Head porting-for SilverXJ

[woodjeep]

Hi, I was reading some advise you had given one of the other members and you suggested not doing a full gasket matching and i was curious why . I have a 96 block and head that will be going into my 92 this spring and i did a full gasket match on the intake and exhaust on both the head side and the manifold side. Did I make a mistake doing this? It will be running a comp 68-232-4 cam with the mopar perf springs and 24 lb ford injectors/stock fuel pump and regulator for the 92. Its sitting in the garage right now with the block and head separate because I didn't want to lube the cam and have it sit all winter with the lube dripping off. Thanks your advise is appreciated

[gradon]

Simon aka 1bolt posted this a while ago:
I copied and pasted, but pics didn't transfer, so here's the link:
http://www.jeepstrokers.com/forum/viewt ... it=porting
Re: When to stop Porting

Postby 1bolt » September 8th, 2009, 11:42 am
there's a sticky thread at the top that has all sorts of great info.

If everyone thought of power as something that is "tuned" like a musical instrument, or a Sub woofer enclosure instead of thinking about it as "adding" power it would be easy to explain why you don't want to hog out an intake or exhaust port. You're not linearly increasing power by making mods... you're moving it around!

In very general terms if you Increase the size of the pipe (exhaust or intake tract) or shorten it, the engine breaths easier at higher RPM's (less restriction naturally but also complex inertial "siphoning" effects) but LOOSES power at lower RPM because air has momentum, and longer (and smaller) pipes create a stronger siphon effect at low RPMs that makes air flow very efficient. This is why the rounded runner intake makes more torque through the RPM range, it has longer runners.

It is also why they made the 0331 head with smaller exhaust ports, and smaller exhaust manifold runners... better siphon effect (as everyone knows in exhaust terms this is called scavenging) than the older larger exhaust ports and exhaust header which are much larger, but don't make as much torque.

You are mostly just "moving" power around, once the engines displacement and build qualities (Cam choice, compression, internal friction, oil pressure losses etc.) are set in stone then you have X amount of potential power, and mods for the most part move the peak power around, or "free up" whats already potentially there, but is being reduced by something (like a restrictive air filter or intake plumbing).

Some general advice... If you want low torque don't increase the size of the ports cross section OR the intake runner; and this includes not "gasket matching". You want to PORT MATCH. Gasket matching is a term coined back when casting technology was so bad that the gaskets were often more consistent than either the intake or the head ports, so the gasket was used as the template to get both pieces to line up. Modern head porters do a PORT MATCH which effectively ignores the gasket unless it needs trimmed to fit the ports. Modern castings are very much improved and often line up with so little misalignment between port and runner, that very little material needs to be removed. A gasket match under those circumstances especially with a old crappy non MLS gasket like this:
Image
Can result in removing so much material that you create a pocket that will hurt low torque AND high horse power, this illustration I did a while ago will help visualize why:
Zoom in (Real dimensions are: 720 x 576)Image
By increasing the cross section of the port and then decreasing it again you make a pocket where air will expand which slows it down, the air behind it will slow down as well, the air IN FRONT will be "pulled" by this pocket, in other words slowing the air down. Loss of velocity is always bad for torque (assuming the port was nominally efficient to begin with) I would guesstimate you could drop 10 or even 20 foot pounds conceivably if you make a pocket in such a crucial area.

On the exhaust side... I hate to say it but I think most people make their worst mistakes here, DO NOT bell out, "radius" or "round" the exit of the exhaust port!
Image
This is the worst exhaust I've ever seen, the guy who was building this stroker and put so much time and effort and money into it (including a meticulous writeup on JeepForum -- then he basically went deafeningly silent after he finished, and eventually he quietly sold the engine... I bet it makes less torque than a budget stroker

For the reason why I think that; First go google "exhaust reversion" don't take my word for it. Leave the transition from exhaust port to gasket to exhaust header a SHARP EDGE. Because exhaust flows BOTH WAYS (I know hard to believe but 100% true), and you only want it to flow out well, you don't want it to flow BACKWARD well. You want to make any reversion as difficult as possible and gas flowing backward from the header back into the port will have an EASY time with a radius, but a sharp edge is almost the best possible shape short of an inverted cone (reversion cone).

Also go with smaller exhaust ports if possible (such as an Alabama Cylinder heads 0331 head), and a smaller diameter header primary size with VERY long (longer the better over 2 feet with somewhere around 48 inches being ideal) primaries. The header part is not easy because the aftermarket is just like the OEM's they know that most people ignorantly key on peak horse power numbers, so they are quite willing to move your torque peak higher in the RPM range to get higher peak horse power numbers to feed you. You might very well never rev your engine to this new higher peak, which means you'll have actually LOST USEABLE POWER because the aftermarket part moved it further up into territory you seldom use.. You can also lose fuel efficiency in this deal

[woodjeep]

Wow..thanks.That was very detailed and will take some time to digest it all ,if ever. I hope I didn't screw myself by trying to do a good job. I will try to find some pictures and post them if that would help. To clarify earlier details...I matched the intake and exhaust ports in the head to the Felpro gasket I am using...then matched the intake to the gasket but have not done any work to the exh manifold. I am pretty sure it is the newer APN exhaust manifold, without the bellows

[SilverXJ]

If doing a home port without experience and testing equipment you can do more harm than good by trying to change the shape of the port or intake runner too much. Basically you want to go in and do a clean up. Smooth out all the casting imperfections and blend the bowl. You can open up the port a bit to better match the intake gasket, but different gaskets are, well, different. They will have a slightly different shape to the port opening. You risk opening the port up too much. On the intake side you want to have the intake port on the head match the port on the runner or slightly larger, but never smaller than the intake manifold side. You want the port to match the intake manifold as close as possible. Also, don't polish the intake port like you would the exhaust side. One the exhaust side you want the port on the head to be smaller than your intake manifold. Don't even try to gasket match the exhaust ports as you will end up opening them up way too much, which will hurt performance and will most definitely make the ports larger than the exhaust manifold, which, like the intake side, will disrupt flow and create reversion. And polish the intake ports as much as possible to prevent carbon build up.

-Chris

[gradon]

He meant polish the exhaust ports as much as possible.

[1bolt]

The abbreviated version is: don't gasket match, all of the gaskets on 4.0 are less accurate than the factory castings, in my experience, and matching to them is more likely to cause worse mismatch than to solve any mismatch...

If you want an extremely accurate port/manifold match use tracing paper,and carefully map out all the aligning dowel locations along with the stock port openings, then overlay it on the manifolds (carefully making sure the aligning dowel marks match up to the holes in the intake)... Chances are you will be pleasantly surprised at just how well matched they already are, and even if one or two are slightly off I think you'll see that just the slop in the dowel pins could cause all the perfect port matching in the world to end up misaligned and mismatched after install... This is probably why the factory leaves the intake manifold side slightly smaller than the port on the head.

Also intakes revert just like exhausts do, worse sometimes, that's why there's always a coating of black greasy gunk (unburnt hydrocarbons) in the first couple inches of intake manifold... the "step" created by the intake manifold being slightly smaller in cross section to the port in the head, can actually mitigate some of this.

The truth is most people like us want to trick out and optimize our stuff, it makes putting it back together and fixing stuff more fun, but when you dig deep into performance you realize a few key things. A) most "high performance" is aimed at drag racing (they don't care about torque below 3000-4000 RPM's, or throttle response) B) most OEM's know full well why they put smaller restrictive ports and manifolding on their cars... It's not because they're stupid and want to throw away power, it's because they know their non-performance vehicles will operate more efficiently and perform better on the street and under load with more torque and less horsepower. C) Both OEM's and Aftermarket know that most people mistakenly think that peak horse power is important. They sell cars (and aftermarket parts) with peak hp numbers. At some point in the 60's we were all duped into thinking that peak hp is the important number even for street cars and trucks.

The truth is If you do nothing but move the same EXACT amount of torque 500 RPM's higher you will get more horsepower on a dyno sheet. You will lose throttle response, you'll have less torque in the lower RPM's where you use it more, poorer idle quality, worse fuel efficiency (unless you change your rear end gears to match the new torque curve) you will lose towing power, and your car will feel slightly less powerful... but you'll have a bigger number on a piece of paper.

[shawnxj]

so how big of a difference would putting a 0331 head on a renix based stroker be compared to a 0720 or 0630? i'm thinking about buying 1 of the alabama 0331 heads to go on my stroker instead of doing what most others are with the 0630 and 0720 and then getting a 99+ intake to match

[woodjeep]

Hi, a while back you had some good detailed info on head porting. For better or worse...i have a 2nd chance to get it right. On the first picture (picture 1) it was my original try at porting. it was a 96 head casting 0630 and it took a lot of grinding to get the intakes to be as big as the gasket openings. ( a standard felpro intake gasket) I also enlarged the exhaust ports quite a bit. Due to a big oops I opened up one of the combustion chambers bigger than 4.00 inches and could not get a regular head gasket with a big enough bore. i had to go with a racing copper gasket and I continue to leak coolant into the oil. i have tried numerous fixes but all no help so i got a new head. it is for a 92 block casting 7120. On this one (see pictures 2 and 3) the intakes are already exactly as big as the gasket holes and the exhaust is quite smaller...probably the same size as the old head before porting.The head appears not to have been ported previously... From your help it appears that I should have left the exhaust ports as is. I will probably just smooth out the roughness in the ports without actually enlarging them . is this a good plan...thanks again

[Dezertxj88]

I stepped my head when I ported it..
As in my intake manifold opening is ever so smaller than the intake port opening. That leaves no edges where air can bounce off and cause turbulance. The exhaust side, the header opening is slightly bigger than the exhaust port, so again no ridges/ledges for air to hit. And it also helps air to not flow backwards.

I ported a Renix head though lol

[SilverXJ]

I would just do a clean up and polish on the exhaust ports. Remove sharp edges, remove rough lines, remove casting finish and polish. I wouldn't open them up any further. You may also want to match the intake manifold runners to the head, make sure it all lines up with a clean transition. Or just make sure there is no wall that the incoming air would hit. I would do the same for the intake but leave it 120 grit, or something similarly rough.

Dezert also has good suggestions.

[Dezertxj88]

I would just do a clean up and polish on the exhaust ports. Remove sharp edges, remove rough lines, remove casting finish and polish. I wouldn't open them up any further. You may also want to match the intake manifold runners to the head, make sure it all lines up with a clean transition. Or just make sure there is no wall that the incoming air would hit. I would do the same for the intake but leave it 120 grit, or something similarly rough.

Dezert also has good suggestions.

Ya clean up, don't remove much material at all!
I polished my exhaust runs to a baby bottoms smooth..intake I did with 80grit rolls. I'm still porting my head honestly. I need to get some pictures!

If you take on this project!Just get a simple porting kit will a bunch of paper rolls. And maybe a few stones. DO NOT get carbide bits..they remove material FAST. The stones and rolls are more forgiving , just post pics as you go, and we will help you along. Don't port first then ask questions..do be shy I asked alot of questions! I know I spent around a week reading every porting thread I could..from every site I could, asked for opinions of many sites!
Get some glasses & a GOOD filter for breathing. Go grab one of those 2 dollar white painting jump suits as well. Helps to stay clean and itch free, and try to use a very well light area, maybe a swivle style lamp so you can get light where its needed!
If you get comfortable enough with it, you can polish your chambers and unshroud the valves a little to..that'll always help, but its best you get some experience first.

[woodjeep]

Thanks..I matched the intake to the original gasket ...the one in the first picture. When I have it all apart...later in the spring I will make sure it matches the new gasket, but it probably will. I was very suprised to see how the 7120 head intake ports were much larger than the newer 96 head. I really had to remove a lot of material (in the 96) to get it to the same size as the gasket where I had to do nothing to the 92

[SilverXJ]

I was completely covered when I did mine. Coveralls, ear plugs and then ear muffs, dust mask and goggles. Simple glasses do not cut it for me as crap always ends up getting past them.

I was going to unshroud my valves, but there wasn't much to unshroud on my 0630.

My gasket didn't match the 0630 head very well, so I opened them up a bit.

[Antifreeze2]

I completely agree with safety goggles/dust mask while porting. I wear glasses normally and was working without proper eye protection, my eye got red and dry. I went to the doc after 3 days, he found a sliver of metal in my cornea with rust already developing. The ironic thing was that I was doing the port job with a dremel, and the eye doc used a similar rotary tool to drill out the rust.

[Dezertxj88]

I completely agree with safety goggles/dust mask while porting. I wear glasses normally and was working without proper eye protection, my eye got red and dry. I went to the doc after 3 days, he found a sliver of metal in my cornea with rust already developing. The ironic thing was that I was doing the port job with a dremel, and the eye doc used a similar rotary tool to drill out the rust.

Haha I am using my riding goggles honestly! They have foam on the back side so they form to your face very very good! They don't let anything by them!

Let us know how your projectors going though man? Any updates yet?