable difference. It only becomes pointless when you know the truth about the answer: that the only exhaust manifolds that will really offer much performance increase are expensive Nismo or Stahl headers.

[Racer Z]

Thanks Daeron, for being able to read and understand what you read.

 

I just love forums, all of them. When I was into bicycles and later sailboats, and now race cars, it's all the same. One person asks a legitimate question and 10 people respond with something not related to the question, and/or suggest the questioner is a moron. And I did do an extensive forum search for answers to my question. Had I have found it, I would not have asked it once more.

 

Our 1973 240z is bone-stock and sat in a garage for 10 years. It's amazingly rust free and has no signs of being crashed. We have been replacing rotted rubber (normal for any 35 year old car). Flushed out the fuel system, rebuilt the flat-top carbs and replaced all the rubber fuel lines. We (me and my brother) put in a MSA roll bar and a 5-point harness. The harness was free and will expire at the end of this year. We rebuilt the flat-top carbs and went through the brakes. We didn't trust the old brake lines and replaced them with steel-braided.

 

Finally took the car out for it's first test drive and got stuck. The points had gone out. This was about midnight in the hills. Fortunately we had a cell phone and our Dad came to rescue us. LMAO Some things never change. I'm 50 and my Dad is still getting me out of jams. We had bought a complete tune-up kit and got to impatient and wanted a test drive.

 

The second test drive was about the same, this time the fuel pump went out. The next time we started the motor it started squealing, loud and high pitched. We looked at each other and said, "Sounds expensive."

 

It turned out that the cam had burned up. The oil-bar had got bent some time in it's past and the cam lifters dried up. We found a good used motor for about the price of a cam-set and went with the complete motor. Now we have spare block we can use to start building a "real" motor with and still drive the car.

 

We finally got the motor swapped and are still attaching the accessories. New motor mounts, radiator, steering coupler and rack bushings. We have a complete Polyurethane Bushing kit that's not installed yet. It all costs money.

 

Something gummed up the freshly rebuilt carbs so we sent the fuel tank out for rust removal and seal up the extra EPA ports. Now we're using the round tops. I can't count the trips to the hardware store for missing bolts and brass pipe-plugs. It's amazing how much it costs to remove some of this EPA crap.

 

We did remove the air conditioner, radio and speakers. The insulation was dust and vacuumed up easy. For now, the interior it in great shape. Even the dash with only one small crack.

 

We had hoped to be on the track some time ago with a lot less work and problems, but....

 

....That's just part of racing.

[Racer Z]

I took some photos of the before, after and progress of filling in the EPA Fresh Air Ports in the 73 exhaust header. Some of the close ups are a bit fuzzy, but the header is installed and this is what I've got to share.

Filling in the EPA Fresh Air Ports

(left to right, top to bottom)

1. BEFORE - The 72 header on top and the 73 header that I used.
   
2. Close up of the 3-4 ports before grinding off the humps and filling in the fresh air ports.
   
3. I ground off the worst of the hump inside the chamber.
   
4. I drilled out the fresh air port to 3/8 inch and cut 3/4 inch off a steel dowel to fill in the hole. The original air tube is shown for effect.
   
5. I braised the steel dowel in and filled the small cavity.
   
6. I then ground it down some more and smoothed it up some. I did a pseudo polish job, but the picture is to fuzzy to bother showing.
   
7. The finished outside. You can see the steel dowel.
   
8. The finished header with the air injector that's going in the scrap pile.
   
9. AFTER - The finished 73 header (bottom) and the original 72 header.

Now it is time to thank my father for letting me use his machine shop and his guidance in this project.