paul there is no substiute for big cubes and long stroke for low RPM torque.
Emory is right, very few gas engines put out the kinds of torque at LOW RPM
that the 455 does.
You have to compare both Horse power and torque at the same RPM, it you are
going to compare engines
.
The Northstar engine is a mouse motor compared to the 455.
with the GMC motorhome you need lots of torque when you first are getting
under way
>Ron:
>
>Not sure I agree with "..the 455 has lots of torque at lower rpm's...".
>Have you ever seen the torque curve for the 455?? It has nearly a vertical
>slope, which means that the higher the rpm's the more torque it makes. The
>torque curve peaks at ~ 2750 rpm, which for the original drive train gearing
>equates to ~ 70 - 75 mph. Therefore, at lower rpm's, the torque is much
>lower.
>
>I also don't see a larger engine working less than a smaller engine. All I
>see is that the larger engine just has a higher capability. I would agree
>though, that the larger engine is working at a lower percentage of its rated
>capacity in the situation you describe.
>
> Paul Bartz
>
>From: Ron Keener [mailto:rkeener]
>Sent: Friday, July 30, 1999 10:44 AM
>Subject: Re: GMC: gas mileage
>
>"The reason I say this is, one of the reasons GM went to the 403 engine was
>for fuel economy during the 70s oil crises. If you look at the distributor
>advance characteristics in the shop manual for instance, you'll see there is
>a big difference between the 403 vs. 455 cid engines in when it comes on and
>when it maximizes.
>Paul Bartz"
>exactly Paul - the 403 was ideally suited for the automobile where the
>torque to weight ratio is much lower - they were able to run at lower rpms
>and still have plenty of response as the engine rpms moved up into the ideal
>torque range but with the heavier motor home it is necessary to keep the
>rpms up to get the torque to fight the wind and weight resistance - higher
>rpm means lower fuel economy - the 455 has lots of torque at lower rpms but
>needs more fuel because of the larger displacement BUT it is running at much
>lower rpms so when pulling high loads the larger engine should actually have
>better economy because it is working less for the same amount of torque this
>is my experience from a farm background where heavy towing is a daily
>necessity
>
>
Emory is right, very few gas engines put out the kinds of torque at LOW RPM
that the 455 does.
You have to compare both Horse power and torque at the same RPM, it you are
going to compare engines
.
The Northstar engine is a mouse motor compared to the 455.
with the GMC motorhome you need lots of torque when you first are getting
under way
>Ron:
>
>Not sure I agree with "..the 455 has lots of torque at lower rpm's...".
>Have you ever seen the torque curve for the 455?? It has nearly a vertical
>slope, which means that the higher the rpm's the more torque it makes. The
>torque curve peaks at ~ 2750 rpm, which for the original drive train gearing
>equates to ~ 70 - 75 mph. Therefore, at lower rpm's, the torque is much
>lower.
>
>I also don't see a larger engine working less than a smaller engine. All I
>see is that the larger engine just has a higher capability. I would agree
>though, that the larger engine is working at a lower percentage of its rated
>capacity in the situation you describe.
>
> Paul Bartz
>
>From: Ron Keener [mailto:rkeener]
>Sent: Friday, July 30, 1999 10:44 AM
>Subject: Re: GMC: gas mileage
>
>"The reason I say this is, one of the reasons GM went to the 403 engine was
>for fuel economy during the 70s oil crises. If you look at the distributor
>advance characteristics in the shop manual for instance, you'll see there is
>a big difference between the 403 vs. 455 cid engines in when it comes on and
>when it maximizes.
>Paul Bartz"
>exactly Paul - the 403 was ideally suited for the automobile where the
>torque to weight ratio is much lower - they were able to run at lower rpms
>and still have plenty of response as the engine rpms moved up into the ideal
>torque range but with the heavier motor home it is necessary to keep the
>rpms up to get the torque to fight the wind and weight resistance - higher
>rpm means lower fuel economy - the 455 has lots of torque at lower rpms but
>needs more fuel because of the larger displacement BUT it is running at much
>lower rpms so when pulling high loads the larger engine should actually have
>better economy because it is working less for the same amount of torque this
>is my experience from a farm background where heavy towing is a daily
>necessity
>
>
