Ignition timing oddity on chassis dyno - Page 3 - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #31 (permalink)  
Old 04-05-2012, 11:14 PM
4 Jaw Chuck's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Mar 2002
Location: Manitoba, Canada
Age: 46
Posts: 4,974
Wiki Edits: 0

Thanks: 2
Thanked 89 Times in 72 Posts
Another explanation is called spark scatter, high cylinder pressure causes a higher load on the ignition system which can cause the coil to delay or jump across the plug gap only after the mixture self detonates.

High compression ratios combined with weak stock style ignition systems are a deadly combination, my bet is this phenomena you are seeing only occurs under load above a certain rpm...if so you are getting a clue of your ignition system weakness.

A good test is to physically lock the timing at a high initial like 18 degrees and repeat the test on the dyno, if your still seeing it assume your ignition system isn't up to the task and needs upgrading.

    Advertisement
__________________
Outlawed tunes from outlawed pipes
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #32 (permalink)  
Old 04-07-2012, 01:18 AM
Registered User
 
Join Date: Mar 2011
Location: NEW JERSEY
Posts: 8
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
ignition

no its just if the cam was dialed you have advanced the engine.so the ignition is just tuning the spark timing.i was allways taught the distributor is the moved bout an inch to a inch and a half prior to the spark of the .so if the #1 spark connection on the distributor is moved to spark bout an inch or so of travel before it lines with its own cable headed out to the #1 spark plug.so the spark is fired then by the time it shoots out to the spark plug ,it has occured ,if it went off at the same time of the distributor #1 being lined up to spark plug #1 it would be to late and the engine wouldnt run.i didnt understand the timing in that engine changing as the rpm raised.i allways buy the best i can afford in equipment and follow the instructions and research on you tube and internet and never once ran into that problem.i helped build a 65 mustang we built and now did a chevy 350 vortec 4 bolt main ,1 piece rear seal.just a 350 sbc but never bore to 60 for heat problems,i try to stay at .030 maybe .040 but even that i dont know cause you alter one part to much and then it starts throwing you Off in other areas.so i just port and polish the heads maybe 1mm off the exhaust chambers to wake it up,dont want my headers overlapping a 1.5 or 1 5/8 primariey.i really get technical bout the bowls ill just buy a pair of junk valves and port like any of us would go ahead and do.want he bowls like mirrors,mirrors i tell ya.lol .hope that cleared it up a little.sorry for confusing the masses.lol.if it makes sense and you wanns motor chat with ,hit me back anytime.bye dude
Reply With Quote Quick reply to this message
  #33 (permalink)  
Old 04-07-2012, 07:43 AM
cool rockin daddy's Avatar
1.21 giga-watts???!!!!
 
Join Date: Aug 2003
Location: wherever cool cars are
Posts: 1,535
Wiki Edits: 0

Thanks: 0
Thanked 3 Times in 3 Posts
Can somebody please translate the above gibberish?
Reply With Quote Quick reply to this message
  #34 (permalink)  
Old 04-07-2012, 11:43 AM
Registered User
 
Last photo:
Join Date: Jan 2012
Posts: 43
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
spark

Hi guy`s

Is it possible that voltage rise time is the real issue.What I mean is hei pick up voltage will rise with r.p.m. and alter timing.


2x4`s
Attached Thumbnails
Click image for larger version

Name:	Aug08020.JPG
Views:	56
Size:	158.1 KB
ID:	64638  
Reply With Quote Quick reply to this message
  #35 (permalink)  
Old 04-07-2012, 12:02 PM
T-bucket23's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Engine basic condition - how to check Last photo:
Join Date: Aug 2005
Location: Massachusetts
Age: 57
Posts: 5,204
Wiki Edits: 26

Thanks: 7
Thanked 116 Times in 101 Posts
If you want to prove if it is mechanical or electronic it is simple and has been stated in this thread several time.
Disconnect the vacuum advance
Lock the timing at something reasonable and see if it still jumps.
If you lock it and it still moves then it is not the advance weights or related parts. I would then look at the module or pickup. Either could cause the issue. A bad pickup may not be up to the rpm task and could be collapsing the field a little to soon at higher rpm or not building the field long enough. I would also check the air gap on the pickup it becomes more critical at higher rpm. The module could also be an issue but the pickup would be my first guess if it is electronic.
I think if the timing chain was stretching you would be loosing timing not adding and it would be inconsistant.
__________________
Artificial Intelligence is no match for Natural Stupidity



Chet
Reply With Quote Quick reply to this message
  #36 (permalink)  
Old 04-08-2012, 10:25 AM
Custom10's Avatar
my KARMA ran over my DOGMA
 

Last journal entry: SS
Last photo:
Join Date: May 2009
Location: Saskatchewan, Canada
Age: 49
Posts: 1,097
Wiki Edits: 0

Thanks: 16
Thanked 28 Times in 24 Posts
Quote:
Originally Posted by cool rockin daddy
Can somebody please translate the above gibberish?
I see the word bowls used allot, I am thinking the bowls are ablaze
Reply With Quote Quick reply to this message
  #37 (permalink)  
Old 04-09-2012, 04:14 PM
Registered User
 
Last photo:
Join Date: Jan 2012
Posts: 43
Wiki Edits: 0

Thanks: 0
Thanked 2 Times in 2 Posts
to 10

Hey 10

Check out these bowls out.of course you have look at them upside down



2x4`s
Attached Thumbnails
Click image for larger version

Name:	IM000093.JPG
Views:	130
Size:	783.0 KB
ID:	64683  
Reply With Quote Quick reply to this message
  #38 (permalink)  
Old 10-28-2012, 05:30 PM
Old Fool's Avatar
Registered User
 
Last photo:
Join Date: Jan 2008
Location: spokane,wa.
Posts: 1,347
Wiki Edits: 0

Thanks: 8
Thanked 40 Times in 34 Posts
back in the day a distributor was put on a distributor machine and had its advance curve set. no guessing, no oh ****s, you knew what you had. That was before they became dizzy's.
Reply With Quote Quick reply to this message
  #39 (permalink)  
Old 10-28-2012, 10:32 PM
Greg T's Avatar
www.krusinklassics.net
 
Last photo:
Join Date: Jul 2007
Location: Escanaba, MI.
Age: 60
Posts: 1,150
Wiki Edits: 0

Thanks: 20
Thanked 41 Times in 32 Posts
Today, I use the MSD E-Curve. Worth every penny.







.
Reply With Quote Quick reply to this message
  #40 (permalink)  
Old 07-09-2013, 10:41 PM
Registered User
 
Last photo:
Join Date: Mar 2009
Location: Burton, MI
Posts: 794
Wiki Edits: 0

Thanks: 38
Thanked 15 Times in 14 Posts
not to be a smart ***** or anything... but did he have the light on the right ignition wire??

I ask this because I went down this road once... when my ignition wires were a rats nest, I missed the #1 wire and got the #2 wire instead.. couldn't figure out why my timing was WAYYY off, and when it got it where i thought it should be, the engine wouldn't run....

spent better part of an hour banging my head against the wall on that one..
Reply With Quote Quick reply to this message
  #41 (permalink)  
Old 08-11-2014, 07:47 PM
Cars, Trucks, Boats
 
Last photo:
Join Date: Dec 2012
Location: Toledo, N.W.Ohio, USA
Posts: 1,606
Wiki Edits: 0

Thanks: 5
Thanked 175 Times in 170 Posts
.
. Sounds to me like the carburetor was too small and high RPMs vacuum was pulling up the vacuum advance a bit...
Reply With Quote Quick reply to this message
  #42 (permalink)  
Old 08-12-2014, 10:31 AM
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 6,822
Wiki Edits: 0

Thanks: 4
Thanked 449 Times in 384 Posts
Quote:
Originally Posted by v8hed View Post
383 with GM HEI distributor (modded with aftermarket module, curve kit, coil and shimmed for end play). Before going to the chassis dyno, I'd set my timing up (with a good timing light) for 34* total. Checked it up to about 4,000rpm and I could see the advance curve adding more timing until around 3,000rpm then it remained static. As I said, I only went up to about 3,500-4,000rpm with the timing light... just enough to see that the advance curve had finished adding timing. On the chassis dyno, we were messing around with the timing (just adding/subtracting a couple of degrees to do some fine tuning). I asked the dyno operator to take it up to 6,000rpm and keep the timing light on the balancer. He said total timing went up to something like 50* by 5,500rpm! We checked with another light and same thing. Couldn't hear any pinging (although the car is v.loud). What I don't understand is how could this possibly be happening? I still don't believe everything is at it seems, since taking timing out resulted in less power. If is was really running up around 50* total timing, there's no way the motor would be making power. I've previously tried experimenting locking the mech advance out and didn't see over 36* (with about 14* initial). Since the holes in the base plate physically limit max advance, what's going on with this wacky timing reading? It had occurred to me that perhaps the ProStreet balancer I'm using could be slipping, but it's pretty new and looks perfectly fine to the naked eye.

Anyone got any other ideas or explanations? If not, my next step will be to try a brand new MSD HEI just to eliminate the distributor from the equation. What about spark scatter or some other kind of effect?
If you're running vacuum advance, which you are, you have to go further than just pulling the vacuum can hose and plugging the port the advance plate also needs to be screwed down so it cannot move, otherwise its position is simply dependent upon the return spring in the vacuum can which can be excited by all the vibrations going on when the engine is running at high RPMs.

Another common event is the natural looseness in the timing chain and how it reacts to high RPM excitement. Then there are a number of clearances such as the clearance between the cam's distributor gear and the distributor's gear. The thrust clearance of the cam, typically the flat tappet chevy is unrestrained in forward thrust except by the distributor gear and there is a clearance of the distributor shaft and the housing allowing it some freedom of movement. Even roller cams have a little thrust freedom that works on the distributor gear mesh. All cams have a lot of rotational shake from the slowing when valves are opened against their springs to accelerations on the closing side. Nothing in this system is truly stable. All these clearances can and do gang up to change the timing. This is the reason why competition engines use the crankshaft as the timing reference to trigger the spark rather than a distributor at the end of a group of gears, chains and shafts. There are also other gadgets sold that apply tension to the timing chain for a more consistent holding of set position by not allowing any slack in the chain. Not as good as a crank trigger for ignition timing but very helpful in keeping the camshaft to crankshaft alignment steady. A thrust button on a flat tappet cam is also helpful to limit its fore and aft travel so that doesn't disturb the distributor gear mesh with the cam. Gear drives can be useful in eliminating the gear chain issues but you buy something of the quality and design of the Shaver-Wesmar to really get the needed effects the popular inexpensive drives don't solve this problem and make a lot of noise not doing it.

Bogie

Last edited by oldbogie; 08-12-2014 at 10:37 AM.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Engine dyno to chassis dyno numbers dedub Engine 3 06-19-2011 07:56 PM
chassis dyno hp to engine hp zephyrc General Rodding Tech 1 06-16-2011 02:19 PM
Chassis Dyno vs Flywheel 428ho Hotrodders' Lounge 1 10-23-2006 06:55 AM
Chassis Dyno Question gt2betubbed Hotrodders' Lounge 5 05-16-2004 07:35 PM
How many of y'all have run on chassis dyno bentwings Engine 2 11-16-2002 03:24 AM


All times are GMT -6. The time now is 05:11 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.