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Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

I've just finished the CAD drawings for an intake manifold and plenum to replace the standard intake as part of an EFI upgrade and while doing a trial fit of a cardboard mock-up took a good look at the intake port to try and match the airflow thru the port end of the manifold with the shape of the port and thought "yuck, how we going to fix that".

Problem is that the port mouth is way too low because of the hole for the injector which means that the port floor is raised way up to allow for the water gallery that runs under the port.

Looking into the port it seems obvious that air entering the port immediately slams straight into the hump in the floor probably causing huge turbulence. (Anyone with formal training in these things please correct me if I'm wrong here).

I figure that as I'm replacing the CIS injectors with EFI injectors mounted in the manifold perhaps the intake port can be "fixed".

OK, so here's the proposal:

1. Fill the injector hole in the head (doing that anyway).

2. Fill the area from the outside of the port to the top of the hump in the port floor.

3. Remove the metal from the high point in the roof of the port to the outside of the head.

4. Weld a laser cut aluminium copy of the NA intake gasket to the outside of the head to give a mounting surface.

The overall effect would be to move the mouth of the port up by around 15mm and give a smooth almost straight path from the port mouth to the back of the valve.

Anyone qualified to comment on the validity of the project?

Anyone experienced in pouring aluminium (to fill the injector hole and fill the port floor)?
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Richard · Joined: 04 Nov 2002 Posts: 617 Location: Pacific N.W.

Peter, we must have had the same dream. I got the same impression just by looking at the picture in the owner's manual. The airflow is awful. I am also just starting on an EFI project by building the Megasquirt kit. Will use a slightly modified 924 intake for now and if it works, go to quad intake.

Go to the link provided in the General discussion forum in the topic "Is this guy truthfull?" This motorcycle tunner uses JB weld epoxy to modify the ports in racing cycles. Pours it in and the grinds it to shape. Says he has never had any problems as long as the substrate is very clean and roughened up.

Call me crazy, but I think there is power in these heads with some experimenting and I don't mean hogging out the ports and putting in huge valves. The trick is to keep the velocity high.

I think Porsche made a whole lot of compromises to adapt this engine to a sports car and Bosch K. EFI gives you a whole new start.

I wish I had the skill an $$$ to CAD CAM a whole new head and make it out of billet.

Joes924Racer · Posted: Sat Dec 07, 2002 4:07 pm Post subject:

If Im not mistaken its best to keep the small valves they had big success with the turbo head.. in indian red porting and polishing grinding a few heads to dust they improved 55 percent more air than the stock head. , by using the stock size valves and flowing more air through them, port velocities had increased radically.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

thanks for the tip about JB Weld, I'll grab some and have a play.

I decided it would be easier and cleaner to build a new intake rather than chop the original one.

After staring at the port for a while today I've decided that I could change the angle of entry of the runners to the port and probably improve airflow that way.

The runners on the standard intake are horizontal so they are basically at 40 degrees to the port mouth. I think that by increasing the angle so the runners point up at the port end the airflow will be more in line with the shape of the port. Only problem is that the runners will need two bends rather than the one bend in my current design. I'm hoping that if I can get a reasonably cheap "plug-n-play" design other guys can use it.

I still want to see how much the intake port can be improved if you take away the constraint of the CIS injector mount.

Next step will be to find a professional with a flow-bench and discuss ideas and cost.

Oh, if you're interested in trying out CAD on a zero budget go to http://www.turbocad.com/ hit the Free Software and download TurboCAD LE. It's an older version of TurboCAD Professional but it's not crippled or time-limited and it will spit out files that will drive a laser or plasma cutter.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

Being that I have carbs on my car the mechanic that did the work plugged the injector holes. Then he claimed he ground down the hump in the head and filled in the top of the runner. This gave the incoming air a more direct shot at the cyclinder.

I have an extra head in the garage and would like to know if anyone have a trashed head. If so what is the thickness of the metal at the hump and the top of the runner. If someone wants to clean up the hump they will know how much to take off and then add. Anyone know these figures.

My plan is to complete the above and then put in bigger valves. I already have the cam and heavy duty springs in my current rebuild.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

I wonder whether some nice caring, sharing, community-spirited person with a cracked head would be willing to band-saw it open across the valve guides so we could all see exactly what the port looks like.

A couple of high-res pics would make it so much easier to work out a porting strategy that would work.

A sliced-up 931 head for comparison would be great.

Pity we don't have some community money, that's a use I'd vote for.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Zuffen · Posted: Sun Dec 08, 2002 9:34 am Post subject:

I've got a head with extreme corrosion in the combustion chamber and I have another head with bad cam journals

Give me a couple of weeks and I'll decide which one to cross section.

Or I could have a friend UT them an dhe might be able to tell me the thickness.

I've been saving the heads to cut up and flow bench different mods.
_________________
Bob Dodd - 924turbo@cox.net
931 1982, 944 1982 euro, 924S 1988SE, 93 968 tip 06 Silver Cayenne S, 06 Black Cayenne S

I have Way too many cars, parts for the 931,944 and 951

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

Bob, that would be soooo good. Some good cross-section pics of the port would mean guys would have a better idea of where to alter the port rather than just ramming a dremel in there and hoping for the best.

If you just sectioned one or two ports you'd still have the other two to experiment on and half a head would be easier to play with than a whole one.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

AFBCamaro · Joined: 03 Nov 2002 Posts: 199 Location: Orlando, FL

That would be Great. I personally would take huge risks in complete reshaping of ports to get more flow. I took a look at some junk heads and have decided that there is much work to be done, and much improvement. Definatly, a cut out would let many see were and how to shape the head. I have personally studied alot on fluid flow, and have aplied much to porting my own heads. Ive had a set of heads that quite frankly made around 20hp less than stock(stupidity), and some that have been amazing. Ive gotten pretty good at it by now!

Peter I am all for comunity money. Maybe a way in which all the money collected could be looked at by all members without interaction,(and update imediatly) and only use the money on what is agreed. (voted on)

But let me guess, im probably 1 out of 300 that would like to do this!

_________________
1982 Porsche 924 in mild restoration process.
1991 Chevy Camaro RS "Freigh Train"

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

AFB, the idea of donations to a community fund has been floated before. The problems seemed to be mostly logistical, how much, how to donate and who could be trusted with such a large amount of money

I think with the voting facility we now have it might be time to raise it again.

This sort of thing might be a good use for community funds. Pay someone to slice up a turbo head and paint the ports and take some pics or get some work done on t-shirts.

If 100 guys were willing to chip in $5 each....
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Geddy T · Joined: 10 Nov 2002 Posts: 149 Location: Bellingham, WA

That JB Weld is amazing stuff. We use it a lot here around the Vehicle Research Institute for everything from complete intakes (without having to weld) to bonding metal to carbon fiber. Here is the problem: it is an epoxy-based composite. Therefore, don't just slag it in there and grind it down. The rule for epoxy as with most thermoset plastics is that you have to cure it at what you want your max service temp to be. In other words, don't go filling anything with JB Weld unless you've got a furnace to cure it in as a cylinder head is exposed to quite a bit of heat. Whatever temperature you guess those ports reach (not so high as they are intakes), add 50 degrees C and cure at that temperature. You won't go wrong that way. Otherwise the stuff will degrade at high temps. Also, cures best under pressure. If you could ram the stuff in like injection molding, hold that pressure on it, and oven cure, it'll be as good as metal.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

thanks for that info Geddy. I was thinking I could use JB Weld to glue my prototype intake manifold together and from what you say it sounds like I can. Once I've got the intake right I can build another one and have it welded.

To cure it do you allow it to fully set (24 hours) and then heat it to the service temp or do you heat it during the setting time? How long should it be heated for?
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Geddy T · Joined: 10 Nov 2002 Posts: 149 Location: Bellingham, WA

No. You CURE at service temp. A thermoset plastic crosslinks during cure. Once that crosslinking is complete, the plastic will remain at those physical properties. Heating it after it cures will just result in degrading it because you're curing it and then immediately heat it up to a temperature now above its service temperature. So oven cure, preferrably under pressure. If it's an intake manifold, you can probably get away with room temperature cure because--especially with an intercooler cooling the charge--it won't see such extreme temperatures. Intake manifolds are one application where JB Weld works great. I would recommend jigging it up somehow with a vice or clamps to keep the area being bonded under pressure during the cure. Also, this stuff is strong. REALLY strong. If you make an intake manifold using it and it's not sloppy and looks good enough for you, there is really no need to then weld up the "real" one. The epoxied one will work just as well. A group of guys up here were putting together a project for a clean-running snowmobile competition. They took out the two-stroke and replaced it with a Yamaha four-stroke and turbocharged it. They were running pretty good boost and the intake manifold held up just fine. It was an aluminum plenum and tuned runners and injector bosses all bonded together with JB Weld with a room temperature cure for a day or two in clamps to apply pressure.

Geddy T · Joined: 10 Nov 2002 Posts: 149 Location: Bellingham, WA

Oh yeah, more properties of epoxies:
The hotter you get it, the quicker it will cure. Autoclaved carbon fiber parts generally don't stay in the autoclave for a week. I imagine that if you do cure at elevated temperatures, you can get away with heating it for less than the recommended cure time. The rule of thumb is that you want to heat it up to service temperature for the duration of the cure. So the hotter you need it, the sooner you can take off the heat. A simple rule of thumb is don't remove it from heat or pressure until it's completely cured. With JB Weld there is a slight color change that can help you determine when this is, unless you really glop it on, then you'll want to wait longer to allow for the stuff in the middle to cure.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2743 Location: Sydney, Australia

OK. Thanks for the tips. Now if I can just get my wife to loan me the oven for half a day

After putting a 931 and 924 head side by side and comparing the intake ports it's interesting to see what Porsche actually did to the 931 head. As far as I can see they did very little. The major thing seems to be filling in the 3mm drop-off in the floor at the manifold end which is what immediately looks "wrong" with the 924 port and removing the 2mm or so lip at the manifold end of the roof. They seem to have ground down the floor hump as well but I can't be sure as I don't have the right gear to measure it. Basically they just straightened everything up.

Be interesting to see what the differences in port volumes are.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you