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My initial thoughts on LS6 manifold install on a pretty much stock LS1 99 coupe

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My initial thoughts on LS6 manifold install on a pretty much stock LS1 99 coupe

Old 07-16-2018, 12:28 AM
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acuevo
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Default My initial thoughts on LS6 manifold install on a pretty much stock LS1 99 coupe

Hoping this can serve as some good info for any other guys like me who are getting to the point where they can finally afford their own vette. OR for guys who have had one for a while who have decided to do some mods.

Finally picked up an LS6 manifold on the SUPER cheap a few weeks ago ($325 from a 26k mile Z) - in great shape. Drove it when I originally installed and saw a noticeable difference. It seems to pull just a little harder, surprisingly its most noticeable in the lower rev range. I was expecting to only really notice top end but I can definitely feel the change from 2k and up. Not sure what real world numbers it gave me, I won't have it to a dyno for quite some time (probably not till I finally cam it). Don't misunderstand, this is a small change... it's not like its suddenly an 11 second car, but you CAN tell the difference. Its easy to see why when you have the manifolds next to each other - even though you can't really see the runners inside you can tell how much extra volume the LS6 manifold has by looking at the bottoms. So a lot of the difference could all just be in throttle response.

I actually first installed earlier this week, but just had it back off for peace of mind. At first, I chiseled off the ribs in the manner that can be found all over the internet to clear the cross over pipes. I noticed it would still rock significantly from drivers rear to passenger front when sitting in its guides without being tightened. Seemed like the front knock sensor wire was holding it up just a little bit. Even though it torqued down with no leaks or driveability issues I wanted to be sure I wouldn't be soldering a knock sensor wire in the future. So I took it all back apart and routed the wire UNDER the crossover pipe instead of over and it helped a lot. Still not completely laying flat on its own but I'm more confident now there won't be any damage to the wire. Side note: that rear vacuum line is my mortal enemy.

So for any guys wondering if its worth it, I say definitely. That is if you can find one at a decent price and in decent shape. The install wasn't bad, just a little tedious. If you can wrench a little bit on cars you should be fine, plus like I said there's tons of info on the web.

Also I have to say, it's been just a little over a year since I got the car and I still get a thrill just by starting the thing. 17 years of wanting one finally paid off and I wasn't disappointed in the least!
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Old 07-16-2018, 01:01 AM
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Sounds great! did you take any pictures? did you keep the stock throttle body?
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Old 07-16-2018, 01:36 AM
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I meant to take some pictures but unfortunately I forgot to. I don't think there is a whole lot of difference between the pre and post 2001 throttle bodies so I just stuck with the stock one. I think the later ones are just a few millimeters wider so its not a huge difference.

Its also worth mentioning its a good time to replace a few other things. I did the PCV valve and new injector o rings with this. Thought about doing the oil pressure sender as well but I peeked in before hand and mine had already been replaced with the aftermarket brass type which is supposedly more dependable so I left it alone. A lot of people seem to get them from O'Reilleys but I'm pretty sure auto zone or advanced has them too.
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Old 07-16-2018, 01:44 AM
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This is something I would consider, I am also stock with just a Vararam CAI, Borla exhaust & diablo tune. I am pretty sure I will NOT do headers and I am liking the way the car runs now. The Vararam did make a noticeable
difference.
I will keep my eyes open for an LS6 intake and maybe it will be this winters project.
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Old 07-16-2018, 01:47 AM
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I would definitely say if you see one, jump all over it. The 325 I paid was really a steal, the cheapest I had seen before that was about 450. Another option is the Dorman aftermarket LS6 manifold, which will flow much better than the stock ls1 but not quite as well as the GM LS6 part.

Last edited by Vetteman Jack; 07-16-2018 at 10:54 AM.
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Old 07-16-2018, 10:38 AM
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I did the LS6 intake (installed by ECS) and then later ARH headers with dyno tune - it runs well for a "bolt-on car".....
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Old 07-16-2018, 10:55 AM
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Nice start to your modding of the car.
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Old 07-16-2018, 11:43 AM
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Since the LS6 intake flows better, does it require a retune? Seems like it would be tuned too lean for this intake...
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Old 07-16-2018, 12:10 PM
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I sell the Dorman version, and have thought long and hard about this swap as a base for more mods down the road. Is there a reputable company that does a decent port-job/casting clean-up that anyone has experience with?
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Old 07-16-2018, 03:52 PM
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Originally Posted by grampi50 View Post
Since the LS6 intake flows better, does it require a retune? Seems like it would be tuned too lean for this intake...
I over research everything I do in life from my cars to my guitars. Never saw an instance of someone needing a tune from the ls6 manifold on a stock car. From what I understand, a tune is worth up to 10hp on a totally stock ls1 as they come from the factory leaning on the rich side for safety, so I don't think anyone would have an issue with it running too lean, even with a CAI (which I also have).

As always, I could be wrong so if anyone knows other wise please do chime in.
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Old 07-16-2018, 04:13 PM
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Originally Posted by acuevo View Post


I over research everything I do in life from my cars to my guitars. Never saw an instance of someone needing a tune from the ls6 manifold on a stock car. From what I understand, a tune is worth up to 10hp on a totally stock ls1 as they come from the factory leaning on the rich side for safety, so I don't think anyone would have an issue with it running too lean, even with a CAI (which I also have).

As always, I could be wrong so if anyone knows other wise please do chime in.
I've also read the stock tune is a bit on the rich side (which seems weird to me considering everything GM did to the C5 to increase it's fuel efficiency), but I didn't know if it was rich enough to handle more intake air....sounds like it is though!

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Old 07-16-2018, 08:57 PM
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Originally Posted by acuevo View Post


I over research everything I do in life from my cars to my guitars. Never saw an instance of someone needing a tune from the ls6 manifold on a stock car. From what I understand, a tune is worth up to 10hp on a totally stock ls1 as they come from the factory leaning on the rich side for safety, so I don't think anyone would have an issue with it running too lean, even with a CAI (which I also have).

As always, I could be wrong so if anyone knows other wise please do chime in.
CAI/TB/manifold/LTH/exhaust-Tune
Cam/Heads/Injectors-Tune
Supercharger or Turbo-Tune

Last edited by C5 Kirkland; 07-16-2018 at 08:59 PM.
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Old 07-17-2018, 04:10 AM
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Originally Posted by grampi50 View Post
Since the LS6 intake flows better, does it require a retune? Seems like it would be tuned too lean for this intake...
Lean is real bad it is like a tourch to your pistons. When I took my car to get tuned the tuner told me is was running super lean. I am glad i got it done
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Old 07-17-2018, 12:03 PM
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Originally Posted by acuevo View Post


I over research everything I do in life from my cars to my guitars. Never saw an instance of someone needing a tune from the ls6 manifold on a stock car. From what I understand, a tune is worth up to 10hp on a totally stock ls1 as they come from the factory leaning on the rich side for safety, so I don't think anyone would have an issue with it running too lean, even with a CAI (which I also have).

As always, I could be wrong so if anyone knows other wise please do chime in.
There were changes to the factory tune made between the early cars - which had slightly larger injectors, and no pup cats, and the models with the pup cats and smaller injectors and the LS6 type intake manifold as standard. Later on, they went back to the larger injectors.

When I put my Halltech Stinger on, the PCU seemed to adjust to the new reality after a few miles, and seemed (I emphasize seemed) a little stronger. I do know that when the K&N folks made kits for both early and later cars, their dyno pulls showed the early cars picked up more power than the later ones. Prob due to being a bit richer ex-factory. Similarly, when Lingenfelter first started modding C5's, part of their package for later cars was to instal the bigger injectors as fitted to the early cars.
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Old 07-17-2018, 10:59 PM
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Well crap. I have a LS6 manifold in the garage, waiting for install. Was kind of hoping you were going to say it wasn't all that impressive and I could wait until I can pop for the 243s to go with the manifold and Z06 cam (also in the garage). Cam will still have to wait, but the manifold will have to go in.
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Old 07-17-2018, 11:19 PM
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Originally Posted by redzg View Post
Well crap. I have a LS6 manifold in the garage, waiting for install. Was kind of hoping you were going to say it wasn't all that impressive and I could wait until I can pop for the 243s to go with the manifold and Z06 cam (also in the garage). Cam will still have to wait, but the manifold will have to go in.
With my luck you won't notice a difference and I'll have to eat my words LOL. Good luck and let me know how it drives after the install!

Last edited by acuevo; 07-17-2018 at 11:19 PM.
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Old 07-18-2018, 09:56 AM
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The main advantage to having the 2001-2004 intake is the increase in torque. GM was only able to find 5 more hp but 25lbs more of torque in 2001+ LS1 vettes.
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Old 07-18-2018, 08:24 PM
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I also did this mod a couple of months ago and it was completely worth it. I found the intake here in the forums for $200 off a 40k mile 04 C5. The best thing of all was, dude was local! I ground down the ribs under the manifold completely. I smashed down the steam tubes very slightly, enough so the manifold wouldn't rock back and forth. My C5 pulled way harder down low and towards the top of the power band. You will feel the difference without a tune, but the LS6 intake is not completely being optimized until the car has been properly tuned. I will be installing a cam very soon, so I will have my car tuned after the cam.
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Old 07-18-2018, 11:10 PM
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you should have installed a steam line kit instead of grinding the manifold, really helps the cooling of the rear cyl. !!!!! (don't have to bleed the air out ether !!!)
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Old 07-19-2018, 10:46 AM
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Did you get rid of the EGR? I am looking into this.
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