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Old 12-10-2012, 11:37 AM
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350 SBC / Vortec Heads: Cam Choice?

Hello,

I'm looking to upgrade the heads on my 350 SBC (mid 70's) to a Vortec design (part: 12558060). I know I'll have to buy a new intake manifold, but would I be able to run my stock cam on this setup?

The truck is going to be a street rod. Not looking to race at the track, and I'm not looking to eek every ounce of HP out of the engine.

If this cam won't work, does anyone have a good secondary option that won't break the bank?

Thanks in advance,

-A

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Old 12-10-2012, 01:19 PM
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Originally Posted by andrewakessler View Post
Hello,

I'm looking to upgrade the heads on my 350 SBC (mid 70's) to a Vortec design (part: 12558060). I know I'll have to buy a new intake manifold, but would I be able to run my stock cam on this setup?

The truck is going to be a street rod. Not looking to race at the track, and I'm not looking to eek every ounce of HP out of the engine.

If this cam won't work, does anyone have a good secondary option that won't break the bank?

Thanks in advance,

-A
It depends on what level of power you want, up to 300 horses will be a mild cam that will run with the factory valve springs. 400 horses will take a more aggressive cam with matching springs with 1.6 to 1 ratio rockers and some porting work with a good intake like the Edlebrock Perfrormenr RPM and a carb with around 700 cfm capacity, good long tube headers and good dual exhaust. 300 horses is pretty easy to obtain with decent factory intake and 600 CFM carb, 1.5 rockers and a cam similar to the old 300 horse 327.

The Vortec head doesn't care about the cam other than it has a limit on lift at the valve which should be considered .450 inch till you actually measure the head you have as some will go to .470 but I wouldn't assume any and every one of them will do that. The spring is 1.25 inch diameter, there are kits that let you run more pressure if needed for a bigger cam like the Comp XE268 if you're shooting for 400 or more.

The Vortec head will be happy with your stock cam and will deliver around 250-260 hp with the typical pre L31 Vortec OEM truck cam and short block.

The L31 head does not have cast-in push rod guides like the older heads, it is designed to use self-guiding rockers. It can be converted to traditional push rod guiding with after market steel guides but these require the use of screw in rocker studs which also require the stud bosses be milled and tapped, so you get to decide what configuration you want to spend your money on. The least expensive option, especially if you're retaining the engine's original cam is to use the OEM sliding contact self-guided rockers.

So you've got some options you need to work through to see what fit your desires and budget.

Bogie
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Old 12-10-2012, 01:22 PM
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Great info. Thanks for the help.

-A
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Old 12-10-2012, 02:56 PM
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The Vortec head uses center bolt valve covers, so your old ones won't fit. The 12558060 heads are advertised to be good for 0.475" lift, but be sure to check the clearance between the seal and retainer if your cam comes anywhere near that much lift. In some cases, insufficient clearance is caused by the valve stem seals not being fully driven down on the valve guide boss, so if you're having clearance issues w/a cam having less lift, check the seals for being installed all the way, first. If your cam is stock this won't be a problem.

If you want to get the mostest from this swap, read up on the quench measurement. You will have the opportunity to improve the quench distance (if needed) by using a head gasket w/the thickness that best suits your engine. It does require some measuring, but nothing that you can't do I'm sure.

Other reading, if you're in the mood:

Vortec heads
Valve spring installed height
Valve train points to check
Valve train geometry
Adjusting hydraulic lifters
Cam break in (not needed unless you were to change cams)
First start up. Mainly useful for getting the distributor back in so it'll start back up easily.
HEI distributor/Timing info- this is very important, especially if the distributor you have is a stock unit. You can gain good power/improved drivability by dialing in a performance advance curve. The stock curve is the pits in almost every case.
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Old 12-10-2012, 05:08 PM
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I love this message board. I have no clue how I'd complete this project without it.

While doing some research last night, I came across this "low cost" 350 SBC build: Small-Block Chevy Build - 391HP Chevy 350 Engine For $2,613 - Hot Rod Magazine

What I liked about the article was the fact they included a full build list in Excel that I could follow. The issue I had with it though was the inclusion of the "oval track" cam.

Everything else seems to line up with the info given here though, so I'm feeling pretty good about it.
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Old 12-10-2012, 06:20 PM
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Originally Posted by andrewakessler View Post
I love this message board. I have no clue how I'd complete this project without it.

While doing some research last night, I came across this "low cost" 350 SBC build: Small-Block Chevy Build - 391HP Chevy 350 Engine For $2,613 - Hot Rod Magazine

What I liked about the article was the fact they included a full build list in Excel that I could follow. The issue I had with it though was the inclusion of the "oval track" cam.

Everything else seems to line up with the info given here though, so I'm feeling pretty good about it.
I had not seen that issue, made an interesting read. I agree with you about the cam BIG TIME. Here again is cam and piston choice raising its head to show you how subtle differences in parts selection make big differences in power. I'd never use one of those circle track cams for a street build; these are often lift mandated cams for which more duration is substituted in an attempt to drive out more power at higher RPMs.

This leads you down several paths not optimum for a street engine

- A rougher, lower vacuum and higher RPM idle. This leads off to several things like limited vacuum for power brakes, a higher stall speed converter for example.

- Lack of compression with this set up, the later closing intake at 71 degrees say compared to the XE268 at 61 degrees requires more compression to get the power up.

- The low lift against the longer duration doesn't take advantage of the Vortec's better porting. Whenever you can use parts that take advantage of more lift with less duration you're better off to go that way at least on the street.

- Excessive cooling, if you read Smokey very carefully, you'll see he leads you to maximum power is achieved with a cold mixture being stuffed into a hot engine. Not a cold mixture into a cold engine. In his waning days on this earth he was working on a super hot engine as an approach to way more power. He's not the first to go down this path, but for half a century it's been in view theoretically but the materials engines are built from and perhaps physics interactions we don't yet appreciate have stymied this effort. Still running cold tap water through the cooling system did nothing to help.

It once again shows that what works for a rules limited race engine and what can be optimal on the street for a performance engine are not the same things in all cases. While close to the 400 horse barrier this engine just isn't going to get there unless you dive into the pistons and replace the cam with less duration having more lift. I mean you can get there with tuning but itíll be too edgy to stay there long; a different parts selection is needed to get up on that plateau and not have to constantly fiddle the thing to stay there. The condition HR found itself in with 1.6 rockers and 1-3/4 headers is that both of these, if not actively working against the combination, certainly didn't add anything. The 1.6 rocker opens the valves faster as well as higher. While higher could work to their advantage on the Vortec head, faster just made the overly rampy cam act like it had more ramp. That worked against the compression ratio and burn characteristics of the combustion chamber with the circular dish pistons. The 1-3/4 tube headers reduced the overlap signal that could have been used to help with initiating intake flow in what David Vizard calls the 5th cycle.

I'm sure with tuning this engine could crack the 400 barrier but it would not be economical to operate with the late closing intake and lacking compression. So while cheap to build it would be more costly than necessary to operate.

Bogie
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Old 12-10-2012, 09:44 PM
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If you'll notice, the design of the piston leaves a LOT to be desired. The round dish is a detriment to good squish/quench action, and in this case it's made even worse by a rather large 45 degree chamfer around the outer edge of the piston deck. That leaves a scant 1/2" band of the top of the piston to provide the quench effect, and that's just not enough.



A much better choice if a dished piston is needed is a reverse dome or D-cup type piston (this one is for a SBC 383 stroker):



X3 on the camshaft- much too much duration @ 0.050" lift. It would run better all the way around w/a cam in the 222-228 duration @ 0.050" range. Nothing wrong w/using a split pattern cam w/the Vortec head, though.
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Old 12-10-2012, 10:29 PM
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Originally Posted by oldbogie View Post
The 1.6 rocker opens the valves faster as well as higher. While higher could work to their advantage on the Vortec head, faster just made the overly rampy cam act like it had more ramp. That worked against the compression ratio and burn characteristics of the combustion chamber with the circular dish pistons.
Bogie
I thought fast ramp rates were better? This is what makes the XE and Voodoo line of cams so good right? And also what makes roller cams better too ó fast ramp rates. Can you explain a little more?
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Old 12-11-2012, 10:50 AM
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I thought fast ramp rates were better? This is what makes the XE and Voodoo line of cams so good right? And also what makes roller cams better too — fast ramp rates. Can you explain a little more?
The XE and Voodoo have short fast ramps of modern design cams. The short-coming of fast ramps is wear, it takes careful break-in and these days a ZDDP additive to preserve them.

The older design cams use a long ramp, this is typical of the muscle car era cams that have this really cool sounding idle but really don't and didn't produce amazing power for their stated durations. Plus they are designed to work with the very high compression ratios of the era which are not practical with unleaded fuel, at least not affordable unleaded fuel, of today.

Where the long ramp gets you into trouble especially with modern compression ratio limits is that they hold the intake valve off the seat for a longer time so the piston as it rises in the cylinder pushes the mixture it drew in on the down stroke back into the intake system. This leaves less mixture, by weight or density, in the cylinder, thus it makes less force on the piston. While the seat clearance isn't very high at this point you have to consider that the backward flow though the valve is considerably higher than the inflow for this lift would have been because the piston is pushing the mixture out with considerable force, much more force than atmospheric pressure pushes mixture into the cylinder chasing the descending piston. So this reversion loss is more than a minor one.

The whole concept behind the late closing intake is that as the RPMs raise there comes a point where the mixture entering the engine develops enough speed which translates to kinetic energy that it will continue to flow into the cylinder at these low ramp lifts against the outward push forces caused by the rising piston. From this critical RPM up to the breathing red line, the engine develops a surprising amount of volumetric efficiency and the power output that comes from this deep breathing. One can play with the critical RPM a bit with sizing of the porting and carburetor. This is where smaller ports, valves and venturies will raise the velocity thus the kinetic energy of the mixture sooner in the RPM band which will pull the power peaks lower and reduce the need for so much compression. The darkside of this change is that it greatly reduces the otherwise possible upper RPMs and the horsepower to be found there.

So a fast acting cam with short ramps (this may be only 10-15 degrees more compared to a slow ramp) clips off the reversion flow that happens below the critical RPM so it doesn't kill the bottom end torque as much as a long ramp cam. Another result of closing the intake sooner is that ultra high compression ratios needed to recover torque below the critical RPM are not necessary such that these fast ramp cams are more compatible with modern un-leaded fuel octane levels. To achieve good top end breathing with these cams the lift can be raised taking advantage of the larger curtain area of the open valve. This of course requires a better flowing port, but one that uses improved location and shape rather than just bigger ports because you still want to have a high velocity flow as soon as possible, but at the same time not restrict the maximum flow of the port to do it. At Chevrolet this lead to the LT1 and 4 ports which found their way into the L31 Vortec and GMPP Fastburn heads while still using production detail parts and processes and fitting within the confines of the production vehicle envelope. Certainly without these constraints one can look to the many and high power efficient GMPP and aftermarket 18 and 15 degrees heads and the many port variations this frees up that were not possible with existing production constraints of engine shape and size into the then current vehicles. The pan still has to miss objects the vehicle has to pass over for example so you can only get the engine so deep in the chassis and the chassis so close to the ground so the engine (Gen I&II) sets rather high in the chassis so the intake system gets shape compomised to fit it under the hood lines the designers want.

Roller cams make it easier to push the lifter open faster and further without tearing the lobe and lifter up. The OEMs went to rollers really for emission purposes. Just to show how things drive other things; back in the 1980s the EPA wanted to get ZDDP out of oil because it contaminated the catalytic converter is a way similar to lead in fuel did, just slower since it is carry over component in the combustion chamber rather than a direct component of fuel. So the OEMs were put in the position of running into wear problems between the lobe and lifter without this additive to which the only viable solution was Parkerizing which was also going away because of pollution issues with the process. So the choice was going to be very expensive to purchase and machine materials to make lobes and flat tappet lifters survivable in the new world or go to a roller. The less costly route was the roller. You will note that the actual timing at the valve of production roller engine such as the L31 Vortec is nothing unusual for a production truck engine, power performance was not what the OEMs went to the roller for, it was a backhanded way of solving an emissions problem.

Bogie

Last edited by oldbogie; 12-11-2012 at 11:01 AM.
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Old 12-11-2012, 11:35 AM
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It's interesting you mention Voodoo cams as that was one of the brands I was looking at as a replacement.

Would anyone be able to decipher what type of cam I currently have? I've looked through countless pages but came up with nothing. The markings are:

Butt end of shaft: K MP
Along the shaft: CWC 29 J3 C6 D6 EP1
(picture attached)

I believe it was originally in a late 70's Monte Carlo, and the cylinders were bored to .030.

If it helps, it was installed in a 350 2-bolt block with Chevy Corvette 327 250 HP heads (Casting is 3795896), and a 1969 2 Barrel SBC Intake 3916313.

Thanks,

-A
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Old 12-11-2012, 04:37 PM
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Vortec Heads

I did the same this past July. With the performance chevy intake make sure you do the cooling update in the first paragraph of the instructions. Then you will need a chip to make it run because it will be too lean. Motorvation is great to work with and they will send you chips till you are happy. Just tell them what you have and what you did and what you want. Very smart on the older fuel injections. Can also be reached through summit. Good luck CYA Joe
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Old 12-11-2012, 05:09 PM
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vortec heads

I have used the vortec head on a couple of my recent builds and they flow great for a stock head, the engine that is on my test stand now has the 062 cast head they have had the studd bosses cut down and tapped for screw in studds only because of the cam i used which is the gmpp LT4 hot cam (525/525) this engine with a stock vortec or zz piston(they are the same) runs awsome(hitting 8000 rpms on the stand no problem),the last engine we did with the vortecs had the voodoo hyd flat tappit, did nothing to the studds,ran the stock self-aligning rocker and a Z28 style spring we just had to cut the valve seal boss down(a cutter for these is cheap and at any nappa or autozone) to prevent bind,which is the only reason you have to keep your lift down soo low on the vortec heads also no self align rocker is needed if you open the pushrod hole in the head with a drill, we have found that the vortec is a great budget head but keep in mind if you try to put alot of money in these you can get a better,thicker casting head new for around 550.00 a pair(rhs) it is not worth doing any port or custom work to these the factory head it is very thin cast and crack prone but for mild street/strip build you cannot top them
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Old 12-12-2012, 04:44 AM
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I recommend that you buy a complete 350 vortec engine (1996 to 2000) and start with that. Comes with a roller cam and vortec heads.
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Old 12-12-2012, 03:15 PM
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Quote:
Originally Posted by andrewakessler View Post
It's interesting you mention Voodoo cams as that was one of the brands I was looking at as a replacement.

Would anyone be able to decipher what type of cam I currently have? I've looked through countless pages but came up with nothing. The markings are:

Butt end of shaft: K MP
Along the shaft: CWC 29 J3 C6 D6 EP1
(picture attached)

I believe it was originally in a late 70's Monte Carlo, and the cylinders were bored to .030.

If it helps, it was installed in a 350 2-bolt block with Chevy Corvette 327 250 HP heads (Casting is 3795896), and a 1969 2 Barrel SBC Intake 3916313.

Thanks,

-A
There's a good chance the cam is a stock or stock replacement stick. Prolly around 0.390" to 0.410" lift and duration @ 0.050" lift under 200 degrees. If you have a caliper, subtract the smallest part of the lobe (base circle) from the biggest part of the lobe, then multiply that number by 1.5 (rocker ratio). The result is the valve lift.

The markings along the length of the shaft are the foundry (CWC) and various factory markings, could be the furnace or mold ID, date code, etc.
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Old 12-14-2012, 12:55 AM
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Vortec Head

I don't see why not. But can you get the cam from that same engine? You don't have to but you must want some power or you would not want the vortec heads. I own a 96 Tahoe and think all the time about how good this engine would have ran in my 73 Impala.
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