2 x 4 set up

[jester]

This is a repost . I had posted it in the 58-64 car section but I did not get a reply

I have a tech. question regarding the 2X4 set up on the w engine. Why is the back carb. the primary. I seams to me that when everything in being driven forward when the car is excelerating the gas in the carb and intake will travel to the rear of the car leaving the front cylinders on the lean side. Any thoughts on the subject?

 

[models916]

it's a gas

Unless you are launching like a Satrun V rocket, the vapor in the manifold is not really affected in the way you describe. It is a vapor not a solid in the manifold (or should be). Liquid in the bowls front or rear are affected the same way.

 

[jester]

Unless you are launching like a Satrun V rocket, the vapor in the manifold is not really affected in the way you describe. It is a vapor not a solid in the manifold (or should be). Liquid in the bowls front or rear are affected the same way.

It sounds good in theroy , but I'm not sold, It takes raw fuel to get vapor, That's why the inside of the intake have channels for the fuel to run in. What about fuel injected engines . Fuel is injected and adomized but none the lease , it is fuel.
In Naturally asperated engines the fuel and air are drawn into the cylinders by a vacuum created by the piston in the down stroke..
Any other ideas? I'm looking for a reason not to make the front carb the primary. Please Help Me.

 

[dq409]

Jester, if you are really worried about it do as I and many others have done,,,,make both carbs pimaries!

I have idle circuits on both carbs. IMO,,, it runs smoother.,,,dq

 

[jester]

Jester, if you are really worried about it do as I and many others have done,,,,make both carbs pimaries!

I have idle circuits on both carbs. IMO,,, it runs smoother.,,,dq

I'm not worried as much as I'm interested in finding out if there is a difference.
I have a friend that has a 68 Road Runner that runs 10.6 without the bottle in the 1/4. As far as engines go, he know what he is doing . He said that every Mopar dual quad he has set up , he has the front carb as the primary for that reason.
I don't know if he is busting my nut or not. I just looking for input.
You would think that the big brains in the Skunk Works would have addressed this issued.

 

[jim_ss409]

I think they used the rear carb as the primary because it's front barrels are much closer to the centre of the manifold than the primarys of the front carb. I don't think G forces from exceleration are much of a problem because under hard exeleration all 8 barrels would be open. I seem to remember reading somewhere that circle track cars will sometimes jet a bit leaner on one side to compensate for centrifical force but I'm not sure, they might have been compensating for the effect that the centrifical force had on float levels. I'd guess that it would take an awfully fast drag car to require changes. I think those fuel channels in the bottom of the manifold are mainly there for cold start and warm up conditions when the fuel won't vaporize properly.

 

[bjburnout]

Primary carb

Hey Jester
If you run the primary up front you run the chance of no fuel getting to the back cylinders. .......I don't think the front of the 2x4 manifold feeds all the way to the back. Where the front barrels of the rear carb feed the engine the manifold definitely reaches all cylinders.

As Jim said the primary barrels are on the rear carb because this is closest to the center which means better distribution and he's also right that under hard acceleration all 8 barrels will be open....

Remember the General ... planned it this way and we shouldn't try to change mother nature........

I like DQ's idea of both carbs being primary and you do see a lot of 2x4 cars now using both primary carbs..........it would be interesting to get a read on a new set of plugs after a long idle with two primary carbs.

bj

 

[jester]

Thanks guy for allowing me to see the error of my ways. I will leave perfection alone.

 

[Bubbletop Bel-Air]

IF IT IS NOT BROKE, DO NOT FIX IT

 

[Mr Goodwrench]

he he.... got you all beat, check out e-bay item # 7961966685 :eek: :eek: holley on the front afb on that back how would you like to tune that set up??? especially when you wanted those vac secondaries to open says he was an expert mechanic though

 

[dq409]

he he.... got you all beat, check out e-bay item # 7961966685 :eek: :eek: holley on the front afb on that back how would you like to tune that set up??? especially when you wanted those vac secondaries to open says he was an expert mechanic though

Gezzzz,, It`s hard enough with two of the same carbs ,,,,, can you say Frank-in-steen !!!

 

[walkerheaders]

Do any of you guys realize that the front carb is also used for idling?. and the intake is designed for the whole engine to share the rear primaries? and that it doesn't sound/run quite right if you rev the engine by it's front carb?
the front carb does not have idle mixture screws, but the curb idle screw holds the blades open a certain amount.
you balance the rear carb mixing screws and both front and rear carb throttle blade screws to get the correct idle. this is according to he factory manual.

as a puppy, i thought this to be all wrong so i drilled a small hole in each rear carb primary blade and used only the rear carb as the primary. it worked good. now i have the same car set to the factory specs above. it worx better, and runs very well.

I do have a problem with that little piston/rod assembly that operates inside the choke housing. no matter what i lube it with, it gets tight again. i've honed it, replaced it............nutz

 

[jim_ss409]

Good point Bob! If you give the front curb idle screw about 1 1/2 turns it'll idle better. When I first got my 409 I tried setting the idle with the front carb completely closed. It didn't idle right. I followed Curt Harveys recomendations for setting the idle and it worked much better. http://www.mr409.com/faq.html

 

[Tic's60]

whats fricken scary is starting that old beast while it's sitting on a block of wood!!!
Least I use a tire or two