Old style intakes.

Discuss the good old days of Hemi racing.
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Posts: 49
Joined: Sat May 04, 2002 9:00 pm
Location: phoenix az

Old style intakes.

Post by john » Sun Dec 07, 2008 9:42 am

Since there's no nostalgia P/S section, I figured this is as good a spot for this as any.
In looking at some of the early P/S Hemis I noticed alot of them have a relatively short runner intake tunnel ram. Does anyone know who made these & exactly why Mopar engineers opted for this shorter runner? Also, if anyone could give me the specs on 'em I'd sure appreciate it, as I 'd like to make my own sheetmetal version.

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Joined: Tue Mar 22, 2005 2:06 pm

Re: Old style intakes.

Post by mart » Tue Dec 16, 2008 5:12 am

I *think* what you're talking about may be the "I.R." ("individual
runner") intakes that were experimented with briefly during the
early 1970's. Basicly they were similar to standard tunnel rams,
but with the plenum section deleted. Instead of having a common
plenum under the carbs, there was simply a carb mounting flange
attached to the top of the runners so that one venturi and throttle
butterfly from each carb would feed one indvidual runner. Holley
even made a limited run of special 'I.R. calibrated' Dominator carbs
that were listed in their catalog for a while. The probem with the
set-up was that even using the modified 1050 and 1150 cfm Holley
Dominators, without a plenum, the carbs still ended up being too
small at high rpms. Also the there were problems with reversion
and fuel stand-off at certain rpms making them hard to tune.
They also tended to be very peaky, would only make power over
a very narrow rpm range and would rapidly run out of breath at
higher rpms. A rule of thumb with manifolds is the bigger the
plenum, the smaller the carb can (or needs) to be for a given rpm
and power level and the wider the power band. Likewise, the
smaller the plenum, the bigger the carb needs to be and the
narrower the power band will tend to be. By eliminating the plenum
altogether on the I.R. set-ups, it turned out that on the pro-stock
Hemis, just to produce more power (or even equal power levels)
than that of the existing "plenum type" tunnel rams, the carbs
would have needed to be almost twice as big as what was then
available, not to mention the other, mostly unsolved problems
of a very narrow rpm range and tuneability problems caused by
reversion and fuel stand-off and certain rpms.


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