350 TBI to Carb with Manual Transmission NV3500

[5SPD350]

From ideas of an LS swap, to a Vortec TBI, back to an LS Swap, now I'm considering just going Carb for simplicity and cost.

While looking into a steering problem on my truck recently (happens to be the steering gear and pitman arm which I'm going to replace with the sport ratio gear box), I noticed a leak. I found that my intake manifold gasket was dripping antifreeze in the drivers side front. So I bought an entire Head gasket/intake gasket set and pulled the heads and put it all back together. The head gaskets were also gone in some areas. While apart the TBI horns/ridges were ground down and radiused into the bore and polished. The intake manifold was also gasket matched as there was a lot of casting left to be taken out safely. After putting it back together and a little trouble getting the timing right, it runs pretty decent. Did plugs, and wires while I was in there too. Still have to get an ignition coil. Has a little bit of a breakup/miss in the higher rpms 3,000-5,000.

Anyways, I think carb may be the simplest, cost efficient way for me to go. But I don't have a full grasp yet on what all is involved.

I'm torn between using my stock block a 2 bolt 350 TBI that Im pretty sure is original and has 183,000 miles and adding better heads and a cam to it. Or, getting a 350 Vortec long block, and putting a carb intake manfold on it. Or any other block I may find. I did find a 70-73 400 SBC for $500 on craigslist as well.

From what I know, I'll need a carb intake for whatever motor I choose, A Fuel pressure regulator, an HEI distributor (but not sure what I need as far as vacuum, mechanical etc.), and a carb (also not sure of mechanical secondary vs. vacuum secondary and what I'll need being that it's a 5 speed and not an auto.

I'd like to use my stock serpentine set up that is on my TBI motor now, which includes A/C. Which I know won't be possible on older style heads that use the V belt setup that don't have the provisions for them. But I d k if the holes/studs are still the same on a Vortec engines heads.

Also, I keep reading about a water bypass on the vortec engines that my TBI does not have that sounds like it could be a problem area. as well as the plastic timing cover on a Vortec engine that doesn't have a timing tab.

My reason for choosing carb is again simplicity, and cost efficiency. The TBI to me just doesn't seem to be performance oriented with it's finickiness of cam selection, vacuum, and tuning. I don't have the money to keep paying for tuned chips until I get one that works semi Ok. I would go LS, but that's still also quite expensive with the cost of a custom harness. Also I have no worries on emissions so EGR can go out as well.

My Goal is to have a motor that makes at least 300fwp although more would be nice. It needs to turn at least 6,000 rpm (that's where I want to shift it at). Able to run pump gas. I'd like to stay 87 octane, but if I have to use 91 or 93 that's fine. And have a nice lumpy idle (not too crazy just enough to know it's cammed when you hear it)

My intial thought is to keep my 350 TBI bottom end, add a flat tappet cam and lifters, used vortec heads, a double roller timing chain, a carb intake, a 4 barrel (not sure how many CFM), Fuel pressure regulator, HEI Distributor, and some headers and call it good.

Who can steer me in the right direction?

 

[vic_v8]

the two best options are (if I was you) swapping to LS, I have one in a 88 V20 Suburban and with no OD and 35" tires, I get 15 mpg and have 330 ish HP or adding stock Vortec heads to your engine, cam, carb intake, and 454 tbi.

 

[5SPD350]

While I'd love to do an LS swap, it's just not within my means at this time. The cost for the harness and tune, let alone finding someone to do the tune is the problem. I'm not interested in doing mail order tunes, and I don't think there is much in the way of tuners where I live that can do real time tuning. The nearest "cities" near me are Williamsport PA, Syracuse NY, Rochester NY, Binghamton NY, and a few others. TBI is completely out, I am not keeping that. They don't support the RPM I want, and they can only handle so much cam. This is why I want to go Carb.

My real questions are wether I should use my stock 2 bolt bottom end and add heads, cam and lifters, carb intake, and 4 barrel, OR if I should find another long block like a Vortec L31 Long block and add a roller cam, carb intake, and 4 barrel, or a L98 TPI block, or maybe a 400SBC.

Also need suggestions on which heads I can use and keep my stock serpentine setup including my A/C. As I know some don't have the provisions for them.

I'd like to just use Vortec heads on whatever setup I use, but want to know more about the water bypass issue and the plastic timing cover on The 5.7 Vortec L31 and not having a timing tab.

Regarding pump gas, how high of a compression can I run with Iron heads? I know the Vortecs are 64cc. and my stock pistons are dished but how far I'm not sure.

Same question as well but with Aluminum heads, as I've heard I can runner higher compression and still run pump gas.

 

[magimerlin]

First off what is your budget? A motor built to handle 6k shifts is not going to be cheap either. 6k is out of almost all motors usable horsepower range.. most small block race motors don't even get shifted that high with out having to be rebuilt midway or after the race season.. let alone run 87 octane trying to due do.

 

[5SPD350]

I'm thinking $2,500 or less.

Considering a stock 350 Vortec rev limiter is at 5,600 or an LT1 at 5,800 rpm for example, I didn't think 400 more rpms would be that expensive but I'm not an expert by any means either though.

I may be day dreaming reading the Budget Vortec builds that super chevy or hotrod, or other magazines have done as they have endless money to build with, but those were all running pump gas with iron heads and making 400 fwhp or more.

This isn't going in a race car or anything. It's going in a 92 C1500 RCSB that will have an NV3500 5 speed and a 454ss 14 bolt rear end with 3.73 gears.

I won't be constantly shifting it at 6,000 rpm either, just when I want to drive it aggressively.

 

[5SPD350]

There is a guy that constantly has long block L31 5.7 vortecs for sale near williamsport PA for $500-$550 with 80,000 miles or less on them.

I figured one of those, change the cam out to a higher lift/duration, cut the guides down to accept the larger lift, add some better springs like beehives, put a carb intake on it, and a 4 barrel and call it good

What I'm unsure of is the water bypass issue on the vortecs, the timing cover being plastic with no timing tab, what kind of distributor to use (mechanical, vacuum, etc.) and the deal with the melonized gear and roller cams, what size cam, staying 1.5 rockers or go to 1.6, what kind of carb to use (CFM size, mechanical or vacuum secondary), and if my TBI serpentine setup can be used on the Vortec Long block. Or if I'll have ot use the Vortec serpentine set up.

 

[Jorge6.5]

I'm gonna be doing a similar build right after tax time. I also have a rcsb truck with 5 speed but it's 4x4.

I'm pretty sure I'm going with a new l31 long block and carb intake if I can't find a decent used vortec 350. I have done lots of research and forum searching about this swap. You should do the same. It's seems pretty straight foward. I believe a tbi timing cover will work if you go with timing set from the early 90s cars like firebird ect. All front accessories should bolt up with I think a tbi balancer. For the coolant bypass you can just drill small holes in the thermostat.

I was set on doing the tbi with carb adapter but like you I don't want to have to deal with custom tunes and issues with bigger cams. But if going carb you would need an hei distributed will melonized gear with the vortec block because of the roller cam.

I read you mentioned some locations in ny, is that where your located? I'm the Catskills myself. If your near by maybe we can help eachother with the swaps.

Good luck!

 

[Jorge6.5]

If you use 1.6 roller rockers you should be able to get more lift without machining but again search about this to be sure. I think you would want to go no smaller then a 600cfm carb.

 

[5SPD350]

I'm in Elkland PA. Which is like an hour or less from Elmira NY.

Good to know about the timing cover, and the water bypass, balancer, and accessories.

It does seem very straight forward. I mean if I wanted to just take my current motor and switch over to carb, I would just need to get a different intake, a carb, a fuel pressure regular, and different distributor and be set for the most part other than re routing lines and such.

It's just the specifics on the specs of the motor itself that have me a little stuck to have it perform the way I want.

But it sounds like an L31 long block will work with a different balancer, timing cover, and the holes drilled in the thermostat. As well as required modifications to the valve guides and springs to accomodate the larger cam.

I did find a Intake manifold + Carb set on Summit for around $650.00. Square bore dual plane vortec intake, 750 CFM manual secondary 4barrel carb, Open air filter, and misc gaskets, bolts, & sealer. But might be able to find that stuff cheaper used. Who knows.

I'm not even sure where to start with the cam, I considered maybe a stock LT4 cam which they redline at 6,300 and removing the dowel on the front for the optispark. or maybe go with some more lump and get an LT4 Hot cam. I'm really not sure what I'm doing as far as Duration, lift, LSA, centerline, cylinder pressure with the cam, advancing, retarding, any of that stuff goes. It's a little over my head to be honest. So many variables to determine what cam is the right cam, and I definitely don't want to choose the wrong one.

 

[skylark]

I believe a tbi timing cover will work if you go with timing set from the early 90s cars like firebird ect. All front accessories should bolt up with I think a tbi balancer. For the coolant bypass you can just drill small holes in the thermostat.

I was set on doing the tbi with carb adapter but like you I don't want to have to deal with custom tunes and issues with bigger cams. But if going carb you would need an hei distributed will melonized gear with the vortec block because of the roller cam.

A standard timing cover will work but if memory serves me correctly there will be 2 holes missing. I've never had an issue with a leak but you never know. The balancer is the same for the vortec and the tbi as well as the lower pulley. All of the tbi brackets, accessories, starter, flexplate/flywheel, water pump, engine mounts, oil pan, valve covers, exhaust manifolds and sensors bolt straight to the vortec. The intake, heads, distributor, timing cover, thermostat and housing, timing set and water pump are all different but it isn't a big deal. As an example, I have purchased a vortec long block from a wrecking yard and removed the intake, distributor and water pump and used it in a tbi truck. I just used a vortec carb intake, made my own carb to tbi adapter plate (cheap and easy), used a tbi water pump, and the tbi distributor. I used a melonized distributor gear, set the timing at 4 degrees advanced and upped the fuel pressure using a flat washer under the regulator spring. They run good this way but you will throw a code for the EGR system and there are more gains to be had by a proper tune but as I said before, they run good like this. I have done 3 like this and only one was tuned afterward.