1976 Corvette, completely stock small block 350.

Is it worth doing a new cam without replacing the heads? If so, what cam should I spec/install to go with the stock heads?

I’m not opposed to new heads, but I’m also looking at it from a cost + time standpoint too.

 

Here's a bump. I'm surprised no one replied.

It's not worth doing anything to an L48. At the very least, pitch the heads in a metal dumpster, and don't look back.

L82? Same result, but sell the heads on Facebook Marketplace.

 

The cam that is frequently advised (for decades) for this application is the Comp 268H. Works well with otherwise stock engines. Slight lope at idle for that racy sound. It was designed for hopping up a stock L48.

Dont confuse this cam with the Comp 268XE. I would not advise that one as they are very fast acting lobes and that brings durabillity concerns for old stock valvetrains.

there are other cams but this one is a proven selection.

 

+1 to the 268H

I would be looking at getting an ignition and carb tune up as well. If you have the factory 2-1-2 exhaust setup you’ll never get the power you want breathing through that.

Keep in mind that even after a cam and a good tune up, you’ll probably only be around 250-275 horsepower. That’s quite a bump over the factory 180 (assuming you have an L48,) but that’s probably all you’re going to get out of that low compression, 2 bolt main, small block. Probably not worth changing heads unless you get them for free.

I’d say do the cam. The experience of tearing the engine apart, installing new parts for fairly cheap, and cleaning it up can be quite satisfying. Then if you’re wanting more power after that you’ll have a fun car to drive around in as you build another engine from the ground up. Small block, or otherwise.

It’s what I’m doing.

 

+2 on the 268H cam.
It was designed for a stock L48.
That cam, real dual exhaust, turbo mufflers, and you are probably adding 50-60HP.
Yes it will run like a different car.
BTDT
ran great.
The stock catalytic convertor, the original pellet style one, first introduced in 75, was a real choke point.
It added 1/2 atmosphere or 7.5 psi of back pressure to the engine and refused to let the engine breathe.
If you do not change the exhaust, I would not bother.
Just look online for the HP drop of an L48 from 74 to 75, that was the only real engine change. 195 HP to 165HP.
The much better flowing and less restrictive honeycomb style convertor did not come out for a few years.

 

Thanks for the Comp 268H recommendation.

I have swapped out my stock exhaust and went to a true dual 2-1/2” exhaust out the back with Magnaflows.

Follow up question:

If I do swap to a Comp 268H, is there anything I need to adjust with the stock valve train? Or is it as simple as a R&R the cams and get back on the road?

Additionally, what should I be looking at for specs with the Comp 268H (lift, duration, etc).

 

Straight from Jeg’s website:


You’ll need new lifters with any new flat tappet cam obviously. Not sure if you’ll need new pushrods. Many people have done this cam and kept the stock rocker arms, I’m sure they’ll chime in with what length they went with. Once everything is back together just give the lifters 3/4 of a turn of preload.

If you have AC you’ll get the cam out until the very last lobe and it will hit the condenser.

Unbolting it and gently rotating it out of the way should give you the clearance you’ll need, being very careful not to kink any of the lines.

 

Max lift for those stock heads is@.480

 

You absolutely can cam up an LFortyGreat. No, it wont make as much power as a rebuilt 350 with compression that isn't in the toilet or any LS, but it can be done and enjoyed. The Comp 268H was the gold standard for this, but there are some clones or near copies of that cam that will work just fine as well. I used the Summit 1065 (SUM-1065) cam in mine when my factory cam took an early retirement last summer. The Isky "264 Mega" cam was another popular choice. The Summit Racing flat-tappet cams are made by Elgin Performance, just Elgin cams in Summit boxes.


Some points of advice: The cam swap in an L48 is worthless without the supporting mods: headers, duals, proper ignition timing setup, and carb tuning (or EFI in my case). Headers are a must. Summit has a spring kit that works with this level of cam and can be used in the break-in as well. You can also search for and get the Elgin "Z/28" spring kit. Neither kit is much money and will work. The Summit cam above can be packaged with their spring kit as well. For lifters, I used the Melling 817 lifters in my engine and had no issues with break-in. The GM lifters with the separated and hardened foot can still be had, but they are more money.

If you go with the Comp Cams 268H, it will come with a packet of red syrupy assembly lube. Throw it in the trash. Get a tube of the Moroso moly paste (or your brand of choice) to use on the cam lobes and lifter feet for break-in. My summit cam came with a tube of the moly paste.

If your engine still has the original timing gear and chain set with the nylon teeth on the cam gear, replace it. True double roller setups can be had from Summit or Cloyes for not a ton of coin.

I guess you could reuse your factory pushrods, but why? 1-piece pushrods that are much stronger than the factory ones aren't that expensive. Any of these cams will use stock length pushrods.

Some others may chime in on this @CharlieDelta , but you didn't say if you had an auto or manual transmission. If you have an auto, the cams above MAY work just fine, but it may be a wiser choice to go with a cam that is one step below these for driveability sake. Comp 260H or Summit SUM-1069.

All of the cams listed above will still provide enough vacuum to run the headlights and the power brakes.

 

I don't really understand cam specs, but the PO of my 1974 L48 put this one below (and springs) in, while the rest of the motor is stock.
I only recently got a proper Qjet put on, and I've only driven a single other L48 and the steering was so sloppy I was afraid to get into the go pedal.

How does this cam compare to the 268H mentioned above? Also, Lars previously told me you'll get nothing but uninformed opinions on cams here and the only cam worth putting in an L48 is one from an L82. Based on what I've seen of Lars, that pretty much closes the argument, to me.

 

The cam card shows a smaller cam. It has 260 degrees of advertised duration where the 268H has 268 degrees of advertised duration. Lift is similar between them both and not particularly significant here.

The 260H would have a little more low RPM torque, less higher RPM power, and smoother idle characteristics as compared to the 268H.

 

The cam Millie74 mentioned is the Comp 260H cam.
It is a step up from the L48 cam, but the 268H is another step up.

Here are their .050" duration specs.
L48 195*
260H 212*
268H 218*
L82 222* / L46 224*

The L46 cam adds about 600-800 rpm up top vs the L48 one, and has an idle lope you can hear, vs the L48 is very smooth.
GM says there is a 50 HP difference between top & bottom.
The others kind of split the difference
Due to other factors, on a stock 8:1 CR block, the 268 will run the hardest of all four, and better than the L82/L46.
On a 10:1 CR block, the one step bigger L82/L46 is the clear winner.
I doubt there is a noticeable seat of the pants difference between an L82 or L46.
They are all good streetable cams, torquey, not big HP cams.
The milder the rear gears you have you should stay near the smaller ones. (268 & smaller) The bigger ones really respond with more rear gear (268 & up).
So you have a 3 step interval, roughly about ~20HP for each step.

 

So this all sounds pretty straight forward, which makes me feel more comfortable doing the work.

Does anyone have a link to a good set of lifters and pushrods for this project? Additionally, is it worth replacing my rocker arms when I have this all opened up or just re-install the factory ones?

Based on what I'm seeing above, I can use stock length pushrods when I replace them. For the L48 I believe they are 7.75"... Can anyone confirm that?

 

The main part that is not straight forward is the initial start and the 20 min cam break-in.
Especially if you have never done this before.
Do it wrong and you will kill the cam in 3 minutes.
I would search on here for our own expert engine builder Jebbysan's procedure on this, his is one of the best I have ever seen.
Do not follow youtube videos for this, it is too important, and there are a thousand variations.
Many engine builders have not done many flat tappet builds, because GM quit using them in the 1980s or so.
A lot of this knowledge is almost lost.
Basically it must fire and run on the first try, you must use the right lube(s), it then needs to run for 20 minutes, and the cam/springs/lifters you buy all matter.
There are a lot of horror stories on this online on flat cams, and usually it boils down to one of the above.
If you have never done the start up before, you may want to get help, but the danger there is they will want to use their own "procedure".
Do not be misled, use Jebbysan's!
If your helper is knowledgeable enough, he will be OK with it. It may have an extra step or two, so what.
If he objects strongly, find a different helper, it is your car.
It can be the difference between a 5% success rate, and a 100% success rate.

 

I definitely would not use the L82 cam in a stock L48. I did that many years ago in a 75 Camaro. Very soggy bottom end. Big mistake. I had to change the cam out to something milder. As recommended in previous posts, 268H cam or the 260H if you have an auto with like a 3.08 gear. Proven results over the years from forum members.

 

By all means, follow @Jebbysan's cam break-in procedure.

Past member @mobird documented his in-car cam replacement on this Forum. Perhaps that is helpful. He replaced the heads at the same time, too.

https://www.corvetteforum.com/forums...ld-thread.html

 

Does anyone have recommendations for lifters, pushrods and rockers for this project?

I'm planning to do the cam swap without removing the heads, so push rods, and lifters will be replaced. Is it worth replacing the rockers too?

 

So I've found a lot of posts detailing different steps of Jebby's break in process. Is there a complete write up for the break in process?

Also, before I go through the break in I presume I need to take care of valve lash first?..... TDC on cylinder 1 at compression stroke, etc. etc. until I've hit every rocker?

Basically just wondering if I have the correct order of operations here.

 

Depending on your mechanical experience this may be all you're comfortable with...but changing the heads is where the power is. Changing the cam will be mostly disappointing and leave you wanting more more than likely.

Aluminum heads WITH a cam is where you want to be. The stock heads are complete junk, as far as power is concerned. They flow like garbage and have huge combustion chambers resulting in very low CR. This low CR severely limits you cam options with a desirable result.
All this talk about HP from each bigger cam is BS if it doesn't have any bottom end torque left. You don't drive around at 5500 RPM.

I have doubts about Lars stating that the best cam swap for the l-48 is the l-82 cam. I have a feeling that was taken out of context.
If he did say that for a swap such as yours, he's mistaken.
Your CR is more like 7.7:1 or lower. The advertised CR is VERY optimistic. Stick to the lower duration cams if you want any low end torque, throttle response or street-ability.

 

Being that those Mellings are hydraulic lifters, and not solid lifters - Does that effect what pushrods I need to get?