Last night I picked up a used Offenhauser 4bbl Intake for $205.00 with shipping.

The thing is I was planning on doing a fuel injection conversion using the Buick 3.8 parts as outlined by Bob DiBiase in the tech archives. But now that I just spent $200.00 on a intake I am having second thoughts about modifying this one and destroying its resale value.

So now I have an intake coming in the mail that from all things I have read will only hurt my fuel mileage and potentially cause all sorts of drivability issues on the street if I run it with a carburetor. So I go online looking for a new Carter 400. Can't find one of course(well I found one, but at $550.00 I'll pass). I hate Holley(just a personal thing, to me Holley is like Chevy, they go hand in hand with the mullet/camaro crowd) so the 390 is low on my list.

So I get to thinking what if I run a Edelbrock 500, but put(weld/epoxy) a plenum divider between the left and right side of the intake. This would effectively let each cylinder only see a staged 2bbl. This in my mind could even boost economy as the primary venturi of the 4-bbl should be smaller than the factory 1-bbl that each cylinder sees right now(at least I think it would be).

I know it is not a simple as I am thinking. I bet that the fact that each primary will have a pause between breathes will decrease the atomization efficiency as compared to a single staged 2 bbl in a two barrel manifold which would always have an intake stroke drawing air through the venturi.

SO FINALLLY, some questions:
Will this split plenum do what I think it will?(better economy/throttle response as compared to open plenum 4bbl)
Will fuel economy have the potential for improvement over single 1bbl?(assuming tuned well, and driver can keep foot off of the floorboard most of the time)
Would running a 400 CFM carburetor still be best even with the split plenum?

This will eventually run on a 225 with a comp 252S cam(.432 I/E) with either headers, DD's or a truck manifold and large single exhaust in a 64 Dart Wagon with 4-spd.


More theory questions:
Does the dual single Offy manifold actually improve low end performance, or does it only really help the top end by boosting overall flow at high rpm? My thought is that each cylinder only sees 1-bbl, just like it would in a standard 1bbl manifold, but with the two seperate 1bbls their is more potential for top end flow because the manifold will not have a traffic jam effect. Also if I am correct than it would help make the case for my split plenum 4bbl.

Sorry for such a long post, but these are the thoughts that keep me up at night. I have a 9PM car rule and I broke it. The rule is that after 9PM I stop thinking about cars, this way my mind will shut off(hopefully) by the time I get to bed at 10PM. Well I screwed that up last night by buying the intake at 9:20. Now I am at work and I am still thinking about cars. [/b]

I think splitting the plenum would really screw up your fuel distribution.

D/W

_________________

If it ain't broke, fix it!

I don't understand that. I am talking about splitting cylinders 1-3 from 4-6. The carburetor would be mounted with the primaries facing the driver side, with the divider perpindicular to the intake mounting surface

Wasn't sure, but figured that's what you meant. I still think it would cause certain cylinders to run richer than others, even more so than a typical /6 intake with an open chamber. I'm betting the fuel economy difference would be negligable. Just put on a 4V and stay out of the secondaries if you want good gas mileage. My Duster still gets decent mileage with a cam, headwork and a four-barrel when I'm not hammering it at the track. I'm thinking that the divided plenum idea would be more effective with a long, more equal length runner manifold like the "hyper-pak".

D/W

_________________

If it ain't broke, fix it!

That actually reduces reversion in the manifold and makes the hpak more 'fun' in the mid range....It doesn't cure the fuel distribution problem...it does make tuning more fun though...

I think on the 'plug and play' average in good tune with timing worked out, both setups (super six/offy) should get similar mileage results....if you stay out of the secondaries in the 4 barrel (or in the case of the holley, install a stiff secondary spring to lock them out).

-D.Idiot