j par
Well-hung Member
I don't consider it to be a long duration either.. mine was much longer than that, but the one in my truck is much shorter and response is spot on in the low end...
408 ignition curver advice
- Thread starter mbaird
- Start date
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What is your curve like ?
Newbomb Turk
Well-Known Member
You need more initial and probably a slower curve. 32 is probably as high as that head needs.
j par
Well-hung Member
Ooops
I brought the duration of the cam down considerably to 245 at 50 (I think.. it's been a while..) and shaved the lift quite a bit... I left the distributor alone.. As long as I didn't get to punchy you with the pedal down low it ran much more predictable at lower rpm's...
Now the lower 9 and a 1/2 to 1 compression 408 I have in my truck. I have a 235 at 50 lift and a wide 18° curve with just the 2 medium Springs in the distributor. And it runs perfect from down low all the way out...
My 410 stroker in my dustor has probably 11.4 to 1 compressiand and when it had a 267 at 50 duration with the 603 lift, I had about 12° of total timing with no vacuum advance and I would run it about 23 to thirty five and an extremely faster curve ... I think the MSD distributor had like the weakest Spring and the second weakest Spring in it....
I brought the duration of the cam down considerably to 245 at 50 (I think.. it's been a while..) and shaved the lift quite a bit... I left the distributor alone.. As long as I didn't get to punchy you with the pedal down low it ran much more predictable at lower rpm's...
Now the lower 9 and a 1/2 to 1 compression 408 I have in my truck. I have a 235 at 50 lift and a wide 18° curve with just the 2 medium Springs in the distributor. And it runs perfect from down low all the way out...
I'll bet it idles better with less throttle blade, and much more power and response on tip in?
Yes . Now I need to adjust the idle circuit.
I understand. I believe though that he's in need of more idle timing and just an all around different curve.
And you believed correctly.
Much better off idle torque with the current curve . I will continue to tweek it over the next few weeks .
340sFastback
Well-Known Member
I used to run 32 fixed/locked timing no curve in my 414. Did that when auto trans used to be in there and converter was too tight for cam. Band aided the in gear idle problems. It never had an issue starting locked in at 32 like some say can happen. Once I got a looser converter in years ago I went with 21 initial to 32 total which is what I still run it at. Can burn tires up just on the primaries half throttle; need a lot more tire on the car apparently. LD340 intake Holley 750 double pumper etc.
Back when I had stock 340 open chamber X heads original pistons stock cam ran 38 total. The old school setups like more timing.
Back when I had stock 340 open chamber X heads original pistons stock cam ran 38 total. The old school setups like more timing.
I'm sure you'll get it optimized. You're open to trying different things and that's good. You should find my thread regarding using manifold vacuum on the vacuum advance can. If you are running a vacuum advance, it might be worth experimenting around with.
My Ford 400 is sitting at 44* at idle. Vixen's slant 6 is close to the same. I forget exactly where it is. They both improved noticeably when I made the change.
You're over thinking this.
Your problem is your Carb.
Despite being a 408, an 850 is too much Carb.
And your sluggishness is typical of too much carb.
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You would be outright amazed at the pickup in your car once you switch to a healthy 750 cfm.
You may even pick up on the top end.
Your problem is your Carb.
Despite being a 408, an 850 is too much Carb.
And your sluggishness is typical of too much carb.
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You would be outright amazed at the pickup in your car once you switch to a healthy 750 cfm.
You may even pick up on the top end.
What do you base this on? Many of us with 408's have found quite the opposite, in fact, mine pics up considerably with a 950 over an 850. I'm not looking to start an argument. I just wonder if this is your opinion, or do you have empirical data to support this?
mopowers
Well-Known Member
How do the venturi and throttle bore sizes compare between the 850 and 950 you've tried? I've found that 850 carbs usually have larger venturis and maybe larger throttle bores than some 950s.
I will check, don't recall off top of my head. Both Quick Fuel carbs, both Q model, one 850, one 950. Both jetted and tuned on dyno.
Thx ! I am running VA and will check out your thread. If you know where it is off hand and could post a link that would be great.
j par
Well-hung Member
I'm in BIG trouble... 1250cfm....
lead69
hopeless car junkie
If only it was still together!
j par
Well-hung Member
Last edited:
Here you bees.
Manifold Vacuum Experiment
I've been noticing a slight stumble off idle and reduced fuel economy on my 75 F250. 400 engine, T18 4 speed transmission and Dana 60 with 3.73 gears. So I started checking it out and quickly found a bad vacuum advance canister. Got a new one and got it installed this morning. I decided to try...
www.forabodiesonly.com
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