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 Demon 750 calibration on a 428 Ford FE 
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Joined: Sun Oct 25, 2015 7:39 pm
Posts: 21
I have an older Barry Grant Speed Demon 750 Twin Squirter (1.4" dia. venturi, 1-11/16" throttles) I'm installing it on a '66 Fairlane with a 0.030" over 428 FE. Relevant specs are as follows:

Ported factory heads
9.6:1 compression
248/254 @ 0.050" 107 LSA solid flat tappet cam
Perf RPM intake
1-3/4" Hooker headers with 3" full dual exhaust
C-6 with 3,800 stall
3.89 gears

I've already replaced MAB, IAB, IFR's and e-bleeds with 8-32 set screws. Factory and modified calibration for the carb is as follows:

Item Factory Modified
MJ 76/83 72/82
Shooter 31/31 31/31
Pump cam pink/pink pink/pink
MAB .039/.039 .026/.026
IAB .070/.062 .073/.073
PVCR .059/none .059/none
PV 6.5"/none 6.5"/none
IFR .033/.033 .032/.032
Kill bleed .028 .028
e-bleeds .031, .031, .031 .026, .026, plug
t-slot jet open/open open/open

I have limited experience tuning FE's particularly with this much cam. It only idles at about 7" Hg. I'm looking for feedback on the modified calibration.


Thanks


Sun May 14, 2017 4:54 am
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Joined: Fri May 20, 2016 5:18 am
Posts: 117
First ting to look in to is the initial ignition setting the engine needs to idle properly in gear and neutral ( highest vacuum reading with out misfiring and high ignition starting problems) then rework your advance curve to get the most desirable total advance for the application
Its very important to have the ignition worked out before carb calibration starts for real.


Sun May 14, 2017 7:00 am
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Joined: Mon Apr 17, 2017 6:57 pm
Posts: 8
I love FE's, tobbemek is right tho, without a high initial the engine won't run well.
My 447ci 2x4 FE runs 22 initial and 32 total.

I don't know what distributor you are using, but with a Duraspark they are easy to adjust by welding up the advance arm and regrinding the slot to size.


Sun May 14, 2017 7:58 am
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Joined: Sun Oct 23, 2016 5:52 pm
Posts: 138
Location: Canada
I LOVE '66 Fairlanes, and with a 428, well, that's just awesome! Pictures?! :thumbr:

By the factory jetting you listed, I assume this is the down-leg 750 DP (1402010) version? Big jump down with the MABs.
Here's a spec chart:

Image

That lists factory PIABs & SIABs at 0.070", so all four at 0.073" could/should be fine. The healthy camshaft in it might like a little more PIFR. Try it and see how it works.

_________________
Mike

1986 Mustang convertible. Originally 3.8L V6 with EEC-IV CFI.
Now has a Holley List-4412-2, and averages 34 (28 US) MPG.
If you're ever bored - some narrow band O2 tuning video of this thing:
http://www.youtube.com/channel/UC9glRIa3jAAtNhaXfg_cZXQ


Sun May 14, 2017 10:30 pm
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Joined: Sun Oct 25, 2015 7:39 pm
Posts: 21
It's currently running an MSD w/o vacuum advance with 15 initial and 35 total. Engine made best power at 35 total on the dyno. I know it needs more initial. I've ordered a OEM Duraspark distributor. This thing only makes about 7-8" Hg manifold vacuum so I'm concerned I won't be able to connect the vacuum advance to manifold vacuum and achieve stable idle timing. If I can, I'll probably set it up with about 20 initial, 35 total, with another 10-12 vacuum.

I recalibrated the Demon to make it closer to a Holley 750. If it were 2-corner idle I'd have used 35 IFR's. I don't have any experience with 4 corner idle carbs, but figured it could use something less than 35's. I'll test and see.


Wed May 17, 2017 3:39 pm
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Joined: Fri May 20, 2016 5:18 am
Posts: 117
If that carby dosnt have ported vacuum for the dizzy vac, i think it will be ok any way at intake vac in that range, just picking up vacuum 10 or so HG just over idle ( like when the throttle blade open up ported vac) and dizzy vac advance go off in same range HG just before power valve opens.
Carb calibration seems to be right on for a good starting point let us know how it turns out.


Wed May 17, 2017 5:40 pm
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Joined: Sun Oct 23, 2016 5:52 pm
Posts: 138
Location: Canada
All good plans. Let us know how you make out.

_________________
Mike

1986 Mustang convertible. Originally 3.8L V6 with EEC-IV CFI.
Now has a Holley List-4412-2, and averages 34 (28 US) MPG.
If you're ever bored - some narrow band O2 tuning video of this thing:
http://www.youtube.com/channel/UC9glRIa3jAAtNhaXfg_cZXQ


Thu May 18, 2017 7:40 am
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Joined: Sun Oct 25, 2015 7:39 pm
Posts: 21
I got the Duraspark distributor installed with 23° initial and 35° total. Had a hard time getting the vacuum advance to work. I tested it on the running engine with a vacuum pump. The advance would increase to a point until the engine would begin backfiring through the exhaust and die. The spark was jumping to the neighboring terminal in the distributor cap. I triple checked the wiring and it was fine according to MSD and other online sources. I reversed the two wires connecting the magnetic pickup to the MSD 6AL and it worked. I now have the orange wire from the pickup connected to the green wire of the MSD. According to every source this is wrong but it works and the timing is stable. The vacuum can pulls 24 degrees which gives 59 total. There is a slight miss at low rpm cruise. I need to fabricate a mechanical stop to limit the vacuum advance to about 12 degrees.

I never did get the Demon installed. I received a Mr. Gasket chrome steel fuel line with brass inlet fittings from Summit. The inverted flare nuts would only engage the fittings about 1 turn before the fuel line seated in the fittings. The soft brass fittings stripped before the nuts were sufficiently tight. Reminded me how the inferior quality of many aftermarket parts makes this hobby frustrating.

However, with the ignition mostly squared away the Holley 750 DP works remarkably well. It has a chokeless contoured main body with the word "Titan" inscribed in the side. It's been a while since I had it apart, but the specs I remember are:

MJ 71/78
IAB 0.073/0.073
MAB 0.029/0.029
IFR 0.032 or 0.033 - 4 corner idle
e holes - 2 per side, 0.026 or 0.028
6.5 power valve
pink pump cams
31 squirters

It still has a pretty lumpy idle with the big cam, but once off idle throttle response is instant and it runs very smooth. I'll bump the SMJ up to 81 but other than that I'll run it for a while.


Mon May 22, 2017 8:55 am
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Joined: Sun Oct 23, 2016 5:52 pm
Posts: 138
Location: Canada
Roadknee wrote:
I got the Duraspark distributor installed with 23° initial and 35° total. Had a hard time getting the vacuum advance to work. I tested it on the running engine with a vacuum pump. The advance would increase to a point until the engine would begin backfiring through the exhaust and die. The spark was jumping to the neighboring terminal in the distributor cap. I triple checked the wiring and it was fine according to MSD and other online sources. I reversed the two wires connecting the magnetic pickup to the MSD 6AL and it worked. I now have the orange wire from the pickup connected to the green wire of the MSD. According to every source this is wrong but it works and the timing is stable. The vacuum can pulls 24 degrees which gives 59 total. There is a slight miss at low rpm cruise. I need to fabricate a mechanical stop to limit the vacuum advance to about 12 degrees.

I never did get the Demon installed. I received a Mr. Gasket chrome steel fuel line with brass inlet fittings from Summit. The inverted flare nuts would only engage the fittings about 1 turn before the fuel line seated in the fittings. The soft brass fittings stripped before the nuts were sufficiently tight. Reminded me how the inferior quality of many aftermarket parts makes this hobby frustrating.

However, with the ignition mostly squared away the Holley 750 DP works remarkably well. It has a chokeless contoured main body with the word "Titan" inscribed in the side. It's been a while since I had it apart, but the specs I remember are:

MJ 71/78
IAB 0.073/0.073
MAB 0.029/0.029
IFR 0.032 or 0.033 - 4 corner idle
e holes - 2 per side, 0.026 or 0.028
6.5 power valve
pink pump cams
31 squirters

It still has a pretty lumpy idle with the big cam, but once off idle throttle response is instant and it runs very smooth. I'll bump the SMJ up to 81 but other than that I'll run it for a while.


Firing previous to even the intake stroke, backfiring out the exhaust, sounds instead like timing retard to me, or an incredible amount of timing advance. Since I need to limit my Duraspark's amount of vacuum advance as well, because it's travel is far too much and I've already adjusted it's diaphragm spring to limit it, (I've put it on the back burner, but am reminded each time upon very light acceleration approaching the top of each gear, some pinging) I'd appreciate it if you'd share your idea/s for doing that.

Nice results :thumbr:

_________________
Mike

1986 Mustang convertible. Originally 3.8L V6 with EEC-IV CFI.
Now has a Holley List-4412-2, and averages 34 (28 US) MPG.
If you're ever bored - some narrow band O2 tuning video of this thing:
http://www.youtube.com/channel/UC9glRIa3jAAtNhaXfg_cZXQ


Tue May 23, 2017 12:30 pm
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Joined: Fri May 20, 2016 5:18 am
Posts: 117
Yeaa does old style Holley 750 carbs, all most never disappoint you :D


Tue May 23, 2017 2:06 pm
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