What headers>?

When in doubt, go big!

Seriously, I'd go with the 1 3/4... but that is not based off anything other than my preference/opinion.

I think you've got enough cubes to provide torque, that you can make a go with the 1.75s.

Usually they also are used with 3" pipes rather than your 2.5s, but I think you'll be breathing deep enough for it to not be a problem. Just my opinion of course...YMMV ;-)

Go with 1 3/4 the smaller 1 5/8 will just choke down the combo you are using.

1.75" headers... do they make torque steps for your application?

Off topic:
IMO you are using the wrong intake.
You have plenty of parts going for torque, the intake on this combo should be able to breathe. My experience with the RPM is that it falls off after 3k rpms compared to a mild single plane intake. Not that it won't spin or make power past 3k, but it gets increasingly choked down while SPs go up-up and away. Below 3k, it has a little more torque, but it is not as dramatic as some would believe, assuming you use a mild SP intake. Besides, you are going to use a 3k stall converter! Why not use an intake that operates best after 3k instead one that falls off in comparision?
Just a comment from experience...
Good luck
Dave

I will tell you from very recent experience and a very similar set up that I have (see below). I had a port matched performer RPM and the car ran a best quarter of 11.70 @ 115 on slicks last year. Low end torque was awesome and I thought the car could not run any better but it seemed to not have the grunt up past 5400RPM, it would pull, but I was not satisfied. SO I went to my local speed shop and went over my build with the owner and ask him what he thought the motor would do with a Vic Jr, when I showed him my documented flow charts of my heads he said I was not getting near the full potential out of my motor and he INSISTED that I do the single plane. Extensive port matching and a few jet adjustments and holy moly, it's like I have a new engine. This thing pulls so hard, and yes even from idle, up top it is insane how much harder the car pulls. Streetability, yep, because I do drive it on the street a couple times a week.

Friday I am off to the welder to put in the new 6 pt cage and harness. I haven't raced yet this year but based on how it's running and even with the extra weight of the cage I would bet my last dollar that I will pick up a good 3 to 4 tenths and probably 4 to 5 more MPH through the 1/4. I could kick myself for not doing a single plane from the start and now I am truely re-evaluating my carb size, although the mighty demon 650 supposedly flows 753 wet. Good luck. Oh, and the headers I have are 1 5/8 w/ 3" collectors. Hooker super comp ceramic coated.

347ci
Comp Cams aluminum 1.6 roller rockers
Mighty Demon 650
Lunati Crank, Lunati street / race rods
KB flat domes w/ 6.5cc reliefs
Probe girdle
Comp cam XE274HE Xtreme Energy roller Cam Duration @.050 224 – 232, valve lift .555 - .565, lobe separation angle 112 degrees
AFR 185 heads ported and polished by Joe Mondella (documented flow charts)
Victor Jr SP intake
Hooker super comp ceramic coated long tubes
Weiland aluminum water pump
Elgin high volume pump
Holley blue fuel pump w/ regulator
MSD 6AL, blaster 2 coil
Currie 9” w/ 3:70 Detroit true trac
TCP Uppers w/ 620 Mustangs Plus 1” coils
5 leaf rear leafs
Sway Bars (front removed)
TCP Sub-frame connectors
TCP Solid Motor mounts
2500 Stall, C-4 Tranny
10.8:1 COMPRESSION

allcarfan said:

u dont think those headers are holding u back?

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It's hard to say, in my 66 coupe the fit was tight with the 1 5/8, not sure if the larger would have been tighter.

The car runs so well I really don't know. It's going to be pulled after this season and I think I am going to go to a Basic Dart or World block, change the slugs out and drop the compression a few points and go to a pro-charger to force some air. I'm addicted to more HP........

washMO66 said:

This thing pulls so hard, and yes even from idle, up top it is insane how much harder the car pulls. Streetability, yep, because I do drive it on the street a couple times a week.

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I am glad someone else has been there/done that...
Folks are brainwashed against SP intakes nowadays.
I did the opposite of your story...
I ran an SP intake forever, then the RPM came out. The guy at my speed shop insisted that I would love the new intake because I would gain bottom end without losing top. He bought Edelbrock's marketing, or just used it to sell me an intake.
Man, it killed my engine. I gained a miniscule amount of low end, 2000 to 3000 felt the same, after 3000 the car felt increasingly choked off. It was really sad.
Needless to say, after 2 weeks of experimenting with porting and spacers, the intake got gone.
Dave

allcarfan said:

I dont know if a Vic Jr Intake would fit under a gt350 hood on a 347 in a 66 stang....anyone?

What about a weiand xcelerator?

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not under a stock hood but under a GT 350 hood it will. That's what I have on my 66 coupe. I have a full size edelbrok triangle air filter and the wing nut just barley peeks out if you look into the scoop.

The Xcellerator is about the mildest SP I have ever seen.
The Torker 289 is a little better IMO and fits the same as the RPM.
The Torker 2, or Torker 302 is a low rise SP and would fit well. It has a large plenum and low runners though, I have never bothered to try one. It is more radical than others I mentioned, but not as rad as the the Victor.
Some other mild SPs
Port-O-Sonic
Holley Strip Dominator (out of production)
Torker 289 is out of production, but is my personal fav.
Sorry we go so far off topic.
This is just a subject I have strong feelings on.
Dave

What difference do you feel (seat of the pants) on the street using a single plane vs. duel plane? Has anyone tried the torker II on a 351W?

thehueypilot said:

What difference do you feel (seat of the pants) on the street using a single plane vs. duel plane? Has anyone tried the torker II on a 351W?

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With the cubic inches you are sporting there is only one intake I personnally would use, the vic junior. I would say on your combo you would see dramatic results. I am suprized that was not your choice from the get go. Change your intake!!! If you dont like the results I'll buy it from you!! Shame on CHP for not recomending the vic jr.

Actually the mustang magazines filled me with their propaganda and scared me away from a single plane on the street. CHP did recommend the victor jr, but I decided I wanted better street manners. Why does a single plane effect a vacuum? I thought it was more the cam design than the intake design.

thehueypilot said:

Why does a single plane effect a vacuum? I thought it was more the cam design than the intake design.

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Long story, I'll try to be short:
The runner diameter/length and the plenum volume have a big effect on how fast air can be accellerated into your engine.
Air velocity is lazy when the engine breathes through large ports or draws from a large plenum. It is good for volume, but not low rpm velocity, where you need vacuum.
When the engine draws air through smaller ports, the air velocity/vacuum is high, but the small ports limit flow at higher rpms.
The plenum volume not only affects vacuum, but affects throttle response and carb efficiency at low rpms. The carb gets less monitoring signal from the engine with a large plenum, so a large fuel shot is needed to keep from bogging off idle, but at high rpm the engine has a large 'reserve' area to draw from and keep the a/f mix more consistent between cylinders... So, there are intakes with small ports, small plenums or small ports and large plenums, and so on, along with varying runner lengths...
This shows the many different stratagies of manifold makers and the many tuning varieties available for about any combo under the sun. These are all things to take into account and can decrease or magnify a cam's effects on an engine.
I hope this made sense!
Dave