[mudbone64]

I have a completely stock '72 454. When I say completely stock I mean it has oval port heads, cast-iton intake, a 9:1 compression ratio (I believe), exhaust manifolds and a quadrajet. About a year ago I replaced the camshaft and have only recently began the exercise of getting the engine running up to par. I am experiencing some detonation and was wondering if anyone has an idea of how much initial and total timing I should be using. This is a link for my camshaft specs.
http://www.compcams.com/Technical/Search/CamDetails.asp?PartNumber=11-207-3

I am by no means an engine specialist so any help concerning this matter is greatly appreciated.

Thanks,
Gene

 

[Schurkey]

Like most other engines; "about" 35 degrees total timing all in by ~3000 RPM, + as much vacuum advance as it will tolerate without part-throttle ping. Mild cams want low initial and more centrifugal; wild cams want more initial and less centrifugal. Either way, you end up with that "middle 30's" total.

Use ported (timed) vacuum OR manifold vacuum for the vacuum advance, whichever the engine seems to prefer.

 

[SWHEATON]

With that cam approx 18 deg initial + 18 deg mech in by 2800-3krpm max = 36 total. Then a vac adv that gives you approx 10-14 additional deg timing depeding on what it will tollerate as mentioned above & i assume your running 93 otc fuel ,yes even for your 9:1 comp.

But since its already detonating and i dont know what initial & total your currently running i would suspect off the bat you need les vac adv.

But with that said set it for 18 initial and then chk total,if not 36 deg at 3k rpm or if goes over 36 deg total when reved past 3kr rpm you need to have the mech adv in the dist limited to 18 deg in by 2800-3k rpms.

Then aftre you get the initial & mech in dist setup correctly for 36 total road test it with vac adv unhooked/plugged and that hopefully doesnt detonte. If that pings back off the initial 2 deg and hopefully the ping will stop again assuming 93 fuel.

Only after getting the inital & total dialed in with no ping is when you should experiemnt with the vac adv.

Since your having detonation issues i would get a vac adv from NAPA thats fully activated at min of 2" lower then the motors lowest idle vac (in gear for auto trans) that only gives you 10-12 deg max additional adv. Then the total 36 deg + 12 deg max = 48 deg for part throttle cruise.

I know that 48 deg cruise timing is a little low (usually 50-54 deg) but i am trying to be conservative to keep you out of detonation since your already experiencing it which can damage your motor. Id rather have you loose a smidge of cruise rpm perf then be silently detonating where you cant hear it casing damage over time.

But as you know the vac adv goes away @ WOT when intake is very low and thats when the total timing of 36deg will be present.

scott

 

[mudbone64]

With that cam approx 18 deg initial + 18 deg mech in by 2800-3krpm max = 36 total. Then a vac adv that gives you approx 10-14 additional deg timing depeding on what it will tollerate as mentioned above & i assume your running 93 otc fuel ,yes even for your 9:1 comp.

But since its already detonating and i dont know what initial & total your currently running i would suspect off the bat you need les vac adv.

But with that said set it for 18 initial and then chk total,if not 36 deg at 3k rpm or if goes over 36 deg total when reved past 3kr rpm you need to have the mech adv in the dist limited to 18 deg in by 2800-3k rpms.

Then aftre you get the initial & mech in dist setup correctly for 36 total road test it with vac adv unhooked/plugged and that hopefully doesnt detonte. If that pings back off the initial 2 deg and hopefully the ping will stop again assuming 93 fuel.

Only after getting the inital & total dialed in with no ping is when you should experiemnt with the vac adv.

Since your having detonation issues i would get a vac adv from NAPA thats fully activated at min of 2" lower then the motors lowest idle vac (in gear for auto trans) that only gives you 10-12 deg max additional adv. Then the total 36 deg + 12 deg max = 48 deg for part throttle cruise.

I know that 48 deg cruise timing is a little low (usually 50-54 deg) but i am trying to be conservative to keep you out of detonation since your already experiencing it which can damage your motor. Id rather have you loose a smidge of cruise rpm perf then be silently detonating where you cant hear it casing damage over time.

But as you know the vac adv goes away @ WOT when intake is very low and thats when the total timing of 36deg will be present.

scott

Before I get too far let me first thank you for your response. I am using 93 octane fuel. Are you saying that my initial timing without the advance being hooked up should be approximately 18 degrees BTDC? I had my timing set at the stock spec of 8 degrees BTDC (advance plugged) and reduced it to about 5 (advance plugged) and I'm still encountering some detonation.

Again any help you can give is greatly appreciated.

Thanks,

Gene

 

[mudbone64]

With that cam approx 18 deg initial + 18 deg mech in by 2800-3krpm max = 36 total. Then a vac adv that gives you approx 10-14 additional deg timing depeding on what it will tollerate as mentioned above & i assume your running 93 otc fuel ,yes even for your 9:1 comp.

But since its already detonating and i dont know what initial & total your currently running i would suspect off the bat you need les vac adv.

But with that said set it for 18 initial and then chk total,if not 36 deg at 3k rpm or if goes over 36 deg total when reved past 3kr rpm you need to have the mech adv in the dist limited to 18 deg in by 2800-3k rpms.

Then aftre you get the initial & mech in dist setup correctly for 36 total road test it with vac adv unhooked/plugged and that hopefully doesnt detonte. If that pings back off the initial 2 deg and hopefully the ping will stop again assuming 93 fuel.

Only after getting the inital & total dialed in with no ping is when you should experiemnt with the vac adv.

Since your having detonation issues i would get a vac adv from NAPA thats fully activated at min of 2" lower then the motors lowest idle vac (in gear for auto trans) that only gives you 10-12 deg max additional adv. Then the total 36 deg + 12 deg max = 48 deg for part throttle cruise.

I know that 48 deg cruise timing is a little low (usually 50-54 deg) but i am trying to be conservative to keep you out of detonation since your already experiencing it which can damage your motor. Id rather have you loose a smidge of cruise rpm perf then be silently detonating where you cant hear it casing damage over time.

But as you know the vac adv goes away @ WOT when intake is very low and thats when the total timing of 36deg will be present.

scott

Before I get too far let me first thank you for your response. I am using 93 octane fuel. Are you saying that my initial timing without the advance being hooked up should be approximately 18 degrees BTDC? I had my timing set at the stock spec of 8 degrees BTDC (advance plugged) and reduced it to about 5 (advance plugged) and I'm still encountering some detonation.

Again any help you can give is greatly appreciated.

Thanks,

Gene

 

[SWHEATON]

Yes Gene,with your comp aftermarket perf cam approx 18 initial is where you should be,if the motor is detonating with only 5 deg initial & 93 fuel something is wrong.

Is it possible you have a lot more compression then you think or the motor is all carboned up increasing the compression?

Possibly the outter ring on the harmonic ballencer has slipped and its not giving you correct timing #'s?

The motor should run like a slug being approx 13 deg retarded on the inital timing not to mention running hotter too due to the overly retarded initial timing.

You need to verify that the harm ballencer & the timing tab on timing cover are ok/correct/accurate. If you dont find any issues with thoses items then you may need to verify if the new cam you installed a while back was lined up correctly .

The cam you have is only 224 deg dur @.05 ,i am running 222 deg dur @.05 in 50 cubes less motor with 9:8 comp and it has high cyl pressure with oner 200psi static cranking compression. Just for ha ha's take a comp test a couple cyls to see what it is,if your cranking compression is over 9:0 it should be pretty high with that mild cam. Make sure to disable the ign and hold primary & secondary wide open with taking the comp test. If you have readings of approx 180-200+psi your cam timing is short for compression being run causing high cyl pressure and you would simply need to install more cam to bleed off some cyl pressure. The comp test is not a great indicator of comp ratio but it gives you an idea if you do in fact have high static cranking comp so chk a couple cyl's & let us know what you find out. you basically running the same cam in a motor 54 cubes larger and can cause higher cyl pressures leading to detonation which i have been warning people about choosing too mild of cams for todays crap fuel to handle since my experience. I used the cam that my machinest & others rec just to find out i was correct in not aggreeing with them and should have listened to mytself and installed a little more cam but i listened to the experienced machinest and got burned with 200psi + cranking comp/not pump gas friendly.

Scott

 

[mudbone64]

Yes Gene,with that comp cam approx 18 initial is where you should be,if the motor is detonating with only 5 deg initial & 93 fuel something is wrong.

Is it possible you have a lot more compression then you think or the motor is all carboned up increasing the compression?

Possibly the outter ring on the harmonic ballencer has slipped and its not giving you correct timing #'s?

The motor should run like a slug being approx 13 deg retarded on the inital timing not to mention running hotter too due to the overly retarded initial timing.

You need to verify that the harm ballencer & the timing tab on timing cover are ok/correct/accurate. If you dont find any issues with thoses items then you may need to verify if the new cam you installed a while back was lined up correctly .

The cam you have is only 224 deg dur @.05 ,i am running 222 deg dur @.05 in 50 cubes less motor with 9:8 comp and it has high cyl pressure with oner 200psi static cranking compression. Just for ha ha's take a comp test a couple cyls to see what it is,if your cranking compression is over 9:0 it should be pretty high with that mild cam. Make sure to disable the ign and hold primary & secondary wide open with taking the comp test. If you have readings of approx 180-200+psi your cam timing is short for compression being run causing high cyl pressure and you would simply need to install more cam to bleed off some cyl pressure. The comp test is not a great indicator of comp ratio but it gives you an idea if you do in fact have high static cranking comp so chk a couple cyl's & let us know what you find out. you basically running the same cam in a motor 54 cubes larger and can cause higher cyl pressures leading to detonation which i have been warning people about choosing too mild of cams for todays crap fuel to handle since my experience. I used the cam that my machinest & others rec just to find out i was correct in not aggreeing with them and should have listened to mytself and installed a little more cam but i listened to the experienced machinest and got burned with 200psi + cranking comp/not pump gas friendly.

Scott

Scott,
I re-checked my initial timing last night and it was actually closer to 6 degrees BTDC. I can't stress enough about how hard it is to se my timing scale. When my engine was disassembled I cleaned all of the carbon from the cylinder heads so I don't think that is the problem. The pistons are simple flat-tops and the stroke is also stock so I am inclined to believe the factory compression ratio of 9:1.

I suppose it's possible for the balancer to have slipped leading to faulty ignition timing numbers. I may have to order/make a piston stop to verify the balancer's relative position to the timing scale. Though I'm not 100 percent sure, I think the timing tab/scale was spot welded to the timing chain cover from the factory, therefore it would be impossible for the timing tab to have moved. However, I am going to check the balancer and the scale in order to verify all is well in that department. The camshaft was "degreed-in" and checked and double checked by a competent engine builder so I don't think there's a problem there either.

Before the engine was dissassembled I had no cooling issues what so ever. Now after the block was cleaned and the radiator was re-cored the engine does want to run hotter (up to 210 degrees) than ever so there is some issue there. Now I'm wondering if the 12 degrees of retarded timing itself is increasing my engine temperature and therefore causing the engine to detonate?

I will perform a compression test as you instruct to check for high cylinder pressures. In the meantime here are my timing numbers taken last night:
Initial timing: 6 degrees
Initial timing with advance connected: 32 degrees
Total timing with advance disconnected: 32 degrees +/- at 2,900 r.p.m.
Total timing with advance connected: approximately 43 degrees (I ran out of timing tape at 40 degrees) at 2,900 r.p.m.

Again I want to thank you for all of your help. I'm going to do some additional checking and testing and I'll post my findings.

Thanks again,
Gene
Here's a visual:

 

[SWHEATON]

When running only 6 initial and 32 total with that mild perf cam i bet your loosing a fair amount of power/perf ,you should be at approx 18 initial/36 total/and then a vac adv with approx 10-12 more deg timing for at part throttle cruise.

You need to pull the dist to have the mech adv recurved for 18 in by 2800-3krpm.

Then you can run 18 initial/18 mech that will give to approx 36 total by 2800-3krpm which is a good ign curve to run with that cam along the vac adv.

But again if your motor truely has 9:1 comp thats not real high but your running lower 91 oct too which isnt very good or very high octane fuel either and the cam you running in your 454 is fairly short on duration for a 454 so you could still be buidling enough cyl pressure to detonate on 91 fuel so keep that in mind.

Unfortunately its looking as though you may need to run some octaine booster to keep it out of ping becausee 91 oct fuel isnt enough octane for your motor with a fairly short dur cam even with 9:1 comp IMHO. If you dont put a ton of miles on each yr it should not be a huge additional cost to run the booster. I would rather run a real quality booster that increases the octane in full pt's then run that motor with only 6 deg inital/32 total with a perf cam,that would make it be a real slug & use more fuel when running the initial/total retartded by 10-12 deg inital & 4 deg total IMHO.

Trust me when i say if you setup the ign timing curve like i stated and run booster so t wont ping you will think there is a new motor under the hood with the additional 10-12 deg initial & 4 deg more total,that will really wake upthat 454 with the mild perf cam your running.

Now the additional initial will tell you just how good you starter/battery/alt,etc are when it comes to hot starts with a bbc & a lot of inital timing that the perf cam needs.

Scott

 

[mudbone64]

Scott,
Your wealth of information is definately appreciated. When I get some additional test results in I'll make certain I post them here. I was just wondering if you've considered a Kentucky vacation? I've got a CR250 with your name all over it. It sits very near to the toolbox. The toolbox also has your name all over it.

Thanks again,
Gene

 

[bochnak]

Like Scott mentioned, you may want to recurve distributor. Are you running points or HEI? There are kits out there that sell for about $8.

Basically, you have 26° mechanical right now. Your engine would probably like around 20°. This will let you bring the initial up with out affecting the total.

You also have 26° of vacuum advance which is very high. You may want to find a can that will only add 16°, (mechanical 36° + vacuum 16° = 52° for cruise).


Search for “ignition 101”, a lot of info on vac adv cans to suit your engine’s needs.

Also, does it detonate if you drive around with the vac adv disconnected?

 

[mudbone64]

Like Scott mentioned, you may want to recurve distributor. Are you running points or HEI? There are kits out there that sell for about $8.

Basically, you have 26° mechanical right now. Your engine would probably like around 20°. This will let you bring the initial up with out affecting the total.

You also have 26° of vacuum advance which is very high. You may want to find a can that will only add 16°, (mechanical 36° + vacuum 16° = 52° for cruise).


Search for “ignition 101”, a lot of info on vac adv cans to suit your engine’s needs.

Also, does it detonate if you drive around with the vac adv disconnected?

I currently have the original distributor with the points. I don't want to use an HEI because I'll loose my tachometer. I very well may wind up performing one of the Petronix conversions. At one time I did block off the advance to see what the affect would be on the detonating problem. Though I can't remeber for sure I think the engine didn't detnoate. I'm going to do some more testing on the engine tonight and I'm going to take the car for a quick spin with the advance blocked off and I'll post the results tomorrow.

Even if I can't get this problem solved this thread has been some great exposure and great fun.

Thanks to all (again)

Gene

 

[bochnak]

I currently have the original distributor with the points. I don't want to use an HEI because I'll loose my tachometer. I very well may wind up performing one of the Petronix conversions. At one time I did block off the advance to see what the affect would be on the detonating problem. Though I can't remeber for sure I think the engine didn't detnoate. I'm going to do some more testing on the engine tonight and I'm going to take the car for a quick spin with the advance blocked off and I'll post the results tomorrow.

Even if I can't get this problem solved this thread has been some great exposure and great fun.

Thanks to all (again)

Gene

You will solve this problem....and a HEI has a tach hookup.

Also, when does it detonate? Cruise? WOT? If it pings under WOT, then vac adv can be ruled out since vacuum goes to zero.

 

[mudbone64]

You will solve this problem....and a HEI has a tach hookup.

Also, when does it detonate? Cruise? WOT? If it pings under WOT, then vac adv can be ruled out since vacuum goes to zero.

Can you get a cable-drive HEI tach-drive distributor? Generally the engine detonates just upon accelleration.

 

[kettbo]

Gene,

You'll play hell getting an HEI into the Vette. Run the stock unit with a Pertronix conversion kit like I do or the Crane unit with the rev limiter. I've run the Pertronix for several years now, no issues.
Link to pics in my signature.
I run my timing at 16+20 around town and 18 or more+20 when I'm feeling naughty.
Your high temps are due to not enough initial. I had a BUNCH of adv in my distributor eliminated with a bronze bushing on the limiter shaft and some creative peening on the open end of the adv slot.

 

[gearbanger]

Mudbone,

I agree with all that is said here. Man your engine looks good. Whoever you have doing the work must be a real professional. I sent my distributor to a guy in Memphis to get it recurved, it turned out really nice. You need to find a guy with a Sun distrutor machine. It allows you to spin the distrutor on the bench and set it up the way you want it. You can get a adjustable vac can from crane or msd or others. You can set it to give you just the right amount of vacuum advance after you get the mechanical dialed in.

 

[mudbone64]

Gene,

You'll play hell getting an HEI into the Vette. Run the stock unit with a Pertronix conversion kit like I do or the Crane unit with the rev limiter. I've run the Pertronix for several years now, no issues.
Link to pics in my signature.
I run my timing at 16+20 around town and 18 or more+20 when I'm feeling naughty.
Your high temps are due to not enough initial. I had a BUNCH of adv in my distributor eliminated with a bronze bushing on the limiter shaft and some creative peening on the open end of the adv slot.

I'm not really in the mood to install an HEI in my 454. It probably won't fit under the ignnition shielding and if there is a performance loss due to the points distributor then I'm willing to accept it. In order to simplify my life I will probably at some point install the Petronix conversion.

Thanks for the information,

Gene

 

[bochnak]

I didn't realize it was a cable driven tach. I only have dealt with HEI's.

 

[mudbone64]

Unfortunately I have no new news since yesterday. I had a lifter that would "peck" upon start-up and decided to re-adjust it last night. Upon the removal of my valve cover I noticed I had a big split in the valve cover gasket so I'm kinda dead in the water until I get some gaskets.

Gene

 

[mudbone64]

The cam you have is only 224 deg dur @.05 ,i am running 222 deg dur @.05 in 50 cubes less motor with 9:8 comp and it has high cyl pressure with oner 200psi static cranking compression. Just for ha ha's take a comp test a couple cyls to see what it is,if your cranking compression is over 9:0 it should be pretty high with that mild cam. Make sure to disable the ign and hold primary & secondary wide open with taking the comp test. If you have readings of approx 180-200+psi your cam timing is short for compression being run causing high cyl pressure and you would simply need to install more cam to bleed off some cyl pressure. The comp test is not a great indicator of comp ratio but it gives you an idea if you do in fact have high static cranking comp so chk a couple cyl's & let us know what you find out.
Scott

Scott,
Well, I'm almost ready to pull the engine now. Just kidding, although it does seem that way with everything I've removed from the engine. I waited until I saw the last available parts store on my way home last night before I stopped to get some valve cover gaskets and wouldn't you know it, they had none. Well all was not lost as I removed all of my spark-plugs (no easy chore for sure) in order check my timing marks and also to perform an abbreviated compression test. I checked the compression on cylinders 1, 5 & 7 and the compression worked out to be 150 p.s.i. for all three. Cylinder number 3 was obscured by the steering box and I was unsuccessful in checking it.

Now I'm wondering about how to make a piston stop. I'm concerned that if I simply screw a bolt into the cylinder too far it could stop the valve actuaction rather than stopping the piston. Do you have any advice concerning this?

 

[SWHEATON]

To be safe i would buy a piston stop from jegs/summit,etc thats mfg not to interfear .

Scott