Running LS engine on just open manifolds

[LS-K]

I'm at the end point for my truck's swap, but I have to drive about 15 miles into Tucson to have my exhaust done from scratch. My engine still has its original CTS-V manifolds.

I had a friend tell me that I ought to stray away from driving that distance on open manifolds since the valves run the risk of "cooling off too quick". He said that may cause the some kind of un-even re-seating of valves or even bend a valve since they wont cool off steadily like they would if I had a full and complete exhaust.

Any help in dispelling this claim would help. It sounded a bit whacky to me but hey what the hell...I figured why not run this through some folks like yourselves who have seen all kinds of things with these trucks and engines.

Thanks in advance,
Eric

[littlevictories]

i did it once on my go-kart when i was a little kid. took the valve out and bent it straight in a vise. haha after it was fixed i just kept a rag to stuff in the end of the straight pipe upon shut-off. maybe have some rags handy? or trailer it? would be an expensive lesson on an LS…not so much on a tecumseh

[LS-K]

Originally Posted by littlevictories

i did it once on my go-kart when i was a little kid. took the valve out and bent it straight in a vise. haha after it was fixed i just kept a rag to stuff in the end of the straight pipe upon shut-off. maybe have some rags handy? or trailer it? would be an expensive lesson on an LS…not so much on a tecumseh

Note taken, I'll probably just end up hauling it to the exhaust shop. Thanks

[BR3W CITY]

Without even getting to the level of mechanical failure, running open manifolds has no provision for the front 02.

While the rear 02's can be deleted physically without completely handicapping the truck, the front 02's don't allow that luxury. Unless the truck is SD tuned, you'll want to run at least 6-8" of "downpipe" on the manifolds to allow for the font 02's.

If you do, you'll still have to deal with erratic readings, but safe driving at mild speeds for a short distance will be fine. Without that first pipe and the 02's, I would not make the trip.

[LS-K]

Originally Posted by BR3W CITY

Without even getting to the level of mechanical failure, running open manifolds has no provision for the front 02.

While the rear 02's can be deleted physically without completely handicapping the truck, the front 02's don't allow that luxury. Unless the truck is SD tuned, you'll want to run at least 6-8" of "downpipe" on the manifolds to allow for the font 02's.

If you do, you'll still have to deal with erratic readings, but safe driving at mild speeds for a short distance will be fine. Without that first pipe and the 02's, I would not make the trip.

Nice!! Brew you always come through. Thanks. The search begins tomorrow for a decently cheap way of hauling it to the shop.

So would you call BS on the whole "valve cool-off" deal my friend spoke of?

[truckdude239]

I've been running my on about 6 inchs of pipe with 02s installed while i finish it up

[Wasted Income]

Your buddy is full of ****.

Running it with open manifolds won't hurt anything...except your ears.

"cooling off too quick"...lol. You mean like the cold air/fuel charge that hits the exhaust valve every time the intake valve opens?

[tinydb84]

I always heard the same thing. I don't know if there is any truth to it. I have ran open headers (long tube and short) for trips to the muffler shop and sometimes longer if I didn't have time to get to the muffler shop.

[Wasted Income]

If it was truly an issue, don't you think that guys running zoomies on max-effort engines would have a problem, much less some dude putting to the exhaust shop?

[BR3W CITY]

Originally Posted by LS-K

Nice!! Brew you always come through. Thanks. The search begins tomorrow for a decently cheap way of hauling it to the shop.

So would you call BS on the whole "valve cool-off" deal my friend spoke of?

Kinda sounds like your friend wanted to pick an explanation too ethereal that you couldn't call bs on it lol. The only thing even close to what he explained that I can think of would be; running NO manifolds (open HEAD) has a complete lack of back pressure and can result in the clean air making the short (1" trip) from the open head to the valve. This can actually BURN the valve, not cool it off.

[boostedc10]

Originally Posted by wasted income

if it was truly an issue, don't you think that guys running zoomies on max-effort engines would have a problem, much less some dude putting to the exhaust shop?

zomg race stuff!!!!

[BR3W CITY]

I'm not a boss because I don't have a fabbed aluminum cover for my exhaust when parked!

[aknovaman]

Enough bs. Now for some facts. Zoomie headers on race engines don't have a computer system that adjusts the air to fuel mixture. Back pressure is a bunch of bs too.

Here is what happens on your cts-v engine. You start it up and it's cold. The engine is in what's called open loop state so the 02 sensors are not warmed up or producing any voltage. The fueling mixture is calculated based on several factors but mainly the open loop AFR table and coolant and inlet air temps among other variables. Once the engine reaches apprx 131 degrees F, PCM file setting dependent, the engine starts looking at the 02 sensor output voltage. They will swing from approx 100-800 millivolts. Averaging about 450 millivolts. As they swing or cycle up and down the PCM looks at their average voltage and starts adjusting the short term fuel trims to bring the fuel mixture to the commanded AFR. As the engine continues to warm up to operating temps the AFR is continuously adjusted based on the 02 voltage. If the voltage is less than 450 it will add fuel. If higher it will remove fuel. As this is going on the short term trims start to adjust the long term fuel trims so the engine will not have to continually have to adjust the mixture a bunch. So it learns where the AFR is at in a specific rpm and load on the engine. It will continue to adjust the mixture unless the throttle is moved past another specific PCM file dependent threshold and it adds fuel as an accelerator pump.

So running the engine at operating temps with no 02 feedback, this is what happens. The readings will be stuck at approx 450 millivolts and it will add fuel and generally run very rich making the bottom of your car covered with raw gas. Does this hurt anything, not really as rich will only make a mess and stink. It will not burn any valves or cause any long term washing of the cylinders unless you drive it for an extended period of time.

Now onto back pressure. One of the reasons exhaust should be used is for cylinder scavenging. More or less the high pressure pulse from one cylinder is traveling down a pipe, the next cylinder fires creating another pulse. The first actually helps pull the pressure pulse down the pipe. This helps smooth the exacuation of each of the 8 cylinders.

Zombies are used to quickly evacuate the cylinder pressures from the ports in a very specific rpm range.

If any engineer type wants to discuss back pressure with my via pm, feel free to send me a message.

[dec010974]

Thanks for the explanation, aknovaman. Knowledge is power.

[BR3W CITY]

[Wasted Income]

Originally Posted by aknovaman

A bunch of stuff

Soooo....basically you're saying the same the same thing as a couple of us...that it won't hurt anything.

Originally Posted by aknovaman

Enough bs. Now for some facts.

So running the engine at operating temps with no 02 feedback, this is what happens. The readings will be stuck at approx 450 millivolts and it will add fuel and generally run very rich making the bottom of your car covered with raw gas. Does this hurt anything, not really as rich will only make a mess and stink. It will not burn any valves or cause any long term washing of the cylinders unless you drive it for an extended period of time.

If any engineer type wants to discuss back pressure with my via pm, feel free to send me a message.

I'm one of those "engineer types"...at least that's what my degree says, so I'd also like to make a correction to your dissertation above. You got your "facts" wrong.

If the engine has no O2 sensor feedback, it will never switch to closed loop...it will remain in open loop and set a DTC and check engine light. Unless the engine is modified pretty far from stock (drastically different cubes, compression, cam, etc), it will run fine, calculating values from the VE table. There will be NO fueling offsets/modifiers based on O2 feedback, or lack of feedback.
I've been tuning LS engines via EFI Live for 10 years.....I'm not "BS"ing anybody.

Originally Posted by aknovaman

Zombies are used to quickly evacuate the cylinder pressures from the ports in a very specific rpm range.

LOL, is this a fact, too?

[littlevictories]

lol zombies

cmon yall cant we just get along

[boostedc10]

I am just trying to figure out how the gas gets out to the bottom of my car with no O2 and where the hell the zombies are at in my engine?

[Wasted Income]

Originally Posted by boostedc10

I am just trying to figure out how the gas gets out to the bottom of my car with no o2 and where the hell the zombies are at in my engine?

zomg facts!

[BR3W CITY]

You gotta refer back to my diagram. The red and blue lasers are for the zombies.

[Super73]

Originally Posted by Wasted Income

If the engine has no O2 sensor feedback, it will never switch to closed loop...it will remain in open loop and set a DTC and check engine light. Unless the engine is modified pretty far from stock (drastically different cubes, compression, cam, etc), it will run fine, calculating values from the VE table. There will be NO fueling offsets/modifiers based on O2 feedback, or lack of feedback.

Wasted, Not trying to correct you, but rather add to your comment. I am sure you will agree with me, it doesn't need to be major changes.

Some items that can and will affect things enough to knock a stock VE in OL/SD "limp mode" to show Ltrims +/- >10 would be:

Changing the intake tube to a different diameter/length
Ported MAF ends (haven't seen them discussed in a long time)
Going to a different intake manifold (LS1 to a Fast 102mm)
Headers with free flowing exhaust


Some of the above mods might not let it "run fine" as the VE hasn't been adjusted for the changes in airflow.

My old 01 SS had a major Ltrim issue with Lid/MAF ends/Ported TB but stock manifolds.

[JNJchev77]

Make sure you have gas in your tank! Haven't seen anyone mention this yet, so thought I would provide some helpful info!

[boostedc10]

Man this post went out to left field quick!

I feel the need to do this forum a favor and provide a quick overview of what we have learned so far:
1. Open headers are ok on go-karts if you have a vise to fix the valve and a rag handy for after the fix
2. You need to have at least 6"s of pipe in your pants to drive it successfully
3. Race stuff uses Zoomies!
4. ZOMG fast stuff!!!!
5. Br3w isnt at boss status because he doesnt have fancy covers for his zoomies
6. On other planets the vehicle will go into Closed Loop without O2 Feedback
7. No O2 feedback allows gas to poor out under the car
7. Zombies are in our exhausts!
8. Knowing is half the battle, as stated by B3ws graphs
9. I am still looking for the Zombies and gas
10. ZOMG Facts!!!
11. Long Term Trims are affected by intakes, modded MAF's, Headers and changes in the intake path
12. DONT FORGET THE GAS!!!

I am pretty sure this summary will provide the next person with this question the facts about driving with open headers!

[Super73]

Never mind.. I was being lame.

[littlevictories]

This turned out to be a pretty good thread.
I am proud of all your guys' hard work and will be renewing my subscription to this portion of the internet.
Chapeau.