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Discussion Starter · #1 ·
Over the past 12 months I have been reading (online) conflicting stories about using rpm air gap or vic jnr manifolds on 347's.

I am currently running an RPM air gap on my 347, ported alloy windsor snr's , 10.2 comp , 650dp holley, 238/[email protected] solid cam (the engine really tappers off around 55/5600rpms), tremec, 4.1 rear in a 68 stang. Its driven on the street maybe once every two to three months.

Does anybody have any opinions, facts or dyno tests between manifolds on 347s?
 

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The air gap should work decent for your combination, although I am partial to using the Vic Jr. in large stroker combination such as yours.

I doubt that the air gap is the cause of your engine tappering off at such a low RPM. I suggest checking your fuel system and for weak valve springs. Are you running a 5/16" fuel line and pickup?

Perhaps there is a timing issue?

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Dennis

65' STANG, 3160 lbs

393W NA, 2.78 Toploader 4 Spd, 9" 3:70 Posi
Pro Comp Heads, Vic Jr. Intake, 750dp, 236/561 Solid Cam, 9.6CR, 1 3/4" Headers, Lakewood, Subframes, Caltracs



<font size=-1>[ This Message was edited by: dennis111 on 9/9/06 7:03pm ]</font>
 

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I have done this test on the dyno and the RPM will make more power up to 5200 to 5400 ,then the jr will pull away. By 7000, the jr is 17 to 20 better. These results were from modified manifolds. Some vi jr will gain 20 to 25 HP from reworking (porting) the rpm will gain much less JOE SHERMAN RACING
 

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In my 347 I shift at 6200 but the car will pull and make good power to 6800. Like Joe said your problem is somewhere else.
 

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Use a vic jr. ! Put a carb on it, a 650 is to small go to a 750, i run a 750 on a 306, 650 would run out of fuel at around 5 grand. I put on a 750 an it will rev to the moon now and picked up 4 mph at the track!
 

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i am also with a victor jr. 650 too small??? my 306 with iron runs 10.90's with a 650 carb. i tryed a 750 and it did nothing for e.t or mph

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<font size=-1>[ This Message was edited by: tonys10sec306 on 9/10/06 9:30am ]</font>
 

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I have a 347 with AFR185's, about 10:1 compression, 650 vacuum secondary carb, 230/[email protected] hydraulic flat tappet cam, C4, 3.55 gears in a 1966 Mustang. I was using a Pro Products Air Gap intake (Edelbrock Air Gap copy). I ran this combo for many months and always ran low 12's at just over 109 mph.

A few weeks ago I swapped to a Vic Jr intake and with no other changes, I went to 112 mph. That is a pretty good power increase but I think there is a lot more in dialing it in and getting it jetted correctly. I have'nt even messed with jets in the 650 yet. But I can definitely say the Vic Jr helped increase power on my combo by about 25 hp.
 

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Dual plane intakes need more carb than a single plane. A 650 might be plenty on a Victor Jr, but to breathe upstairs, a dual plane on a 347 will usually benefit from using a 750.

Most cars that pick up the most from switching from an RPM to a Victor Jr are using a 650 on both intakes.

The best manifold for YOU depends on what you do the most with your car. If the car makes more than enough power in the low and mid range for you, and you want some more power up top.... install the Victor Jr. If the car is rarely gutted out on top, and midrange is where you like your power, keep the RPM/Air Gap.

Good Luck!
 

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I agree with n20mike. The thing is that on a dual plane intake the engine only sees half the carburetor at any given time during any given rpm. You go to an open plenum and the egine sees a full 650 cfm of carb if that is what you are running. Otherwise you cut the carb size in half with the dual plane allowing each cylinder to see 325 cfm of the 650 carb. Most dual plane engine conbos will bennefit fronm a larger carb. That is why some 302/306 engines end up repsonding to the larger 750 over the smaller 650 when running a dual plane intake.
 

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On 2006-09-10 17:44, JAM1775 wrote:
I swapped from Weaind Stealth to V-jr and found the motor picked up 15-20 from 4800 to the 6200 redline on my 351W.
On the street cruising/playing around the Stealth felt better but in a race the V-Jr after each shift just pulled like mad.
Although not the same as giddyup1's 347, I too had similar performance gains with my 393w when I went from the Stealth to the Vic Jr. MPH went from 105's to 108's in the quarter with more pull on the upper end. Shift is also at 6200.

I still have great driveability with negligible differences on the street. As a matter of fact, the car (with no choke) comes to and maintains a cold idle faster than I could ever get with the dual plane and same carb. It still pulls well from 1500 in fourth gear.

The Stealth is not going back on.

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Dennis

65' STANG, 3160 lbs

393W NA, 2.78 Toploader 4 Spd, 9" 3:70 Posi
Pro Comp Heads, Vic Jr. Intake, 750dp, 236/561 Solid Cam, 9.6CR, 1 3/4" Headers, Lakewood, Subframes, Caltracs




<font size=-1>[ This Message was edited by: dennis111 on 9/11/06 7:08pm ]</font>
 
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