Good evening, I have a 1968 cutlass convertible with a stock type rebuilt 455 and a five speed TKX. The car is going to be a driver, not a race car. The stock manifolds I was going to use were found to be cracked. Looking for a recommendation as to whether I should go with the either the Fusick or Thornton reproduction manifolds then get those ceramic coated or to go with Thornton‘s ceramic coated Shorty headers. Any suggestions or input would be appreciated. Thank you, Vin

 

With what you are doing I would stick with factory manifolds. Headers can be a BITB on an Olds. You may also be able to find a nice set of used manifolds. Place a add in the parts wanted on this site, or check Ebay.

 

x2 on using manifolds. You might actually take your current manifolds to a welder to see if the crack can be repaired.

 

I run the Thornton shorties on my '72 and I think they're a great visual upgrade from stock manifolds - doubtful they make any additional power but they fit perfectly and have given me 0 trouble in the 2+ years they've been on my 350.

They eliminate that 'converted' look the stock manifolds have - i.e. having to cap off the right manifold crossover port if you're running them on a straight dual exhaust.

Especially if you've replaced your exhaust at some point you might have to modify the curvature of the down pipes to line up with them, but other than that no issues.

 

Use the Thornton manifolds. I pretty sure that Fusick is also selling the Thorntons. The shorty headers actually choke the exhaust port down to the tube size. I can't see that ever being good for power or gasket longevity. I have all three and definitely prefer the manifolds on the drivers.

 

You obviously have no clue how headers actually work. Flow means next to nothing in this scenario.
Op-If you’re going to buy new, get the shorties, they do offer a small benefit over ANY manifold, at about the same price I believe.

 

I have the first gen manifolds on my 350 from Thornton. I had them ceramic coated 8 yrs ago. Still lol brand new. No issues I did bore out the outlet on it to remove some of the flash etc from the casting.

 

Yes Mark, I actually do. But I don't believe the shorties actually add enough benefit to overcome how badly they choke down at the flange with the 1-5/8 tubes, over a set of the Thornton manifolds. Much different then talking about a set of 1-3/4 or 1-7/8 long tubes.

 

I would get a set of WZ's. Assuming you have disc brakes, the distribution block doesn't need to be relocated, (which it does for long tube headers)

I don't know anything about the Thornton Shorties except everyone has asked if they're been dyno'd and no one seems to have done it. I know Mark suggested them, maybe he's dyno'd them

 

FWIW, I have the coated Hedman headers on my 71 98. I suppose they're good for power on the butt-dyno. I've had them over 10 years and the coating has since failed. In that time I removed them to clean and repaint them. They just look sort of lame now. I might go back to the manifolds. Especially if I swap to my good 455.

 

Good morning all, based on everyone’s input, I believe I’m going to go with a new set of reproduction manifolds and get those ceramic coated. For this build, I’m really just looking for no leaks and long lasting good looks. Again, appreciate everybody chiming in and thanks again!

 

I did, they’re worth about 10-12 over manifolds but still 25+ shy of full length headers.

 

You are going through all the trouble and expense of installing a 455 and you want to handicap it with manifolds or shortie headers?

 

If you decide to go to full-length headers I wouldn't buy any that need massaging. They should fit without interference.

 

Makes sense.

But that makes sense as well.

Vin442, if you change your mind shorties are essentially fools gold. Makes you think you did something but you didn't. Unless you cant find factory exhaust manifolds or already have them. When someone has shorties and brag they have headers its cringe to the informed. Even if you can eek out a gain long tubes blow them away. Unless fitment is absolutely impossible why spend the money, it's not a bragging right. It's mostly a feel good visual mod. From a market created for those looking for real header gains but not wanting the additional headaches, that ends up a worthless compromise.

Cutlassefi tested shorties versus full length and saw a 23.3 hp gain with the long tube. On a 400 hp small block 350. https://classicoldsmobile.com/forums...eaders-177221/

Oldsmobile tested full-length headers on the 1970 W30 and saw a 24 hp gain over the stock W/Z exhaust manifolds, net flywheel. https://classicoldsmobile.com/forums...-specs-141238/

Whether Cutlassefi can eek out a gain with shorties or not you still end up with the same result when modified to full length. There much better. Even if you don't go to the track you will feel 24 hp. And full length headers speak for themselves no bragging needed, because you hear it loud and clear.

Now personally seeing that I enjoy 1/4 mile racing, I could see myself trying the shortie because I am satisfied with a 1/10s of a second reduction. And would go ad-nauseum till I saw it. But most would want a serious bang for the buck. Shorties may show me a 15.4 at the track vs my stock 15.5 but well tuned full length could show a 14.9 , you will feel a 1/2 second reduction on the street. All else the same, I assure you.

P.S. you can get lucky at the track and also see a 1/10 reduction stock as is but you are not seeing a 1/2 second reduction under the same scenario.

 

Absolutely appreciate all the input in here, this is why I posted it! OK, let’s say I was going the header route, what would be the best choice for fitment and clearance issues for this car since my goal is really just for good looks and longevity with no clearance or fitment issues? Since the last time I actually bought new headers was an awhile ago I’m not really well-versed on what new offerings are out there (if any). I’ve had Cutlasses since I was 16 in ‘82 so I’m quite aware of starter, oil filter, dipstick issues, etc. I can deal with those, However, I do NOT want them to scrape. What brand and part number should I consider?

 

If goals are a ‘looks and no leaks’ scenario over a hp gain what’s the general consensus on the decibel/noise level manifold vs headers. Will it depend on the mufflers downstream and not be big difference?

 

Cast iron manifolds will always be quieter than thinwall tube headers. If you don't care about the extra HP and are only getting headers for appearances, then get W/Z manifolds. Shortie headers give you all of the cost and leaking gaskets of real headers with none of the pesky extra HP.

 

Just get the Thornton oversize manifolds. They are nice pieces.

 

I spoke with Thornton last week before I posted here for real reviews and she was super nice, said they have the oversized WZ manifolds in stock and they can powdercoat them at their shop. After everything that said here,
I’m gonna take a ride out there sometime next week and pick them up. Once I get them back and installed on the motor and in the car, I will post some completed pictures. Thanks to all!

 

Your car your choice. I have shorties on my 66 for the last three years, have yet had to retighten them or have developed a leak. Long tubes are a total pain in the *** unless you are looking for maximum horsepower. If it’s a street car forget about tubes since you are putting a stock 455 in the car. If it was built with cam and pistons etc then by all means maximize your power band.

 

As another member mentioned and fixed is the available off the shelf down pipes being close to 2" at the exits. Cutlassefi still gained 12 HP with shorties with only 2.25" dual pipes vs 2.5" with the full length. Starter and clearance in many places including moving brake lines are all par for thr course with full length headers. No starter issues, even the large factory starter with shorties. The Hedman shorties also have very long collectors pointing straight down limiting ground clearance. Sanderson shorties have hit or miss welds. But both have 3" outlets which require custom down pipes and are small block only. The Thornton are the best deal price wise, stainless vs mild steel on the other two. The thick flange headers rarely need retightened vs the thin flange headers in my experience. There is a power gains on shorties vs manifolds and obviously fill the gap between manifolds and full length in power and convenience.

 

If you have a cam with a wide LSA there is less of an advantage for headers over the manifolds. Thorton is now releasing repro W and Z manifolds with a 2 1/2" outlet vs factory 2 1/4" outlet.