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Author Topic:   Lack of torque below 3000
Pierre
Gearhead

Posts: 118
From: France
Registered: Apr 2002

posted 04-15-2002 01:23 PM     Click Here to See the Profile for Pierre   Click Here to Email Pierre     Edit/Delete Message   Reply w/Quote
Hi Guys,

With only a few hundred mustangs in the country (France), finding someone
who can help you with technical questions around here is a challenge. So I
was very excited about your site, hoping that you can give me some
pointers.

Here is the context:
Mustang 67, with 302 (1971). Aside from forged aluminium pistons, the lower
block is stock. Heads are Edelbrock aluminium with 2.02+1.60 valves. Cam is sporty
but reasonnable at 214 int. (@0.050) and 224 exh. I degreed it with a wheel
and everything checked out. Intake is performer RPM with 600 cfm
(Edel/Carter) on top. A 1" heat spacer seats in between. Distribution is
new (mallowry with vaccum advance) No ignition box. All this work was done
a few hundred miles ago. (Tranny is a new T5 and rear is Curries limited
slip at 3.5 ratio)

Even though it is difficult to gage what power I am getting and what I
should be expecting , it seems that I am not getting much torque below 3000
RPM. It feels almost like a flat spot that gradually goes away as the
throttle opens & RPM climbs. I have narrowed down the possible causes to
either a wrong ignition curve (below are my present setting) or too lean an
A/F mixture in that range. I have a hard time believing that the valves'
size are entirely responsible for my problem.

For the A/F curve I am going to change the rod springs to stronger ones
(Which will bring the rich stage sooner) as soon as my order comes through.

As for the ignition I have been reading your archived documents and am a
little puzzled. Here we run 95 or 98 octane (I usually use 95 which is
already 4$ a gallons !!). I can set my initial timing anywhere from 11 to
18 and my idle will be very good to decent (At 18 I can tell that the
starter is working hard though when the engine is hot !!). At 2000 RPM I
have around 38 (crank advance), It will then climb slowly to 45-55 (Yes,
TDC is approx correct at the marker !!). I have been playing with the
vaccum and initial timing adjustments but do not seem to get any noticeable
change in my situation.

Here are my questions:
1 - Considering the octane situation, what total maximal advance should I
get (at high RPM) without taking chances (55 seems huge !)
2 - Does the curve described above seem usual ? it seems like it takes a
radical hump before 2000 and then flattens out. I understand that each
engine is different but there should be some guidelines (ie: 2000= 30 to
40, 3000= x to y,...........). FYI: This is a performance/street
application.
3 - Do you think that changing the spring rods in the carb is a good move ?
4 - What does "pinging" means ?

Any help would be greatly appreciated.

Thank you in advance

IP: Logged

steve'66
Gearhead

Posts: 4182
From: Sonoma,CA,USA
Registered: Mar 2000

posted 04-15-2002 01:53 PM     Click Here to See the Profile for steve'66   Click Here to Email steve'66     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Pierre:

Here are my questions:
1 - Considering the octane situation, what total maximal advance should I
get (at high RPM) without taking chances (55 seems huge !)
2 - Does the curve described above seem usual ? it seems like it takes a
radical hump before 2000 and then flattens out. I understand that each
engine is different but there should be some guidelines (ie: 2000= 30 to
40, 3000= x to y,...........). FYI: This is a performance/street
application.
3 - Do you think that changing the spring rods in the carb is a good move ?
4 - What does "pinging" means ?

Any help would be greatly appreciated.

Thank you in advance



1 and 2. Maximum total advance should be about 40 degrees, and it should be fully advanced by 3000 rpms.

3. You'll have to wait for a Edelbrock carb expert to respond. I prefer Holleys.

4. Pinging is spark knock, also known as pre-ignition or detonation. It happens when the combustion mixture ignites before the pist reaches top dead center and can cause severe engine damage.

Welcome to MustangsAndMore!

SteveW

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bluestreek
Gearhead

Posts: 785
From: Athens,GA
Registered: Jul 2001

posted 04-16-2002 08:47 AM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
With that cam and heads you should be able to set your initial timing to 16 degrees and unhook the vacuum advance. An aftermarket camshaft and stick shift doesn't need it. You should then check the mechanical advance with it unhooked and should curve your distributor springs to GRADUALLY get 36-38 degrees total advance in by 3000 rpms.

Personally, I never got a Edelbrock carb to make a SB Ford run like it should. Changing the step rods, springs, or jets, may help. It takes a lot of trial and error and is very costly and time consuming. A stock Holley 600 idles a little rich on SB Ford but always feels much stronger at middle to wide open throttle.

Good luck,
BS

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Pierre
Gearhead

Posts: 118
From: France
Registered: Apr 2002

posted 04-17-2002 03:48 PM     Click Here to See the Profile for Pierre   Click Here to Email Pierre     Edit/Delete Message   Reply w/Quote
Thanks Guys for your advices, I will load myself with patience and try every angle. I will let you know the outcome. Will probably get a Holley "Avenger" when wife recovers from last expenses !!

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