Alright to keep it short and simple, i'm building a 400 for my 80 comp. mud bogging truck, i have the cam (.512 @ 290*int, .536 @300*exh), and will go to flat top pistons, already have a single plane high rise intake and holley 750dp carb, along with some long tube headers and an hei conversion.

For the heads i had orginally planned on using a set of 4v quench heads (came off an overheated motor though, and theres all the fun that goes with that), but recently i've decided to stick with the 2v heads for a few reasons, as 1. i've got at least 4 good sets of spares and few junk cores 2. only 1 set of quench heads 3. don't know of anyone that can tig weld the intake to match the 4v ports.

So now my goal is to get the most out of the 2v heads that i will be using. And thus my post here . Now i have all the tools needed to port the heads (need to get a few new bits for the diegrinder buts that about it), and i know how to use the tools quite well. But what i'm not sure of is to where remove material to get the best flow out of the 2v head. I do know to get rid of bumps in the exhaust passages, and to port match both the intake and exhaust ports along with the intake and headers, but after this i'm not sure. Will unshrouding the valves help, or what about cleaning the exhaust port floors up by that nasty elbow these heads have?

Now any tips tricks and hints of where to get some better flow out of these heads is greatly appreciated, and if anyone has any pictures to go along they're explanation would be even better (i will practice on the bad sets of heads before doing a good set).

 

I have a pretty good 6 page article in my Files called Port or Abort: Worst porting mistakes and how to avoid them. I can't post it here though. You'll have to look on my forum.
http://autos.groups.yahoo.com/group/...1Boss351HO400/

 

That's a great article! It's dead on the money when it comes to porting especially if you've never done it before. One thing to take special note of, nowhere in that article does it mention port matching. That's because it's a waste of time, energy and isn't going to get you anything except lost bottom end torque. Increasing port volume slows down the A/F mixture in a normally aspirated engine. This hampers the ability of the fuel system to fill the combustion chamber at low RPMs. Result: Lost power on the bottom end. So you spend all this time & energy port matching the intake to the head and you end up losing performance. Sounds brilliant to me.

Focus your energy on reducing the guide bosses, cleaning up the pockets and unshrouding the valves. The 400 is a torque monster. Built right it will pull hard right through the RPM range but it's not going to scream up to 6000 RPM.

 

Do a little homeword on what you are wanting for cr before you unshroud the valves. You could easily get your chambers to 80ccc or more and that will reduce your cr. Use a calclator like this one to work out your numbers before you start grinding away.http://kb-silvolite.com/calc.php?PHP...8a4c4f13feafcd

 

Good point. As the article states you're looking at maybe a 1/16th of an inch here. The valves in the Cleveland 2V aren't badly shrouded because of the open chamber design. Some minor grinding is all that's necessary.

 

This may be a stupid question, but is port matching the same thing as gasket matching,or is it something different?

 

Yeah they are pretty much the same thing roush. But yeah i didn't think of that for the intake side, but for the exhaust side i thought that it would help out a lot as thats where these heads need the most help, please correct me if i'm wrong there .

Yeah as far as the CR i'm planning on having a bit of machin work done to the heads (already have to have them machined for the taller springs), and i am going to have the heads milled slightly (on that note how much can one mill these heads before having problems?), then i'll be running flat top/ or domed cleveland pistons (or 400 pistons, just whatever i can get the best deal on, and yes i know i need to have the 400 rods bushed to fit the 351c pistons) ideally i'm looking for as close to 1:1 cr as i can get, as the ddk200 numbers show 420ish (don't have the program to recheck numbers in front of me but this is a ballpark). and around 450is ftlbs of tq.

Haven't been able to check that forum out yet, just joined up though, will check it as soon as i can. but yeah thanks for all the help so far.

 

"...is port matching the same thing as gasket matching?"

The end result is the same. The port opening on the manifold and head line up evenly so there is no obstruction. Gasket matching is the delusional practice where some clown thought the intake gasket should be used for something other than sealing the port.

The gasket is used to scribe an outline, somehow thinking this was supposed to be an ideal cross section for the port, then hog out the head and intake ports so they are the same size opening as the gasket. Use this link as an illustration, NOT as a guideline.
http://www.sa-motorsports.com/diyport.shtm

What this does 9 out of 10 times, is reduce or eliminate the slight tapering effect the manifold manufacturers designed into the port. Air velocity slows down momentarily, fuel droplets fall out of suspension and stick to the port wall. Fuel dribbles into the chamber rather than floating into chamber.

I affectionately refer to gasket matching as "Porting for Dummies". I'm amazed there are still articles on this. Port matching is the same practice to a lesser degree. It has some applications IF you know what you're doing, but otherwise can have the same effect. Countless Performer 2V intakes have been ruined by port matching.

A port mismatch is not necessarily a bad thing. There are some anti-reversion benefits that a rarely discussed, but those benefits don't sell porting kits. Do they?

 

Brian and Bill... thanks for the great information. I have been trying for quite a while to find someone who does good port work near me and everyone either looks at me like I'm asking for spaceship parts or wants waaaaay more than it's worth to do (and honestly, I can see why full out race shops would not want to waste their time on my aluminum 3.8L heads).

Reading what you guys have makes me feel like I'm armed with a little info when I talk to the places I've been looking at to do my work.

 

As far as cuttting down the heads, only do what is needed to clean them up. Because you are doing new pistons that is the place to make your cr what wou want. If you go with something like th eBadger flat tops you may wat to deck the block as they will sit in the hole about .060-.070. As I said before use that calculator and you can play with all of the variables that will affect your cr.

 

When you take a look at that article you'll see why hogging out ports is not the best way to increase flow whether it's incoming or outgoing. The port's efficiency is highest, around 95% out by the manifolds. Efficiency is lowest, around 50% in the valve pocket itself. Spending a lot of time grinding to try to match the port size to the manifold/header size isn't going to do much good if the exhaust gas can't get out of the cylinder past the valve pocket. Picture it this way, if you took a 2" fire hose and hooked it up to a hydrant you'd get a ton of water out of right? Now stick a 3/4" hose adapter in between the hydrant and the fire hose. What do you think that's going to do to the flow?

Even on the exhaust side you need to focus on the valve guide boss and valve pocket. You can spend some time reducing the radius of the exhaust passage to make a smoother flow out to the header but your biggest gains are going to come from work inside the pocket. Leaving some mismatch between the port & header also helps in scavenging by preventing reversion which is the exhaust gas getting sucked back into the cylinder when the intake valve opens at the end of the exhaust stroke.

Also in the exhaust side smoother is better. It doesn't need to be polished but if you want to use a finer grit abrasive like 100 or 120 the exhaust side is the place to use it. 60-80 grit is perfect for the intake side.

 

Awesome bill, thanks for clearing that up .

But yeah thats an awesome site , huges thanks Brian, awesome info, i just spent a good couple hours reading info on that sight .


So just to be sure i'm getting this right (i know i might be getting annoying, but better safe than sorry ) its not just port flow, but port velocity (as per the garden hose reference on brian's site), on the clevo head its best to leave the ports alone, as the are plenty big already, but concentrate in the valve bowl area, shape it to createthe best swirl effect one can (ie shape the outside of the runner), and unshroud the valves the best one can, eliminate any nasty restriction such as egr bumps in the exhaust passages, polishing has little effect on flow, as its shape that does.

Alright i think i know what to do, well enough to go practive on some junk clevo heads, and as i am doing the port work i will post up my progress just to make sure i'm not overdoing it or repeating mistakes that will screw the final set of heads up.

Lasty (for now anyway ), how much relistic gain chould iexpect to see from this, i'm assuming from all the info i've looked at would a 30hp gain be unreasonable, or would there be more?

Thanks again .

 

with an open plenum and big carb you should be wanting to flow some big numbers and will be worrying about high-end performance...right? Thats the idea with 4v heads. So low end should not be much of a concern and threre may be benefits to port matching and getting the max flow. It's my understanding that the big guys with big hp do this as a standard...but could be wrong. Most build the 400 to near rv spec.

If your concerned aout low end and a low end torque curve you best rethink your whole build IMO. Whats the build for?

Also matching cr to the cam will be important- big duration needs more compression and different pistons such as TMI's 0 deck height.

IMO, of course!

 

Work on tapering the valve guide boss so that it looks like a volcano. The bowl work should mainly be kept to the area 3/4" past the valve seat. Deep porting can create a bulge in the pocket opposite the short side radius and a good chance of hitting a water jacket.

Wall thickness may be only 3/16" thick and anything much less than 1/8" remaining will probably crack. Don't forget the short side radius and don't go overboard trying to improve the swirl effect. Small swirl improvements would come from the side of the port closest to the cylinder wall.

Some illustration pics. Ignore the part about the gasket matching.
http://raceabilene.com/kelly/hotrod/newmotor2.html

I don't think a 30hp gain would be unreasonable. To gain more I think you need a more aggressive cam, some extra cubes, or professional porting.
What's the bore size going to be?
Do you have any more cam specs, duration @ .050", lobe separation angle?

 

I take by your post that this engine is for mudbogging only. I run a 400 in my mudrace truck also and the 2V heads with 4V valves. If I had it to do over and if I rebuild the 400 again I will use open chambered 4V heads. I was concerned about losing lowend performance also when building my motor, so I stuck with the 2V heads. One pass down the track displaced that. Spinning in the mud is going to create max RPM's of your motor and once you get going you'll be turning it hard. Tim Meyer has pistons that will create zero deck (and even better they are on sale right now) that would come up to about 11:1 compression with a 400 crank and milling the heads .010., but with that compression you better start thinking about racing fuel. The open chambered heads will also allow you to advance your timing a little more than with quench heads for a little more jump outta the hole.