You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!
My buddy has a GTO with a intake, LM exhaust, big cam and just installed a 150 wet shot. We where out playing today and he sprayed it for the first time. Well at the top of the pull it started spuddering so we went back to my house and pulled the plugs. 2 of the tips of the plugs where gone. Not the center electrode, but the side electrode, what you gap. We replaced the plugs and it was still popping. So I pulled the plugs back out, one was firing fine, the other not at all. I checked the plug to make sure it wasn't a bad one and it sparked, just not firing in the camber. Pulled the valve cover to check the spring, good. Checked compression, big fat 0! Hooked a air line to the spark plug hole and could hear air from the exhaust pipe. Obviously a bent valve. We're going to pull the head this week sometime and replace it.
My question is, because I know nothing about NOS, what could have caused this. TWO plugs to break that were less than a month old and I'm assuming that's what bent the valve, but won't know for sure til we pull the head. Running too hot??? I asked about he size of the shot being to big and he said stock GTO's run them all the time with no problem. I then asked about the tune and he said it was tuned when he installed the cam, but not the spray. I'm guessing if you run a wet shot it adds the fuel needed?
Well, usually a N/A tune means that timing was advanced to extract more power. Nitrous is the opposite when it comes to tuning. You need to retard timing to get more power and do so safely. So the sputtering you experienced could have been detonation. That means he got lucky with just a bent valve, since his engine could have gone kaboom.
In addition, you need to run 1 step colder plugs with nitrous to help with the cooling of the chamber. I'm guessing he lost the tips of the plugs due to the chamber being excessively hot coupled with advanced timing map he's probably running for the N/A tune.
Before firing up the engine again, I'd make sure to do a thorough inspection of all the components just to be on the safe side.
BTW, does he know the AFR when he's spraying? All the vehicle specific nitrous kits will only give you an estimate of what the jet sizes should be, but as you should know, no cars are alike. That means that just because the jet sizes worked on 1 car, it doesn't mean it will work on another. This is especially true for modified cars. Do yourselves a favor and find out the AFR and get a tune for nitrous.
What I'd do is spray a small shot (using the recommended nitrous and fuel jets) and see what the AFR is. Then move up a little on the shot size but with slightly bigger fuel jet. Check the AFR and see how it changed. Continue this process when going up to a slightly bigger shot but play with the fuel jet as best as you can. Once you reach your shot size (I guess 150 for you), get the AFR where you want using the fuel jet, and then fine tune it on the dyno. I started out with a 35 shot to gauge my car's response, repeated with a 50 shot, then 75 shot (this is where I luckily guessed right the first time for the perfect AFR on the dyno). I then moved up to a 100 shot and luckily with some common sense, I had guessed the perfect jet sizes for the AFR goal. I didn't have to change my fuel jets on the dyno to fine tune because I happened to guess correctly, but don't expect this to happen to you. Just as a reference, my fuel jet is much much bigger than what was recommended by the manufacturer.
Thanks guys. I'm gonna talk with him today to find out about the timing. I thought he said they took out timing, but am probably mistaken. The damn thing will hardly idle b/c the cam is so big.
on LS engines, when you install for the fuel on the end of the fuel rail there (the nice AN fitting thats factory installed) you HAVE to take that tire stem looking thing out of it, if not, NO fuel will get to the fuel solenoids. Did you do that?
Also, cams with a low LCA (the rough idle usually) and a short exhaust duration (what you find in aggressive NA cams) is not what you want to run with nitrous. A wider LCA and more exhaust duration is safer.
yea, just look in the fuel rail there, if there is an air relief valve, that was your problem. But anyone that has ever installed the kit should know about that
Okay so here is the deal. He WAS running stock temp plugs w/ a 150 shot. He is taking it back to the guy that installed the NOS & cam to replace the valve. He is being charged over $500 for the repair and something to me just doesn't add up. He said that they had to pull a lot of timing to stop spark knock after the cam install. I didn't get to check for the ARV before he took it to the shop. I just feel real bad and would like to help him out anyway I can.
@ the noob shop/customer. They all should do some research first before adding anything. It sounds like negligence/ignorance from both parties. At least he learned his lesson, though, right? Good luck and keep us updated.
I'm not really laughing too much. Especially since my friend who isn't a mechanic took his car to a known performance shop in this area to get it done right and still wound up with his car messed up and now has a $500 repair bill when it seems it was the shops fault. It's not like he bought the kit and the shop told him how to install it. He PAID them to do it and ASKED about having a tune to make it safer and they told him it wasn't necessary. I know when you get into performance nothing is guaranteed. I just think he's getting screwed here.
Oh btw, my friend is no noob. He's had more than one 10 sec street car. This is just his newest toy. He doesn't build them, just drives them.
Sorry, I didn't mean to offend. However, one must realize that spending money and owning something is not the same as actually learning about the item(s) being owned before use. With the kind of people that are out there, he should have known better - reputable or not.
I'm not sure of the extent of HIS knowledge of NOS. It's my knowledge of the squeeze that's not that good. lol I know his black Z28 had spray and that was his low 10's car.
Well the shop pulled head. After he gets the car back I will look for the bleed valve. He said he may just get rid of the car now but either way is not letting that shop do anymore work to his car.
Help me figure out what happend please.
@ the noob shop/customer. They all should do some research first before adding anything. It sounds like negligence/ignorance from both parties. At least he learned his lesson, though, right? Good luck and keep us updated.
