'71 402 engine questions

[deadshort52]

I have a 1971 C20 with a stock 402 motor. I had planned on buying one of the Edelbrock top end kits that comes with the aluminum heads, camshaft, intake lifters and other required trinkets to do the job. I called last week to order the parts... I have been procrastinating for a year to order. I learned that I had two things against me at this point. First is Edelbrock is relocating their manufacturing facility and second apparently covid had caused them to fall behind. I was told that the earliest I could expect delivery is May 15th. I of course have time and want to do it now. If I don't do this project now I won't get to it for two more years. I will be building a new house and shop that will eat up my time.

All that I am looking to accomplish is to add a little pep to this way under powered motor. I don't know the history of the motor but the engine is healthy, it burns no oil, has good compression, no smoke etc. I have been driving it for 5 years now and it's reliable and sound. I had planned to pull the engine and disassemble, clean up and assess where to go from there as to whether it needed further machine work etc.

Now that I can't get my parts and I don't really want to wait I am looking for ideas. I am thinking of just doing the cam, lifters, rockers, intake because I can find these items individually, there are no heads available. I have built many SBC for my own race cars but never have even opened up a BBC. I am seeing the term oval, peanut and square port terms being thrown around with regards to head and intake runners. What did these trucks come with? Is the only way to know for sure to get casting numbers or pull it apart? I have done an in the truck cam swap a couple of times in a square body truck for buddies of mine years ago. How big of a PIA is it on one of these? AM I still better off to just pull the engine?

Thanks in advance...

[Steeveedee]

I got nothing on the hot dog add-on parts, mine is bone stock except for a bore job and "RV" cam. From what I see, you could just wait two years. Mine loses water and oil with nothing on the ground, so I know I'm going to have to do something about it someday. How weak is it?

[70STOVEBOLT]

The heads will be oval port. You you can put a pretty big cam in without worrying about piston to valve clearance. I have a .501/.527 lift cam and had the heads milled .020” and I checked it with modeling clay and still had over .100” clearance. The engine is low compression due to the large chamber heads so milling them along with a decent cam will help with compression.

[72c20customcamper]

Stock heads make great hp if you do them right .

[Steeveedee]

Originally Posted by 72c20customcamper

Stock heads make great hp if you do them right .

OK, how much HP are roller rockers worth? Is there something else there that I am missing?

[72c20customcamper]

Originally Posted by Steeveedee

OK, how much HP are roller rockers worth? Is there something else there that I am missing?

No real horse power but reliability. No need for high zinc oil and the reduced friction on the cam and rockers helps a little on the hp

Also has a roller cam

What I'm saying is stock heads done right make big hp no need for aluminum heads in a car/truck that 100lbs could make or break it in the 1/4 mile

The engine in my chevelle

[i82much]

Originally Posted by 72c20customcamper

No real horse power but reliability. No need for high zinc oil and the reduced friction on the cam and rockers helps a little on the hp

Also has a roller cam

What I'm saying is stock heads done right make big hp no need for aluminum heads in a car/truck that 100lbs could make or break it in the 1/4 mile

The engine in my chevelle

I don’t think roller rockers have any bearing on whether you need zinc (ZDDP) in your oil, it’s whether you have a roller cam or not. And mild flat tappets seem to do fine with the lower ZDDP levels, it’s the aggressive flat tappets that get you in trouble.

[deadshort52]

Like I said the motor is healthy but just seems wimpy. It gets up and goes and pulls okay but anything beyond half throttle all it does is make more noise and doesn't go much faster. As I understand it the big blocks in these truck were severely under cammed and the intakes don't flow every well. I am not looking to build monster HP but I want just a little more snort. I know that stock iron heads can be done up to build big HP. My thoughts were by the time I do a valve job with new guides, seats, valves, locks, retainers, seals, and the corresponding machining I will have almost the same money as a set of new aluminum heads that come assembled.

What are some good camshafts to research to accomplish my goals?

Thoughts on doing the cam swap in the truck?

[i82much]

OP - when you try to get more power out of an engine by installing high-flowing heads or a bigger cam, you move the powerband up and can actually lose low-end power.

If you really need more power, consider a 454 or 496 build instead of modifying your 402. I don’t think you’ll be thrilled with the outcome. For instance, you might find the engine wants to stall in gear because of the bigger cam with the stock converter, or you need to set the idle really high to stop that from happening, etc.

[i82much]

A hydraulic roller retrofit with a mild cam could give you some more power everywhere and improve drivability. If you don’t want to replace the engine completely, that’s probably a better bet IMO.

[72c20customcamper]

K . But I dont think any reputable builder would put roller rockers on a flat tappet cam .

[i82much]

Originally Posted by 72c20customcamper

K . But I dont think any reputable builder would put roller rockers on a flat tappet cam .

really? i have never heard that and i don’t see why that would be the case.

[72c20customcamper]

Originally Posted by i82much

really? i have never heard that and i don’t see why that would be the case.

Really ? Mix new with old ? Sorry I would never do it . So explain why roller rockers would be better with flat tappets other than solid lifters?

We’re talking bout a street engine not a 800 and up track engine that the power comes on a 5grand

[i82much]

Originally Posted by 72c20customcamper

Really ? Mix new with old ? Sorry I would never do it . So explain why roller rockers would be better with flat tappets other than solid lifters?

i mean people upgrade rocker arms all the time. say you had a mild hydraulic flat cam with stamped steel 1.5 rockers on it. how could switching to 1.65 roller rockers hurt, assuming you checked pushrod length, coil bind, piston to valve clearance, etc.?

i don’t think the cam and lifter care whether there is a roller rocker or a stamped stock-style rocker at the end of the pushrod? it’s not like it puts more pressure on the cam/lifter interface, that’s dictated by the valve spring pressure.

[72c20customcamper]

Once you start changing the ratio you put more pressure on the tappets and the cam just by compression of the spring. On a mild engine it may work for 50 thousand miles. In my experience it’s better to make the whole valve train up to the task

[garyd1961]

Originally Posted by 72c20customcamper

K . But I dont think any reputable builder would put roller rockers on a flat tappet cam .

I have a roller cam with regular old stamped rockers, came from the factory that way.

[i82much]

anyway - roller rockers are fine on a flat tappet, but you still need to think about zddp levels unless you switch to a roller cam.

[deadshort52]

Originally Posted by i82much

anyway - roller rockers are fine on a flat tappet, but you still need to think about zddp levels unless you switch to a roller cam.

I am glad that we got that straitened out. I guess I don't understand what all of the squabbling was about. I never asked anything about roller rockers or flat tappet cams. I do know when I was building engines more frequently I always used flat tappet cams, some with hydraulic lifters and some solid lifters. Almost always used some type of roller tip rocker or full rolling fulcrum rocker arms. The hype then was that it reduced oil temperature and valve train wear. It also seemed to make a tick smoother power. I guess I wouldn't hesitate to do it again. I never had a bad result on account of it.

[72c20customcamper]

Not squabbling just a discussion.

[i82much]

here is a link to a flat tappet build with roller rockers:

https://www.hotrod.com/articles/ccrp...que-383-build/

[weq92f]

.

Pull the valve cover off to get the casting numbers of the heads. That will tell you Oval or Peanut.

If you have peanut port heads, that might explain why the engine runs the way it does and you'll need to pickup a set of #781, #049 or similar cast heads. I bought a set of #781s for 100 bucks off craigslist not so long ago.

Calculate your compression ratio.

Use that to select appropriate cam which will give you the necessary springs required and the data to set them up properly. Then the heads, springs and related parts to the machine shop to get refreshed ( 1000 to 2000 ). I did my #063 heads this way w/ stock valve sizes and walked for about 1400 w/new stainless valves ( et al ), valve job, the proper springs/setup and required machining ( includes the cost of the head parts ).

I went with a COMP 11-422-8 retrofit roller cam on my stock 402 bottom end at about 9:1 compression, Edelbrock Performer 2-O intake. Also installed the COMP lifters at the time. Recently I replaced those lifters with Howards 91161, which is what I should have used to begin with! Upgraded from manifolds to long tube headers as well.

This setup woke the thing up BIG TIME!

Hth,

-klb

[deadshort52]

Thanks for the good information. This is the type of post that I was looking for. Tell me what you didn't like about the Comp Cam lifters and what you liked about the Howards lifters. Did you leave the bottom end together or give it a re-ring kit?

Originally Posted by weq92f

.

Pull the valve cover off to get the casting numbers of the heads. That will tell you Oval or Peanut.

If you have peanut port heads, that might explain why the engine runs the way it does and you'll need to pickup a set of #781, #049 or similar cast heads. I bought a set of #781s for 100 bucks off craigslist not so long ago.

Calculate your compression ratio.

Use that to select appropriate cam which will give you the necessary springs required and the data to set them up properly. Then the heads, springs and related parts to the machine shop to get refreshed ( 1000 to 2000 ). I did my #063 heads this way w/ stock valve sizes and walked for about 1400 w/new stainless valves ( et al ), valve job, the proper springs/setup and required machining ( includes the cost of the head parts ).

I went with a COMP 11-422-8 retrofit roller cam on my stock 402 bottom end at about 9:1 compression, Edelbrock Performer 2-O intake. Also installed the COMP lifters at the time. Recently I replaced those lifters with Howards 91161, which is what I should have used to begin with! Upgraded from manifolds to long tube headers as well.

This setup woke the thing up BIG TIME!

Hth,

-klb

[davischevy]

I changed the cam in one stock 402 half ton. It helped some but still wasn't impressive.

The 402 I have now was built when I got it and has an unknown RV cam. I ran fine and had ok power, but leaked oil at the rear main and started missing a while back. I suspect a flat cam.

I thought about rebuilding it, but it cost no more to build a 454. I have a 454 with a set of 781 heads so I decided to build it. I am using a roller cam and rockers.

I will use the original intake manifold which doesn't make any sense except that's what I want.

[weq92f]

Originally Posted by deadshort52

Thanks for the good information. This is the type of post that I was looking for. Tell me what you didn't like about the Comp Cam lifters and what you liked about the Howards lifters. Did you leave the bottom end together or give it a re-ring kit?

Nope, we just did the top on this cash dump! Bottom has less than 10k ~easy~ miles on it

The COMP lifters made a lot of noise all the time whether hot or cold. I made several attempts at adjusting the preload -- 1/4, 1/2, 3/4. Decided miles might cure so drove it over 1000 miles at 1/2 turn... no change.

Some research indicated this was a common issue! Soon after deciding to swap them for something else, I was lead to Howards as a suitable replacement.

Hth,

-klb

[i82much]

Originally Posted by weq92f

.

Pull the valve cover off to get the casting numbers of the heads. That will tell you Oval or Peanut.

If you have peanut port heads, that might explain why the engine runs the way it does and you'll need to pickup a set of #781, #049 or similar cast heads. I bought a set of #781s for 100 bucks off craigslist not so long ago.

Calculate your compression ratio.

Use that to select appropriate cam which will give you the necessary springs required and the data to set them up properly. Then the heads, springs and related parts to the machine shop to get refreshed ( 1000 to 2000 ). I did my #063 heads this way w/ stock valve sizes and walked for about 1400 w/new stainless valves ( et al ), valve job, the proper springs/setup and required machining ( includes the cost of the head parts ).

I went with a COMP 11-422-8 retrofit roller cam on my stock 402 bottom end at about 9:1 compression, Edelbrock Performer 2-O intake. Also installed the COMP lifters at the time. Recently I replaced those lifters with Howards 91161, which is what I should have used to begin with! Upgraded from manifolds to long tube headers as well.

This setup woke the thing up BIG TIME!

Hth,

-klb

do you have an automatic and if so does it have a stock converter? curious how that cam would do with a stock converter. what’s your idle rpm?

from the original post it sounds like the heads would be original oval ports, i thought the peanut ports didn’t show up until the smog engines? also i think the peanut port heads have enough head flow for a 396, they actually make decent power on a 454 or 496. but i would imagine peanut ports from a smogger 454 would have abysmal compression on a 402.