Did basic tuning on new build and still running meh. Help with advanced tuning? - Page 2 - CorvetteForum - Chevrolet Corvette Forum Discussion

Go Back  CorvetteForum - Chevrolet Corvette Forum Discussion > C3 Corvettes, 1968 - 1982 > C3 Tech/Performance
Reload this Page >

Did basic tuning on new build and still running meh. Help with advanced tuning?

Notices
C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette

Did basic tuning on new build and still running meh. Help with advanced tuning?

Old 02-10-2018, 08:24 PM
  #21  
HeadsU.P.
CF Senior Member
 
HeadsU.P.'s Avatar
 
Member Since: Aug 2017
Location: Cool Northern Michigan
Posts: 1,550
Thanked 257 Times in 247 Posts
Default

One more thing then I give up. Take the dizzy cap off. Grab that rotor and turn it CCW then let go of it. Does it snap back or is it sluggish? Try it a few times to verify the springs are truely working and not stuck in either position of the rotor.
HeadsU.P. is offline  
Old 02-10-2018, 10:16 PM
  #22  
Shdggsdv
CF Senior Member
Thread Starter
 
Shdggsdv's Avatar
 
Member Since: Jun 2014
Location: Las Vegas Nevada
Posts: 350
Thanked 12 Times in 11 Posts
Default

Originally Posted by HeadsU.P. View Post
One more thing then I give up. Take the dizzy cap off. Grab that rotor and turn it CCW then let go of it. Does it snap back or is it sluggish? Try it a few times to verify the springs are truely working and not stuck in either position of the rotor.
Yeah, it snaps back with ease

Last edited by Shdggsdv; 02-10-2018 at 10:16 PM.
Shdggsdv is offline  
Old 02-11-2018, 03:06 AM
  #23  
dmruschell
CF Senior Member
 
Member Since: Oct 2011
Location: Jarrettsville Maryland
Posts: 597
Thanked 33 Times in 31 Posts
Default

What transmission, stall converter (if automatic) and rear end ratio are you using?

Comp recommends a 2200+ stall with this cam (http://www.compcams.com/Company/CC/c...x?csid=87&sb=0). Using a stock converter will mean that it is sluggish up until 1800 RPMs (where Comp claims the power band starts). The stock converter catches around 1200 RPMs or so, so off the line performance will likely suffer as a result. A low-numbered rear is going to exacerbate that problem by not allowing the engine to rev up into its power band quickly.

In my 79 with a 4-speed, I used to have an Edelbrock Performer RPM camshaft. With a square-bore carb (and always cold-air coming into the inatke), the engine would buck and stumble until it finally crested 1500+ RPMs. With a smaller camshaft (Lunati Voodoo 268), that RPM decreased to 1200 RPMs. With a heated intake charge (working ThermAC system) and a Quadrajet, my car will not buck, even down to 800 RPMs in first gear.

The cam should really come alive above 4,000 RPMs, though. If the secondaries on your carb are opening late, you might not be getting all of the airflow that you should be getting at higher RPMs under load. For a short time, I used a Holley Ultra Street Avenger on my 79, and I could tell when the secondaries would open (I didn't use it long enough to get it really dialed in), and it was usually around 3500-4000RPMs.

Last edited by dmruschell; 02-11-2018 at 03:07 AM.
dmruschell is offline  
Old 02-11-2018, 04:46 PM
  #24  
Shdggsdv
CF Senior Member
Thread Starter
 
Shdggsdv's Avatar
 
Member Since: Jun 2014
Location: Las Vegas Nevada
Posts: 350
Thanked 12 Times in 11 Posts
Default

Originally Posted by dmruschell View Post
What transmission, stall converter (if automatic) and rear end ratio are you using?

Comp recommends a 2200+ stall with this cam (http://www.compcams.com/Company/CC/c...x?csid=87&sb=0). Using a stock converter will mean that it is sluggish up until 1800 RPMs (where Comp claims the power band starts). The stock converter catches around 1200 RPMs or so, so off the line performance will likely suffer as a result. A low-numbered rear is going to exacerbate that problem by not allowing the engine to rev up into its power band quickly.

In my 79 with a 4-speed, I used to have an Edelbrock Performer RPM camshaft. With a square-bore carb (and always cold-air coming into the inatke), the engine would buck and stumble until it finally crested 1500+ RPMs. With a smaller camshaft (Lunati Voodoo 268), that RPM decreased to 1200 RPMs. With a heated intake charge (working ThermAC system) and a Quadrajet, my car will not buck, even down to 800 RPMs in first gear.

The cam should really come alive above 4,000 RPMs, though. If the secondaries on your carb are opening late, you might not be getting all of the airflow that you should be getting at higher RPMs under load. For a short time, I used a Holley Ultra Street Avenger on my 79, and I could tell when the secondaries would open (I didn't use it long enough to get it really dialed in), and it was usually around 3500-4000RPMs.
So my stall converter is stock and too low. I was planning to take it to a trans shop sometime next week to have that fixed, but even above that it's struggling like crazy. I believe my rear is 3:55 so shouldn't be giving me much issue

I can definitely tell when the secondaries open, but still has little power. It revs up really high and just moves accelerates slow like the stock engine. How do you tell if they're not allowing enough air flow at high RPMs?
Shdggsdv is offline  
Old 02-11-2018, 08:57 PM
  #25  
dmruschell
CF Senior Member
 
Member Since: Oct 2011
Location: Jarrettsville Maryland
Posts: 597
Thanked 33 Times in 31 Posts
Default

Originally Posted by Shdggsdv View Post
So my stall converter is stock and too low. I was planning to take it to a trans shop sometime next week to have that fixed, but even above that it's struggling like crazy. I believe my rear is 3:55 so shouldn't be giving me much issue

I can definitely tell when the secondaries open, but still has little power. It revs up really high and just moves accelerates slow like the stock engine. How do you tell if they're not allowing enough air flow at high RPMs?
I don't remember if it was mentioned or not, but verify that the carb butterflies are opening fully at WOT. If they're not, then the secondaries will never fully open, and you won't get full power. With the stock engine, the camshaft and heads were choking the airflow at high RPMs. If the butterflies aren't fully open, they'll do the same thing.
dmruschell is offline  
Old 02-11-2018, 10:34 PM
  #26  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Originally Posted by Shdggsdv View Post

Distributor is an MSD Streetfire 8362.

I got my initial set to 12 degrees and according to specs my springs and dizzy should be giving me all in 34 degrees by 3k RPM (Might turn it up to 14 initial to get 36 total later on after getting everything else down).
I need you to post the "specs" you used, exactly, and I will test it here.

I have a brand new 8362 here. I just took it out of the box, chucked it up in my Sun506, and tested it.

It is the worst POS curve I have ever seen:Name:  Street Fire HEI.jpg
Views: 165
Size:  182.9 KB

Excuse the rough graph, but its stupid and worthless. I didn't bother with vacuum yet. Yes. 40* advance at 4K RPM. No, not 20*, 40*
Big2Bird is offline  
Old 02-12-2018, 01:05 PM
  #27  
Shdggsdv
CF Senior Member
Thread Starter
 
Shdggsdv's Avatar
 
Member Since: Jun 2014
Location: Las Vegas Nevada
Posts: 350
Thanked 12 Times in 11 Posts
Default

So I ended up trying something different for my curve. I swapped out my springs for some ones in an old HEI of mine. They felt light and figured why not. I'm getting something like 16 degrees of advance at about 2800 RPM. Then I did the Lars method where I set my dialback light to 34 degrees, set my idle to 3k, and just turned the distributor till the mark went to 0 (Setting my all-in at 34)

But, my timing mark seems to wobble around about a degree. I hadn't noticed it before. Could there be some issue with the distributor?
Shdggsdv is offline  
Old 02-12-2018, 01:24 PM
  #28  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Originally Posted by Shdggsdv View Post
So I ended up trying something different for my curve. I swapped out my springs for some ones in an old HEI of mine. They felt light and figured why not. I'm getting something like 16 degrees of advance at about 2800 RPM. Then I did the Lars method where I set my dialback light to 34 degrees, set my idle to 3k, and just turned the distributor till the mark went to 0 (Setting my all-in at 34)

But, my timing mark seems to wobble around about a degree. I hadn't noticed it before. Could there be some issue with the distributor?
Did you install a stop bushing of any kind? If not, your chasing your tail.
The EXACT same unit here has 20* of distributor degree advance. That's 40* of engine advance. With 9* distributor degrees of vacuum advance, that's a total range of 58* from idle to full advance.(Dizzys turn 1/2 speed of the crank). Even if you set idle to 0*, the total advance would make the engine go nutz.
Setting it at 16* at idle would give you 56* total without vacuum advance.
It's NOT the carb. It's the dizzy.
Big2Bird is offline  
Old 02-12-2018, 01:29 PM
  #29  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

When I have time today, I'll take it apart and figure out the cure. I have to check the slot. A bushing would have to center in the range, but if the slot is wrong, the rotor phasing would be off as well.

The advance chart with the dizzy is close, but in DISTRIBUTOR degrees.
Big2Bird is offline  
Old 02-12-2018, 01:47 PM
  #30  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Name:  20180212_093615.jpg
Views: 144
Size:  3.34 MB

Name:  20180212_093631.jpg
Views: 145
Size:  3.85 MB

Name:  20180212_093634.jpg
Views: 147
Size:  3.89 MB

Name:  20180212_093607.jpg
Views: 145
Size:  3.41 MB

To verify , I locked the rotor with my hand.

One picture shows at rest, the next is the total mechanical advance range.
20* distributor degrees. That is TWICE what you need.
Big2Bird is offline  
Old 02-12-2018, 09:22 PM
  #31  
SFOcean
Junior Member
 
SFOcean's Avatar
 
Member Since: Aug 2017
Location: San Jose CA
Posts: 13
Thanked 4 Times in 3 Posts
Default

I didn't think anyone still had one of those machines, wonder how many decades old it is; sure makes tuning easy
SFOcean is offline  
Old 02-12-2018, 09:34 PM
  #32  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Originally Posted by SFOcean View Post
I didn't think anyone still had one of those machines, wonder how many decades old it is; sure makes tuning easy
My stuff is 70's-80's. I find things that would take ages on a car.

I can't tune like Lars. He has more toys, but I think he would agree, Dyno testing of carbs and dizzys is important. They proof guns, right?
Big2Bird is offline  
Old 02-12-2018, 09:41 PM
  #33  
SFOcean
Junior Member
 
SFOcean's Avatar
 
Member Since: Aug 2017
Location: San Jose CA
Posts: 13
Thanked 4 Times in 3 Posts
Default

Yep, good analogy.
Hope the OP gets a 9 degree or so bushing into his distributor.
SFOcean is offline  
Old 02-12-2018, 09:54 PM
  #34  
twinpack
CF Senior Member
 
twinpack's Avatar
 
Member Since: Mar 2009
Location: Monson MA
Posts: 910
Thanked 14 Times in 14 Posts
Default

I am just throwing this out there because I am in the process of building my motor and learning a lot of things I never gave thought to. One is degree-ing the cam. The OP stated he installed a cam. Through all my conversations and readings, it is clear that a cam MUST be degree'd or you will chase your tail. Just a thought. I saw no mention of this.
twinpack is offline  
Old 02-12-2018, 10:38 PM
  #35  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Name:  20180212_182359.jpg
Views: 119
Size:  3.21 MB

Name:  20180212_182416.jpg
Views: 119
Size:  3.05 MB

Name:  20180212_182410.jpg
Views: 116
Size:  3.21 MB

So I checked rotor phasing. The start is at ignition point at zero advance to start. Top to bottom. Zero, 10*, 20*.

Clearly the rotor and cap can handle 10* distributor degrees max advance.

At 20* (40*engine), it's gonna misfire all over the place.
Big2Bird is offline  
Old 02-13-2018, 12:38 PM
  #36  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Name:  20180213_082909.jpg
Views: 101
Size:  3.64 MB

Name:  20180213_083130.jpg
Views: 106
Size:  3.27 MB

So , two more quick pictures. First is the advance at rest. The second is full advance.
The internal dimensions of the rotor is the only stop on this dizzy. In the second picture, the weights are up against the inside of the rotor, and the "stop" pin is still not engaged.
Today I'll pull it apart, and find the cure.
Big2Bird is offline  
Old 02-13-2018, 01:51 PM
  #37  
69427
Tech Contributor
 
69427's Avatar
 
Member Since: Jun 2004
Location: I tend to be leery of any guy who doesn't own either a chainsaw or a handgun.
Posts: 11,957
Thanked 170 Times in 144 Posts
Default

Originally Posted by Big2Bird View Post
I need you to post the "specs" you used, exactly, and I will test it here.

I have a brand new 8362 here. I just took it out of the box, chucked it up in my Sun506, and tested it.

It is the worst POS curve I have ever seen:Attachment 48253904

Excuse the rough graph, but its stupid and worthless. I didn't bother with vacuum yet. Yes. 40* advance at 4K RPM. No, not 20*, 40*
Hey 'Bird, I think I got that same printer when I got my Sun machine.
69427 is offline  
Old 02-13-2018, 03:46 PM
  #38  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Originally Posted by 69427 View Post
Hey 'Bird, I think I got that same printer when I got my Sun machine.
What printer Mike? Or do you mean the same results?

I jambed in the largest bushing I had and clearanced the slots. Still way too much. Going to weld a slot shut and drill my own hole.

Last edited by Big2Bird; 02-13-2018 at 08:04 PM.
Big2Bird is offline  
Old 02-13-2018, 08:30 PM
  #39  
69427
Tech Contributor
 
69427's Avatar
 
Member Since: Jun 2004
Location: I tend to be leery of any guy who doesn't own either a chainsaw or a handgun.
Posts: 11,957
Thanked 170 Times in 144 Posts
Default

Originally Posted by Big2Bird View Post
What printer Mike? Or do you mean the same results?

I jambed in the largest bushing I had and clearanced the slots. Still way too much. Going to weld a slot shut and drill my own hole.
My curve "printouts" look remarkably like yours.
69427 is offline  
Old 02-13-2018, 08:46 PM
  #40  
Big2Bird
CF Senior Member
 
Big2Bird's Avatar
 
Member Since: Dec 2006
Location: Anaheim Ca.
Posts: 6,141
Thanked 307 Times in 295 Posts
Default

Originally Posted by 69427 View Post
My curve "printouts" look remarkably like yours.
What was your solution?
I guess you can change weight cams, but in their own curve kit the cam doesn't fit.

Last edited by Big2Bird; 02-13-2018 at 09:35 PM.
Big2Bird is offline  

Thread Tools
Search this Thread
Quick Reply: Did basic tuning on new build and still running meh. Help with advanced tuning?


Sponsored Ads
Vendor Directory

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2018 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: