why the different plunums - ZR-1 Net Registry Forums

xxxscimitarxxx · 08-14-2009

sure this is not a new question but ouldnt find an answer in search

why is there a difference....is one better than another

LGAFF · 08-14-2009

Stock one on the left has individual runnners, the one on the right has had the primary and secondary runners merged together or siamesed for greater flow. The siamesed runners are not a stock option, most were done by Jeal or other tuners.

Locobob · 08-14-2009

The full siamese plenum pictured on the right can support a higher volume of air than the stock plenum casting will allow. It is a fairly pricey mod and is best suited for use on highly modified engines - usually strokers.

Kevin · 08-14-2009

wait till ya throw in the dropped plenums

blackjack · 08-14-2009

dropped plenum ????
bj

billybaloneey · 08-17-2009

Quote:

Originally Posted by Locobob

The full siamese plenum pictured on the right can support a higher volume of air than the stock plenum casting will allow. It is a fairly pricey mod and is best suited for use on highly modified engines - usually strokers.

No one ever responded to the question about, "What is a dropped plenum?" Can anyone describe the difference between a dropped and stock plenum? Anyone have a side by side picture of a dropped and stock plenum?

Also, are siamesed plenum's made from stock plenum's with aluminum/metal filler, or some type of fiberglass or bondo as a filler in the valley's between the runners? Are siamesed plenum's...besides the runners...typically ported also?

Locobob · 08-17-2009

Quote:

Originally Posted by billybaloneey

No one ever responded to the question about, "What is a dropped plenum?" Can anyone describe the difference between a dropped and stock plenum? Anyone have a side by side picture of a dropped and stock plenum?

Also, are siamesed plenum's made from stock plenum's with aluminum/metal filler, or some type of fiberglass or bondo as a filler in the valley's between the runners? Are siamesed plenum's...besides the runners...typically ported also?

A dropped plenum has extra internal volume added to it by cutting out part of the bottom section and welding it back together with some added material. I don't have a pic handy but it kinda resembles a deep sump oil pan.

A fully siamesed plenum is made by cutting out the outside center sections of the two side by side runners then welding in some curved sheet aluminum in its place. Some have metal filler added to the outside to smooth out the appearance. Typically these types of plenums have some agressive porting involved as well.

Here are a few pics of a full siamese job in progress.

xxxscimitarxxx · 08-17-2009

I thought l had thrown in a post on the dropped plenum....but it seems to have vanished

see the DRM website and the pic of the LT5 with the huge injector ram pipes ..... pretty sure they are on a low 'dropped' plenum

Kevin · 08-18-2009

Quote:

Originally Posted by billybaloneey

No one ever responded to the question about, "What is a dropped plenum?" Can anyone describe the difference between a dropped and stock plenum? Anyone have a side by side picture of a dropped and stock plenum?

dropped plenum does the same thing. the lower part of the plenum is cut and rewelded to make it a larger volume of air that can be moved through it.

scholtmj · 08-19-2009

Found these pictures online of the motor Corey Henderson built for Bonneville. Siamese ports and dropped plenum. Hope he doesn't mind me posting these!

08-14-2009	#2
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	Re: why the different plunums Stock one on the left has individual runnners, the one on the right has had the primary and secondary runners merged together or siamesed for greater flow. The siamesed runners are not a stock option, most were done by Jeal or other tuners. __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

08-14-2009	#3
Locobob Join Date: Jan 2004 Location: Portland, OR Posts: 1,057	Re: why the different plunums The full siamese plenum pictured on the right can support a higher volume of air than the stock plenum casting will allow. It is a fairly pricey mod and is best suited for use on highly modified engines - usually strokers. __________________ Robert ZR-1 Net Registry Oregon State Director 91 ZR-1 #431 Black/Black LPE 368

08-14-2009	#4
Kevin Join Date: Jun 2005 Location: pittsburgh Posts: 4,632	Re: why the different plunums wait till ya throw in the dropped plenums __________________ It's not the car, it's the people - Doug Johnson 90 r/r "KEYS ON" nick named "T.L.B"

08-14-2009	#5
blackjack Join Date: Aug 2005 Location: north of montreal Posts: 510	Re: why the different plunums dropped plenum ???? bj

08-17-2009	#8
xxxscimitarxxx Join Date: Mar 2008 Location: England Posts: 219	Re: why the different plunums I thought l had thrown in a post on the dropped plenum....but it seems to have vanished see the DRM website and the pic of the LT5 with the huge injector ram pipes ..... pretty sure they are on a low 'dropped' plenum

08-19-2009	#10
scholtmj Join Date: Nov 2008 Location: Grand Rapids, MI Posts: 384	Re: why the different plunums Found these pictures online of the motor Corey Henderson built for Bonneville. Siamese ports and dropped plenum. Hope he doesn't mind me posting these!