Nah akhirnya ada jawaban juga kenapa karburator landy suka sesak nafas :)
From: firstname.lastname@example.org (Jim Allen)
Subject: Performace Carbs for 2.25
To All Series Owners,
Some of you may have seen the “Power Feed” article in the Summer
Issue of LROI. A lot of good data was edited for space considerations so I
thought you might like to see the missing parts. Print this one out and
stick it into your magazine as a companion. Enjoy!
Here’s the part that tells you how to figure CFM requirements for
any engine at any speed.
CFM=3D rpm X displacement
____________________ X volumetric efficiency
Lets break the formula down.
RPM: Usually the maximum rpm of the engine is used here but you can
in any engine speed.
DISPLACEMENT: In cubic inches, the size of the engine.
3456: This is a constant that converts the upper figure to CFM at 1.=
VOLUMETRIC EFFICIENCY (VE): This is the engine’s theoretical
breathe versus it’s actual ability as measured in real life. VE vari=
according to engine speed. It’s higher at the engines maximum
low speed) and lower at the engines max power (a high speed). A low
performance engine like the 2286 would have a 75% VE at max power
80% VE at max torque.
Plugging in the four-cylinder numbers would look like this.
4250 rpm X 139.5 cid
128.6621 CFM=3D _____________________ X 0.75
If you compare this figure to the tested ratings of the stock
carburetters, you’ll find they match fairly closely. If you run one of
these engines, you will also know from personal experience that the engine
is definitely breathing hard above 3500 rpms. A slightly larger carb can
enhance upper rpm performance.
RE: Oil Bath Air Filters
The original oil bath air cleaner has the theoretical airflow to
keep up with the engine. In practice, I have felt a big gain in power by
eliminating it. I was in a quandary on this question until Earl Davis,
K&N’s dyno guru, explained a possible reason.
“It isn’t just raw airflow capacity, ” he said, “it’s also
velocity. If the air cleaner is slowing the velocity of the air, it could
effect performance.” Earl noted that the 90 degree elbow and corrugated
hose might have a deleterious effect and recommended trying a smooth hose
and an elbow with a shallower radius and/or moving the radius farther away
from the carb by about 3-4 inches.
Some owners have reported adapting the factory oil bath filter to
the big Weber two-barrels and claim good results. I have to reserve
judgement on this, having tested the combo with very poor results. At
3800rpm the engine fell flat on its face due to lack of airflow. Mike
Pierce reported similar results when he was developing his Weber 2-barrel
kit. Obviously, these folks never rev the engine much above 3500.
Some Test Data They Didn’t Print
To save your calculator some wear and tear, I’ve run the figures for a 2286
from 2000 to 5000 rpm. Compare these figures with the airflow tests of the
various carbs, manifolds and air filters.
2286cc Theoretical Airflow Requirements
Engine RPM CFM
2000 1 64.6
2500 1 (peak torque) 80.7
3000 1 96.7
3500 2 105.9
4000 2 121.1
4250 2 (peak power) 128.7
4500 2 136.2
5000 2 151.4
1- At 80% volumetric efficiency
2- At 75% volumetric efficiency
Single Barrel Carburetters
Carburetter Orig. Application Venturi Size CFM Rating
Rochester Chevrolet 230cid
Model BV=DD 6-cyl. mid-’60s=DD 30.9mm=DD 167CFM @ 1.5″
Aftermarket Replacement for LR 29mm 138CFM @ 1.5″
LR Factory 2-1/4
from engine suffix J
36-IV or IVE (from about 196 27mm 127CFM @ 1.5″
LR Factory 2-1/4
to engine suffix J
Solex (to about 1967) 28mm 115CFM @ 1.5″
=DD- Model B and BC Similar.
Carburetter Original Application Venturi Sizes CFM Rating
38-DGAS =DD=DD Various 36/36mm 424CFM @ 1.5″
28/36-DCD=DD=DD=DD Various 26/27mm 224CFM @ 1.5″
32/34-DMTL=DD=DD=DD LR Factory
2-1/4 & 2-1/2
from 1983 26/27mm 194CFM @ 1.5″
32/36-DGV=DD=DD=DD Aftermarket in kit
for 2-1/4 26/27mm 191CFM @ 1.5″
=DD=DD- Simultaneous opening 2 barrel.
=DD=DD=DD- Progressive opening 2-barrel
Original Application Type CFM Rating
K&N Part #RU-0600
for 1-barrel Zenith/Weber Oiled Cotton Gauze 1554 CFM @ 1.5″ merc
K&N Part #56-1030
for Weber DGV Oiled Cotton Gauze 617 CFM @ 1.5″ merc
for original 1-barrel
applications Oil Bath 190 CFM @ 1.5″ merc
Type CFM Rating
Pierce 2-barrel as comes in
Weber 2-barrel kit 297CFM @ 1.5″
=46actory 1-barrel, modified 235CFM @ 1.5″
=46actory 1-barrel, unmodified 189CFM @ 1.5″
(Modified manifold has had locating sleeve removed and inside edges
radiused towards ports)
Last edited by Big Sandy; 4th Jan 2008 at 23:50.