Arch,
Highway cruising is somewhere around 2400-2800 RPM. We will take ours as
high as 4000 RPM in lower gears when towing the trailer to avoid lugging
after upshifts. While aftermarket intakes do not usually improve much over
most stock intakes until higher RPMs, the stock GMC intake is a pretty poor
design. The intake runners sit down into the motor a little and then have
to come back up to get to the intake ports of the heads. This causes spots
for fuel to puddle. It does, however, let the Toronado have a flat hood
and the GMC have a flat engine cover. I believe that the poor design
allows the aftermarket intakes to outperform this stock intake even in low
RPM situations. The downside is that you need to raise a section of the
engine cover to install one. Actually, IIRC the Performer intake is really
just a copy of one of the better Olds stock intakes. I don't think you'll
find any charts comparing any aftermarket products to the GMC/Toronado
intakes or the 'J' heads because it is not a very common setup. They
should though, because it would make their products look that much better
.
The cam also plays an important role. The stock cams were developed at the
beginning of the SMOG laws, and were an easy way to get vehicles to pass.
When we installed the Edelbrock Performer intake, Performer camshaft, and
Holley 4 barrel carb (with secondaries pinned shut for fuel mileage), we
observed a HUGE increase in power and towing gas mileage. We went from
getting 3.5-4 MPG towing to about 7 MPG towing. The non-towing mileage did
not pick up significantly, but the power did.
I was using our setup of the Edelbrock performer intake and Mondello's
ported E heads to show that the aluminum heads are probably even more
overkill for GMC use. We picked up from the intake and the cam, but the
heads seemed to do very little for normal driving RPMs. These E heads
probably flow even less than the aluminum ones making the aluminum ones
even less likely to improve low end power. Edelbrock even suggests the use
of their Torker intake for the aluminum heads which is 2 RPM ranges above
the Performer on Edelbrock's scale. This leads me to believe that the
aluminum heads would really only show the 150 HP increase that was claimed
at a very unusable RPM (probably >5000). If I am wrong, then we are very
interested in a set of these aluminum heads.
Just our experiences,
Zak
>Zak
>
>When I look at the curve for most of the manifolds offered they
>really do not start to perform until about 3000 rpm. Again I dont
>have much road time on mine but from what I have read I dont
>see us in that rpm range much of the time. Am I missing something
>here???
>
>Take Care
>Arch
Highway cruising is somewhere around 2400-2800 RPM. We will take ours as
high as 4000 RPM in lower gears when towing the trailer to avoid lugging
after upshifts. While aftermarket intakes do not usually improve much over
most stock intakes until higher RPMs, the stock GMC intake is a pretty poor
design. The intake runners sit down into the motor a little and then have
to come back up to get to the intake ports of the heads. This causes spots
for fuel to puddle. It does, however, let the Toronado have a flat hood
and the GMC have a flat engine cover. I believe that the poor design
allows the aftermarket intakes to outperform this stock intake even in low
RPM situations. The downside is that you need to raise a section of the
engine cover to install one. Actually, IIRC the Performer intake is really
just a copy of one of the better Olds stock intakes. I don't think you'll
find any charts comparing any aftermarket products to the GMC/Toronado
intakes or the 'J' heads because it is not a very common setup. They
should though, because it would make their products look that much better
. The cam also plays an important role. The stock cams were developed at the
beginning of the SMOG laws, and were an easy way to get vehicles to pass.
When we installed the Edelbrock Performer intake, Performer camshaft, and
Holley 4 barrel carb (with secondaries pinned shut for fuel mileage), we
observed a HUGE increase in power and towing gas mileage. We went from
getting 3.5-4 MPG towing to about 7 MPG towing. The non-towing mileage did
not pick up significantly, but the power did.
I was using our setup of the Edelbrock performer intake and Mondello's
ported E heads to show that the aluminum heads are probably even more
overkill for GMC use. We picked up from the intake and the cam, but the
heads seemed to do very little for normal driving RPMs. These E heads
probably flow even less than the aluminum ones making the aluminum ones
even less likely to improve low end power. Edelbrock even suggests the use
of their Torker intake for the aluminum heads which is 2 RPM ranges above
the Performer on Edelbrock's scale. This leads me to believe that the
aluminum heads would really only show the 150 HP increase that was claimed
at a very unusable RPM (probably >5000). If I am wrong, then we are very
interested in a set of these aluminum heads
. Just our experiences,
Zak
>Zak
>
>When I look at the curve for most of the manifolds offered they
>really do not start to perform until about 3000 rpm. Again I dont
>have much road time on mine but from what I have read I dont
>see us in that rpm range much of the time. Am I missing something
>here???
>
>Take Care
>Arch
