How fat is to fat

[soslojoe1970]

What can happen by running the kit to fat... and or taking too much timing out. What can it hurt other then ET???

[68 chevelle]

When your pistons look like this its way to fat

[dadnova]

My question is< Just how fat were you running to cause that damage?????

[sc racing]

How tall is she

[stroker1]

Don't mean to take away from the fat point but that ain't the most sturdy looking ring pack I ever saw either!! The top ring is way down in the hole, but the oil ring has got to be WAY into the wrist pin. And that also (IMO) causes ring lands to fail just as the top ring too far up. I guess it's just give and take.

When your pistons look like this its way to fat

[soslojoe1970]

So what will happen from taking too much timing out... same thing cus it doesn't have enough time to burn all the fuel???

[71Hellride]

So what will happen from taking too much timing out... same thing cus it doesn't have enough time to burn all the fuel???

I know this is an old post but I was going to share what I've learned. Monte Smith said the only thing that low timing will do is kill horsepower. He runs what people would think to be extreamly lean tunes. Any extra fuel just beats up your rings and will in the end lift ring lands. I used to run square tune ups in my fogger but by the end of the year it would smoke from losing ring seal. Now I run an 8 or 10 jet spread on one system and parts are living alot longer.

[soslojoe1970]

Thanks..... I have a weak piston combo due to the rod ratio and head configuration. The intake valve is deep and gets real close to the edge of the piston. I have several pistons that have broken at the bottom of the valve relief pocket to the inside of the top ring land, and lifts the top of the piston and brakes off. Didn't start untill I jetted it up with higher hp level and started running it fatter thinking it would be safer.

[71Hellride]

Weak valve pockets seems to be a real problem. It seems the higher horsepower settings the leaner you need to make the fuel. On my fogger I have a 32n 24f and I have another tune up that is 40n 30f. Both at 5lbs through a 73 jet. I used to think being a little rich won't hurt but it does. Even more so when you go to two and three stages. Monte has a customer with a 63n 36f tune in one fogger. Sounds crazy but it has 80+ passes on it and not hurt a part. Over timed and too rich will kill pistons worse than lean anyday. Not trying to sound like an expert, just passing on information.

[Chevyfireball]

What can happen by running the kit to fat... and or taking too much timing out. What can it hurt other then ET???

I'm thinking too fat can allow unburned fuel down the sides of the pistons blowing apart ring lands and trying to weld rings to cylinder walls, too lean or too much timing will get detonation and blow holes in the tops of the pistons. Sound right to you guys?

[John_Heard]

I've heard the fuel getting behind the rings and burning theory many times before but I don't buy that one, just doesn't make sense to me. You don't see blower or turbo cars doing this and I've seen them so fat they look like diesels going down track.

We all know on a Nitrous engine it's typically happens with too much timing and/or too much fuel, and it usually happens at the weakest part of the piston near the intake valve relief. I believe it has to be something to do with too much friction in the ring/s - they are micowelding to the bore / wanting to stick and that breaks the ring land at that point. Next oil gets past the ring stack and it starts a meltdown with all the sharp edges then it's all over.

The question is, what is making the rings want to stick bad enough to break the ring land? Is it lack of lubrication to the cyl wall? Did they get too hot, expand and stick in the groove? Did the large amount of fuel wash the oil off the cylinder? Or did the ring get so hot it lost tension, ring seal went away and combustion gases start getting by that area driving temperatures to the moon, weakening the piston till it fails at it's weakest area?

I don't think anyone really has a good for sure answer...

[Craig W.]

I'm going to have to start leaning on my tune-ups more now that they've limited our jet at the Valley in Outlaw 8.5.

So who has a good NX Pro Power plate tune-up they'd share? I've got a NX/Supersucker Pro Power plate I'm starting to play with. NX's jet sheet has about a 13 jet spread at 8 to 10 psi or a square at 5 psi. I tried the 13 jet spread at 9 psi and it seemed fine, but not overly powerful. Plugs looked safe, but there's room for improvement.

[71Hellride]

It's a hell of a debate thats for sure. Hey craig if you don't mind I was wondering what nitrous and fuel jet your running, and what your timing is with the nitrous on. I really understand if you don't want to say though. I've just heard guy talking about 20 and 25 jet spreads on plates at 5 to 6lbs. Also do you guys have a/f meters. I've been thinking about putting some on my car.

[Craig W.]

My big shot tune-up was always squared jetting at 5.5 psi. Ran hard, plugs looked good, never hurt any parts.

The only tune-up I've tried in the NX plate was 70n/57f at 9 psi. Plugs weren't terrible, but it was rich.

NX rates their tune-ups on similar jets higher than NOS. They say a 82 jet is a 300 shot, NOS says that would take about a 102. My chassis dyno results are closer to the NOS numbers. I'd normally pull 8 degrees on a 82/82 tune-up. That's always put the line on ground strap right at the bend.

I'm just going to have to look at a lot of plugs and get back comfortable with the new plate.

[Deborah-WFO]

What can happen by running the kit to fat... and or taking too much timing out. What can it hurt other then ET???

I'm thinking too fat can allow unburned fuel down the sides of the pistons blowing apart ring lands and trying to weld rings to cylinder walls, too lean or too much timing will get detonation and blow holes in the tops of the pistons. Sound right to you guys?

Generally its correct that too lean = a hole in the top of the piston and too rich = a burn in the ring land.

The piston pictured above did not suffer damage from being too rich. The ring gap was too tight and the rings butted breaking the side of the piston as shown. If the piston had been damaged by being too fat, the side of the piston would be melted. What we see is a clean break in the photo.

To answer your question John. When an engine is too rich, it detonates. The detonation at extreme rattles the rings either lifting the ring land enough or breaking the quench area (the weak point at the valve relief above discussed) The result is that the damage allows the piston (combustable contents) to catch air thus causing the effect of a blow torch that follows the path of air, so to say, that in turn melts the side of the piston.

There is a balance between too rich and too lean with a nitrous motor. It is better to make a mistake running a bit fat than too lean

The tune up in a nitrous motor is affected by many things. I think when you are pushing a bigger tune up that changes in the weather is what gets people. Have you ever been to a race where almost every nitrous car is in the pits with a burnt piston? Guess what- Weather!

Taking timing out when in doubt is a good rule of thumb. Learn to read your spark plugs. You can only read a plug one time on a brand new plug. Once you learn, you will be able to see fuel, timing, and watch for detonation. Reading your plugs and keeping good written records of your engines response under different conditions will save you time, money, and frustration. Start with a conservative tune up and step it up as you learn what your motor does.