gapping cut back plugs

[motorhead]

What shuld be the gap on a cut back racing plug for a sbc 13.5:1 comp using gas and a msd 7al. Also any tricks to gapping the since there cut.

[Awesome Bill]

There is absolutely no power gains in any trick gapping process, even the distance from .020 to .060 produce no power gains or losses. A good horizontal gap between the electrode and the ground strap is best, it is better to leave the ground strap alone and not even try to bend it for a perfect air gap. If its not bent, leave it alone. If you think I'm kidding, get your dyno guy to do some testing for you. Indexing the plugs will yeild a little hp and is worth doing. Proper heat range and the proper fuel will do 20 times more power than any gapping procedure.

[motorhead]

Thanks Bill, should the gap be good right out of the box if its not bent?

[lun40119]

I would at least check them for consistency. Maybe not to change the gap, but perhaps just to make sure they are all close. I also index them for consistency. Just my two cents

Jake

[Awesome Bill]

Right out of the box if not bent is what we use. If its bent, we send it back!. They are all pretty consistent.

[lun40119]

We are going to have to agree to disagree on that one Bill. It takes 30 sec to check them. JMHO.

Jake

[Awesome Bill]

If the ground strap is 90° to the electrode, its ready to install. A good eye can see that from arms length. Autolite and others have spent millions to get these plugs to perform perfectly and the only reason they don't is someone drops them then puts them back on the shelf. Then, you come and buy them and then you drop them putting them in and don't really think about it.

Those ground straps are hardened and should not be twisted to your secret gap!. That just weakens the strap and leads to failure let alone you prying on the electrode with a steel object as I have seen people do? Go figure, then they wonder why the centers fall into their engines while racing and when the plug comes out and its gone we think we made to much power or something and the plug could not take it?

We were cutting the ground strap right off years ago and never seen any performance gains let alone we have dyno tested gaps from .010 to .080. Very little difference if any. We do like to see anywhere from .030-.040". If the ground strap is bent over when you purchase it, pretty good chance the plug has been dropped so ask for another one. Always look at the porcelain body to make sure its not cracked, another boo boo. Either way, the right heat range for the application will make way more power than any gap anyone can come up with. jmo

[lun40119]

I do agree to not be prying and bending plugs, however I do disagree with the earlier comment you made about if they are not bent, run them. Like I said it takes 30 sec to check them before you put them in.

Jake

[motorhead]

Ok lets talk about heat range. Whats a good starting point? How do you decide to go up or down? What are you looking for? Whats good and whats bad? I'm learning everyday!

[Awesome Bill]

If you read my post, I said, if the ground strap is 90° with the electrode, put them in. Anyone with half vision can see a 90° angle. If you think you should bend your ground stap and gap your plugs, you should keep doing it. Funny how no one talks about real power like indexing all the plugs. This in fact actually can make up to 5 extra hp!

[Awesome Bill]

If your using racing gasoline, then I would need to know what fuel your running, what rpm your running, and how much power this thing is supposed to make. Also, are you running NOS? If this was mine with this basic information, I would run 110 fuel and an AR3935 Autolike racing plug. The plug will run nice and clean if the fuel curve is correct and never foul.

[lun40119]

If you read my post you would see that I do in fact index all my plugs, and I also agreed with you not to be prying on the straps, merely check them. CAN YOU READ!!!!!!!!!!!!!!

Wise man say......."Listen with ears, not mouth" or in your case eyes not fingers.

Furthermore, is this how you approach all things in your shop. The crank looks straight, run it, the bearings say they are the right size, run them. Why measure anything, if you aren't going to be thorough??????????

Furthermore, this is a forum full of people with opinions. If there is an opinion that is different than yours, it isn't an attack on you. It is merely another opinion.

Take care

Jake

[motorhead]

I'm not running NOS, rocket fuel 111, rpm's no more than 6800, 13.5-14:1 comp. Hoping to get 550+hp out of it.

[lun40119]

Could also try the NGK R5671A-7. I have been running them, they are alittle cheaper, and seem to work well. It all comes down to what your brand preference is. I like the autolite plugs too. AR3935.

Take Care

Jake

[lun40119]

Is this the 355 you are talking about in the Head Gasket Thread? What other information do you have about this engine. Cam, intake, carb, internals, what is the 6800 limiter. What do you do with this combo. Just curious. Have a good 4th.

Jake

[BAD67]

Furthermore, is this how you approach all things in your shop. The crank looks straight, run it, the bearings say they are the right size, run them. Why measure anything, if you aren't going to be thorough??????????

Furthermore, this is a forum full of people with opinions. If there is an opinion that is different than yours, it isn't an attack on you. It is merely another opinion.


He does have a point here,take it easy Bill your not the only motor head in the world:D:D:D:D

[motorhead]

Its in a bracket car shifting at 6800, solid roller cam, vic jr intake 750 holley.

[Awesome Bill]

Hoping for is one thing, getting it is another. It seems we get way off from your original question like most people do with opinions. Everyone got some and non of them are worth the time its takes to put it on a thread.

I would run 40° total timing, shift it around 6800 like you have been and check your e.t. out. Fuel supply is critical, no 3/8" fuel line stuff to the carb! Proper air etc etc. You can run any heat range plug from AR3933 to AR3935 and you won't see much difference. I like the hotter plug, 35 would be my choice. I do not worry about checking the plug gap if I look at them and they all look normal. I can see without checking if it is correct. Close is good enough in this area. We don't get excited about this distance. We apply our real measurements where they count and have found they make power. We do own something to confirm that. While others guess!

I would lock my timing curve out with no mechanical advance, run the car and see if the e.t. picks up. After the run, let me know what the crossing rpm is at the time over the finish line, weight of the car, gear& tire size. That is all I need to get you pointed in the proper direction. You can use stock plugs for all I care and it really won't matter with racing gas. Pre--igniton lights it all off from hot spots in the chamber.

These are 2 different problems with engines. Detonation, being the second happens from not good enough fuel being lit off from compression and then the ignition lights it off and you have 2 flame fronts coming together. Either of these can make the pining sound we hear when mufflers are on our stock engines and most likely pump gas.

I do not think you will have this to worry about with the fuel your using and the compression your running with just 6800 rpm. Your fuel is safe up to 7500 rpm with 14/1 compression and most likely to good for your application. I would much rather you use the RED VP 107. I have found more hp in the proper fuel for the proper application then some new hot lick cams, carbs, intakes, heads, etc. etc. You have to try this if you do not intend on running your engine in on a dyno and getting it tuned first. jmo, and don't need any other opinions on my opinions, just post your opinions! If we ever get to a track and want to see whose opinions are faster, that will not be an opinion, just the facts!

[motorhead]

Thanks for the input Bill, Ill see what she does.

[Awesome Bill]

you have to start somewhere and find out what she's got. So just pay attention to the trap rpm and get back to me. You will run o.k. being it is a drag car with a ton of converter. Hopefully not to much slippage. 355 engines make plenty of power to put you way in the 10's and sometimes high 9's with a light car with no problems.