I am installing a LS6 intake manifold on a LS1 that has the steam port crossover pipe running under the stock intake mani. This won't fit unless I modify the LS6 intake or change the crossover pipe setup to not run under the manifold. I see you can buy a stock LS6 crossover pipe that only goes across the front of the heads and then ITC Billet and others make block off plates for the ports in the rear of the heads. Is there any downside to running this setup? Or should I just KISS and modify the bottom of the LS6 manifold?

 

The LS6 has the rear blocked off from the factory. I dont think it will be an issue blocking off the rear.

If youre going to track the car its a good idea to keep all 4. I used a truck front crossover on the back of mine and ran hose to the front with a tee fitting.

 

To be honest, the rear steam ports aren’t big enough to move enough water to aid in cooling in any capacity. GM capped them early on and never looked back. From a track perspective, you’d want to enlarge the rear ports to a -6 fitting and custom build your own lines to aid in balancing rear cylinder temps…but it’s only useful in a road race type environment where rpm’s are up for 20+ minute sessions.

 

Awesome, thanks for the info! That's kind of what I figured but didn't want to cause any issues. I'll definitely look into the truck setup with the tee fitting if I end up doing anything other than cruising/commuting with this car

 

I did the same to mine with my fast intake.

 

I kept my 4 port steam pipe setup on my 2000 C5 when I ran the LS6 intake on my LS1. I never had a problem. You could put some white paint on the pipes and install the intake evenly and carefully. You should get a witness mark on the bottom of the intake, which you could then relieve with a Dremel or similar tool. I didn't even do that. I just bolted it down. The intake can flex a bit. Up to you, but I never had any issues in 35,000 miles, and I had a mid 12 second stock motor A4 trans. YMMV.....

 

So my 98 Wrangler with a LS6 swap with a LS6 intake with 4 ports I just kind of pushed the rear tubes down a bit. It's been 16 years with no issues.
On my other later model LS swaps with L92's I used 2002 Camaro FEA with the truck front cross over tube. No rear vents.
I cut the nipple off the front cross over tube. Drilled and tapped it for 1/8" NPT and then using -3 brake line connect it to the radiator with a bung welded into the radiator.
Has worked perfect over the years.

 

IIRC, GM sells some sort of rivet plug to block off the steam ports. I think that's what the factory uses, and they dont leak or come loose......

 

I don’t agree with anything said here really. Do your own research and read why GM did away with them and what they are really designed to do.

They weren’t designed to flow or move heavy volumes of water. That’s not the point at all. The passages and tubing are kept tiny on purpose to keep the velocity/pressure up. Their purpose is to assist in “Scraping” the tiny air bubbles that are trapped in the head. Opening them up or moving to large diameter ports or tubing slows velocity and drops pressure. So it doesn’t “Scrape” the air bubbles out as well. You want the passages and tubing tiny. This is straight form the head of GM engineering race team. GM blocked the rears as they found it increased the velocity slightly and did a better job of eliminating the trapped bubbles that way.

 

The common misconception…and what this thread is discussing primarily is if the rear steam ports, and the early LS1 4 corner steam vents, aid in cooling, or more specifically, cooling the rear cylinders. I’ve done enough testing to say that the Oem size of the rear STEAM ports do not allow enough flow out of the hottest part of the heads, to help with rear cylinder cooling. I’ve built a lot of track engines and can attest to what my clients are telling me in feedback. Water pressure can be adjusted manually with pump speeds, and often vary with engine temps also. What’s important to note here is that 99.999% of LS engines do not get ran hard enough to consider them a performance engine, so GM did not have their race program in mind when they 86’d the 4 corner STEAM vent setup. It was simply an item that wasn’t needed to successfully move the air bubbles….which turn to steam at temp….out of the system. It’s not really the ultra fine air bubbles that hurt engines. It’s the large bubbles that have enough volume to turn into steam and cause ultra hot spots during low rpm usage such as idle. The coolant circuit through the block and heads is so refined on the LS platform that the GM engineers realized the 4 corner setup wasn’t needed to successfully remove all air from the system…so it’s no longer used.
What I can also add to the discussion here is that by enlarging the rear steam ports to a -6 does help with rear cylinder cooling. It’s a process that we used as far back as 1992 in the GEN1 platform to help cool rear cylinders, and more specifically help cool the area of the heads between cylinders #3 & #5 and #4 & #6 because the exhaust valves were adjacent to each other on that platform on those cylinders, and caused hot spots. But again, the vast majority of engines on either platform don’t see race rpm, so it’s irrelevant in most applications. Good discussion here guys.

 

Aside from quoting GM’s head of performance directly—where he was specifically talking about his fleet of road racing cars—I don’t have any personal data to argue one way or the other.

I just find it interesting that the head of racing and development says otherwise. He mentioned that he and other teams used to do exactly what you’re describing, assuming larger four-port venting was the “right way.” But according to him, their data showed that keeping the rear ports blocked and running OEM-sized vents up front actually did a better job of eliminating hot spots.

Maybe the big four-port setups really do help with rear cylinder cooling. But from what I understand, that’s not really the main purpose of the steam vents—they’re meant to reduce hot spots and purge trapped air from those areas. I’m guessing the guy in charge of racing and development had access to testing tools and data most of us don’t—probably some high-end thermal imaging on an engine dyno or something along those lines.

All I can say is, I’ve left them “as is”—rear ports blocked, factory vents up front—on several drag-and-drive cars that run in the 8s, with no issues. I’ve also got friends who’ve blocked all four, and others running the -6 four-port adapters, and they’ve had no issues either. So unless someone can actually monitor these hot spots in the heads and compare each setup directly, it’s hard to say there’s one “best” way to route them.