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Help me read my nitrous plugs!
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GrandSportC3
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Location: Lakeland, FL
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1968 Chevrolet Corvette

PostPosted: Fri Jan 19, 2007 12:22 pm    Post subject: Reply with quote

William Jones wrote:
If you are shifting at 6500 and the switch is at 6800 there is a good chance you are hitting it. That is pretty close you get about 300 rpm increase during a shift. Maybe next time try moving the window switch up a little more.

The rev limiter is set to 7000 and if I set the window switch off at 6800 so that I won't hit the rev limiter with the nitrous on.. I don't want to raise the rev limiter as I want the engine to last and therefore I'll keep it under 7000 RPM.
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Big Dave
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PostPosted: Fri Jan 19, 2007 4:15 pm    Post subject: Reply with quote

Need to move your camera back about an inch from were you took the last photograph as you are experiencing a depth of field problem (the center of the plug is in sharp but it falls off before and after the focal point.

Black spots is soot from fuel fouling plugs on the short run back to pits, I'd say your still a tad lean on your pass (I tend to err on the side of too rich than too lean as parts are less expensive). Only way to know for sure is to cut ignition and have someone with a tow vehicle haul you back into the pits.

Can't say more until I know more.

Big Dave
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af2
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PostPosted: Fri Jan 19, 2007 6:15 pm    Post subject: Reply with quote

Along with the plug read: I am scared at the swaying as Paul P is. FIX that problem before you have nothing to worry about because the car is gone and hopefully not you. If the car is not stable don't try to go faster!!! Corvettes can go 200+ on racecourses you're car should be able to stay straight at you're speed going straight.
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Big Dave
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PostPosted: Fri Jan 19, 2007 7:03 pm    Post subject: Reply with quote

I wasn't going to say anything without more info but I agree with af2. Did that spool ever get put in? If your posi starts to slip you will experience torque steer from one tire or the other pushing harder than the other with a slipping clutch pack in a posi-traction rear end. I'll wager you are pushing the ragged limits of a posi now N/A, with a little gas you may have crossed the line.

Big Dave
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clay
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PostPosted: Fri Jan 19, 2007 7:57 pm    Post subject: Reply with quote

All of the plug is still there - that's the best sign of all. It might be a little lean, but hard to tell without cutting the plug apart like 86GN said and looking at the fuel ring at the base. As 86GN also said, the timing looks good to me from what I have read and seen about the ground strap color change point. What did your O2 read during the pass? On a 1/4 mile run on a 150 shot, mine started out around 12:1 and gradually got richer until it was around low to mid 10's at the end - I assume from bottle pressure dropping. There are ways to avoid this, but they start adding complexity to the system. Clay
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Knarley Darley
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PostPosted: Fri Jan 19, 2007 9:02 pm    Post subject: Reply with quote

Get a 15 or 20 pound bottle to avoid pressure loss or run twin bottles. Without being biased from everyone elses opinion my first impression is to rich however the plug read doesnt mean much if you drove back after the run. The NGKs are the best and easiest to read in my opinion. All you have to do is look at the thread of a new plug after one run, it should turn the plugs threads blue about 3 threads in from the combustion chamber, less than 3 is too rich and more than 4 and things are going to start to get hurt. I usually screw in 2 new plugs before each pass(one on each side) when I am tuning a new combo(usually the front 2 because I am lazy and they are easy to get to) The miss and lost time could be due to plug gap (miss) being to large for the increased load(gap at .25 to .2Cool The colder plug will yield a slower E.T. if you are Too rich on the carb jetting. The smaller gap and colder plug make it more sensative to proper jetting Slightly lean on the carb is better than rich in this scinerio. The last thing is the grey specs which are mistakenly (in some cases) thaught to be piston melting and getting on the plug. Those little spots or specs are on the new plugs before you ever run them and gain color after the plug is run. Remember the most reliable indicator is the discolored threads of a new plug on your tune. 3 threads is between 12 and 1300 degrees
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GrandSportC3
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1968 Chevrolet Corvette

PostPosted: Sat Jan 20, 2007 12:40 am    Post subject: Reply with quote

Big Dave wrote:
Need to move your camera back about an inch from were you took the last photograph as you are experiencing a depth of field problem (the center of the plug is in sharp but it falls off before and after the focal point.

Black spots is soot from fuel fouling plugs on the short run back to pits, I'd say your still a tad lean on your pass (I tend to err on the side of too rich than too lean as parts are less expensive). Only way to know for sure is to cut ignition and have someone with a tow vehicle haul you back into the pits.

Can't say more until I know more.

Big Dave


I'll raise the fuel pressure to 7 psi (at idle) on my next nitrous run..

Thanks Cheers
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GrandSportC3
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1968 Chevrolet Corvette

PostPosted: Sat Jan 20, 2007 12:42 am    Post subject: Reply with quote

af2 wrote:
Along with the plug read: I am scared at the swaying as Paul P is. FIX that problem before you have nothing to worry about because the car is gone and hopefully not you. If the car is not stable don't try to go faster!!! Corvettes can go 200+ on racecourses you're car should be able to stay straight at you're speed going straight.


I talked to a guy that runs a '68 Big Block Stock Eliminator Vette with the same tires.. He told me to run 22 - 23 psi in the tires. He said that his car was also swaying below 20 psi.. Those radial slicks just act completely different than bias ply slicks..
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GrandSportC3
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1968 Chevrolet Corvette

PostPosted: Sat Jan 20, 2007 12:44 am    Post subject: Reply with quote

Big Dave wrote:
I wasn't going to say anything without more info but I agree with af2. Did that spool ever get put in? If your posi starts to slip you will experience torque steer from one tire or the other pushing harder than the other with a slipping clutch pack in a posi-traction rear end. I'll wager you are pushing the ragged limits of a posi now N/A, with a little gas you may have crossed the line.

Big Dave


The spool will go in in April as I don't have any races in that month.. The company that installs spools in my type rear end takes about 3 - 4 weeks.... I never even thought about that the problem could be the posi.. It is possible but I'll try to raise the tire pressure as recommended by the friend who races a stocker with the same tires!
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GrandSportC3
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1968 Chevrolet Corvette

PostPosted: Sat Jan 20, 2007 12:46 am    Post subject: Reply with quote

clay wrote:
All of the plug is still there - that's the best sign of all. It might be a little lean, but hard to tell without cutting the plug apart like 86GN said and looking at the fuel ring at the base. As 86GN also said, the timing looks good to me from what I have read and seen about the ground strap color change point. What did your O2 read during the pass? On a 1/4 mile run on a 150 shot, mine started out around 12:1 and gradually got richer until it was around low to mid 10's at the end - I assume from bottle pressure dropping. There are ways to avoid this, but they start adding complexity to the system. Clay


I didn't have the camera on, so I didn't record the reading.. I was so busy keeping the car straight that I didn't have time to read the gauges during the run.. I'll have the camera on next time. I'll also run slightly more fuel pressure..
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GrandSportC3
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Joined: 11 Jul 2003
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Location: Lakeland, FL
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1968 Chevrolet Corvette

PostPosted: Sat Jan 20, 2007 12:49 am    Post subject: Reply with quote

Knarley Darley wrote:
Get a 15 or 20 pound bottle to avoid pressure loss or run twin bottles. Without being biased from everyone elses opinion my first impression is to rich however the plug read doesnt mean much if you drove back after the run. The NGKs are the best and easiest to read in my opinion. All you have to do is look at the thread of a new plug after one run, it should turn the plugs threads blue about 3 threads in from the combustion chamber, less than 3 is too rich and more than 4 and things are going to start to get hurt. I usually screw in 2 new plugs before each pass(one on each side) when I am tuning a new combo(usually the front 2 because I am lazy and they are easy to get to) The miss and lost time could be due to plug gap (miss) being to large for the increased load(gap at .25 to .2Cool The colder plug will yield a slower E.T. if you are Too rich on the carb jetting. The smaller gap and colder plug make it more sensative to proper jetting Slightly lean on the carb is better than rich in this scinerio. The last thing is the grey specs which are mistakenly (in some cases) thaught to be piston melting and getting on the plug. Those little spots or specs are on the new plugs before you ever run them and gain color after the plug is run. Remember the most reliable indicator is the discolored threads of a new plug on your tune. 3 threads is between 12 and 1300 degrees


thanks!! I've never heared about checking the thread!! I'll check the thread of the plugs!!
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Knarley Darley
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PostPosted: Sat Jan 20, 2007 1:52 pm    Post subject: Reply with quote

Meant to say .025 to .028, darn kids Surprised LOL And the other plug companies coat them black which makes a heat read on the threads impossible. NGKs also made 5 more horsepower than any other plug on the dyno, and they have that nice transperant yellow coating which makes them beautiful to read.
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GrandSportC3
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Joined: 11 Jul 2003
Posts: 1231
Location: Lakeland, FL
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1968 Chevrolet Corvette

PostPosted: Mon Jan 22, 2007 12:32 pm    Post subject: Reply with quote

Knarley Darley wrote:
Meant to say .025 to .028, darn kids Surprised LOL And the other plug companies coat them black which makes a heat read on the threads impossible. NGKs also made 5 more horsepower than any other plug on the dyno, and they have that nice transperant yellow coating which makes them beautiful to read.


The NGK's were highly recommended to me and that's why I went that route...
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