winters97gt

Just curious if any of you guys have an idea what is going on with my car. Made good power, but the powerband has shifted quite a bit with the addition of meth. The car just falls flat on its face, when I think an FI car should pull to 6800-7k.

Stock ls3 vette with a votech SI, 3.8 pulley, meth injection, mufflers. Belt isn't slipping. The only other things are maybe valve float, cats being toasted, or something in the tune. Was running 131mph in the 1/4 with just the SC, and was hoping for 133-134 with meth, but it looks like that powerband just falls off so hard.

Thanks for any suggestions.

black98ws6ta

iTrader: (77)

To me both runs on the graph look bad for a car with a vortech on it. I would agree to looking into the cat's. Stock manifolds and cat's or headers with high flow cat's?

winters97gt

Stock manifolds, stock mid pipe and stock cats.

The car pulled great with just the SC. I ran consistant 129-131 trap speeds. Would blown out cats result in the power diving on all 6-8 dyno pulls at exactly the same RPM?

Thanks guys.

Rob Raymer 2

At that power level, boosted, you NEED valve springs. Personally, I use the Patriot Gold valve springs. They're reasonable and I've made over 1000rwhp with them.

And that graph looks like exactly what we see on the dyno with boosted engines and stock/weak valve springs. Aside from needing those, it could also be your cats. Unless you have to, I wouldn't run them on a boosted car. My .02.

Lastly, if you're running meth, I'd want to see the A/F a little richer than that. But that's just me....

Hope that helps.

winters97gt

Tuner said he suspected possible valve float. Car is still at the shop and he is going over the numbers tonight and going to keep working on it. We have plans to do new springs in the next month. Thanks, Rob


Edit. Rob, don't want headers, because I like the sleeper car. Might do it to bring some boost out of it, though.

Mark

black98ws6ta

iTrader: (77)

Turbo cars are alot harder on valve springs then supercharged cars. I have a ls1 c5 with 140,xxx HARD HARD miles that is on 14 psi and is running fine on the stock springs and pushrods. I would do something with the cats and try springs if you dont find anything else.

Rob Raymer 2

No problem Mark.

One more thing, looks like you could also pick up some power and torque down low with a little more tuning. The A/F looks GREAT as far as being straight as an arrow, but on a cent blower setup, it's better to be a little leaner down low and then ramp up the fuel along with the increase in boost throughout the rpm. If you look at your graph, you'll see that right around 2800, it starts getting richer, and at the same exact time the HP and TQ both drop right along with it. Then at 3500 when it leans out just a tiny bit, the HP and TQ both climb right along with it.

BTW, I'm not knocking the tune at all, just offering up a suggestion that might help out a bit.

winters97gt

Thanks! you guy are really good over here. Both the springs and cats, we were suspicous of.

With respect to you guys, the one thing that has me puzzled, is that the car ran so hard last weekend, with less boost and power, and then it just nose dives after 5800rpm a few days later. I was shifting the car at 6700rpm at the track the last 2 weeks. I don't see how I could have run 131mph if it was down on power. The first pull, it made max power where this run was. Seems like I would have fealt that loss in power and shifted the car earlier at the track, but it was still pulling so I shifted right before redline. Thanks again for the help, and keep the suggestions coming.

Rob Raymer 2

Exactly the opposite of what I would do, because the risk of hurting the engine from weak valve springs is much greater than the cats hurting it. Plus, it seems pretty unlikely that power would drop at exactly the same rpm on every single pull if it was a converter issue. It would vary based on how hot the cats were on a given pull. At least from my experience that's the case.

But that's the great thing about opinions.....

lynx853

iTrader: (8)

maybe you are flooding it with too much meth at high rpm?

winters97gt

I'll have to ask about that one. Not the tuners first rodeo, highly respected for vettes in Houston.

Rob, he wanted to stay around 11.4, but we brought it up a tad as it wasn't making power. I'm sure when we find out what it is, we can bring it back down.

Rob, what's your opinion on upgrading the springs, but not the rest of the valvetrain?

Rob Raymer 2

11.4 is about perfect for SC'd and meth, IMHO. But my opinion is also that the reason he needed to lean it out is due to valve float. I think the car will really wake up if you do nothing more than replace the springs.

As far as upgrading anything else, if you're still running stock cam, it wouldn't really be "necessary" to replace the pushrods. But Summit sells some nice Trick-Flow pushrods so cheap, it's hard not to go ahead and throw em in while you're doing the springs. Last I checked, 7.40's were only like $69! That's why I'm runnin em....

Please make sure you keep us posted on what you figure out!! Inquiring minds want to know!

Rob Raymer 2

One more thing. I tuned a Grand Prix GXP today with the 5.3, LS6 intake, LS6 valve springs, and stock cam. It was making 340rwhp/425rwtq and was AUDIBLY floating the valves at anything over 6200. Is that "normal"? No. But it just shows what happens when you have a weak set. And on boosted C6's that I've tuned, we've seen gains of 40+ rwhp with nothing more than upgrading the valve springs from stock to Patriot Gold's (no, I don't sell them, lol). And it always seems to be an issue at your approximate HP level (600+/- rwhp).

winters97gt

Good to know that my tuner has almost word for word said exactly what you have said. Car won't get a cam, fiancee won't have it after my Z06. Also why she doesn't want headers, and as I said, I like a sleeper car.

Do you see any issues with me making 5-6 passes, shifting the car at 6200rpm this weekend? Think I will gain ET or MPH with more power, but a shorter powerband?

Thanks, and I will def. keep you all updated.

winters97gt

http://www.youtube.com/watch?v=z7ACR3Ty9nk

Rob Raymer 2

Sounds to me like your tuner is a GENIUS!!!!

Actually, looking at your graph again, I wouldn't take it past 5800. And I certainly wouldn't want to tell you that I think it would be completely safe to run it like that. Simply for the fact that if it IS valve springs, it's real easy to have em start smackin the pistons. Know what I mean? And can you imagine the hell you'd have to go through with the fiancee if you did hurt it?? lol

Anyway, best of luck either way. Feel free to PM or call me if there's anything else I can do to help.

winters97gt

Thanks for being a standup guy. Thought this forum was just full of "I'll drag your ***" guys, since I only post in the Texas Section.

Rob, I have a few grudge races this weekend with close friends(non forum guys), so I have to order the springs tonight. I'm not waking up my tuner, but I ran comp 921's in my Z. What exact spring and part number do you rec. so I can overnight them and have them here Friday morning?

Rob Raymer 2

LMAO. No problem at all. Hopefully it helps.

Man, I hate to say this, but I honestly don't know the part #. But they are Patriot "Gold" Dual Springs. And with the Titanium retainers they're about $275ish? (they're direct bolt-on's btw) I'm sure you can search this forum though and find the exact part number. I'd do it, but it's almost 2:30am here and I'm beat! Long day at the dyno today!!

With you being in Houston, I would think one of the speed shops around you would have them in stock! Cuz I was under the impression that you guy's had EVERYTHING there! Fast cars, fast dragstrips, etc. I was getting so jealous I considered moving there!

Rob Raymer 2

Well, a quick search got me this (from LMP's website):

LMP Part #: 005031
Manufacturer #: PP8401
Your Price: $255.00 - (Save $24.50)
Regularly: $279.50
Shipping: FREE

Now I'm goin to bed!

winters97gt

Thanks for the help!