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Terry Cloyd
Banned
Joined: March 23, 2004
Posts: 2218
Location: Valley Center "SO CAL"
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 Posted: Sat Oct 23, 2004 1:03 pm Post subject: Timing adjustment "losing horsepower" |
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| What is the total degrees of advancement at 3000 RPMs, before the motor starts losing horsepower? Terry |
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Glenn 
Mr. 010
Joined: December 25, 2001
Posts: 79473
Location: Sneaking up behind you
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| Posted: Sat Oct 23, 2004 1:24 pm Post subject: |
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It depends on the cam, combustion chamber and fuel.
I run 32 degrees @ 3000rpm with 93 pump gas, 9.25:1 cr.
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Glenn
74 Beetle Specs | 74 Beetle Restoration | 2180cc Engine
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עַם יִשְׂרָאֵל חַי |
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Jake Raby
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Joined: August 23, 2003
Posts: 7433
Location: Aircooled Heaven USA
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| Posted: Sat Oct 23, 2004 3:36 pm Post subject: |
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After 4500RPM if we have the ability (EMS, retard box) I start pulling timing away. Most curves start at 12 degrees at idle, progress to 28 around 3500 and then back down from 28 to 24 or even 22 above 5K...
Most people run 32 because the added advance makes the car feel faster as the higher overall timing is boosting initial timing and the advance curve. A typical engine with a 009 runs 8 degrees at idle to get 28 full, that makes for a lazy bottom end.
By running more timing down low and a faster curve the timing helps the car to pull better tyhen the limited and retarded timing in the upper revs keep over advance down. As piston speed increase with RPM the need for advance diminishes quickly..
Many people run 32 degrees of full timing, and create undo heat in their heads..... Added CR also decreases the need for timing due to efficiency, it is impacted by camshaft as well...
The only time my engines need more than 28 degrees full advance is if they are ran on race fuel with limited CR at which point the extra timing helps the charge to fully burn...
Do a search on the STF, you will find detailed posts there from guys that I have helped tremendously with this tuning assistance. One guy dropped head temps 40 degrees and picked up 6 MPG!
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Jake Raby
Raby Engine Development
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"I've never given anyone Hell, I just told them the truth and they thought it was Hell" |
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Terry Cloyd
Banned
Joined: March 23, 2004
Posts: 2218
Location: Valley Center "SO CAL"
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| Posted: Sat Oct 23, 2004 9:08 pm Post subject: |
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| Glenn wrote: |
It depends on the cam, combustion chamber and fuel.
I run 32 degrees @ 3000rpm with 93 pump gas, 9.25:1 cr. |
Glenn the Cam is FK89, combustion chamber is 31.5 cc, AV gas 100 plus Terry. |
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Jake Raby
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Joined: August 23, 2003
Posts: 7433
Location: Aircooled Heaven USA
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| Posted: Sat Oct 23, 2004 10:32 pm Post subject: |
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Damn, you must have takll deck, or super high CR...
The AV gas operates at weird cylinder pressures because it has a coolant as well as lead in its composition and is not designed for an engine that runs over 3600 RPM as a general rule...
It will totally change your timing necessity and optimization. You'll have to start from scratch.
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Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell" |
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Terry Cloyd
Banned
Joined: March 23, 2004
Posts: 2218
Location: Valley Center "SO CAL"
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| Posted: Mon Oct 25, 2004 8:24 pm Post subject: |
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| Gentlemen, Thanks for the info. I have never change timing because of cam,fuel "gas or methanol", size of motor, compression, 010, 09, 019, distributors or mag. I bring the motor up to 3,000 rpms and set at 31 degrees. Terry |
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Jake Raby
Samba Member
Joined: August 23, 2003
Posts: 7433
Location: Aircooled Heaven USA
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| Posted: Mon Oct 25, 2004 8:47 pm Post subject: |
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Then that means you have not been tuning the engines to their peak...
I have seen engine be happy with as little as 20 degrees of full advance, or as much as 53 degrees!
At 31 degrees full advance many engines are overadvanced above 5,000 RPM and their powerband is shortened, and HP is lost. They feel faster through the low end and middle range because of added initial advance and more advance in their curve- it is just a trick- don't believe it.
Going to a fully adjustable dizzy is the key, have all your cake and eat it too!
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Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell" |
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TWD
Samba Member
Joined: May 11, 2004
Posts: 976
Location: Georgia
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| Posted: Tue Oct 26, 2004 6:10 pm Post subject: |
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| I am running cooler with a much crisper lower end with a Mallory unlite set at 12/28 with gray springs. Thanks again Jake. |
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nsracing
Samba Member
Joined: November 16, 2003
Posts: 9743
Location: NOVA
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| Posted: Wed Nov 03, 2004 11:17 pm Post subject: timing...timing...timing.. |
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| Jake Raby wrote: |
After 4500RPM if we have the ability (EMS, retard box) I start pulling timing away. Most curves start at 12 degrees at idle, progress to 28 around 3500 and then back down from 28 to 24 or even 22 above 5K...
Most people run 32 because the added advance makes the car feel faster as the higher overall timing is boosting initial timing and the advance curve. A typical engine with a 009 runs 8 degrees at idle to get 28 full, that makes for a lazy bottom end.
By running more timing down low and a faster curve the timing helps the car to pull better tyhen the limited and retarded timing in the upper revs keep over advance down. As piston speed increase with RPM the need for advance diminishes quickly..
Many people run 32 degrees of full timing, and create undo heat in their heads..... Added CR also decreases the need for timing due to efficiency, it is impacted by camshaft as well...
The only time my engines need more than 28 degrees full advance is if they are ran on race fuel with limited CR at which point the extra timing helps the charge to fully burn...
Do a search on the STF, you will find detailed posts there from guys that I have helped tremendously with this tuning assistance. One guy dropped head temps 40 degrees and picked up 6 MPG! |
Look folks..this is high end tuning lingo here. But for us people NOT in the know...this is all foreign. Jake gave the high points but left out the goodies.
There might be some people here that want the mechanics on how all these things come about Jake.
This is according to textbook:
OPTIMUM TIMING of the spark is the number of crank degrees that build PEAK CYLINDER PRESSURES at 12 - 14 degrees AFTER top dead center. This means that you want to ignite the fuel charge when the cylinder pressure is the highest.
As engine speed increases, there is LESS TIME for the FLAME front to consume the fuel and build pressure in the cylinder. This means that you have to advance the POINT at which you start the fire. The good thing though is that FLAME SPEED INCREASES almost in exact proportion with engine speed. The theory is that, as the turbulence increases in the combustion chamber, more of the fuel turns to vapor and can react with Oxygen more quickly. So because this happens, the amount of advance required is fairly stable on the top end.
When the engine speed reaches a certain RPM, the amount of ignition advance the engine likes tends to stabilize. (Jake made this point already on the high end). BUT before that point, the engine likes varying amounts of advance.
BELOW 2500-3000 RPM, more crank degrees from point of ignition are required for the cylinder pressure to reach maximum pressure than it does above 3000 RPM. This means that you have to feed in advance in lower RPMs. Now...the exact amount and proportion depends on the engine. THE MORE EFFICIENT THE COMBUSTION CHAMBERS, the MORE the NEED FOR STEEPER ADVANCE.
Another important point..... the RATE OF BURN CHANGES WITH THE DENSITY OF AIR/FUEL CHARGE.
At part throttle, when the manifold vacuum is high and the air is little, and the fuel is little, things are just loafing along and it will TAKE MORE TIME FOR THE AIR and FUEL to react. This condition will need more ignition timing....that is why under 2500 -3000 RPM will need more timing than beyond that. Things get more efficient on the top end when things are moving fairly fast and reacting fairly fast...so timing is less needed.
Under light loads, the engine will NOT need ..(12.7 : 1) ...air/fuel ratio. The engine needs less...even far less than stoichiometric or (14.7 : 1) for some of us NOT in the know. But the timing advance needs to be more since things are not moving fast enough.
Clear as mud so far?
SHOULD WE TALK ABOUT DETONATION NOW IF TOO MUCH ADVANCE?
Have a nice day folks. |
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Muffler Mike
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Joined: October 10, 2002
Posts: 1054
Location: Lawndale Ca.
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| Posted: Thu Nov 04, 2004 8:04 am Post subject: |
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not that its likely if you are running a 009 type distributor but have you checked timing past 3000 rpm to make sure it still not advancing?
Ran into this on an mds distributor. assisted some one that said that similar thing. checked it out my self and it was WAY up there past 3000. it didnt stop advancing till 4000
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nsracing
Samba Member
Joined: November 16, 2003
Posts: 9743
Location: NOVA
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| Posted: Thu Nov 04, 2004 8:24 am Post subject: more timing? |
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| Muffler Mike wrote: |
not that its likely if you are running a 009 type distributor but have you checked timing past 3000 rpm to make sure it still not advancing?
Ran into this on an mds distributor. assisted some one that said that similar thing. checked it out my self and it was WAY up there past 3000. it didnt stop advancing till 4000 |
Hey Mike,
That is why I use the Snap-On TOP-LINE-TIMING light...the best money can buy. This sucker is nice!
If the timing advance keeps going beyond 3000 RPM may be an indication that the distributor is worn out.
I like 28 degress total timing...all in by 2500 RPM and no more beyond that, if all possible. I set initial timing at 7-8 degrees idle.
nice day all. |
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Terry Cloyd
Banned
Joined: March 23, 2004
Posts: 2218
Location: Valley Center "SO CAL"
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| Posted: Fri Nov 05, 2004 10:30 pm Post subject: |
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| I hold the gun at 3 thousand RPMs and the "09s spring" starts changing timing on the dregree wheel. The 010 maybe 6300 RPMs and it drops off. Terry |
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