JDMZ28

iTrader: (1)

I have center bolt TPI heads. My friend ports heads and he will do mine for free. To what extent should I have them ported? This is for the Z28 with the mods listed below(350, headers, intake). I'm going to install either comp cams 268XE or 274XE.

The questions are: Which cam should I use? and how much port work should I have done? Again, cost is not an issue.



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1986 CAMARO Z28 ->
151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, B&M Ripper shifter, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframe connectors, all bushings are urethane, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Extreme Energy 268 cam, Holley street dom intake.

1987 TRANS AM ->
73,000 miles, 305TPI, auto, gutted air box.

Guest

CHILL OUT!

What do you mean how much? Have him do whatever he will, without enlarging the overall size (cc) of the port too much. That means cleaning up the casting, match up the port, do some bowl work, and clean up the seat area. The bowl/seat area is the most critical. Porting is not taking away as much material as possible, its taking away what needs to be taken away. In some cases there are areas where little is done.

8Mike9

I might add, to get the best bang, you'll want the heads ported to flow, as to match the cam profile.

If cost isn't an issue, then I'd suggest going with one of the many cnc'ed Al. heads, out of the box, they'll be better than most profession port guys, can match.

Camaroz28.com has a guy who does a rolling GP on AFRs.

Otherwise, what you want to tell the guy is to make sure the chambers match, and each flow the same when done, I believe optimal I:E ratio is 75%, so shooting for that on the L98 heads, will limit what he can do anyway. He can make'em better for sure, but too much grinding leaves you with junk.

See what he get's them to flow to, then pick a cam to match up well.

JDMZ28

iTrader: (1)

What I mean by how much is:

I was thinking of having him polish the chambers, mill them, gasket match the intake ports, smooth everything including the short radius turn, and pocket port the intake ports.

I heard these heads respond really well on the exhaust side so I want to keep the work to a minimal so I can use a dual pattern cam.

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1986 CAMARO Z28 ->
151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, B&M Ripper shifter, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframe connectors, all bushings are urethane, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Extreme Energy 268 cam, Holley street dom intake.

1987 TRANS AM ->
73,000 miles, 305TPI, auto, gutted air box.

Damon

The exhaust side on most stock heads is the FIRST place to look for more power. THey typically flow only about 60-65% of what the intake side does and that's the first "bottleneck". Like was said above, most of the improvement to a head's flow happens by working on the area jsut below the head of the valve in the port. Smooth transition from the seat into the port and making sure the short-turn raduis is just that- a SMOOTH RADIUS, not a sharp angle like almsot all factory heads are. Multi angle valve seats can add flow, too, as can using upgraded valves with backcuts on the back of the head, swirl polishing and undercut stems. Same applies to the intake side, too. It's just the exhaust port usually needs the heaviset massaging, in my expereince.

A $200 "pocket porting" job as it's called can give you great "bang for the buck." However, if you are thinking about FULLY porting the stock heads I'd recommend going to one of the many excellent aftermarket heads now available, rather than extensively working factory castings.

JDMZ28

iTrader: (1)

Is there a point at which I'm going to loose power from porting? I want to do what I can and still be in the safe area.

This is what I was going to have done. Chamber polishing, gasket match intake ports, smooth all rough surfaces (including the short radius), and pocket port the intake side.

Should I go ahead and have him pocket port the exhaust too? This would mean I would be better off with a single pattern cam right? Maybe I could get comp cams to costume grind me a 274XE with the exhaust profile the same as the intake, so I would have 230/230 .487/.487. Does this sound good?

Thanks guys



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1986 CAMARO Z28 ->
151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, B&M Ripper shifter, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframe connectors, all bushings are urethane, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.22@ 106.4MPH 3300lbs less driver and speakers Next mods-> Extreme Energy 268 cam, Holley street dom intake.

1987 TRANS AM ->
73,000 miles, 305TPI, auto, gutted air box.

Damon

I would take the $$ you were going to take to gasket match the intake and get the exhaust side pocket ported. Gasket matching is one of those things that FEELS so right to do, but in reality it's close to worthless for a street engine. There's just damned little flow/power to be gained from gasket matching. That area of the port just ISN'T the bottleneck. Right up close to the valves is the bottleneck.

I would port the exhaust side of the heads BEFORE even doing the intakes, as I said before. But really it's better to do BOTH if you have the $$. I would also suggest spending another $120 on a set of Manley Stainless Street Flow vavles (they're avaiable in 1.94/1.50 and 2.02/1.60 sizes) if you can swing them- they already have the underhead area backcut, swirl polished and have undercut stems, all of which improves flow. Don't forget to have them do a multi-angle valve job, either. It improves low-lift flow which helps build torque.


If for all these efforts your exhaust ports end up flowing 75% or better than the intake AND you plan on running best with the headers uncorked (not through high flow mufflers) then get a single pattern cam, otherwise I'd go with a dual pattern cam for just about any street engine (although I regularly go against my own advice by running single pattern cams in street engines with excellent results anyway, so don't get too bent out of shape over the single-dual pattern cam issue).

Another issue you should think about:

THose stock heads can only take about .470" lift before the bottom of the retainer hits the top of the stock push-on intake guide seal. Also, if it's got stock vavle springs in it they will coil bind at not much more lift than that anyway. If you are seriously thinking about doing that cam at a later point (or now!) you REALLY need to address BOTH of these issues with stock heads. While the heads are off it's easy to change the springs (follow cam manufacturers recommendations EXACTLY on this). As, for the retainer-to-guide interference it's a simple machining operation to mill the guides down a little. Just make sure you don't have any metal-to-metal contact at the cam's maximum lift (which is quite high on the XE 268 and 272 even using stock 1.5 ratio rockers). Valvetrain is NOT something you want to take for granted.

BTW- that 86 is FLYING for the mods you've done.



[This message has been edited by Damon (edited April 26, 2001).]

JDMZ28

iTrader: (1)

I want to get as much work done that I can. I metioned above but you must have missed it, that I'm getting this work done for free from a friend that works at a head shop.

Since I'm getting the chambers polished how much increase in compression will that allow me? I'm at 9.5:1 now I was looking at 10.0:1.

Can I get the stock valves cut at multi-angles? With all this work done to the heads should I be looking at 20hp?

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1986 CAMARO Z28 ->
151,000 original miles, 43,000 on 89' vette 350 block, Holley 650 DP, Weiand intake, 1.6 rockers, 1 5/8" headers, no cat, 2 1/2" Flowmaster catback, Mallory coil, March pulleys, B&M Ripper shifter, T5 with 3.35 1st gear and 0 miles, 90% Centerforce clutch, 3.73 posi, Eibach 1" drop springs, Spohn LCA's, Spohn adjustable panhard rod, Subframe connectors, all bushings are urethane, 2 12" Sound Streams, 2 Infinity 6X9's, 2 Pioneer 6X9's, 800 watt Lanzar Vibe amp. ET 13.32@ 106.4MPH 3300lbs less driver and speakers Next mods-> Extreme Energy 268 cam, Holley street dom intake, ported heads.

1987 TRANS AM ->
73,000 miles, 305TPI, auto, gutted air box, gutted cat.

88SC

Re: Gasket matching. there seems to be an assumption out there that the gasket manufacturers have sized the intake openings to optimize flow. Not true!

I guess that the gasket serves as a convenient reference for port matching and alignment, but IMHO its more important to ensure that the aero-step is positive (i.e. gets wider instead of narrower) at the manifold/head interface.

Beefy89

Just have them fully ported if its free!

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Fast as a shark~~~~~~~~~~~~~~~~~ SAVE NAPSTER!!!

Kevin91Z

iTrader: (1)

Try this link:
http://www.sa-motorsports.com/diyport.htm

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
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