OK. I am glad you said that. After reading another thread by Z06sarge and the responses by ATV and some other people I started thinking the article was wrong.

 

Yeah, there was someone in that thread that had it wrong too... they pasted it out of the article.

 

Here is a pic of a plug with the threaded portion cut off so you can see where the fuel ring is (yellow arrow)... and the timing mark (red arrow)...

 

Awesome pic. In that pic, is that where the lines "should" be?

 

Pretty close - at this point, you could add a degree and watch the MPH on the time slip to fine tune it... tuning is about using all of the data that you have available, not just one indication...

 

I am guessing that you tune for the leanest cylinder? Is there certain plugs that are better than others to check?

If I remember #7 normally runs the leanest? If that's a word.

 

Tune for the leanest cyl. Start pulling all of them and then once you find out what your leanest 2 or three cyls are, pull those for fine tuning (7 will be one of them).

 

I know I haven't posted in here for a while but I had another question. I've been reading a few other threads about people reading their plugs.

1.) With a small shot, 50 or 75 can you still see the marks? I thought that I read on a small shot it's difficult/impossible to see them.

That does and doesn't make sense to me, that's why I'm asking here.

2.)Also, what kind of difference is there between tuning for an 1/8 mile versus a 1/4? Which one is better for "off road racing"?

3.)When people say to take out or add fuel I am guessing they are talking about changing the fuel jet. How many jets do you need? Does the nitrous jet stay the same and just adjust the fuel?

Thanks for the help. #3 has been bugging me for a while.

J

 

LilJay, I'm no expert and am just learning like you, but on #3 you can adjust your fueling needs by either method depending how much adjustment is needed and how you are setup. I didn't see you mention anything about running a stand alone fuel setup but with a stand alone you can get the fueling close using the jets, then use the fuel regulator to add or reduce pressure to fine tune your fueling needs.

With that said I'd imagine on the size of shot you are planning on running, you'll be fine getting it dialed in using various fuel jets.

 

You can see the marks NA if the tune is aggressive enough.

The difference in the tune between 1/8th and 1/4th is the level of load and heat placed on the motor. The timing mark is a representative of the heat in that cylinder. If you make a longer pull with a motor with more heat, the timing mark moves accordingly.

This goes hand in hand with why you cannot get a "nitrous tune" off of a dyno. They dyno does not place the load, there fore not the heat either, that the same combination would see at the track.

So if the tune up is very aggressive on a dyno, it is typically way too aggressive for the track. This is based on the extra heat the car will see going down track.

If you race "off road" and only do say 0-120. Your tuneup will be basically identical to the 1/8th mile. If you do any 40-140 style racing. You need to be aware that you have to keep the tuneup more conservative because of the load your motor will see if you make that long a pull.

I hope all that was clear.

You can tune your fuel either way. Typically you will not see the nitrous jet moved as often because people want XXX shot size.

78N/46F is our 200hp jetting for a plate.

If we step down to a 77N jet, we will run richer. If we go to a 47F jet, we will go richer.

If we go to a 79N jet, we are leaning out the mixture. If we go 45F jet, we will lean out the mixture.

The last option is to make Fuel pressure adjustments is we have a stand alone, or a separate fuel pressure regulator.

All of these can be used to get the tuneup where we want it.

 

Graham thanks for the great reply. Thanks for taking the time.

I'm running off the rail and can't see myself spraying more than 125 maybe 150 on the stock short block and those won't come till I figure out how to read plugs.

I am running off the rail but do have a racetronix pump and hotwire kit.

I will have to go over the jet sizes you mentioned as I'm not familiar with any of them yet and what they mean.

Thanks!

 

No problem.

On the jet sizes, its just the size of the orifice. Bigger number, larger opening. All jets are the same a .088 jet is the same jet size no matter what brand system or if it is used on the fuel or nitrous side.

78N = .078 orifice jet used on the nitrous side of the nozzle/plate/direct port.

The same jet could be used as fuel tho.

78F = The same .078 orifice jet used on the fuel side of the nozzle/plate/direct port

When your ready to spray the larger shots and are ready to get down on some plug reading let me know. Ill give you the correct procedure so that you can get a good plug read. Then we can look over them together and get everything safe and dialed in.

 

Bump for a good thread. Any updates to add to this jay? I am as green as they come with this...

I haven't started to do any leg work for researching on this but are there any more threads to help piggy back off this? ATVracer and someone else was listed that helped clear up some misinformation that was in the plug reading link that was posted. Can you post those threads jay if you still have them?

 

lol@ the comment that the strap on the plug only shows a timing mark and not heat.