Thread: Help with SBC cam selection

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I got a '78 chevy k10 4x4 4 speed 31" tires and 3.73 gears I'm currently building a 400 sbc to drop in it, it will be stock bore with stock dish pistons, 062 vortec heads with steamholes drilled, and headers I was wondering what would be a good cam for this engine,I'd like a cam with a lobe at idle to, I'll be using it for towing cars and stuff every now and again and the truck hardly ever revs over 3,000 rpms

Welcome to CHR:

You may have a couple conflicting goals with your cam in this vehicle. While I like the Vortec heads as they breathe “ever-so-much-better” than you stock heads you’ve still got a truck and the weight associated with such. With the 3.73 gears and 31” tires you’re close to 3.40 equivalent gearing. With the stock stall converter, you don’t want to go too big on the cam or you’ll be very disappointed. Stay with something that has specs close to the following:
- Advertised Duration (Int/Exh): 262/272
- Duration @ .050 (Int/Exh): 204/217
- Lift (Int/Exh): .420/.442
- LSA: 112

Summit Racing SUM-K1102 is a kit for $90. There are others from Lunati and others, but stay close to these specs unless you want to go with taller gears and a higher stall speed than stock converter (2400RPM). You’ll have a slight difference in idle, but still have good vacuum and it will pull well off idle through 4500RPM.

You did not mention what you're doing for carb and intake - I'd go with a Performer RPM and AVS 1805, 650cfm Edelbrock.

Have fun with you project and let us know what you decide.

Regards,
Glenn

Originally Posted by glennsexton

Welcome to CHR:

You may have a couple conflicting goals with your cam in this vehicle. While I like the Vortec heads as they breathe “ever-so-much-better” than you stock heads you’ve still got a truck and the weight associated with such. With the 3.73 gears and 31” tires you’re close to 3.40 equivalent gearing. With the stock stall converter, you don’t want to go too big on the cam or you’ll be very disappointed. Stay with something that has specs close to the following:
- Advertised Duration (Int/Exh): 262/272
- Duration @ .050 (Int/Exh): 204/217
- Lift (Int/Exh): .420/.442
- LSA: 112

Summit Racing SUM-K1102 is a kit for $90. There are others from Lunati and others, but stay close to these specs unless you want to go with taller gears and a higher stall speed than stock converter (2400RPM). You’ll have a slight difference in idle, but still have good vacuum and it will pull well off idle through 4500RPM.

You did not mention what you're doing for carb and intake - I'd go with a Performer RPM and AVS 1805, 650cfm Edelbrock.

Have fun with you project and let us know what you decide.

Regards,
Glenn

Thanks for replying I forgot to say the truck is a 4 speed manual does that make much of a difference

Yup - four speed will allow a bit bigger cam as your left leg becomes the stall converter as you control the engagement.

Given it is a larger SBC,it will be more accepting of a bigger cam.But cam alone won't mean much if it is bottle necked by the choice of heads.Rather than the Vortec's,I suggest Iron Eagles the 180 cc runners cut to a good SCR.You could actually go to a 195 CC runner because of it being a 400.

Might want to consider a hyro roller cam conversion too.

Originally Posted by 1gary

Given it is a larger SBC,it will be more accepting of a bigger cam.But cam alone won't mean much if it is bottle necked by the choice of heads.Rather than the Vortec's,I suggest Iron Eagles the 180 cc runners cut to a good SCR.You could actually go to a 195 CC runner because of it being a 400.

Might want to consider a hyro roller cam conversion too.

yea probably would but I don't have that much money to put into aftermarket heads and roller cam it's just gonna be a daily driver work truck so the vortec will work fine for me

You have kind of picked a combination that you may not be too happy with (don't ask me how I know). Like what has been said before, a truck is a bit heavy to realize any performance mods that you might install. You are going to wind up with a gas hog that you can't afford to drive that very well might be a dog. One thing that I might recommend, if you have a Pull-A-Part junk yard close by, go and spend some time checking out some of the later model trucks that you might find there. Sometimes you can luck out and find a pretty decent engine for less than $150 with all the accessories on it.
The last engine I bought was out of a 97 Tahoe 4X4. I dropped a 383 stroker kit in it and that particular block took almost no clearancing for the crank. You can get a 377 kit for it also. The only difference between a 383 and 377 is .030" bore. The best thing about the later model blocks is that you can find one with 200,000 miles that you might be able to get by without boring. Because of the hypereutectic pistons and the low friction rings, I have found 350 blocks that I could still see the factory hone marks on the cylinder wall that had well over 200,000 miles on them. On top of that, most of them in that year range should be factory roller cams. You can buy a decent roller cam reasonable sometimes, new and used. The roller cams do not wear like a flat tappet cam. The factory hydraulic roller lifters have been known to run for 750,000 miles.
You can also find used factory high performance roller cams pretty reasonable. The reason I mention this is I went through the same thing you are talking about. I bought a brand new 1977 Chevy Cheyenne and pulled the engine with less than 500 miles on it (absolutely STUPID). I put a small block 400 in it, bored .060, 12.5 compression ratio, high performance cam, aluminum intake and a nice new Holley 750 carb. It absolutely sucked. My gas mileage went from 11 MPG to about 6-7 MPG and I hardly noticed any improvement in power at all. It pulled heavy loads a bit better because of the longer stroke of the SBC 400. You could not hold a gun on me and make me do that again.
You will get a better performance gain and better fuel economy by installing a factory roller cam 350. You don't have to take my word for it, if you are bent on doing this, you will remember what I am saying here. Back when I did that, I thought I was smart and no one could tell me any different. I am smart enough now to realize I wasn't so smart at the time.

Ed

Back in the 70's I run Isky #201262 cams that had 262 degrees advertised duration, .435 lift, and 108 degree lobe center in SBC 4X4's. Good low end torque and gave a bit of a lope at idle due to the lobe center. This cam made good low end torque and worked real good with a 2 plane intake manifold and up to a 650 cfm carb. 600 cfm carb worked best.

Originally Posted by 1978chevy

I got a '78 chevy k10 4x4 4 speed 31" tires and 3.73 gears I'm currently building a 400 sbc to drop in it, it will be stock bore with stock dish pistons.

Heavy truck, big tires, not enough gear. Stock dished pistons will not have enough flat area on the crowns to facilitate a good squish, so you need to install pistons that will have enough flat area on the crown to mate up with the underside of the cylinder head to generate a good strong "squish" across the chamber. Not only that, but a 400 with stock pistons and 64cc heads will make close to 11.0:1 static compression ratio. You'll never get it to run on pump gas without using so much cam that you'll make power between 3000 and 7000 rpm's. There goes your towing ability.

Originally Posted by 1978chevy

I'd like a cam with a lobe at idle to

It's not lobe, lobe is the part of the cam that lifts the lifter. Lope is what you mean. Most of you fellows haven't enough experience to understand that lope does not equate to horsepower. It means that the motor is inefficient at the speed where the lope occurs. In addition, the word "to" is not what you meant here. The word "too", meaning "also" is the word to use.

Originally Posted by 1978chevy

I'll be using it for towing cars and stuff the truck hardly ever revs over 3,000 rpms

All the more reason to use a low static compression ratio, mated to a mild cam that will make power where you want it to, a cam that will close the intake valve at the appropriate time to make good cylinder pressure with the static compression ratio of the motor.

I just know that one day I'm gonna read one of these posts, pull out my revolver and dispatch this computer to another astral plane.

OK dude, listen up. Add up the stack of parts you will use. Half the stroke (radius) will be 1.875", the rods will be 5.700" (I don't use long rods on a build like this because it puts the wrist pin up into the oil ring land on the piston.) The pistons will be something like these, 22cc D-cup with a 1.433" compression height....
KB Pistons for Automotive Applications
Adding 1.875, 5.700 and 1.433 gives you a stack height of 9.008".
Take the block to the machine shop, have them check the mains for being round and parallel (align hone or align bore the main saddle to clean them up if necessary). Now, registering on the mains, cut the block decks to 9.018" block deck height. This will leave the piston down in the bore by 0.010" at top dead center. It will also equalize the block deck height front to rear on both banks so that the heads will sit level and be an equal distance from the centerline of the main bearing bore. This will also allow the intake manifold to seal up, preventing a vacuum leak from the crankcase to the underside of the intake manifold ports where they match up with the head ports. Buy the pistons in 0.030" oversize and have the shop bore the block to match the pistons. Hypereutectics need a very tight piston to bore clearance and a wider top ring gap, so pay attention.

Here comes the static compression ratio math.
Cylinder (4.155" x 3.75) 833 cc's
Chambers 64 cc's
Piston crown 22 cc's
Piston deck height 2 cc's
Compressed gasket 9 cc's
Fel-Pro Q1014 - Fel-Pro Performance Head Gaskets - Overview - SummitRacing.com
Add all the values together and find 930 cc's. Now drop out the cylinder volume and find 97 cc's. Now, divide the larger by the smaller and find 9.59:1 static compression ratio.

Now comes the part where you match up the cam timing events with the static compression ratio to set the cylinder pressure.
This is actually more cam than you need, but using the 64cc heads limits the static compression ratio to 9.59:1 and we need this much cam to be able to make the correct cylinder pressure to run on pump gas.
272 H10 Hydraulic Flat Tappet Camshaft and Lifters for Chevrolet 1957-1987 V-8, 262-400
The Dynamic Compression Ratio using this cam and 9.59:1 static works out to 8.565:1dynamic. Use any cam you want to, so long as you're closing the intake valve at 33-35degrees ABDC @0.050" tappet lift.

Bolt on a set of tuned, equal-length headers, an Edelbrock Performer RPM (not the Air Gap model) and a 600-650 carb of your choice. This combination of 406 cubic inches and the L31 heads will make an ungodly amount of torque from 1500-4500 rpm's and do it on crappy pump gas without detonation, thanks to properly engineered components that work together toward a common goal. That's the secret, a combination where everything compliments everything else. Having all these pieces work together also will allow you to feed in the proper amount of ignition timing.

If you go ahead with the stock pistons, be ready for a surprise when the motor won't run on pump gas without detonating. Then you find that you have to pull all the ignition timing out of the motor to get it to run at all and it won't make any power.

L31 heads, due to the very efficient chamber design, don't need too much spark timing, so I would curve the dizzy for 14 degrees at the crank and 20 degrees in the weights. Use vacuum advance with the hose plugged into intake manifold vacuum.

I really don't expect you to follow my recipe, but it is there for other fellows to use.

Hi Tech,

I was wondering if you would chime in. How are things in Union County? You know, I can't blame anyone for trying to achieve a lot of power and torque, I did when I was younger and didn't know better. Problem is that without the correct combination of parts it seems to go backwards. I found a long time ago that what a lot of people perceive as a high performance engine doesn't do well in a (daily driver) 4 X 4 truck, especially when trying to tow with it. Installing a bumpstick does not make it a high performance engine. Now that they are talking about the price of gas nearing $5 a gallon by early summer it will be even worse.
1978chevy, you are like a lot of guys just trying to make the best of what you have, but it is not the vehicle to do it with. By the time you follow Techinspectors "recipe", I fear that it will be out of reach. I know it would be for me using what you have. Just the torque of the stock small block 400 in your truck will be better than what you are wanting to try. As you can see from my earlier post, I tried it back in 1977 on a new Chevy 4 X 4 shortbed. It may not have been the worst thing I ever did, but it ranks way up there. 35 years ago and I still hear about it from my wife.
I hope we didn't burst your bubble too bad, just trying to save you some grief.

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