66 283 timing? - Impala Tech
Troubleshooting Diagnosing problems

 
LinkBack Thread Tools
post #1 of 15 (permalink) Old 10-03-2009, 06:41 PM Thread Starter
Member
 
Join Date: Aug 2009
Location: north carolina
Posts: 56
 
Unhappy 66 283 timing?

I recently got a 66 4dr impala for my son. He picked it out. The 283 was "rebuilt" in the past 3 years. My question is what is the best timing setting for it? The factory setting is 4 degrees BTDC. I've got it currently at 8 BTDC with the dwell set at 30. It has a holley 4160 on it with an elderbrock manifold and headers.
Also, where can I find the code on the block that verifies it's a 283?
ben.baker is offline  
Sponsored Links
Advertisement
 
post #2 of 15 (permalink) Old 10-03-2009, 09:58 PM
Moderator
 
Join Date: Jan 2006
Posts: 12,456
 
If you go to http://www.Moretec.com they have not only a full list of all of the casting numbers (cut and paste the list of block casting numbers into Microsoft word then use the find function of Word to find your casting numbers) but pictures and arrows showing you where to look for the casting numbers for blocks, and heads.

A 283 block is going to be different from a 327 or 350 block as it has a smaller bore size 3-7/8th inch compared to the 327's 4 inch bore.

Big Dave
Big Dave is offline  
post #3 of 15 (permalink) Old 10-03-2009, 10:21 PM
Senior Member
 
Join Date: Mar 2008
Location: Moneta, VA
Posts: 830
 
The Timing sounds good to me. Also the Dwell at 30 is the correct setting.

If you post the Engine Code (on the pad at the front and bottom of the passenger side head) we can also verify what engine you have.

Bill
62BillT is offline  
 
post #4 of 15 (permalink) Old 10-04-2009, 06:00 PM Thread Starter
Member
 
Join Date: Aug 2009
Location: north carolina
Posts: 56
 
Smile block code

Thanks for the info. On the pad is T0428GF. According to oldride.com library section the GF engine code stands for a 283 with 195hp, powerglide and 2bc. It stills has the powerglide. The moretec.com website is for sale.
I'm struggling with it running smoothly. I believe the settings on the carb have been "adjusted". The holley website is not very informative. There's a adjustment screw on both sides of the carb. Which one does what? They are both currently set at 3.5 turns out. It doesn't want to acceralate very well, but idles o.k.
ben.baker is offline  
post #5 of 15 (permalink) Old 10-04-2009, 06:24 PM
Moderator
 
Join Date: Jan 2006
Posts: 12,456
 
Sorry, my error there is no 'e'. Here is the web site:

http://mortec.com/

Big Dave
Big Dave is offline  
post #6 of 15 (permalink) Old 10-04-2009, 08:23 PM
Senior Member
 
Join Date: Mar 2008
Location: Moneta, VA
Posts: 830
 
I'm not familiar with a "4160" Holley, but the 2 adjusting screws should be: one side for "Air" the other side for "Gas". I always set my carb with a vacuum gauge, setting it to the highest vacuum on the low side (screws more turned in than turned out). The 3.5 turns out sounds too much to me. Before we used vacuum gauges we would turn them out 1 1/2 turns each and fine tune it by ear from there.

You have mentioned "Edlebrock, Holley and Headers". Are you sure that it doesn't have a High Performance Cam in it? If it does, it is supposed to idle rough.

Keep us posted.

Bill
62BillT is offline  
post #7 of 15 (permalink) Old 10-04-2009, 11:33 PM
BA.
Moderator
 
Join Date: Aug 2008
Location: Miamisburg, Oh.
Posts: 3,165
Blog Entries: 15
 
I agree with Bill on 8 degrees being fine. I've always achieved my best carb tunes with a vacuum gauge just like he said too.
It would be good to know what vacuum you've got at idle. That'll tell us a few things too.

The 4160 is the body style for the 3310/1850 model of carbs if memory serves correctly. (3310 = 750cfm, 1850 = 600cfm)

Ben, those screws adjust the air/fuel ratio for the "idle & low speed" circuit. That actually handles fuel delivery up to around 2000rpm or so I think before it blends in with the fuel delivered via the jets.

The screws make the mixture 'richer' when turned counter-clockwise (out). I've always had mine much like Bill stated. Usually about 3/4 - 1.5 turns out from a "fully seated" position. (be gentle when going to fully seated; clockwise)

There should be numbers stamped into the front of the air/choke horn on the carb. Let us know what those are, they'll cross-reference to a CFM rating. Hoping it's not a 750cfm carb on a 283 motor.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
BA. is offline  
post #8 of 15 (permalink) Old 10-05-2009, 07:42 PM Thread Starter
Member
 
Join Date: Aug 2009
Location: north carolina
Posts: 56
 
Smile vaccum issues

The holley is stamped 1850-1, which means it should be a 600cfm. I bought a vaccum gage and put it on. Apperantlly it wasn't running as smoothly as I thought.
At idle, it will increase RPM briefly then back down. The vaccum gage is all over the map. At idle it bounces between 15 and 30. When it increases rpm (on it's own) the gage decreases it bounce and is around 30, with a 5 degree variant. I lossened and retorqued the carb to the intake. Holley recommends 60 to 80 in/lbs. I torqued it to 12 ft/lbs. I did dial both screws down to 1.75 no change in run condition.
The first valve forward on the driver's side head is noisey. It's not a hard clack but more of a combination clack and flutter. I'm assuming that I'm losing vaccum/ compression off of this valve and that could be the source of the gage swinging wildly. I attempted to adjust this valve ( I have those little clips you put on the rods) but only succeded in getting oil all over the header wrap.
Do you agree that the valve is the source of my vaccum loss? Would that also account for the momentary increase in idle speed?
Thanks for all your help, it's been 25 years since I last dove under the hood and then it was a 327 w/350 cam in a 41 plymouth coupe. My first car.
ben.baker is offline  
post #9 of 15 (permalink) Old 10-05-2009, 09:51 PM Thread Starter
Member
 
Join Date: Aug 2009
Location: north carolina
Posts: 56
 
Cool cam

Just got a call back from the previous owner. He put a SSI cam in it 4 steps over stock. So I guess I can put the timing light away. Is there any other method of setting the timing other than by ear?
ben.baker is offline  
post #10 of 15 (permalink) Old 10-05-2009, 10:25 PM
BA.
Moderator
 
Join Date: Aug 2008
Location: Miamisburg, Oh.
Posts: 3,165
Blog Entries: 15
 
Once you've got aftermarket parts, you either gotta set by ear, driveability or on a dyno.
It's a little time comsuming but in a nutshell, you keep increasing by 2-4 degrees until you hear engine knock under load, or the engine is too hard to start when hot,....then you back it down 2-3 degrees.

I looked for a chevy SSI cam at PAW but only saw one, and it was waaay big. No way you had that particular one.

Your summation that a fluctuating vacuum gauge is caused by valve issues is correct.
The next step is either to take them off and get them rebuilt with new valve seats and guides or to do a compression test and leakdown test on all cylinders. Neither is hard to do at all, just need a couple of hours and the right tools which might run ya 40-80 bucks. (pressure gauge to at least 125-150psi, an air compressor and an air regulator, and sparkplug hole fittings.)
By the way, a compression and leakdown test will also tell you if you have good piston rings (seal) or not.

Once a compression test is completed...you'd hope all cylinders are within 10% of each other,....if one is low then you would then do the leakdown test.
On a leakdown test, just in case you aren't familiar,.....the air compressor would attach to the spark plug hole, then that air pressure would then leak out of any bad cylinder sealing. (valves or rings) If you hear air hissing at the carb, then the intake valve is leaking,.....air noise at the exhaust pipe = exhaust valve seal,....air noise in the oil fill hole = ring leakage,...which you might hear a little there anyway....just looking for excessive noise.

Whew! let us know what you do/find.

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
BA. is offline  
post #11 of 15 (permalink) Old 10-06-2009, 12:23 PM
Senior Member
 
Join Date: Jun 2008
Location: Near Chicago
Posts: 703
 
My suggestions: If the engine has an aftermarket cam in it and the prev owner advanced the cam with a degree wheel then you will need to find a "sweet spot" in the static timing where the engine likes to run. My 396 has a Summit cam from the previous owner and it likes the static timing pretty advanced, even though the rest of the engine is stock. it does not like 4° BTDC.

Also, you may have an overlap issue depending on your cam grind, thereby causing fluctuating vacuum signals to your carb. That jumpy idle issue could be an incorrect power valve issue within the carb. But, if you have large fluctuations in the vacuum reading while idling, you may even have a bent valve that isn't closing. ...Or a cracked valve or worn seat. The valve could be allowing air to leak past it. This could also cause the power valve to be operating in an erratic fashion that would affect your idle speed. It would be best to find the cam card and know the specs. If it is a high lift/duration cam then your carb may be too small and someone tried (and failed) to compensate by turning the mixture out so far. But if you hear a valve ticking and attempting to adjust it doesn't change it that would be the first place to start.

Also, you might want to turn the mixture screws in more. 1 & 3/4 turns out sounds kind of fat on the mixture. You want to work within a range of zero to 1.5 turns out- max. Your best range should be between .75-1.25" turns out if the carb is giving the correct CFM for the cam grind and it is jetted correctly. The mixture setting will best be observed by reading the plugs after driving with different adjustments. Many novice tuners think turning the mixture way out is better but this is not the case. If it's idling in the garage and your eyes are burning it's a sure sign it's too fat.

The poor acceleration could also be from the mixture too fat, but can also be a number of other things. I'm sure that's not what you want to hear. If you don't have a harmony of correct mixture, correct CFM, correct centrifugal timing advance and a cam that has a power band too high in the RPM curve, combined with a tall rear end gear you have all the makings for poor acceleration. Also, if that Holley has vacuum secondaries, you may have to purchase a spring kit to match the engine so that the secondaries open sooner.

It's tough trying to fix issues from previous owners. Don't forget, you bought something someone else sold and may have given up on due to inexperience. Those can be excellent buys though if you know what you're doing.

-Scott
1968 Caprice 396 is offline  
post #12 of 15 (permalink) Old 10-09-2009, 03:33 PM Thread Starter
Member
 
Join Date: Aug 2009
Location: north carolina
Posts: 56
 
Red face lastest adjustments

I've been moving the distributor a little bit each day, then driving it. I made a splash guard how of AL flashing and adjusted the valves. Once the valve stopped slapping the vacumm settled right down. I adjusted the mixture screws (in and out) until I got the highest setting. It runs pretty good, no lag in acceleration, no bogging down, idles pretty steady.
Next question, how accurate are most vacumm gages? Reason being, at idle it holds steady at 16 and occasionally wanders down to 15.5 at most, then comes back up. It's NOT bouncing, more like a slow drift. Is this more the gage or is something else going on with the engine?
ben.baker is offline  
post #13 of 15 (permalink) Old 10-09-2009, 09:53 PM
BA.
Moderator
 
Join Date: Aug 2008
Location: Miamisburg, Oh.
Posts: 3,165
Blog Entries: 15
 
Scott - excellent advice.

Ben - Way to go man!! I am impressed.

I used to run around with a vacuum gauge in-car and I think at idle that mine might have done that slight fluctuation also. Someone may chime in differently, but I really don't think you have anything to worry about there.
I assume you had to do the "chasing" of the timing setting, A/F mixture screws and idle speed when looking for your highest vacuum readings at idle. It's a little of a cat & mouse game.
At 15"-16" of vacuum, it sounds like a nice cam. Not too crazy, not too small. (just a guess)

HOW A NOVICE REBUILDS A 66 IMPALA CONVERTIBLE:
http://www.impalas.net/forums/blog.php?u=1432
BA. is offline  
post #14 of 15 (permalink) Old 01-28-2010, 07:10 PM
Senior Member
 
Join Date: Jun 2009
Location: tavares florida
Posts: 116
Blog Entries: 16
 
Send a message via AIM to csf64ss Send a message via Yahoo to csf64ss
man that was good!

Quote:
Originally Posted by 1968 Caprice 396 View Post
My suggestions: If the engine has an aftermarket cam in it and the prev owner advanced the cam with a degree wheel then you will need to find a "sweet spot" in the static timing where the engine likes to run. My 396 has a Summit cam from the previous owner and it likes the static timing pretty advanced, even though the rest of the engine is stock. it does not like 4° BTDC.

Also, you may have an overlap issue depending on your cam grind, thereby causing fluctuating vacuum signals to your carb. That jumpy idle issue could be an incorrect power valve issue within the carb. But, if you have large fluctuations in the vacuum reading while idling, you may even have a bent valve that isn't closing. ...Or a cracked valve or worn seat. The valve could be allowing air to leak past it. This could also cause the power valve to be operating in an erratic fashion that would affect your idle speed. It would be best to find the cam card and know the specs. If it is a high lift/duration cam then your carb may be too small and someone tried (and failed) to compensate by turning the mixture out so far. But if you hear a valve ticking and attempting to adjust it doesn't change it that would be the first place to start.

Also, you might want to turn the mixture screws in more. 1 & 3/4 turns out sounds kind of fat on the mixture. You want to work within a range of zero to 1.5 turns out- max. Your best range should be between .75-1.25" turns out if the carb is giving the correct CFM for the cam grind and it is jetted correctly. The mixture setting will best be observed by reading the plugs after driving with different adjustments. Many novice tuners think turning the mixture way out is better but this is not the case. If it's idling in the garage and your eyes are burning it's a sure sign it's too fat.

The poor acceleration could also be from the mixture too fat, but can also be a number of other things. I'm sure that's not what you want to hear. If you don't have a harmony of correct mixture, correct CFM, correct centrifugal timing advance and a cam that has a power band too high in the RPM curve, combined with a tall rear end gear you have all the makings for poor acceleration. Also, if that Holley has vacuum secondaries, you may have to purchase a spring kit to match the engine so that the secondaries open sooner.

It's tough trying to fix issues from previous owners. Don't forget, you bought something someone else sold and may have given up on due to inexperience. Those can be excellent buys though if you know what you're doing.

-Scott
im just readin an relaxin...what a great post!....you covered all bases from the bench!......sounds like the classic " well if we put a big cam in it ........".lift and overlap issues....where the valves arent closing to build pressure for the cyl..............nice call!

MR.CHARLIE
CSF64SS
csf64ss is offline  
post #15 of 15 (permalink) Old 01-30-2010, 03:17 PM
Senior Member
 
Join Date: May 2006
Posts: 1,063
Blog Entries: 1
 
I don't see where that info on on this link?

Paul

1966 Impala SS

Please Visit our new site:
http://www.winvoices.com/
1959 through 1988* window stickers, car shippers, dealer invoices, retail sales orders and tank stickers, expertly reproduced, for most Chevrolet Models.





fsc66 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Impala Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
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:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



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

 
For the best viewing experience please update your browser to Google Chrome