Big increase in power in my 1977 403ci engine.

[Bob Dunahugh]

David.There's an old saying that goes. There's always more then one way to =
skin a cat. And you covered another method of performance timing. I build, =
and race engines that are out on the edge of maximum torque at full throttl=
e in the 7 to 8,000 RPM range. I'm looking to get every half a foot pound =
of torque at the end of the crank. And there have been times that I've twis=
ted the end of the crank off. I machine down my oil pumps to reduce the oil=
volume out put of that pump. That detail helps to increase engine torque o=
ut put. I set the 4 carbs, and timing to the air temps, humidity, barometri=
c pressure, and gas that I'm using THAT day. ( As I bring my own tested gas=
with me ) All these change from day to day. I'm so close in timing that a =
settings I use one day. May blow the top of the piston out the next. Bringi=
ng this close of settings this close to our GMC's bring it's own issues. As=
the gas we get one day. May not be the same the next day. And all the ite=
ms listed above have changed. And with all of these changing ranges. How c=
lose to maximum timing advance do you want to get. The GM factory specs are=
listed to handle all of these changing conditions. With a safety factors i=
ncluded. So is one way better then the other. That is all in your comfort =
range. As for me. My stock 78 Royale, 403 with a 2-1/2 exhaust, no heade=
rs, and a 3:70 FD. With Linda's lift van I have a GVW of 17,000 lbs. With t=
he enclosed race trailer I'm at a GVW of 21,000 lbs. All with factory stoc=
k timing. That's my own personal comfort zone. Bob Dunahugh

 

[Bob Dunahugh]

GM's big thing, and all manufactures. Is to have their engines perform for=
many, many years. That's what brings customers back. There isn't an engin=
e built in the world that you can't get more horse power/torque out of. Man=
ufactures are out for longevity. So their tuning parameters deliberately fa=
ll short of maximum HP/torque. There are two ways to operate any engine. 1=
. How fast can I climb the mountain. Or 2. How many mountains do I want to=
climb over how many years. We BS horse power. We drive torque. Tuning in =
it's true form is done on an engine dyno. I've run engines on a dyno for d=
ays to get an engine to it's absolute max. Thus lots of part changes along =
the way. And I've scattered my fair share of engines in the proses. But I'm=
not interested in longevity. I'm just interested in not seeing the back =
of someone's car at the end of the day. So. Putting on a bigger carb won't =
help. Big exhaust won't help. A cam change won't help. But putting on matc=
hing parts will bring out the magic. I have the knowledge, and equipment to=
build a killer 403 for my 78 Royale. Or any engine for that matter. My GVW=
is always in the 17 to 21,000lbs range. Our last 78 Royale 403 got that GM=
C 152,000 miles with no internal issues. It got done what I needed done fro=
m coast to coast. I'm happy. As a note. I'm not saying that anyone is right=
, or wrong. We all need to do what makes us comfortable in what we do. Bob =
Dunahugh ________________________________ From: Bob Dunahugh Sent: Monday, June 5, 2017 8:46 PM To: gmclist=
gmcnet.org Subject: Re; Big increase in power in my 1977 403ci engine. =
David.There's an old saying that goes. There's always more then one w=
ay to skin a cat. And you covered another method of performance timing. I b=
uild, and race engines that are out on the edge of maximum torque at full t=
hrottle in the 7 to 8,000 RPM range. I'm looking to get every half a foot =
pound of torque at the end of the crank. And there have been times that I'v=
e twisted the end of the crank off. I machine down my oil pumps to reduce t=
he oil volume out put of that pump. That detail helps to increase engine to=
rque out put. I set the 4 carbs, and timing to the air temps, humidity, bar=
ometric pressure, and gas that I'm using THAT day. ( As I bring my own test=
ed gas with me ) All these change from day to day. I'm so close in timing t=
hat a settings I use one day. May blow the top of the piston out the next. =
Bringing this close of settings this close to our GMC's bring it's own issu=
es. As the gas we get one day. May not be the same the next day. And all t=
he items listed above have changed. And with all of these changing ranges.=
How close to maximum timing advance do you want to get. The GM factory spe=
cs are listed to handle all of these changing conditions. With a safety fac=
tors included. So is one way better then the other. That is all in your co=
mfort range. As for me. My stock 78 Royale, 403 with a 2-1/2 exhaust, no=
headers, and a 3:70 FD. With Linda's lift van I have a GVW of 17,000 lbs. =
With the enclosed race trailer I'm at a GVW of 21,000 lbs. All with factor=
y stock timing. That's my own personal comfort zone. Bob Dunahugh