Making any comparisons to our GMC drivetrain to a modern car, or truck. Is =
like saying that a small apple, and a very large watermelon are comparable=
. There both carbon based. That's about it. Modern drivetrains are designed=
from the ground up for low RPM's at 65 MPH. Lots of gearing ratios. They =
shift ratios a lot at the slightest increase in throttle movement to preven=
t luging. I took two short trips in our latest 78 403 Royale before I could=
change out the 3:07 to the 3:70. The low RPM's, and all the shifting down.=
Drove me crazier then I already am. GM did a great job in the design/build=
of these GMC's. Except putting the 3:07 FD in. That was stupid. Back then=
. GM only put ratios of 3:70 to 4:56 in anything that had a GVW in the 9 =
to 12,000lbs range. Engines were built to operate at higher RPMs. One of my=
COPO Yenkos has an idle of 2200 RPMs. Can't stay running any slower. Opera=
tes up to 8000 RPM. All with stock GM rods, valve train, and crankshaft. ( =
I do use forged pistons. ) Been doing high speed track event since 1991. Al=
l that time. I've broken 2 vale springs. And broke 3 valve stims. Bob Dun=
ahugh 4 Original COPO Yenko Stingers ________________________________=
From: Bob Dunahugh Sent: Friday, January 25, 20=
19 8:56 PM To: gmclist Subject: RE: Tid Bits. Should we=
be concerned about over reving our Olds engines. The best way to g=
et to the top of the mountain. Several years ago. I was climbing out of Den=
ver. Up to the Eisenhower tunnel. That's a long steep climb. While pullin=
g one of my Yenko's on a trailer. With a GVW of 17,000 LBS. 3:70 FD, and a=
403. I put the trans in first. Ran the 403 up to 4400 RPM's. Then used no=
more the half throttle. As for speed. Got what I got. Didn't care. So what=
was going on here. First. With half throttle. I was reducing the amount of=
BTU's going into the engine. With the RPM's up. The engine water pump was =
taking more engine heat to the radiator. The engine fan was pulling more =
air in to keep the engine cooler. The trans fluid pump was also caring more=
heat off to the trans cooler. Jim Hupy's e-mail covered piston FPM well. =
GM should have never installed a 3:07 FD in these GMC's that weigh 11,000 =
lbs. The 3:21, 3;42, 3:55 are of alittle help. Towing or not. The 3:70 has =
been proven to be the best choice. Also with gas mileage going up. Because=
your running a higher intake manifold vacuum. Bob Dunahugh 78 Royale =
________________________________ From: Bob Dunahugh Sent: Thursday, Jan=
uary 24, 2019 10:40 PM To: gmclist Subject: Tid Bits. S=
hould we be concerned about over reving our Olds engines. The stock 45=
5 that we have is good to 5000 RPM's. The stock 403 is fine to 6000 RPM's=
. But with the cam profiles that our engines have. There is no reason to g=
o much be on 3900 RPMs. Engine cam profiles are based on many factors. Bu=
t mostly on how the engine is going to be used, engine cubic inches, final =
drive ratio, tire diameter, and expected gross weight to be moved. There ar=
e more. But these are the main ones. GM had to make a car engine perform t=
he duties of a truck engine. Our engine were built to produce it's peak hor=
sepower, and torque in the 2400, to 2800 RPM range. We drive torque. Not ho=
rsepower. Torque is what gets us up that next hill. A torque chart starts a=
t 600 RPM's. And continues to climb till the engine hits it's peak torque R=
PM point. Then the torque produced will state to drop off. The torque curve=
chart will be in the shape of a bell. The cam shaft lob profile is the ma=
gic that make our engines able to perform to move us along so well. Whenev=
er I start climbing long steep grades. Sift to second. Run the RPM's up to =
3700, to 4000 RPM's till I get to the top. And never have the throttle mor=
e then half open. I have a personal game I play. In trying to see how high =
I can get the number of cars that I can get to go around me before I get to=
the top of the pass. ( GRIN ) When someone says that any RPM's over 3300 =
RPM's. will just burn the engine up. Due to high piston speeds. That is ab=
solutely, positively not true. Bob Dunahugh 78 Royale
like saying that a small apple, and a very large watermelon are comparable=
. There both carbon based. That's about it. Modern drivetrains are designed=
from the ground up for low RPM's at 65 MPH. Lots of gearing ratios. They =
shift ratios a lot at the slightest increase in throttle movement to preven=
t luging. I took two short trips in our latest 78 403 Royale before I could=
change out the 3:07 to the 3:70. The low RPM's, and all the shifting down.=
Drove me crazier then I already am. GM did a great job in the design/build=
of these GMC's. Except putting the 3:07 FD in. That was stupid. Back then=
. GM only put ratios of 3:70 to 4:56 in anything that had a GVW in the 9 =
to 12,000lbs range. Engines were built to operate at higher RPMs. One of my=
COPO Yenkos has an idle of 2200 RPMs. Can't stay running any slower. Opera=
tes up to 8000 RPM. All with stock GM rods, valve train, and crankshaft. ( =
I do use forged pistons. ) Been doing high speed track event since 1991. Al=
l that time. I've broken 2 vale springs. And broke 3 valve stims. Bob Dun=
ahugh 4 Original COPO Yenko Stingers ________________________________=
From: Bob Dunahugh Sent: Friday, January 25, 20=
19 8:56 PM To: gmclist Subject: RE: Tid Bits. Should we=
be concerned about over reving our Olds engines. The best way to g=
et to the top of the mountain. Several years ago. I was climbing out of Den=
ver. Up to the Eisenhower tunnel. That's a long steep climb. While pullin=
g one of my Yenko's on a trailer. With a GVW of 17,000 LBS. 3:70 FD, and a=
403. I put the trans in first. Ran the 403 up to 4400 RPM's. Then used no=
more the half throttle. As for speed. Got what I got. Didn't care. So what=
was going on here. First. With half throttle. I was reducing the amount of=
BTU's going into the engine. With the RPM's up. The engine water pump was =
taking more engine heat to the radiator. The engine fan was pulling more =
air in to keep the engine cooler. The trans fluid pump was also caring more=
heat off to the trans cooler. Jim Hupy's e-mail covered piston FPM well. =
GM should have never installed a 3:07 FD in these GMC's that weigh 11,000 =
lbs. The 3:21, 3;42, 3:55 are of alittle help. Towing or not. The 3:70 has =
been proven to be the best choice. Also with gas mileage going up. Because=
your running a higher intake manifold vacuum. Bob Dunahugh 78 Royale =
________________________________ From: Bob Dunahugh Sent: Thursday, Jan=
uary 24, 2019 10:40 PM To: gmclist Subject: Tid Bits. S=
hould we be concerned about over reving our Olds engines. The stock 45=
5 that we have is good to 5000 RPM's. The stock 403 is fine to 6000 RPM's=
. But with the cam profiles that our engines have. There is no reason to g=
o much be on 3900 RPMs. Engine cam profiles are based on many factors. Bu=
t mostly on how the engine is going to be used, engine cubic inches, final =
drive ratio, tire diameter, and expected gross weight to be moved. There ar=
e more. But these are the main ones. GM had to make a car engine perform t=
he duties of a truck engine. Our engine were built to produce it's peak hor=
sepower, and torque in the 2400, to 2800 RPM range. We drive torque. Not ho=
rsepower. Torque is what gets us up that next hill. A torque chart starts a=
t 600 RPM's. And continues to climb till the engine hits it's peak torque R=
PM point. Then the torque produced will state to drop off. The torque curve=
chart will be in the shape of a bell. The cam shaft lob profile is the ma=
gic that make our engines able to perform to move us along so well. Whenev=
er I start climbing long steep grades. Sift to second. Run the RPM's up to =
3700, to 4000 RPM's till I get to the top. And never have the throttle mor=
e then half open. I have a personal game I play. In trying to see how high =
I can get the number of cars that I can get to go around me before I get to=
the top of the pass. ( GRIN ) When someone says that any RPM's over 3300 =
RPM's. will just burn the engine up. Due to high piston speeds. That is ab=
solutely, positively not true. Bob Dunahugh 78 Royale
