High Rise Manifold

[robert schoner]

Good Day to all,

First, thank you Wayne for responding to my request for gvwr for the GMC.
The information is useful and it looks like a "typical" coach shoud have
ample carrying capacity for a retired couple.

I have a new question. The coach I am considering has a rebuilt engine with
a "high rise manifold". The current owner did not know much more than that
about the engine other than he thought this was a "typical modification that
improved performance". With all the postings about engines lately I don't
recall anyhting about a high rise manifold. Does anyone know of any
benefits or problems (space) with this mod?

Also, the coach's dash air is not working; has a leak. Has anyone converted
to R134A and is it worthwhile?

Thanks to All,

Bob Schoner
rschoner

 

[patrick flowers]

>
> I have a new question. The coach I am considering has a rebuilt engine with
> a "high rise manifold". The current owner did not know much more than that
> about the engine other than he thought this was a "typical modification that
> improved performance". With all the postings about engines lately I don't
> recall anyhting about a high rise manifold. Does anyone know of any
> benefits or problems (space) with this mod?

Hi Bob,

The original Toro manifold is a well known poor breather. GM sacrificed
a lot to get that low hood line. The reason most of us don't consider
replacement manifolds is that they require surgery on the engine cover.
Heinz has some pics of his at the bytedesigns.com site. Also, Darren
Paget has some pics out there of an aluminum engine cover he's making
that's extended to house the raised carb. The type of manifold is
pretty critical - you want a "street" type that makes power from idle or
1,000 rpm to about 2,800 rpm. Anything above 3k is pretty much wasted
in a motorhome. In addition to Heinz, I think Zak is running an
aftermarket intake. I'm sure that there are others.

Patrick
- --
Patrick Flowers
Mailtoatrick

The GMC Motorhome Page
http://www.gmcmotorhome.com

 

[darren paget]

The Edelbrock intake manifold I installed has an additional 2.5" of rise from OEM.
It is rated for optimal flow from 1500 to 4500 rpm. A little high but lower rpm
type do not exist AFAIK. The Holley carb I matched it to is a 750 cfm with primary
chambers considerably larger than the Q-jet. With an electric choke and vacuum
secondaries it should give me better performance in highway range, including
passing and on hills. The setup is quite nice and easy to tune. Being, as it is
still new and relatively untested I can't comment on actual performance at this
time. I will have a full report in Albuquerque. After 1600 miles I figure I should
know something. The biggest problem I had was, the dimensions I was using for the
engine cover were incorrect. On the box of the intake manifold it said it would
raise the mounting for the carb only .75 inches. Well they were two inches short
of actual. Add this to the extra 1.75 inches for the carb and, voila Engine
cover is 2" too short. Oh well. Life in the faster lane.
Darren

PS anybody want the first production Engine cover with a 2.75 " rise??

> >
> > I have a new question. The coach I am considering has a rebuilt engine with
> > a "high rise manifold". The current owner did not know much more than that
> > about the engine other than he thought this was a "typical modification that
> > improved performance". With all the postings about engines lately I don't
> > recall anyhting about a high rise manifold. Does anyone know of any
> > benefits or problems (space) with this mod?
>
> Hi Bob,
>
> The original Toro manifold is a well known poor breather. GM sacrificed
> a lot to get that low hood line. The reason most of us don't consider
> replacement manifolds is that they require surgery on the engine cover.
> Heinz has some pics of his at the bytedesigns.com site. Also, Darren
> Paget has some pics out there of an aluminum engine cover he's making
> that's extended to house the raised carb. The type of manifold is
> pretty critical - you want a "street" type that makes power from idle or
> 1,000 rpm to about 2,800 rpm. Anything above 3k is pretty much wasted
> in a motorhome. In addition to Heinz, I think Zak is running an
> aftermarket intake. I'm sure that there are others.
>
> Patrick
> --
> Patrick Flowers
> Mailtoatrick
>
> The GMC Motorhome Page
> http://www.gmcmotorhome.com

- --
Darren Paget
76 Experimental
Another Fab Day
paget

 

[blank]

>
> The biggest problem I had was, the dimensions I was
> using for the engine cover were incorrect. On the
> box of the intake manifold it said it would raise
> the mounting for the carb only .75 inches. Well they
> were two inches short of actual. Add this to the
> extra 1.75 inches for the carb and, voila Engine
> cover is 2" too short.

Darren,

Edelbrock doesn't make a Toro manifold, so the dimensions were for a
"regular" 455. Two inches sounds about right - is it any wonder that the
Toro manifold is asthmatic. Edelbrock only needed .75 to generate more
horsepower and we're 2 inches below stock.

Patrick