Bog off the line ?
Hey guys.
I am having troubles with a bog / stutter off the line. I have gotten used to launching the car like this but I would like to know what the cause of the bog is its a mild 355 Flat top pistons Hydraulic roller cam .510/.520 lift (not sure on the duration) Edelbrock performer RPM heads It has a 750 holley (vaccume secondarys) on it right now currently jetted at 68 - 73's it used to have 70 - 75's but the change did not seem to make to big of a difference I do have access to a 750 holley mechanical secondaries would this be significantly better ? i've heard the vaccume secondaries are more for street use and bog off instant WOT ? Like i said it just kind of stutters and then takes off. any help is appreciated, Thanks. Craig C693 |
Re: Bog off the line ?
go up 1 size on squirter, and pos .5 to 1.0 higher # power valve if vaccum will allow, what kind of vac nos does it pull idling in gear
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Re: Bog off the line ?
I agree that you need a different squirter. I would take a bigger swing at it than one size though.
what size is in it now? probably a low thirties. I'd go up into t he low to mid 40's on squirter size. you have a momentary lean condition which is causing this problem. |
Re: Bog off the line ?
Craig,
what are your 60ft time? |
Re: Bog off the line ?
1. Make sure you have full travel on acc pump arm with.015 clearance at full stroke
2. Use red pump cam as i remember it is a #330 in the full postion. 3. If you get into a .040 range squrt. You need the hollow pump screw. Don't over tighten it. 4. It would also help to open the Idle Feed restriction in metering body about .003 (usally .033 or.035. Quote:
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Re: Bog off the line ?
Hey, guys thanks for all your help. Here are the specs on my carb
holley 750 4150 PRI Shooter - 25 PRI Pump Cam - 330 #1 Power Valve - 6.5 Second Spring - Purple The car runs mid - low 13's and ive cut a best of a 1.880 but this is with my 12 bolt in my cutlass with stock upper and lower control arms, my pinion angle was off by a mile. Now it's set up right with adjustable 12 bolt uppers no hop bars drag shocks ect. I'm racing this weekend and i'm going to try some changes to the carb on the friday test and tune. |
Re: Bog off the line ?
Thanks, I went to mopac today and picked up some bigger squirters 37's were the biggest they had should be a big difference from the 25's i had in there ? and I also picked up a 7.5 power valve 1 size up from the 6.5 i had. I will try it at the track tomorrow.
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Re: Bog off the line ?
Take your squirter and calipers to a hobby shop and buy a pin vice and drill bits its cheaper than buying squirters. There very easy to drill out. Have a great day
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Re: Bog off the line ?
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Re: Bog off the line ?
I think your sec. spring is too light for your combination. Start your weekend out with the plain (stock) spring and be prepared to try a heavier one.
The heads might be a little big for your combination and might also need a bigger squirter to make up for lack of velocity. Is this a #3310? My bracket car has a 3310 on it. It runs mid 11s. Plain spring, 72 76 jets with a 028 squirter. Good luck. |
Re: Bog off the line ?
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Ya this carb is a 3310. I will try the .037 squirters and a stock spring this weekend, Thanks again. |
Re: Bog off the line ?
Your "bog" is very likely a lean condition like stated. Try the bigger squirters, AND make one change at a time, and keep notes.
Jody -- will the spring affect the launch much? I am thinking not much, if any. If anything, it will stay lean a little longer. Clark Doukas |
Re: Bog off the line ?
Does the car idle well in gear?
Are the throttle blades manually adjusted to be open too far and uncovered the transfer slot? |
Re: Bog off the line ?
Last item I have is an article that talks about baseline setup, and the transfer slot:
http://www.carcraft.com/howto/77958/index.html |
Re: Bog off the line ?
Well guys, changing the squirters was night and day difference, car launches way better with no stutter at all.
I tried it today the way it has always been set up and it went a 13.20 - 1.870 60 ft. and with just the .037 squirter change it went a 13.08 with a 1.840 60 ft. So im very happy with how it is launching now Thanks for all the help ! |
Re: Bog off the line ?
Clark, spring would definetely affect the launch. A bog from a too light spring can also cause consistency issues.
C, glad to hear you fixed it. If you have time this weekend or another weekend humor yourself and try that spring. It should help. Good luck. |
Re: Bog off the line ?
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Thanks Jody, At the next test and tune I will try a heavier spring for sure. Thanks, Craig - C693 |
Re: Bog off the line ?
Jody, using the .37 squirter and your choice of 72/76 jets works like a charm on this carb and my set up !
but now at idle i am getting a "pop" every once in a while, does not seem to be affecting the performance or anything, just wondering what this could be ? Thanks, Craig |
Re: Bog off the line ?
one of your posts said you were going to put in a 7.5 power valve in place of the 6.5. you should be going to a lower #.
Check your vacuum at idle. Being a drag car you can use anything under the vacuum it idles at. 3.5 might be a good choice. It sounds like a lean pop but it could be the power valve leaking too much fuel into the engine??? Have you tried a different spring yet? |
Re: Bog off the line ?
Thanks for all your help jody
It is not a very big duration cam, i checked the vaccume at idle and im reading about 13-14, so I figure the 6.5 power valve that i have in now would be perfect ? I tried a 7.5 power valve at mission on a test and tune friday and it did not like it at all, slowed more then a tenth. Also, I have not tried a heavier secondary spring yet. Right now i have a "purple" spring. |
Re: Bog off the line ?
So how about trying one that's lower than your 6.5?
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Re: Bog off the line ?
Do you think a lower one would work better ? Holley reccomends your vaccume at idle \ 2 so for me 6.5 would be about right ?
Thanks. |
Re: Bog off the line ?
I think the \2 is at cruising vacuum. I get the car cruising at 35 mph and check the vacuum reading, the green duster used to maintain about 7.5 lbs so i used a 5.5 power valve.
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