347 carb...a new question...

synthartist69 · Apr 7, 2011

Hey guys,

I appreciate everyones input on my last thread regarding a carb for my 347. Today I discovered that I need to put a new bearing kit in my rear end. I have chosen to change the ring and pinion while I am in there. I am swapping the 3.00 for a 3.55. I chose the 3.55 because I want my rpms around 2,150 at 70 mph and no higher. The calculators show that this is the gear I want. I want to see if the opinions on running my holley 750 vac sec is different now. I already own this carb and cannot send it back so I am hoping to be able to use it. Here is my new set up. Thank you in advance for your advice!

This will be a street/highway racer....no dragstrip. Here is the set up...

1965 mustang GT350 tribute

347 block
Ford Racing F303 Cam
Hipo manifolds...for now (headers later)
Pro Comp castings
2.02 exhaust 1.90 intake
Performer Rpm intake
3.40 rear end
T5Z 5 speed (,63 5th gear)

robbz28 · Apr 7, 2011

If anything that probably helped you....just because you have a 750, the beauty of a vacuum secondary is that, that carb is only going to give you the CFM's you need....80% of the time you will be running around on the front 2 barrels, which is approx 375 cfm. Bigger gears = Bigger load on the engine and the engine might require those CFM's more now than they did. IMO

synthartist69 · Apr 7, 2011

robbz28 said:
If anything that probably helped you....just because you have a 750, the beauty of a vacuum secondary is that, that carb is only going to give you the CFM's you need....80% of the time you will be running around on the front 2 barrels, which is approx 375 cfm. Bigger gears = Bigger load on the engine and the engine might require those CFM's more now than they did. IMO

That works for me! Now the main thing missing here is headers but they will have to wait a few months.

NMEMJCM · Apr 7, 2011

I had your setup a few years back (youe gear choice and a 750 carb). Was not good on the street. Swapped to a 650 and the car ran much nicer. Been there done that. I would sell your 750 and buy a 650, world of difference.... and you dont get that gas smell as bad (rob is right, the 750 will work, its just a bit much for your application and therefore not the best choice). Heck, I have a 650 on my 347 now, and I have 380 end gears and it runs great! Just relaying my experience to ya.

blown65 · Apr 7, 2011

If you have 4.11's Id still say a 650

clement · Apr 7, 2011

with a 347, id run a real 4150 like one from prosystems

restomoded66 · Apr 7, 2011

synthartist69 said:
Hey guys,

I appreciate everyones input on my last thread regarding a carb for my 347. Today I discovered that I need to put a new bearing kit in my rear end. I have chosen to change the ring and pinion while I am in there. I am swapping the 3.00 for a 3.40. I chose the 3.40 because I want my rpms around 2,000 at 70 mph and no higher. The calculators show that this is the gear I want. I want to see if the opinions on running my holley 750 vac sec is different now. I already own this carb and cannot send it back so I am hoping to be able to use it. Here is my new set up. Thank you in advance for your advice!

This will be a street/highway racer....no dragstrip. Here is the set up...

1965 mustang GT350 tribute

347 block
Ford Racing F303 Cam
Hipo manifolds...for now (headers later)
Pro Comp castings
2.02 exhaust 1.90 intake
Performer Rpm intake
3.40 rear end
T5Z 5 speed (,63 5th gear)

Hi! I have to question your choice on gear. most trans shop recommend 3.73 gear with a t5z. I had 3.55 gear in my 66 with a t5z also, found it a bit to tall. I have put 3.89 gear in now but have not driven it yet.

jcode68 · Apr 7, 2011

I am running 3.73 rear gears with my 347,T5 and 670cfm carb. Super responsive on the streets and very comfortable on the highway in 5th gear. I don't have a tach yet sadly so couldn't tell you the rpm at 70.

synthartist69 · Apr 8, 2011

NMEMJCM said:
I had your setup a few years back (youe gear choice and a 750 carb). Was not good on the street. Swapped to a 650 and the car ran much nicer. Been there done that. I would sell your 750 and buy a 650, world of difference.... and you dont get that gas smell as bad (rob is right, the 750 will work, its just a bit much for your application and therefore not the best choice). Heck, I have a 650 on my 347 now, and I have 380 end gears and it runs great! Just relaying my experience to ya.

Thank you for the advice!

synthartist69 · Apr 8, 2011

restomoded66 said:
Hi! I have to question your choice on gear. most trans shop recommend 3.73 gear with a t5z. I had 3.55 gear in my 66 with a t5z also, found it a bit to tall. I have put 3.89 gear in now but have not driven it yet.

The goal has been to keep the highway rpms around 2,000. However, I have now decided to go with the 3.55 ratio. According to the calculator it should put me around 2,150 at 70mph.

blown65 · Apr 8, 2011

clement said:
with a 347, id run a real 4150 like one from prosystems

Prosystem's is definitely a good way to go. Patrick's customer service is one of the best IMO. If your buying a carb its only a few bucks more really to get a carb setup around your build.

synthartist69 · Apr 11, 2011

blown65 said:
Prosystem's is definitely a good way to go. Patrick's customer service is one of the best IMO. If your buying a carb its only a few bucks more really to get a carb setup around your build.

The local dyno shop is pointing me towards a 650 double pumper as well. This may be the way to go over the 750 vac sec.

synthartist69 · Apr 11, 2011

jcode68 said:
I am running 3.73 rear gears with my 347,T5 and 670cfm carb. Super responsive on the streets and very comfortable on the highway in 5th gear. I don't have a tach yet sadly so couldn't tell you the rpm at 70.

Depending on your tire size, I would think that you are between 2150 and 2350 at 70mph. It mostly depends on if you have a T5 or a T5Z. The T5 as you probably know has a .68 final drive and the T5Z has a .63. It is enough to give you about a 150 to 175 rpm difference in 5th gear.

synthartist69 · Apr 11, 2011

jcode68 said:
I am running 3.73 rear gears with my 347,T5 and 670cfm carb. Super responsive on the streets and very comfortable on the highway in 5th gear. I don't have a tach yet sadly so couldn't tell you the rpm at 70.

Ok, I see now that you have the T5Z! Nice mustang!

synthartist69 · Apr 11, 2011

NMEMJCM said:
I had your setup a few years back (youe gear choice and a 750 carb). Was not good on the street. Swapped to a 650 and the car ran much nicer. Been there done that. I would sell your 750 and buy a 650, world of difference.... and you dont get that gas smell as bad (rob is right, the 750 will work, its just a bit much for your application and therefore not the best choice). Heck, I have a 650 on my 347 now, and I have 380 end gears and it runs great! Just relaying my experience to ya.

I appreciate the input and I think you guys have nailed it on the head!

synthartist69 · Apr 11, 2011

NMEMJCM said:
I had your setup a few years back (youe gear choice and a 750 carb). Was not good on the street. Swapped to a 650 and the car ran much nicer. Been there done that. I would sell your 750 and buy a 650, world of difference.... and you dont get that gas smell as bad (rob is right, the 750 will work, its just a bit much for your application and therefore not the best choice). Heck, I have a 650 on my 347 now, and I have 380 end gears and it runs great! Just relaying my experience to ya.

Very much appreciated!
I bet the 3.80 ratio pulls pretty hard huh?

NMEMJCM · Apr 11, 2011

Yah its nice... I suffer a little more on the freeway (65mph at 2500 rpm) than other cars with 3.50 (or 3.55) but its a kick in the butt when Im tryin to make it threw the stale green or fresh yellow lights.

347 carb...a new question...

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