I won't harp on about an engine swap... But a 2.41 axle is gonna kill you what with an auto trans and fairly tall 15" wheels. Even going to a 3.08 ratio is a 28% increase in torque multiplication!

Try and get your hands on whatever brands of header you can to see the quality yourself. I've had bad luck with Flowtech (awful welds, leaks, horrible flanges), but others may have nothing but praise. The Hedmans that I've handled are nice, and you can order them with the ceramic coating - very durable. I've only seen good quality on the Hookers - don't they offer something at a reasonable price?

As for size, get long primary tubes and don't exceed 1 3/4" diameter, they're probably all 3" collector - nothing wrong with that.

 

Thanks for your advice.

Ok, has anyone used Hooker Headers part # 3901 HKR on a 1979 403 Trans Am? Some sites (including the Hooker site) indicate that they should fit only 1977 403 T/As. Other sites (mostly vendor sites) indicate that they should fit 1977-78 T/As. I've been old by a Hooker site rep that they won't clear the 1979 chassis, though he does not know which part of the chassis would interfere with the headers. I want to know if the headers would fit with minor modification. As my car is currently under restoration, and as such it has been completely taken apart, it should be fairly easier to install the headers when I assemble the front chassis and engine.

The only option that hooker has for my application (3107 hkr) are priced at more than twice the price of 3901 hkr, and they're out of my budget.

Any help will be appreciated!

 

No answers to my question above? Has anyone installed those Hooker Headers on a 403 1979 Trans Am?

 

my $.02
spend your money on deeper gears that WILL yield results you can actually feel at all rpms and even just driving normal....

headers do add some HP "at" the HP peak rpms but with your tall gears and 3400lbs you won't feel much....
at street rpms, driving normal, they contribute very little,,,the motor is only putting out 1/3 to 1/2 of the HP peak value....
your cam and intake will work fine with stock (hogged out) manifolds and a H pipe and duals....
the stock manifolds are designed for darn close to the cam and intake rpms range!!!
street fun is all about TQ!!!! not HP...

simple demo for what happens with lower rear gears:
floor a car from a stop in low....
next floor it from a stop in reverse which is just a bit lower gear ratio in the tranny....

 

Thanks for your reply! Your help is appreciated. One question: What does "hogged out" mean?

I wanted to install headers since I know they're not easy to install, and since the car is right now completely apart due to its restoration it would be easier to do it now than at a later date. But now your answer raises some doubt about the headers (to install or not to install, that is the question...). I think I have the original manifolds somewhere.

As for the rear-end, I have a set of gears from a 1981 Turbo Trans Am (which I think are 3.08), so a gear swap is no problem. But I've heard that a numerically higher set of gears will be overkill on a 403. Add that to the fact that I live in a tropical island... and the 403 will be working under high temperature conditions. The car will only ocassionally visit high RPMs, though.

Now I have a "difficult" decision to make... Headers or manifolds???

 

hogged out=stock manifolds get "0" clean up inside after casting,,,,lots of casting flash and flow restricting extra thickness for strength....

just clean up, open up, and smooth the insides with a die grinder/dremel tool/whatever....

a simple trick I came up with to insure the head ports and exhaust manifold are truly centered/lined up when tight...
(the manifold bolt holes are way too big for the bolts)
go get a few copper or steel bushings from HD/Lowe/Ace Hardware that fit the hole/bolt combo....
(usually just a drill will round the cast hole so the bushing will fit)
loosely install the manifolds with bushings and bolts, install and tighten the rest of the bolts, remove the bushings and tighten those bolts...

also works for centering the intake manifold match up for front/rear/left/right

 

leave the stock rear in it for now,,,,it may well give you all the "zip" you want once the motor is dialed in....
400 cubes means 400ft/lbs plus motor tq.....
(the old 455 firebirds had like 2.4??? gears and they hauled butt)
you can swap gears later...

re: hot temp
you can over-gear but deeper gears means less load on the motor driving normal so less btu's produced....
ex:
a trailer tow option will almost always include a deeper gear set,,,partly needed to keep the motor cooler with the more load...

illustration for the gear swap idea/reason:
400ft/lbs X 2.46? first gear X 2.41 rear gears = 2371 ft/lbs of force on the tires
400 X 2.46? X "3.08" rear gear = 3030 ft/lbs of tire twsting force on the tires!!!!
(and that's still less than 1ft/lb of acceleration force per lb of car weight {3400lbs?})

LOL,
it's RAIN and "rough" roads and traffic on the "Isla del Enchanto" you need to consider for how deep are the gears!!!
really deep gears will make the rear end break loose on a wet road....
on purpose, my car is currently set up with only 1ft/lb per car lb for FL rain safety....
that's 0-60mph at just over 5 seconds, chirps the tires on the 1-2 shift with 225 tires and quick enough for me at my age and 90% intown driving....
(and I do let family and friends drive it who aren't used too it)
340ft/lbs, 3.55 gears, 24" tall tires, 3200lbs

tires/gears calculator (and others):
http://www.tciauto.com/Products/TechInfo/Calculators.asp#6

 

First, the header manufacturer should know if their header fits your chassis. They ARE trying to sell them, aren't they? If they say they don't fit, then don't buy the headers. simple huh?

Second, one major consideration about headers that virtually nobody discusses is the thickness of the flanges. Cheap headers= thin flanges= lots of warpage and gasket leaks.= PIA no fun.

Also cheap headers tubes are usually thinner metal and burn out sooner.... not to mention the questionable metal quality.

Third, Use good gaskets.
The 1/8 inch thick graphite gaskets or copper gaskets seem to work the best. Sure they are more money, but how many times do you want to have to replace gaskets?

Fourth, Don't forget good fasteners that are safetied and won't loosen.

Fifth, drop the headers into the chassis BEFORE you drop in the engine.

Sixth, definitely use NEW motor and transmission mounts so the engine isn't sagging and making the headers hit.

Seventh= Consider that the entire length of the long tube header and the weight of the exhaust system is hanging from the header flange. Vibration and shaking combined with the super hot metal of the flange allows the flange to warp. Consider using a header support bracket from the collector area to the transmission to remove the swaying and vibration stress on the flanges.

Most people don't realize that their headers get cherry red during a full throttle run, especially if it is longer than 15 seconds....
JMO

 

First, the header manufacturer should know if their header fits your chassis. They ARE trying to sell them, aren't they? If they say they don't fit, then don't buy the headers. simple huh?

You would THINK that header manufacturers are trying to sell their product, but this apparently does not apply to Oldsmobile headers. For example, there is an urban myth perpetuated by virtually every header manufacturer that Cutlass Supremes are somehow different from every other Cutlass and thus their headers won't fit. Sometimes they claim it's due to some mythical offset engine problem. Other header manufacturers claim that their headers won't fit Cutlass convertibles. In all cases, this information is false and the regular Cutlass headers fit Supremes and convertibles just fine. I have repeatedly contacted various header manufacturers about this and continually get "form letter" brush-off responses.

I don't personally know what the difference is between 77 and 78-79 Trans Ams, but the subframe is the same, the motor mounts are the same, the block and heads are the same - there is no substantive difference I am aware of that will change how the headers fit.

 

Hooker headers are junk- they should stay in Mexico where they are manufactured.