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Unread 10-24-2008, 08:20 PM   #16
BESRK
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I agree with everyone else about why not to run a 3x2 setup on a 304.

However, if you're dead set on it, you could probably just take something like that Offy manifold above, mill out a plate to mount the carbs, mill off the top of the old manifold and tig weld the new mount in place.

If you were able to do all that, you'd bolt the 3x2 onto the 304, run it for a short time, and swap it for a single 4bbl because you'd figure out it's just too much carb for a mundane AMC 304.

If you want the 3x2 just for the "look", you could mill an adapter plate that would mount to the stock manifold. You could make the center carb the only "functioning" carb and the two outboard carbs could be just for looks.. basically just bolted to the adapter plate.

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Unread 10-24-2008, 09:29 PM   #17
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Six pack set ups provide some interesting drawbacks. First, running three 2bbl carbs ( using the 2G series as an example), your going to be in the 900CFM range at WOT. Way too much for an engine that size which probably won't see 5000 RPM's. Also, the two "secondary" carbs will be mechanical, basically giving you a 300 CFM 2 BBL primary in the middle with two 300 CFM secondaries on each end, much like a huge Holley double pumper. While it would be cool to do and a fun package to fabricate, the application would be totally street oriented and without the rest of the engine built to use it, I think would net you very little in the way of extra performance.
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Unread 10-24-2008, 09:39 PM   #18
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I agree with the others, it's way too much for a 304, but you're probably going for the cool points, and that'd be good...however, as others have also mentioned, I don't think anyone ever made a 3x2 intake for an AMC....if they did, it'd be hard to find.

If cool points are all you're after, get a 2x4 intake, and either disconnect the secondaries on both carbs, or get two really small carbs, like Holley 390's.

The CFM requirement charts you see around usually tell you to get a much smaller carb than an AMC or any other V-8 would need to make its max. power......I think they tell you you only need 500cfm or less for a 360, which is clearly wrong. If you take two identical 360's, put a 470 on one, and a 650 on the other and tune them to their peak, the one with the 650 is going to walk off and leave the one with the smaller carb.

So you could use two 390's...that'd be definitely too much carb, but you could use vacuum secondary carbs and put stiffer springs in so they secondaries wouldn't open until higher rpm's. That's really easy on a Holley.
It'd still run fine, and you would definitely have a conversation piece.
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Unread 10-25-2008, 10:02 AM   #19
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so yall are sayin it would be better too go the 1 4 barrel than the 6 pack or 2 quads route im just tryin to find out what i wanna do to this motor if i was to go with the 4 barrel would yall go with the high rise or low rise i done reasearch but i can't find anything comparing the two. thanks for the replies
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Unread 10-25-2008, 11:09 AM   #20
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Originally Posted by 79cj7stone View Post
so yall are sayin it would be better too go the 1 4 barrel than the 6 pack or 2 quads route im just tryin to find out what i wanna do to this motor if i was to go with the 4 barrel would yall go with the high rise or low rise i done reasearch but i can't find anything comparing the two. thanks for the replies
It would absolutely be better to go with one 4bbl over any other carb option.
No research is really needed....a single 4bbl is always the best for a stock V-8, or even a fairly well modified V-8.

As I mentioned before, unless you're after the cool points for the "look"....stick with a single carb.

It's not that a multiple-carb setup wouldn't WORK...it would, but a 304 definitely doesn't NEED it.
If you WANT it, that's a different deal....but just talking about the functionality, the single carb is better.

So....if you simply want multiple carbs because it looks cool.....you CAN make them work.

Keep in mind...the most famous 3 carb setup was probably the Pontiac Tri-Power. Pontiac quit using it when they found out that a single Quadrajet made more power.
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Unread 10-25-2008, 01:01 PM   #21
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Put a 4 bbl on a low rise intake. Your rpm's won't go high enough to justify a high rise and most Jeepers want low end torque, not high end horsies.
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Unread 10-25-2008, 01:13 PM   #22
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Put a 4 bbl on a low rise intake. Your rpm's won't go high enough to justify a high rise and most Jeepers want low end torque, not high end horsies.
The Offenhauser Dual Port is designed to give you good low end with decent high speed performance. I imagine Edlebrock has a similar offering.
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Unread 10-25-2008, 04:02 PM   #23
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The Offenhauser Dual Port is designed to give you good low end with decent high speed performance. I imagine Edlebrock has a similar offering.
Edelbrock Performer
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Unread 10-25-2008, 04:43 PM   #24
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Quote:
Originally Posted by 79cj7stone View Post
so yall are sayin it would be better too go the 1 4 barrel than the 6 pack or 2 quads route im just tryin to find out what i wanna do to this motor if i was to go with the 4 barrel would yall go with the high rise or low rise i done reasearch but i can't find anything comparing the two. thanks for the replies
I think we are going about this backwards. What we need is for you to tell us what your trying to accomplish, both with the engine as well as the Jeep. These two criteria will drive both your engine build as well as the rest of your upgrades.
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Unread 10-25-2008, 07:58 PM   #25
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as mentioned above, a "6 pack" 304 would be WAY overcarbbed, WAY to expensive to build (in relation to how much power you will get out of it), and probably a nightmare to tune. Yeah, it would have LCF, but really worth it? Not likely. Search threads from JEEPHAMMER - he has numerous posts about how to aprropriately size a carb to an engine. A two barrel carb around the 390cfm mark is about perfect for the 304, IIRC. Also as stated above, if it is power you want, the 304 is pretty much a boat anchor vs a 360 which would run you the same price to buy/rebuild. I have a 304 in mine and it runs well and has good power for my driving, BUT if you are looking to shred tires a 304 is not what you want. Now I WOULD entertain the thought of a 401 with a six pack....still probably too much carb, but at least you'll get some bang for your buck that route.
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Unread 10-25-2008, 08:29 PM   #26
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Six packs are simply way cool. I've always wanted one for the SBC I have sitting in the garage. I almost put it in my CJ7. Edelbrock sells a six pack manifold for a chevy, but I've not seen one for a 304. What about Wieand or Offy?
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Unread 10-25-2008, 08:44 PM   #27
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Originally Posted by Lawless_Jeep View Post
Six packs are simply way cool. I've always wanted one for the SBC I have sitting in the garage. I almost put it in my CJ7. Edelbrock sells a six pack manifold for a chevy, but I've not seen one for a 304. What about Wieand or Offy?
If you think six packs look cool, Man-A-Fre used to make a 4 Rochester 2 barrel setup that sat right over the intake ports. They referred to it as direct port induction.
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Unread 10-25-2008, 09:01 PM   #28
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jeepdaddy my bad for going at this backwards my first plan to do to the motor was : mild cam, OTF headders, highrise intake, 4 barell carb 600 or 650 cfm then i started thiking one day and was wondering how a 6 pack would do on a 304 so i was thinkin about doin the above just wth a 6 pack as yall have told me it won't work as good as the one 4 barell so i have gone back to my original plan i young and i got time so i want to make the best choice for my jeep my jeep will b a daily driver but will do some time off road i want power but i have to beable to go at highway speeds so tell me wat u think please
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Unread 10-25-2008, 09:21 PM   #29
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With what you're building, your original plan is the best. 600cfm Holley is the best for your application.

Use and Edelbrock Performer intake with it.

I know the carb sizing charts will tell you that you only require a much smaller carb than a 600cfm, but I can say that they are definitely wrong.

Yeah, a smaller carb would be more responsive....as would most any smaller carb on any engine.

But, if you build two identical Jeeps like yours, and use that 390cfm on one, and the 600 on the other, the 600 is going to leave that 390 in the dust from 0-however fast you care to run.
Most of those cfm charts are VERY conservative, and their recommendations don't hold up in the real world. That's why people have been ditching their 2bbls off their 304's and 360's for years and putting 600-650cfm 4bbls and they run MUCH stronger.

Go with your original plan, it'll run great. Years ago, a friend had his 304 built with a Comp Cams 268H in it. Mostly stock, otherwise.
He had a Performer intake, and we put a Holley 600cfm carb on it that I rebuilt for him. We spent an evening tuning it, and it ran GREAT. He had Quadratrac and he'd scald front and rear tires from a stop.
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Unread 10-25-2008, 11:45 PM   #30
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With what you're building, your original plan is the best. 600cfm Holley is the best for your application.

Use and Edelbrock Performer intake with it.

I know the carb sizing charts will tell you that you only require a much smaller carb than a 600cfm, but I can say that they are definitely wrong.

Yeah, a smaller carb would be more responsive....as would most any smaller carb on any engine.

But, if you build two identical Jeeps like yours, and use that 390cfm on one, and the 600 on the other, the 600 is going to leave that 390 in the dust from 0-however fast you care to run.
Most of those cfm charts are VERY conservative, and their recommendations don't hold up in the real world. That's why people have been ditching their 2bbls off their 304's and 360's for years and putting 600-650cfm 4bbls and they run MUCH stronger.

Go with your original plan, it'll run great. Years ago, a friend had his 304 built with a Comp Cams 268H in it. Mostly stock, otherwise.
He had a Performer intake, and we put a Holley 600cfm carb on it that I rebuilt for him. We spent an evening tuning it, and it ran GREAT. He had Quadratrac and he'd scald front and rear tires from a stop.
I tend to disagree (this is what is wonderful about a forum!). Off idle and midrange response is best served not so much by total CFM, but by the size of the primaries. The smaller they are the better the low and mid range will be (these are the areas best served by a 4X4). This is usually found either in small four barrel carbs or spread bores. The defining factor is the total RPM's you plan on running. You need to be realistic about this number. The excepted formula for this is (CID divided by 2) X (total)RPM's divided by 1728) X volumetric efficiency (call it 1 for 100%) Don't worry, it will be less, just use the number)=CFM. So a 304(divided by 2) running 5000RPM's (divided by 1728) X 1 (Volumetric efficiency) =CFM
152 X 3 X 1 = 456CFM. This is the max if you are planning to actually run 5000RPM's.
99% of all driving is in the off idle to 3500 range. These are realistically better numbers for a daily driver, especially an off road vehicle. This might change a bit if your planning on running higher RPM's due to sand or mud, and cams will play a factor. My personal experience is to err on the side of caution. A bit small seems to always be better than a bit big.
Whatever you decide, I would recommend a carb with vacuum secondaries.
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