400 SBC timing question - 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
  #1 (permalink)  
Old 04-29-2007, 10:25 AM
Member
 
Last photo:
Join Date: Dec 2003
Location: Milford, IL
Age: 28
Posts: 128
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
400 SBC timing question

I put together a 400 small block chevy for my '79 pickup. It runs well, but Im no master of tuning and Ive got a few questions.

The truck is a half ton 2wd with a TH350 and 3.08 open rear end. I plan to replace the rear end with a 3.73 setup in the future.

The bottom end of the 400 isnt fancy. Stock crank, stock 5.565" rods, speed pro hyper flat tops with 4 valve reliefs. The heads are 70cc Edelbrock Performer RPMs. Compression on paper is 10.25:1 or so. I did not cc the chambers so that figure is rough. The cam is a Comp 270H, .480 lift, 224 duration @50. Edelbrock performer RPM Q-Jet intake and a Jegs remanufactured Quadrajet on top. Ignition is a factory HEI. The truck has headers and dual 2 1/2" exhaust.

The truck is sluggish down low. The rear end gear doesnt help any. It really wakes up at 4000rpms but the bottom end isnt stout so I keep the revs below 5500. Ive got the initial timing set at 6 degrees. Is this too slow? Can a factory HEI be recurved or should I invest in an aftermarket distributor? Any advice or suggestions are welcomed.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 04-29-2007, 11:09 AM
Member
 
Last photo:
Join Date: Dec 2004
Location: Issaquah, WA
Posts: 288
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Not that you want to take the engine apart again... but you could have advanced the cam timing say 3-4* to have it start the powerband a little earlier. Did you check your cam timing at all when it went in? That cam I would think should start making power earlier than 4k rpms.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 04-29-2007, 11:18 AM
blown67SS's Avatar
67 chevelle SS
 
Last photo:
Join Date: Apr 2007
Location: naples,FLORIDA
Age: 28
Posts: 20
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
do you know what your total timing is at??

try setting your initial timing at 8 degrees..see if that wakes it up
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 04-29-2007, 06:56 PM
Steve karch's Avatar
Member
 
Last photo:
Join Date: Feb 2002
Location: Regina, Saskatchewan
Age: 55
Posts: 414
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
My initial timing on my 406 is 18 deg with 34 total at 2500 rpm or so. That is with iron Sportsman ll heads. Your set up should support 14-16 degrees and 34 total. Your compression is on the high side but aluminum heads will support that compression ratio. Make sure to back off the idle after setting the timing. This will also allow a lower base idle setting on the carb and will allow it to stay in the idle circut when cruising at lower rpm. Your engine set up, even with 3.08's should really wake up at lower rpm's. Play around with the timing. Hook your vacuum advance to a manifold source so that it will advance your timing at no load situtations and retard it under high load situtations. This will also help with smoothing your idle out and creating better throttle response and better driveability. Your engine set up is good. You just need to work the kinks out. Have fun.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 04-30-2007, 07:15 AM
NAIRB's Avatar
Hotrodders.com Moderator
 
Last photo:
Join Date: Sep 2002
Location: cimarron, ks
Posts: 1,658
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Quote:
Originally Posted by JohnyR17
I put together a 400 small block chevy for my '79 pickup. It runs well, but Im no master of tuning and Ive got a few questions.

The truck is a half ton 2wd with a TH350 and 3.08 open rear end. I plan to replace the rear end with a 3.73 setup in the future.

The bottom end of the 400 isnt fancy. Stock crank, stock 5.565" rods, speed pro hyper flat tops with 4 valve reliefs. The heads are 70cc Edelbrock Performer RPMs. Compression on paper is 10.25:1 or so. I did not cc the chambers so that figure is rough. The cam is a Comp 270H, .480 lift, 224 duration @50. Edelbrock performer RPM Q-Jet intake and a Jegs remanufactured Quadrajet on top. Ignition is a factory HEI. The truck has headers and dual 2 1/2" exhaust.

The truck is sluggish down low. The rear end gear doesnt help any. It really wakes up at 4000rpms but the bottom end isnt stout so I keep the revs below 5500. Ive got the initial timing set at 6 degrees. Is this too slow? Can a factory HEI be recurved or should I invest in an aftermarket distributor? Any advice or suggestions are welcomed.


You've got too much cam for a truck with 3.08 gears and an automatic.

You need to get those gears changed, and use a little more stall speed in the converter. Otherwise, you need to go to a camshaft with about 205 degrees intake duration@.050.
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 04-30-2007, 11:18 AM
hotrodf1's Avatar
Chasing dreams with a ball bat
 
Last photo:
Join Date: Dec 2003
Location: Evansville, IN
Age: 37
Posts: 545
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by Steve karch
My initial timing on my 406 is 18 deg with 34 total at 2500 rpm or so. That is with iron Sportsman ll heads. Your set up should support 14-16 degrees and 34 total. Your compression is on the high side but aluminum heads will support that compression ratio. Make sure to back off the idle after setting the timing. This will also allow a lower base idle setting on the carb and will allow it to stay in the idle circut when cruising at lower rpm. Your engine set up, even with 3.08's should really wake up at lower rpm's. Play around with the timing. Hook your vacuum advance to a manifold source so that it will advance your timing at no load situtations and retard it under high load situtations. This will also help with smoothing your idle out and creating better throttle response and better driveability. Your engine set up is good. You just need to work the kinks out. Have fun.
What he said! right on

need more timing
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 04-30-2007, 02:37 PM
Big Mouse's Avatar
Stroked Z28
 
Last photo:
Join Date: Oct 2006
Location: Escaping the rat race...
Posts: 230
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Did you say a factory stock HEI from 1979?

If so, check when your timing comes all the way in. My '80 HEI came all-in at 4600 RPM's

I bought a timing curve kit (about $10) and put one light and one medium spring on the mechanical advance. That really woke up my old 400. Once I hit the 3000 RPM mark the motor pulled nicely. Worked for me... I could clearly tell the difference. On my motor, I was then all-in by 2400 RPM's (but I had much lower compression). You should be good if you are all in by 3000 RPM (if you ping, back it off a little).

+1 on better gears.

Just my $.02...
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 04-30-2007, 04:55 PM
Member
 
Last photo:
Join Date: Dec 2003
Location: Milford, IL
Age: 28
Posts: 128
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Yes the HEI is a factory stock 1979 model.

Will a summit 'HEI advance curve kit' (pn SUM-G5212) include the necessary items to correctly recurve the distributor? Does another manufacturer make a more complete kit?

Would it be smart to also buy an adjustable vacuum advance canister?
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 05-01-2007, 07:20 AM
Big Mouse's Avatar
Stroked Z28
 
Last photo:
Join Date: Oct 2006
Location: Escaping the rat race...
Posts: 230
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
I used a kit very similar to this example:
http://store.summitracing.com/partde...0&autoview=sku

I simply cleaned up my mechancial advance mechanism (they get gummy over time) and I only used the springs from the kit.

The vacuum advance depends on your engine. How many degrees does your vacuum advance move your timing right now? Check your timing at idle with vacuum advance plugged. Then recheck your timing with the vacuum advance hooked up.

I have not had to mess with my vacuum advance; however, many people here have. Do a quick search here to see how many degrees is recommended. Then, compare that to what yours is doing. You'll then be able to determine if you need the adjustable VA or not.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 05-13-2007, 05:15 PM
Member
 
Last photo:
Join Date: Dec 2003
Location: Milford, IL
Age: 28
Posts: 128
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Finally got some time to play with the timing this afternoon.

I got a HEI recurve kit, installed the weights and used one light sping and one medium spring.

Set the initial at 15 degrees (vac adance unplugged). Checked the total timing and at 3000 rpms, where the advance should be all in, and it is only 25 degrees.

So if I understand correctly, the mechanical advance in the distributor adds only 10 degrees?? Does a recurve kit limit the amount of mechanical advance?

I neglected to check the total timing before I switched the springs and weights in the distributor. The initial advance was set at 6 degrees and the engine ran better before I installed the recurve kit.

The distributor is a factory '79 model and the recommended initial setting is 4 degrees which would lead me to believe that there was originally much more than 10 degrees of mechanical advance in the distributor. Any advice is appreciated.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 05-13-2007, 05:33 PM
Blazin72's Avatar
You got a leaky spark tube...
 
Last wiki edit: Rearend removal
Last journal entry: General Lee
Last photo:
Join Date: Jul 2005
Location: Union, WA
Age: 32
Posts: 2,868
Wiki Edits: 19

Thanks: 0
Thanked 2 Times in 2 Posts
Nevermind...

Last edited by Blazin72; 05-13-2007 at 05:35 PM. Reason: oops...
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 05-13-2007, 05:58 PM
Registered User
 
Join Date: Mar 2007
Location: wisconsin
Age: 41
Posts: 45
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
first the basics
run as much base timming as you can (hot) .....your starter will let you know if too much

make sure all of your timming is in @ the rpm you are in when you are going cruize speed (whatever your speed limit is in your state)

this way all your timming is in @ lets say 70mph and 2500rpm you dont have overheat problem on freeway=extended engine life as well as performance
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 05-13-2007, 10:20 PM
Member
 
Join Date: Dec 2004
Location: Madison, WI
Posts: 1,885
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
It sounds like your weights are sticking and not allowing the full advance. Is everything clean inside and appear to be rotating smoothly?

Having run cams in that range with truck with your rear ratio it's not the cam. That's not a big cam for a 400 with your compression.

If the distributor is old and the internals look shot it would be worth it to get a small cap MSD with an external coil and retrofit your truck. You are going to want to bush the new distributor to give you around 36 to 38 degrees of timing with some reasonable base timing, 14 max. You dial in too much base and in combination with the high compression you'll detonate the piss out of it.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 05-14-2007, 03:35 PM
Member
 
Last photo:
Join Date: Dec 2003
Location: Milford, IL
Age: 28
Posts: 128
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
The recurve kit came with 3 sets of plastic bushings that the supplied weights ride on.

It is possible that the set of bushings I used are too snug and do not allow the weights to swing out properly. Ill pull the distributor back out and inspect it.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 05-15-2007, 08:39 AM
hotrodf1's Avatar
Chasing dreams with a ball bat
 
Last photo:
Join Date: Dec 2003
Location: Evansville, IN
Age: 37
Posts: 545
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Just a dumb question: did you try running the motor up to 3500, 4000 RPM to see if the dist. was still adding timing? Perhaps it would add more past 3K, which means you need to use lighter springs yet.

FYI: I have had decent luck using the factory weights and then using the springs from the recurve kit. I always think the recurve weights fit like crap and just dont generally seem very well designed. I just lighten the springs up, and watch what happens to the curve with my dial back light. Course, factory weights are different for different motors, so your "mileage" may vary.

But, the recurve kits I think do limit the amount of mechanical timing, by how much I'm not sure. The bottom line is, unless you get a nice MSD or other brand distributor that is made to be more easily adjustable (like the advance stop bushings that were spoke of earlier), you will have to trial and error your HEI until it does what you want. It's sometimes not easy to get them to cooperate!
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:
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
Long Awaited 400 SBC Dyno Results Mad Maggot Engine 19 10-14-2011 07:29 PM
400 cid SBC Shades_o_Grey Engine 20 02-04-2008 12:28 PM
timing question 85 vette Engine 11 12-17-2004 07:27 AM
400 SBC Newbie thecamaroguy Engine 13 12-08-2004 08:09 AM
SBC Timing gremlin agfinance1 Engine 7 10-28-2004 01:04 PM


All times are GMT -6. The time now is 04:14 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.