Slant Six Forum :: flat spot

Joe,

Quote:

So I guess I need to do some recurving work or lock out the amount of mechanical advance? What is the best way to accomplish this, I have never tried modifying a distributer before.

Check the Recurve instructions on the Engine FAQ.

Example: If you have a 15R governor you could be adding as much as 30 degrees mechanical advance let's say it was accompanied with a VC-208 vacuum advance adding another 22 degrees for 52 degrees plus your initial advance, you could be going well over 60 degrees total. Check for a broken or missing spring. Find out what governor & vacuum advance you have and go from there......I personally like to run 12 to 14 degrees initial for the added punch off idle and have had to limit the mechanical. Check the photos of the springs. Doc has some good ones plus the MOPAR recurve instruction he scanned into 4 jepgs.

Check the recurve articles and get some stock MOPAR springs from "bigslant6fan".

I have over done it before and went to high with out pinging (with higher octane gas) so I didn't realize it. The engine just goes flat if you don't have your foot to the floor. By that I mean at 0 vacuum you have taken the vacuum advance out of the equation so you only have initial plus mechanical. If you let up and start to see some vacuum on the gauge, then you will feel it go flat or hear it ping.

Hope this helps.

Author:	oklahoma joe [ Fri Aug 13, 2010 10:06 am ]
Post subject:	flat spot
Hi, I have been trying to get rid of a dead spot my cars acceleration. For everyday normal driving she runs like a champ no problems. Idle is steady acceleration is responsive. But if you floor it she accelerated great though 1st gear steady all the way to 5500 rmp and then starts to lose her punch in 2nd and 3rd gear over 3000 RPM. Its like some one takes the wind out of her sails at about 3000 rpm under heavy load. There is also a slight intermitent miss over 2500 that can only be felt with your hand on the engine or at the exhaust outlet. I seemed to notice it right after I put on a new exhast (2 1/4" flowmaster to a 2" tailpipe). I did not drive the engine much before the new exhaust was put on so it may have been that way before also. I am wondering if it is possible the engine is leanning out under load at higher RPMS. I had a small amount of pinging under load and changed to a higher octane gas (89) and that seemed to take care of it. But I thought it was strange to have that problem at a 8.4 compresson ratio. The engine also seems to be putting out a lot of heat when it is ran hard, normal driving no problem. The exhaust seems really hot out the tail pipe after some hard driving. Has anyone had a problem with not enough fuel with a BBD? If so how did you go about fixing it? open to any new ideas igniition, transmission) 198 engine 8.4 compression ratio .060 of the head 3.460 bore 198 crank and rods stock pistons with cast rings Stock cam bumped up to a true .44 intake lift at valve degreed and set 3 degrees retared stock valves with hardened exhaust seats ported intake and exhast runners super six intake and exhaust gasket mached to head Carter bbd from a v-8 pre emmissions Stock timming chain

Author:	ceej [ Fri Aug 13, 2010 10:11 am ]
Post subject:
The only thing with your build that stands out is the V8 BBD. See if you can find a Slant Six BBD, as there are differences. PM SlantSixDan and see if he has any sources for an NOS carb. CJ

Author:	Doc [ Fri Aug 13, 2010 11:44 am ]
Post subject:
What is the total timing? It sounds like it could be too much high speed (mechanical) ignition advance. DD

Author:	emsvitil [ Fri Aug 13, 2010 1:11 pm ]
Post subject:
The fuel pump may not be keeping up with the carb.... You're out of 1st before you empty the bowl, so you don't notice it. In 2nd (and 3rd) let up for about 20 seconds to give the pump a chance to fill up the carb bowl, then floor it and see what happens. If it works, you have a restriction somewhere (fuel filter or sock) or the pump doesn't have enough capacity.

Author:	ESP47 [ Fri Aug 13, 2010 1:21 pm ]
Post subject:
Quote: The only thing with your build that stands out is the V8 BBD. See if you can find a Slant Six BBD, as there are differences. PM SlantSixDan and see if he has any sources for an NOS carb. CJ If you close off the holes in the throttle plates, there should be no really difference in the BBD carb vs. the slant six carb other than the choke linkage. At least I think thats what Dan used to say.

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Author:	carlherrnstein [ Fri Aug 13, 2010 3:20 pm ]
Post subject:
I second emsvitil's theory of the carburetor draining fuel quicker than it can be fed. I had a similar problem with my Holley 2280 I changed the fuel filter then pump and problem went away Good luck

Author:	oklahoma joe [ Fri Aug 13, 2010 3:24 pm ]
Post subject:
Quote: What is the total timing? It sounds like it could be too much high speed (mechanical) ignition advance. DD I got home and hooked up the timing light and the timing mark went way off the scale as the rpm approached 3000 rpm. I don't know how to get a good measurement of total timing because the timing mark goes way off the indicator. So I decided to retarded the ignition timing by 10 degrees and see what happened. The motor now has poor low end but the top end pulls steady and strong up to 5500 rpm. Thanks For the tip Doc So I guess I need to do some recurving work or lock out the amount of mechanical advance? What is the best way to accomplish this, I have never tried modifying a distributer before. Joe

Author:	Doc [ Fri Aug 13, 2010 3:43 pm ]
Post subject:
If you do not have a dial-back timing light, use the current timing tab, set balancer at zero, pen mark it at the highest advance increment. (15 degrees) Move the new mark to zero and mark it again at 15... that will be 30 total. Run a check to be sure that new mark comes into view when reving the engine... then punch or engrave it into the damper. Start reading-up on distributor recurving. DD

Author:	oklahoma joe [ Fri Aug 13, 2010 3:54 pm ]
Post subject:
i will try that tonight. thanks Joe

Author:	Aggressive Ted [ Fri Aug 13, 2010 5:34 pm ]
Post subject:
Joe, Quote: So I guess I need to do some recurving work or lock out the amount of mechanical advance? What is the best way to accomplish this, I have never tried modifying a distributer before. Check the Recurve instructions on the Engine FAQ. Example: If you have a 15R governor you could be adding as much as 30 degrees mechanical advance let's say it was accompanied with a VC-208 vacuum advance adding another 22 degrees for 52 degrees plus your initial advance, you could be going well over 60 degrees total. Check for a broken or missing spring. Find out what governor & vacuum advance you have and go from there......I personally like to run 12 to 14 degrees initial for the added punch off idle and have had to limit the mechanical. Check the photos of the springs. Doc has some good ones plus the MOPAR recurve instruction he scanned into 4 jepgs. Check the recurve articles and get some stock MOPAR springs from "bigslant6fan". I have over done it before and went to high with out pinging (with higher octane gas) so I didn't realize it. The engine just goes flat if you don't have your foot to the floor. By that I mean at 0 vacuum you have taken the vacuum advance out of the equation so you only have initial plus mechanical. If you let up and start to see some vacuum on the gauge, then you will feel it go flat or hear it ping. Hope this helps.

Author:	oklahoma joe [ Fri Aug 13, 2010 5:53 pm ]
Post subject:
Checked total advance and it looks like this. 10 degrees initial advance 15 degrees mechanical 25 degrees vacuum 50 degrees total Which is better to cut back the vacuum or the mechanical advance or a little of both. Joe

Author:	oklahoma joe [ Fri Aug 13, 2010 5:59 pm ]
Post subject:
Quote: Joe, Quote: So I guess I need to do some recurving work or lock out the amount of mechanical advance? What is the best way to accomplish this, I have never tried modifying a distributer before. Check the Recurve instructions on the Engine FAQ. Example: If you have a 15R governor you could be adding as much as 30 degrees mechanical advance let's say it was accompanied with a VC-208 vacuum advance adding another 22 degrees for 52 degrees plus your initial advance, you could be going well over 60 degrees total. Check for a broken or missing spring. Find out what governor & vacuum advance you have and go from there......I personally like to run 12 to 14 degrees initial for the added punch off idle and have had to limit the mechanical. Check the photos of the springs. Doc has some good ones plus the MOPAR recurve instruction he scanned into 4 jepgs. Check the recurve articles and get some stock MOPAR springs from "bigslant6fan". I have over done it before and went to high with out pinging (with higher octane gas) so I didn't realize it. The engine just goes flat if you don't have your foot to the floor. By that I mean at 0 vacuum you have taken the vacuum advance out of the equation so you only have initial plus mechanical. If you let up and start to see some vacuum on the gauge, then you will feel it go flat or hear it ping. Hope this helps. Thanks I printed it off for some good reading tonight. I was looking for that kind of info but did not know the FAQ was up there . I'll start reading all that good stuff. Joe

Author:	Aggressive Ted [ Fri Aug 13, 2010 6:43 pm ]
Post subject:	Distributor recurve info
Joe, It might want to try a different vacuum advance. Instead of the 11R like you have, find a vacuum advance arm stamped with a 8.5R or lower. Another option is to tune the vacuum advance that you have. Doc's last jpeg shows you how to do that. Also take a look at the vacuum advance listings of the different cans. If you were just trying to get a best mileage at cruise you got a great set up! But you need to tune it for your cars needs and how you drive. If you have a light car and light touch and on the gas pedal and a low rear end ratio, small tires, you could experience that flat feeling. If you drove a little harder, had a heavier car or taller gear ratio, or bigger tires, the vacuum would be lower and less advance. What does your vacuum gauge show at cruise? and tach? Your close in your tuning. It sounds like your putting out some good power! You need to fine tune the balance of advance a little so it is at the right amount under load and at cruise. You have 25 degrees with the initial and mechanical, which is good because your under 30 degrees total so the vacuum advance is the biggest variable. You may need to fine tune your vacuum advance a little. I run a 11R can a VC-208 however, I run it 3 turns out so it delays the starting point. That allows for mid-range freedom before it engages. When I am cruising at high vacuum 18" to 22" it comes on like an overdrive and provides some real good mileage.

Author:	oklahoma joe [ Sat Aug 14, 2010 2:02 pm ]
Post subject:
set initial timing to 10 degrees and disabled the vacuum advance. A took it for a drive with the video camera. Will work on finding a vacuum advance with less pull. Thanks for all your help. This site has really helped me out over the last few years with this project. See video below. Is there a way to calculate horse power from 0 to 60 times? I think it is about at 13 sec right now. http://www.youtube.com/watch?v=bwY4PS3B3PE Joe

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