4 barrel carb on 225?

my jeep has a offenhouser 4 barrel intake manifold, the PO for some reason used an adapter ontop so he could re use the stock carb. i would like to put a 4 barrel on but i have a few questoions. does it give more power? better or worse mpg? whats the best carb to buy? any downfalls? tell me everything you can

 

I'd say a 4bbl would not be necessary for power concerns. 165 hp (or whatever you're making) only requires as much fuel as it can use. Bigger carb cannot change that fact. What bigger carb will do is give better breathing at high revs. Are you looking for low to mid grunt or high RPM power? For low revs a conservative carb will behave much better. Chances are your cam isn't made to rev anyhow so even if you toss on a big carb your cam will run out of breath before the big carb can do what you paid it to do.

A big carb can do other things for (to) you: it will not idle as well. It will be a pain in the arse to tune the dead spots out of the transitions between the different fuel circuits. It will be prone to stalling due to lower vacuum and poor "signal" across the venturis. You'll probably have to jet down so it isn't running rich, taking the carb out of balance.

That's not to say a 4bbl is out of the question. It would have to be a small 4bbl, I think. And they're not all that common. Can't speak for the 225 but I've read of a lot of guys trying that Holley 390 4bbl on I6 engines and not having very good luck. I'd say a good 2bbl would be my pick.

 

I have a holly 390 on mine and have had troubles. I was thinking of using the smallest holly truck avenger they make, since others here have had good luck with it. I'm still on the fence about a 4bl.

 

i dont really care about power 165 is plenty of power for me. im more concerned with it running well and reliable. so what i need is a small cfm 4 barrel?

 

My list of 4BBL carbs in order of merit. Rochester Q jet, Holley 450 economaster, and the venerable AFB. The first two are spread bores which allow you to retain good low end power due to the small primaries. The Q jet is way too big for the 225 however I am currently running one and have been very happily surprised. The Economaster is a great carb, however they are hard to find. If you are going to retain the Offy manifold(I am assuming it is a spreadbore) these would be my choices. As Sparky stated above, if you are looking for claw hammer reliability and good off road characteristics, the 2G series is virtually unbeatable. There is also a Rochester duo jet that will bolt on to your spread bore maniflod. I believe Sparky has some experience with that one as well.

 

Sorry man, I thought it was you I talked to about one in a previous post over on Jeepforum.com. Oh well, when I get home I'm gonna have to find one and give it a try.
BTW it is the front (primaries) half of a Q jet. Early models will bolt directly on the GM spread bore style manifold.

 

I had a Holley 390 on one of mine with an Offy manifold. It was awful going up or down hills...which is what its all about. So I went to a 70's vintage Q-jet for a 231 cu.in. Buick. I had to put on an adapter cause the Offy. manifold is for square bore carbs as Warloch said. What a difference. They call them poor mans fuel injection and now I know why. If you open the secondarys fuel mileage is poor but the primarys are smaller than a 2GC(which I have on another 2A) so it feels like bottom end power is somewhat better and if I want to rev. it for power I can. I like it. My next thing is to put on a Holley 300-22 manifold that is made for spread bore carbs and ditch the adapter.

 

i have a factory manifold in my garage that i could swap in, and 3 rodchesters. What does an offy manifold go for these days?

if i do decide to keep it and do the TA 470, will i have any problems? it will be fine going up and down hills? idle?

 

Offy 360's came in square and spread bores. I have seen a couple and only one was square. That being said, prolly wouldn't hurt to go see which it is. Adapter plates are available. I'm not trying to sell you on keeping the 4BBL, but heck, it,s already on there.

 

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