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Old 10-10-2010, 02:59 PM
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Rebuilding a vortec 350 any recommendations?

I just bought a 96 Chevy Express Conversion van. It has the Vortec 350 engine in it. The rod came through the pan and I just got another engine from a 97 Tahoe for it. The new engine has 145,000 miles on it so I am looking to rebuild it for peace of mind and to pump it up a little bit and increase fuel economy.

I was thinking of doing a complete overhaul. Looking to go .030 over with forged pistons, maybe new rods (what are your thoughts) and new oil pump and of course bearings. I know the bottom end it a standard SBC so i could go hog wild but my main goal is drivability too. The heads are good flowing heads but I have the 906 castings and I here there is some work to be done on the exhaust side. I would like to upgrade the cam to a .500 lift but I have read that if I do that I will need to machine the valve spring seats and replace the springs. Here is where I get lost? Is there more needed to increase lift to .500? Do I need new valves or retainers? I want to keep the roller style cam/lifters. I also want to clean up the ports match to gasket on the intake side and clean up and smooth out the exhaust side. there is also a step from what I have read in the combustion chamber and it could use a bit of work. I am learning a lot but if there are any recommendations I would love to hear them now before I start buying all of the parts? I was thinking about upgrading the Fuel Spider and maybe enlarging the Throttle body too. Thanks for for reading this long ***** post
Thanks
Chuck

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Old 10-10-2010, 05:04 PM
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I say keep it a 350 because a 355 will use more fuel. Just put a nice cam in it and get the heads ported. You could also run a 4bbl instead of tbi if you want.
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Old 10-10-2010, 05:10 PM
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Quote:
Originally Posted by bigdog7373
I say keep it a 350 because a 355 will use more fuel. Just put a nice cam in it and get the heads ported. You could also run a 4bbl instead of tbi if you want.
Wouldn't carb'ing it throw codes? I would think that the SFI would be more fuel friendly?
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Old 10-10-2010, 05:23 PM
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You trying to fly a barn door?

Forged pistons are overkill, unless this conversion van is for truck pulls. your rods will be fine, resize and re-use.

Boring to 355 will not effect gas mileage. But you would hate a .500 lift cam in this vehicle. Aside from the fact that the heads need machine work. The springs and retainers have to be replaced. Low compression will not support the cam

MOST of the aftermkt .500 lift cams are not going to have the low end that you need for a van.

A new chip would have to be burned just to get the thing to run.

Build a sensible replacement motor. Then build a HOT ROD motor for a HOT ROD..

I just went thru a similar situation with a customer. He complains every week about performance.. I warned him first.. But, customer is always right!!
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Old 10-10-2010, 05:45 PM
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The pistons are not that expensive and I will most likely need to go .030 anyway. I thought a .500 cam would help breathing while under normal accelerating or would require less pedal to maintain on the hwy? I would get it dyno'd either way and have the computer reflashed to match the build. my reasons for the rods was because that was the original failure of the engine that is in the van now. I am not looking for a race car. I just want to build it once! If I can beef it up while i'm at it them ok! I thought this vortec had 9.3:1 compression? What would you do for extra pep and mileage if you had to rebuild? I think the factory cam lift is .462? I seen that comp cams has:
Cam Style Hydraulic roller tappet
Basic Operating RPM Range 1,800-5,800
Intake Duration at 050 inch Lift 230
Exhaust Duration at 050 inch Lift 234
Duration at 050 inch Lift 230 int./234 exh.
Advertised Intake Duration 280
Advertised Exhaust Duration 284
Advertised Duration 280 int./284 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.474 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.474 in.
Valve Lift with Factory Rocker Arm Ratio 0.474 int./0.474 exh.
Lobe Separation (degrees) 111
Computer-Controlled Compatible Yes
Grind Number X4280HR
Valve Springs Required Yes

Just a thought.
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Old 10-10-2010, 06:14 PM
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If you run a carb you won't have to worry about getting the computer to work with cam. Also better performance, imo.
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Old 10-10-2010, 06:19 PM
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in Pa it won't pass inspection.
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Old 10-10-2010, 09:34 PM
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i think edelbrock makes a line of carbs that are pass inspection. idk for sure though
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Old 10-11-2010, 10:36 AM
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You can leave the ports alone and save the headache. They'll flow enough to support much more HP than you're looking for, and you just risk reducing port velocity which can hurt TQ and MPG.

What I would do is have the heads rebuilt with a good valve job. A good back-cut 3-angle valve job will probably increase flow as much as port matching would and won't affect velocity. While they're being rebuilt, spend the money on the spring/retainer kit that allows .550" lift. Since you'll probably be selecting a different cam anyway, you'll need new springs to match the profiles. Might as well get the ones that let you get a bit more lift. That way you don't have to machine spring pockets or anything. If its not much more money, there is a beehive/ovate spring choice but in my opinion its not necessary. The idea is to reduce weight at the retainer, but that is mostly for high-RPM stability which you don't really need.

The stock "spider" will support mild increases in displacement/power but not much. If you run out of factory adjustability, I suggest an adjustable fuel pressure regulator for a tiny bit more pressure to compensate.

Keep the cam mild. The factory cam is 191/196 duration with 111 LSA. Very little overlap. I would think about a similar overlap with something like a Comp 260XFI. Its a 210/218 duration with about 111-112 LSA if I remember right. The stock computer should be able to learn this cam, if not you may need programming and/or adjustable FPR. You will also want to use 1.5 rockers. With 1.6 rockers it will put you over .550" lift.

That will also keep really strong low end, but bump your HP to the 325 range and keep your MPG.
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Old 10-11-2010, 07:26 PM
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Thanks for the info!!!

I was thinking about just cleaning the casting in the runners on the intake side and trying to really smooth out the Exhaust side. I hear the exhaust has major restriction on the 906 (truck) head. I forgot about doing a 3 angle valve job. I want to do springs and retainers to allow for a little more lift but I keep hearing that the seat needs to be cut for the different springs? Is the regulator built into the spider? or is it removable. I am going to look up the cam you mentioned! What is the ratio of the factory rocker? It looks like if you want to upgrade rockers that you need to stud the heads? I will be getting the car dyno tuned once it is built so I can match the computer to the engine properly. I will be doing the bottom end also and i want to make sure it has the right stuff in it the first time! if you have any bottom end suggestions i'm up for any and all advice!
Thanks
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Old 10-11-2010, 09:45 PM
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Quote:
Originally Posted by chucksrt
I was thinking about just cleaning the casting in the runners on the intake side and trying to really smooth out the Exhaust side.
Intake runners need to retain the stock rough casting finish, which aids in keeping fuel in suspension in the intake fuel mixture charge. The exhaust runners can be polished to a mirror finish if you have the time and effort to do it. Don't change the shape or size, just polish out the casting roughness. Be advised though, that I would only do this on a $10,000 and up engine build, not on a daily driver motor. Gasket matching will result in a port that looks like an Anaconda swallowed a pig and the air flow will slow down as it goes past the larger diameter point. When the air flow slows down, fuel drops out of suspension. Don't waste your time matching the intake ports to the gaskets. You may do more harm than good.

Quote:
Originally Posted by chucksrt
I hear the exhaust has major restriction on the 906 (truck) head.
Some L31 heads had a hardened exhaust valve seat installed rather than using an induction hardened seat. Some clown along the way has concluded that this is a "major restriction". BULL HOCKEY!! Other than a good valve job, leave the heads alone in the ports. You'll do more harm than good.

Quote:
Originally Posted by chucksrt
I forgot about doing a 3 angle valve job. I want to do springs and retainers to allow for a little more lift but I keep hearing that the seat needs to be cut for the different springs?
Have your shop put as many angles on the valves and seats as you can afford. If they'll do it and you can afford it, put a 101 angle job on them. Of course I'm being facetious, but the more angles you use, the better the flow is, all other things being equal.
Stock valve spring diameter is around 1.250" on stock L31 heads. When you install a cam with more lift, you usually increase the diameter of the valve springs to facilitate more travel if you cannot find enough travel with a stock diameter spring. Here's an interesting quote from Crane Cams...

"How do you increase spring travel?
The valve spring must have sufficient travel (plus .060" safety margin) to accommodate the amount of valve lift created by the camshaft and/or an increase in rocker arm ratio. To increase spring travel you can either raise the installed height (but this will lessen the spring tension), or change to a spring with additional travel. If there is not a standard diameter spring available with enough travel, the cylinder heads will have to be machined and a larger outside diameter (O.D.) spring installed.

Crane Cams offers some special valve springs in standard diameters which eliminates having to machine the cylinder heads. For example, a small block Chevrolet engine can use spring kit part number 11309-1 to handle .550" to .600" valve lift. The 85-00 302 Ford hydraulic roller engines can use spring kit part number 44308-1 to handle .550" lift."

Here's a Crane spring and retainer kit for the L31 heads that drops right into place with no machining....
http://www.summitracing.com/parts/CRN-10309-1/

Quote:
Originally Posted by chucksrt
What is the ratio of the factory rockers
1.5:1

Quote:
Originally Posted by chucksrt
It looks like if you want to upgrade rockers that you need to stud the heads?
The stock rockers are stamped steel rail rockers that have a recess in the tip to hang down around the tip of the valve and keep the rocker in place over the valve tip. There are several makers of roller rockers with recessed roller tips that will work on the L31 heads and stock pressed-in studs. There is a limit though, to the pressure of the valve spring that you can use before you begin pulling the studs out of the heads. Mr. Gasket makes a stud pinning kit to keep the pressed-in studs in place with stronger springs......
http://www.summitracing.com/parts/MRG-806G/

You will run into a serious problem if you try to use the stock L31 dogbone arrangement with a lift much higher than 0.530" though, using the stock ratio 1.5:1 rocker arms. The problem is with the smaller base circle of cams that are ground for more lift/duration. When the base circle gets too small, the lifter drops down out of the dogbone with the lifter on the base circle of the cam and things get ugly. The only way to get more lift than that is with a 1.6:1 ratio rocker arm. For instance, you could use a cam that gives 0.530" lift with 1.5 rockers, but would lift to 0.565" with the same cam and 1.6 rockers.

Last edited by techinspector1; 10-11-2010 at 09:51 PM.
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Old 10-11-2010, 10:13 PM
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Quote:
Originally Posted by bigdog7373
If you run a carb you won't have to worry about getting the computer to work with cam. Also better performance, imo.
a carb is better performance if you don't know what you are doing with the fuel injection (no offense to anyone). If the van is a 96 you will have the electronic shift transmission which is controlled by the ecm through the throttle position sensor and the vehicle speed sensor, and I am sure there is more. Build the engine to run with the fuel injection setup you have and make life easier on yourself. I do believe that someone makes a setup to run the electronic shift transmission with a carb if you have deep pockets. What are your plans with this van?

P.S. sometimes a big engine can be big problems, do yourself a favor and listen to a choice few guys on here, they really know what they are talking about
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Old 10-11-2010, 11:48 PM
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Quote:
Originally Posted by bigdog7373
If you run a carb you won't have to worry about getting the computer to work with cam. Also better performance, imo.
and good luck getting your 4L60-E to work.
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Old 10-11-2010, 11:50 PM
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This is what i would do.

-KEEP the Vortec CSFI
-build the engine, Make sure to use a SINGLE row timing chain, not a double, there is a wheel in behind the timing cover to trigger the crank sensor, a double row will be to thick
-Get the PCM tuned for you specs, and you should be good to go.

I would NOT get rid of the EFI, makes no sense ot go to cabr in a van that sounds like it gets daily use.
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Old 10-11-2010, 11:52 PM
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Quote:
Originally Posted by crussell85
a carb is better performance if you don't know what you are doing with the fuel injection (no offense to anyone). If the van is a 96 you will have the electronic shift transmission which is controlled by the ecm through the throttle position sensor and the vehicle speed sensor, and I am sure there is more. Build the engine to run with the fuel injection setup you have and make life easier on yourself. I do believe that someone makes a setup to run the electronic shift transmission with a carb if you have deep pockets. What are your plans with this van?

P.S. sometimes a big engine can be big problems, do yourself a favor and listen to a choice few guys on here, they really know what they are talking about
Im using a holley TPS kit (~$150) on my Street Avenger to run my 4L60E, it isnt a bad swap, all you need to do is keep the crank sensor, TPS and a CTS, but it makes no sense to go carb when EFI is available and the price of a tune is cheaper then a new carb.
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