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T1H5_TA3 said:
boy that 4 to 2 adapter sure lookes like a great way to over carb an eng. nothing like killing port volocity in an effort to make torque:flipoff2:

some people just need to go back to freshman year shop class...:rolleyes:
Are you talking about the machined 4bbl intake, or the 4-2 "bolt on" carb adapter?


If it's the machined intake..

Is it really killing port velocity? It necks it down which should increase velocity vs two "huge/straight" holes, right?

And I'm not looking for <2000rpm throttle response, either.. if I could find a good single-plane intake for the 304...

On the 4-2 adapter.. It was an experiment. Unfortunately, with two weekends of racing behind me, I found NO improvement with the 600cfm square-bore Holley 4-2 over the 500cfm 2bbl Holley.

I'll drag race it on Memorial Day and see if my ETs drop at all.. if I'm still right at 7.0s that'll help verify "no change"..

But maybe I'll have my machined 4bbl intake ready to go by then.
 

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from the looks of the adapter etc there is just a taper, not a venturi effect, so the port speed at the botom of the adapter is prob ok, but the air speed in the carb is prob almost non existant. remember the 2 holes can only flow so much air regardless of how big the carb is.. yes, if there was a venturi effect, it would slightly increse the air flow, but not by much.

i know you race alot so you are fermiliar with volumetric eficancy etc, and you are probably avare of how to calculate airflow (displacement*max rpm*ve/3456=total airflow)
so a 304 turning 5500 rpm would move 483cfm assuming 100% ve. and unless you have a highly tuned, ported head etc id be more inclined to guess more along the lines of 80-85% ve for most well tuned ih motors.... so, just over 400 cfm @5500 rpm...
the only reason i see to put more than a 500cfm 2 barrel on is if you inject it, then id prob run a common 670 cfm throttle body.
 

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T1H5_TA3 said:
from the looks of the adapter etc existant. remember the 2 holes can only flow so much air regardless of how big the carb is.. yes, if there was a venturi effect, it would slightly increse the air flow, but not by much.
OK, do note that the two holes are significantly larger than the stock 2-holes. You can't quite punch a 304 intake out far enough to put a true 4150 pattern down without breaking out into the runners - which is what my first 4bbl intake was like, and why it's now a counter-weight on a cherry-picker.

But they're bigger/longer then the stock 2bbl holes at the bottom.

Running the 600 on the 4-2 adapter, I might have verified that the two *stock* holes will only flow X amount.


you have a highly tuned, ported head etc id be more inclined to guess more along the lines of 80-85% ve for most well tuned ih motors.... so, just over
Probably being generous on most IHs with 80-85%.. but this one did receive a lot of headwork.


400 cfm @5500 rpm...
the only reason i see to put more than a 500cfm 2 barrel on is if you inject it, then id prob run a common 670 cfm throttle body.
What I see is both carbs appear to run out of steam at 5300rpm. I haven't experimented with advancing the timing some more (beyond the current 25-30 static BTDC) and running straight race fuel, but I AM fairly certain that in 3rd gear it won't rev itself past 5300rpm or so, no matter how hard I try to bend the gas pedal (good thing we boxed up the brand new gas pedal..)


With the 600cfm 4bbl on it (via a 4-2 adapter).. I'm not sure if it's the intake limiting flow (my hope), or that the heads just won't cut it.

I think I eliminated the 500cfm 2bbl carb as the specific culprit.

I'm doubtful the 2.25" straight pipe sections are restricting flow enough to choke it off that badly.

My other suspect item is the camshaft. I might just need to try running more cam.

Waiting to try the intake first. Would it make a difference if I mentioned the intake was flow benched to 750cfm?

I don't know what the max-flow of the stock 2bbl intake is..

At the moment, I want to exceed my current 5300rpm.. but my goal is over 6k. I need at least 6300rpm to be competitive in my class at least on trap speed.

The loss of that 1000rpm is killing me the last part of the race.


In any case, maybe I've proven the point that 99% of the 304s out there do not *need* a 4bbl.. and for that matter, most would run better with a 350cfm.

Interesting point.. max RPM with the 350cfm? IIRC, around 4300rpm.. running something like #75 jets.
 

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mu personal guess.. id say you are more than likely running out of cam......

reason i say this is holley rares 4 barrels at 1.5" of vaccume, but the 2 barels are rated a 3".... so all things being equal , a 500 cfm 2 barrel rated at 1.5" only flows about 400 cfm if i remember corectly...

an easy way to check if the carb is your limitation would be to simply hook up a vaccume gauge to manifold vaccume.

oh, and no, i doubt the 2.25" duals are limiting you. if its manderal bent, and has no restriction, its capable of flowing enough air to easly suport about 800 hp or 1700 cfm.....:flipoff2:
 
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