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Author Topic:   idle
two89w
Gearhead

Posts: 319
From: sydney australia
Registered: Sep 2002

posted 10-10-2002 05:01 AM     Click Here to See the Profile for two89w   Click Here to Email two89w     Edit/Delete Message   Reply w/Quote
i have spoken to several people(engine builders) over the last month and half of them say that i could get as good idle/drivablility with a four barrell as i have with my webers is this possible?? does anybody have good idle/drivability with a cam or bigger cam than mine?? 560 lift 248 @.050 110 lobes solid flat???

[This message has been edited by two89w (edited 10-10-2002).]

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two89w
Gearhead

Posts: 319
From: sydney australia
Registered: Sep 2002

posted 10-10-2002 08:03 AM     Click Here to See the Profile for two89w   Click Here to Email two89w     Edit/Delete Message   Reply w/Quote
now it makes more sense

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Daniel Jones
Gearhead

Posts: 898
From: St. Louis, MO
Registered: Aug 99

posted 10-10-2002 01:30 PM     Click Here to See the Profile for Daniel Jones   Click Here to Email Daniel Jones     Edit/Delete Message   Reply w/Quote
> I have spoken to several people (engine builders) over the last month and
> half of them say that i could get as good idle/drivablility with a four
> barrell as i have with my webers is this possible?? does anybody have good
> idle/drivability with a cam or bigger cam than mine?? 560 lift 248 @.050
> 110 lobes solid flat???

Assuming your Webers are mounted on an independent runner (IR) intake
manifold and the 4 barrel carb is on a plenum intake, the Webers should
give much better idle and drivability. It's more a function of the
independent runner intake, though. With a V8 and a common plenum intake,
reversion from one cylinder will foul any adjacent firing cylinders.
Reversion increases with overlap and causes the lopey hot rod idle.
Also, the exhaust back pressure plays a big role. A friend built an
engine with big cam and had zoomies on it for a while and it would idle
right down. As soon as they put a street exhaust, it got a lumpy idle.

One of the guys in the Pantera club has run 48IDA Webers and IR EFI
with solid flat tappet cams in the 250 to 260 degrees @ 0.050" range
with 108 LSA in a 351C and they worked fine on the street. Another guy
in the club recently converted to IR EFI from a tuner re-worked Holley
700DP on a dual plane intake. The cam he runs is around 250 degrees
duration @ 0.050" with a really narrow 105 lobe separation. With the
Holley, it was a real window rattler at idle and didn't really smooth
out until 3000 RPM or so. With the IR intake, he's wondering where
the idle went (wants a bigger cam now) and it'll pull from 1500 RPM
in 5th gear.

Dan Jones

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'69Stang
Gearhead

Posts: 205
From: Detroit, MI USA
Registered: Jan 2002

posted 10-10-2002 03:11 PM     Click Here to See the Profile for '69Stang   Click Here to Email '69Stang     Edit/Delete Message   Reply w/Quote
Dan Jones: Is there a big trade off in horsepower when going to the IR systems with Webbers or FI? It seems to good to be true to be able to have a smooth idle and have a 250+ duration cam @ .050. Seems like the IR/FI systems make a 250 cam act like a 230 cam @ .050. Any thoughts would be appreciated.

Luc

------------------
'69 Mustang Fastback, 302, Holley 600 DP, Edelbrock RPM, GT-40 heads (54cc's), 9.7:1, headers, UD pulley, windage tray, Top Loader, 3.89 9" rear

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Daniel Jones
Gearhead

Posts: 898
From: St. Louis, MO
Registered: Aug 99

posted 10-10-2002 06:15 PM     Click Here to See the Profile for Daniel Jones   Click Here to Email Daniel Jones     Edit/Delete Message   Reply w/Quote
>Webers or FI?

Not if the Weber carbs or IR EFI throttle bodies are properly sized.
Historically, Webers were developed for smaller European engines.
The largest of the commonly available downdraft Webers were 48mm
which were fine on most small blocks but not on high horsepower stuff
or big blocks. There were a few sets of bigger bore Webers made but
they are rare, however, Berg makes a copy in larger sizes. For EFI,
TWM and others make throttle bodies in various sizes to support much
high horsepower levels.

In cases where carbs are not large, a plenum allows cylinders to share
flow effectively reducing the

>Seems like the IR/FI systems make a 250 cam act like a 230 cam @ .050.

The cam timing events determine its best operating RPM range. Isolating
the intake runners from each other, simply removes much of what upsets
the idle and low RPM operation of a plenum intake. You can still get
reversion in each individual cylinder which may affect the tuning at a
particular RPM. However, with IR, you can alter the stack height to
tune the inlet tract for different RPM, something that's not easy to do
with a plenum intake.

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