.060" spark plug gap?

[2112]

OK, I just made the transition to a complete MSD ignition/distributor and I am re-reading the manual and they (MSD) recommend for engines less than 10.5 to 1 compression to run spark plug gaps of .050"-.060".

I have run.035" in everything from 9 to 1 motors to the one 11 to 1 engine (24' Warlock)I had several years ago.

I have to admit I must not fully understand the need to gap the plugs based on compression. I thought it had more to do with plug location in the chamber and whether you have a tight chamber vs. a big chamber.

I am just a tick above 9 to 1 with my current cometic gaskets but I have relatively tight chambers (78cc). Should I be gapping my plugs to .050"-.060"? :confused:

[Geronimo36]

Not sure if it matters either but I've been doing .045 on my MSD setup.

[imco offshore]

OK, I just made the transition to a complete MSD ignition/distributor and I am re-reading the manual and they (MSD) recommend for engines less than 10.5 to 1 compression to run spark plug gaps of .050"-.060".

I have run.035" in everything from 9 to 1 motors to the one 11 to 1 engine (24' Warlock)I had several years ago.

I have to admit I must not fully understand the need to gap the plugs based on compression. I thought it had more to do with plug location in the chamber and whether you have a tight chamber vs. a big chamber.

I am just a tick above 9 to 1 with my current cometic gaskets but I have relatively tight chambers (78cc). Should I be gapping my plugs to .050"-.060"? :confused:

higher compression can blow out the spark ( so to speek)

[LAKE EFFECT]

I did alot of research last year, but more toward heat ranges with a blower motor combo. I talked to an Autolite tech a couple times, and recall the saying "blowing out the spark", thats where the tighter gap is necessary. All or most of the Autolite racing plugs come with a .025/.035 gap. He also mentioned bigger gaps and emmisions, but did say keep a tighter gap in the boat engines(or any high performance engine) to help prevent misfires.

I would look up Autolite's website or call them. Their AR(racing) plugs have a thick shell, cut back electrodes and a fair price(under $3). They also cover a ton of heat ranges. Plus being a Ford guy, you should know Autolite makes all the Motorcraft plugs.

If I had to guess about MSD wanting a larger gap, I would say that the stronger spark will jump the larger gap, and smaller gaps may wear out a plug faster. But you want no misfires or a loading up condition at idle and such, plus I'm sure new plugs get put in every season, so your not going to wear out a plug.

LE

[JIMG]

when you have higher compression the actual cylinder pressure goes up. this in turn makes the air/fuel mixture more dense. the more dense atmosphere is harder for the spark to jump accross. it is as if it had to jump farther in th open. this is why your spark will jump accross a 1/2" spark checker and only a .040" plug gap. the higher the compression the smaller the gap it can theoretically jump accross.

[DAREDEVIL]

The MSD recomendation is all for car engines,,not for Boat motors.

.35 is a good overall #, in my 12:1 COMPR. Engine i run .35 !!!!!!

[imco offshore]

The MSD recomendation is all for car engines,,not for Boat motors.

.25-.35 is a good overall #, in my 12:1 COMPR. Engine i run .25 !!!!!!

with an msd scott i think i would consider opening up to 35 / 38 and your motor would run cleaner , ( i heard it at sarasota ) pluss u run race fuel

[Geronimo36]

IMCO, I could see the bigger gap helping idle quality with the CD ignition.

When I opened up my gaps from 35 to 45 I noticed less wear/tear on the MSD dist. caps where the rotor hits the coil lead.

I never noticed any differnce in how it ran but did notice the wear on the cap.

[PatriYacht]

10.5 to 1 is considered low compression in the racing world. The plug fires easily over a large gap that low. The higher compression or boost will make it harder to fire so you have to narrow it down from there. I think an MSD will fire almost anything at .035. That said, I gap mine at .040 because the plugs don't look like they were made to have the gap opened any farther. The angle between the electrode and the strap looks wrong.

[Trim'd Up]

I believe Autolite and NGK make plugs for wider gaps.
Regardless, I have always ran .035-.040 in about everything and it seems to work.

[DAREDEVIL]

with an msd scott i think i would consider opening up to 35 / 38 and your motor would run cleaner , ( i heard it at sarasota ) pluss u run race fuel

George,,your right ,,,i run .35 !!!!!!!!! Sorry

[mbam]

We used to test gap on the dyno, open up until misfire than back down .005 or .010, much cleaner low end & idle.

Back in the day there was a gapping pliers that would help keep the ground electrode @ 90 deg.

.045 was where we wound up with the MSD.

[Geronimo36]

.045 was where we wound up with the MSD.

:)

[jeffswav]

I run a Marine DUI HEI distributor at .050 with AC rapid fire plugs. I run 8.9 comp and never had a mis.

[MikeyFIN]

with an msd scott i think i would consider opening up to 35 / 38 and your motor would run cleaner , ( i heard it at sarasota ) pluss u run race fuel

The plugs we put in Clearwater was gapped at .35 and still issues with getting the plugs clogged at the no wake...and yes Race fuel.

If you ask me I would next time open them up to .45

[MikeyFIN]

I run a Marine DUI HEI distributor at .050 with AC rapid fire plugs. I run 8.9 comp and never had a mis.

No wonder with that comp..

[MikeyFIN]

10.5 to 1 is considered low compression in the racing world. The plug fires easily over a large gap that low. The higher compression or boost will make it harder to fire so you have to narrow it down from there. I think an MSD will fire almost anything at .035. That said, I gap mine at .040 because the plugs don't look like they were made to have the gap opened any farther. The angle between the electrode and the strap looks wrong.


And a pump gas engine if you do it carefully.

[Strip Poker 388]

I was told the larger the gap more it put alot of load on the ignition,Its suppose to make a bigger spark.

Just think most plugs are made for around .035, that means your bending the ground electrode up.So it will have a angle .To me if its flat like at 035 it will use all of the flat surface on the center electrode and the same area of the ground electrode,with it bent up I would think it would make ground contact at the edge of the center electrode,being a smaller spark.

Hows that sound:)

side gap indexed
http://i160.photobucket.com/albums/t188/covertrussian/Sentra%20SE-L/Performance/Spark%20Plugs/SparkPlugDyno.jpg




I don't know if you all remember when MSD came out with there box, they had a test fixture to show the spark.The speed shop here had one on display showing the difference between stock at the MSD,the fixture had a adjustable gap.it would spark around 4 inches,ya could lite you cig with it:).

[jeffswav]

No wonder with that comp..When I set the engine up I thought is was more like 9.3 to 1. However when I switched over to a roller cam RMbuilder ran the numbers and it was really 8.9 to 1 when you figure in gaskets and all the variables. A lot of people probably think their compresion is higher than it really is. We really do not have good enough fuel available to run higher comp anyway.

[DAREDEVIL]

I was told the larger the gap more it put alot of load on the ignition,Its suppose to make a bigger spark.

Just think most plugs are made for around .035, that means your bending the ground electrode up.So it will have a angle .To me if its flat like at 035 it will use all of the flat surface on the center electrode and the same area of the ground electrode,with it bent up I would think it would make ground contact at the edge of the center electrode,being a smaller spark.

Hows that sound:)

side gap indexed
http://i160.photobucket.com/albums/t188/covertrussian/Sentra%20SE-L/Performance/Spark%20Plugs/SparkPlugDyno.jpg





I don't know if you all remember when MSD came out with there box, they had a test fixture to show the spark.The speed shop here had one on display showing the difference between stock at the MSD,the fixture had a adjustable gap.it would spark around 4 inches,ya could lite you cig with it:).

I think the shortest way is what it will look for ,,,smaller spark ??? NO . because the ground is ground no matter where !!!!!!!!

But bigger spark does not mean its hoter and thats what u want.
eficient and hot !!!!!! NOT BIG and all over the place.

[imco offshore]

The plugs we put in Clearwater was gapped at .35 and still issues with getting the plugs clogged at the no wake...and yes Race fuel.

If you ask me I would next time open them up to .45

i,m not an engine man of sort,,,, but i would think the carb is a little fat or the power plug is too high

[MikeyFIN]

When I set the engine up I thought is was more like 9.3 to 1. However when I switched over to a roller cam RMbuilder ran the numbers and it was really 8.9 to 1 when you figure in gaskets and all the variables. A lot of people probably think their compresion is higher than it really is. We really do not have good enough fuel available to run higher comp anyway.


Offtopic.

Also Deck heights and head deck heights are nothing even close to blueprint standards as there is material left to machine while new.
It´s not a wonder sometimes brand new GM long blocks are off by a a lot in compression.
At 8.9 compression you can run your engine with almost anything, no need to worry there.

Our octane ratings in Europe are higher because we use RON ( Research octane number) on the pump which applies more on idle and low detonation while MON ( Motor octane No) is more applied on High temp/Rpm and on load. The average of these two numbers is AON ( Average ) or PON ( Pump octane # in U.S.).
So actually our fuels like 95 RON is close to your Regular and our 99/98´s are like Super(?) for you.

I guy that writes on another site told that his best numbers with a Vortech X Centrifugal blown 548 was 1025hp with regular 95 RON on a boat motor any higher octane made it worse so I think you´re more than safe...His base comp is 8.33:1

And here´s a pump gas 950hp blown Marine one plus some..
http://www.youtube.com/watch?v=ZtaYdzoCzl8

[MikeyFIN]

i,m not an engine man of sort,,,, but i would think the carb is a little fat or the power plug is too high

Yes of course it is as the velocity at idle is what it is...can´t help that. Engine would be a hell of a engine in a twin engine or a lighter boat...

The plugs pulled from a high rpm run looked just fine before Clearwater while testing, just the way a boat motor should be to be on the safe side IMO at least.
Maybe it would work better with a Tunnel ram and two 600cfm´s ;)

So the only remedy for a racecourse like with a long idle time would be open the gaps as we speak.

[DAREDEVIL]

High compression race fuel engines DON'T like to idle !!!!!!

If i would of known that the idle time in Clearwater was 25 min. i would of ran #7 plugs instead of #9,,,but u lose power that way.

It cleared up as soon as we got on plane.

Also in Sarasota,,,just for the note George,,i had an other issue and only ran on 7 cylinders because of a small hole in the intake runner so oil was pumping on to the valve and fouled up #3 plug so it could not clean out.

Thats why i did not finish Lauderdale & Sarasota,,,it tock me that long to find the problem.:(

Mika ,,a Tunnelram ,,,u lose exselleration,,thats what i need most.

But this thread is not about ME or my engine. LOL:rofl:

[MikeyFIN]

Mika ,,a Tunnelram ,,,u lose exselleration,,thats what i need most.

But this thread is not about ME or my engine. LOL:rofl:

But with small throttle barrels It Might actually work, just a brainstorm.... LOL.

[DAREDEVIL]

But with small throttle barrels It Might actually work, just a brainstorm.... LOL.

The farther the carb/s is/are away from the block,,the less tourqe u have !!!!!!!!!!!!!!!!

[MikeyFIN]

No --- the opposite..the longer the runners are the more torque you have down low..but they also have to keep up the velocity to work which tunnels seldom doesn´t as the runners are too big.

Think (Smokey) Crossram (http://images.google.fi/images?rlz=1C1CHMG_fiFI308FI308&sourceid=chrome&q=Crossram&um=1&ie=UTF-8&sa=N&hl=fi&tab=wi) for example..works like Gangbusters or Individual runners.

Scotty I´m a Roadracer/oval Tracker at heart... not a Drag racer... and it´s allbout torque there.
also a Big plenum gives a lot of air for the initial throttle opening so the engine doesn´t need to suck thru a straw.
http://www.sporttruck.com/products/0903st_2008_sema_show_top_50_products/photo_27.html

[Geronimo36]

have you tried opening up the secondary butterflies or changing the air bleeds? With some work I bet you can get it to idle, probably just take some time to do it right.

[2112]

I believe Nickerson drills extra air bleed holes in the throttle body so you can richen the carb up top without making it sooty at idle. That is, among other upgrades they offer.

Here is the MSD recommendations I mentioned;

[MikeyFIN]

Nickerson ain´t the only one... I can drill too ;)

That´s an old trick bytheway which you necessarily doesn´t need to do with a 4500 Holley.
And Geronimo you´re right. It takes time to get a carb to work good thru the whole powerband a lot more than just doing WOT and High RPM tuning.

[2112]

Carbs require a special talent. If you have it great! I don't and I sure like bolting on a Carb that has been tuned by someone who does so all I do is set is idle speed and and get boating. :USA:

Nickerson has done me a a great service solving many of the Dominator hassles I just lived with for years.
.

[DAREDEVIL]

If u buy a Holley new in the box,,they are usually tuned very well, for saftey reasons a little on the rich side.

[2112]

If u buy a Holley new in the box,,they are usually tuned very well, for saftey reasons a little on the rich side.

Mine were way lean up top. When I jetted it to get it right it was so fat at idle it blew soot and fouled plugs.

They were 1250 dominators BTW. Nickerson said that is exactly what they expect out of the box on the 1250.
.

[Trim'd Up]

My 1150 was close enough to run, but thats it. It was real fat in the mid range and lean up top.

[Geronimo36]

Mine were way lean up top. When I jetted it to get it right it was so fat at idle it blew soot and fouled plugs.

They were 1250 dominators BTW. Nickerson said that is exactly what they expect out of the box on the 1250.
.

Worked on a 42' Fountain, triple engine, 600 hp with big solid roller cams and 850 Nickersons (basically an HP Holley with air horns cut off and worked)...

Couldn't get the darn thing to idle worth a damn...shipped it back to him and they came back perfect. He flow benches the carbs. I remember him telling me he works the metering blocks a bit and said that by all means do not attempt to re-set the mixture screws on his carb. Well, that's what got me into that mess to begin with... We put big cams in and I was setting them up and messed with the settings which sent the carb off the deep end.... Even Nickerson told me his stuff has a tendency to do that. :cuss:

As far as Holleys out of the box, it's been my experience that a properly sized holley should be pretty close, it'll pull as much fuel as it needs and 1-2 jet sizes either way to perfect it.

If running too big a carb it'll run lean up top out of the box, too small usually runs fat out of the box...

This has been my experience, yours may vary! :)

[MikeyFIN]

Carbs require a special talent. If you have it great! I don't and I sure like bolting on a Carb that has been tuned by someone who does so all I do is set is idle speed and and get boating. :USA:

Nickerson has done me a a great service solving many of the Dominator hassles I just lived with for years.
.


Well I´ve fiddled all mylife with Holleys. Qjets (love them), Carter AFB´s and Weber DCOE´s.

Gotta Say the Qjet is the best 4 barrel in general. Especially when dialed in.
But no match for a stack of DCOE´s in any 4 Barrel.

[MikeyFIN]

If u buy a Holley new in the box,,they are usually tuned very well, for saftey reasons a little on the rich side.

The Power Valves are all up the place where there ain´t no sun...
I don´t trust an out of the box Holley.
Yes they are somewhat rich but when you know which carb is the one for you´re apllication it´s quite ok.
All the double pumpers though are too general to suit any engine...

I once put Qjet on top of a boat engine ...ran out of jets and drilled the jets to the size ( went a tad rich) but on the dyno the dyno operator fiddled 2 hours with jets and timing and couldn´t better more than 3 hp on the top the midrange being equal...

[DAREDEVIL]

The Power Valves are all up the place where there ain´t no sun...
I don´t trust an out of the box Holley.
Yes they are somewhat rich but when you know which carb is the one for you´re apllication it´s quite ok.
All the double pumpers though are too general to suit any engine...

I once put Qjet on top of a boat engine ...ran out of jets and drilled the jets to the size ( went a tad rich) but on the dyno the dyno operator fiddled 2 hours with jets and timing and couldn´t better more than 3 hp on the top the midrange being equal...

Mika,,,i know u know alot ,,but stop it .

If u order a new 1050 dominator MARINE carb it is dialed in +2 on the rich side.
End of discussion.:reddevil:

[PatriYacht]

The air bleeds they use in Dominators now are too large. If you jet to be clean in the midrange, they will be lean at top end. I think it may be to make them run well on near stock 454's and 502's. They don't require the kind of fuel that a 700hp 540 or 598 requires. I went from .038 high speed air bleeds to .027 and it was a huge improvement. I went down 6 jet sizes and it was proper mixture from mid to top end. Sorry for the hijack, now back to the thread.

[Blue Thunder]

The air bleeds they use in Dominators now are too large. If you jet to be clean in the midrange, they will be lean at top end. I think it may be to make them run well on near stock 454's and 502's. They don't require the kind of fuel that a 700hp 540 or 598 requires. I went from .038 high speed air bleeds to .027 and it was a huge improvement. I went down 6 jet sizes and it was proper mixture from mid to top end. Sorry for the hijack, now back to the thread.

When you say flat thru the mid on up do you mean the a/f ratio stayed at say, 13 at 3000 and 13 at 5500? My dominators are lean in the mid range and fatten up on the top due to the power valves I presume.

Oh yeah, I run .038" gaps, with tbolt ignition and blowers. No misfires I can detect.

[Indian Outlaw]

when you say flat thru the mid on up do you mean the a/f ratio stayed at say, 13 at 3000 and 13 at 5500? My dominators are lean in the mid range and fatten up on the top due to the power valves i presume.

Oh yeah, i run .038" gaps, with tbolt ignition and blowers. No misfires i can detect.

well goodie for you!!:03:

[Airpacker]

I only had about 20 hrs of fine tuning in my dominator / Victor jr intake on a 540. Sucker would idle all day long and never foul a plug. The PITA is drilling air bleeds to JUST the right size. Had a few ooops, too big episodes but, in the end the carb was perfect. Idle, mid and WOT.

It just takes some serious time and lots of trial and error to get them right.

[MikeyFIN]

Mika,,,i know u know alot ,,but stop it .

If u order a new 1050 dominator MARINE carb it is dialed in +2 on the rich side.
End of discussion.:reddevil:

Agreed and Gotcha. just the way I like it. Rather change plugs than valves...

Regarding Patriyachts case I´d say his power valve comes on a bit late ?

[MikeyFIN]

I only had about 20 hrs of fine tuning in my dominator / Victor jr intake on a 540. Sucker would idle all day long and never foul a plug. The PITA is drilling air bleeds to JUST the right size. Had a few ooops, too big episodes but, in the end the carb was perfect. Idle, mid and WOT.

It just takes some serious time and lots of trial and error to get them right.

My Dad´s a goldsmith so I usually go and get his small reamers to do the job... you can go one thousand of an inch up...
Shhhh... don´t tell him.:sifone:

[PatriYacht]

When you say flat thru the mid on up do you mean the a/f ratio stayed at say, 13 at 3000 and 13 at 5500? My dominators are lean in the mid range and fatten up on the top due to the power valves I presume.

Oh yeah, I run .038" gaps, with tbolt ignition and blowers. No misfires I can detect.

Not exactly but sort of. Originally I was up to 98 jets and the top end was still a little lean while mid range was rich. With the air bleed change, I was able to drop down to 92's and the top end and mid range were good.

Power valves add 6-8 jet sizes. Changing them changes when they open but not how much fuel they pass. At wide open throttle they all add 6-8 jet sizes and that wasn't enough. Btw, new Dominators come with removable air bleeds. You can change them just like jets.

[MikeyFIN]

OK so you left the power valves to open late to richen the top end ?

[Geronimo36]

Power valves add 6-8 jet sizes. Changing them changes when they open but not how much fuel they pass.

Zul taught my buddy a trick with that.... he drills the orfice in the metering block where the power valve goes!

Mid-range on this particular engine was perfect but needed a tad more up top (when PV opens) so he drilled it out larger and it was perfect!:driving:

[2112]

Zul taught my buddy a trick with that.... he drills the orfice in the metering block where the power valve goes!

Mid-range on this particular engine was perfect but needed a tad more up top (when PV opens) so he drilled it out larger and it was perfect!:driving:

I believe Nickerson will do that for those of us who only adjust and idle screw. :sifone:
.

[PatriYacht]

OK so you left the power valves to open late to richen the top end ?

Yes

[MikeyFIN]

Zul taught my buddy a trick with that.... he drills the orfice in the metering block where the power valve goes!

Mid-range on this particular engine was perfect but needed a tad more up top (when PV opens) so he drilled it out larger and it was perfect!:driving:

That goes into fine tuning and yes it´s really a delicate tune to do to get your engine just right.

[Geronimo36]

I'm happy to say I have learned a lot of tricks from some of the best in the business over the years and apply them on my own!!

[MikeyFIN]

Same goes here.... something you don´t learn in the Universities...