Additional power changing to 4 barrel carb

G72Zed

Veteran Member
Sep 8, 2015
4,418
Canada
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.

Yes, that would be the best way to do it. When I was 16, I got a 4 to 2 bbl intake adapter and installed a Qjet on my old 350 2bbl intake, it was the only thing I could afford, was it a waste of money/time, yep, pretty much....but your learn as you go.
 

jeff swisher

Veteran Member
Apr 26, 2018
1,962
Yukon Oklahoma
I have had a few 305" engines and 1978 was 2 of them.
Heads are 1.72-1.50 valves.
Nothing wrong with the valve size if you port them.

Back in High school I put dual exhaust on the 78 Nova 305 2 barrel engine.
No headers and picked up a lot of power.
Next thing I did was add a recurve kit to the distributor to make the timing come in sooner.

Another cheap big gain.
2.56 rear gears in that Nova.
I have ran those 78 2 barrel heads on a 350" engine and went 12.51 at 111 mph with stock tiny valves and porting in the 78 Nova without any power adders.

In 1985 the 305 got some better heads the HO305 601 heads with 53.5cc chambers and larger intake valve 1.84"
Love those heads. Ran dozens of them and into the 11's.

Curve kit and exhaust and some gear and probably a 2200 stall converter is what I would do first.
Gear changes are amazing in these low power things.

I have built 305" engines for marine use and the little 268H is amazing in one with 4 barrel intake and porting to the heads.
If you want 300HP that is.

I have ran a lot of 2 barrel engines and they respond better to exhaust first before intake first
if you are starting with single exhaust that is.
 

Rustbucket350

Veteran Member
Sep 4, 2013
1,367
Oviedo, Florida
Yeah. Everything that has been said will make more power. Those engines were detuned from the factory to meet emissions so it's not hard to make them decent. Here's a good example. My 78 2500 has a 73 350 with 882 heads. I have the timing set at 36 total with a vacuum secondary, basic 4 barrel holley, and a crane 274h06 cam. Now I know this combo probably makes all of about 275 hp and maybe 350 lb ft but I guarantee it's fun. It also starts easy every time and runs on 87. It actually has two different heads on it but that's a different story.
 

mallard

Veteran Member
Oct 3, 2013
2,144
SK, Canada
If it were me I might try a TBFI setup as I believe those will fit under the stock air cleaner. However if that doesn’t add much zip then I’d go to a 350. (Or maybe just go to the bigger engine from the get go)
 

tom3

Veteran Member
Aug 1, 1999
15,163
ohio
I think it's great that you want to maintain the stock look under the hood. What I'd do is drive it as is while saving up cash to do it right. Ideally I'd want a stroker 383, mildly built, painted and dressed as stock as possible. Something to think about anyway.
 

sandlapper

Veteran Member
Oct 9, 2020
1,767
SE CSA
right now, you're stuck with a 305's teeny bore, its crappy heads & wimpy cam.
it's not practical to change much without changing block.
A good 2 bbl is rather responsive from idle into mid-range.
Given what you have to work with, suggest keep the 2 bbl in good tune --- until you swap to a bigger motor with bigger (better breathing) bores.

*tip: begin a search for a good, rebuildable core Vortec 350 aka L31 motor from 96-2002 lite-mid GM truck with 8th character in VIN is an "R" --- build that up AND install EFI. Yes, L31 Vortec bolts directly in place of older 305/350 and all come with roller lifters and an improved 1-piece rear main seal design. Last but not least --- those very good, game-changing Vortec heads.
 

sandlapper

Veteran Member
Oct 9, 2020
1,767
SE CSA
^^^this^^^
but, ya won't fool anyone that's savvy --- one 10-foot glance at an intake bolt. Ya can't have it all. Pick your poison and go with it. Tell 'em, yes it's an L31 --- that it's the lump that fell out of uncle Bob's old retired hi-mile Savana van. Are they really looking and does it matter? JMO --- lotsa folks appreciate it if it simply looks nice and runs real good --- and if it seems you did most of the work without breaking the bank.
 




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