Moparts
Its a juggling act.....Compression and spark advance.
Posted By: Kern Dog
Its a juggling act.....Compression and spark advance. - 04/25/11 09:40 AM
I know the theories, but what about REAL world applications?
I have a 440 stroked to 493, 10.8 to one with aluminum heads. MP '509 cam straight up. With the highest octane pump gas, I have to limit my spark advance to 31 degrees. I have looked at charts showing varying compression ratios depending on combustion chamber volume. It looks like each CC of volume equates to about 1/10 of a point of compression.
My thoughts are: Putting in thicker head gaskets to lower compression slightly, allowing MORE spark lead, leading to more power. The Fel Pro head gaskets in my mill are .039 compressed. There are off the shelf composite gaskets with .051 thicknesses as well as custom Flatout or Cometics with made to order specs. A .060 gasket will likely only lower the compression 1/2 a point. That MAY be enough to ward off detonation, but its only a guess.
I am fully aware of the limitations of the MP '509 camshaft. I used it for this build because I already had it along with the matching lifters. I've considered switching to a modern cam. I ran 2 different Comp XE285HL cams in the past. Better idle and slightly more power. I am unsure which change would give more benefit: The thicker head gaskets with MORE spark advance OR the modern camshaft. Any opinions?
Posted By: Dodgem
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 01:30 PM
If you unhook the vacuum advance does it still ping if you give it some more total??
your close to what 93 should allow. you could go up a couple jet sizes and try that. you did not say what carb and jets.
how tight is the converter?
Posted By: JimG
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 05:31 PM
You've got EXACTLY the same engine as mine. Same cubes, same CR (I calculated mine at 10.9:1, but close enough), same cam, aluminum heads (mine are Eddys, you didn't say what yours are). I have a Performer RPM with a 850 VS Holley.
I have no problem at all running 35 degrees total with a quick-ish curve. I have about 12 degrees of vacuum advance and use whatever 93 octane pump gas is handy.
How's your carb tune? Have you checked it with a wideband meter or a 4 gas meter on a chassis dyno? Barring that, how's the spark plug color?
Posted By: 1_WILD_RT
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 05:41 PM
Quote:
You've got EXACTLY the same engine as mine. Same cubes, same CR (I calculated mine at 10.9:1, but close enough), same cam, aluminum heads (mine are Eddys, you didn't say what yours are). I have a Performer RPM with a 850 VS Holley.
I have no problem at all running 35 degrees total with a quick-ish curve. I have about 12 degrees of vacuum advance and use whatever 93 octane pump gas is handy.
How's your carb tune? Have you checked it with a wideband meter or a 4 gas meter on a chassis dyno? Barring that, how's the spark plug color?
You live in Virgina, we live in California... you have gasoline, we have cow piss..
Posted By: Baxter61
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 06:34 PM
well if your engine has good quench now running a thicker head gasket to lower compression is going to hurt more than it helps. additionally what rpm are you at full advance? you could delay that out a little. how hot is it running? how much does your car weigh? what gears? converter? tire size? air/fuel ratio? what spark plugs? lots of things that make a difference.
Posted By: 451Mopar
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 06:44 PM
If you have good 0.040" quench, thicker head gaskets may make the pinging worse even though the compression is slightly lower.
I'm calculating the cranking compression pressure should be about 153psi? which should be ok, but with the hydraulic cam if the lifters are bleeding down it will make the cam seem smaller and raise cylinder pressures.
Anyhow, if pulling the heads, I would try to maintain good quench clearance, and take a few cc's out of the cylinder head chambers, unshrouding the valves and polishing the chambers.
Posted By: HotRodDave
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 06:44 PM
Octane is octane no matter where you are. You may have more ethanol (actual 10% vs mabey 10%) but ethanol helps ward off detonation not increase it.
Something else is wrong, like too much vaccume advance, too hot of engine temp, too lean of carb mix... that cam should be more than enough to bleed off any excess compression unless it is advanced too much. I would check over the combo real good before ditching precious compression and possibly quench. What pistons are you running and how far are they above or below the deck?
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 06:51 PM
Okay...thanks for the replies!
Edelbrock heads, 84 cc. Performer RPM intake, Barry grant 850 VS with 85/90 jets and a 3.5 power valve. 3000 stall converter. MP electronic distributor with vacuum advance. It usually does NOT ping at part throttle with the advance connected. Initial timing is at 17 degrees.
I have heard that quench is lost at anything over .055 inch. My pistons are .017 or .018 in the hole, and the Fel Pro gasket is .039. That means that I am already at the edge of having no quench as it is. If I'm wrong, who has the right info?
Oh, with the 2" TTI headers, checking plugs after a hard run is NOT easy. I've burned my hands enough. Emissions/smog type exhaust testing on a dyno may be the only way to determine the proper carburetor settings.
Posted By: 1_WILD_RT
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 09:04 PM
Quote:
Octane is octane no matter where you are. You may have more ethanol (actual 10% vs mabey 10%) but ethanol helps ward off detonation not increase it.
True but in most parts of the country you can get 93 octane... In California we get 91 octane...
Posted By: Viol8r
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 11:15 PM
We are running 11:1 with a similar set-up at 35º and no problems. I run a smaller cam than that so you should be OK. I would really be interested to know what plugs you are running?
You should be NGK 6 or colder or Champion 10 or colder.
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 11:27 PM
Spark plugs.... That subject has come up before. I have used the plugs recomended by Edelbrock: RC12YC. I suppose that the "12" is the heat range? A 10 number would make it a colder plug and therefore LESS prone to detonation?
Whats the downside to running a colder spark plug? The motor has about 1000 miles on it. I doubt that it would oil foul with properly seated rings.
Posted By: Viol8r
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 11:31 PM
Before you get too involved I am going to say that 12's are way too hot for a true 10.8:1.
Champion 10's may be closer, you will know right away.
We run NGK 6's with 11:1 on the street and 7's for the track.
For you it would be Champ 10's for the street, 9's for the track.
Posted By: 1_WILD_RT
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 11:34 PM
Quote:
Before you get too involved I am going to say that 12's are way too hot for a true 10.8:1.
Champion 10's may be closer, you will know right away.
We run NGK 6's with 11:1 on the street and 7's for the track.
For you it would be Champ 10's for the street, 9's for the track.
I've got the NGK 6's & would use them long before the Champions
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 11:37 PM
I have read good things about the NGK plugs..... Tell me more!
can anyone explain the science behind the "hot versus cold" plug heat range? Is it correct that the colder plug resists detonation better?
Posted By: 1_WILD_RT
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 11:58 PM
Colder plug resists detonation but if you go to cold it will be prone to fouling... The more compression the colder the plug needs to be...
Posted By: Viol8r
Re: Its a juggling act.....Compression and spark advance. - 04/25/11 11:59 PM
Its a fine line and sometimes trial and error. The science I may not be able to explain but the coldest plug you can run without fouling the safer it is for the engine especially for higher compression......is there an echo!
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 12:00 AM
Okay. I guess I can try the NGKs and see how she runs. Whats another $20 anyway? If nothing else, I can rule them out if they don't help. Thanks for the help.
Posted By: Viol8r
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 12:03 AM
I think you will be surprised. Good luck.
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 12:04 AM
A GOOD surprise? Lets hope so!
Posted By: 1_WILD_RT
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 12:12 AM
Quote:
.is there an echo!
Hello...Helloo...Helloo... 
Posted By: BSB67
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 12:33 AM
I'm at 10.8 as well. Unlike others, mine is on the edge of detonation, and my intake valve probably closes later than yours. I run 22 initial and 35 total, and 93 octane. The car is heavy, tight converter, and tall gear.
What is your cranking pressure, and what do you call straight up on your cam install?
The Champion 12s are way too hot IMO. I run the NGK 7s all the time on mine w/o a fouling issue. Make sure that you have good fuel pressure at the carb under WOT as well.
Posted By: ireland383
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 01:55 AM
Quote:
Spark plugs.... That subject has come up before. I have used the plugs recomended by Edelbrock: RC12YC. I suppose that the "12" is the heat range? A 10 number would make it a colder plug and therefore LESS prone to detonation?
Whats the downside to running a colder spark plug? The motor has about 1000 miles on it. I doubt that it would oil foul with properly seated rings.
Didn't we already mention to run a much colder plug in a different post? What are you waiting for?!
Posted By: frank
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 03:17 AM
My 496 ran best with 34 degrees total. I went the other way; I gave up compression for timing and I have no regrets. My compression is 9.7/1. The engine made 640 torque and 567 hp. It will do this all day long and run on regular unleaded to boot. I don't remember the figures but there was a big difference between 31 total and 34.
Posted By: RapidRobert
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 03:48 AM
Quote:
The engine made 640 torque and 567 hp. It will do this all day long and run on regular unleaded to boot.
Frank do you know your cranking compression
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 07:07 PM
I had the motor apart 2 months ago to address an oil control issue. Before the teardown I looked everywhere for the cause of oil loss... Valley pan, oil pan, timing cover, valve stem seals....AND i did a dry compression check. The highest cylinder was around 190 and the lowest was 179. While the motor was out, I had the block honed and douched out, then file fitted new rings and screwed it all back together. It runs cleaner with no smoke and certainly makes more power than before I pulled it.
I have always used these Champion plugs and ALWAYS had to limit my ignition timing. It WILL be interesting to see if the colder plugs help. I'm going to install some NGKs today.
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 09:22 PM
I've been to three auto parts stores and NONE of them know what an NGK 6 spark plug is. I had each guy try to cross-reference a RC12YC to an NGK, and still no luck. What is the EXACT NGK part number that I should be looking for? NGK FR6?
Posted By: Von
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 09:54 PM
The NGK number for stock heads is R5670-X with the X being whatever heat range you want. 5 being hottest.
Dont know what heads you are using, maybe they take the same plug??
Posted By: 1_WILD_RT
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 10:16 PM
BCPR6EP-11
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/26/11 10:42 PM
Wild R/T: Is that a plug spec'd to fit an Edelbrock head?
Posted By: BSB67
Re: Its a juggling act.....Compression and spark advance. - 04/27/11 12:16 AM
Quote:
The NGK number for stock heads is R5670-X with the X being whatever heat range you want. 5 being hottest.
Dont know what heads you are using, maybe they take the same plug??
I think the R5671A-X are the non-projected tip version.
Posted By: 1_WILD_RT
Re: Its a juggling act.....Compression and spark advance. - 04/27/11 12:39 AM
Quote:
Wild R/T: Is that a plug spec'd to fit an Edelbrock head?
Yes
Posted By: frank
Re: Its a juggling act.....Compression and spark advance. - 04/27/11 03:19 AM
Quote:
Quote:
The engine made 640 torque and 567 hp. It will do this all day long and run on regular unleaded to boot.
Frank do you know your cranking compression
No I don't
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/27/11 04:26 AM
Thanks wild man!
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/29/11 02:46 AM
Man, these plugs aren't the easiest things to find.
You go "off the reservation" a little ways and things get murky. I went to 4 different auto parts stores and only ONE was able to help. I wanted NGK plugs, but for some reason, most of the computer systems are set up for part numbers for OEM applications. Deviate from there a little and the parts guy gets lost.
When I worked in Auto parts retail, there was ONLY the spark plug number. You need a RC12YC ? Look on the shelf. Now that number is joined by a "stocking" number. If there isnt an OEM app for that plug, finding the stocking number is very difficult. One guy at an O'Rielly took the time to email Champion to get info on the RC10YC that I wanted. NGK? unless these stores had them on the shelves, they said they weren't able to order them. I can't understand why. I ended up buying some RC9YC plugs only because they are an ON SHELF plug and readily available. I dont race much, and at least 80% of my driving is at half throttle or less. I'm sure that these will foul quicker than the 12 series, but without camping outside the Champion factory, its all I can do.
Thanks for the help.
Posted By: Viol8r
Re: Its a juggling act.....Compression and spark advance. - 04/29/11 04:09 AM
http://www.summitracing.com/parts/NGK-6779/At your door in like 2 days. You won't find these plugs in stores, gotta use outside sources my friend.
These are the ones I use. Come with a slightly wider gap out of the box, .040 or so.
Posted By: Kern Dog
Re: Its a juggling act.....Compression and spark advance. - 04/29/11 05:22 AM
I've bought plenty of things from Summit over the years, but I never considered them for spark plugs. Thanks... GREAT tip!
Posted By: Viol8r
Re: Its a juggling act.....Compression and spark advance. - 04/29/11 06:35 PM
Quote:
I've bought plenty of things from Summit over the years, but I never considered them for spark plugs. Thanks... GREAT tip!
http://www.summitracing.com/parts/NGK-5632/
V-power version of the one above
http://www.ngksparkplugs.com/techinfo/spark_plugs/partnumberkey.pdf
NGK numbering system.
Posted By: moper
Re: Its a juggling act.....Compression and spark advance. - 04/30/11 01:05 AM
You may want to look very closely at thtat carb's metering blocks. I've found them running very lean because of aluminum "hangers" where the drills broek thru but the shard was left attached. I found three of them in one carb... Also, FR6 are a great plug and are close to the Champion heat range 9. I get them at my local Car Quest.
Posted By: Charger VJ RB
Re: Its a juggling act.....Compression and spark advance. - 04/30/11 07:43 AM
It should be zero deck with that combination, as others have said try the colder plug if no good I would certainly consider that comp cam you have.
