Plenum porting surface roughness question - ZR-1 Net Registry Forums

mike100 · 03-07-2011

Long explanation short- gonna leave as much of the rough texture below the injectors as possible, but as far as the ported I/H lengths and plenum radius- should I purposely rough up the sides? They are far from polished, but feel smooth to the touch.

Does it really matter?- I'm sure the volume increase is going to add hp as it is a well documented mod.

the plan is to open up the head primary a little -maybe about 1 inch down from a semi-tapered i/h port to about 35mm on the bottom.

sammy · 03-07-2011

i would pm loco bob on your ?his work is amazing and he freely shares with those that ask .

Locobob · 03-07-2011

The research I have done on the subject seems to indicate that surface texture is at best a minor consideration. A very smooth, polished surface is generally thought to be counter productive as far as air flow is concerned. It does however help inhibit carbon deposits. Fuel puddling is largely thought to be a non issue for direct port fuel injected applications. On an LT-5 the injectors have a relatively narrow stream and are pointed almost directly at the valves anyhow. I usually just finish the intake side to 40 or 60 grit since those are readily available and allow consistency, I see no advantage to going finer. Trying to purposefully rough up the port beyond that is going to be difficult to do consistently and may end up being counter productive if it results in jagged edges. I prefer a much finer finish on the exhaust in the interests of keeping carbon deposits in check.
From the stock and ported intakes I have inspected after use, I have noticed less carbon buildup on those with a rough sanded finish vs unfinished castings. Obviously this is far from a controlled scientific test.
I'm always on the lookout for new research on the subject, if anyone finds something interesting on this topic post it up.

LGAFF · 03-07-2011

From what I have read the 60 grit is good, just like when you drive a car in the rain, the water drops on the windshield move slowly even at higher speeds, because you develop someone of a "dead zone" above the surface if too smooth.

The guy who fixed the set of ported heads I bought actually bead blasts the surface flowing the flow of the air path. This leaves very lightly disturbs the surface, but feels fairly smooth to the touch.

But lets face it, we are probably splitting hairs at this point. As long as the runner does not look like the Rockies I think you are OK.

flyin ryan · 03-11-2011

A 'Sharp' 80 grit or dull 60 grit is my preferance...years of experiance

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03-07-2011	#1
mike100 Join Date: Feb 2011 Location: San Marcos CA Posts: 1,802	Plenum porting surface roughness question Long explanation short- gonna leave as much of the rough texture below the injectors as possible, but as far as the ported I/H lengths and plenum radius- should I purposely rough up the sides? They are far from polished, but feel smooth to the touch. Does it really matter?- I'm sure the volume increase is going to add hp as it is a well documented mod. the plan is to open up the head primary a little -maybe about 1 inch down from a semi-tapered i/h port to about 35mm on the bottom.

03-07-2011	#2
sammy Join Date: Jun 2010 Location: back in lone pine Posts: 591	Re: Plenum porting surface roughness question i would pm loco bob on your ?his work is amazing and he freely shares with those that ask .

03-07-2011	#3
Locobob Join Date: Jan 2004 Location: Portland, OR Posts: 1,057	Re: Plenum porting surface roughness question The research I have done on the subject seems to indicate that surface texture is at best a minor consideration. A very smooth, polished surface is generally thought to be counter productive as far as air flow is concerned. It does however help inhibit carbon deposits. Fuel puddling is largely thought to be a non issue for direct port fuel injected applications. On an LT-5 the injectors have a relatively narrow stream and are pointed almost directly at the valves anyhow. I usually just finish the intake side to 40 or 60 grit since those are readily available and allow consistency, I see no advantage to going finer. Trying to purposefully rough up the port beyond that is going to be difficult to do consistently and may end up being counter productive if it results in jagged edges. I prefer a much finer finish on the exhaust in the interests of keeping carbon deposits in check. From the stock and ported intakes I have inspected after use, I have noticed less carbon buildup on those with a rough sanded finish vs unfinished castings. Obviously this is far from a controlled scientific test. I'm always on the lookout for new research on the subject, if anyone finds something interesting on this topic post it up. __________________ Robert ZR-1 Net Registry Oregon State Director 91 ZR-1 #431 Black/Black LPE 368

03-07-2011	#4
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	Re: Plenum porting surface roughness question From what I have read the 60 grit is good, just like when you drive a car in the rain, the water drops on the windshield move slowly even at higher speeds, because you develop someone of a "dead zone" above the surface if too smooth. The guy who fixed the set of ported heads I bought actually bead blasts the surface flowing the flow of the air path. This leaves very lightly disturbs the surface, but feels fairly smooth to the touch. But lets face it, we are probably splitting hairs at this point. As long as the runner does not look like the Rockies I think you are OK. __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359 Last edited by LGAFF; 03-07-2011 at 09:40 PM.

03-11-2011	#5
flyin ryan Join Date: Aug 2006 Location: Edmonton, Alberta or Phoenix, Arizona Posts: 2,741	Re: Plenum porting surface roughness question A 'Sharp' 80 grit or dull 60 grit is my preferance...years of experiance . __________________ There are no limit's mans ingenuity, just as mans ingenuity will never conquer the forces & behavior of this planet...Smokey Y.