Bone stock 85 305 upgrade

[75gmck25]

Start out with determining a rough budget. Then price out a 350 or 383 roller block, and either Vortec iron or aftermarket aluminum heads. This should be your starting point for upgrading.
- A Vortec or aftermarket aluminum head will outperform any camel hump or other gee-whiz head from the 60’s. Your goal is a good flowing head and about 9.5 compression (to run on regular). Your stock smog-era heads are really horrible.
- with a roller cam you won’t need to worry about wiped lobes and can use more aggressive ramps without breaking anything. The only downside is that it costs more up front. For best gas mileage you would use around 195 or 200 duration, but up to about [email protected] will give you more power without screwing up gas mileage too much.
- by mid 80’s GM had mostly solved the bowl leak issue with the Quadrajet, but throttle shaft wear is still something to look for. Don’t have sticker shock when you find out how much a quality rebuild will cost.
- switching out your 3.73 gears is not worth it when you have a 700R4 already. It’s actually a very desirable ratio for both power and gas mileage.

My GM 350 crate has the upgrades above, along with headers and full duals, but I have 4.10 gears and a TH350, and full-time 4WD NP203. My highway gas mileage is about 10.5 MPG if I keep it down to 65-70 mph. When I looked at old car magazine reviews of these trucks I found that even then they only got 14 MPG when driven on the road.

 

[xm20k]

The downside is a new vortec block is twice what they were just 5yrs ago

Pardon Our Interruption

I built a non roller 2 bolt block recently I bought a short block for $1500 swapped in a set of hyper pistons $325, 4340 rods $320, roller cam $550, retro roller lifters $700, aluminum heads $1000, stainless roller rockers $330, intake and 850 carb $800, headers $300, summit dizzy and box $500, gaskets sealer misc $250

Accessories, bracketry, starter, fuel pump, stuff I already had on the shelf.

$6600 roughly however this is probably closer to 375-400HP

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A 300HP roller long block may be a bit of a time saver but depending on what extras you need may or may not save you money.

Pardon Our Interruption

 

[blackdot25]

In 2023 a friend and I replaced the stock 305 from his 1984 GM Square-body Shortbox. Same color as yours. We found a freshly rebuild 1980 355 with vortec heads and swapped that in place of the leaky 305. The truck had a TH350 with lock up converter and we chose t o rebuild that and add a higher stall converter instead of going the 700R4 route. We replaced the 2.73:1 rear axle gears with Richmond Gear 3:42:1 Gear Set using Auburn Gear Grip-N-Loc Limited Slip Differential Carrier. The 305 always droned annoyingly on the highway so we founds some really nice sounding Borla mufflers and added them behind the Hedman Standard Duty Black MAXX Ceramic-Metallic Coated Mid-Length Headers. We are very pleased with how it all turned out.

 

[peats]

300 hp and 20 mpg is a wet dream IMHO.

 

[BadBowtie]

I would ditch the 3.73s and move in a new set of 3.42 gears. Also slide a non-EGR aluminum intake under the Rochester carb. Definitely need aftermarket aluminum or GM Vortec heads, do some port and polish work. Add the biggest external trans cooler that will fit behind that radiator grill- If it doesn't already have one. Good luck...

 

[JBswth]

so what you got is a 40 year old, 2wd survivor,...that may get 14mpg on a good day.

18-20mpg on straight uninterrupted highway (no idling / poking along in town)
and 285~300hp.
= a 5.3 gmc engine truck from 1999-2006 era.

for time / energy/ sanity of while building a house on your brain, such would be 1999-2006 with the truck attached to it.
(if to swap, I would suggest a running / wreck / rust bucket of a 1999-2006, so you can get all the major / minor / forgotten parts at your finger tips)

but that is just my initial assessment. (plenty of people here with better ideas / builds , ...welcome aboard though).

If you put a more aggressive cam in it, you can't use taller gearing, as more aggressive cams mean LESS torque, except at high RPM. Ditto gas mileage. Aggressive cams mean BAD mileage. Mild cams mean GOOD mileage. Swapping to a 350, but leaving it stock, will give you more torque, therefore more fun, but souping it up might make it incompatible with truck-duty.

J. B.

 

[JBswth]

Hello members:

New member here. I purchased a bone stock 85 2WD long bed this past spring. 2 tone brown. 43k miles on a bone stock 305 (VIN Code H LE9). Stock 4 speed auto with a shift kit the previous owner had installed.

She's pretty loaded: Power locks, power windows, A/C, cruise, cassette, Silverado trim. The 2 tone brown (technically, "Saddle Tan over Indian bronze") seems invisible to the cops. I call it "grandpa brown 2 tone."

I was specifically looking for a unmolested survivor. The paint could use a polish, but it looks pretty darn good for 40 year old single stage.

It still has the AIR pump, EGR, everything. With 43k original miles, the 305 runs fine, but leaves something to be desired in the "fun" department (and the valve seals, along with every other rubber seal on this 40 year old engine, are shot).

I am looking to upgrade to a Gen 1 350. I live in northern Michigan. This is my daily driver in the summer and fall.

Here are my goals:

Retain Quadrajet and Q-jet manifold (I love the sound of the Q-jet's secondaries opening). And 99% of the time, I'm not into the secondaries anyway. I will address the Q-jets weaknesses of fuel bowl leaks and throttle shaft vacuum leaks with epoxy and bronze bushings.

Retain original air cleaner. I have the giant 5.5" tall air cleaner with what appears to be a pretty darn good factory cold air setup.

Get 300 hp at the flywheel with exhaust manifolds (I don't like burnt spark plug boots / exhaust leaks).

I have some aluminum "Camel hump" heads. These have no exhaust crossover so EGR will be deleted on new engine. Looking for a stock looking and stock sounding Gen 1 small block. These have 2.02 / 1.60 valves, so the 305s bore size is out. Hence the 350.

Goal is 20 mpg on the highway at 70 mph on 87 octane. She currently gets around 15 at 70 mph.

Rear axle ratio is 3.73:1. With my tires, it turns about 2,200 RPM at 70 mph in OD. I am willing to go to a 3:55 or something even taller (3:23) - even at the expense of torque. This extremely mild 350 with 3:23s will still be leaps and bounds past the stock 305 with 3:73s in that department.

Basically, I'm looking for a bone stock looking Gen 1 small block with a more modern power to cubic inch curve. I also want a very smooth idle (and good mpg), so I'm not going crazy in the cam department. Looking for 18" plus of manifold vacuum at idle.

Usage will be many 80 mile round trips to to Menards. We are building a new house this spring. Wanted a little more grunt for passing on the 2 lanes, It's pretty scary with the 305. She takes her time from 50-70 mph.

Asking about if I should go with a Vortec or Gen 1 style 350 block. I like the Vortec for the 1 piece rear main seal but is there anything else to know using a Vortec block with Gen 1 style heads? Are there modern 2 piece rear main seals that are just as reliable as the Vortec style 1 piece? Hunting for either a Vortec or Gen 1 350 shortblock will open up more options for me.

Advice appreciated

Thanks

Also, do you live in a smog exempt area? If not, then you CAN'T do what you are saying. They will not pass you, in many localities, even if it passes at the tail pipe, as it is supposed to be and look EXACTLY FACTORY STOCK under the hood, so you have to leave all the smog junk on it. If you are up to it, you can remove it, but put it back on for smog checks, then take it back off.

J. B.

 

[Traucht]

Also, do you live in a smog exempt area? If not, then you CAN'T do what you are saying. They will not pass you, in many localities, even if it passes at the tail pipe, as it is supposed to be and look EXACTLY FACTORY STOCK under the hood, so you have to leave all the smog junk on it. If you are up to it, you can remove it, but put it back on for smog checks, then take it back off.

J. B.

Or you can move to a free(r) state!

Kind of reminds me of my co-worker who had a very hot built 454 in a chevelle. He got pulled over once after totally smoking the tires through an intersection after taking off when the light changed. The cop said "you know you CAN'T do that". My friend said "I think I just showed that I can".