Slick 60's

We are switching intakes on the 240 Six We are going with the Offenhauser 4v. Checked into Carbs the Holley 390's run around $400. Everything we have read says Bigger is not better. Has anyone done this Conversion and used a Bigger Cfm Carb. Or what are the other options if any?

first off, get the dual plane not the C manifold. I had a c on my 300, due to the carb sitting in line with the engine, the cylinders got very different mixtures. The rear cylinders tended to run rich and the front ran lean due to the primaries not being centered - they were closer to the rear since i had to rotate the carb to get the throttle cable to work. The DP manifold has the carb oriented at a right angle which simplifies your linkage and provides a more consistent mixture. I run the 390 CFM, but got it with the original manifold. Holley also makes a 450 CFM carb that is intended to be used as part of a dual quad setup, but is much less expensive than the 390. I ran a 500 CFM Edelbrock while trying to figure out the mixture issue, it ran OK. These run about the same as the holley 450 cost wise.

bigger is not always better in fact i used a holley 2v, worked fine and no issues

The "cheaper" 450 intended for dual quad setups is cheaper for a number of reasons. It is a purely mechanical secondary carb, has no choke (or provisions to add one without doing machine work). I have them on my Maverick. Mileage would be horrible, even with one on a 6 cylinder, they are just not made for that use.




Holley does make a 450 vacuum secondary carb but it costs in the same neighborhood as the 390.

Watch what you buy. There are also 390 mechanical secondary race carbs out there. They are double pumper with metering blocks on each end and center hung float bowls. They look just like a 750 or 850 double pumper but have a tiny bore. You do not want one of those for a street engine.



Stick with the vacuum secondary 390, this is the style engine it was developed for and works best on.

JMO,
SPark

Think most people tend to over-carburete, especially with the Y-Blocks. I would think the 390 CFM would work well or as Ice suggested a 2 bbl.

I run a Edelbrock 500 AVS on my 300. You just have to run a .25" gasket to get the linkage to clear.



I also run an Offy "C" intake with long tube headers. Runs Great!

i had a clifford, holley 390 and headman headers on a 240 and it was at least twice the engine my stock 240 is. i am getting ready to do it all again. i also had an offy dual plane with the same 390 and headers on the same engine. i didn't notice much difference. but i didn't drive the truck enough or pull any plugs to gauge a/f mixtures from one to the next.

also, clifford seems to be in cahoots with webber. they strongly suggest running the ggas or whatever carb with their manifold. they swear it will out perform the holley 390 and edelbrock 500. just saying.

hi Dakota - I suggest that the 240cid's, like mine, seem to get along with the 390cfm. I am running the following:

Clifford open plenum aluminum intake: http://www.cliffordperformance.net/

Clifford headers (coated): http://www.cliffordperformance.net/

Holly 390cfm: http://www.holley.com/0-8007.asp
: I converted from electric choke to manual using Holley's kit (guess I have control issues... also didn't want more wires)
: Recommended jetting -
::: 240 cu. in. 8.5 POWER VALVE .031 (tube type) discharge nozzle .048 main jets
::: 300 cu. in. 8.5 power valve .035 (tube type) discharge nozzle .052 main jets.


I'm happy with the setup. Hope this helps,
Von Dud

VERY clean and impressive engine compartment, Von Dud!

BarnieTrk

BarnieTrk wrote:VERY clean and impressive engine compartment, Von Dud! BarnieTrk

I agree, very nice looking.

Along with the real world advice posted here, this should help fine tune your set up: http://www.holley.com/TechService/Library.asp

Like the stock firewall. How old are your headers?

Von Dud wrote:hi Dakota - I suggest that the 240cid's, like mine, seem to get along with the 390cfm. I am running the following:

Clifford open plenum aluminum intake: http://www.cliffordperformance.net/

Clifford headers (coated): http://www.cliffordperformance.net/

Holly 390cfm: http://www.holley.com/0-8007.asp
: I converted from electric choke to manual using Holley's kit (guess I have control issues... also didn't want more wires)
: Recommended jetting -
::: 240 cu. in. 8.5 POWER VALVE .031 (tube type) discharge nozzle .048 main jets
::: 300 cu. in. 8.5 power valve .035 (tube type) discharge nozzle .052 main jets.


I'm happy with the setup. Hope this helps,
Von Dud

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We went with the Offy Dual Port Headman Headers and the Holley 390 Wo whoo Ty taught me how to post pictures... What pressure does the stock fuel pump put out Holley suggests 5 to 7.5 is anyone running a regulator??

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Now to run Fuel lines and mount the carb. I just had to post another picture.

run the coolant passages as well. at least clifford claims more constant fuel temps in the plenum.

Chris I don't believe the Offys have coolant passages. Do you know what kind of fuel pressure a 1965 240 Mechanical fuel pump runs for pressure. Fired up the Truck tonight and the truck runs away on us we are thinking it is the fuel pressure. We will pickup a regulator in the morning.