I was just wondering what kind of performance difference porting & polishing would make, and if it would be worth the money. Mods listed in sig.

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1986 Z28
383 ci Stroker, Dart Sportsmen 2 heads, roller rocker arms, Crower Hot Street Beast cam, edelbrock 750cfm carb and performer rpm intake, Corvette Servos, shift kit and 2600 rpm stall convertor, 3.73 gears and Eaton limited slip posi rearend.

 

If you are going to switch to say Aluminum heads, no. If you are going to stick to what you have, you will see some gain. Not 100HP tho. Maybe 20-50 if you port your intakes and heads.I prefer to get Aluminum heads tho. You can run a little more compression and it is much lighter.

 

So you are implying that porting Aluminum heads is useless? I don't understand... I thought that the point to porting heads was to get them to flow more. You seem to say that one should port Cast Iron heads and not Aluminum heads? Explain.

~My opinion- Yes it does help. You will see 20 hp on a good home port job and I think 12 Ft. #'s of Torque. Gasket matching and siamesing will also help a lot. I am still up in the air as to whether I am buying a Stealth Ram or Hog the crap out of the TPI unit.

 

I think what he was saying if he is going to buy new heads port thoughs and dont waste time and money on the old ones. If you dont plain on buying new heads it's good for about 30hp.

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91 RS Camaro 5-speed black w/t-tops 305 TBI now TPI
MODS: SLP cold air intake w/K&N, air foil,Accel 19 LB injectors, March aluminum under drive pullies, Alburn pro posi, Aluminum drive shaft, Random Technology 3'' cat-back, 8.5mm MSD wires, 160 thermo, jet fan swich, Custom chip with 91 vette computer, SSBC slotted rotors, optima battery in the rear, BMR adjustable lower control arms and panhard rod, Kenny Brown strut tower brace, TB bypass, no egr, no air

 

I noticed he's using sportsman 2s right now. The dart heads flow decent out of the box but really respond to porting. The exhaust side is especially gonna like the extra room. But porting anyhead properly will increase the potential flow thus HP of a car, and depending on how radical youre coming from and Going to the hp will vary. If youre just porting the heads you have and not making any cam etc. changethen 20 to 40 hp is the norm.
I would pass on the polishing since youre carbed and the rough surface would enhance fuel atomization.
Perry

 

Thanks for the responses guys. So it sounds like it does at least give a noticeable gain.

 

I'd port anything be it aluminum or steel. I probably wasn't clear but I would not port the heads you have (steel) if you were planning on buying some Al heads in the future. At that point, you can order the heads and have them ported. In the meantime, tough it out with your steel heads.

All heads can benifit from porting and poilishing which costs money. So if you are planning to switch, why spend the money now?

I prefer Al heads because they are lighter and can dissipate heat better. The latter reason allows you run a little more compression and compression is power. The lighter weight up front allows your car to raise a little more off the line. I had a loaded pair of TFS heads with Roller Rockers and valve covers and they weighed a little less than a bare steel head.

Sometimes a good Al head is worth the cost. Gasket matching helps any head. I am not a fan of home porting but you can clean up some areas. I prefer to send it out because it can be run under a CNC machine and flow benched for consistency. All of this costs money. That was why I recommended thinking bout whether to keep the steel heads or not. If not, don't waste money on them and just save up for the Al heads.

Personally, I prefer the stealth ram. I saw much improvement when I stuck the 1000 cfm TB on the setup. However my friend actually ran 1/10 slower with just the same TB. After he hogged out the TPI unit, he picked up the tenth he lost and another. I picked up a whole lot more 3/10 with the SR unported.

 

Since the Sportsman 2 is an older design, a lot of people have used them and a lot of people know what needs to be done to get good numbers out of them. Call around and ask a few shops if they've ever done them and if they like them. Find a shop that says they have good success and let them do some work for ya. goodluck!

And since that's a big runner head, i'd look into a bigger and better cam to take advantage of the new air Maybe spin the motor a little higher if the botom end can take it(ie: if it's built!)...maybe go with a higher stall converter too..later man

 

Just to impose a little scientific rationale on this discussion, if you take two absolutely identical sets of heads--one iron and one aluminum--the IRON heads will produce more hp than the aluminum ones.

This is a FACT, whether the folks with aluminum heads fancy it or not.

 

I'll bite. Why? Does detonation come into play or are you reducing it to say 9.5:1 because I believe you can bring it up to 11:1 with Amuminum heads.

That and the weight savings and the ease of the car nose going up during launch would swing it in favor of the Al heads, IMO

 

You don't polish the intake side only the exhaust.

There's also a chance of too much. Just like carbs, header tubes, cams, converter stall and gears, you can have too much.

Start off with a simple bowl blend and gasket match. If the car responds well to the changes and it should, consider removing the heads at a later date to do more porting. If you hog out too much metal you can actually decrease performance depending on the rest of the engines design. A .500" lift cam doesn't need 300+ cfm of air flow unless you're spinning the engine over 7000 rpm.

You want incoming air to go as straight as possible from the intake opening to the valves.



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Stephen's racing page
or check out the race car

87 IROC SuperPro race car
461 big block
Best ET on a time slip: 11.589
Best MPH on a time slip: 116
Best corrected ET: 11.079

Altitude corrected rear wheel HP: 468
Best 60 foot: 1.646
Member of the Calgary Drag Racing Association

 

Alright, so I'm still kinda new, so explain what I need to do to do a bowl blend and gasket match?

 

Newby, a gasket match is where you line up a gasket on the plenum lets say, and you then scribe around the inside of the gasket. You then remove all metal thats inside that line, that way, there are no flat areas for the incoming air to hit, air flowing through a hole goes much faster than air traveling through baffles right? Same principle, Remove all restrictions.

Bowl cleanup: here's what I'd do. Get a book on it. I can't really explain how to do it unless I know that you know the complete layout of a cylinder head. I'll try though. There is basically a sharp drop off above the valve seat inside the head. Think of a winding stream if you will. The water travels around the inner turn, the one with the shorter radius, and what does it do on the other side of the turn? Creates turbulence and you get a little whirlpool action off the exit of the radius. Air, being that it holds true to fluid dynamics also, does the same thing. Now picture a straight stream. The water just flows along smoothly, no turbulence just perfect straight flow. To do a bowl cleanup you have to remove this pocket where the air forms an "eddy" I believe is the term for it. smooth it out and round it so that its the straightest line it can be from the entrance of the port. I know, "smooth it out and round it so that its the straightest line" doesn't make much sense but you'll see.

[This message has been edited by RedIrocZ-28 (edited July 23, 2002).]

 

I said porting properly, not hogging out.

 

Alright, that makes sense. So if I did port it, do you think I would be better off with a little bigger cam then? My engine is supposed to be pretty built.

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1986 Z28
383 ci Stroker, Dart Sportsmen 2 heads, roller rocker arms, Crower Hot Street Beast cam, edelbrock 750cfm carb and performer rpm intake, Corvette Servos, shift kit and 2600 rpm stall convertor, 3.73 gears and Eaton limited slip posi rearend.