Low RPM/High Load detonation
April 30th, 2011, 11:33 AM
#1
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
Low RPM/High Load detonation
Can you please help me with my ignition timing...
I can't get rid of low rpm/high load detonation. I've retarded initial timing to a point where the engine will overheat at idle, exhaust starts to smell and the carb has to be opened too far (idle speed screw) exposing the transition slot too much...(under 6° initial)....than I would use the stiffest advance springs, and still the engine will detonate when accelerating with WOT from a slow cruise in final gear.
This will only delay the detonation but it would still be there...I can also feel/hear it at WOT/high RPM transmission shifts.
No vacuum advance at this point... just wanted to set in the mech. timing first before tuning in the vacuum advance.
The engine likes about 20° at idle if I disregard the detonation. I get 19in of vacuum at 700rpm, and transition slot exposed just right at 20°, smooth idle. It also responses very good from idle to cruise (up to 2/3 throttle) with about 12° initial, 10° manifold vacuum and medium advance springs, but than I dear not to punch the accelerator from a slow cruise.
The engine... mild, almost stock '76 Olds 455, nothing fancy, J heads, no emmisions, cranking pressure 160psi, the final drive is pretty stiff, 2.41
I've tried gas from 95 to 100 octane and it makes no difference, tried various carb. metering rod/jet/spring combinations (thought I might be running lean)...also no difference.
Any advice will be appreciated!
Thanks!
I can't get rid of low rpm/high load detonation. I've retarded initial timing to a point where the engine will overheat at idle, exhaust starts to smell and the carb has to be opened too far (idle speed screw) exposing the transition slot too much...(under 6° initial)....than I would use the stiffest advance springs, and still the engine will detonate when accelerating with WOT from a slow cruise in final gear.
This will only delay the detonation but it would still be there...I can also feel/hear it at WOT/high RPM transmission shifts.
No vacuum advance at this point... just wanted to set in the mech. timing first before tuning in the vacuum advance.
The engine likes about 20° at idle if I disregard the detonation. I get 19in of vacuum at 700rpm, and transition slot exposed just right at 20°, smooth idle. It also responses very good from idle to cruise (up to 2/3 throttle) with about 12° initial, 10° manifold vacuum and medium advance springs, but than I dear not to punch the accelerator from a slow cruise.
The engine... mild, almost stock '76 Olds 455, nothing fancy, J heads, no emmisions, cranking pressure 160psi, the final drive is pretty stiff, 2.41
I've tried gas from 95 to 100 octane and it makes no difference, tried various carb. metering rod/jet/spring combinations (thought I might be running lean)...also no difference.
Any advice will be appreciated!
Thanks!
April 30th, 2011, 02:36 PM
#3
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
Thanks for the advice!
Been there, done that, ended up at 6° BTDC and 2 heavy springs, ruined the performance and throttle response by doing that and it still detonates at high load...not as much as before though...
Been there, done that, ended up at 6° BTDC and 2 heavy springs, ruined the performance and throttle response by doing that and it still detonates at high load...not as much as before though...
April 30th, 2011, 07:07 PM
#5
Registered User
Join Date: Jan 2010
Location: central Indiana
Posts: 5,231
How much centrifugal advance? Do you have an advance style timing light? Is this an HEI style distributor? I bet you will have to take some total timing out of the distributor to run the 20 degrees of initial timing the engine like. You can weld the slot in the distributor to limit the total advance, kind of hard to explain. If I had any ideal how to post pictures Id show you how to do this.
April 30th, 2011, 07:25 PM
#6
Registered User
Join Date: Jun 2010
Location: Rogues Island, USA
Posts: 3,613
There's no way you should be uncovering that transition slot unless the cam is huge. But then your vacuum shouldn't be as high as you say which goes with your mild build as you described it. I'm confused as to why your vacuum changes depending on what initial lead you use, that shouldn't be. Do you have a vacuum leak? 20 degrees initial is a lot, I'm surprised it cranks over at start up. Your 160psi cranking pressure suggests a mild build it should run fine on low octane. What do you mean the exhaust starts to smell, smells like what? Do you have a possible coolant leak (bad head gasket) and that's what you smell? Anti-freeze in your combustion chamber would rattle and overheat.
April 30th, 2011, 07:29 PM
#7
Registered User
Join Date: Sep 2010
Location: Shorewood, Il.
Posts: 3,057
It's not your timing!!
Athough you've tried different jets, springs, etc. it still sounds to me like a carb problem.
I'd try a different carb form a pre-converter car, as they were set-up entirely different, especially the transition circuit from primary to secondary.
Athough you've tried different jets, springs, etc. it still sounds to me like a carb problem.
I'd try a different carb form a pre-converter car, as they were set-up entirely different, especially the transition circuit from primary to secondary.
April 30th, 2011, 11:52 PM
#8
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
I use an HEI aftermarket distributor, the center plate has 24° advance in it. I started with about 12° initial and added 10° vacuum (manifold) advance at idle. It idles very nice and smooth with this setting, very responsive from dead stop, I just can's hit the "pedal to the metal" as it would start to knock, not as much in 1st and 2nd, as it would at low RPM in 3rd-final gear (automatic) . It sounds and feels like driving over a bih hole on the road. If I turn up the volume of the radio inside the car I can't tell the difference from knocking or driving over a BIG hole. Preignition perhaps? Vacuum at 20-22° at idle and 700rpm is 19in and steady.
The exhaust smells when I retard the initial. It smells like a very, very hot painted metal, I can't smell fuel in the exhaust at any setting. Nor any coolant, smoke of any kind, collant level has been the same for a year or so...
Compression...I guess around 9-1. Perhaps a bit more. I used TRW L2323 pistons, with a very thick gasket, only surface polished the block and heads, J heads.
I started with the Edelbrock Performer on this and went 2 stages richer in cruise and power mode (8%) and used lightest power mode springs. I found no difference altough I also still suspect a carb problem. I now have a stock Q-jet (rebuilt) that acts the same.
One thing does make me go Hmmm... The 1976 Toronado 455 stock smogger engine has 4° initial and uses a 6° (only!) distr. center plate (#365). that makes just 10° total. What's up with that?
The exhaust smells when I retard the initial. It smells like a very, very hot painted metal, I can't smell fuel in the exhaust at any setting. Nor any coolant, smoke of any kind, collant level has been the same for a year or so...
Compression...I guess around 9-1. Perhaps a bit more. I used TRW L2323 pistons, with a very thick gasket, only surface polished the block and heads, J heads.
I started with the Edelbrock Performer on this and went 2 stages richer in cruise and power mode (8%) and used lightest power mode springs. I found no difference altough I also still suspect a carb problem. I now have a stock Q-jet (rebuilt) that acts the same.
One thing does make me go Hmmm... The 1976 Toronado 455 stock smogger engine has 4° initial and uses a 6° (only!) distr. center plate (#365). that makes just 10° total. What's up with that?
May 1st, 2011, 05:17 PM
#10
Administrator
Join Date: Oct 2009
Location: Poteau, Ok
Posts: 40,515
Try setting your timing @ 12 deg btdc and then connect your vacuum advance to the timed side of your carb (basically 0 vacuum at idle). Using 2 heavy springs would not work for most people in the past.
May 1st, 2011, 10:14 PM
#11
Registered User
Join Date: Apr 2011
Posts: 2,703
I use an HEI aftermarket distributor, the center plate has 24° advance in it. I started with about 12° initial and added 10° vacuum (manifold) advance at idle. It idles very nice and smooth with this setting, very responsive from dead stop, I just can's hit the "pedal to the metal" as it would start to knock, not as much in 1st and 2nd, as it would at low RPM in 3rd-final gear (automatic) . It sounds and feels like driving over a bih hole on the road. If I turn up the volume of the radio inside the car I can't tell the difference from knocking or driving over a BIG hole. Preignition perhaps? Vacuum at 20-22° at idle and 700rpm is 19in and steady.
The exhaust smells when I retard the initial. It smells like a very, very hot painted metal, I can't smell fuel in the exhaust at any setting. Nor any coolant, smoke of any kind, collant level has been the same for a year or so...
Compression...I guess around 9-1. Perhaps a bit more. I used TRW L2323 pistons, with a very thick gasket, only surface polished the block and heads, J heads.
I started with the Edelbrock Performer on this and went 2 stages richer in cruise and power mode (8%) and used lightest power mode springs. I found no difference altough I also still suspect a carb problem. I now have a stock Q-jet (rebuilt) that acts the same.
One thing does make me go Hmmm... The 1976 Toronado 455 stock smogger engine has 4° initial and uses a 6° (only!) distr. center plate (#365). that makes just 10° total. What's up with that?
The exhaust smells when I retard the initial. It smells like a very, very hot painted metal, I can't smell fuel in the exhaust at any setting. Nor any coolant, smoke of any kind, collant level has been the same for a year or so...
Compression...I guess around 9-1. Perhaps a bit more. I used TRW L2323 pistons, with a very thick gasket, only surface polished the block and heads, J heads.
I started with the Edelbrock Performer on this and went 2 stages richer in cruise and power mode (8%) and used lightest power mode springs. I found no difference altough I also still suspect a carb problem. I now have a stock Q-jet (rebuilt) that acts the same.
One thing does make me go Hmmm... The 1976 Toronado 455 stock smogger engine has 4° initial and uses a 6° (only!) distr. center plate (#365). that makes just 10° total. What's up with that?
1. Find out how much MECHANICAL advance your distributor has. It should be listed in the Distributor Manual as you stated you have an aftermarket HEI type distributor.
2. Remove the VACUUM advance tube from your carburetor and plug the carburetor vacuum port with a rubber cap
3. Set initial timing so that; INITIAL + TOTAL = <35
In other words, if your distributor has a changeable MECHANICAL advance bushing...find out what bushing is installed and how much ADVANCE it allows. Subtract that number from 35 and then set your INITIAL timing to the remainder. Stock Oldsmobile engines should never see above 35 degrees advance, unless in part throttle cruise where vacuum advance can advance timing up to 50 degrees or so.
I don't know your experience, I apologize if I seem condescending. I'm trying to simplify it as best I can.
May 1st, 2011, 10:21 PM
#12
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
Heavy springs don't work...you're right. The car hesitates from a dead stop and I can feel once the centrifugal advance kicks in just below1000rpm or so. The thing about vacuum advance is I've tried to adjust initial/centr. advance first without any vacuum advance at all (and dial vacuum in later) and it still knocks. Vacuum advance makes no difference at this point other than lowering the idle vacuum/speed and making the engine to run hotter at idle...
Only once I have initial/total in without knocking will I be able to dial in the vacuum advance.
Thanks!
Peter
Only once I have initial/total in without knocking will I be able to dial in the vacuum advance.
Thanks!
Peter
May 1st, 2011, 10:25 PM
#13
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
The HEI I have has 24° of mechanical advance in it. I went as low as 6° initial and the knocking is still there, ebven with heavy springs. Not as much as before though...Only at heavy load/low rpm.
Thanks!
Thanks!
May 1st, 2011, 10:49 PM
#15
Registered User
Join Date: Apr 2011
Posts: 2,703
In any case, there will always be a heavy load on your engine due to the really high (numerically low) gear you have. These are torque monsters but even they have their limit.
May 1st, 2011, 11:26 PM
#17
Registered User
Join Date: Apr 2011
Posts: 2,703
Well, by lowering the initial to 6 deg you are lowering the total. I think what you meant is you'll lower the mechanical advance and then time the initial...
By having a lower mechanical advance bushing it allows more INITIAL timing where the car idles smoothly, but keeps the TOTAL timing the same.
By having a lower mechanical advance bushing it allows more INITIAL timing where the car idles smoothly, but keeps the TOTAL timing the same.
May 3rd, 2011, 12:38 PM
#20
Registered User
Join Date: Jun 2010
Location: Rogues Island, USA
Posts: 3,613
A lean condition would cause overheating and might explain a lot. But if it were that lean you'd notice a surging condition as the car was moving at part throttle. Stuck primary piston in the QJet would cause a lean condition, that's rare though. Everything shows you have a mild build so I'm a bit stumped here. I suppose it could be your carb, rebuilding it can't hurt at this point.
May 3rd, 2011, 12:57 PM
#21
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
It is running a bit hot on the highway, not overheating just hot. The temp climbs up to 200F, 210F on a hot day, on the highway, while it is in the high 180'sF in the city. The thing is the carb is new (rebuilt). I had an Edelbrock Performer before and changing rods, jets and springs didn't make any difference. It knocked just the same before as it is now... And there was never any surging condition.
Retading timing does delay the knocking, but the street "drivebility" goes down the drain at those low timing values.
Retading timing does delay the knocking, but the street "drivebility" goes down the drain at those low timing values.
May 3rd, 2011, 07:54 PM
#22
Registered User
Join Date: Apr 2011
Posts: 2,703
A lean condition would cause overheating and might explain a lot. But if it were that lean you'd notice a surging condition as the car was moving at part throttle. Stuck primary piston in the QJet would cause a lean condition, that's rare though. Everything shows you have a mild build so I'm a bit stumped here. I suppose it could be your carb, rebuilding it can't hurt at this point.
Any way you can give some specifics as to what your build is? Cam, compression, intake, heads, etc.?
May 3rd, 2011, 10:57 PM
#23
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
The engine is from a 1976 Toronado. "J" heads, no EGR, no AIR, only PCV as far as emissions, aftermarket alum. recessed intake much like Toronado's, L2323 TRW pistons but with thick head gaskets, CompCams 260H cam with 112° lobe separation. I used to have JM18-20 at first but it had slightly rough idle and rich exhaust smell at idle and same detonation problems (The new one is really smooth without any smell and performes just as well off idle.)
And that's it...I've tried different carbs I now have a stock '76 Toro Q-jet. I've tried 100octane gas and found no difference. Do you think a booster could make a difference? Might as well try...
The car is a 1981 Cadillac Eldorado (same as the 79-85 Toronado as far as the drivetrain and frame goes) that used to be powered by the 350 Diesel...
The compression with 80ccm heads should be 9.48 according to the piston specs. With "J" heads (80-82ccm) and head gaskets 1/9in thick I ended up lower than that...
One more thing...I used to have stock Delco spark plugs most of the time, R46SZ or SX and recently switched to NGK non resistor1-range colder plugs
(don't have the nuber with me but they fit VW beetle) and the idle is MUCH smoother now. I used to have a bit of exhaust popping at idle before as well. I'll go even colder once I get the NGK R5670-6 plugs I've ordered...
And that's it...I've tried different carbs I now have a stock '76 Toro Q-jet. I've tried 100octane gas and found no difference. Do you think a booster could make a difference? Might as well try...
The car is a 1981 Cadillac Eldorado (same as the 79-85 Toronado as far as the drivetrain and frame goes) that used to be powered by the 350 Diesel...
The compression with 80ccm heads should be 9.48 according to the piston specs. With "J" heads (80-82ccm) and head gaskets 1/9in thick I ended up lower than that...
One more thing...I used to have stock Delco spark plugs most of the time, R46SZ or SX and recently switched to NGK non resistor1-range colder plugs
(don't have the nuber with me but they fit VW beetle) and the idle is MUCH smoother now. I used to have a bit of exhaust popping at idle before as well. I'll go even colder once I get the NGK R5670-6 plugs I've ordered...
May 4th, 2011, 04:45 AM
#24
Registered User
Join Date: Oct 2009
Location: Erie,PA
Posts: 3,814
If you retard the timing too much,it can actually fire out the exhaust,so that smell is probably the exhaust manifolds.I've seen an engine that was too retarded,and the header pipes were actually glowing red at the head flange.The timing was adjusted,and that problem went away.
May 4th, 2011, 08:04 PM
#25
Registered User
Join Date: Apr 2011
Posts: 2,703
The more I think about it, you said that car was a diesel originally and was likely the reason it has 2.45 gear ratio. I am inclined to lean towards the load being put on the engine with such a high gear. The 455 makes a lot of torque but not at the same low RPM that a diesel is going to make it. When you take off with that 2.45 gear you are demanding that a gas engine produce enough torque at 1500-2000 RPM to get that heavy car rolling. I may be way off here but you've checked everything else.
If you're doing 50 mph and drop it a gear and punch it does it still ping?
If you're doing 50 mph and drop it a gear and punch it does it still ping?
May 5th, 2011, 07:11 AM
#27
Connoisseur d'Junque
Join Date: Sep 2010
Location: The Hudson Valley
Posts: 21,183
The more I think about it, you said that car was a diesel originally and was likely the reason it has 2.45 gear ratio. I am inclined to lean towards the load being put on the engine with such a high gear. The 455 makes a lot of torque but not at the same low RPM that a diesel is going to make it. When you take off with that 2.45 gear you are demanding that a gas engine produce enough torque at 1500-2000 RPM to get that heavy car rolling. I may be way off here but you've checked everything else.
If you're doing 50 mph and drop it a gear and punch it does it still ping?
If you're doing 50 mph and drop it a gear and punch it does it still ping?
- Eric
May 5th, 2011, 07:55 AM
#28
Forget an octane booster their useless. If you're using 100 octane that's waaaay more than enough to stop pinging unless your CR is not what you think, or your running waaaaay too lean. Can you borrow a carb from someone and put it on and see what happens?
May 5th, 2011, 08:45 AM
#29
Connoisseur d'Junque
Join Date: Sep 2010
Location: The Hudson Valley
Posts: 21,183
May 5th, 2011, 11:06 AM
#31
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
These cars were also originally equipped with a 350 Olds gas carburated engines, and 79's even have a stiffer 2.19 final drive. Although, Yes, it does feel like the 3rd gear/final drive combo is to stiff...feels like it, I'm not quite sure if that's the real reason behind this. The car weights about 3800lbs...
The original spark plugs R46SX have a 0.080 gap, a lot, I know. The funny thing is, the engine runs much better with these (at idle) than on NGK V gap (XR45) or iridium plugs (XR45IX). And the originals are over 30 years old, used plugs! Ever since I've tried out the B5HS NGK, nonresistior plugs (one range colder) that I found (by the way, they fit a VW Beetle) the car idles smoother. I'll go one range colder with R5670-6 from NGK and see...
I've tried Accel and Pertornix perfomance wires, makes no difference.
A new Q-jet acts the same, or, as you've said, I am waaaaay to lean on both. I'll hook the A/F gauge on and see.
The balancer could be off, It's OEM, bought new and now has some mileage. But even so, I can retard the ignition to the point where the engine is all but useless (whatever that initial at that point is) and it would still detonate at high load/low RPM in 3rd.
If I drive 50mph and manually drop it into 2nd, and punch it...it will not ping. That's exactly what I do when I overtake...
The original spark plugs R46SX have a 0.080 gap, a lot, I know. The funny thing is, the engine runs much better with these (at idle) than on NGK V gap (XR45) or iridium plugs (XR45IX). And the originals are over 30 years old, used plugs! Ever since I've tried out the B5HS NGK, nonresistior plugs (one range colder) that I found (by the way, they fit a VW Beetle) the car idles smoother. I'll go one range colder with R5670-6 from NGK and see...
I've tried Accel and Pertornix perfomance wires, makes no difference.
A new Q-jet acts the same, or, as you've said, I am waaaaay to lean on both. I'll hook the A/F gauge on and see.
The balancer could be off, It's OEM, bought new and now has some mileage. But even so, I can retard the ignition to the point where the engine is all but useless (whatever that initial at that point is) and it would still detonate at high load/low RPM in 3rd.
If I drive 50mph and manually drop it into 2nd, and punch it...it will not ping. That's exactly what I do when I overtake...
Last edited by 455Eldorado; May 5th, 2011 at 12:14 PM.
May 5th, 2011, 07:44 PM
#37
Looks like you covered a lot of the basics, including trying a different carburetor to rule out any issues there. Other items I can think of:
1 - Spark plug heat range. Colder plugs will lessen detonation but you already stated your engine like the 46's more than the 45's. If you have 44's laying around, you can try throwing them in to see if it makes a difference.
2 - Do you have any oil consumption going on? I had a customer come in with the same problem and I found that the intake manifold gasket was leaking and pulling oil out of the engine and sucking it into the cylinders. Top of the pistons were caked with deposits, which effectively raised compression. Cleaned the pistons off, replaced gaskets, and no more problem.
3 - Check spark to make sure it looks like you're getting a strong spark. This happened to me with my 63 Riv. Coil was defective and not giving a strong spark, causing your fuel air charge to ignite late (detonate) instead of when the spark fires. Is your coil new? If you have another good distributor laying around (and coil), you could throw that in to rule out any potential issues coming from your new aftermarket dist. and coil.
5 - A vacuum leak will cause a lean condition and detonation. 19 inches at 700rpm is obviously excellent vacuum. Just to be sure, what do you have hooked up to draw vacuum from your engine? Do you just have the essentials hooked up (vacuum booster, pcv, transmission modulator)? If not, try leaving the rest disconnected to rule out any potential issues and then retest to rule out any other issues. Condition of all your vacuum hoses?
Make one change at a time and see if any of these makes a difference. Hope this info helps! Good luck and keep us posted.
1 - Spark plug heat range. Colder plugs will lessen detonation but you already stated your engine like the 46's more than the 45's. If you have 44's laying around, you can try throwing them in to see if it makes a difference.
2 - Do you have any oil consumption going on? I had a customer come in with the same problem and I found that the intake manifold gasket was leaking and pulling oil out of the engine and sucking it into the cylinders. Top of the pistons were caked with deposits, which effectively raised compression. Cleaned the pistons off, replaced gaskets, and no more problem.
3 - Check spark to make sure it looks like you're getting a strong spark. This happened to me with my 63 Riv. Coil was defective and not giving a strong spark, causing your fuel air charge to ignite late (detonate) instead of when the spark fires. Is your coil new? If you have another good distributor laying around (and coil), you could throw that in to rule out any potential issues coming from your new aftermarket dist. and coil.
5 - A vacuum leak will cause a lean condition and detonation. 19 inches at 700rpm is obviously excellent vacuum. Just to be sure, what do you have hooked up to draw vacuum from your engine? Do you just have the essentials hooked up (vacuum booster, pcv, transmission modulator)? If not, try leaving the rest disconnected to rule out any potential issues and then retest to rule out any other issues. Condition of all your vacuum hoses?
Make one change at a time and see if any of these makes a difference. Hope this info helps! Good luck and keep us posted.
May 6th, 2011, 06:37 AM
#38
Registered User
Thread Starter
Join Date: Oct 2010
Posts: 35
Thanks for the post Darrell1
1. I have a new set of colder spak plugs. I'll replace them over the weekend and see what that does...
2. No oil consumption. Less than half a quart per 6000+ miles oil change
3. I had some exhaust popping and idle miss. before I changed the spark plugs. That's why I replaced the spark plug wires and tried all sort of combos with coils, modules, reluctors, and tried with new and rebuilt HEIs. They all perform the same apart from the advance setup
4. All the hoses are new. I use Hydroboost brakes (a diesel setup) that run from the PS pump. I only have cruise control and AC/heater hooked to vacuum. I will disconect the two and give it a try...although I think I did that already a while ago.
I thought it might be the PCV valve, since the engine acts kinda like it has a vacuum leak, but only at low manifold vacuum. The PCV could open to much (wrong flow range) at WOT and make it run lean. I disconected the PCV and plugged the carb port but there was no difference...
Peter
1. I have a new set of colder spak plugs. I'll replace them over the weekend and see what that does...
2. No oil consumption. Less than half a quart per 6000+ miles oil change
3. I had some exhaust popping and idle miss. before I changed the spark plugs. That's why I replaced the spark plug wires and tried all sort of combos with coils, modules, reluctors, and tried with new and rebuilt HEIs. They all perform the same apart from the advance setup
4. All the hoses are new. I use Hydroboost brakes (a diesel setup) that run from the PS pump. I only have cruise control and AC/heater hooked to vacuum. I will disconect the two and give it a try...although I think I did that already a while ago.
I thought it might be the PCV valve, since the engine acts kinda like it has a vacuum leak, but only at low manifold vacuum. The PCV could open to much (wrong flow range) at WOT and make it run lean. I disconected the PCV and plugged the carb port but there was no difference...
Peter
Last edited by 455Eldorado; May 6th, 2011 at 06:44 AM.
May 6th, 2011, 06:46 AM
#39
Connoisseur d'Junque
Join Date: Sep 2010
Location: The Hudson Valley
Posts: 21,183
I'm starting to wonder if you don't need to pull a head, cc the combustion chambers, and see if you don't have higher compression than you think you have - it'd be less effort than all of the other stuff you've done already.
- Eric
- Eric
May 6th, 2011, 06:47 AM
#40
Registered User
Join Date: Jun 2010
Location: Rogues Island, USA
Posts: 3,613
You mentioned exhaust popping. Does this happen when you let off the throttle? If so that is a clear indication of a lean mixture. You'll see this when people put headers on the car without richening the primary jets. Putting headers on and richening the primaries is not always a given. Sometimes you can get away with it and not have to do this but not often. Making the exhaust flow more efficient usually requires some sort of enrichment. It has a distinct popping sound when they let off the gas. I know everyone here has heard this at some time or another.
