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In 4th gear, the combustion chamber has more time to get too hot. What =
about
trying say 30=B0 maximum advance to check if detonation has something =
to do
with it?
Marcel
_____ =20
Van: Fot [mailto:fot-bounces@autox.team.net] Namens John Styduhar
Verzonden: maandag 28 november 2016 23:04
Aan: Mike Harmuth
CC: FoTTriumph
Onderwerp: Re: [Fot] Intake manifold vacuum and no high RPM
I had the same problem in my TR3 racer. I corrected the lean condition =
by
installing a stronger damper spring in the carb and oil in the piston. =
This
created more vacuum in the throat of the carb at the higher revs and =
caused
more fuel to be drawn through the jet via the venturi effect. Choking =
the
carb does basically the same thing.
On Mon, Nov 28, 2016 at 4:23 PM, Mike Harmuth <ofracer@gmail.com> wrote:
I'm tracking down a problem with the Spit race car (1296 Small Journal, =
12;1
compression, APT TR74 cam 295 duration and 0.324 lob lift, head ported =
as
per Kas's book). Rebuilt European SU HS4 carb setup with AAA needles
(manifold and carbs checked for vacuum leaks), Advanced Distributor for
spark (34 degrees at full, mechanical only, advance @ 3.5K RPM)
The problem I have has followed me on two different short blocks, I can
easily pull 7500RPM in 1st-3rd ( Close ratio TR7 gearing in a Spitfire =
case,
4th gear is 1;1, 4:11 locked diff ) gears. In 4th I'm struggling to get
over 6K, no matter how long the straight. Just before the last race of =
the
season, I installed an air fuel ratio gauge on the header (stahl) and =
found
out I'm running (progressively) very lean (19:1) in 4th over 5K. At 2K =
I
adjusted it rich, to 12;1 and it keeps in the 13.5- 14.5 range until I =
get
over 5K when it really leans out. If I pull the choke to 1/2 full over =
5K,
I get a good ratio again, 13.5- 14%.=20
To me that seemed like the carb pistons aren't pulling all the way up so =
I
drilled and tapped the manifold to get a vacuum reading. It was steady =
but
low at 6K, ~20 Inches but would jump to ~28 briefly as the revs dropped =
if I
blipped the throttle. Under 6K, it was in the 15 inch range. Normal air
filters are K&N with stub stacks but I get the same results with open =
carbs.
Am I correct in assuming that the vacuum is too low or is it that due to
overlap with a performance cam? Any ideas on where to look to get the =
ratio
"normal" at higher revs? Fuel pump is Holley Red, adjusted to 3 PSI at =
the
engine compartment and steady through all revs.
I have dyno time scheduled in a few weeks but I'd like to use that time =
to
tune not debug things.
thanks
mike h
63 spitfire
_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
html
Archive: http://www.team.net/archive
<http://autox.team.net/mailman/options/fot/johnstydo@gmail.com>
options/fot/johnstydo@gmail.com
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<BODY>
<DIV dir=3Dltr align=3Dleft><FONT color=3D#0000ff size=3D2 =
face=3DArial><SPAN=20
class=3D610360508-30112016>In 4th gear, the combustion chamber has more =
time to=20
get too hot. What about trying say 30=B0 maximum advance =
to check=20
if detonation has something to do with it?</SPAN></FONT></DIV>
<DIV dir=3Dltr align=3Dleft><FONT color=3D#0000ff size=3D2 =
face=3DArial><SPAN=20
class=3D610360508-30112016>Marcel</SPAN></FONT></DIV><BR>
<DIV lang=3Dnl class=3DOutlookMessageHeader dir=3Dltr align=3Dleft>
<HR tabIndex=3D-1>
<FONT size=3D2 face=3DTahoma><B>Van:</B> Fot =
[mailto:fot-bounces@autox.team.net]=20
<B>Namens </B>John Styduhar<BR><B>Verzonden:</B> maandag 28 november =
2016=20
23:04<BR><B>Aan:</B> Mike Harmuth<BR><B>CC:</B> =
FoTTriumph<BR><B>Onderwerp:</B>=20
Re: [Fot] Intake manifold vacuum and no high RPM<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=3Dltr>
<DIV class=3Dgmail_default style=3D"FONT-SIZE: small">I had the same =
problem in my=20
TR3 racer. I corrected the lean condition by installing a stronger =
damper spring=20
in the carb and oil in the piston. This created more vacuum in the =
throat of the=20
carb at the higher revs and caused more fuel to be drawn through the jet =
via the=20
venturi effect. Choking the carb does basically the same=20
thing.</DIV></DIV>
<DIV class=3Dgmail_extra><BR>
<DIV class=3Dgmail_quote>On Mon, Nov 28, 2016 at 4:23 PM, Mike Harmuth =
<SPAN=20
dir=3Dltr><<A href=3D"mailto:ofracer@gmail.com"=20
target=3D_blank>ofracer@gmail.com</A>></SPAN> wrote:<BR>
<BLOCKQUOTE class=3Dgmail_quote=20
style=3D"PADDING-LEFT: 1ex; BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px =
0px 0.8ex">
<DIV dir=3Dltr>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>
<DIV>I'm tracking down a problem with the Spit race car (1296 Small =
Journal,=20
12;1 compression, APT TR74 cam 295 duration and 0.324 lob lift, head =
ported as=20
per Kas's book). Rebuilt European SU HS4 carb setup with AAA needles =
(manifold=20
and carbs checked for vacuum leaks), Advanced Distributor for spark =
(34=20
degrees at full, mechanical only, advance @ 3.5K RPM)<BR><BR></DIV>The =
problem=20
I have has followed me on two different short blocks, I can easily =
pull=20
7500RPM in 1st-3rd ( Close ratio TR7 gearing in a Spitfire case, 4th =
gear is=20
1;1, 4:11 locked diff ) gears. In 4th I'm struggling to get over =
6K, no=20
matter how long the straight. Just before the last race of the season, =
I=20
installed an air fuel ratio gauge on the header (stahl) and found out =
I'm=20
running (progressively) very lean (19:1) in 4th over 5K. At 2K I =
adjusted it rich, to 12;1 and it keeps in the 13.5- 14.5 range until I =
get=20
over 5K when it really leans out. If I pull the choke to 1/2 =
full over=20
5K, I get a good ratio again, 13.5- 14%. <BR><BR>To me that seemed =
like the=20
carb pistons aren't pulling all the way up so I drilled and tapped the =
manifold to get a vacuum reading. It was steady but low at 6K, ~20 =
Inches but=20
would jump to ~28 briefly as the revs dropped if I blipped the =
throttle. Under=20
6K, it was in the 15 inch range. Normal air filters are K&N with =
stub=20
stacks but I get the same results with open carbs.<BR><BR></DIV>Am I =
correct=20
in assuming that the vacuum is too low or is it that due to overlap =
with a=20
performance cam? Any ideas on where to look to get the ratio "normal" =
at=20
higher revs? Fuel pump is Holley Red, adjusted to 3 PSI at the engine=20
compartment and steady through all revs.<BR><BR></DIV>I have dyno time =
scheduled in a few weeks but I'd like to use that time to tune not =
debug=20
things.<BR><BR></DIV>thanks<BR></DIV>mike h<BR></DIV>63=20
=
spitfire<BR></DIV><BR>______________________________<WBR>________________=
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href=3D"mailto:fot@autox.team.net";>fot@autox.team.net</A><BR><BR><A=20
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_______________________________________________
fot@autox.team.net
http://www.fot-racing.com
Archive: http://www.team.net/archive
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