Headers or iron manifolds?

[L31MaxExpress]

The only SBC vehicle I have had in 15 years that has had manifolds is the 87 G20 I built as a cruiser van for my mom to also use for road trips. It has the Hooker manifolds on it and they seem to do an adequate job on a ~375 hp L31. They claim they have the same flow area as 1-5/8" primary headers and they definitely appear to. They also have a 2.5" outlet. That being said I feel ANY header even a shorty will have better scavenging and offer more torque. This one was built as a cruiser not a hot rod, so I used the Hooker manifold because they were cheaper than headers when I bought them, and I am honestly tired of burning spark plug wires and melting wiring harness convoluted looming with header setups. The castings are smooth, clean and use a moly material like the GM 8.1L manifolds and thus more resistant to cracking. No complaints with them for the application and I have even considered putting a pair on my 383 in place of the Thorleys. The Thorley header flange has always been a complete PITA on my 97 and I am about fed up with them. The Thorleys will be removed at some point soon. The stupid donut gaskets have cracked apart yet again causing small but noticeable exhaust leaks. The flange bolt arrangement is terrible, Thorley could not have oriented the flanges any worse for access. 90* turn on the flanges would have been 1000x easier to access the bolts. Whether they get V-band flanged and recoated or they get replaced with manifolds, I am not sure yet. I have considered removing them, installing Hooker coated manifolds, then changing the exhaust to 2.5" pipes to the cats. Less aggravation and less under hood heat. Then if the engine ever needs to come out, it is less work to remove as the engine will come out with the manifolds still attached. That being said I have had headers on other vehicles and they are great and that includes an earlier Thorley design on my 83 G20. Those were great headers and had a better, more accessible design on the collector that used a standard flange gasket. The donut flange on my Express headers was a real screw the pooch design by Thorley. V-bands have been around for decades, and Thorley definitely should have used on their Express headers. I wish I could nut kick the guy that decided to use a standard 3 bolt flange, use a donut flange to seal the stupid thing and then decided on the worst possible angle to install said flanges for clearance.

 

[L31MaxExpress]

I guess I should also add, I do not feel my 383 would run the way it runs without having headers especially tri-ys on it. It is just that I am not sure overall it is worth the additional frustration to have the headers. They have been nothing but a pain. The convoluted looming starts to melt in less than a year and that is in places that are more than 1 ft away from the headers.

Good power, pain in the butt in more than one way. Thorley did not even engineer their headers for the L31 Express to work with the stock spark plug wire loom brackets. That required more $ and some creative changes. Stupid all around.

xc_hide_links_from_guests_guests_error_hide_media

 

[pgutier1]

Hello.
I am working on an 88, 4wd, 3/4 ton pickup.
It will be street driven and I plan on doing some towing and hauling.
Stock 350 is getting a mild cam, early 70's heads (1.94 x 1.50), 600 cfm carb, edelbrock performer intake, hei dist.
I am not looking to squeeze every ounce of power, but I don't want to cork this thing up, either...
I contemplated shorty headers, but it looks like I would never see my spark plugs again.
Are they that bad?
Are there cast iron manifolds that would do me better than the factory TBI units, power-wise?
I would like to run dual exhaust if possible, unless an aftermarket y-pipe could give similar results.

Thanks.

I installed Gibson shorty headers and absolutely love the difference in how my rig drives, it feels as it's a different truck.

BTW, don't install a paper gasket, upgrade to a copper gasket. I removed the iron manifolds and the paper gaskets were all disintegrated and fell apart. Also, upgrade the hardware to stainless APR manifold bolts...just my .02 cents.

If you do install headers, buy the spark pug spacer kit as well, it makes a difference.

 

[Erik the Awful]

A properly sized and plumbed single exhaust will always make more power and torque than a similar dual exhaust, no matter the vehicle or engine.

In some cases a properly sized single exhaust can make more power than a dual exhaust. Especially if the dual exhaust doesn't have a crossover, and especially in a smaller engine with a smaller cam.

No matter the vehicle or engine? Puff, puff, pass.

 

[Road Trip]

...This one was built as a cruiser not a hot rod, so I used the Hooker manifold because they were cheaper than headers when I bought them, and I am honestly tired of burning spark plug wires and melting wiring harness convoluted looming with header setups.

...I have considered removing them, installing Hooker coated manifolds, then changing the exhaust to 2.5" pipes to the cats. Less aggravation and less under hood heat. Then if the engine ever needs to come out, it is less work to remove as the engine will come out with the manifolds still attached. That being said I have had headers on other vehicles and they are great and that includes an earlier Thorley design on my 83 G20. Those were great headers and had a better, more accessible design on the collector that used a standard flange gasket.

I was trying to find a dyno test on the SBC Hooker cast iron manifolds, but no joy. Instead, I rediscovered
an old multiple header dyno comparison test, where they came up with some thought-provoking results:

You must be registered for see images attach

More specifically, to your point concerning how much heat that stock (uncoated) headers can radiate
into everything around them, check out the section from ~4:44-8:16 in the video, where they ran
identical headers, one set coated, the other set plain, and they commented on the differences in
the direct temp readings as well as the ambient temps in the test cell:

xc_hide_links_from_guests_guests_error_hide_media

On a semi-unrelated note, one test they performed (that completely changed my appreciation
of just how hard it is to translate the power made in dyno testing to an actual engine bay) was
where they ran a set of headers with and without collector extensions. The difference in
torque production (back-to-back tests, no other changes made) was up to ~57 ft/lbs right where
this would make a huge difference on the street. (3000-4200 rpm range, see attached graph.)

Q: How many custom exhaust setups include the correct-length extensions to ensure
this mid-range torque production doesn't get lost? Or get the collector extensions right, but then
cork it up afterwards, still managing to negate the majority of the performance benefits from
the tuned long-tube header installation?

****

I guess the point I'm trying to make is that I'm not against headers. Far from it. In all cases
they made the engine bay look better. In a lot of cases (because we didn't get it right either upstream
with our parts combo or downstream with the exhaust) ...the headers only contributed visually to
the performance of the car, despite big, optimistic promises to the contrary made by yours truly. :0)

And until I started safety-wiring the bolts, I was burning/replacing header gaskets more often than
I desired. And until we adopted the 'spend the extra for the coated or forget it' rule, we were blistering
the insulation on nearby wires from the radiant heat from the uncoated headers. (!)

Just my 2¢ worth. Like Icarus on his wings of feathers & wax, in our pursuit of more power by
installing headers, we have to be mindful of just how close we fly to the sun.

@L31MaxExpress , I feel your pain.

EDIT: PS - At the end of the video they test a shorty header and discuss the pros & cons
of going that route. Unlike some videos on the topic, the guys at Westech really reward the
viewer with a of good info for the time spent watching. Recommended viewing.

 

[Orpedcrow]

Do the Holley manifolds have O2 ports? I didn't see O2 ports on the ones I looked at.

I do not know my 454 tbi has the o2 in the y pipe. did all 305 and 350 tbi engines (87-95) have the o2 in the manifold or did some get put in the y pipe like on my 454?

My 97 350 has all 4 sensors in the (305) wye pipe.

 

[L31MaxExpress]

I was trying to find a dyno test on the SBC Hooker cast iron manifolds, but no joy. Instead, I rediscovered
an old multiple header dyno comparison test, where they came up with some thought-provoking results:

You must be registered for see images attach

More specifically, to your point concerning how much heat that stock (uncoated) headers can radiate
into everything around them, check out the section from ~4:44-8:16 in the video, where they ran
identical headers, one set coated, the other set plain, and they commented on the differences in
the direct temp readings as well as the ambient temps in the test cell:

xc_hide_links_from_guests_guests_error_hide_media

On a semi-unrelated note, one test they performed (that completely changed my appreciation
of just how hard it is to translate the power made in dyno testing to an actual engine bay) was
where they ran a set of headers with and without collector extensions. The difference in
torque production (back-to-back tests, no other changes made) was up to ~57 ft/lbs right where
this would make a huge difference on the street. (3000-4200 rpm range, see attached graph.)

Q: How many custom exhaust setups include the correct-length extensions to ensure
this mid-range torque production doesn't get lost? Or get the collector extensions right, but then
cork it up afterwards, still managing to negate the majority of the performance benefits from
the tuned header installation?

****

I guess the point I'm trying to make is that I'm not against headers. Far from it. In all cases
they made the engine bay look better. In a lot of cases (because we didn't get it right either upstream
with our parts combo or downstream with the exhaust) ...the headers only contributed visually to
the performance of the car, despite big, optimistic promises to the contrary made by yours truly. :0)

And until I started safety-wiring the bolts, I was burning/replacing header gaskets more often than
I desired. And until we adopted the 'spend the extra for the coated or forget it' rule, we were blistering
the insulation on nearby wires from the radiant heat from the uncoated headers. (!)

Just my 2¢ worth. Like Icarus on his wings of feathers & wax, in our pursuit of more power by
installing headers, we have to be mindful of just how close we fly to the sun.

@L31MaxExpress , I feel your pain.

Definitely things to learn with a dyno and usually equals more questions than answers. I remember a test where an intake extenstion was added to a GenIII Hemi. It added a big chunk of torque having snuffalopagus on the front of the throttle body. Impractical for any kind of vehicle except maybe an air boat or jet boat, but wild to see. The reality of an engine is that anything from the air inlet of the air box to the outlet of the tailpipe can effect the torque curve and output. Seeing that intake tube, made me wonder how much a 90* bend close to the throttle body would change the output.

You must be registered for see images attach

 

[L31MaxExpress]

I have an exhaust setup I have dreamed up for the van that would probably add some power to it. The speed engineering offroad dual exhaust X-pipe for a GMT800 with their headers. Looks like it should come really close to fitting the van out of the box if I V-band my header collectors. I would then hang a high flow cat on the back of each pipe coming off the X and then on to the dual inlet muffler I already have on it. I feel the X close to the front where the exhaust is hot would help add some additional scavenging as well as allow the cats to be less restrictive since the exhaust pulses can travel through both cats at the same time, evening out flow and slashing backpressure even more.

 

[Orpedcrow]

Seeing that intake tube, made me wonder how much a 90* bend close to the throttle body would change the output.

Like the top hat thing on the vortec’s? Some things you can just look at and know it’s not optimal

 

[L31MaxExpress]

Like the top hat thing on the vortec’s? Some things you can just look at and know it’s not optimal

Well the one on the van is 1/2 the height of the truck one and the internal passageway is much more restricted. I know the Suburban and Tahoe both ran a lot better with a Volant intake and its much more streamlined ducting. The air hat on the Express van probably cost it 20-30 hp. Even with an open throttle body on a quick WOT test the 80mm throttle body itself is showing 5 kpa of restriction. The vans air intake pulls 10 kpa of vacuum at 5,500 rpm. Its pulling 6 kpa vacuum already at 4,000 rpm. If I were dynoing an engine with a carb on the dyno, it would be getting a larger carb if I saw that much intake vacuum.