big blocks: long vs normal glow plugs?

[RobH]

Originally posted by SkyMaxx
I'd first check to see what the manufacturer of your engine recommends, and try those. If they don't work, I run long glo plugs in my big block engines. The plugs for the small blocks tend to die too quickly if they work at all.

I don't mean to pick on SkyMaxx or call him out, but this sniplet from one of his posts on a different thread spured me to ask this question that has been bugging me for a while.

If you've ever looked at the threaded end of a long glow plug and a normal glow plug, they are the same. You can swap one plug for the other and not have to worry the the piston is going to cause injury to itself on the glow plug.

That being said, someone at our track pointed out that the long plugs have more air space inside them (longer coil and longer coil compartment). Therefore, a long plug would produce less compression than a normal plug.

Another little piece of the puzzle clicks in when someone at the bashfest said that the guys at his LHS were playing around with different glow plugs in the Hyper .21 8-port. According to their research, the OS #A3 plugs work better than the long plugs that should go in the engine. This person's 8-port seemed to have pretty damn good power too.

I have only owned 2 .21 engines (8-port and OFNA force .21 / Savage / Lightning stock engine) and my experience is limited. What are the pro's and cons of running long vs normal plugs? Would I get more power if I switched to an A3 or A8 plug? Would I be doing any harm to my engine?

Thanks in advance,
Rob

 

[Çh®i§tiªñ]

I'm sorry - but whoever told you that that was the only difference was completely wrong.

Go to the LHS, take a caliper with you and measure from where the plug would bottom out (where the washer resides) to the end of the threading. I assure you, you will find plugs longer than others.

Longer plugs can provide more power because they reduce the amount of space inside the piston area and thus, advance timing. This can give you a performance boost. Although I have seen cold longs perform the same as medium shorts (or regular depending how u look at it).

OFNA/Picco give you two washers with their plug because they are so long, that only running one washer on a new mill makes compression that much harder. So, the 2nd one allows a slightly easier start. Once broken in, switch to 1, and you should see a performance improvement if you played your cards right at break-in.

Some mills just flatout perform better with a long vs. a short plug. I've seen this happen and so has Sky for certain. Keep in mind, I have also seen well used mills go to poop with the use of a long plug because the piston head actually slammed into the plug causing problems. Granted, the rod was stretched, but it is still something to listen for. If you hear PING PING PING PING when you are trying to start the mill, IMMEDIATELY remove the long plug and make sure the piston isnt slamming into it.

You are better off running what your mill calls for, Long, Short or Turbo. And then, play with the temp of the plugs to change performance. This is your safest bet.

 

[SkyMaxx]

Feel free to call me out. I am only speaking from my personal experience, and that is why I recommended first talking to the manufacturer.

I have looked at several long plugs. Whether they have more thread or not is not the issue. The length of coil is. The coil is longer and thus places the heat source closer to the chamber advancing the timing by getting the ignition to happen much more quickly.

Your bashfest information is mostly correct, but the volume of "space" is not detrimental to the compression in the fashion that you think. By comparison you are looking at perhaps a 1 - 2 percent increase in chamber volume with a long plug. Although tempermental engines might notice this, most of them will not. The extra length of the coil causes the combustion process to happen before the compression really becomes an issue.

In the end, you know your engines. You trust or distrust your sources of information based on your personal experience. In my experience with one Hyper 8-port and one RB Concepts engine, the long plugs fired right up every time...the not so long plugs would start with the glo-ignitor on and a bit of work, but would not stay running. As for recommendations within a particular brand of plugs, I have used almost everybrand out there and they all seem to work equally well. The OS, McCoy, and now Fox Gold Series seem to last the longest in my engines.

I still maintain that you should start with what the manufacturer recommends and deviate as you see fit. The manufacturer will know what the design tolerances are for their engine, and will have a better grasp for what the "stock" plug should be. Anything beyond that is considered fine tuning.

Hope that clears things up a little...

BTW, what makes you think you could possibly pick on me in any fashion that would matter?
:hamster:

 

[TRDStreetFighter]

I think I was the who posted that question. Turns out that my LHS says there are no difference and just use DuraTrax gold plug and I am all good... Since it was a new engine I should always use a new glow plug...

 

[RobH]

When I went to the LHS to buy my "long" glow plug. He happened to have the elusive, long, Odonnel glow plugs at the time. He had them on order for 6 months and only ended up with 7 of them when they finally came in. I took two. LOL

Anyway, the Odonnel long glow plug looks the same as any other plug when put side by side. I say "looks" because I'm doing just that -- looking. This is about the 4th time in this hobby that I wish I had a pair of calipers.

Even the coil doesn't look like it sticks out of the plug any futher than any other plug.

I have yet to switch to anything other than my long plugs -- 1 1/2 gallons later and the second plug is still in it's package.

-Rob

 

[SuperMaxx97]

i was running the McCoy #59 plug in my XTM 24.7 engine. it workded good for a while but then my engine just wouldnt run right. so i went to the lhs and got me an O.S A#3. now it hauls butt and works perfect.

bryan

 

[TexSavage]

Hey Rob, you should be able to tell the difference between long and short plugs just by looking at them. Look at the threaded end and count the threads. I found short plugs to have four threads vs. long plugs having five.
I have run nothing but long plugs in my .21 engines. I just go with the manufacturers' recommendation.

Tex

 

[RobH]

Maybe it's just these oddonnel plugs. They don't look any different from an A3 or an A8 plug on the threaded end. The other end is noticably larger.

I think I'll stick with my long plugs / factory recommended plugs.

 

[SkyMaxx]

So your purpose for starting this thread would be?

Just curious considering you are running long plugs and seem to not need the information you requested.

 

[coloradoNitro]

The only engines I've seen that require a "short" plug is OS. Every other engine I've owned used long/regular. I know some guys run Os plugs in motors that take long plugs with good results. Odonnell makes two plugs, short for os motors, and long for rb,rex,novarossi,picco ect. Not to say you can't mix and match. If you put a short plug in a motor designed for long your lowering compression a tad, and the dome of your combustion chamber won't be quite as smooth. Don't know that I'd want to run longs in a os.

 

[RobH]

Originally posted by SkyMaxx
So your purpose for starting this thread would be?

I love it when you're punchy SkyMaxx. So Sexy. :hump:

Originally posted by RobH
What are the pro's and cons of running long vs normal plugs? Would I get more power if I switched to an A3 or A8 plug? Would I be doing any harm to my engine?

That right there would be the reason why I made the thread. I wanted to get everyone’s thoughts on the subject and bring the long vs short glow plug issue to the forefront of other people minds so they too would know the pros and cons.

After being told that a short plug may increase compression, I thought maybe that was the reason DarthRacer's hobby shop told him to put an A3 in his 8-port.

Darth said that he was at the LHS to buy some fox long glow plugs when the LHS told him that they did some testing and found that the OS #A3 plug worked much better. Seeing that Darth's 8-port seemed to have some balls, I started to wonder if an A3 in my engine (8-port as well) would make it faster.

When I asked my LHS about it, he seemed to be concerned about pre-detonation and that having the plug poking further down in the chamber would have ill effects. Looking back on that conversation, I think he had inverted what I had asked. I think he thought I wanted to put a long plug in an engine designed for a short plug.

SkyMaxx, I apologize if you were under the impression that I started the thread at your expense. Saying that you put long plugs in ALL of your big block engines just brought up more questions in my mind. I started this thread to settle the confusion once and for all.

I think we've done that.

-Rob

 

[SkyMaxx]

Originally posted by RobH
I think I'll stick with my long plugs / factory recommended plugs.

RobH, your only saving grace on this thread is that there are others that will benefit from the discussion. My "punchy" response as you put it was in direct response to this statement. If you were already decided on the long plugs, then why ask for pros or cons? You were already decided.

Any other comments in defense or otherwise can be sent to me directly via PM.