I am running the ZZ4 stock aluminum L98 Corvette heads. I have heard mild porting is worth 30-40HP. Is this true? I was thinking about pocket porting and gasket matching my heads. Is it worth while, has any one out there done this and have data to back up their improvements?

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84 Camaro ZZ4 with HOT cam. 1.88 60' (12.98 @ 105MPH E.T.)
Other Mods: You name it and I have probably changed it.

91 Firebird 5.0L TBI

ASE Certified CHEVY DEALER Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

 

COME ON! As if anyone does'nt know this one!

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84 Camaro ZZ4 with HOT cam. 1.88 60' (12.98 @ 105MPH E.T.)
Other Mods: You name it and I have probably changed it.

91 Firebird 5.0L TBI

ASE Certified CHEVY DEALER Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

 

Definitely! Check out this months Car Craft in the Ask Marlan section. He tells you how to port the L98 heads.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

Thanks Kevin! That is a good article. I have just ordered a porting kit from Summit and am looking forward to easy HP.

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84 Camaro ZZ4 with HOT cam. 1.88 60' (12.98 @ 105MPH E.T.)
Other Mods: You name it and I have probably changed it.

91 Firebird 5.0L TBI

ASE Certified CHEVY DEALER Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

 

I just did a search on "L98 head porting" and found this message from a year ago. Does anyone have a copy of this CC article that they'd scan/sell/loan to me? I've never ported heads before (did pretty good on my TPI intake though) and would like to get all the tips I can find, before starting!

 

If you buy the Standard Abrasives porting kit, it comes with a really good guide book....

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"So many Mustangs, so little time..."
ICON Motorsports

 

www.sa-motorsports.com/diyport.htm

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87 IROC-Z
Minirammed Solid Roller 377

 

Gonna need more than a little pocket port.
Give 'em a good hoggin' out. They're 163cc's
stock you're looking for around 185cc's
finished. Look into a set of 2.00"/1.55"
LT4/FastBurn Valves too. These heads really honk when they're done right.

 

Thanks for the info.. I had read the Standard Abrasives stuff, and it does seem like a good general introduction to head porting.

What I'm most interested in are tips specific to this particular casting. I'm not sure my skills are up to what it would take, though, to radically enlarge the ports like what was just mentioned!

 

Pick up David Vizzards Building Small Block Chevy Cylinder Heads book. Its an excellent book and has a lot of good porting information inside it. It has a whole chapter devoted to the aluminum L98 heads. They show how to get approx. 240cfm out of them.



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Current
86 TA 350 TH350, hardtop
99 Ducati 750 Super Sport
76 Yamaha RD400 track bike

Former
85 Z28
94 TA

 

Thanks! My introduction to performance mods was through reading books by David Vizard. I like his writng style.

 

For my own edification, I am going to re-type the entire article:

" GM's zz3/zz4 crate engines respond well to cylinder-head mods and a hotter camshaft. Looking at the heads first, the corvette-style aluminun castings have lots of potential when properly reworked. Avoid hogging them out; this is counter productive and in fact will probably break through the water jacket. You can keep the existing 1.94 intake and 1.50 exhaust valves.

On the intake side, concentrate porting efforts in the throat and valveguide area. One side of the port is closer to the guide than the other side; port to equalize the area on each side of the guide. Streamline the guide itself. Open up the port where it pinches down to get around the pushrod hole. Up to .050 inch of material may be ground off the "pinch" without breaking through. Properly reworked, the intake side should flow 225-230 cfm at 28 inches of water.

Use a similar technique on the exhaust side: The short-turn radius and throat area need to be Widened, radiused, and straightened so that it's dimensions are within 88% of the valve head diameter. Clean-up the exhaust port overall, raise the roof slightly, and open up the pushrod bulge. Properly reworked, the exhaust side should flow around 185 cfm at 28 inches water. The best reslts will be achieved by a competent shop that has prior experience on these heads..."

p.89, Car Craft, December 2000

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355 c.i.
Dart 180 Heads
Lunati 224/224 cam
Harland Sharp 1.5 rockers
Performer RPM Manifold
Holley 600 cfm double pumper
Hooker Super Competition Headers
Flowmaster Exhaust
Competition Engineering Sub-frame connectors
Super T-10
GM posi 3.42 rear
Hurst Roll Control
13.9@102

 

Hey, umm.. not to kick a dead horse, but I noticed that on my heads, the valve guide inserts protrude quite a distance into the port.. at least 1/4" further than the casting itself.

Is there much benefit to grinding the guide down? If so, should it be shortened all the way to the aluminum casting, or maybe not that far?

I got the head porting book by David Vizard and in one picture, it looks like he might have done that. The picture isn't resolute enough to say for sure, though.

As long as I'm asking questions, it looks as though the intake valve seats are "sunken down" into the casting, while the exhaust seats at least look like they have a smooth radius where the aluminum meets the seat in the chamber. I plan on doing the same to the intake, although that procedure isn't mentioned anywhere in what i've read. Good idea or bad?

 

Unfortunately, I don't have the answers...but I have the exact same question!!!!

Someone has got to have an answer on this...

 

I am no pro when it comes to these heads but in all my home porting efforts I have NEVER shortened the guide itself. All efforts were around making it skinny with a nice flow-friendly shape, but never shortening it up to the roof of the port. I was told by a head porter I trusted that was a no-no in every case.

 

Ok.. I will just smooth them out, not cut them down. I have one more question, though, before I shut my trap and start porting

I noticed that the valveseat diameter is narrower than the opening in the port. This creates a "step" that, I would think, would interfere with flow into the chamber, but maybe not so much with flow OUT of the chamber. This sounds like something I should radius on the intake side, but maybe leave alone on the exhaust. Ideas?