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Old 03-16-2014, 07:10 PM
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And after months upon months, I have officially nickeled and dime'd my way up to the big leagues! I bought a pair of 062 Vortec Heads! I have a completely stock 1991 350 tbi with long tube headers and true duals with Flow master 50's on it.... My believed compression ratio with the tbi heads are 9.3-1. I am unaware of what the compression ratio will be after I put the vortec heads on. But that's the least of my worries at this point. Right now I am more worried about what all I need to accomodate with my new heads. For instance can I use my stock rocker arms or should I go with some self aligning comp cam roller rocker tips? Should I use roller lifters or will my stock lifters do just fine? The reason I ask this is because since I will have it torn that far down I want to go ahead and put a cam in it just for street use so I can shred the tires off when I need to, and wont be forced to upgrade the the valve springs. But any how, has anyone on here ever done a stock 350 and vortec heads with a cam? what cam did you use and why did you use it? should I stay away from flat tappet?
Another question I have is what would be the best cheap intake I could use? I want to just throw an addapter plate on the intake so I can keep my tbi that way I can put 454 injectors on it for more fuel!

So all and all main questions are what do I need to have a fun daily driver? Good Cam?
Good Intake?
Good Adapter?
Good Rocker Arms?
Good Lifters?

Once again thankyou very much for the input! It is much appreciated
God Bless

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Old 03-17-2014, 07:52 AM
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get a vortec marine intake.. they are like 40-50 bucks for the tbi ones.. no adapter needed
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Old 03-17-2014, 10:25 AM
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Originally Posted by SilveradoRunner1991 View Post
And after months upon months, I have officially nickeled and dime'd my way up to the big leagues! I bought a pair of 062 Vortec Heads! I have a completely stock 1991 350 tbi with long tube headers and true duals with Flow master 50's on it.... My believed compression ratio with the tbi heads are 9.3-1. I am unaware of what the compression ratio will be after I put the vortec heads on. But that's the least of my worries at this point. Right now I am more worried about what all I need to accomodate with my new heads. For instance can I use my stock rocker arms or should I go with some self aligning comp cam roller rocker tips? Should I use roller lifters or will my stock lifters do just fine? The reason I ask this is because since I will have it torn that far down I want to go ahead and put a cam in it just for street use so I can shred the tires off when I need to, and wont be forced to upgrade the the valve springs. But any how, has anyone on here ever done a stock 350 and vortec heads with a cam? what cam did you use and why did you use it? should I stay away from flat tappet?
Another question I have is what would be the best cheap intake I could use? I want to just throw an addapter plate on the intake so I can keep my tbi that way I can put 454 injectors on it for more fuel!

So all and all main questions are what do I need to have a fun daily driver? Good Cam?
Good Intake?
Good Adapter?
Good Rocker Arms?
Good Lifters?

Once again thankyou very much for the input! It is much appreciated
God Bless
Yikes, this is an improvement that takes some up front planning, it is not as simple as it seems because GM changed things between the Swirl Port TBI engine and the Vortec, it actually crosses the engine management divide between On board Diognostics (OBD) I and OBD II that phased in with the 1996 model year which is considerable and at that having a 1991 is really still in the early phase of OBD-I which has an enhancement starting in 1993 through 1995.

Let me start at the EGR system. EGR is built into the computer code you cannot terminate this function without risking engine damage from a lean cruise mixture unless you install a new chip into the computer, but more on chips later. The vortec head does not support EGR with an exhaust passage within the head as the Swirl Port has. The EGR on Vortecs is all external with an intake that has the mount and passages for the EGR valve and is connected to an exhaust manifold in the case of production or to a header tube in you case with an adapter welded to the header tube and a pipe and fittings from there to the intake.

The intake manifold of the Vortec has a very different bolt pattern from that of the Swirl Port L05 engine you have. GM does make a conversion intake for TBI injection to Vortec L31 heads, it is a bit pricey but solves all the match up problems and provides a mount for the EGR. Otherwise you'll need a 4 barrel carb intake with a 4 bbl to TBI adapter plate. EGR is still an issue as even if the intake has an EGR mount as the heads cannot act as the supply because there is no exhaust feed internally from the valve pockets as with earlier production heads. So you need to determine whether the engine gets EGR or not that depends in large measure emission regulation and testing where you live.

Rocker arms, you stock self aligning rocker arms will work on Vortec heads they are in fact the same as that which came in L31 engines. The rockers you have are self aligning so the push rods are not guided nor hardened. Roller rockers are nice, but they are costly, given what your going to discover from these writtings money may become an issue so I'd table rockers as something easy to change out somewhere in the future.

Camshaft, the TBI is limited to how much cam it will tolerate, it calculates fuel flow and ignition timing based on formulas the start with the relationship of manifold vacuum, GM calls it Manifold Absolute Pressure (MAP), to RPM's to throttle position. Changing the cam changes one element of these measures which throws the calulation for fuel and ignition into an error compared to what's needed. Pushing the cam timing to about 200 degrees at .050 lift is about the limit without a chip. Pushing the cam to about 215 degrees is the upper limit even with a chip. There are cams noted as specific to TBI or early TPI these are what to buy don't go exploring beyond that as it easy to make a big mistake and costly to fix it. You engine has a flat tappet cam you cannot run roller lifters on it. The cam and lifter type need to be the same. Your block might be provisioned for a roller cam, if it is you will have seen 3 protusions extending upward from the main oil passage casting in the valley under the intake. They need to be drilled and tapped so as to mount a thing called the spider that holds the gadgets (dogbones) that align the roller tappets to their cam. Often in these truck blocks the provions may or not be drilled and tapped, you'll have to look. This type block will also have the raised lifter bores for the taller hydraulic roller lifter that GM uses. When removing the timing cover there should be a boss to either side of the cam bore that fastens the roller cam's thrust plate, these may or not be drilled and tapped for the plate. If the provision is there then along with the spider and dog bones which can be had from most parts houses this block can be converted to a factory roller cam at minimal cost. The roller cams take a different timing set (gears and chain) you need to pay attention to this when ordering. Also, there are double row roller sets listed they do not fit without some minor grinding on the snout of the main oil galley where it protudes into the timing case to clear the backside of the cam gear. 1996 L31 vortecs take a different timing set again they run under a plastic cover that fits a crank position sensor, it's easier to just avoid these. In all cases keep an extra timing cover gasket as sometimes whn using a double row roller it will brush the cover so an extra gasket offers just enough clearance to alliviate that problem should it occur.

The L31 Vortec head cannot accept valve lifts much beyond .45 inch because the high valve guide will be struck by the under side of the spring retainer, basically this won't be a problem with TBI as compatible cams will not have that much lift. There are tools for the home craftsman to cut the guide down with an electric drill or for about the same cost your local automotive machine shop can do it. If your truck has the ---193 casting number Swirl Port heads they have the same chamber volume as the L31 Vortec head so your compression ratio will be the same between them for the same head gasket thickness.

The 670 cfm TBI unit with 2 inch bore throttles is a PIA to mount on anything, you will need an adapter that blends this into the manifold throttle bores. The 670 CFM units use considerably higher flow injectors, roughly LO5 uses 60 pound per hour injectors and 670 CFM units from Holley or off a 454 use 80 to 90 pound per hour injectors. Therefore, an entirely new program needs to be put into the computer because a 350 will be flooded out with these injectors everywhere except on the extreme top end, which you can't get to anyway because there is a rev and speed limiter in your stock chip so that also has to be reprogrammed. It is there to prevent your throttle foot from going further than the original injectors can fuel. At 60 pounds per hour times 2 injectors that's a total of 120 pounds of fuel per hour. It takes about one half pound of fuel per hour per horsepower at WOT so 120 pounds per hour of fuel delivery caps the engine's top power output at 240 horses. Of course an LO5 doesn't make anywhere near that so there's a saftey margin for the factory warranty. The factory L31 Vortec is rated around 240 horses with a cam of about 191 degrees intake and 196 exhaust which compared to the LO5 cam of about 166 and 175 is a considerable improvement. A cam that works very well with TBI is the 1995-97 LT1 p/n 12551705 which is 201/208 degrees and .447/.459 lift with a 1.5 rocker. This cam has a wide 117 degree LSA which makes a very stable idle that MAF based injection like TBI really likes yet brings a fair amount of punch to the game. The LT1 head insofar as porting and chamber efficiency is very similar to the L31 Vortec.

So there ya go a lot of details to be nailed down.

Bogie
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Old 03-17-2014, 10:48 AM
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Thank you very much Bogie. What a friggin' nightmare.......
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Old 03-17-2014, 11:16 AM
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Thank you very much Bogie. What a friggin' nightmare.......
I shouln't say LOL, he's got a serious problem that's gonna take some time and bucks to work out.

Bogie
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