92 Gt W/351w Advice Needed

stykthyn said:

2 o'clock would have it firing on 8 would it not?

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I was saying turn it so number 1 is now where the 8 is. I have just found that this gives you the most clearance for adjusting timing when the vacuum point is straight out. I know it will work where it is, I just find it easier this way.

No worries. Aslong as it works. I post in these to learn as much as the op. Not trying to argue.

I always referred to this, but that's just me. Different applications may apply.

sharp2377 said:

I always referred to this, but that's just me. Different applications may apply.

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I guess that's more of the 1 o'clock spot lol

adumb said:

v8stang289, that diagram for the duraspark wiring is pretty straight forward. the one question i have is i know the red wire goes to the coil but it also needs a ignition on source correct? where can i pick that up from in the engine bay? i am guessing i will need to splice two wires onto the red one and have one go to the coil and the other to my keyed source right?

adam

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Yes, keyed power to the red wire on the box and the coil. You can pick it up from the wire on the factory engine harness that went to the coil +, if you still have that harness. If not there should be another keyed + wire, but I'm not sure which one(s).

adumb said:

was a little busy the past couple weekends but I finally had all my ducks in a row and got some work done.

the front of the motor is all back together. plus i got the mechanical fuel pump installed. it has been slow moving but i am being carefull and trying to not make any mistakes. I haven't put coolant back in the car yet, i am not to confident the timing cover will seal. it was alot of sliding and moving around to get it on there and bolted down. I also bought a 85 mustang throttle cable and got that bolted up.

i ended up buying a holley 4150 carb. 750 double pumper with manual choke. I didn't want to go used but a speed shop near me had one they tried on a motor two months ago for the dyno and didn't like it. so it is in great shape. i got it for 285. plus i was able to get a dual feed line off of the guy for another 5 bucks. I was pretty pumped about that because the dual feed line stuff is like 65 bucks on summit.

v8stang289, that diagram for the duraspark wiring is pretty straight forward. the one question i have is i know the red wire goes to the coil but it also needs a ignition on source correct? where can i pick that up from in the engine bay? i am guessing i will need to splice two wires onto the red one and have one go to the coil and the other to my keyed source right?

adam

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So then, you went from asking if a 750 vacuum sec carb was gonna be too much ( which it was) to buying a used mech secondary 750 anyway?

Firstly, why do you spose they had a " used" 750?............Two guesses.

It was either too big, or too small for the previous application. And given that the norm is to over carburet the engine, it's already been too big once. That one has already gotten 1 strike against it.

Do you know what you have to do to try and make a carb that is too big less of a pig?

It gets opened up, and rejetted. Squirters get changed, power valves get changed, and it was probably still too big. You'll be able to tell that by looking at the four screws that hold the bowl on, there may be evidence of tool marks like are on the float height adjustment screws.

Don't take my word for it, take it from the manufacturer of your carburetor.

http://documents.holley.com/techlibrary_selecting_a_carburetor.pdf
They've already got an example of your C.I. and VE ratio ( 85%) for you to see.

Even if you use the top chart and figure your engine at 100% VE, ( which it ain't. Most used engines are only capable of 85%, and that's being generous).if you redline the engine at 6000 RPM, the recommendation is for a carb rated to 600 CFM, and if you increase the redline to 7000 RPM, the recommendation only goes up to 700 CFM. When you take the 15% differential back out of that, you get a real world recommendation for a 600 CFM carb.
Then, for a real taste of a reality sandwich, look at the next chart rated for a double pumper where they recommend going even smaller than rated CFM. recommendation because of how much extra fuel gets added when you mat the gas pedal .
Even if it hasn't been opened up, it will be. You're probably gonna to drop jet sizes significantly to get it lean enough ( if you even can) where you won't have black smoke coming out the tail pipe, and burning your eyeballs out while idling. And what does black smoke mean besides the obvious boys and girls?...,.......less power.


Let's talk about jets. Know what's involved changing jets in a 4150?

Gas. Gas all over the place. You have to remove the float bowl to get to the jets ( which last time I checked were like 15.00 a set, and you're probably gonna have to do it more than once.) the float bowl is full of gas. And when you remove the bottom screw, it all drains out on your intake. Now that's not the end of the world, you can get things to catch the fuel, or even use an old rag to drain into or You can also remove the carb entirely to do that, but the fact remains, that you'll have to.
Additionally, there are float bowl, and metering block gaskets that typically stick, and tear when you remove the bowl, so make sure you buy those too. After all of that, it may still be too big.

( if you could make a 750 run as lean as a 650, there wouldn't need to even be a 650)

Secondly, a used carb may have been some bodies gremlin. Unless I knew the guy selling the carb, and knew why he was selling it, I wouldn't buy it. When they work properly, they still need to be fiddled with every now and then. When they don't, you go out and buy a Taurus .38, turn it 180*, stick it in your mouth, and pull the trigger.

There's always an exception. A 750 DP on a 351 drag raced exclusively may run great, it may need even more. But a drag raced engine is ran WOT 95% of the time. It doesn't have to idle that well, it doesn't have to cruise, and gas mileage is of zero concern. Do yourself a favor, spend the money, and get the right thing. Take that one back before you fill it with gas, and bite the bullet, and either buy that Summit 600 CFM vacuum secondary unit that one guy offered that only costs 259.00, or one of 650 CFM pieces that I posted,
Summit bought the design from Holley, and it's theirs exclusively. That carb comes in both 600, and 750 sizes, the top comes off entirely, so there's no need to drain the fuel out for jet, and power valve changes. It uses standard Holley tuning junk, and Summit stands behind the thing w/a dedicated tech department specifically for getting the carb dialed in. I had the 600 on my 4.6 in the last car. I had to drop the jets in the thing significantly to get it to run lean enough on that tiny assed engine, but after that, it ran perfect.

you can thank me later.

Somebody once something about horses and water.

It's your car. You are the one that will live with the choices you make. Believe it or not, everything you have listed as far as performance add ons are just north of stock. The cam you chose runs out at 5500 RPM, the heads may support power to 6k. Your intake, the same.

The carb recommendation was based on 7000 RPM.
And that formula recommended a 600.

Reduce that to your actual RPM redline 1000-1500 RPM lower, and it's even smaller. You may as well just get a 1 gallon gas can and pour gas in the engine for all the good that 750 will do you.

But again, I'm just some guy on the internet trying to give you advice to save you money, get better results, and have a carb that'll have a warranty, support, and be closer right out of the box than that used 750 will be.

Cause, after all. I haven't been drag racing cars since the late 70's, I haven't worked the parts counter at a speed shop for several years, and I'm not recommending something that I haven't used myself.

So it stands to figure, I've got nothing to gain.

adumb said:

i read that document you posted. on the second page they are even saying it is a toss up between the 650 and 750 for a light car with quick gearing. Also by looking at the line on the drawing it is looking at about 685.

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That's 100% VE. You do not have a race engine. You need to reduce the recommended number by 15%.

adumb said:

cam goes to 6000. http://www.summitracing.com/parts/cca-35-246-3

still won't help me out that much. The ironic part is i was almost dead set on a 650 and i had a topic on another forum saying the exact opposite of you and how much of a silly choice a 650 would be. I will find out who is right one way or the other

Cu in x RPM ÷ 1728 (cu in conversion to cu feet) × .5 only. Your 351 comes in at 660 cfm for 6500 rpm. this is the forumla they used.

hopefully i don't get punished for this but this is the other thread that I have where pretty much everyone is on board with the 750 idea. 351w carb choice - Ford Mustang Forums : Corral.net Mustang Forum

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My last input on this topic.

It is not me saying that. It's the manufacturer of your carburetor.

Also consider that most advice you get is for racing application only.

I think the 750 is a little big. My brother ruined a 351 truck motor with a 750 dp that's right spun the bearings in the bottom end becaus of the extra gas making its way to the oil pan now granted this took a while to do and a lack of oil change and check but the day it lost oil pressure I pulled the stick and all I could smell was gas and I asked him ain't you check the oil in this thing it's full of gas. all because he got a good deal on the 750 dp but he neglected to get it right

We mean well.