Throttle Response - Chevy Nova Forum
Visit our sponsor, National Nostalgic Nova
 
Steve's Nova Site is an automotive enthusiast website dedicated to the 1962 - 1979 Chevrolet Nova, Chevy II and Acadian automobiles. We work together to preserve, restore, drive, show, race and provide fellowship for these classic cars. This is one of the best places to find information about parts, rebuilding, restoration and racing. This website is not affiliated with GM, General Motors or Chevrolet in any capacity.

Go Back   Chevy Nova Forum > Body, Chassis and Mechanical > Drivetrain & Performance


StevesNovaSite.com is the premier Chevrolet Nova Forum on the internet. Registered Users do not see the above ads.
Reply
 
Thread Tools Display Modes
Old 15th-September-2012, 08:15 AM   #1
iroc343
(OP)
 
iroc343's Avatar

Title: Nova Guru
iTrader: (1)
Status: Offline
Join Date: Feb 2011
Location: erie,pa
Nova(s): 1970 SS L78
Posts: 587
Throttle Response

355, 9.6-1 comp, AFR 195 heads, Big Mutha Thumpr roller cam, 780 Holley carb. Off idle throttle response is not what I think it should be. It runs fine, but I don't know how to explain it, the initial throttle response is hollow, not crisp. Once you get beyond that it runs fine. No stumble accelerating from anything but idle. I've got a 31 squirter in it and it squirts immediately upon moving the linkage. It's a four speed and you deal with this everytime you take off from a stop. The secondary throttle plates are positioned properly to the transition slots. That made a huge difference in the idle quality issue I was having. I drilled two 1/16" holes in the primary blades, but the blades are still above the transition slots on the primary side. Should I open the holes up to get the blades positioned closer to the transition slots? The car runs great, just this little annoyance off idle.

Last edited by iroc343; 15th-September-2012 at 08:20 AM.
  Reply With Quote
Sponsored Links
Advertisement
 
Old 15th-September-2012, 06:13 PM   #2
cdahl383
 
cdahl383's Avatar

Title: Nova Guru
iTrader: (0)
Status: Offline
Join Date: Apr 2012
Location: Detroit, MI
Nova(s): 1972 Nova
Posts: 3,990
Garage
I had an off idle stumble in my Edelbrock 800 on my 383 for a little while before I tinkered with the carb this summer. I had to put in bigger squirters, adjust the accelerator pump arm linkage, and raise the floats up a little, and bump my initial timing up some. Once I did that it got rid of the stumble. Now it just takes off and goes like it should.

Maybe try these ideas:

1.) Run more initial timing. If that cam has decent duration numbers you might be able to run as much as 18-22 initial without any problems. Just be sure to limit your mechanical advance so your total timing isnt out of wack.

2.) If running vacuum advance, try hooking it to manifold port so its there at idle. Might help with off idle transition. Some cars it helps, others it doesnt, just have to try it out and see.

3.) Could try a little bigger pump squirter for more fuel off idle. Could just need a little more fuel until the primary circuit takes over.

Running a little more initial timing might allow you to turn down your idle speed screw enough to get your transition slots lined up properly.
__________________
Carl
1972 Chevy Nova owned since I was 15 yrs old
12.36 @ 109.65mph w/ 1.72 60ft
  Reply With Quote
Old 15th-September-2012, 06:47 PM   #3
Philip
 
Philip's Avatar

Title: Moderator
iTrader: (17)
Status: Offline
Join Date: Mar 2004
Location: Marana AZ 85653
Posts: 11,493
Very good info from Carl
What intake are you using?
__________________
64 Nova 400 series 4 door

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
SOLD 01/15

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

  Reply With Quote
 
Old 16th-September-2012, 08:30 AM   #4
iroc343
(OP)
 
iroc343's Avatar

Title: Nova Guru
iTrader: (1)
Status: Offline
Join Date: Feb 2011
Location: erie,pa
Nova(s): 1970 SS L78
Posts: 587
I do have the vacuum advance hooked to manifold vacuum. I have an MSD distributor adjust to 18 degrees initial with 38 degrees total. It's got an Edelbrock RPM manifold. I'll try a bigger squirter. I just thought going from the 25 it came with to a 31 was a big jump. Thanks for the suggestions, looks like I'm playing with the right things.
  Reply With Quote
Old 16th-September-2012, 08:54 AM   #5
sbc1320
 
sbc1320's Avatar

Title: Nova Guru
iTrader: (0)
Status: Offline
Join Date: May 2008
Location: Houston,Texas
Nova(s): 1972 Nova
Posts: 19,240
I have a 383(AFR 195's)-18 degrees initial and 18 degrees mechanical(no vacuum) , Lunati Voodoo cam, Performer rpm intake, all MSD, and an 850 carb.

I just upped my squirters from a 33 to a 35. Mine had a very slight tip in when I would just give it a tad of gas in drive. It took care of mine, but it still had excellent throttle response. When I checked the 33's I took off, one of the holes wasn't opened up enough. I checked them with a tip(cutting torch) cleaner I have and the cleaner would pass thru all the holes in the 33 except one. I checked my 35's and then installed them. I think once you go past a 37 or so that you need to install the 50cc pumps.

Once you get a lot of duration(@.050) in your cam you usually have to play with the pump cams and or squirters if your carb wasn't set up for them.
  Reply With Quote
Old 16th-September-2012, 11:08 AM   #6
cdahl383
 
cdahl383's Avatar

Title: Nova Guru
iTrader: (0)
Status: Offline
Join Date: Apr 2012
Location: Detroit, MI
Nova(s): 1972 Nova
Posts: 3,990
Garage
Not sure on the duration/lsa on that cam, but you could switch bushings in the MSD distributor to the 18 degree one and run 20 initial and 18 mechanical for the same 38 total. Probably wont fix the problem entirely, but might help, especially if you have some serious duration.

I had to install the biggest squirters Edelbrock makes in my 800 carb to get it to feel right off idle. It came stock with .035" squirters and I installed the larger .043" squirters. I also adjusted the accelerator pump so it squirted more shot. Holley carbs are different I know so I cant really help you much with that. I know they make different cc pumps and cams and stuff so you have a lot more combos to work with than an Edelbrock.

What kind of converter are you running? What stall speed? I know with my car I just have a 2200 stall in there right now and its way too low for the way the car is setup now. If I had a 3000-3500 stall I know the car would take off much faster out of the hole, but for now its what I have to work with. Running a converter with too little stall speed for your setup will also result in poor off the line performance.
__________________
Carl
1972 Chevy Nova owned since I was 15 yrs old
12.36 @ 109.65mph w/ 1.72 60ft
  Reply With Quote
Old 16th-September-2012, 11:10 AM   #7
cdahl383
 
cdahl383's Avatar

Title: Nova Guru
iTrader: (0)
Status: Offline
Join Date: Apr 2012
Location: Detroit, MI
Nova(s): 1972 Nova
Posts: 3,990
Garage
You can also order additional advance limit bushings from FBO from their website. They make a 10 and 14 degree limit bushing. You could run 24 initial and 14 mechanical for 38 total. That might be too much initial for your setup, but just another thing to consider.

I recently switched from an HEI to the MSD distributor and I have to run 14 initial and 18 mechanical for 32 total where before I had 16 and 16 for 32. I'm thinking of ordering those bushings just so I can run 18 initial and 14 mech. for 32 total just to see how that feels.
__________________
Carl
1972 Chevy Nova owned since I was 15 yrs old
12.36 @ 109.65mph w/ 1.72 60ft
  Reply With Quote
Old 16th-September-2012, 11:56 AM   #8
the FLYER
 
the FLYER's Avatar

Title: Nova Guru
iTrader: (24)
Status: Offline
Join Date: Feb 2004
Location: TudorpostVille
Nova(s): The Pillars of Society
Posts: 26,232
it's a manual tranny.
__________________
the Flyer Special
'64 411 377-Tko600-3:73's


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
  Reply With Quote
Old 16th-September-2012, 11:56 AM   #9
Philip
 
Philip's Avatar

Title: Moderator
iTrader: (17)
Status: Offline
Join Date: Mar 2004
Location: Marana AZ 85653
Posts: 11,493
Quote:
Originally Posted by iroc343 View Post
I do have the vacuum advance hooked to manifold vacuum. I have an MSD distributor adjust to 18 degrees initial with 38 degrees total. It's got an Edelbrock RPM manifold.
How many degrees of timing advance is the vacuum adding? I limit mine to 14. When it had more than that the engine would have a small flat spot off idle.
__________________
64 Nova 400 series 4 door

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
SOLD 01/15

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

  Reply With Quote
Old 16th-September-2012, 08:06 PM   #10
cdahl383
 
cdahl383's Avatar

Title: Nova Guru
iTrader: (0)
Status: Offline
Join Date: Apr 2012
Location: Detroit, MI
Nova(s): 1972 Nova
Posts: 3,990
Garage
You mean you dont have a converter in front of your 4 speed? Haha! Sorry I missed that, whoops!

Philip is right, when I had my other distributor, it came preset to 16 degrees, way too much, it took off funny and surged at cruise. I dropped it down to 10 degrees and it ran perfect then.

Are you running a carb spacer? Sometimes carb spacers can throw things off a little depending on the engine. Some cars it helps, others it hurts.
__________________
Carl
1972 Chevy Nova owned since I was 15 yrs old
12.36 @ 109.65mph w/ 1.72 60ft
  Reply With Quote
Old 17th-September-2012, 06:52 AM   #11
iroc343
(OP)
 
iroc343's Avatar

Title: Nova Guru
iTrader: (1)
Status: Offline
Join Date: Feb 2011
Location: erie,pa
Nova(s): 1970 SS L78
Posts: 587
Thanks for all the info. I upped the timing to 18 degrees initial and with the blue bushing I'm seeing 38 total. I went from a 31 to a 37 squirter and the hollow spot is gone. It's amazing what a little fine tuning can do. Thanks again, you guys are awesome.
  Reply With Quote
Old 18th-September-2012, 11:08 AM   #12
cdahl383
 
cdahl383's Avatar

Title: Nova Guru
iTrader: (0)
Status: Offline
Join Date: Apr 2012
Location: Detroit, MI
Nova(s): 1972 Nova
Posts: 3,990
Garage
Sweet, glad you got it figured out! I had to go to bigger squirters too. Fine tuning definitely makes the car more fun to drive!
__________________
Carl
1972 Chevy Nova owned since I was 15 yrs old
12.36 @ 109.65mph w/ 1.72 60ft
  Reply With Quote
Old 18th-September-2012, 05:05 PM   #13
cstraub

Title: Nova Senior Member
iTrader: (0)
Status: Offline
Join Date: Oct 2006
Location: Tri-Cities, TN
Posts: 328
You can not use those cams with AFR heads because of their high I/E ratio. It will never run well with that cam. Sorry it just won't.
  Reply With Quote
Sponsored Links
Advertisement
 
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
No response bidder---what do I do? Carl Stevenson Ebay, etc. Discussion 16 29th-December-2006 01:44 AM


Site best viewed set to 1024 x 768.

All times are GMT -4. The time now is 04:50 AM.

Custom Designed for Steve's Nova Site by: vBSkinworks

 
Powered by vBulletin® Copyright ©2000 - 2017, Jelsoft Enterprises Lt
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
 

Garage Plus vBulletin Plugins by Drive Thru Online, Inc.