Additional power changing to 4 barrel carb

jimf81

New Member
Aug 23, 2022
22
Does anyone know if a stop 78 305 would gain any power if I upgraded from 2 barrel to a 4 barrel carb? if so would it be noticable? Also how about if I converted to fuel injection? would that add a decent amount of horses? if so how much estimated do you think? Trying to see what options I have to increase power besides replacing engine entirly, currently its the origional 305 in it runs great still only 69k miles on it.

thank you
 

72BIGBLOCK

Veteran Member
Feb 2, 2008
2,939
SF
If it was me with current gas prices 609-625 I’d leave the two barrel, enjoy the car and start looking for a new motor on the side like a 5.7 or a 5.3
 

jimf81

New Member
Aug 23, 2022
22
So i take that changing carb will add very little extra power maybe 5-10 horses max? Due to this being bought by my dad new in 1978 I would like to keep as much of this original. Besides some modifications to get some more power out of it. Would like to get at least 200+ horses if I can currently stock is only 145hp on this as of now. Trying to see what I can do. Any advise would be greatly appreciated.
 

72BIGBLOCK

Veteran Member
Feb 2, 2008
2,939
SF
To get that from 145 to 200 I’m assuming you’re going to need, carb, headers, exhaust, intake, and maybe even some heads and a cam but you’ll still have a 305, I’m only guessing here I’m sure someone with more experience will chime in.

Those years has low hp numbers especially on a 305. You can always drive it as is which I’m sure drives well having low mileage or remove the engine and store it because adding those parts ain’t cheap unless you do it yourself

Have you tried maybe just doing some maintenance like plugs ? Cap? Rotor? Wires etc ? Maybe that will wake it up a bit if it’s been sitting for a while
 

jimf81

New Member
Aug 23, 2022
22
i replaced plugs already they were bad all gaps were different as well. That made a big difference. I ordered wires but somehow they delievered to wrong address so never got them. autozone is shipping new ones maybe that will help more. Have not touched cap and rotor yet. Im not to sure how to play with those im learning things as I go, so if anyone has videos on doing that I would appreciate it.
 

Twisted_Metal

Administrator
Staff member
Lifetime Gold Member
Feb 26, 2004
31,660
Bloomington, MN
Vortec heads would help but that will require a different intake manifold.

A 4-bbl carb has more potential but the heads and intake need to get more air/fuel to the cylinders and out the exhaust before you will see (or feel) much improvement.

Major improvement would come with raising the compression (different heads) and swapping a camshaft chosen to work with the rest of the parts AND your goal for the way you want to use the car.

Think of an engine as an air pump.

Improving the flow in and out improves the output.

Individual engine parts all have their role and changing one thing at a time can make a difference but usually only moves the air flow bottleneck to another part of the system.
 

G72Zed

Veteran Member
Sep 8, 2015
4,228
Canada
Going from a Holley 2bbl to a 4bbl on the same 4bbl intake is about a 7-10% HP gain, slightly more if going from a 2bbl intake to 4bbl, again many variables.

You are at @ 145hp now, and if the goal is 200hp, that's a 38% increase you are looking for.

Most likely heads/cam/intake/carb/ignition/headers/exhaust will get you there with that 305 base staying put.

More than that, it would be best to go with a 350 based engine.
 

jimf81

New Member
Aug 23, 2022
22
Thank you, so basically going from the stock rochester 2bbl to a 4bbl holly would add about 15hp, so to get best results I would have to try to find a intake from a 350 to go with it.
 

Chevyforever

Veteran Member
Jan 4, 2011
1,512
Canada
Back around 1979, my best friend in high school had a 1973 Camaro 307 2bbl. My father had just bought a 1978 Z28 and removed the stock Q-jet and cast iron intake to make some mods. My friend swapped the factory 2bbl intake combo to that of the 350 and there was a noticeable improvement in seat of the pants acceleration. Was not long after until the 307 blew up and we had an excuse to replace it with a 350. Great memories.
 




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