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alex Dork
10/13/09 7:27 p.m.

Yeah, I'm starting a new thread, guys.

I recently bought an '88 GMC 1/2 ton with a 305 as a work truck. The motor is healthy, but a little breathless. Not too surprising, considering I've seen dyno numbers around 190 ponies as stock. Eventually, in addition to a reliable work truck, I'd like to make this into a bit of an entertaining sleeper - drop it a couple inches, fat sway bars (recommendations on both are welcome, off topic), and a torquey motor.

So, I'm looking for streetable, bolt-ons. I'm happy to do anything that doesn't involve actually pulling the motor.

And I realize the answer might be: swap in a 350. If that's your argument, convince me that it's worth the extra effort.

2002maniac Reader
10/13/09 7:41 p.m.

I think the heads are a huge choke factor. I'm sure someone who actually knows will chime in though.

06HHR GRM+ Memberand New Reader
10/13/09 7:51 p.m.

Yes, but it's not just the heads. The bore size on a 305 is much smaller than a 302, 327 or 350. Which means you just can't stick heads with bigger valves on the block. The small bore size shrouds the valves. There are 305 specific speed parts out there, but you have to treat them a bit different than a 4.00 bore SBC because of their smaller bore size.

aussiesmg SuperDork
10/13/09 7:56 p.m.

305 V8 performance = there is no such thing

Spinout007 GRM+ Memberand Reader
10/13/09 8:12 p.m.

BAH don't listen to the naysay'ers with a little work the vortec heads bolt on, most 305's have the pistons way down in the hole at TDC so you'll have to shave the heads WAAAY down, 52ccish chambers work well to wake up the motor. Cam, roller tip rockers, a good breathing intake assuming it's a TBI setup you can look into a rpm air gap that bolts to the vortecs, that accepts the throttle body, or you can use the short ram intake and use corvette/camaro fuel rails. A little work and the Short ram is the much better way to go. Not as much torque down low but it won't run outta breath past 4500 rpm. Also assuming you have a 700r4 tranny, a B&M shift kit, and a 2300-2400 rpm stall torque converter will really wake things up. Depending on your rear end gears you may need more stall, but hopefully this gives you something to look into. Also look into back issues of Chevy Hi performance or Super Chevy, they did a series using the vortecs and short ram on a 3rd gen Camaro. Wish those parts had been around when I had my 3rd gen.

Still debating on using a 305 and nitrous in a challenge car one day, just to prove to some people that performance can come out of a 305.

ManofFewWords Reader
10/13/09 8:13 p.m.

Not only is swapping in a 350 more cost effective, its is very easy in that truck. Huge engine bay.

psteav Reader
10/13/09 8:18 p.m.
ManofFewWords wrote: Not only is swapping in a 350 more cost effective, its is very easy in that truck. Huge engine bay.

Because a 350 is physically much bigger than a 305?

Vigo New Reader
10/13/09 8:19 p.m.

^ not at all, they're externally identical for all intents and purposes. Its just that having such a huge engine bay makes doing anything to the motor, like pulling it out, that much easier. As a mechanic, any time i end up working on an 80s chevy pickup, i usually end up crouched somewhere IN the engine bay.

Pulling the motor in a truck like that is super easy. I would trade up to a 350 if your goal is acceleration, considering how easy it is.

tuna55 Reader
10/13/09 8:23 p.m.

Spinout has the right idea. They can be made to work. The bore size is going to limit you though. If you're aiming for 15 second 1/4 mile times, keep it, swap the heads and intake and exhaust (I prefer the carb route though, and it's way cheaper), but if you're looking for any faster than that, go with a 350. Not only can you peruse through core blocks and rotating stuff, but you get something already opened up that you have inspected, and your truck stays running until you plan an engine swap day. Yeah, I said day. It doesn't take long. You'll save more time and effort working on the engine on a stand than you'll save by sticking with the 305.

While you're at it, keep an eye out for a virgin 400 short block - 100 cubes makes a TON of difference. If you build your engine to even 0.9 hp/cu in, that's nearly 90 hp and an equal or better amount of torque gain.

My recipe for any of these engines in a truck is a Vortec head assembly from scoggin dickey, a performer air gap intake, BG demon carb (or holley, if you prefer), headers into an honest dual 2 1/2" system and pick the cam based on displacement.

It'll be fun.

tuna55 Reader
10/13/09 8:26 p.m.

Oh, and definitely throw in a bigger stall converter and some 3.50ish gears - whatever you find will be pretty close. Not to mention dirt cheap - I found a set of 3.73s in a rear axle for $20 for a 12 bolt. I think that has a 10 bolt, but you'll have the same success.

pres589 Reader
10/13/09 9:00 p.m.

Oooh, lookit here;


One of these plus an adjustable fuel pressure regulator could let you keep the decent (not amazing but reliable and, again, decent) TBI unit with, say Vortec heads and an Edelbrock Performer Air-Gap manifold. Then cover the exhaust side of things and maybe a light shift kit and you'd probably be in much better shape.

patgizz Dork
10/13/09 9:26 p.m.

just drive the thing, and if/when the time comes you want more power you'll have been saving up for a vortec headed roller cam 350 this whole time.

belteshazzar SuperDork
10/13/09 9:57 p.m.

don't spend money on a 305.

take your time rounding up parts to build yourself a 350. For a $1000 all-together you'll have something the 5.0 could never be.

96DXCivic HalfDork
10/13/09 11:48 p.m.

I agree with the people saying to find a 350. The 305 isn't a bad engine for a work truck but while the 305 can be made to perform, the 350 is a better starting platform.

914Driver GRM+ Memberand SuperDork
10/14/09 6:00 a.m.

I've had three 305s of similar vintage. Two puked out because the camshaft is only case hardened. With enough miles, the lobes of the cam wear past the thin hardness and once into the 1018 like steel, dies rapidly.

Lifters don't get lifted, some valves get bent. If you replace the cam (can be done without removing the engine) go for an RV cam, better economy near the red line but lots more bottom end grunt.

The heads, specifically exhaust ports seem to be the bottle neck.

Just drive it. Toss $10 in a jug once in a while for when the inevitable happens.


curtis73 GRM+ Memberand HalfDork
10/14/09 8:34 a.m.

The 305 can be made to perform as long as you have realistic goals. The tiny bores dramatically limit valve size and therefore flow. Supporting a 305 past 5500 RPMs gets progressively more expensive.

The argument I always give is this: let's say your goals are 300hp. You'll spend less getting to 300 hp using a 350... even with the cost of buying the 350 included.

Given the fact that you can find running 350s for $300, its just not worth the effort to build a small-bore 305. For that matter, buy a 275 hp Vortec out of a truck for $500, stab in a cam for $200, put on a carb intake for $200, and a Qjet and HEI for $50. $950 invested and you'll make 350+ hp. You won't be able to do that with the 305 for that money.... not to mention the 350 will do it with far more torque at a lower RPM, use less gas, and have more potential in the future.

The other thing to consider is this. If you ever sell it, a 350 is actually worth something. If you put $1000 into a 305 and then try to sell it on CL or Ebay, good luck getting $50 for it.

If you're just looking to "wake up" an engine with a few more ponies, do the 305 but know that your investment won't be financially sound. If you want to really wake it up and make better torque and power for less money, go 350.

alex Dork
10/15/09 9:39 p.m.

These are compelling arguments. Thanks, guys. I'm definitely giving the 350 more serious consideration than before. It's not that I'm against it, by any means. It's just that I like underdog motors. But I also like a high power:money ratio. Food for thought, for sure.

Given what Dan said about the camshafts, it seems like a swap is in order as 'preventive maintenance.' Heh, heh. If I were going to swap cams, what other relatively cheap bolt ons would complement the cam that would serve to wake up the poor old 305? (And just out of curiosity, Dan, what mileage did that problem rear its head?)

914Driver GRM+ Memberand SuperDork
10/16/09 6:12 a.m.

IIRC around 130,000. When it happened to me it took out some valves, bent some pushrods and for whatever reason, took the little pin that pushes the fuel pump.

I can't send you to any site that references the problem, wish I could; but it's not uncommon.


pres589 Reader
10/16/09 6:32 a.m.

See, and I've never heard of the camshafts themselves wearing out on a 305 as a widespread problem. I know that these blocks may be inaccurately machined as far as the lifter bores (which mucks up the lift timing somewhat per lifter) and valveguide wear is well known.

$250 or so should get you a new camshaft and lifters and would probably help wake the truck up anyway so this isn't a terrible problem to have. That said, if you really are leaning towards a 350 buildup, you might as well wait and throw a new camshaft into a different motor during buildup.

ultraclyde GRM+ Memberand Reader
10/16/09 6:34 a.m.

Alex - I've got a set of small chamber (62cc?) 305 heads off a 78 Z28 with new double springs I'll give ya CHEAP. email or PM me or whatever if you're interested. They're just taking up space in my shop. I've posted them twice to CL and gotten no response.

My dad has a 72 p/u with a 305 that shucked a timing chain, bent a bunch of valves, etc. He rebuilt the top end in the yard and it's run great ever since. Not fast with a 2bbl, but strong enough and dead reliable.

In a truly grassroots moment, when the exhaust fell off he bent up a new set of duals out of 2" chainlink fence toprail. Cheap-cheap and never rusts!

maroon92 SuperDork
10/16/09 7:26 a.m.

305 bits are exponentially more expensive than 350 parts.

That hasn't stopped me in the past, but, in your case, you should build a 350. My buddy in high school had a Suburban with a built 350 going 15's in the 1320...then he stuffed it in a 2000 dollar corvette and dropped that time down to the high 12's.

44Dwarf HalfDork
10/16/09 7:41 a.m.

80 vintage 305 had huge problems with #7 cam lubes wear. I've got one here with 40,000 on it with bad cam. I recall several Friends with camaros in high school losing the cams too.

Rob_Mopar Reader
10/16/09 8:52 a.m.

Yea, back when your truck was new I was still in high school. Had a '78 Malibu with a 305 that ate the cam. The early 305's were known to eat cams, but I don't know about the later ones.

At that time, and it probably holds true today, it was cheaper for me to swap in a rebuilt 350 than to rebuild the 305.

If you are using this as a work truck, I agree with the others here who said to leave it alone ans save your money for a 350 swap later. A Vortec 350 would be the way I'd go.


lesabre400 New Reader
10/16/09 1:47 p.m.

I think all that needs to be said has been said already but I'll just throw in one more vote for the 350. Heads and cam on 305s are lousy. If you don't want to pull the motor right away, spend some money on rear gears, a mild stall converter and maybe a shift kit for the trans. That'll wake it up more than bolt-ons. Or a 200-shot of NOS would also help...

pete240z Dork
10/16/09 2:11 p.m.
alex wrote: The motor is healthy, but a little breathless. Not too surprising, considering I've seen dyno numbers around 190 ponies as stock.

My wife had a 1979 Berlinetta Camaro that had a 305 with a 2-barrel carb. I think they estimated it at 160 hp.

I would drive it until it died and drop in a 502 cid engine. LOL

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