L31 engine swap questions
 

Good day all.

My son and I are in the process of switching out my his tired sbc350 in his 86k20.

Well not really tired but started making a clicking/knocking sound towards the bottom rear/ flex late area. I told him if its the flex late its an easier fix.
If it is internal we are swapping engines.

I fell into a killer deal with a crate engine with 3k miles,
co workers son wrapped an el Camino drifting into a telephone pole. ins company totaled the car, but I got the engine.

The block is an 880 block with I believe to be an L31 Vortec engine
1 piece RMS.
My dilemma is should I run it with the current serp set up (no ac brackets)
or switch his V belts back on and keep his ac

Re: L31 engine swap questions
 

It's really just a matter of choice, as you can do it either way. I have the serpentine setup from a 98 Silverado on my L31 in my 72 Blazer. To make it work, you might have to change out the rear fitting on the PS pump (if yours isn't metric) and adapt some AC lines. The L31 also uses a reverse-rotation water pump with the serpentine belt, so you need both the water pump and the fan. It's a little complicated, but nothing that can't be handled by someone who can remove and replace an engine.

Re: L31 engine swap questions
 

Truckster,

Thank you for the reply, the engine I have came with everything minus the electric fans.
It already has the alt, p/s pump to include the water pump. When I got the engine my intent was to show my son how to tear em down an re seal, rebuild them.
I was not imagining anything like what we ended up with.
I was told all it needed was a carb an electric fan.
After my son and I inspecting it we came to the same conclusion.
Do you have any images of your set up by chance.

Re: L31 engine swap questions
 

If you want AC then there is only one choice that you are presenting to us. If you don't want AC, then don't swap it.

Also, if its really a vortec motor, you need an electric fuel pump. It will not run a mechanical.

Re: L31 engine swap questions
 

Tom,

I was under the impression that some vortec motors had the provision for mechanical fuel pumps?
Also only 8 bolts for the intake all of them vertical, vice the 12 an at an angle?

I took to the cover off the fuel pump access plate, and can clearly see the slot for the fuel pump.
maybe I need to dig more into the markings and the block.
When I get home later tonight I will get more pics and see what I can some up with as well as post the number here.

Re: L31 engine swap questions
 

I have an L31 Vortec out of a 98 Chevy truck. It had a blockoff plate for the fuel pump, which means it was drilled for a mechanical pump. I did have to change the camshaft to get the fuel pump lobe. And yes, 8 vertical bolts for the intake.

This is a picture of it while it was under construction.

Re: L31 engine swap questions
 

4 bolt main blocks came drilled out for mechanical fuel pumps on most 4 bolt blocks well into the l31 engine run

You will need to check if cam has a fuel pump lobe on it and run a roller cam fuel pump rod the older style fuel pump rods and roller cams do not mix

They make ac delete plates to replace ac compressor with a idler pull
Nice engine I like the serpentine setup more then the old vbelts

Re: L31 engine swap questions
 

With the block and heads being different colors and the heads having the GM LS valve springs, it's hard to say what is inside. It may very well be a stock L31 or it may not. If it is a stock L31, that cam does not have a fuel pump lobe. But since the valve springs have been upgraded, I would guess that the cam is not a L31 cam. The heads have obviously been off at some point. I would also check the distributor gear for wear.

Re: L31 engine swap questions
 

thank you all for the input
I'm almost positive it's an l31
it does have the lifter retainer an I can see the lobe for the fuel pump rod.
I'll post pictures either later this evening or first thing tomorrow.
I plan on replacing all the gaskets this Friday.
I wonder if by taking off the timing chain sprocket I will find sl.e numbers for the cam
or am I better off removing it to look to look the numbers on it

Re: L31 engine swap questions
 

I noticed in the pic of the rockers that it appears they are adjusted quite a bit. Lots of threads showing.
Could be you need to check pushrod length and rocker to retainer clearances.

Re: L31 engine swap questions
 

As promised here are some pictures I took last night, one confirming roller cam
the other a stamping of NOV with an open end wrench. This mark is on both the head as well as the block.
The LS springs not sure where those came from.
As far as the paint not matching, it seems as if the previous owner only did have a paint job, the entire back side is black, were as the front is all blue.

I also did some google foo this morning and came across this on motor tech
block # 10243880...350...95-00...2 or 4...Vortec truck, Gen.I crate motors and "ZZ4", roller cam, one piece rear seal

12558062...98......350..........L31 Vortec, truck, 64cc chambers, 1.94/1.5, 170cc intake port

Since My block has the slot for the full pump push rod, although it had the block off plate, I think I'm going to get a Carter fuel pump P7040 to get the psi for the Edelbrock 1406 (read a post from on here from 2016)

I appreciate all the responses and guidance, Im off tomorrow so I will be able to do more investigating

Re: L31 engine swap questions
 

I had a vortec motor that had the pump pad machined but the hole wasn't drilled from the factory, along with the fact the factory cam won't push a fuel pump rod.
This may have started as an L31 but it doesn't seem to be one anymore with the changed cam and springs.

Re: L31 engine swap questions
 

Tom,
I will play it safe and run an electric fuel pump Carter4070 or is there a recommended one.
I just replaced both saddle tanks(86 20 gallons) and sending units along with the selector valve and dash switch.
I have a good HEI unit, but will replace the guts just to play it safe.
We will be keeping the serpentine system an add the ac compressor later down the road.
As well as converting to electronic fan's maybe dual windsors unless there's a better recommended set.
We plan on replacing the normal gaskets, especially since we took the oil pan an valve covers off, to include the timing chain cover.

Truckster what did you end up using for fans?
Also I see you kept the Quadrajet, seems like the same one that we have currently installed
once again I thank everyone for the tips, replies

Re: L31 engine swap questions
 

I didn't want electric fans, because I like the thermal clutch on the SBC. I used an original fan shroud, but the 19" fan from the 98 Silverado wouldn't fit. I did some checking around and found that the same year of S-10 (4.3 V6) had a 17.5" fan. It almost centered perfectly in my shroud. I trimmed about 1/4" off and there's no interference.

The Quadrajet is a 1978 model, because I wanted the electric choke.

You don't need to "play it safe" with the fuel pump. You can determine if there's a fuel pump lobe on the camshaft really easily. Remove the blockoff plate and put a drift punch in there. Push it against the camshaft as you turn the engine by hand. If the drift punch pushes out as you rotate the engine, it's got a fuel pump lobe.

Re: L31 engine swap questions
 

Thanks for the advice
I will be trying it later today. I'll look around for a fanz size similar to yours. Are you routing the plug wires behind an underneath the ram horn manifolds. Also are you running single outlet or true duels. I fully convinced my teenager to stick to cast iron manifolds vice headers. especially for a 4x4
I want to eventually go efi on the truck. My son plans on keeping it for a long time.
Especially since it's his first car an does everything he wants it to do for now.

Re: L31 engine swap questions
 

The truck had headers on it when I bought it. I didn't really like the headers, so when I put the L31 in it I installed 2.5" rams horns. Currently I have the old exhaust from the headers back. I just welded up some 2.5" tube that I bought at Speedway Motors (see this link: http://www.67-72chevytrucks.com/vboa...d.php?t=817921), but I plan to replace the entire exhaust this summer. The existing exhaust is 2.25" with some really crappy bends and really crappy turbo mufflers. They are dual exhausts exiting behind the rear wheels.

The wires I used are for a 76 Corvette with HEI. I ran them under the rams horns. One of them is a little tight, but it works. I used Taylor 8mm wires, but any wires for that application should work. The other option is to buy cut-to-fit wires.

Re: L31 engine swap questions
 

memo if you're going to retain the use of the Qjet and use an electric fuel pump, you'll want to check the pressure at the carb. They like 6-9 psi

Re: L31 engine swap questions
 

I used Camaro TPI brackets on my 880 L31. It kept the A/C compressor on the passenger side of the engine. :metal:

Re: L31 engine swap questions
 

Truckster
Thanks for the tip, its verified no cam lobe for the fuel pump. So I will be looking up electric fuel pumps as well as wiring for them. I want to incorporate a cut off switch like the oil pressure switch.
Big Dave my set up currently has the ac delete on the diver side, and what looks like a Delphi 140 amp alternator. I'll have to get it tested an figure out the plug to be able to use with my sons stock harness.
Truckster, Bigdav160 thanks for the pics.

"almost last questions" how did you wire the alternator
did you use some special harness or just splice the connector into the stock alternator harness


Memo

Re: L31 engine swap questions
 

I rewired the entire truck, so my setup is going to be different from yours. I also swapped in a voltage gauge in place of the stock ammeter in the 72.

Since yours originally came with an internally regulated alternator, I would think you would just need an adapter for the alternator wiring.

Re: L31 engine swap questions
 

Well we.managed to take the old engine out today. Started to dry fit everything before installing the new one tomorrow as well as finish installing the Carter electric fuel pump.
the one issue we ran into was the passenger side stock manifold does not fit.
The bolt holes do not line up, I am willing to continue with the install an get it fired up.
Just need a better solution for either ram horn style manifolds or short tube headers.
Truckster did you end up using for your set up. I recall you mentioning 2.5 ram horn style curreny on the truck?
mine is a 4x4 so those "should" fit correct.
Bigdav what exhaust are you using.
I will post some pics of the install as well as the severely busted up flexplate..

Memo

Re: L31 engine swap questions
 

I installed Tru Rams

4x4 also and it still required a little grinding around the motor mount brackets to clear.

Re: L31 engine swap questions
 

Mine is a 72 4WD Blazer. I have 2.5 rams horns. I'm pretty sure I bought them from Speedway Motors. They're a perfect fit and I didn't do any grinding on the frame. For my application I used the straight-down manifolds, but I don't know how those would work in your truck.

However, any stock SBC manifolds should fit the Vortec heads. The exhaust ports are slightly different, but the bolt pattern is exactly the same. You might need to chase the holes in your manifold. Your problem might be rust in the bolt holes, or it's possible your manifold has warped.

Re: L31 engine swap questions
 

Rwd trucks generally used rams horns that angle dump to help clear the cross member
4x4 trucks have the engine back and use straight dump rams horns

I am going to say with out a doubt you did not thread chase out the bolt holes in the one head as they old heads and vortec heads use the same pattern

The other thing to check after you thread chase the bolt holes is to see if your manifold has warped in any fashion to distort it too much to bolt in
Check face with a straight edge to see if it is flat and not cupping the outer bolt holes throwing them off alignment

Re: L31 engine swap questions
 

Exhaust bolt pattern hasn't changed on small blocks since 350's were invented at the very least, if ever.