how do you determine what plug you need, and the gap for a given compression ratio and amount of nitrous being sprayed?

currently- 150 shot single stage direct
future- upwards of 250-275 multi stage

the stock milled heads are 56cc
the pistons come out of the hole .016
compressed gasket thickness is .050
pistons have around 4cc removed from them

does anyone have a graph or what not?

 

Check out the sticky at top for insight.
Robert

 

the ONLY sticky that deals with plugs only gives part numbers for each heat range. when do you switch from heat range 6 to 7 or to 8? how do you know what to gap that heat range 7-8 plug to when your shooting a 250-275 on a C14-C16 mix in the stand-alone fuel system? how about the heat range 6 when your only shooting a small 100-150 shot on pumpgas?

 

On a 100/150 shot most use the NGK TR6 gapped at about .035. The smaller the hit, the larger you can gap. So, on a 100 shot some use a .038 gap which may blow out at 150hp or above. Cat3 is our site plug guy, give him a pm.
Robert

 

I have never seen a chart. Although it may be possible to come up with one. Most guys just go on what the start point is being stock and NA and then work backwards from there as compression and shot size go up. Most just from experiance.

It will all depend on several factors. Fuel type, compression, shot size, staged or progressive or single, What rpm you spray etc.

I have sprayed TR6s with a 300 shot for a total of 725 rwhp. But that was with 110 leaded race gas and it was staged. Tq was never above 730 ft/lbs or so.

On the same setup I usually ran BP7EFS heat range 7 with just 100 octane. and that worked fine.

Anything more than 800 rwhp and/or 400 shot I used the 8s

I havent had any plug issues yet.

HP is one thing...but TQ peaks seem to uncover when your too hot on the plugs. So if you are hitting an all in one 300 shot at 3000 rpm...where TQ is likely to be in excess of 850+ ft/lbs and cylinder pressure is through the roof...you may need the 8s.

That same 300 shot in stages or progressive where Tq is less than 700 ft/lbs and you may in fact get away with 6s

Peak HP #s dont mean squat...you really have to look at the broad picture of the pressures and forces at work inside the engine with your given setup. Especially in the nitrous world. You could have 2 engines both making a peak HP or 750 rwhp with a 300 shot. But one could be in excess of 850 ft/lbs at its TQ peak and the other maybe be 650ft/lbs. Those two motors could require a different plug depending on other factors such as fuel octane.

 

sweet! thank you you two! do you kill the engine right after a pass/pull to see how the plugs are doing?

 

I pulled this from Colnels N2O web page:

Generally, for every 50 hp that you add you need to decrease the gap by .004. If you add 150 hp over stock you should decrease the gap .012. You have to account for all the power that you have added. Not just what you've added with N2O. So if you've added 50 NA hp and 150 N2O power you would decrease the gap by .016. Starting from .060 we get .044. Better to be a little narrow rather than wide since the gap tends to gradually widen as the plugs age so in this case we might go with .040-.042 just for good measure.

Dan

 

how do you know when your plug is to hot?

 

They can possibly melt and kinda ruin a motor.

 

and to cold will foul out and not run right, which is why i am asking

 

Yes they will. So when this happens, you just rebuild your motor and try a cooler plug. If it happens again, rinse and repeat as necessary.

 

but i can only rebuild it so many times....

 

Why do you think people resleeve their blocks.

 

well...if your reaching for any type of sizable shot hopefully you have a few tools at your disposal. Like EFI live of something to monitor knock. Tuning on a dyno helps to to see if power is smooth. Then if your concerned about plug range you should be reading them after every pull. Look for signs of overheating. You can doo a google search on plug reading and there will be plenty of info on what they should and shouldnt look like. of course if the tips are metled off...its too hot...lol. Actually melted electrodes is usally a sign of a lean tune. A good tune/correct octane can save things alot more than a plug slightly out of heat range. But they all go hand in hand.

When in doubt use more octane and/or colder plug. If your fouling them out...step up a range. Better to foul out first than burn things.

 

how do you know you are blowing out the spark?
is there a way to look at the plug and tell?

 

this is what i'm looking for also. symptoms of a blowout