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Username Post: Does 42 degrees total timing sound excessive for SBC?        (Topic#184852)
DZ302LC 
Member
Posts: 166

Reg: 03-29-04
03-17-08 11:29 AM - Post#1390084    

I have a high revving huge bore tiny stroke 11:1 SBC complete with 40lb crank and all the other light weight stuff. It's a Solid roller with a pretty healthy high lift cam. It's currently set at 38 degrees total (locked) timing. I've not really heard of many engines requiring more than 38 degrees, yet my engine builder said it may well like 40 or even 42 degrees. First of all, is that excessive. And second of all, how will I know when I've got it right? Short of a dyno, can I tell seat of the pants or possibly by ear?? Any help or explanation would be appreciated. Thanks

 
smasher0219 
Senior Member
Posts: 863

Loc: joisey
Reg: 06-09-03
03-17-08 12:08 PM - Post#1390132    
    In response to DZ302LC

You'll know when it's pulling in 2nd or 3rd gear. If you hear something like rocks shaking in a coffee can, then you are detonating and need to back off the timing.

You also have the timing too advanced if your starter struggles to turn over the motor.

Too little advance will mostly cause a bog on hard accelleration, sputtering, and poor performance.

40 or 42 degrees is a little much unless you're running race fuel, especially with an 11:1 motor.

 
ZZiggy 
Senior Member
Posts: 655
ZZiggy
Loc: Joplin,MO
Reg: 04-18-02
03-17-08 12:51 PM - Post#1390164    
    In response to smasher0219

You may find 42-44 very helpful in first gear, 38 or so in 2nd and 36 in 3rd.
Locked timing isn't an answer its a crutch.

High gear retard can help.
A low cost way back in the dual point days was to use both points in low and only one set in high it retards the timing a few degrees.
71 Camaro 355 NA
11.1650 @ 119.30
1.5028


 
smasher0219 
Senior Member
Posts: 863

Loc: joisey
Reg: 06-09-03
03-17-08 01:18 PM - Post#1390184    
    In response to ZZiggy

How do you get variable timming with a HEI?

 
sgian 
Valued Contributor
Posts: 4524
sgian
Loc: MO
Reg: 12-25-03
03-17-08 04:02 PM - Post#1390299    
    In response to smasher0219

by locked do you mean that the mechanical advance is locked in place, so that you get 38* all of the time? The only time I saw a chevy engine idle nicely at over 40* was an engine with a cracked head---it needed the extra timing because of all the water in the mix.
90 C1500, 05 Tahoe 4WD


 
55chevy383 
Senior Member
Posts: 1302
55chevy383
Age: 45
Loc: Noble, Ok.
Reg: 12-08-05
03-17-08 04:49 PM - Post#1390348    
    In response to sgian

You may not feel it in the seat of your pants, but look at your MPH, if you're racing it at the track. An increase in MPH, means your getting more power a decrease means your losing power, this assumes a consistent launch, track prep, etc. A horsepower increase will always show as an increase in MPH on the top end.

Phil
11.66 @ 115 N/A.
Phil's '55


 
DZ302LC 
Member
Posts: 166

Reg: 03-29-04
03-17-08 05:30 PM - Post#1390398    
    In response to 55chevy383

Yes, I mean locked as in a constant 38 degrees. And yes, I know that locked timing is not ideal. I should explain that I plan on converting to sequential fire EFI, so the locked timing via the crank trigger will turn into computer controlled timing soon. I just want some time to dial the new motor in with a carb first. But yes, I am running race fuel. So basically, what my dad use to say is true? Advance the timing until you hear it pinging and then back it off?

 
sgian 
Valued Contributor
Posts: 4524
sgian
Loc: MO
Reg: 12-25-03
03-18-08 06:53 AM - Post#1390835    
    In response to DZ302LC

that's one way to do it, advance till it pings and back off.

don't you get hard starting and poor idle at 38*? it sounds like something may be wrong if you don't.
90 C1500, 05 Tahoe 4WD


 
ChevroletR 
Senior Member
Posts: 341
ChevroletR
Loc: Mt. Airy, Maryland
Reg: 01-24-03
03-18-08 08:38 PM - Post#1391518    
    In response to sgian

I was just about to make a post like this one! I bought myself an Actron adjustable timing light like this one: to check my total timing on my very mild 383 and at 2500-3000 RPMS, when I adjust the light all the way until my mark on my balancer lines up with the mark on the timing tab, the timing light reads 45 degrees! Am I doing this right or could something be off from my balancer or timing tab? The engine cranks easily when starting and runs like a champ. I was just checking it for my own curiousity and 45 degrees just doesn't sound correct. Help is also appreciated. Thanks
1970 Monte Carlo
1988 Buick Reatta
1994 S-10
1984 Buick Regal
1995 S-10
1995 Caprice
2002 Avalanche
2008 Yamaha Raider


 
Vaughn 
"12th Year" Gold Supporting Member
Posts: 14662

Loc: Colorado Springs, CO
Reg: 08-08-04
03-18-08 09:30 PM - Post#1391577    
    In response to ChevroletR

36 degrees total is the normal limit on a SBC. There are instances when you might want to exceed that, but it is almost always in race motors.

 
sgian 
Valued Contributor
Posts: 4524
sgian
Loc: MO
Reg: 12-25-03
03-19-08 06:50 AM - Post#1391731    
    In response to Vaughn

At 2500 to 3000 rpm 36 degrees total (initial + mechanical) is fine. For 45*, are you sure that you disconnected the vacuum advance before checking total timing?

At idle, like 600 to 1000 rpm, 38* timing is normally excessive unless there is something wrong. On a normal engine, that could lead to hard starting, detonation, overheating, bad idle, and dieseling among other things.
90 C1500, 05 Tahoe 4WD


 
ChevroletR 
Senior Member
Posts: 341
ChevroletR
Loc: Mt. Airy, Maryland
Reg: 01-24-03
03-19-08 11:31 AM - Post#1391901    
    In response to sgian

After finding my original post, I read where I was suppose to disconnect vacuum advance and I don't think I tried that. How much will that add? The reason I'm asking is because it won't be until May before I can check it again because I'm 10 hours from home at school and I'm really curious what I have. Thanks
1970 Monte Carlo
1988 Buick Reatta
1994 S-10
1984 Buick Regal
1995 S-10
1995 Caprice
2002 Avalanche
2008 Yamaha Raider


 
sgian 
Valued Contributor
Posts: 4524
sgian
Loc: MO
Reg: 12-25-03
03-19-08 08:00 PM - Post#1392265    
    In response to ChevroletR

it varies
90 C1500, 05 Tahoe 4WD


 
ChevroletR 
Senior Member
Posts: 341
ChevroletR
Loc: Mt. Airy, Maryland
Reg: 01-24-03
03-19-08 09:57 PM - Post#1392325    
    In response to sgian

Ah, oh well. I'll just have to go back and check it. Thanks
1970 Monte Carlo
1988 Buick Reatta
1994 S-10
1984 Buick Regal
1995 S-10
1995 Caprice
2002 Avalanche
2008 Yamaha Raider


 
Vaughn 
"12th Year" Gold Supporting Member
Posts: 14662

Loc: Colorado Springs, CO
Reg: 08-08-04
03-20-08 09:37 AM - Post#1392595    
    In response to ChevroletR

Vacuum advance effects drop off as you open the throttle (ie, vacuum drops off as you open the throttle). So, there is less and less effect from it as you get higher in the rpm band.

Vacuum advance will affect base timing (4-12 btdc), but will have little effect on the overall total timing. This is why you want to plug it when adjusting base timing, because it has the greatest effect at idle.

 
smasher0219 
Senior Member
Posts: 863

Loc: joisey
Reg: 06-09-03
03-20-08 11:05 AM - Post#1392647    
    In response to Vaughn

Head to Advance Auto or NAPA or elsewhere and RENT a timing light for about $10 for the day.

 
ChevroletR 
Senior Member
Posts: 341
ChevroletR
Loc: Mt. Airy, Maryland
Reg: 01-24-03
03-20-08 11:30 AM - Post#1392669    
    In response to smasher0219

Funny you mention auto parts stores...I work at Advance Auto Parts and have for 5 years now, but we don't rent Timing lights. Sounds like an AutoZone thing though, I know they do more rentals than we do.
1970 Monte Carlo
1988 Buick Reatta
1994 S-10
1984 Buick Regal
1995 S-10
1995 Caprice
2002 Avalanche
2008 Yamaha Raider


 
sgian 
Valued Contributor
Posts: 4524
sgian
Loc: MO
Reg: 12-25-03
03-20-08 07:03 PM - Post#1392988    
    In response to Vaughn

It certainly is true that as the throttle opens vacuum drops, as can be seen when increasing rpm to 3000 rpm for example. However, when holding rpm at 3000 rpm throttle is decreased from when accelerating to 3000 rpm, so vacuum builds back up. So the vacuum advance is a factor when checking total timing, because if you hold the rpm at 3000 rpm for example, vacuum advance will kick back in.

My C20, for example, which has a mild Goodwrench/Targetmaster 350, holds around 15" Hg or more at 3000 rpm on the highway (I have vacuum gauge in the instrument cluster). Going uphill it will drop of course, but going downhill it will go as high as 25" Hg at 3000 rpm. If it can hold 15" Hg under load going around 60 mph, then it could easily get 15-20" Hg without a load at 3000 rpm (it idles at 800 rpm with just under 21" Hg). So that is enough for 10-20* vacuum advance on some canisters even at 3000 rpm.
90 C1500, 05 Tahoe 4WD


 
bearcat 
Member
Posts: 105
bearcat
Age: 53
Loc: Santa Fe, NM
Reg: 12-29-06
03-20-08 07:39 PM - Post#1393018    
    In response to sgian

It is, I believe, a factor of the cam you use. I have a healthy solid roller cam in my 427 and I have to run a lot of timing too. About like what you run, maybe even a little more. If I dare set my timing at 36 degrees total, it pops and acts like it's timing retarded.

Basically, if your engine responds favorably to it and you're not detonating, then don't worry about it. Bigger cams can require more timing than street cams. In fact, some racers even lock out their timing advance and set it up to have all their timing all the time.
1968 427 4-sp Corvette Convertible
1968 465 Firebird Coupe
1986 2.2 Turbo Intercooled Dodge Shelby Charger
1952 355 4-sp GMC 3/4 Ton Pick-Up
2002 Grand Am GT


 
sgian 
Valued Contributor
Posts: 4524
sgian
Loc: MO
Reg: 12-25-03
03-21-08 06:23 AM - Post#1393191    
    In response to bearcat

A mismatch of a cam to compression ratio (other words low DCR) certainly does require extra advance to run well. I've done that too, and had around 20* initial and around 40* total at 3000 rpm. However, the original poster has his timing locked in at 38* for all rpm. That is 38* at idle, and all the way up. The only time I've seen a Chevy engine idling nicely around 40* at idle without difficulty cranking was when I had a 250 with the head cracked in at least 7 different places. It needed the extra advance to compensate for the water in the mixture. So 40 total at 3000 rpm and around 20 at idle is likely a low DCR but still driveable, but 38 at idle seems to be something that should be fixed on a street car.

Now if the car is only going to be raced and won't see much low rpm, then it isn't as much of an issue.
90 C1500, 05 Tahoe 4WD


 
Rick_L 
Honored Member
Posts: 25457

Loc: Katy, Tx, USA
Reg: 07-06-00
03-21-08 06:56 AM - Post#1393214    
    In response to sgian

Usually, the smaller the displacement, the more total timing the engine will like and need. A 283 or 302 will want more timing than a 350 or 383.

Another huge factor in total timing will be the combustion chamber configuration. The old camel hump heads from the 60s will want more total timing than a modern combustion chamber like that on a Vortec or fast burn style chamber.

The weather is another factor. You can run and need more timing in hot humid weather than in cool dry weather.

For drag race engines, I've run more than 50┬║ on a cast iron head .030" over 283. But the same bore/stroke combo wanted only 40┬║ with a Dart Buick head. If the engine displacement went up to 350, the cast iron head would want only 45-46┬║, maybe even less, and the Buick head 37┬║ or so.



 
todd2059 
Lurker
Posts: 21

Loc: Southeast Kansas
Reg: 07-01-07
03-24-08 05:21 PM - Post#1395789    
    In response to Rick_L

To ChevroletR:

Are you running an MSD ignition setup? I never got the Actron to work correctly on setting my timing, and was told it was not "compatible". It would give me different readouts with no changes being made by me.

Went back to "old school" timing light, and solved that problem.

 
ChevroletR 
Senior Member
Posts: 341
ChevroletR
Loc: Mt. Airy, Maryland
Reg: 01-24-03
03-24-08 08:31 PM - Post#1395960    
    In response to todd2059

Yeah, I'm running an MSD 6A box. Where did you see it was not compatible? What do you mean by different readouts like the timing "jumping around" or different every time you checked it? Just wondering what to look for next time I check
1970 Monte Carlo
1988 Buick Reatta
1994 S-10
1984 Buick Regal
1995 S-10
1995 Caprice
2002 Avalanche
2008 Yamaha Raider


 
todd2059 
Lurker
Posts: 21

Loc: Southeast Kansas
Reg: 07-01-07
03-25-08 05:38 PM - Post#1396588    
    In response to ChevroletR

I run a 455 Pontiac in No-e with MSD ignition.11.10 at 119. I would dial it in with 35 degrees total before leaving for the track, and enjoy the day. Do my 'normal maintainence' during the week, or two weeks, and eventually check the timing again. It would be either retarded or advanced anywhere from 2 to 4 degrees.

Drove me banana's for awhile, I figured the clamp was slipping, or dampner was tweaked, or whatever. Not.

Two racers at the track said to go back to the standard timing light without the adjustable advance, because of incompatibility with the MSD. So I set it at 35 degrees total, and it remained at the corrrect setting on my degreed dampner. No more wandering period.

It wasn't really anything I read in a brochure from MSD, or Actron. It just worked.

 
Gary_K 
Senior Member
Posts: 1441
Gary_K
Loc: Deep in the Heart of Texa...
Reg: 04-11-01
03-25-08 06:48 PM - Post#1396663    
    In response to Rick_L

Rick,
Out of curiosity my 402BBC in my truck reacts differently to your temp vs timing summary. In 100 hot weather detonation is wanting to start vs cold weather never wants to ping. This is without any adjustments made to accomodate. Maybe other variables involved, but just curious.
thanks,
gk


 
ChevroletR 
Senior Member
Posts: 341
ChevroletR
Loc: Mt. Airy, Maryland
Reg: 01-24-03
03-25-08 07:46 PM - Post#1396707    
    In response to Gary_K

That's interesting Todd. Guess I'll get me some timing tape and use my old Craftsman light. Thanks!
1970 Monte Carlo
1988 Buick Reatta
1994 S-10
1984 Buick Regal
1995 S-10
1995 Caprice
2002 Avalanche
2008 Yamaha Raider


 
Rick_L 
Honored Member
Posts: 25457

Loc: Katy, Tx, USA
Reg: 07-06-00
03-26-08 05:20 AM - Post#1396884    
    In response to Gary_K

Gary, I was talking total timing (WOT) with adequate cooling. Maybe your coolant temperatures are creeping up and becoming a factor. Humidity will definitely reduce detonation though - are you familiar with water injection?

 
Jim_Elliott 
Senior Member
Posts: 250

Loc: La Quinta Calif
Reg: 11-06-01
03-26-08 09:32 AM - Post#1397032    
    In response to Rick_L

Rick & Gary
This is what I have found on my (454) motor home..
Carb inlet air temps measured with a digital meat probe laying in the air cleaner (rear) produced the high/low temps below....

Stock...driving in 110┬║+ temps at 60 MPH the carb temp was almost 160┬║ with pinging (slight) occuring with a nudge of pedal pressure.

Within a 1 hour period to change out and extend the air cleaner snout to in front of the radiator the temps AT THE CARB dropped to 132┬║ which is huge.

I have since wrapped (insulated) the air cleaner and the stock 84 blazer intake hose has been insulated also and the temps are down/around 115┬║-120┬║ and NO pinging.....

Cause of the ignition system cranked up to the max (10┬║ base & 22┬║ mechanical) during the cooler months I can now run 89 octane instead of the normal 91 rot gut....

That digital meat probe with a 3 foot cord cost about $15.00 at Walmart, Another tool for testing.

Jim

 
Greggy 
Senior Member
Posts: 541
Greggy
Loc: Perth, Western Australia
Reg: 05-22-03
04-21-08 09:27 AM - Post#1416430    
    In response to DZ302LC

Racing engines can sometimes need (and tolerate) alot of ignition advance because they often use high octane fuels and only run at high RPM levels when under load. Race engines designed for use with Methanol or Nitromethane need an even larger amount of advance to ignite these slow burning racing fuels in time to make power. If you loaded them up at a low RPM they would likely detonate severely.

Street engines are different and need to operate within a wide band of RPM, anywhere from idle through to redline, which is more difficult to get 'just right'. Any street engine needing alot of ignition advance is a sign it has a problem or was not designed correctly (i.e. the combination of parts is wrong).

Some examples of why a large amount of ignition advance might be required include:
- compression ratio too low
- cam too big for the rest of the combination
- engine too cold (e.g. no thermostat)
- blown head gasket/cracked head leaking water into cylinder(s)
- fuel mixture too rich

Generally a healhty well designed street SBC will like approx 6 to 12 degrees initial advance and about 28 to 34 degrees total (mechanical) advance.

Some engines like more than this but in my opinion they have potentially been poorly designed.

Blown (supercharged) engines are an exception, as they like high amount of initial advance e.g. 16 to 18 degrees.

Regards,

Greggy

 
motorman 
Super Senior Member
Posts: 5160

Loc: south western pa.
Reg: 01-25-00
04-21-08 01:01 PM - Post#1416557    
    In response to Greggy

a lot depends on where the spark plug is located as the newer fast burn heads only need 30/32 degrees total. with old style heads and big domes on the pistons we ran 44/45 degrees
retired race engine builder,former NASCAR tech inspector. new corvettes owned 1959,1962,1963,1964,1965, 1966,1997,1999,2002,2005, 2008 plus 30+ other chevy cars and trucks along the way. 2008 corvette sold and waiting on a C-7.


 
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