Should I build some new headers?

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GRTfast
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Should I build some new headers?

Post by GRTfast » Sun Oct 22, 2017 10:40 pm

I’m thinking of building some new headers for my rod. Currently it has 1 7/8 primaries that are around 28 inches long. Collectors are 3.5 inch (not merge collectors) and about 10 inches long with slip on side pipe mufflers. The engine is a 454 BBC and makes 530 ish torque at 4400 rpm and 500 ish horsepower at 5600 rpm (at the flywheel). Cam signs off pretty hard at 6k. 9.5:1 compression, hydraulic roller, Brodix heads, rpm airgap.

Do you guys think my current headers are giving up a lot of power? I know the primaries are a little short, but they allow the side pipes to exit in front of my doors so the car is easier to get in and out of. I’m willing to sacrifice that if a significant power gain is possible.

Thoughts?

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Re: Should I build some new headers?

Post by prairiehotrodder » Sun Oct 22, 2017 11:10 pm

on a 700 + hp 540 i just changed from 2" primary headers to 2.25". Gained nothing at the track. I have no dyno experience but i don't think you will gain much with the bigger headers. Now on the other hand if you have restrictive mufflers they can suck up alot of power.
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Re: Should I build some new headers?

Post by bigjoe1 » Sun Oct 22, 2017 11:46 pm

You would see VERY LITTLE or NOTHING as far as a gain





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Re: Should I build some new headers?

Post by MadBill » Sun Oct 22, 2017 11:49 pm

<EDIT> written before Joe treed me; I was almost going to say: "I'm sure Big Joe would tell you to forget it." :)
2X.
On a moderate build like yours, I doubt the most perfect headers would make enough difference to be worth it. On the other hand, I've seen poor side pipe mufflers lose 20 + HP on a 450 HP SBC, so I'd try to evaluate them via dyno, track or butt.
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Re: Should I build some new headers?

Post by GRTfast » Mon Oct 23, 2017 8:32 am

MadBill wrote:
Sun Oct 22, 2017 11:49 pm
<EDIT> written before Joe treed me; I was almost going to say: "I'm sure Big Joe would tell you to forget it." :)
2X.
On a moderate build like yours, I doubt the most perfect headers would make enough difference to be worth it. On the other hand, I've seen poor side pipe mufflers lose 20 + HP on a 450 HP SBC, so I'd try to evaluate them via dyno, track or butt.
Thanks for the feedback. I always suspected the sidepipe baffles could be a power killer. I’ve drilled some holes in them to open them up a little bit, but that also makes them louder (as one would expect). I feel like I have a good balance now. I’ve driven the car with the baffles out of the sidepipe and it wasn’t detectably faster to the butt dyno, but it was insanely loud. I’m thinking of trying some of those auger style baffles, but the nice ones are pricey. Trying to decide if i want to drop the $$$ just to test them.

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Re: Should I build some new headers?

Post by Newold1 » Mon Oct 23, 2017 8:36 am

X3

Sounds like your camshaft might be a better place to look for some more power if you're in a mind to change it.

If so let on the post what the specs are on your existing camshaft.

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Re: Should I build some new headers?

Post by racear2865 » Mon Oct 23, 2017 9:05 am

Will make a huge difference--maybe 5 hp dont know if will gain or lose that 5
reed

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Re: Should I build some new headers?

Post by F-BIRD'88 » Mon Oct 23, 2017 9:26 am

The muffler inserts and the hyd cam that is "signing off hard".
Unfortunately with side pipes the method of getting sound volume attenuation ( make it quieter)
is restriction with those simple baffle inserts.
you might try building your own custom built slide in inserts that are like the inside of a Borla muffer.
3 perforated pipes surrounded by sound packing wrap with inlet/outlet flow merge transitions in and out.
Nobody I know offers these off the shelf but you can custom build or get a fabricator to build your own.
Look at the Borla muffer for inspiration.

You can add a Super trap end that also slides into the end of the side pipe.
The Supertrapp end primarily works on restriction + 90 degree sound diversion for sound reduction effect.
The more flow plates added the less restriction and louder volume.
The less plates the quieter but at the cost of flow.
But are easy to change in the go as needed for volume.

The Borla style 3 perfed pipes baffle with wrap + the Supertrapp end work in combo.
if you are happy with the sound volume level of the Borla style insert alone you can pass on the added Supertrapp end piece.

is this a Vette with side pipes?

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Re: Should I build some new headers?

Post by F-BIRD'88 » Mon Oct 23, 2017 9:29 am

On the cam get a Suitable solid roller mechanical street roller cam and see the difference
on a BBC.

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Re: Should I build some new headers?

Post by GRTfast » Mon Oct 23, 2017 9:53 am

Newold1 wrote:
Mon Oct 23, 2017 8:36 am
X3

Sounds like your camshaft might be a better place to look for some more power if you're in a mind to change it.

If so let on the post what the specs are on your existing camshaft.
The engine is for sure undercammed. I’m somewhat hesitant to go more radical because it’s a manual trans street car. Drivability in the 1750-2500 RPM range is a concern. The cam is a comp cams hydraulic roller “Thumpr”. I’ve since realized it probably isn’t the best selection, I kinda (stupidly) fell for some marketing hype when I was shopping for cams during the build 4 years ago. Maybe it’s possible to keep my cruising drivability with a more radical cam, I’m not sure though.

Cam specs are:

Intake lift: .547
Exhaust lift: .530
Intake duration @ .050: 227
Exhaust duration @ .050: 241
Lobe separation: 107
Intake centerline: 102

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Re: Should I build some new headers?

Post by GRTfast » Mon Oct 23, 2017 9:56 am

F-BIRD'88 wrote:
Mon Oct 23, 2017 9:26 am
The muffler inserts and the hyd cam that is "signing off hard".
Unfortunately with side pipes the method of getting sound volume attenuation ( make it quieter)
is restriction with those simple baffle inserts.
you might try building your own custom built slide in inserts that are like the inside of a Borla muffer.
3 perforated pipes surrounded by sound packing wrap with inlet/outlet flow merge transitions in and out.
Nobody I know offers these off the shelf but you can custom build or get a fabricator to build your own.
Look at the Borla muffer for inspiration.

You can add a Super trap end that also slides into the end of the side pipe.
The Supertrapp end primarily works on restriction + 90 degree sound diversion for sound reduction effect.
The more flow plates added the less restriction and louder volume.
The less plates the quieter but at the cost of flow.
But are easy to change in the go as needed for volume.

The Borla style 3 perfed pipes baffle with wrap + the Supertrapp end work in combo.
if you are happy with the sound volume level of the Borla style insert alone you can pass on the added Supertrapp end piece.

is this a Vette with side pipes?
Thanks for the suggestions. I can for sure fab up my own baffles, I have a basic machine shop (mill, lathe, Tig, chop saw, etc..).

I like the idea of the borla design. I’ll look into it.

The car is a scratch built chopped sedan style hotrod, kinda inspired by model A and Model T rat rods, but with my own body and frame design. It’s solidly engineered and constructed.
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Re: Should I build some new headers?

Post by prairiehotrodder » Mon Oct 23, 2017 10:38 am

open headers vs mufflers can be deceiving to the butt dyno. All the noise kinda makes it feel slow even though it may be going faster than with the mufflers on.

When i take my car to the track its faster without the exhaust but it feels slower. All the noise ringing in my ears seems to steal away the feel of the acceleration.
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Re: Should I build some new headers?

Post by GRTfast » Mon Oct 23, 2017 10:48 am

prairiehotrodder wrote:
Mon Oct 23, 2017 10:38 am
open headers vs mufflers can be deceiving to the butt dyno. All the noise kinda makes it feel slow even though it may be going faster than with the mufflers on.

When i take my car to the track its faster without the exhaust but it feels slower. All the noise ringing in my ears seems to steal away the feel of the acceleration.
I agree. The fact that it doesn’t seem to feel much, if any faster with the open headers makes me think my current setup isn’t too bad (regarding the mufflers).

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Re: Should I build some new headers?

Post by F-BIRD'88 » Mon Oct 23, 2017 10:56 am

Yup that cam is going to "SIGN Off" early.

i have a few recommendations for you.
These are relativly Mild BBC solid street rollers. But will have a much more extended power band.
Great "drivability".

Comp cams #11-770-8 Extreme street roller XR274R-10
Degree in "straight up" 110/110 centers instead of advanced 106/114 centers.
Set the valve lash COLD at .010". It will be quiet like a hyd and stay set forever.
use correct valve springs. The springs you got will not work.
This cam is relatively mild in BBC cam terms.

if you are willing you can step up the next cam 11-771-8. XR280R-10
Install as rec 106-114 centers.
Again set he valve lash tight .010" COLD set and forget no fuss.
More top end more rpm Still very much a Street cam.
its the LS6 BBC cam in a modern street roller form Great power.
The Comp K Kit" cam kit for this gives you everything except the cam button
EG: comp #K11-770-8 for the XR274R-10 cam + K kit. The price it right too.

With either of these you will have the bark and the bite too yet are "street driver" cams.
The solid roller lifter performs MUCH BETTER at 6000+rpm in BBC with its heavy valvetrain than a hyd roller lifter does.

Alternative brand but same same is a Howards cam #120183-10 (110LSA) or 120183-12 (112LSA)

All these cams will drive find in your stated critical driving rpm point.
The 112LSA cam has a slightly nice idle.

All these will show a much nicer overall powerband than the Rabbit cam in a BBC.
Nicer drivers too.

I bet you will find the tone of the exhaust nicer too overall.
Not so soundy.
You get the idea.

Remove all the current "Rabbit cam" cam and components stick them in the comp Boxes and ebay the whole thing. This will minimize the net cost. You'll be way ahead of the game.
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Last edited by F-BIRD'88 on Mon Oct 23, 2017 11:14 am, edited 1 time in total.

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Re: Should I build some new headers?

Post by F-BIRD'88 » Mon Oct 23, 2017 11:04 am

That is the kind of cool street rod that you put the Edelbrock Dual QUAD's on.
That motor and car needs the Dual Quad RPM air gap Induction setup and one of these lil Comp XR mechanical street roller cams.

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