I know this may be a very common question but I'm trying to get more power out of the stock L-48 engine in my 1978 corvette. I'm not interested in an engine swap of any kind. I found a pair of 1984 HO 305 heads with 58cc. Casting number 14014416. I want to know if I can bolt these on without having to make any changes to the rest of the motor. Should I have any concerns about the increased compression being an issue? (I also plan on getting a better camshaft than the stock one, that will come next.) I'm not looking to get a crazy amount of power, I just want some more punch than the base 185hp. I'm relatively new to engine modification and I would really appreciate the guidance and help.

 

those 58cc heads along with a 0.015" shim gasket will make right at 10:1 SCR with a Perfect 0.040" quench ...
... an effective quench, in and of itself, helps prevent detonation.

AFAIK, they'll bolt up. More compression & more cam is exactly what an L48 needs.

If you swap cam at same time & use a wider duration ... that'll effectively bleed-off a little compression.

From what you've expressed as what you want, seems like it should do it. G'luck

 

Honestly you could probably get a similar hp/torque boost just by upgrading the exhaust. In terms of cost, deleting the cat is probably the best bang for buck out there. Very cheap, very quick and probably at least 30hp.
Nothing wrong with swapping heads, some of the head bolts are a pain to get to if the engine stays in the car(I’ve ruined my cam
bearings once swapping cams with the engine in the car). If you’re just looking for 50ish hp, id consider starting with the easy stuff like exhaust and recurving the distributor. If it’s not enough, jump into head and cam swap

 

I couldn't agree more with the first two responses, better exhaust ,(proper free flowing from the engine back), and a quicker advance curve in the distributor and you'll think you've found 50 hp. The heads will help and it's been mentioned by a gentleman on the Chevelle board that uses 305 heads alot - that you don't need to worry about using the original 1.84" intake valves either, a larger 1.94" valve gets shrouded by the small chamber.

"randallsteel" has it right and that's the way to start, and just do the new cam, (smallish cam), with the heads swap when that time comes.
None of it's that expensive either.
Happy Holidays ! $.02

 

Heads and flat tappet cam of moderate lift .475-.489, short duration 219, along with those heads and you should easily get 50-75 Gross HP, assuming the bottom end is in good shape.....That 180 Net HP on the 78 L-48 would turn into about 250 Net HP which is almost identical to a stock 74 L-82 with 250 Net HP before emissions but with better lower RPM power than the L-82 of the time....

 

Do not waster your money and time on those. They have pathetic intake ports and a 1.76 intake valve....any gain you make through compression will be negated by an intake port that doesn't even flow 200 cfm. They are meant for a 305 bore at 3.760".....stock 350 is 4"......it is totally not worth it, even the later L-98 Tuned Port heads are not really worth it. The only GM head swap that is worth it is the 96-99 Vortec head and it requires some extra equipment to use them.
If you are bucks down.....do these four things:

Install a Comp 268H cam....this cam was designed for low compression 350's in the 80's and it works. Use Elgins "Z-28" valve springs and spring lock retainer kit with new umbrella seals.
Install a 2101 Performer manifold with 1204 Fel pro intake gaskets. This will shave 25 lbs. off the front end and do away with the woeful low rise Q-jet intake. It will compliment the cam nicely.
Install a set of long tube headers and a real 2.5" dual exhaust. H and X pipes help but are an added expense and not too helpful at this level.....use a Magnaflow or Pypes muffler.
Curve the distributor or buy an MSD Ready To Run unit and curve it. Read Lars papers on timing and curves.....E-mail him and he will send them to you. This curve is VERY important to power and overall operation.

This will give a healthy L-48 and pretty huge jump.......you will be at just a touch over 330 horse at this point.....or about 260 at the tire. Now to put that in perspective, that is what a 97 Camaro SS LT1 makes at the tire.....now scorching but good power.....It will run better than an early 350/300.
At this point......if you want heads......install them! You now have a real cam, intake and exhaust to supplement them. Or pocket port the stock heads....but only if they are in pristine condition.....wore out heads are a diminishing return.

Yes the L-48 is a low compression engine, but it responds well to mods. Move on from 305 heads though.

Jebby

 

w/jebby. Unless you do real heavy mods those heads are a waste of time. Lots of guys talk them up mainly the 305 die hards, sorry but out of the box they are the farthest thing from a performance head even though they give more CR

Ig you are $ limited do a decent valve job, bowl blends are cheap and the proverbial 256-268 type cams. headers etc.

 

More Intake flow (Eddy 2101), more exhaust flow (headers) more head flow (cam lift) BUT you still have those tiny-little valves to choke everything up.

 

The 1.94 valve is much larger than the 1.76 on the 305 heads....
And most of us know that the factory 2.02 intake valve was worthless on a stock head....GM never did a decent valve job or open the throat....very little actual gain....
Yes....real heads are the answer but not everyone has the budget....

Jebby

 

I can see where you're coming from, but I cant afford most of that, the 305 heads I found are super cheap while still being in good condition, I already have an aftermarket dual exhaust on the car. I just want to know if its worth it to put the 305 heads on with a decent cam and just call it good there. How much hp could I gain without doing anything more than that?

 

Heads and cam is where power is made. So if you do the cam and those 305 heads you will see a little increase in power just for a slightly better cam. The heads are not going to give you any noticeable power gains unless your stock heads are in real poor shape. Honestly I would not waste time or money on 305 heads. They are pretty pathetic heads as far as performance goes. Save for a better set of heads.

 

My opinion, do it. Raising the compression ratio will really make a noticeable difference on the low end. A lot of people have commented on how those heads have too small of valves to flow well. Which is true, but that won’t be an issue till 3500+ rpms. I think you could get 30 wheel horsepower gain on the lower end by raising CR 1.5 points.
Flip side, you definitely will not lose power, so if they are really cheap and good shape, I’d do it.
I think we’d all appreciate hearing the results

 

Kick the 305 crap to the curb and grab a pair of Vortec heads. It'll also require an intake but will be the biggest bang for the buck possible.

 

If a head swap is something that you really want to do, and the "305 style" heads are up your alley, 'World Products' made an "improved" casting, specifically designed for the small bore, 305 engines. I thought about a pair of them, for a while, for a mid-80s, 305 engined Firebird that I used to own. I'm not sure, however, if WP still makes them....or if WP is still in business, for that matter.

 

None....did you read my post? The increase in compression is negated by an intake valve that is .180 smaller than stock.....
Do not waste your time.....
DO do the four things I mentioned.....intake, headers, cam, curve.....

Jebby

 

World Products is alive and well. Most after market suppliers, Jegs, Summit, offer their heads. Here is a link to their Facebook page https://www.facebook.com/World-Produ...4505837561735/

 

I get it, small money. Do It. But of Course, First put a good tune & curve on it. TRUE duals, right? ... 2 separate mufflers ... one for each bank, right?
Lotsa 305 heads have teeny 1.76" intakes, but not all. Those x416 L69 305 HO heads probably have 1.84" intakes, not 1.76" ... 0.100" smaller than L48's 1.94" intakes.
If HO heads are really cheap, do it.
You Must ensure spring setup can handle whatever lift you choose. I would stay below .480" lift as the heads won't perform above that anyway. I would install New springs.
That 268H cam is a good suggestion but Summit's cam & lifter kit https://www.summitracing.com/parts/s...make/chevrolet compares favorably and actually has ramps a bit more gentle and much easier price (K00172 cam+lifter KIT $143).
Unless you've recently changed timing set, you should get a new set as well ... for this, spend no more than $35 on name brand set. Plus New cover seal & gasket.
Unless you've recently changed damper, you should FIRST assure it's still good by verifying Zero groove on damper aligns with timing tab Zero when #1 PISTON is at True TDC ...
... But If you do need a New damper, for this you Don't need one for a race car ... replacement grade such as Pioneer is fine.

 

Even the world products units aren't great for a 350. Look on racing junk or other sites for a bargain on decent heads. But be careful.

 

World Products now part of PBM-Erson family ... still USA-made ... still showing the 305 head S/R ... has bigger 1.94" intake w/ 58cc chamber
They also offer 50cc chamber S2s
http://www.pbm-erson.com/UserFiles/D...eb-version.pdf
http://www.pbm-erson.com/catalog/world-products

I had a set of WP S2s ... those were good heads

 

compression ratio is not as big a jump as people think. 8 to 9 is 4%. 9 to 10 is 3%. above 10 is 2% per point of compression. not really enough to justify replacing heads for C/R only.