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Discussion Starter · #1 ·
I'm buying a 350 Vortec , the only thing I want to do is make the right carureter decision , most of threads I've looked at are old , Thanks , I'm backing it up with a muncie 4 spd. cam choices will be liked as well but I don't want to spend money on a tear down and machine experience , Thanks again .
 

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First off, let's make sure that you're getting a real Vortec engine. There is a lot of misconception about these engines. A real Vortec engine is only found from 1996 through 2000.

After that, with a little work on the heads you can run a comp HR or a comp 268 HR.
Both of those cans will make really good torque. And depending on how much your car weighs, gear ratio, and tire size, Etc... they may, or may not be a good choice for you.
 

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A real Vortec engine is the L30, 305 or the L31, 350 with multipoint fuel injection, the intake bolts to the heads with a total of 8 bolts not 12 and has a computer controlled distributor. These engines aside from crate engines built 2001 and up only are used in trucks and vans for 1996 to 2000 they appear in no other wheeled vehicle. Often the 1987 through 95 LO3, 305 and LO5, 350 with Throttle Body Injection (TBI) are sold as Vortec’s but they are not what we talk about when we use the term “Vortec” which GM applies to most everything in sight. Rodders specifically intend this term to be the L31, 350 engine.

Converting these or the earlier TBI engines to a carb also involves installing a conventional HEI distributor. These blocks do not have a mechanical fuel pump’s installation provisions machined nor operation equipment installed an occasional exception is sometimes found but not often. These are fuel injected engines using a high pressure electric pump mounted inside the fuel tank. The TBI uses about a 20 psi pump the multi point uses about 50 psi. The cam on these engines does not have a mechanical fuel pump lobe.

The L30 and L31 use a plastic timing cover and a modified coolant pump. The crankshaft from 1986 up uses a one piece rear seal that does not mate to flywheels its flex plates earlier than 1986.

So there is some adaption needed to get these operating in earlier vehicles or when converted to a carb inside the years of vehicles they appear in.

Bogie.
 

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Here is a link to a lot of camshaft discussions for the Vortex 350 Boogie is talking about, if you go to post #25 you will see Boogies feed back on cams for this motor.


Also a little more info on what you plan to use this in and your goal will be helpful in giving you solid information.
 

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Discussion Starter · #5 ·
First off, let's make sure that you're getting a real Vortec engine. There is a lot of misconception about these engines. A real Vortec engine is only found from 1996 through 2000.

After that, with a little work on the heads you can run a comp HR or a comp 268 HR.
Both of those cans will make really good torque. And depending on how much your car weighs, gear ratio, and tire size, Etc... they may, or may not be a good choice for you.
Hey excellant auto , I've done my homework on finding the right vortec , 1999 chevy truck , will hear run before being pulled , I'll be helping this week ,thank you , And , I'm still doing my homework . L31
 

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Discussion Starter · #6 ·
A real Vortec engine is the L30, 305 or the L31, 350 with multipoint fuel injection, the intake bolts to the heads with a total of 8 bolts not 12 and has a computer controlled distributor. These engines aside from crate engines built 2001 and up only are used in trucks and vans for 1996 to 2000 they appear in no other wheeled vehicle. Often the 1987 through 95 LO3, 305 and LO5, 350 with Throttle Body Injection (TBI) are sold as Vortec’s but they are not what we talk about when we use the term “Vortec” which GM applies to most everything in sight. Rodders specifically intend this term to be the L31, 350 engine.

Converting these or the earlier TBI engines to a carb also involves installing a conventional HEI distributor. These blocks do not have a mechanical fuel pump’s installation provisions machined nor operation equipment installed an occasional exception is sometimes found but not often. These are fuel injected engines using a high pressure electric pump mounted inside the fuel tank. The TBI uses about a 20 psi pump the multi point uses about 50 psi. The cam on these engines does not have a mechanical fuel pump lobe.

The L30 and L31 use a plastic timing cover and a modified coolant pump. The crankshaft from 1986 up uses a one piece rear seal that does not mate to flywheels its flex plates earlier than 1986.

So there is some adaption needed to get these operating in earlier vehicles or when converted to a carb inside the years of vehicles they appear in.

Bo
t
 

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Hey excellant auto , I've done my homework on finding the right vortec , 1999 chevy truck , will hear run before being pulled , I'll be helping this week ,thank you , And , I'm still doing my homework . L31

I did one a few years back that had 199000 miles on it. Tore it down, and it still looked very good inside.
Not even a ring Ridge at the top of the cylinders. I went ahead and put rings and bearings in it, but it probably wasn't necessary.
I put a 276hr Comp Cam in it, and it ran like a scalded dog with a 670 vacuum secondary and HEI ignition. I'm sure it could have handled a 750 vacuum secondary plenty good...
 

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Discussion Starter · #9 ·
Looks like my work is cut out for me making the right guess on a carb. Thanks
I do not want to have to machine heads for big cam , Thanks , I'm putting it in a 65 corvette . which does not have the correct engine , I want the roller cam because I've read all about the bad cams and oils . AS we all have for years , personally I've broken in flat tappets and never had an issue , I'm too old do dick around now , swapping engines over winter and I will be done , no more projects , Thanks
 

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Discussion Starter · #10 ·
I did one a few years back that had 199000 miles on it. Tore it down, and it still looked very good inside.
Not even a ring Ridge at the top of the cylinders. I went ahead and put rings and bearings in it, but it probably wasn't necessary.
I put a 276hr Comp Cam in it, and it ran like a scalded dog with a 670 vacuum secondary and HEI ignition. I'm sure it could have handled a 750 vacuum secondary plenty good...
Did you have to machine headfs ?
 

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Crap, it's not even summer yet!
These guys on here will help you pick out the best cam. Having more information like the car it is going in is going to help.
65 Corvette should be fun. You will have to change out the flywheel, but that's not a big deal.
Also you have a few options out there without having to send the heads out to the Machine Shop.
 

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Discussion Starter · #12 ·
Crap, it's not even summer yet!
These guys on here will help you pick out the best cam. Having more information like the car it is going in is going to help.
65 Corvette should be fun. You will have to change out the flywheel, but that's not a big deal.
Also you have a few options out there without having to send the heads out to the Machine Shop.
Thanks , I've got my mechanical tach working with an HEI now that will be used in the Vortec , Heck I've got an Quadrejet ,750, that i'M USING NOW and I just my use that carb. Without machiung heads , would a cam swap even be worth it , I've done a lot of reading and most all cams I've liked neede heads machined for bette springs . I know these vortecs are not big revers but with a carb and the hei The stock engine will be better than I have now . Thank You
 

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The 10241264 cam times at zero 255/266 whch GM used .004 inch of lift to define as the zero point. The .050 inch duration is 191/196. Lift is .276/.285 at the lobe. The LSA is 111 degrees.

This cam times pretty close to the old 250/300 horse 327/350 flat tappet cam 3896929 on .050 timing of 195/202 with lobe lift of .260/.273 having an LSA of 112 degrees.

This is why I say the 264 roller in an engine with 9.5 or 10.0 to 1 compression and a 4 barrel carb will perform like the old 300 SAE gross power rated 350. In reality this engine produced between 290 and 305 hp. GM rates the L31, 350 at 250 or 255 hp SAE net.

The difference in gross to net power ratings occurred around 1973. The earlier SAE gross rating was crankshaft power without the drag of accessories or the back pressure of an exhaust system. The SAE net power is with accessories though the alternator is spinning but not producing electricity and there is a semblance of an exhaust system this pretty much drops peak power at the crank hub compared to SAE gross by about 50 horsepower. Also, it is easy to correlate that the L31 tested to the pre 1973 SAE gross test would be 290 to 305 hp. In reality the L31 has a much better head than the old double humps and as tested for SAE gross it actually pumps out 330 hp with the stock roller cam and a GMPP intake and a Holley 4bbl which I’m pretty sure was a 650cfm.

I’ve done a few of these conversions with the stock L31 cam with the earlier 87-95 TBI system. If the engine is in good shape the minimal amount of self learning GM provides for wear compensation is sufficient to pick up the bigger cam and better breathing heads as well as headers. Keep in mind this isn’t instant ‘block learn’ has to repeat I think it’s a hundred times before it gets permanently addressed. So it might be a little bit wonky on and off for a while.

Bogie
 

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Discussion Starter · #14 ·
Did you have to machine headfs ?
The 10241264 cam times at zero 255/266 whch GM used .004 inch of lift to define as the zero point. The .050 inch duration is 191/196. Lift is .276/.285 at the lobe. The LSA is 111 degrees.

This cam times pretty close to the old 250/300 horse 327/350 flat tappet cam 3896929 on .050 timing of 195/202 with lobe lift of .260/.273 having an LSA of 112 degrees.

This is why I say the 264 roller in an engine with 9.5 or 10.0 to 1 compression and a 4 barrel carb will perform like the old 300 SAE gross power rated 350. In reality this engine produced between 290 and 305 hp. GM rates the L31, 350 at 250 or 255 hp SAE net.

The difference in gross to net power ratings occurred around 1973. The earlier SAE gross rating was crankshaft power without the drag of accessories or the back pressure of an exhaust system. The SAE net power is with accessories though the alternator is spinning but not producing electricity and there is a semblance of an exhaust system this pretty much drops peak power at the crank hub compared to SAE gross by about 50 horsepower. Also, it is easy to correlate that the L31 tested to the pre 1973 SAE gross test would be 290 to 305 hp. In reality the L31 has a much better head than the old double humps and as tested for SAE gross it actually pumps out 330 hp with the stock roller cam and a GMPP intake and a Holley 4bbl which I’m pretty sure was a 650cfm.

I’ve done a few of these conversions with the stock L31 cam with the earlier 87-95 TBI system. If the engine is in good shape the minimal amount of self learning GM provides for wear compensation is sufficient to pick up the bigger cam and better breathing heads as well as headers. Keep in mind this isn’t instant ‘block learn’ has to repeat I think it’s a hundred times before it gets permanently addressed. So it might be a little bit wonky on and off for a while.

Bogie
So Bogie , this cam 264 , would I have to do any head machineing ? I will replace the springs and use roller rockers , Carb and HEI , Thank You
 

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Discussion Starter · #15 ·
Crap, it's not even summer yet!
These guys on here will help you pick out the best cam. Having more information like the car it is going in is going to help.
65 Corvette should be fun. You will have to change out the flywheel, but that's not a big deal.
Also you have a few options out there without having to send the heads out to the Machine Shop.
Excellence Auto , what are my options for a hopped up cam where the heads do not need machineing ?Thank You , I'm also reaching out to Bogie with the same question about the 264 grind .
 

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I provided the specs for the 10241264 L31 cam which is stock to that engine. The earlier TBI should adjust to it. The stock heads can run a 1.6 ratio rocker without modification to the valve guides with that cam. However as a caution this would have the exhaust side pretty close to maxed out on lift. Factory springs are fine nothing more is needed with that cam.

Basically if you keep the idle vacuum at 16 inches or higher the TBI factory program will figure out any changes to the cam it’s expecting. The factory TBI cam is about 165 degrees intake so the L31 cam which itself is considered very mild has already 30 more degrees than the stock TBI cam. So this is like count your blessings that this works, but this is the upper end of cam timing for this computer program without investing in a custom PROM.

Bogie
 

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I provided the specs for the 10241264 L31 cam which is stock to that engine. The earlier TBI should adjust to it. The stock heads can run a 1.6 ratio rocker without modification to the valve guides with that cam. However as a caution this would have the exhaust side pretty close to maxed out on lift. Factory springs are fine nothing more is needed with that cam.

Basically if you keep the idle vacuum at 16 inches or higher the TBI factory program will figure out any changes to the cam it’s expecting. The factory TBI cam is about 165 degrees intake so the L31 cam which itself is considered very mild has already 30 more degrees than the stock TBI cam. So this is like count your blessings that this works, but this is the upper end of cam timing for this computer program without investing in a custom PROM.

Bogie
I think this one's going in a 65 Vette. With an HEI and a carburetor.
 

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Then if the OP is changing cams the limit is about .470 inch at the valve without some sort of remedial action.

The head’s can have the upper guides machined for clearance. This requires the head’s be submitted to a machine shop or with the tools to take the valves out can be done with the purchase of the cutting tool and a decently powerful electric drill.

There is the so-called ghetto grind of hacking the guide down with an angle grinder. This requires a decent touch and the ability to dress the roughness and chips out.

A similar cut is to thin the bottom of the cup of the spring retainer, it doesn’t really hold the locks in place, how much it contributes to retainer strength is subject of debate but I’m not keen on this.

An other option is going to beehive springs especially good if adding some cam because there are better behaved springs. It incurs the additional cost of a set of Comp 787-16 retainers to bridge the gap from the metric spring and GM metric 8mm valves so you can use these springs with the older 11/32 stem valves of the Gen 1 and 2 SBC. Going to the beehive and Comp retainers buys about .050 inch this gets you to .520 lift at the valve.

Along with the exercise above there are stem locks that raise or lower the the groove key from .030 to as much as .060. You can use a positive offset lock to move the retainer .050 inch higher that along with .050 inch spring shim will move the spring and retainer up that much for .570 inch lift at the valve. However, these need to be mocked up with an assembled valve train on the engine to check for rocker to retainer clearances and are likely to require longer push rods. You also have to check where the retainer nuts are on the rocker studs, you can run out of stud threads with all of these tricks.

The same goes for guide with oil seal clearance, you gotta check all this stuff once you start deviating from what the General built. A good rule for clearance between moving parts including one spring coil to the next is .050 inch.

Bogie
 

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Discussion Starter · #20 ·
ExcellanceAuto is correct , thanks to you and thanks to Bogie , For the engine ,approx. 160K miles , I think I'll use the cam in it , the lifters , New springs , new 1.6 roller rockers , and run it ,Sounds like it will be a fine street engine , with no worries .
Sincerely , Bob
 
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