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I am adding a four barrel eldebrock 500 cfm carb. and headers to my c code 66 289, how much horsepower do you think I will gain?
 

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This upgrade works best with new exhaust too, or at least having true dual exhaust. I have the 500 cfm Edelbrock, and it has been great, no tuning out of the box other than a slight idle adjust.
 

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I'd say closer to 25, since you are basically turning a C code into an A code. Factory specs were 200 and 225, respectively. The headers really don't come into play until you hit very high RPM's, but the dual exhaust is beneficial throughout the RPM range.
 

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Not entirely true Joe, as the A codes had flat top pistons that would make a bit more power out of the extra tuning and larger carb. The most significant increase in power comes moreso from good tuning and tweaking than the extra carb. Add some head work, more aggressive cam, and a decent exhaust system will get you even more (sarcasm).
 

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Heads and compression are where you make most of your horsepower.
 

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How about a little more info on your present exhaust system? Are you just adding headers or a whole new system? I bought a slightly used factory style 2" for my 66. I tossed the mufflers because inside, they necked down to something like 1.25" inside! Talk about restriction. I used Dynomax instead. Switching from the single system to this made a huge difference even with the stock exhaust manifolds. Felt like the engine gained 50 CU IN.

Probably won't notice too much difference with headers around town but in the higher RPMs you will.
 

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I have 2" duel exhaust now but the mufflers are leaking and I am replacing them, what do you recommend?
 

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Which intake do you plan to use? Gonna swap to a logical cam? There are lots of muffler choices; I prefer Flowmaster, 50 series Deltaflows. With a cross pipe, there is a noticeable increase in torque and horsepower.
 

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Not entirely true Joe, as the A codes had flat top pistons that would make a bit more power out of the extra tuning and larger carb. quote]

I learn something new every day. I did not know the pistons were different, except on the K code.
 

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I have 2" duel exhaust now but the mufflers are leaking and I am replacing them, what do you recommend?
I suggest Magnaflow, Dynomax Ultraflo, or Dynomax super turbo (mild sound). I have the Ultraflo mufflers on mine and love it. I have had Blowmaster of various models on different vehicles and the hollow tin can sound and drone from them is terrible.

I would guess about 20 hp gain.

Do you already have the headers? I would consider HiPo manifolds.
 

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Make sure you put your edelbrock and summitracing stickers on your back window. Those are easily worth 10hp....each. ;P
 

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Joe, actually the A code and K code shared the same pistons. The only real difference was the rod bolt size on each rotating assembly. Obviously, there were other differences as well.
 

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I am adding a four barrel eldebrock 500 cfm carb. and headers to my c code 66 289, how much horsepower do you think I will gain?

Hi,
As has been noted, you "do" want to add an improved true dual exhaust system, preferably, 2 1/4 or even 2.5 (for future growth). Choose headers that make torque. After all, this is what you feel when you kick it in the arse as a street warrior.
The ever popular and well known headers, are the classic TRY-Ys and should be coated. Being coated, they will last just about for ever. I've had mine since '96 and they do work well and, by all means, add a balance tube to the system.

BTW, good first choice on the carb size. Before you change anything, note all of your basic settings to baseline. This includes idle RPM, timing, point setting, engine vac. and check the plug settings too!
After you install the carb and reconnect your dizzy vac, warm the engine and, hopefully, the engine will idle, out of the box.
Set the idle RPM (700-800).
Next install a vac gauge to the one port that offers "full" vac at idle, as there will be three (ported, PCV, & Full vac). Your engine vac needle should steady with a reading of between 15-22, or so. The higher the better with 18-20 being about avg.
If no problems, and the engine idling at 700-800, or so, timing at 10-12 or whatever, slowly begin to turn one of the mix screws CW, noting the reaction on the vac gauge. If it starts to drop, slowly reverse until you get the highest reading on the vac gauge. You may likely see the Rs rise, as well. If for example, your baseline vac is 18 Hgs., and it rises to 18.2-3 and stops, this is good. If, at the same time, the idle crept up a few Rs, lower to the baseline setting.
Repeat for the other mix screw. Having an engine vac gauge is a valuable tool. Having a dial back digital timing light is another valuable tool.
Knowing how to use them is ......"priceless"!

Documenting this stuff will provide important baseline compared to your tuning data going forward.
Good Luck!
 

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Take the advertised gains, multiply by 0.10, and that is about what you will see in your application.
15 horsepower sounds about right. The 2v cam won't give you enough top end for more.
 

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Make sure you put your edelbrock and summitracing stickers on your back window. Those are easily worth 10hp....each. ;P
That only works on Chevys. And only if they have a tunnel ram intake on a stock 307ci engine, slotted mag wheels, spring shackels and N-50 tires with the back end 10 feet in the air. Oh, and I almost forgot, Pete Jackson gear drive on the cam whining so loud you can't hear the motor.
 

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I forgot to say it before. Nice 66 by the way. It looks alot like my 65.
 
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