Moparts
Expensive but effective way to fix detonation??
Posted By: Spraygoon
Expensive but effective way to fix detonation?? - 06/03/11 04:49 AM
70 cuda 4 speed 3.54 gear 440 6 pack Mopar 484 cam, Hooker Super Comp headers. I feel the combo I have now is not very detonation tolerant, I have fattened the mixture and run colder plugs and can still not make it take more than 28 degrees total without the plugs looking like porcupines. Currently has 452 heads with KB 237 Silvolite pistons. With the 88 cc chambers and the piston .010 in the hole and a 5 cc valve relief, this gives me 9.7 CR.
I am considering using the Source 440 aluminum heads with a closed 80 cc chamber. If I swithched the heads only, my qeunch would be about .050 ( gasket + .010)much better than what I had with the 452"s (is .150 even considered quench??) but boosts CR to about 10.5 which even with the aluminum heads I feel I may be back in the same situation. I have heard aluminimun heads are worth a point in compression but even if thats true my true effective CR would be 9.5, not much less than 9.7.
KB makes a forged piston with a 12cc dish which would give me 9.6 CR with the 80 cc chambers and I couldalways cheat with a gasket .010 or so if I wanted, or I coud get the heads milled a bit to get it up some. Not looking to build a drag engine or something for max power, just looking for a nice running engine that I don't have to worry about detonation. Any thoughts. I realize I am looking at about 2k to do this I just can't endure the clatter and the consequences anymore, who knows, I may be able to lean it out a bit and/or run a hotter plug to keep things cleaner. BTW jetting is "stage 2 as per moparts forum guy (very helpful) not sure what the plug is but reccomendation came from the same source as the jetting. SO what do you think??
Posted By: 73rrak
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:00 AM
I had a pretty bad detonation problem with my 512 stealth headed motor 11.3:1 comression. I changed the power valve from a 3.5 to a 5.5 upped the jets by 4 dropped the heat range on the plugs down 2 and got the corn ( ethanol) gas out of it and put pure gas in it. The detonation problem went away. I think getting rid of the corn gas and putting the colder plugs in it made the biggest difference.
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:03 AM
"Stealth Headed" are those aluminum? I hate corn too. Are your heads open or closed chambers? Piston style???
Posted By: ahy
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:06 AM
The change may take you from "beyond the ragged edge" to the ragged edge. With a moderate performance cam, I always figured 9.5 was max with iron heads and little to no quench. You are higher than that "rule of thumb" with your current setup. With Al heads, 10.5 is max. You would be right at that figure with better quench to help.
The upgrade to Al heads/10.5 CR would help but enough? I don't know. If you could use a small dish to get in the low 10's I would say no problem.
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:11 AM
I agree, with the closed chamber heads I could check piston to valve clearance and then mill the heads to get 10 or so. According to the CR calculator I would need to heads down to about 77 cc's to get an even 10. Not sure what that means millingwise but might be possible. Sorry I misread the compression height on the 12 cc pistons so I would get 9.833 with the new heads and the 12 cc dish pistons and .050 quench.
Posted By: Kern Dog
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:27 AM
I have 10.8 to one squeeze in the 493 in the Charger. Edelbrock aluminum heads, MP '509 cam. Performer RPM intake, BG 850 carb and TTI headers. I'm also limited in my advance timing. In my case, its 30-31 degrees. I've been running Champion RC12YC plugs as per the Edelbrock instructions. I have a set of RC9YCs, but I have yet to swap them in. Several members here have suggested colder plugs for my detonation issues. Its been unseasonably cool here lately, so detonation has been limited. I'll swap them in soon though. THEN I'll know if they helped at all.
I've wondered for years: Do you make more power with LESS compression and more spark advance ..... OR more compression and LESS advance?
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:31 AM
I'm sure there is a balance somwhere, seems you would make more usable power without the prescence of detonation since the plugs and combustion chambers should stay cleaner (hopefully).
Posted By: 70SWGR
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:39 AM
Have you thought about running aviation gas?
Posted By: jbc426
Re: Expensive but effective way to fix detonation?? - 06/03/11 06:44 AM
Throw a Snow water injection system on it.
Posted By: 451Mopar
Re: Expensive but effective way to fix detonation?? - 06/03/11 08:56 AM
It's likely the open chamber (no quench) causing the problems more than the compression.
Wayne Smothers DVD on how to supertune your engine talks about the same issue. It is no so much the compression ratio, but the open chamber is allowing multiple flame fronts which collide causing pinging.
Link to Video on Amazon:
http://www.amazon.com/Performance-Engine-Building-Carburetor-Tuning/dp/B002QWJ1DM
Posted By: 73rrak
Re: Expensive but effective way to fix detonation?? - 06/03/11 01:29 PM
Yea the 440 source heads are stealth heads and they are aluminum closed chamber. I don't remember what "piston style" I have
Posted By: HotRodDave
Re: Expensive but effective way to fix detonation?? - 06/03/11 03:58 PM
Cheapest easiest fix it to run 85% corn fuel (E-85) you will make more power and contrary to the guys bashing it on here it help control detonation NOT cause detonation. There are lots of guys running 15 or 16 to one on e-85 with no problem. When I am in OK city visiting my folks I use it in my cars, it is every where down there. I ran it all the time in Tennessee and I wish it was available here. It also carrys more oxygen with it so you can richen up the mix and make more power with no engine mods nessacary so it is way cheaper than tearing you engine apart and replaceing heads and pistons.
Posted By: jbc426
Re: Expensive but effective way to fix detonation?? - 06/03/11 05:57 PM
Quote:
Throw a Snow water injection system on it.
Look here...
http://www.snowperformance.net/product.php?pk=77
Posted By: JohnRR
Re: Expensive but effective way to fix detonation?? - 06/03/11 06:04 PM
Do you have the vacuum advance on the distributor connected ?
You are a little light on max timing advance and that may be making the problem worse because your running a little hot ?
.050 is the edge or getting the advantage of quench , what you have now with the 452's is nothing .
Posted By: Rug_Trucker
Re: Expensive but effective way to fix detonation?? - 06/04/11 02:22 AM
Posted By: Viol8r
Re: Expensive but effective way to fix detonation?? - 06/04/11 04:05 AM
First, you have not told us what plug you are running. There is no reason with that compression you should not be able to run a NGK XR5 type heat range. Something elso is not right here.
What is your ignition system? In order run more advanced timing you need to make sure you have a good ignition. I would start there. I had a very similar combo and actualy had 10:1 with 452 heads and ran 36º total timing.
That MOPAR cam is not helping you out at all. I would consider a change to more modern cut like Lunati Voodoo.
Posted By: dodgeboy11
Re: Expensive but effective way to fix detonation?? - 06/04/11 06:01 AM
Quote:
I have 10.8 to one squeeze in the 493 in the Charger. Edelbrock aluminum heads, MP '509 cam. Performer RPM intake, BG 850 carb and TTI headers. I'm also limited in my advance timing. In my case, its 30-31 degrees. I've been running Champion RC12YC plugs as per the Edelbrock instructions. I have a set of RC9YCs, but I have yet to swap them in. Several members here have suggested colder plugs for my detonation issues. Its been unseasonably cool here lately, so detonation has been limited. I'll swap them in soon though. THEN I'll know if they helped at all.
I've wondered for years: Do you make more power with LESS compression and more spark advance ..... OR more compression and LESS advance?
You make more power with more compression and the least amount of timing. But let me explain my response. The less timing you need the more efficient your combustion chamber is. Notice I said "need". If your engine needs less timing because it's detonating, that doesn't make it an efficient chamber. I built a 360 with magnum R/T heads. Pistons come out of the bores between .003" and .005". .039" head gaskets gives me a fairly tight quench. I was running 39 degrees locked timing because it started fine and I didn't have access to a dyno. Well I finally put it on a chassis dyno and started playing with it. Dropped the timing and it made more power. Finally settled on 34 because I didn't think it'd ever like less. Yanked the motor out to freshen and put it on an engine dyno exactly as it came from the car. Finally made best power at 31 degrees. Proper quench and a good chamber make great power. It never even attempted to detonate that I could hear and there were no indicators upon teardown that detonation was an issue.
Finally built a 440 for my truck. KB flat tops that come out .007-.009" 452 heads and piston to head clearance average about .110" This engine made best power at 38 degrees total. Well, that's where I stopped anyway. My elevation is high enough that the compression isn't an issue. Running cold NGK plugs (can't think of the number offhand) They will load up when it's cold, but once the engine is up to temperature and cleared out, it runs fine.
Ideally, I'd have quench type heads (preferably Victors, Indy or Brodix), pistons that were out .003" and a dyno to sort it all out with. Other than that, all you can do is start at the beginning. Throw in a colder plug. Go extreme if you must and go warmer from there. Keep the timing at 28 degrees and no lower. That'll save your exhaust valves from overheating. If it still detonates, verify your cam timing. Do you have the 108 lobe separation cam or the 112? If the 112, that could be part of your problem. What jets, exactly, are stage 2?
Might be worth taking it to a shop that has a chassis dyno and paying them to sort it out. Make sure they have the equipment to test it with O2 and all that.
Posted By: ademon
Re: Expensive but effective way to fix detonation?? - 06/04/11 07:04 AM
i think its your tune, i run 11.2cr with j heads and 205 cyl psi on 93
Posted By: ademon
Re: Expensive but effective way to fix detonation?? - 06/04/11 07:06 AM
that 484 cam should be bleeding a good amout of cyl psi,
you have your heat crossover blocked correct???
Posted By: 360view
Re: Expensive but effective way to fix detonation?? - 06/04/11 11:52 AM
It is useful to know which of the eight cylinders is detonating.
The inexpensive 'Fires in Oil' sparkplug extension sleeves can be used to find which cylinder is the most prone to pinging.
The extension sleeve has an effect like retarding the ignition timing in that particular cylinder,
plus it adds a couple cc's to the combustion chamber, which slightly drops compression ratio.
Another trick to narrow down the source of detonation is to temporarily use 2 cycle synthetic oil.
This more expensive 'ashless' oil has a much better 'blending' octane rating that 4 cycle oil,
and if the pinging goes away on a test drive with the 2 cycle oil in there, it indicates an oil control problem in one or more cylinders.
Since you are still using a conventional distributor and cap,
once you find the troublesome cylinder(s) it is possible to modify the interior posts on the cylinder cap to retard the ignition timing cylinder by cylinder.
As you approach the 'ideal' ignition timing for a cylinder's performance,
called the 'Mean Best Torque' or MBT timing,
you will find that there is about a six degree span over which torque does not increase or decline... kind of a flat plateau instead of a sharp peak.
The timing needs to be on the 'retarded' edge of this plateau, because unlike torque not changing,
detonation likelihood increases even faster with ignition advance as you approach the limit.
Posted By: RapidRobert
Re: Expensive but effective way to fix detonation?? - 06/04/11 05:23 PM
Quote:
I've wondered for years: Do you make more power with LESS compression and more spark advance ..... OR more compression and LESS advance?
The 1st one. to the OP .050" is no quench the same as .150". When people speak of corn gas (ethanol) they are referring to E10 not E85. E85 (85% ethanol) does have potential. I'd run AV gas or drop the CR w pistons plus the alum heads plus .035"-040" quench 
Posted By: HotRodDave
Re: Expensive but effective way to fix detonation?? - 06/04/11 06:22 PM
E-10 is better than e-0 and e-85 is better than e-10, just a natural progression of improvement with the higher whisky content
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/05/11 07:12 PM
Thanks for all the input. After long hard thought, I am going to go with the 440 Source "Stealth Heads" which have an 80 cc chamber. If I use the KB 184 piston (I now have the 237 and both are a silvolite)i can hone and not bore. The quench pad on the 184 is .140 tall and I figure I will need to have half of that removed to get in the ballpark of .040 to .050 quench and should have a CR of 9.6. I can also deck the heads to get the CR up to 10 if I wanted and still have optimum quench.
Yes my heat risers are blocked and I appreciate all the tips but I feel if I start out with a better combustion chamber design to begin with I will be better off in the long run. I will post again in about 2 months. Anyone have reservations about the 440 Source Stealth heads??
Posted By: JohnRR
Re: Expensive but effective way to fix detonation?? - 06/05/11 10:50 PM
Quote:
Thanks for all the input. After long hard thought, I am going to go with the 440 Source "Stealth Heads" which have an 80 cc chamber. If I use the KB 184 piston (I now have the 237 and both are a silvolite)i can hone and not bore. The quench pad on the 184 is .140 tall and I figure I will need to have half of that removed to get in the ballpark of .040 to .050 quench and should have a CR of 9.6. I can also deck the heads to get the CR up to 10 if I wanted and still have optimum quench.
Yes my heat risers are blocked and I appreciate all the tips but I feel if I start out with a better combustion chamber design to begin with I will be better off in the long run. I will post again in about 2 months. Anyone have reservations about the 440 Source Stealth heads??
Why would you do something as silly as buying pistons and cut the quench domes on them when you already have the piston you need , if you want good quench just have the block decked to put the pistons at zero , it will cost less than buying new pistons and all that machine work ?
edit ... I just reread your original post , put on the stealths , use a .041ish gasket and change the cam, buying pistons is crazy talk ....
Posted By: RapidRobert
Re: Expensive but effective way to fix detonation?? - 06/05/11 11:22 PM
Quote:
Anyone have reservations about the 440 Source Stealth heads??
do have em checked out & maybe buy them thru a board sponsor like Shady Dell & I'd highly recommend some basic porting. Do keep the piston/head (quench) at .040" max to benefit from it.
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/06/11 01:20 AM
If I use the piston I have it puts me @ 10.6 cr with the 80 cc heads and a .039 gasket. I do not want to deck the block as it is a #'s match for the car which is kinda why I like the stealth heads. When you say change the cam, any one in particular and please give reason for doing so. BTW the piston is .010 in the hole now. The 84 cc edelbrock heads would put be compression and quench where it should be but vanity has the better of me so I am using the Stealths.
Posted By: RapidRobert
Re: Expensive but effective way to fix detonation?? - 06/06/11 03:08 AM
Quote:
BTW the piston is .010 in the hole now.
You'd want a .025"-.030" gasket(s) & might check into if you can plunge cut/unshroud the 'source heads to gain some cc's to lower the SCR
Posted By: mr_340
Re: Expensive but effective way to fix detonation?? - 06/06/11 03:10 AM
"As you approach the 'ideal' ignition timing for a cylinder's performance, called the 'Mean Best Torque' or MBT timing,"
Close. "Minimum advance for Best Torque" or "MBT".
http://autospeed.com/cms/title_Knock-Knock-Part-1/A_110829/article.html
Posted By: JohnRR
Re: Expensive but effective way to fix detonation?? - 06/06/11 03:00 PM
Quote:
If I use the piston I have it puts me @ 10.6 cr with the 80 cc heads and a .039 gasket. I do not want to deck the block as it is a #'s match for the car which is kinda why I like the stealth heads. When you say change the cam, any one in particular and please give reason for doing so. BTW the piston is .010 in the hole now. The 84 cc edelbrock heads would put be compression and quench where it should be but vanity has the better of me so I am using the Stealths.
What does it being a matching number block have to do with cutting the deck? I just did the math and you piston is .007 higher than it should be so someone has definitely cut that block considering I see posted on this board that blocks are usually higher than blueprint deck?
Don't worry about the quench if you are stuck on vanity, no one ever did back in the day and the engines performed fine. Plus until you actually have a pair of stealths in your hand I would take the 80cc claim with a grain of salt , they are probably a tad bigger than that .
Posted By: Mr.Yuck
Re: Expensive but effective way to fix detonation?? - 06/06/11 03:28 PM
That thing shouldn't be detonating. 9.7:1 isn't bad. Have you check your distrib? I bet it advancing way past 28* you should be able to run that at 38* all in full at 2400. I run my 11.19:1 440 at 36*. I added a Snow Performance meth kit so I can run 93. It was about $250. If it were me I'd pull the distrib and curve it and have it welded in full around 36-38. No vac advace either.
Posted By: ireland383
Re: Expensive but effective way to fix detonation?? - 06/06/11 03:34 PM
Quote:
Quote:
If I use the piston I have it puts me @ 10.6 cr with the 80 cc heads and a .039 gasket. I do not want to deck the block as it is a #'s match for the car which is kinda why I like the stealth heads. When you say change the cam, any one in particular and please give reason for doing so. BTW the piston is .010 in the hole now. The 84 cc edelbrock heads would put be compression and quench where it should be but vanity has the better of me so I am using the Stealths.
What does it being a matching number block have to do with cutting the deck? I just did the math and you piston is .007 higher than it should be so someone has definitely cut that block considering I see posted on this board that blocks are usually higher than blueprint deck?
Don't worry about the quench if you are stuck on vanity, no one ever did back in the day and the engines performed fine. Plus until you actually have a pair of stealths in your hand I would take the 80cc claim with a grain of salt , they are probably a tad bigger than that .
my older Stealths supposedly were 84 cc and wound up being 86ish. I had them milled .030 to reach 80. I have 9.9:1 with .064 no quench and run 93 with no problems. As said check your distributor.
Posted By: JohnRR
Re: Expensive but effective way to fix detonation?? - 06/06/11 04:59 PM
Quote:
Do you have the vacuum advance on the distributor connected ?
You are a little light on max timing advance and that may be making the problem worse because your running a little hot ?
.050 is the edge or getting the advantage of quench , what you have now with the 452's is nothing .
HELLO ??? Also what ignition system are you using , initial timing is ?
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/07/11 01:40 AM
#'s matching means you can always take it off but you can never get it back (metal on the block, yes it has been decked once) I agree with you that I should get the heads in my hands and truly see what they are, thanks. The guy @ 440 source said it shouldn't be a problem cutting 4cc (that would put me @ 9.8 with .049 quench) out of a bowl without issues but they were unwilling to do it and talking to my machine shop they were VERY uncertain about doing it.
Also the engine is already out of the car so changing plugs and timing or other things are not going to happen. However, I beleive total timing (no va) was about 28, initial was 13-15. MSD box with mallory magnetic pickup, Mallory coil.
Posted By: Mr.Yuck
Re: Expensive but effective way to fix detonation?? - 06/07/11 01:54 AM
Still don't see why you need source heads. What you have should work fine. Even with new heads if your distrib isn't curved right or is advancing way up you'll have the same issues. At 28* you should be able to run a 13.5:1 motor on pump gas...it'd run like poo poo but it'd run. Me thinks you have other issues, like timing and/or fuel delivery. Did you or did you not block off you cross over? running vac advance or not? using a stock distrib or one w/ light springs? I'd mess with that before I dropped $900+ for heads then another $2-300 to have them checked out.
Posted By: Mr.Yuck
Re: Expensive but effective way to fix detonation?? - 06/07/11 02:00 AM
w/ the 6-pack (and I have one) and that cam you should be running a 3.5PV or maybe 4.5. 66 jets, and 31-33 squirtters. also make sure your outboards are opening all the way. If it were me I'd yank the cam and get a good one instead of swapping heads. I was running a 11:1 iron headed 440-6 in this before w/ a 528 M/P solid. Had no detonation issues at all..ran like a MoFo. I had timing in full at 2400 at 36*
Posted By: Viol8r
Re: Expensive but effective way to fix detonation?? - 06/07/11 03:43 AM
You asked "what do you think"?
Dude you have to listen to people in here. I have the TRW .140 dome piston uncut with the stealth heads at 11:1 on pump gas.
Aluminum heads eat a point of compression so you will have effectively an 8:1 motor.
Have fun my friend.
Posted By: ahy
Re: Expensive but effective way to fix detonation?? - 06/07/11 04:07 AM
Quote:
#'s matching means you can always take it off but you can never get it back (metal on the block, yes it has been decked once) I agree with you that I should get the heads in my hands and truly see what they are, thanks. The guy @ 440 source said it shouldn't be a problem cutting 4cc (that would put me @ 9.8 with .049 quench) out of a bowl without issues but they were unwilling to do it and talking to my machine shop they were VERY uncertain about doing it.
Also the engine is already out of the car so changing plugs and timing or other things are not going to happen. However, I beleive total timing (no va) was about 28, initial was 13-15. MSD box with mallory magnetic pickup, Mallory coil.
I think you are on the right track looking for a better combustion chamber/quench. The open chamber 452 and similar heads were an emissions and manufacturing compromise... not a very efficient setup. I run Ed heads and the 440 source are similar. You will get better airflow, more efficient combustion and detonation resistance. .045" - .050" quench helps... .040" is better. It would be worth considering a thinner Cometic gasket (.028" minimum from memory) to get the quench closer to .040 and compression up a bit. A CR in the low 10's should be very robust against detonation with .040 quench and your cam. My
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/14/11 03:52 AM
Got the Stealth Heads Friday. One head is 80-80.5cc and the other is 82-82.5 (spread is lowest to highest chamber). I am going to have my machine shop take them apart and make sure everything is cool before I cut on them.
Question: there is a lot of meat on each side of the plug in the chamber and the plug hole has a protrusion in the casting that covers the threads, other than the fact that the plug may get a little buildup on the threads, does anyone know of any reason I shouldn't remove the protrusion. Remenber I am looking to add cc's to the chamber to lower CR a bit.
Also, I think I'll have the larger volume head decked to get 80 cc and then work on the chambers of all of them to get 84. Splitting hairs?? Overkill??
To get .040 quench here is the cc I would need to get each CR WITH the pistons I have now (KB 237's)
86=10.1
84=10.3
82=10.5
80=10.7
Posted By: ahy
Re: Expensive but effective way to fix detonation?? - 06/14/11 04:07 AM
10.3 CR and .040" quench sounds good. The "rule of thumb" with good quench, street driven and a moderate performance cam is 10.4/10.5 max. Just a touch conservative sounds good. I went with 10.2/.040" quench and it has been very robust against detonation with a
243@.050 intake duration cam. That way if I run it hard and long, or get a tank of less than perfect tank of gas, I shouldn't hurt the engine.
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 06/14/11 04:14 AM
Just took 4cc's out of the bruette and put in in a cup, doesn't look like alot of material, I think just removing the spark plug hump should get me at least 1 cc
Posted By: Mr.Yuck
Re: Expensive but effective way to fix detonation?? - 06/14/11 12:20 PM
did you do anything with your distrib? if not you might have the same issues as before except you're out $900+
Posted By: 360view
Re: Expensive but effective way to fix detonation?? - 06/15/11 03:48 PM
As a rough rule of thumb
the most effective way to increase combustion chamber volume to decrease detonation
is to remove from the exhaust valve side.
On the exhaust side
for performance engines
'de-shrouding'
the exhaust valve surroundings
will increase high lift exhaust flow.
If there is a 'bump' around the sparkplug hole
that looks odd to the casual eye
I would not remove any of that bump
until I had thoroughly researched it.
An odd shape around the sparkplug may be either for increasing turbulence
or
for protecting the sparkplug gap initial spark from being 'blown out'
For example
it is worth looking at the bump around the sparkplug hole of the
stock 1992 Magnum,
RT Magnum and
aluminum Viper combustion chambers.
To my eye
there were subtle changes
that may have been refinements
to 'high swirl'
fast burning performance.
It is also worth asking yourself:
as Squish pushes out a
'tidal wave'
or turbulent gas from either side
where will it mostly head toward,
and will it increase or decrease
clockwise or counterclockwise
spin of the gases?
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 09/25/11 10:00 PM
Car is back together and I think mom would be proud ( she passed away in March and she bought me some car parts!). Used the stealth aluminum heads and left the pistons alone (KB237), used a .020 Cometic gasket that gave me .040 quench, Dist is set up with Vacuum advance running on manifold vacuum which give it 30 degrees at idle, mechanical is all in @ 3000 @ 34 degrees, 1.7 rockers on the exhaust, Mcleod diaphragm clutch, new flywheel, aluminum driveshaft, FBO dist recurve and ignition and a ton of little stuff I hope to forget soon. Stock six pack jetting, may go up a size. Final compression was 10.2 with an 85 cc chamber.
The way it runs now is unbelievable, once the tach hits about 2200 the tone of the exhaust begs you too nail it. Slight gas smell at idle but not bad. I have run about 1/2 tank of 93 through it and there is not a hint of detonation and plugs read just right. My only regret is not doing it sooner and giving my mom a ride. Thanks to all.
Posted By: RapidRobert
Re: Expensive but effective way to fix detonation?? - 09/26/11 02:38 AM
Paul glad that ended up working out well. Did you have anyone check over the guide/seats/valves or were they left untouched.
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 09/26/11 03:37 AM
New, one head cc'd 80 and the other was 83-4. At the recommendation of my machine shop (Boyd Machine Norman OK)they opened up the throat area just under the seat to just slightly smaller than the ID of the seat and then I blended it all in, aluminum is SO much easier to work than cast iron, I had them done in about 3-4 hours using a dremel and a flapper wheel and finished it off with a scotch brite wheel. They then sunk the valves with a 3 angle valve job to get the 85 cc I was after. They did check all the guides too. You could probably run them as is but by the time you pay for the heads ($900) and another $320 for the valve work its still cheaper than some others and they look really good on a stock appearing engine. In my case I also had to take a LOT of material out for pushrod clearance. I have adjustable rockers with a hyd cam.If I had known then what I know now I would have had the machine shop ream that too about .050. I also had to shim the rocker shafts .060 to make the pushrods work out. Not real sure why that was necessary since theoretically I only dropped the head .017 which is the difference between the .037 Fel Pro and the .020 Cometics but it works.
Posted By: JohnRR
Re: Expensive but effective way to fix detonation?? - 09/26/11 02:16 PM
Quote:
I also had to shim the rocker shafts .060 to make the pushrods work out. Not real sure why that was necessary since theoretically I only dropped the head .017 which is the difference between the .037 Fel Pro and the .020 Cometics but it works.
You did that WRONG , you need to look at the wear pattern of the rockers to the valve tips , if you didn't have a geometry problem you may now , you really need shorter pushrods , ASSuMEing the geometry of those heads is correct to begin with.
Posted By: Mr.Yuck
Re: Expensive but effective way to fix detonation?? - 09/26/11 02:50 PM
Quote:
Quote:
I also had to shim the rocker shafts .060 to make the pushrods work out. Not real sure why that was necessary since theoretically I only dropped the head .017 which is the difference between the .037 Fel Pro and the .020 Cometics but it works.
You did that WRONG , you need to look at the wear pattern of the rockers to the valve tips , if you didn't have a geometry problem you may now , you really need shorter pushrods , ASSuMEing the geometry of those heads is correct to begin with.
with those 1.7's I would have had a set of push rods custom made.
Posted By: Spraygoon
Re: Expensive but effective way to fix detonation?? - 09/26/11 03:04 PM
The shims also improved the geometry, I didn't realize I had to go into such detail. The exhaust rockers are 1.6 my mistake