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  #16 (permalink)  
Old 08-11-2010, 07:40 PM
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Quote:
Originally Posted by gofastz
well iv ben thinking somemore, i could use the tbi heads with flattop pistons? or the double humpers "461" heads with D-shaped dish pistons? still leaning on the eddy's tbi cam with 1.6 roller tip rockers to give the engine better breathing, i know the tbi heads are not worth a darn but if the valves are wore out then mayb put some 2.02/1.60 valves in them? i have a motor here that is 87' 350 with flat tops, and the double hump heads and the performer camshaft, i could put the tbi heads on it, change the cam and all that good stuf???
Bigger valves are not the TBI swirl port heads problem and offer no solution. The Swirl Port head has a big vane that is cast from the valve guide toward the port wall that favors the inside of the cylinder. It projects into the air stream to force the flow onto the outside wall causing the mixture to develop a spin as it enters the cylinder. While all this spin is good (called swirl) the vane greatly reduces the ports ability to flow, so much so these engines cap off the revs around 4,000.

When the port is the limiting factor to flow, increasing the size of the valve has no effect because the port can't feed it. At this point there are two solutions to be used; one increase port flow or the other increase the time the valve is open. But the vane limits the former and the vacuum sensed TBI system the latter.

The vane can be ported out, there was a whole group of people who are enamored enough with this they had a web site, which I can't find anymore, but punch in Porting Swirl Port Cylinder Heads on your browser and ton of stuff will show up.

The other problems with high mileage heads are that the valve stems and guides are worn out and so are the springs. By the time you get them cleaned and crack checked, the guides reconditioned, valves repaired or replaced, valve springs replaced, new seals, head milled flat again, etc. you've put nearly as much money into them as set of new Vortecs which will out run your fully prepped Swirl Ports by an easy 30 horsepower and they don't mess with manifold vacuum doing it like a bigger cam would so your TBI's computer isn't left in the lurch trying to figure out why the engine vacuum for the RPMs and throttle position don't match the what the fuel and ignition maps are expecting to see which leads to a new chip when that happens.

Bogie

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  #17 (permalink)  
Old 08-12-2010, 06:53 PM
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Bogie, this is good stuff, can u tell me more? the motor has 215669 miles on it so u can bet the heads r wore out.....
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Old 08-12-2010, 07:03 PM
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There is a user on another forum that I go to that had good luck porting 193s.

Quote:
I recently ported a pair of TBI 350 193 swirl ports as an experiment. I went into it knowing that they are swirl ports and can only have so much potential. Thing is when I got done and had a buddy flow bench them, the flow #s suprised the hell out of me. Not bad for 8 hrs with a air grinder.

Valve Lift------Intake Flow---------Exhaust Flow
.050--------------35.6----------------------31.0
.100--------------72.4----------------------60.5
.150-------------105.8---------------------87.3
.200-------------133.4--------------------124.2
.250-------------154.1--------------------147.3
.300-------------180.6--------------------171.5
.350-------------195.5--------------------184.7
.400-------------209.3--------------------196.3
.450-------------217.4--------------------203.7
.500-------------224.3--------------------215.6
This thread also has links to other articles and a nice little debate that went on at the time.
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Old 08-13-2010, 06:48 PM
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like when i go to grinding on them, do i just go down as far as i can in the ports? and how wide and tall is the limit on these, and could i open up the exh ports some too???
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  #20 (permalink)  
Old 08-13-2010, 08:10 PM
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If you plan on porting heads yourself, I wouldn't start on this build. You should find someone with some experience that will show you the ropes and/or pick up a good book on it and start with junk heads. Not something you just jump into with trial and error at the start of a build.

To answer your question though, don't grind down as far you can in the ports. You're just going to hit water really quick on stock castings. Unless you know what you're doing, Hogging out swirl port heads is not the way to power, you'll ultimately make them flow much worse. Yes, the exhaust side should be touched up, they flow pretty poorly stock.
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Old 08-14-2010, 03:15 PM
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ok, what if i use some older heads "non centerbolt", and gride the four center bolt holes on the tbi intake to make the older heads fit? iv seen this done on a 96' chevy w/t, he used the double hump heads with tbi, it ran real good...if i use small cc chambers ill use dish pistons, if i use open cc chambers ill use flattops......
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Old 08-14-2010, 05:56 PM
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come to think of it, i do have some 305 heads that has been litly ported on the intake and way hogged out on the exh side, with 1.84,1.50 valves, with dish pistons ill be running around 9.5:1 CR, i think?? would that be a better head than the swirl ports??
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Old 08-15-2010, 12:34 PM
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i could go carberated, put on a set of older heads, or mayb even the votec heads, a good intake like performer, performer eps or rpm? idk then bc being fuel injected is cool and good trottle response too, the heads are going to be the prb bc if they are wore out, it cost about as much as a new set of vortecs cost, but the you go buy some @ the junk yard 80% of the time they will have to be bulit too, then a vortec intake for the tbi whew $$!
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