Good Afternoon All,

I am wrapping up the LS6 swap into my '75 coupe and I noticed that some people recommend not running the steam vent from the engine through the manifold and just run it to the coolant system (I was going to run it to the upper radiator hose) directly. What is the benefit/downside to this? Is the purpose of this to keep it from freezing up in cold weather like the old heat riser tubes? I do not plan on driving in cold weather so can I just cap the manifold tubes and go directly from to the radiator hose?

Thanks,

Scott

p.s., it will be 70° and sunny in MD this week so at least one of the other 4 vettes will be pulled out of the garage for a cruise in the next few days.

 

On my 98 Wrangler LS6 swap I am running the coolant vent tube thru the throttle body but that's due to the chilly weather in the winter and I use it to plow snow.
In sunny FL I wouldn't worry about it and bypass the throttle body if it makes connecting to the upper radiator easier.

 

Let’s make sure we are talking the right stuff here. The LS6 crossover tube looks something like this.

https://images.app.goo.gl/eNeYKnerMnbVe7gdA

In this configuration the small rubber hose does not connect to the intake but connects to the throttle body and as you mentioned prior helps prevent intake icing. The older style like shown below WILL NOT FIT BELOW A OE LS6 intake

Either way you need a crossover kit to purge air out of the heads and prevent and airlock in the cooling system. What you plumb it back into is your call but it needs to be the cooling system in some capacity. I T’d into a heater hose on my LS swap in my S10 but that may or may not work in your application.

Personally I would plumb everything into the throttle body but that’s me. I live near Frederick MD and while yes the car might only see warmer weather those of us that have been around the block a time or two have seen icing issues with an engine even when warmer.

The case that comes most immediately to mind is on my mom and dads farm they had an old farmall 450 tractor that was just a cold blooded beast. Anything below 50 degrees outside you had to give the tractor 15 minutes of running at idle before you could put it to work. If you got after it too quick you could actually see ice forming on the outside of the carb and ice would basically freeze over the jets and needle valve/seat in the float bowl jets starving the engine until it died and also overfilling the float bowl with fuel causing it to overflow into the carb to air cleaner tube. Yep, raw fuel would puke out of this thing. You try to get busy too quick and stall that tractor out from the icing issue and good luck getting it started for the next 30 minutes or so. The only fix was wait for it to get some heat in it.

Granted I kinda rambled there alittle but the point I’m trying getting at is due to the velocity of the air going through there it doesn’t have to be near freezing to cause icing problems. Does it cause some HP loss? Most likely. How much? On a warm summer day after the car has been running for 20 minutes in the sun, probably little to no difference. Could it improve drivability? Definitely, and GM wouldn’t have put it there unless there was a reason.

 

A fellow Corvette enthusiast from Frederick, it seems I should know you somehow! I think we are on the same page here, I will post some pictures in the next day or two.

Scott

 

Earl's makes a nice kit (ls9806erl) but you have to make your own -4 connector hose. Weld a male -4 bung to the radiator near the upper hose connection and run the line from the Earl's block to there. Block off rthe rear ports on the heads with the GM covers.

 

I have a LS6 intake on my LS swapped Wrangler and I believe I used the stock LS1 coolant vent tubing. As I recall I had to "squish" the tubing down a bit and bend the tubes to clear the bottom of the intake. I think I also removed a foam that's typically on the bottom of the intake. My LS6 started out as a LS1. I added LS6 heads, cam and intake/throttle body. I don't recall buying a LS6 specific vent tube assembly.
BUT I did this swap over 12 years ago so the memory is a bit fuzzy.

 

So to rephrase my question so it is a bit more clear. I am contemplating taking the hose indicated by the arrow on the right and running that directly to the upper radiator hose using a fitting in the bottom photo. I would cap the fittings coming out of the throttlebody that are indicated by the left and center arrows.

 

Yes, that will work just fine. It is a very common modification to the EFI engines with the coolant passages in the throttle body. I did it on my LS1 after pulling the intake.

 

If you aren't using the throttle body tubes you don't need to cap them. On another LS project I just cut them off so you couldn't see them.

 

Agreed you can do that. It goes back to my previous statement of what does it gain you HP wise vs what you lose drivability wise. I’m not sure but something to consider.

It does clean up the plumbing some and I have seen throttle bodies spring a leak in the past as well.

 

Another thing I've done on the LS6 intakes. On the left hand side of the intake near where the throttle body bolts on there is a brass fitting/nipple which I believe was for EVAP or fuel tank fumes. Unless you need it I carefully cut the the nipple off, drill and tap it for 5/6"? button head bolt. Thread sealer on the bolt so no vacuum leaks. I do this with the intake and throttle body off so I can make sure no drill shavings in the intake.