Bob and Listers,
OK Bob You asked............Time to relive my drag racing days.
As long as you have a decent repeatability it is likely that you will see
some difference on your road test.
As far as our small Block Chevy we made 620 HP with a modified Bo-Lawes
(BLP) racing "750" that when corrected flowed 1030 CFM at the base plate.
they do this by balancing the flow of each bore of the carb maximizing the
venturi effect to accelerate air through the carburetor achieving higher
than previously possible airflow. The Rocket guys are probably better to
explain this Venturi effect but on our car it had very impressive throttle
response, it was instantaneous. I had another modified carb previously on a
Drag/Pro-Street car that started out as a 750 annular discharge until TRC
(Total Racing Carburetors) did some improvements and in the end it flowed
1090 CFM. I don't recall the amount of vacuum that they tested them at as I
don't know where the flow sheets are (11years ago....Bob you are probably
beginning to wonder if I have ever really done any of this at all or maybe I
B.S. well). The first carb was on a 355 with Brodix-8 cylinder heads with
180cc Intake runner volume and a Crane IR-260 Roller tappet cam, 6" Rods and
an HVH modified Intake and worked really well and did not in any way seem to
be too big especially considering the incredible throttle response. The
second carb was on a small block 406 inch engine with 5.85" rods, crane
TR-242 Roller tappet cam, heavily ported 292 turbo castings and a ported
Edelbrock Victor Intake. The TRC carb was a more highly modified piece but
it worked so well it encouraged us to buy the BLP one for the 355. The TRC
carb was an unbelievable piece with heli-arced throttle plates with half of
the throttle shaft milled out on top of the wafer thin throttle
blades...part of how they increase the airflow... and they also completely
reshaped venturis. I think part of the modification was to increase the
diameter of, or use a base plate off of a 800 CFM carb. The reason i started
to explore these modified carbs is that when i was power tuning my 406 at
any RPM over 7400 the car would start to lay down and after testing found
that the Vacuum would start to climb as the engine hit 7500. After much
discussion and deliberation we determined that at High RPM the engine could
not get enough air through the carb and was starting to create significant
vacuum. The problem was that as it started to climb it climbed really
quickly. With the roller and the Automatic (5500 Rossi stall converter) In
order to get the engine to idle in gear, as it made little vacuum at
idle(4.5"), I used 3.5 power valves. At 8000 the vacuum was climbing to over
2.5 inches...by my gauge... was it accurate ...I dunno. The point is that
there was some vacuum and if it ever got to 3.5" KABOOM!!! as this would
close off the main fuel circuit and force an engine twisting at 8500 to make
do with only enough fuel to idle. MAJOR LEANOUT!!!
The point of this dissertation is that the CFM demand of an engine is unique
to the combination of parts on the engine. While there is some limitations
to the volumetric efficiency of a specific engine displacement, It would not
surprise me in the least that I can make a 600 work very well on the 260 and
a 650 DP work extremely well on a 302 as long as I can modify cylinder heads
and exhaust. I know that the 347 stroker with a roller and twisted Wedge
heads should have the same demand for air as our old 355 but I may not go so
aggressive that I put the 1090 CFM modified 750 on it as the durability of
those race pieces is just not there. On a side note, the CFM rating on a
factory produced Holley may or may not be exactly as they state. My
originally configured 750 actually flowed something less than 750 CFM (725
if I remember correctly) What Holley is trying to tell you is that the carbs
flow somewhere...... around....... 600 CFM........This fits into RACE MOTTO
#3: YEAH, YEAH! SURE, SURE! The corollary being: "Don't believe everything
you are told until you prove it to your self!"
RUMOR: The Nascar guys order carbs in sets of ten flow them all and keep the
best 2 and sell the rest to schmucks like us.
I bet I get lots of comments on this email !!
Good Night all,
Tim Ronak
B382000680
----- Original Message -----
From: Bob Palmer <rpalmer@ames.ucsd.edu>
To: Tim Ronak <timinvan@fox.nstn.ca>; Steve Laifman <laifman@flash.net>
Cc: Tiger News Group Address <tigers@autox.team.net>
Sent: Thursday, July 15, 1999 1:51 PM
Subject: Re: Air Filters
> Tim,
>
> You've inspired me to add one more parameter to our acceleration tests
Tim:
> with and without air filter. Maybe with and without stub stack too.
>
> I have a Holley #1860 600 cfm. I removed the choke assembly with a hacksaw
> and file. Not real pretty, but real cheap. I sure don't need a choke down
> here in S. California, but I still have the manual adjust hooked up so I
> can conveniently fine-tune the idle speed. Solves the run-on problem, etc.
> An important factor, in addition to air flow, is air density; i.e., colder
> air is better. In fact, probably most of the benefit you get from "ram
air"
> is the fact that it's cooler, not the increased pressure. Arranging to get
> cool intake air under a Tiger's hood is problematic unless you have a hood
> scoop as with the LAT-25 or LAT-79 or equivalents and implement some kind
> of seal between the intake and the hood.
>
> I have long held the opinion that 600 cfm is way plenty of carburetor for
> even the most high performance 289/302 engines. However, if you are trying
> to squeeze every last pony out, maybe this isn't completely true. Do you
> have any comparable experience with small block Chevy motors? Of course,
> with the flow limitations inherent with the Tiger installation, the
> limiting factor is even more likely to be the air filter, etc.
>
> Well, TTFN,
>
> Bob
>
> At 11:59 AM 7/15/99 -0600, Tim Ronak wrote:
> >Steve You wrote:
> > > Tim,
> > >
> > > What is a "stub stack", and will it fit the stock Tiger air cleaner
> >housing with
> > > the correct K&N main filter?
> > >
> >Steve and listers,
> >Maybe it is yet another canadian innovation like the 6-bladed fan!
> >
> >Short answer....NO!
> >
> >Long answer Maybe or why would we want to.....
>
> Robert L. Palmer
> UCSD, Dept. of AMES
> 619-822-1037 (o)
> 760-599-9927 (h)
> rpalmer@ucsd.edu
> rpalmer@cts.com
>
>
>
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