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Tech Tips
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http://www.clubcobra.com/forums/tech-tips/)
| Alex Donghi |
12-27-2002 12:36 PM |
Springs on Vacuum secondaries on 2X4 holly
Any body have any suggestions which springs to use to regulate the secondaries opening on dual 650 holly set ups? The holly book said to use lighter springs for light cars as the vacuum generated is not as great. Of course it was very general and not specific to a 427SO.
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| Tony Radford |
12-27-2002 02:13 PM |
Alex, did you ask Bill? If you don't ask him, I'm going to tell him you didn't ask him and you'll be in deep sh*t! I've got to get the heat off myself somehow.
Incidentally, I moved the weekend thread to the DSCC forum per your advise.
T
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| Mr.Fixit |
12-27-2002 03:28 PM |
Get the spring kit, start working through them. You will pull less vacuum, but you allready have 4bbls open, so the rears can open later. If you can FEEL the secondaries open, you are really just feeling your motor recover from the bog it was in due to having the secondaries open too soon. Connect the tops of the vacuum pods to one another with a 1/4" hose to link them. This is one of those times where a 1/4 mile and a G-tech would help, cause the seat of our pants will only get you so close.
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| rdorman |
01-08-2003 09:56 AM |
General spring recommendation
What I have seen recommended and done with sucess..... Stand on it in one of the upper gears at the minimum RPM you plan on full throttle use. If the motor is pulling well and then all of a sudden pulls REALLY hard at high RPM, like a turbo kicking in, generally your secondaries have yet to open(sure, could be other things!). Go to a lighter spring. Try again. Keep doing this until the car bogs or falls on its face and takes time to recover. Go back to the previous spring and test drive. Keep the spring the same in both carbs.
Rick
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| Alex Donghi |
01-08-2003 11:54 AM |
Thanx for the help guys. I was able to get one spring kit but they do seem hard to come by. Anyone know in Atlanta who might have the kits?
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| 427 S/O |
01-08-2003 12:48 PM |
Barnett performance warehouse,
404-522-1320, parts arrive next day.
The quick change kit is a must if you don't already have it.
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| rdorman |
01-08-2003 01:41 PM |
Jegs high performance
Ditto on the quick change kit, even if you never change them again! You'll need two sets of springs!
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| Mr.Fixit |
01-08-2003 02:06 PM |
Re: General spring recommendation
Quote:
Originally posted by rdorman
What I have seen recommended and done with sucess..... Stand on it in one of the upper gears at the minimum RPM you plan on full throttle use. If the motor is pulling well and then all of a sudden pulls REALLY hard at high RPM, like a turbo kicking in, generally your secondaries have yet to open(sure, could be other things!). Go to a lighter spring. Try again. Keep doing this until the car bogs or falls on its face and takes time to recover. Go back to the previous spring and test drive. Keep the spring the same in both carbs.
Rick
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If the motor comes on really strong all the sudden, you probubly allready have the secondaries open, the RPM's just got high enough to require them open, so you are feeling the motor recover from overcarburation. It should be a smooth powerband all the way through, if the motor "comes on" partway through the powerband, the secondaries are opening too early or too late. A vacuum gauge in the manifold that is viewable in the cockpit can help you determine if the secondaries are opening too late. |
| Alex Donghi |
01-09-2003 07:52 AM |
Thanks again Barnett has this stuff in stock. This motor doesn't seem to have any surge points like the cam etc coming on strong Unlike my 63 ford 427. That motor at around 3800 rpm the car felt like it was hit in the *ss by a wrecking ball. In fact the tires would break loose in 3 gears. It had a 22 degree advance cam and the 12X1 pistons. A lead fuel eater. It also had mechanical progressive linkage maybe I was putting my foot in that old car too soon and was over carbing it under 3800. Wish I had that old car 63 1/2 galaxie XL
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| SCOBRAC |
01-10-2003 03:56 PM |
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| SCOBRAC |
01-10-2003 03:59 PM |
Alex,
It is quite likely enless you are running the lightest springs or the next to the lightest the secondaries may not fully open at any rpm with 1300 cfm..
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| KobraKarl |
01-20-2003 10:28 AM |
Alex
dont know if you got your springs setup right yet, but im running 2x4 4160s and i tore them down last night to refresh and both secondary springs are coded YELLOW , they have always perfect.
Karl
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| 427 S/O |
01-20-2003 11:23 AM |
Thinking about trying twin 450's, no choke/manual secondaries, as soon as I can find a couple to rebuild?. Got some pretty good feedback from folks running them on their FE's.
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| 427 S/O |
01-20-2003 11:30 AM |
I like Barnett performance because you always talk to a real honest-to-god human being and, their priced at or below everyone else. I don't have any interest in them, just like good service.
They do have a 1-800, don't have it with me.
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KobraKarl is right on the color of the springs. The factory 2X4 carbs came with the "long" yellow. There is a "short" yellow also available that will open earlier. If memory serves me correctly, the white spring is as light as they get.
The reason for the extremely light springs in the two four carbs is due to the vacuum signal to each carb being reduced by half thereby necessitating a lighter spring to get the secondaries to open at the correct rpm. Whenever a second carb is added, air flow that was normally available for one carb is being split between the two carbs making the air flow basically cut in half of what it was for each carb.
There are some other tricks that can be performed on the secondary opening circuit to make the secondaries more responsive or if you've put the lightest springs in and the secondaries are still opening at too high an rpm.
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