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Old 09-23-2018, 12:36 PM   #1
tdangle
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Replacing a tired 350 with a L31 Vortec 350

Just spend some time searching and really have not found what I am looking for. My goal is to install a L31 in place of my Gen1 350. Looking to get some sort of parts list together and have everything ready for the swap when the time comes.

I know I need:

electric fuel pump
different (melonized) for HEI dist.
vortec intake manifold (not sure of the brand yet. square or spread bore ??)
new flex plate (153 tooth??)
rear AC bracket that mounts to the manifold
Holley carb with electric choke (like the quadajet but don't want to loose choke)

I want to change the timing cover out and just reuse mine off of my 350 including the harmonic balance. (going to run the original v belts and have a short water pump)

Am I missing anything else? the original motor has factory AC (working) and power steering
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Old 09-23-2018, 09:41 PM   #2
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Re: Replacing a tired 350 with a L31 Vortec 350

Which intake you get will depend on the carb you plan to use.

The new flex plate is due to the change from a 2-piece to a 1-piece rear main seal.

If you want to reuse your harmonic balancer (which I don't recommend) you need to remove the reluctor behind the timing gear on the crankshaft. You might as well install a double roller timing set. The Vortec balancer is shorter to accommodate the reluctor.
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Old 09-23-2018, 11:45 PM   #3
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Re: Replacing a tired 350 with a L31 Vortec 350

why do you not recommend using an earlier harmonic balancer?
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Old 09-23-2018, 11:57 PM   #4
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Re: Replacing a tired 350 with a L31 Vortec 350

You can use your quadrajet if you use an electric choke conversion.
With your electric pump you should set up a return style fuel regulator. Electric pumps don’t like to be deadheaded.
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Old 09-24-2018, 01:01 PM   #5
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Re: Replacing a tired 350 with a L31 Vortec 350

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why do you not recommend using an earlier harmonic balancer?
That's not what I said. I said I wouldn't re-use your harmonic balancer. The rubber ring is 45+ years old. It's time for a new one. The old style is fine; that's what I have on mine.
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Old 09-24-2018, 02:20 PM   #6
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Re: Replacing a tired 350 with a L31 Vortec 350

you must have missed this thread . http://67-72chevytrucks.com/vboard/s...d.php?t=763121

i have not got mine fired yet but dropped right in place and bolted up good . http://67-72chevytrucks.com/vboard/s...d.php?t=755514

even used the cam sensor block off plug in the link provided by another member . it was 20 bucks . https://www.eficonnection.com/home/p...illet-aluminum

fit n finish of the edelbrock intake for square bore carbs 1450 series was o.k. for my needs going holley sniper unit .

make sure to give radliy chevy a call were i got mine from . they were the best price i found for the 4 bolt main version shipped to my work . https://www.ebay.com/itm/GM-OEM-NEW-...4AAOSwysRas9qX
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Old 09-30-2018, 12:11 AM   #7
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Re: Replacing a tired 350 with a L31 Vortec 350

Did your gen1 350 have a 153 or 168 tooth flexplate ?
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Old 09-30-2018, 02:09 PM   #8
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Re: Replacing a tired 350 with a L31 Vortec 350

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Did your gen1 350 have a 153 or 168 tooth flexplate ?
Not sure. I do remember dad having a lot of problems with the starter when new and something about Chevy replacing the flexplate. Never thought to identify what I had when I swapped a 200r4 trans for the th350
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Old 09-30-2018, 03:42 PM   #9
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Re: Replacing a tired 350 with a L31 Vortec 350

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Did your gen1 350 have a 153 or 168 tooth flexplate ?
If I remember when I installed my L31 it was not so much the tooth count , its the fact of the L31 has a one piece seal and the old 350 have 2 piece seal and the bolt hole will not be correct also , you will need a flexplate for the 96-99 vortec engine,but also specify if you have a 2 bolt or 4 bolt vortec engine , I believe the 1500 series trucks had 2 bolts and the 2500 series had 4 bolts . my L31 is a 4 bolt ,So I ordered a flexplate to fit a 1998 5.7 2500 series truck , I had a TH 400 and then put in a 200 4r with no issues .
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Old 09-30-2018, 11:17 PM   #10
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Re: Replacing a tired 350 with a L31 Vortec 350

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Not sure. I do remember dad having a lot of problems with the starter when new and something about Chevy replacing the flexplate. Never thought to identify what I had when I swapped a 200r4 trans for the th350
Just going off your first post on items you may need for the activity you are trying to perform, the starter maybe something to look at as well....
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Old 10-01-2018, 03:41 PM   #11
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Re: Replacing a tired 350 with a L31 Vortec 350

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my L31 is a 4 bolt ,So I ordered a flexplate to fit a 1998 5.7 2500 series truck ,
Ummmm yeah, the number of bolts holding the main caps to the block have absolutely nothing to do with a 1 or 2pc rear main seal, which is the only difference. Any flexplate from 1pc rear main truck would work, which is what 1986 or so?
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Old 10-01-2018, 03:48 PM   #12
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Re: Replacing a tired 350 with a L31 Vortec 350

Friendly reminder. A lot of folks forget that that trans behind the "tired" engine is ALSO "tired". Then you get everything going and a few thousand miles later the trans craps behind all that new found power. I'm just saying be ready and not surprised when it happens.
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Old 10-02-2018, 02:47 PM   #13
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Re: Replacing a tired 350 with a L31 Vortec 350

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Friendly reminder. A lot of folks forget that that trans behind the "tired" engine is ALSO "tired". Then you get everything going and a few thousand miles later the trans craps behind all that new found power. I'm just saying be ready and not surprised when it happens.
Trans just got rebuilt prior to the trans swap. Maybe 600 miles and I have a 2 year warranty on it. Engine is running OK now, but I'm looking at being prepared and would like to spread the cost out over time.

I didn't know that I would need to run a fuel return line, so that's something else I need to look into.

Basically looks like my list is fuel delivery system, vortec intake manifold, probably a new carb, flexplate plugging the crank sensor hole, timing marks, and long water pump (I have a short one now, which is new) and making a rear AC bracket.
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Old 10-02-2018, 05:54 PM   #14
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Re: Replacing a tired 350 with a L31 Vortec 350

On my 78 it had a gas tank vent line I didn't use anymore, it was like a 1/4" and with a return style regulator not regulating anything it gave me 6psi at the carb due to the return limiting flow lol. You can run the pump dead head/not return style, but it will last longer and run cooler with a return style regulator.
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Old 10-02-2018, 08:00 PM   #15
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Re: Replacing a tired 350 with a L31 Vortec 350

Early Subarus with electric fuel pumps had no return pump and those pumps tended to last 100,000 miles. It might shorten the pump's life some, but you might not ever notice it.
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Old 10-03-2018, 09:10 AM   #16
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Re: Replacing a tired 350 with a L31 Vortec 350

Which would be a good dependable fuel pump
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Old 10-03-2018, 07:04 PM   #17
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Re: Replacing a tired 350 with a L31 Vortec 350

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Early Subarus with electric fuel pumps had no return pump and those pumps tended to last 100,000 miles. It might shorten the pump's life some, but you might not ever notice it.
Every car made today uses a returnless regulator for emissions reasons. The pumps are built to handle it just like starters on vehicles with start/stop tech. Doesn't mean the old tech will hold up to that use.
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Old 10-03-2018, 09:38 PM   #18
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Re: Replacing a tired 350 with a L31 Vortec 350

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Which would be a good dependable fuel pump
I've had good luck with Wagner.
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Old 10-25-2018, 01:48 PM   #19
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Re: Replacing a tired 350 with a L31 Vortec 350

FYI Blue Print Engines sells a Vortec 5.7 long block for $2600 that has the provision for the mechanical fuel pump. Might save you the trouble of an electric pump. I'm looking at this one to replace my Gen 1 350. You can get it through Summit and get free shipping.
https://blueprintengines.com/
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Old 10-25-2018, 02:08 PM   #20
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Re: Replacing a tired 350 with a L31 Vortec 350

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FYI Blue Print Engines sells a Vortec 5.7 long block for $2600 that has the provision for the mechanical fuel pump. Might save you the trouble of an electric pump. I'm looking at this one to replace my Gen 1 350. You can get it through Summit and get free shipping.
https://blueprintengines.com/

wow $2600 bucks to keep electric fuel pump . . . gm crate engine = $1800 and change shipped . not telling you what to buy just letting you know your options . do little cam swap and have about the same power level as there engine for less .
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Old 10-29-2018, 02:32 PM   #21
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Re: Replacing a tired 350 with a L31 Vortec 350

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Originally Posted by RodnRudy View Post
FYI Blue Print Engines sells a Vortec 5.7 long block for $2600 that has the provision for the mechanical fuel pump. Might save you the trouble of an electric pump. I'm looking at this one to replace my Gen 1 350. You can get it through Summit and get free shipping.
https://blueprintengines.com/
Will save the trouble for fuel pump. I put a call into BluePrint. I am curious to see the numbers matched up against the roller 383. They are away at SEMA this week.

This looks like a good value to me. It's a new offering from BluePrint. You get the cam, head work, pump provision and clutch boss. Seasoned Block and heads. I think that covers the extra cost.

I will see when they send the dyno sheets, then I will probably have to pay for the displacement!


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Old 11-14-2018, 08:19 PM   #22
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Re: Replacing a tired 350 with a L31 Vortec 350

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Will save the trouble for fuel pump. I put a call into BluePrint. I am curious to see the numbers matched up against the roller 383. They are away at SEMA this week.

This looks like a good value to me. It's a new offering from BluePrint. You get the cam, head work, pump provision and clutch boss. Seasoned Block and heads. I think that covers the extra cost.

I will see when they send the dyno sheets, then I will probably have to pay for the displacement!


j
I am now very interested in this BP3503CT1 after a brief correspondence with BP. Looking to do an install after the 1st of they year. Still weighing my options, but this is now on the sort list.


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Old 11-15-2018, 09:57 AM   #23
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Re: Replacing a tired 350 with a L31 Vortec 350

I recently bought a truck with a new gm crate 350. It couldn't get out of its own way so I put on new vortecs, cam and headers. Lost my a** on a POS Holley Sniper after a month so I tossed it and went back to an Edelbrock carb. She runs great, is reliable and doesn't require an engineering degree in software development. However, in hindsight, I'll never go old school again. You can get a used LS engine/trans with overdrive for slightly more money up front. It will run better, be cleaner, live longer and have OEM reliability. Buy once-cry cry once they say.
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Old 11-15-2018, 12:56 PM   #24
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Re: Replacing a tired 350 with a L31 Vortec 350

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I recently bought a truck with a new gm crate 350. It couldn't get out of its own way so I put on new vortecs, cam and headers. Lost my a** on a POS Holley Sniper after a month so I tossed it and went back to an Edelbrock carb. She runs great, is reliable and doesn't require an engineering degree in software development. However, in hindsight, I'll never go old school again. You can get a used LS engine/trans with overdrive for slightly more money up front. It will run better, be cleaner, live longer and have OEM reliability. Buy once-cry cry once they say.
An LS is always tempting. I plan to keep this swap-out to a weekend perfunctory. I need to replace my exhaust system anyway, so I'm not considering that as part of this budget. I'm thinking I can keep this to right around 3K and minimize the cost creep. So I'm looking at an intake and maybe a carb.

A lot of people are going to look at this and say no 4bolt or HD heads, but its not a concern to me, neither is the seasoned block. The stock 350 currently in the truck was replaced about 100k ago. I put that engine in as a dirt cheap reman, I used to use this truck for work back in the 80s. And believe me, this engine has been both lugged and revved under load. It's been wound out rung out and beat like a rented mule. Now it's tired, but the last thing I'm worried about is its 2bolt main! So, that's always been my position on stock'ish 350s. If this engine is built and assembled properly, it will probably outlast me, or my ownership, at this point.

Still weighing my options though, but I like the power for the price on this, plus it keeps my swap cheap and easy!


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Old 11-16-2018, 10:00 AM   #25
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Re: Replacing a tired 350 with a L31 Vortec 350

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it keeps my swap cheap and easy!
Cheap and easy= Cheasy.

Reliable-Cheap-Easy, you may choose 2.
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