Need a carburetor recommendation - Vintage Mustang Forums
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post #1 of 15 (permalink) Old 04-16-2019, 01:15 PM Thread Starter
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Need a carburetor recommendation

(I cross-posted at 69stang.com, so if you made a recommendation there, dont feel the need to repeat it here. I am watching both places)

Currently, I am running a prepped Holley 650 mechanical secondary carburetor with the hoke horn milled off. Why? Because back in my younger years, I had bolted a supercharger to the engine, and needed something that would work in that application. Supercharger is gone, but the carburetor remains. Here are the vitals:

AOD with 2500 stall
3.89 gears in the back
Stock 351C-2V long block with a Lunati 000093 camshaft (.536/.562 lift, 290/300 adv duration, 224/234 @0.050)
Weiand single plane intake
Headers and dual exhaust
I am thinking a 600CFM vacuum secondary of some flavor. I am rabidly anti-Edelbrock, so please dont recommend it. Holley, Summit (actually heard good things about them), or some sort of Holley clone? What is important to me is smooth performance and easy tuning. Not looking for top power right now (or I would have left the supercharger on the engine).

Thoughts?

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post #2 of 15 (permalink) Old 04-16-2019, 01:43 PM
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What I like about the Summit is that they use annular boosters. Theyíre more responsive to airflow along with atomizing the fuel better. This is exactly why Ford used them. The problem Ford was having was a slight bog as the throttle opened up. When you open the throttle, you reduce vacuum signal and the typical straight or down leg canít react to pull fuel through and goes lean. The annular still sees that reduced signal but has enough area to overcome and still flows fuel through the circuits.

An odd ball carburetor I liked was the Motorcraft 4180 used on the mid 80ís Mustangs and trucks. Annular primary booster along with 4 corner idle mixture. Even though Holley built it for Ford very few parts interchange. The worst part is they have like 3/8Ē vent tubes for emissions in the top of both float bowls. Youíre stuck with those float bowls, the Holley wonít fit. Neither will the primary fuel block or base. You canít even use a Holley carb kit. But they sure do work nice. Iíd look at any carbs with annular boosters.
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post #3 of 15 (permalink) Old 04-16-2019, 01:44 PM
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I've run 2 summits lately. I like them, and especially like the price.
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post #4 of 15 (permalink) Old 04-16-2019, 02:05 PM
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Summit 750 vacuum

I have the original Holley version and it works very well.

Nothing worthwhile is ever quick, cheap or easy, those that can't do, complain

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post #5 of 15 (permalink) Old 04-16-2019, 02:10 PM
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Quote:
Originally Posted by Huskinhano View Post
An odd ball carburetor I liked was the Motorcraft 4180 used on the mid 80ís Mustangs and trucks. Annular primary booster along with 4 corner idle mixture. Even though Holley built it for Ford very few parts interchange. The worst part is they have like 3/8Ē vent tubes for emissions in the top of both float bowls. Youíre stuck with those float bowls, the Holley wonít fit. Neither will the primary fuel block or base. You canít even use a Holley carb kit. But they sure do work nice. Iíd look at any carbs with annular boosters.
I'm running a hot rodded version of the 4180 and I'm very happy with it for the reasons you listed. That said, if I didn't have a greybeard buddy to do that voodoo modification to it, I would be looking really hard at the Summit carb, again, for the reasons you listed.

I'm not an expert, but I play one on the internet.
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post #6 of 15 (permalink) Old 04-16-2019, 02:44 PM
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I have an aluminum body 670 Street Avenger sitting on the shelf after an EFI conversion. PM me if you might be interested.
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post #7 of 15 (permalink) Old 04-16-2019, 03:08 PM
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Quote:
Originally Posted by BlakeTX View Post
I'm running a hot rodded version of the 4180 and I'm very happy with it for the reasons you listed. That said, if I didn't have a greybeard buddy to do that voodoo modification to it, I would be looking really hard at the Summit carb, again, for the reasons you listed.

I did very little to make it work well. I drilled 1/8Ē holes on the bottom plate so I could push out the steel plugs blocking access to the idle mixture screw. Most people at the time just broke off the casting on the outside. I thought that was a rather crude method. I went up 1 jet size I believe along with a bigger accelerator cam. There was a recall on the factory cam. Ford skimped on the lobe for CAFE reasons but didnít drive well. Oh when I adjusted the idle mixture screws, out of the 4, 3 were set differently. After that it worked real well.

Every once and a while it would run like it was on 4 cylinders. No rhyme or reason it would act up out of the blue and just as fast as it happened it would clear up. I could never isolate a condition for it to happen. One time it happened I shut the car off and pulled the carb apart. It was a small spec of black paint chip in one of the primary jets! Somehow it got in there when the carburetor was assembled at the factory. It would float in the gas.

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post #8 of 15 (permalink) Old 04-16-2019, 03:58 PM
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Back in the 70s there was a magazine article that I wish I could find again. It was a scan from Hot Rod or similar magazine. Anyways, they had a Gran Torino with a stock 351C 4V. They swapped the stock 4V dual plane for a low rise single plane and used a normal aftermarket carburetor. They found it easy to tune and it ran and idled well in all conditions. It said the Cleveland is one of the few engines that would run so nice on the street with a single plane.
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post #9 of 15 (permalink) Old 04-16-2019, 04:44 PM
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The Summit has a lot of benefits found in the original Autolites, but not difficult to find or astronomically expensive. Unfortunately it took Summit three tries to get my friend a good one. First one came with a completely warped body and/or top plate, second one came with a mangled accelerator pump. I'd still recommend the carb, but check it over thoroughly when you get it.

I have a factory refurbished Street Avenger 670 I got off Ebay. It's getting dyno tuned today but I will say it actually worked well out of the box. No bog, no hesitation, decent idle. Every motor is different and every carb should be fine tuned but it was nice to be up and running enough to drive the car several miles. I'd definitely consider the one rhutt is selling which actually has some features my refurb carb doesn't have like float bowl sight glass and, I think, four corner idle adjustment if I'm not mistaken. The Street Avengers also have a quick change for the secondary spring which is nice.
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post #10 of 15 (permalink) Old 04-16-2019, 05:04 PM
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Quote:
Originally Posted by Hemikiller View Post
Summit 750 vacuum

I have the original Holley version and it works very well.
750 is a bit too much for a 351 ci motor. I'm running 750 on my 414 ci and I had to jet it down a bit to get a proper A/F ratio. I've also heard to use a Vacuum Secondaries on an auto trans, and Mechanical Secondaries on a manual trans. Vacuum secondary carburetors work for nearly any vehicle from light-weight to heavy. They are more forgiving because the secondaries open based on engine load. Mechanical secondary carburetors work best on a light-weight car with a manual transmission or an automatic with a high stall and low rear-end gears.

You can play with Holley's carb selector to see what they recommend.

https://www.holley.com/retailer/carbselector/
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post #11 of 15 (permalink) Old 04-16-2019, 07:47 PM
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I'm running the Summit carb on my 351 Cleveland and I really like it. Very easy to set float levels and it uses Holley jets which makes it easy to calibrate.

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post #12 of 15 (permalink) Old 04-16-2019, 09:21 PM
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Edelbrock AVS 2 thunder series .... best street carb I've put on my 351c ...
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post #13 of 15 (permalink) Old 04-17-2019, 12:32 AM
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Quote:
Originally Posted by 69GT350H View Post
750 is a bit too much for a 351 ci motor. I'm running 750 on my 414 ci and I had to jet it down a bit to get a proper A/F ratio. I've also heard to use a Vacuum Secondaries on an auto trans, and Mechanical Secondaries on a manual trans. Vacuum secondary carburetors work for nearly any vehicle from light-weight to heavy. They are more forgiving because the secondaries open based on engine load. Mechanical secondary carburetors work best on a light-weight car with a manual transmission or an automatic with a high stall and low rear-end gears.

You can play with Holley's carb selector to see what they recommend.

https://www.holley.com/retailer/carbselector/

750 is not too much for a 351 Cleveland with the cam he has.

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post #14 of 15 (permalink) Old 04-17-2019, 05:13 AM
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Really, "too much" carb is kind of a hard thing to judge. A lot of it has to do with the boosters, etc.

What you need to be asking is how will the car be used, and whether it will support good atomization in the RPM range it's most commonly seeing.

I think a better rule of thumb is figuring out how many horsepower the engine will realistically be using, and size the carb for that, because that way you've got a better idea of how many CFM you need at WOT to prevent loss of power from too much intake vacuum.

With a typical 4V setup on the street, you're better going "a little bit too small" than "a little bit too big", because with a big carb, the air going through your boosters will be so slow, all you'll get is big fat drops of gas as you run around town. Your car will run "rich", get lousy mileage, and foul plugs, even though it acts "lean". A smaller carb will have better atomization and much crisper throttle response.

For a car that only sees use on the strip, going "too big" may be just right, because who cares about cruise or idle, so long as it runs? You want every last horse you can wring out of it, and having little to no vacuum drop at WOT (from carburetor restriction) is an effective way to get that. While 900 CFM is kind of silly for a 500 horsepower motor being street driven, on the top end, it might make 5-10 more horses than a 750.

Annular boosters are awesome on the street, because at any speed, they are very effective at creating a fine mist of fuel/air for your motor to burn. Some racers feel that they cause too much restriction to be effective for track use, but I think it's more that not too many "performance" carbs have them, and the carbs that do tend to be smallish/hard to tune/find parts for - like the 4100.
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Last edited by Grimbrand; 04-17-2019 at 05:17 AM.
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post #15 of 15 (permalink) Old 04-17-2019, 08:48 AM
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I believe the Autolite 4100 carburetor is one of the best carbs ever designed.

We have used a 1:12 NHRA legal one for a long time on a 289 Super Stock engine that made 460 hp and revs to 9K

The summit carburetor is just an updated version of the old Autolite, I haven't used one yet but have a buddy that has a couple on his street cars and seems to like them.



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Last edited by 65AScoupe; 04-17-2019 at 08:49 AM. Reason: add 4100
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