Performance Timing specs
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
Performance Timing specs
This is in my '67 Camaro, but I thought the topic might be helpful to folks here, too...
Now that my 406 has a few thousand miles on it with a safe "break in tune" (as I refer to it), I wanted to see what the engine experts think:
Cam is a 282 Hydraulic roller from comp--it is a 406, makes 9" vacuum at idle.
Dart Iron Eagle Heads 200cc intake runners, 10:1 compression ratio
as I put a performance tune on it, here is what I am thinking:
10* initial
Silver bushing (MSD ready to run small body HEI), which gives 25* mechanical advance, all in by 3000.
B28 can hooked to full manifold vacuum--will yield 16 crankshaft degreees.
At cruise--that should put me right in or "near" the sweet spot with 51* total timing....
I have a 3.73 gear, so cruising at 70mph puts me in the low 3000's for RPM.
Current setup is 6* initial, 25* mechanical, B28 Can on ported vacuum...runs very cool and well as-is, but I know I am leaving something on the table with this tune
Thanks!
Now that my 406 has a few thousand miles on it with a safe "break in tune" (as I refer to it), I wanted to see what the engine experts think:
Cam is a 282 Hydraulic roller from comp--it is a 406, makes 9" vacuum at idle.
Dart Iron Eagle Heads 200cc intake runners, 10:1 compression ratio
as I put a performance tune on it, here is what I am thinking:
10* initial
Silver bushing (MSD ready to run small body HEI), which gives 25* mechanical advance, all in by 3000.
B28 can hooked to full manifold vacuum--will yield 16 crankshaft degreees.
At cruise--that should put me right in or "near" the sweet spot with 51* total timing....
I have a 3.73 gear, so cruising at 70mph puts me in the low 3000's for RPM.
Current setup is 6* initial, 25* mechanical, B28 Can on ported vacuum...runs very cool and well as-is, but I know I am leaving something on the table with this tune
Thanks!
Burning Brakes
Joined: May 2014
Posts: 884
Likes: 128
From: Rhine Georgia
My setup that I'm happy with...
14 Initial
15 from AR31 can connect to full manifold
this gives be close to 30 at idle with can connected
20 mech all in by 2800ish
49 total
Whats your idle timing with vac can connected? should be around 30 for performance tune.
14 Initial
15 from AR31 can connect to full manifold
this gives be close to 30 at idle with can connected
20 mech all in by 2800ish
49 total
Whats your idle timing with vac can connected? should be around 30 for performance tune.
Last edited by Bloodzone; Apr 12, 2018 at 09:03 PM.
Melting Slicks
Joined: Dec 2009
Posts: 3,224
Likes: 652
From: Thunder Bay
I think you're on the right track. You will need at least 12 deg of initial with that cam. 14 would be better. Depending on what you have for heads, you will want a total of 32-36 deg of mechanical advance all in around 3000 rpm. You will have change the bushing to reduce the mechanical advance.
Your vacuum advance seems about right. If its adjustable, you can play with how it comes in. Hopefully the right advance curve will improve your vacuum situation. 9" seems awfully low for that cam.
Your vacuum advance seems about right. If its adjustable, you can play with how it comes in. Hopefully the right advance curve will improve your vacuum situation. 9" seems awfully low for that cam.
Last edited by drwet; Apr 12, 2018 at 08:46 PM.
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
I think you're on the right track. You will need at least 12 deg of initial with that cam. 14 would be better. Depending on what you have for heads, you will want a total of 32-36 deg of mechanical advance all in around 3000 rpm. You will have change the bushing to reduce the mechanical advance.
Your vacuum advance seems about right. If its adjustable, you can play with how it comes in. Hopefully the right advance curve will improve your vacuum situation. 9" seems awfully low for that cam.
Your vacuum advance seems about right. If its adjustable, you can play with how it comes in. Hopefully the right advance curve will improve your vacuum situation. 9" seems awfully low for that cam.
http://www.compcams.com/Technical/Dy...2HR-10_001.asp
The dizzyhas the silver busing, which limits to 25* + 10* initial is where I got my 35* number...The B28 can is non-adjustable, with 16 Crank degrees when fully deployed...
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
Currently connected to ported vacuum--no vac advance deployed.
Melting Slicks
Joined: Oct 2008
Posts: 2,154
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From: Regina Sk Canada
My little 355 SBC makes 350 HP and 390 TQ. I have 25 initial and 35 total all in by 3000 RPM,played with the springs till we got a nice gradual curve. Car runs like a champ, thats the way it came off the dyno.
Last edited by Grumpy 427; Apr 12, 2018 at 09:39 PM.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
You talk about these bushings and cans as if their specs are gospel. Are you CHECKING where full advance ends up, either with adjustable light or, better yet, a timing tape so you can SEE full advance? Initial went roast pistons.
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Had a 1976 L-82, 4-sp
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Suggest you set initial to 20*, retard mech'l to 14*, set idle 900-1000 rpm, use manifold vacuum for vacuum advance. Now start tweaking from here. Verify with timing light as stated above.
Last edited by resdoggie; Apr 13, 2018 at 07:47 AM.
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
I will obviously CHECK once I have the setup in place....If you refer to my original question, will this get me close--am I thinking correctly?!
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
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From: Harrisburg PA
20* initial--do you ever have any issues with starting/starters--that seems like a pretty heavy load on the starter--no?
Race Director
Joined: May 2006
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switch to the blue bushing giving you 21 degrees and set the initial to 15 giving you a total of 36 mechanical. The other choice is the black bushing giving you 18 degrees and set the initial to 18 for the 36 total.
Last edited by MelWff; Apr 13, 2018 at 12:24 PM.
Had a 1976 L-82, 4-sp
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From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
Le Mans Master
Joined: Apr 2011
Posts: 6,284
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From: Hermosa
What are the rest of the specs for that cam?
Your vacuum sounds really low for a 282 cam on a 406CI engine. Are you running a single plane intake?
In any case I would run with at least 16* or more of initial with manifold vacuum and then adjust the travel of the centrifical advance and the vacuum advance. I'm running 19* on my 350 with a 270/270 cam with a 108 LSA and 10.6 CR.
Your vacuum sounds really low for a 282 cam on a 406CI engine. Are you running a single plane intake?
In any case I would run with at least 16* or more of initial with manifold vacuum and then adjust the travel of the centrifical advance and the vacuum advance. I'm running 19* on my 350 with a 270/270 cam with a 108 LSA and 10.6 CR.
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
Likes: 27
From: Harrisburg PA
What are the rest of the specs for that cam?
Your vacuum sounds really low for a 282 cam on a 406CI engine. Are you running a single plane intake?
In any case I would run with at least 16* or more of initial with manifold vacuum and then adjust the travel of the centrifical advance and the vacuum advance. I'm running 19* on my 350 with a 270/270 cam with a 108 LSA and 10.6 CR.
Your vacuum sounds really low for a 282 cam on a 406CI engine. Are you running a single plane intake?
In any case I would run with at least 16* or more of initial with manifold vacuum and then adjust the travel of the centrifical advance and the vacuum advance. I'm running 19* on my 350 with a 270/270 cam with a 108 LSA and 10.6 CR.
Duration @ 0.006": 282° / 288° Duration @ 0.050": 230° / 236°
Max Lift w/ 1.5RR: .510" / .520" Lobe Separation: 110°
I did move the timing to my initially noted specs...10* initial, manifold vacuum. I am now pulling 12-13" vacuum.
I will continue to tune as some have suggested here, increasing timing incrementally. unfortunately, I've not been able to get the car our for a test run with the new specs yet.
What vacuum should I expect, as I continue adjustments?
As stated, the comp sites, when dyno testing the cam, showed 9" 800rpm on a 355...
Le Mans Master
Joined: Apr 2011
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From: Hermosa
Cam Specs:
Duration @ 0.006": 282° / 288° Duration @ 0.050": 230° / 236°
Max Lift w/ 1.5RR: .510" / .520" Lobe Separation: 110°
I did move the timing to my initially noted specs...10* initial, manifold vacuum. I am now pulling 12-13" vacuum.
I will continue to tune as some have suggested here, increasing timing incrementally. unfortunately, I've not been able to get the car our for a test run with the new specs yet.
What vacuum should I expect, as I continue adjustments?
As stated, the comp sites, when dyno testing the cam, showed 9" 800rpm on a 355...
Duration @ 0.006": 282° / 288° Duration @ 0.050": 230° / 236°
Max Lift w/ 1.5RR: .510" / .520" Lobe Separation: 110°
I did move the timing to my initially noted specs...10* initial, manifold vacuum. I am now pulling 12-13" vacuum.
I will continue to tune as some have suggested here, increasing timing incrementally. unfortunately, I've not been able to get the car our for a test run with the new specs yet.
What vacuum should I expect, as I continue adjustments?
As stated, the comp sites, when dyno testing the cam, showed 9" 800rpm on a 355...
With a 406 and that cam I would expect in the neighborhood of 14" or so of vacuum @ 800 RPM.
That cam has 65* of overlap. Overlap, or the period in which both intake and exhaust valves are open effects vacuum as well as other factors ie dual plane vs single plane intake. My 57* of overlap on my 350 and an altitude of 4000 ft gets me around 13" to14" of vacuum on most days. Lower atmospheric pressure and hotter day will be less and high pressure and cool days will be more. If I were at sea level it would likely be around 15" of vacuum.
You're at 10* now however I would not hesitate to go right up to 14* and you may end up around 16* of initial.
Then however your vacuum advance may need to be limited as well as the mechanical to get the desired 32* to 36* of total and 51* or so at cruise. It will run without doing these things, just not optimally.
The idle quality is going to tell you when the timing is optimal, that and your off idle response, assuming proper tuning of the carb.
Last edited by REELAV8R; Apr 22, 2018 at 09:31 AM.
Thread Starter
Racer
Joined: Feb 2012
Posts: 421
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From: Harrisburg PA
A 355 is going to produce less vacuum on the same cam due to the volume of air that it can draw. Give an engine with more displacement and it can draw more air on each intake stroke.
With a 406 and that cam I would expect in the neighborhood of 14" or so of vacuum @ 800 RPM.
That cam has 65* of overlap. Overlap, or the period in which both intake and exhaust valves are open effects vacuum as well as other factors ie dual plane vs single plane intake. My 57* of overlap on my 350 and an altitude of 4000 ft gets me around 13" to14" of vacuum on most days. Lower atmospheric pressure and hotter day will be less and high pressure and cool days will be more. If I were at sea level it would likely be around 15" of vacuum.
You're at 10* now however I would not hesitate to go right up to 14* and you may end up around 16* of initial.
Then however your vacuum advance may need to be limited as well as the mechanical to get the desired 32* to 36* of total and 51* or so at cruise. It will run without doing these things, just not optimally.
The idle quality is going to tell you when the timing is optimal, that and your off idle response, assuming proper tuning of the carb.
With a 406 and that cam I would expect in the neighborhood of 14" or so of vacuum @ 800 RPM.
That cam has 65* of overlap. Overlap, or the period in which both intake and exhaust valves are open effects vacuum as well as other factors ie dual plane vs single plane intake. My 57* of overlap on my 350 and an altitude of 4000 ft gets me around 13" to14" of vacuum on most days. Lower atmospheric pressure and hotter day will be less and high pressure and cool days will be more. If I were at sea level it would likely be around 15" of vacuum.
You're at 10* now however I would not hesitate to go right up to 14* and you may end up around 16* of initial.
Then however your vacuum advance may need to be limited as well as the mechanical to get the desired 32* to 36* of total and 51* or so at cruise. It will run without doing these things, just not optimally.
The idle quality is going to tell you when the timing is optimal, that and your off idle response, assuming proper tuning of the carb.
I'll play around with the timing a bit more over time this spring/summer. Aside from installing an adjustable can, what is the best way to limit the vac advance?
What should the timing come in at at idle with vac + initial?
Last edited by keithl1967; Apr 22, 2018 at 11:48 AM.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
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From: Hermosa
My current specs are 17* vac advance with 19* initial. This gives me a total of 36* timing at idle, so in the 30’s for timing at idle is not unusual for performance timing.
The length of the slot on the vac advance rod can be filled with something like JB weld. What I did was use a wire welder to carefully put some weld in the slot to limit the length of the pull of the rod. Over filled a little then used a round file to file some away to get exactly the length I wanted.
You can measure the total travel of the rod with a micrometer and divide that distance by the number of degrees. This will give you distance per degree and give you an estimated distance of rod travel that you will want to get the number of degrees desired.
IE. if the total travel of the rod is .600 inches and that gives 20* of advance then divide .600 by 20 and you get .030 inches per degree of advance.
If you then want 14* of vac advance you will need .030 x 14 of travel or approximately .420 inches.
The length of the slot on the vac advance rod can be filled with something like JB weld. What I did was use a wire welder to carefully put some weld in the slot to limit the length of the pull of the rod. Over filled a little then used a round file to file some away to get exactly the length I wanted.
You can measure the total travel of the rod with a micrometer and divide that distance by the number of degrees. This will give you distance per degree and give you an estimated distance of rod travel that you will want to get the number of degrees desired.
IE. if the total travel of the rod is .600 inches and that gives 20* of advance then divide .600 by 20 and you get .030 inches per degree of advance.
If you then want 14* of vac advance you will need .030 x 14 of travel or approximately .420 inches.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
I agree with Mike -
Here are the specs I'd run with that combo:
18 - 20 degrees initial timing. You're currently running really retarded - that cam needs at least 18 initial.
34 degrees total timing at 2800-3000 rpm
(This requires a centrifugal advance curve that is only 14 - 16 degrees long)
12 degrees of vacuum advance hooked up to manifold vacuum, which will give you actual timing at idle of about 30-32 degrees.
I run a big solid roller on my 407 and I run 24 degrees initial timing. No problem with hot starts.
Lars
Here are the specs I'd run with that combo:
18 - 20 degrees initial timing. You're currently running really retarded - that cam needs at least 18 initial.
34 degrees total timing at 2800-3000 rpm
(This requires a centrifugal advance curve that is only 14 - 16 degrees long)
12 degrees of vacuum advance hooked up to manifold vacuum, which will give you actual timing at idle of about 30-32 degrees.
I run a big solid roller on my 407 and I run 24 degrees initial timing. No problem with hot starts.
Lars
Last edited by lars; Apr 22, 2018 at 09:15 PM.