390 4V versus 350 2V

[CobraSix]

Okay, I know we've been over this before, but I just want to make sure that I got the right idea.

Assume both carbs are Holleys.

the 2300 350CFM 2V and the 8007 390CFM 4V.

Which will perform better on the Aussie head? It seems to me after re-reading all the venturi and flow rate threads of late, that the 390 CFM would work better since in the primary range the flow across the venturies is faster providing a better signal. Also, even if the secondaries are operating, since you are using 4 smaller venturis vice 2 larger ones, the 4V should respond better, right?

Am I way off there? Thanks.

Slade

 

[xctasy]

You are firing an all six cylinders Slade.

The 390 4v is a better carb for drivablity on a little 2.0 or 2.3 Ford ohc compared to the 350 and 500 cfm Holleys 2v's on the same engine.

Source: David Vizard, 1988 edition on Modifying Fords SOHC engine.

 

[rbohm]

8) very definately the 390 4v is better than a 3502v. in fact if you were to use a 450 4v carb, it would still be better than a 350 2v carb, again because of the smaller venturi's.

 

[CobraSix]

hmmm...dangerous thinking.

The only thing with the 450 is that the secondaries would open less, right? But is that neccesarily a bad thing?

Slade

 

[SuperMag]

And how would that be different from running a big 2V? The 450's primaries are bigger than the 390's, and wouldn't mix as efficiently. Chances are, you'd only very seldom use all the 390's capacity anyway.

 

[CobraSix]

I only plan to go up to a 390.

Slade

 

[rbohm]

8) yes the 450's primaries are bigger than the 390, but still smaller than the 350's. the only problem i see with the 450 is that they are mechanical secondaries, so to use one on the street you would have to have some serious disipline, big problem around here

 

[Rustang Racer]

Can anybody tell me what the dimensions are between the bolt holes for the 390? Cobra Six, are you planning on making a funnel adapter or is there enough room on the big log head to mill the carb mounting flange down and do a direct mount? Sorry for my ignorance on the subject but I just decided to go with a 250 instead of rebuilding my 200 so my carb plans have changed completely.

 

[rbohm]

8) the 390 has the same bolt pattern as the 600 cfm holley 4bbl carb.

 

[xctasy]

On the #2300 series 2-bbl, the bolt pattern is about 5.15" wide on the width. I guess its about 5.15" square.

To make a 4-bbl work, you'd have to do a Clifford 3-carb-style alloy plate on top of a log head with the bigger 1.75" intake hole. There would be a bit of work, but if you were smart, you could do it.

It would be like bolting on the alloy carb plate on an old Cross Boss (302 )Mustang, Cross Ram (302 Z-28) ,Cross Fire (twin throttle body 82/84 350 Corvette) or Grumpy Jenkins Rat Roaster V6 intake manifold. The trick is making enough room for the ports to flow, and clamping it into the existing cast iron log with 7/16 cap screws. The cost would be high, but less than the 2V if you worked out a good design.

Another option is using the plate to mount two 350 cfm 2-bbls and get better fuel distribution. The loss of small primaries and good secondaries on a comparable 390 or 450 would be okay as the engine would get fuel delivery close enough to get mild pulse tunning. Grumpy Jenkins used twin 500 cfm Holleys on his old 270 cubic inch odd fire small block Chevy V6's, and got 375 hp with a very flat torque curve.

 

[CobraSix]

I'm going with an Aussie Head, then converting it to a 4V application.

Slade

 

[SuperMag]

Can anybody tell me what the dimensions are between the bolt holes for the 390?

I measure 5-5/32" x 5-5/8".

 

[Rustang Racer]

Thanks for the help. Wow, thats pretty big for the log. I guess some kind of funneling will be needed. I'll figure it out.