Hello Sofa and other exalted gurus,

At the risk of getting flamed, when swapping from a ‘87 L69 305 to a ‘98 L31 Vortec 350, can I use the 305 water pump?

If I’m not mistaken, a Vortec engine (‘96-‘02)water pump is opposite rotation?
Can the old (a new 305 replacement water pump)be used & work correctly?
In my case, it’s going in a ‘87 Monte Carlo SS.
I’d like to keep it simple as far as the accessory component brackets, etc. if possible.
thank you

 

if you use V belts yes use the old pump
if you use the much better newer serpentine set up then you need a reverse pump.

 

Are you just swapping long blocks but keeping everything else stock 87 Monte Carlo under the hood?

 

Yes, swapping long blocks, but going non-computer QJet, Performer Vortec intake, non-computer HEI, smog pump delete, mid length headers.

Wanted to put this L31 engine in my IROC T5 vert, but there’s some issues found with a 400 sbc I purchased used.

 

Iirc, some vortec engines don't have the waterpump bypass port drilled in the block.
In 1988 the waterpumps went reverse rotation on the f-body w serpentine belt.
just use the pump that works with your accessories

 

Thank you guys!

 

As was previously stated, the water pump goes with the accessory belt configuration. Both design work with the L31 motor.

The comment on the bypass is true no matter which style water pump you use. You will need to plumb in a bypass for the L31 block.

 

TransAmGTA350…..
I have read the following, on the interwebz of course lol.

If (2) or (3) 1/8” or so holes are drilled in the t’stat that could serve as a bypass on a Vortec L31?

 

I have not done that, but I have also heard that it works.

 

Make sure the little bypass hole on the pass side of the WP is plugged where it goes against the block. If the block isn't flat there (should be, butt in case it's not) plug the hole in the WP.

For an actual bypass, put a hose nipple in the fitting on the top of the WP, and hook it to another one on the front of the intake. Make it small, like 3/8" hose or something; since it "bypasses" the pump's function of pumping coolant through the radiator, it only needs to be large enough to keep the WP from cavitating or otherwise misbehaving. The one you're replicating, between the WP and block, is only about that size anyway.

 

Thanks Sofa!
Sure appreciate your specific details.