MFI Manifold & Stack Identification & Modification

triplesn8s · 11-22-2004, 11:23 AM

I am seriosly considering a Megasquirt retrofit into my '72 2.4 MFI setup with 'E' cams. I want 32mm ports. In doing a port size check I found the following:

Head intake ports 30mm (An unpleasant '72 anomaly, valves standard size) I can enlarge them, no problem.

Intake manifolds 30mm at the head but can obviously & easily opened up to 32mm, ~36mm at the stack.

Plastic stacks 911.110.316.1R 30mm at the manifold! In other words it goes from 30mm at the bottom of the stacks to about 36mm at the top of the manifolds to 30mm at the bottom of the manifolds. Tres bogus IMHO.

The question is do the plastic stacks have enough wall thickness to port out to 32mm recognizing I will have to blend a fair way up the stack to make sure the diameter is never less than 32mm?

What are my other stack options? An 'E' set? Are they actually different? What should I pay for the stacks only less manifolds? Anyone with a set to sell?

I know my webers are OK but you can't beat programmable FI for that last 10% of power/drivability. Besides the stock MFI stuff looks way cool & minus the original MFI pump I believe it is lighter than the Weber setup.

Apologies for the longwinded questions but I am new to 911 performance applications.

TIA,

Bill

Tim Walsh · Tim Walsh's Garage

I've looked at the stacks and I do belive that T,E and S stacks all were made from the same mold, just different milling.

Eagledriver · 11-22-2004, 12:31 PM

I don't know for sure but I've heard that the T/E stacks are too thin to bore to "S" specs. Maybe they would go to 32mm though. My car has the old Magnesium stacks that have enough thickness to bore out.

-Andy

triplesn8s · 11-22-2004, 12:44 PM

I am trying to distinguish between the stacks or "trumpets" & the manifolds. My manifolds are magnesium and can be bored. My "trumpets" are plastic and 30mm on the bottom. What I am trying to be sure of is whether the 32mm T/E "trumpets" are the same as mine via part number or measurement and wether or not they can be machined.

Are some of the earlier T/E trumpets 32mm AND made of magnesium? What years?

Thanks,

Bill

Walko · Walko's Garage

Bill

I have a set of plastic S stacks they are probably for sale.

I will measure them and let you know what the top and bottom measurements are.

Michael

Jim Richards · 11-22-2004, 01:21 PM

Quote:

Originally posted by Eagledriver
I don't know for sure but I've heard that the T/E stacks are too thin to bore to "S" specs. Maybe they would go to 32mm though. My car has the old Magnesium stacks that have enough thickness to bore out.

-Andy

Andy, Eurometrix is boring out a set of 72-73T (plastic) stacks to S/RS specs (36mm) for me. When I get them back, I'll let you know how they turned out.

triplesn8s · 11-22-2004, 01:40 PM

Micheal,

I only want to go to "Normal T/E" of 32 mm from my current 30mm.

Jim,

Please let me know how that turns out. Some well lit digital closeups would be cool.

Thanks,
Bill

Walko · Walko's Garage

Bill,

Do you want plastic or metal??

Michael

triplesn8s · 11-22-2004, 02:05 PM

I suppose the plastic 72-73 32mm T/E that will work with may air cleaner assy etc. Got a digital camera? BTW I'm in the States & I see you are in Australia. Great country, my sister lived there for a year. A popular topic of discussion in my extended family is lets all move to Australia as the States is heading the wrong direction at full speed.

Only problem for me is all of my sports cars would wind up with the steering wheel on the wrong side.

Contact me directly at triplesn8s@neo.rr.com

Bill

Walko · Walko's Garage

No stay there.

Only joking

As long as your cars are over 30 Years old it doesn't matter what side the sterring wheel is on.

I have got a digital camera. can i use it? sort of, I can take the pictures just haven't figured out how to put them on the computer.

Michael

NevenM · 11-22-2004, 02:51 PM

Bill

I have a set the same (must be off a TE) I think Porsche crippled them this way. like you I can't understand the 'step' between the TB's and the Stacks (36mm -> 30mm) yet the Stacks open to 36mm at the top , I can only think they did this to reduce the manufacturing cost of the TB's and stacks (ie they didn't need to change the butterflys or the mould at the trumpet end of the stacks), The plastic stacks are about 45mm OD so I can see no problem with boring them to 36, What would be interesting to know is if the butterflys are the same across the three TB types (TE, E and S/RS) and if the trumpets are the same diameter

Anyone got calipers?

Neven

triplesn8s · 11-22-2004, 04:41 PM

Michael,

I can empathize. The surest way to ruin a great thing is to have it become popular...

Neven,

Same TE experience. According to the thoery I have read the ideal configuration would be to have about a 4 degree taper without steps from the bell to the port corner. Second best would be a straight bore with no steps. Steps are never good. There was some cost savings through the range going on here.

Thanks for the info. I will likely try to bore mine out. Because of the shallow taper they will likely have to be bored quite a distance in.

I believe the TB's can be bored to 36 at the bottom to match the 36 at the top. Not being able to would not make any sense at all from a manufacturing cost savings perspective.

Bill

Matt Smith · 11-22-2004, 07:37 PM

What Neven should have said there is that he USED to have a set of TE stacks. They are now sitting in my garage

I think it was a cheap way to cripple them too. It just goes against every instinct to have that big step in there.

How would you bore them out? Are we talking hand porting? I doubt it..

914/6 · 11-23-2004, 11:00 AM

Plastic stacks are all different T , E , S all are differnet bore taper. The T and E can be opended up to S . I have a Tool that cuts them to the same taper bore as factory S. No hand job.
If anyone is interested. Jeff

NevenM · 11-23-2004, 11:03 AM

Can you post a picture? where abouts are you?

Thanks
Neven
1973 911E
1970 914/6

914/6 · 11-23-2004, 11:10 AM

I will post pics.

triplesn8s · 11-23-2004, 01:23 PM

Want to rent your reamer? I have a buddy with a CNC mold shop who can perform the operation. I am working on a self-piloting reamer to take the 30mm head ports out to 32mm. Meeting with the tool grinder tomorrow.

914/6 · 11-23-2004, 01:47 PM

here is some pics top one T stacks with center one openened up to S bottom set is E stacks. top of trumpet dia T 35mm, E 39mm , S 43mm . I dont want to lend it, but will do yours

914/6 · 11-23-2004, 01:49 PM

ned911 · 11-24-2004, 06:58 AM

The easiest way to check which stacks you have are to measure the inside diameter at the top of the stack.

34mm - T
39mm - E
43mm - S

These are valid for the 2.4 not sure about the smaller engines. Also the top of the throttle bodies are the same for all 3. You can bore the bottom of the throttle bodies to the correct specs.

Ned