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305 heads on a 350

thebluemax

thebluemax

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I found a shortblock 350 that the guy said he'd throw in a set of heads with it free, but the heads have an unknown history. I have a 305 in my truck right now and I know the heads and engine were rebuild at some point before I got the truck years ago. The truck has been sitting pretty much since 02. I've run the engine here and there. But never really put the truck on the road for any length of time. Would it be better to use the 305 heads or the 350 heads?
 
Use the 350 heads, the 305 heads have tiny valves and intake runners. Plus they'll raise your compression ratio which will require premium fuel.
 
I put 305 heads on my dads 350 and it worked well, i can even say the truck runs better now.
 
The truck is an 84 K10, I don't need it to be a hot rod. Heck I was happy when I put an Edelbrock Performer Intake Manifold/Carb/I've heard opinions both ways on this idea, keep the advice coming.
 
I wouldn't unless you are going for a high compression performance motor. As stated above, the valves are tiny and your engine wouldn't breathe well. My machinist actually discouraged me from using 327 heads on my 350, so I definitely wouldn't use 305's. my .02
 
38377k5 said:
Use the 350 heads, the 305 heads have tiny valves and intake runners. Plus they'll raise your compression ratio which will require premium fuel.
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Like Chris said:rolleyes: , small valves and ports, combined with higher compression do not equal a good idea. Find a set of used vortec's if you dont mind changing intakes or look into a decent set of rebuilt/ reman / or aftermarket heads for a 350.

I have to admit I am speaking from expierence (or lack of :doah:) I put a set of 305 heads on a 350 when I was 17 or so.
My first K5 was a 305 truck and when the engine died I replaced it with a used 350, I took the 350 heads to a machine shop to have screw in studs, new valve springs and a valve job done only to find out they were cracked. In my haste for wanting my truck up and running I took the 305 heads in and had them done instead. What a waste :mad: , it never ran great, would pinge unless it was drinking high test and could not run much timing in it either. About a year later I swapped in a set of redone double hump 1.94 heads, night and day difference, more power better mpg and I could run regular fuel with more timing and no pinging.:D
 
The engine I have in my 86 has 305 heads on it, but the pistons have enough dish in them to not be a problem. I am not an engine builder. If it wasnt rebuilt to accomodate the compression bump and you want it to run high RPMs dont use 305 heads.
IME Kenny
 
How does this sound as far as a buildup for a mild 350. 4 bolt main block, bored .30 over, maybe a set of flat top pistons, performer intake, either a performer cam or a crane 4x4(not wanting an aggresive cam), 3 angel valve job, maybe some porting and polishing?, edelbrock performer 600 cfm with an offroad needle and seat, hedman elite headers, dual 2 1/4 exhaust with cats and 40 series flowmasters straight out the back? It sounds good on paper but anyone running a similiar setup? How does it work out?
 
Before you can even begin to plan an engine build you need to know how you plan to use the vehicle and other parts of the vehicle are going to dictate how the engine build goes.

Porting and polishing is a huge waste of money unless you plan on running high RPM's constantly (over 6K), gasket matching would help though slightly. If you are looking for torque then a single 3" exhaust will produce more low end torque over a true dual exhaust. Also Crane cams is now out of business. Comp cams has been the choice of cams for many years now with their leading edge technology.

Also, stay away from the 305 heads as they will raise your CR 2 points over a 350 head. If you run an iron head you want to keep the CR close to 8.5:1 to be pump friendly on gas, and if running aluminum heads you can go as high as 10:1 on the CR and still be pump friendly on the gas.
 
Never seen a 350 bored .30" over :eek1:........okay, just busting your chops as I'm sure you meant .030". But keep in mind the ONLY reason to bore the cylinders this amount is if you are rebuilding the engine and the cylinder walls need freshened up, not for power reasons.
 
I'm running a similar setup with my new 350: bored .030 over, flat top pistons, comp xtreme4x4 cam, performer eps intake and performer 600 carb, hedman hedders, 2 1/4 true duals, msd HEI dizzy, iron heads (not 2.02's), and a flex fan...

I like how it runs, it has way more low end grunt than I ever saw out of the old 350, average compression, and a good idle considering the aftermarket cam. The key to building an engine is to fit it to your needs. I didn't worry about gasket matching or port/polish because this engine will probably never see the other side of 5000 rpms, but makes most of it's torque and power between 2500-3000, with a good amount of it right off idle. I researched all the components for weeks before I ever ordered them, to find a combination to fit how I would use it. Just like Scott (4x4High) stated above.
 
stock 305 and 350 head use the same 1.94" intake and 1.5" exhaust valves... i don't see why y'all said not to use them because of the tiny valves...?

i built a 350 in my first '70 Chevelle and had 305 heads done on it... stock valves with a 3 angle job and ported and polished... ran like a raped ape...! ran mid-10's in the eighth through the stock powerglide and mini-spooled 3.08 rear...

i'm getting a Blazer that's got a 305 in it... i think the heads are going on my 350, since i run premium anyway (no matter what i time it at it ping'd on 87) - this was a government truck with no cat's on it (yeah, in '86) and the fuel inlet is big enough to take the old 'premium' pumps...
 
305 heads mostly used 1.84, some had 1.72's The 305 bore will not accomodate anymore than that.

Scott pretty much nailed this one....take heed to his advice. See below:


Before you can even begin to plan an engine build you need to know how you plan to use the vehicle and other parts of the vehicle are going to dictate how the engine build goes.

Porting and polishing is a huge waste of money unless you plan on running high RPM's constantly (over 6K), gasket matching would help though slightly. If you are looking for torque then a single 3" exhaust will produce more low end torque over a true dual exhaust. Also Crane cams is now out of business. Comp cams has been the choice of cams for many years now with their leading edge technology.

Also, stay away from the 305 heads as they will raise your CR 2 points over a 350 head. If you run an iron head you want to keep the CR close to 8.5:1 to be pump friendly on gas, and if running aluminum heads you can go as high as 10:1 on the CR and still be pump friendly on the gas.
 
If I'm not mistaken, the problem is that the 305 chambers are small, which means that even with the smaller valves, they are shrouded. You get very little benefit (all things being equal) from a mild compression increase, head efficiency is where you make power, and why Vortecs and all similar KILL these old designs in every aspect, at every RPM.
 
86-1ton said:
stock 305 and 350 head use the same 1.94" intake and 1.5" exhaust valves... i don't see why y'all said not to use them because of the tiny valves...?
Click to expand...

You are dead wrong on that statement. Read the 3 posts above this one.
I cant say more than what has already been said.
 
While I agree that 305 heads aren't a great idea, they can still work OK. When I bought it, my camaro had a 350 with ported 305 heads (450 casting, IIRC) and was otherwise a stock TPI motor. It made respectable midrange power, ran on 87 and got great mileage. Would have been great in a truck when you compare them to most stock 70's truck heads... when $ is a concern. I'm certainly not a pro engine builder either though:doah:
 
USSkoval said:
While I agree that 305 heads aren't a great idea, they can still work OK. When I bought it, my camaro had a 350 with ported 305 heads (450 casting, IIRC) and was otherwise a stock TPI motor. It made respectable midrange power, ran on 87 and got great mileage. Would have been great in a truck when you compare them to most stock 70's truck heads... when $ is a concern. I'm certainly not a pro engine builder either though:doah:
Click to expand...

I wonder how much better it ran with correct heads though. The 305's can work, its just choking the engine for air. Just think of it as a big air pump, the more you can pull in to the cylinder, the more output you can get out of the engine. The 305 heads are like putting a restrictor plate on a Nascar engine. It will run, just not as good as it could.
 
76zimmer said:
I wonder how much better it ran with correct heads though. The 305's can work, its just choking the engine for air. Just think of it as a big air pump, the more you can pull in to the cylinder, the more output you can get out of the engine. The 305 heads are like putting a restrictor plate on a Nascar engine. It will run, just not as good as it could.
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The same 350 now has a set of edelbrock heads on it and it can now hang in there with the stockish LS1 cars, but there are many more things that were done besides the heads. My only point was that the 305 heads are a decent choice when you're on a tight budget.
 
Would I be better off using a complete Vortec 350 out of a early 90's 1 ton? I've got one that's been pulled and is sitting in the back of a truck. I bought it off my friends grandad who pulled it to put a crate engine in the truck. My friends dad said that the engine just needed a rebuild. Since he's been turning wrenches for close 40 years professional I took him at his word. Anyone have a ballpark idea on how much a rebuild would cost roughly? Assuming the engine doesn't need a lot of machine work? I have no idea where to even start on this.:confused:
 
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