Tuning a 145HP 350ci V8

Hello,
My 1975 camaro with 350ci, 2-barrel V8 has a mere 145 HP. It is one of the lowest HP camaro's ever I believe.
What would be the first thing to upgrade on this V8?
Should I buy new carburettors, or new headers? Does replacing both at the same time make more sense?
I am not looking for a 500HP beast, but surely, a doubling of the performance should be possible?
Also, what is the difference between a 2-barrel and a 4-barrel engine?
Thanks,
Bram Stolk
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Hi Bram,

efficiency of air going into and out of the engine will increase your power output.
My first suggestion would be to get a larger carburetor. A two barrel carburetor keeps the engine from drawing in as much air as it could. This limits power. It's fine for economy and gas mileage but if you're looking for performance a four barrel is the way to go. A four barrel carburetor would decrease the restriction, thus increasing power. Along with this carburetor you would also need a four barrel intake manifold. I have used Edelbrock aluminum intakes many times. They're weigh less than the cast iron stock intake so they're easier to handle, they allow you to decrease the weight of the car a little and are tailored more for performance over the stock intake.
At the same time you would want to decrease the exhaust backpressure. Again, think of an air pump. If the engine has a front end, 4bbl (4 barrel) carb and intake, but it can't get the exhaust out easily, you will limit your engine's potential. Headers, and dual exhaust will help take care of that.

Replacing the camshaft would be the next thing to do if you're still not satisfied with your power output. A 265-270 duration cam with ~0.46 inches of lift will give you much more performance over stock, yet it will still idle well and your vacuum accessories, power brakes, A/C, etc. will still work properly.

are mixed. They are good for economy but not the best choice for performance. A four barrel carburetor has 4 barrels where fuel and air is mixed, 2 called the primary and 2 called secondary. Primary barrels provide fuel for steady speeed cruising. Secondary barrels provide extra fuel and air mix when you stop on the accelerator.
I hope this helps.

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On Sun, 07 Mar 2004 16:26:15 GMT

David, it does, thanks!
So I'll probably start with the carburettor. However, I think 4-barrel GM original carburettor will be of little use: Chevrolet sold 4-barrel camaros in '75 that only had 10 HP extra. (155 HP for 4-barrel 350ci, 145 HP for 2-barrel 350ci)
I've heard a lot about 'Holly' carburettors. So I will check those out.
Another camshaft sounds very expensive, as the block would require opening up. My chevy specialist garage doesn't come cheap, so I'll start with carbs and headers then.
Bram
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snipped-for-privacy@nospam.chello.nl says...

can't get it back out. The exhaust was restrictive as a part of the emmission control system. Headers, larger tail pipe and a free flowing muffler (Magnaflow or Flow Master) will cost less than a carb/intake and show more improvement per $.
The small improvements with the GM 4 bar. carb. were due in part to the lame cam put in the cars that were more for economy and emmissions than performance. You would have to change the cam to see any real improvement with a bigger carb.
You have to remember what was going on in the 70s. Gas lines and the beginning of the CAFE standard along with concerns about green house gasses, acid rain producing products, lead, and such leaving the tailpipe. The engine it's self is basically the same as the higher horsepower 350s of the 60s. They just need the "oomph" put back in.
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Hi Bram,

The 4bbl carb was called a Rochester and it wasn't the only thing that contributed to the 155hp rating. In 1975 the fuel crisis was in full swing and all carmakers were detuning engines for better economy. If you wanted to use a Rochester it could be tuned to produce more power than stock.

Holley. It's a nice carb too. It depends on what you're looking for. Both carbs have advantages and drawbacks.
What follows my opinions, maybe someone else could add their thoughts as well:
Rochester: Advantages: - Primary barrels are very small compared to the secondaries. This means that if you drive gently and accelerate slowly, you'll get better mileage than a Holley. - Once, they're tuned, you just leave them alone. They don't need periodic adjustments. - It may be easier to adapt your linkages, kickdown cable, etc. to a Rochester Quadrajet.
Disadvantages: - It's not as tunable as a Holley. - The wells in the float bowl can leak causing excess fuel to seep down into the engine. This is correctable, but it is something that does happen with that carb. - To the best of my knowledge there's only one cfm (cubic feet per minute) rating for a Rochester, limiting your engine power if you're looking for top end performance.
Holley:
Advantages: - Very tunable. There are many books and sites on the internet about these carbs. There are many modifications you can make on these to increase power, flow, etc., etc. - I personally think it's a better looking carb than a Quadrajet.
Disadvantages: - Holley's seem to need periodic adjustment to keep them idling well. Not much mind you, just a tweak of the idle mixture screws every once and a while. - You'll need to buy brackets for the kickdown cable (assuming you're running an automatic transmission), and I'd suggest an in-line fuel filter between the fuel pump and the carb. (Rochester's filter is built into the side of the carb).
There are many people in this newsgroup that have very strong opinions on each carb (almost as strong as Chevy vs Ford fans!). There are also other carb manufacturers, Predator, Edelbrock, etc., but I have no experience with these carbs.

not ready for that. That's okay. If you decide to go with a 4bbl carb (whatever flavor), you'll need to remove the 2bbl intake and replace it with a 4bbl intake that will fit the carb you're planning to use.
Some of the aftermarket intakes are taller than stock. Make sure that the one you choose will still allow the hood to close once the carb and air cleaner are back on!
Once, that's done your ready to drain the coolant from the block, remove the old carb, pull out the distributor (make sure you mark on the block or the firewall which way the rotor is pointing so you get it back in correctly), then take out the intake bolts, pry up the intake, cleani the heads and block mating surfaces, and install the new intake. Make sure that you have new gaskets, plenty of sealant, etc. For someone who has done it before it takes a couple of hours tops. If you haven't done it get a book and read up on it and take your time. If this is your only means of transportation consider starting the project on a Friday evening after work and have a friend on call with a car who can take you to the auto parts store if needed.
David
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The best time to have the cam done is:
When he has the manifold off the replace it with the four barrell manifold. A decent bit of the labor is already done.
I'd look into a camshaft at this time too, so the manifold won't have to be removed again. (costing you that labor twice)
Refinish King
wrote:

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You've got to have more horse than that... My 3.8 has 200 stock. I can't wait to make it faster.!!!
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