So while my 914-6 oil tanks are being machined I going to start working through my header with heat exhanger design out of stainless.. I do not have non compete on these with m&k so that gives me design freedom.. However I will use similar design process as the m&k/ rarlyl8 design. So my question is 1.5" the most common size or allot of you using 1.625

Most common aftermarket is 1 5/8" OD for 3.2 and under and 1 3/4" OD for 3.6 motors.
The factory six concours guys will probably stick with the stock 1.5" OD heat exchangers

I would like 1 5/8 for my 3.2. I want your first set.

I'll be in for a set. Would be for a 2.4L Right behind ya Mark!

If these have heat, I would like to see what they would look like. Probably 1 5/8

From Dempsey's book

2.0-2.4 = 1 1/2 or 1 5/8
2.5-2.8 = 1 5/8
3.0-3.2 = 1 5/8 or 1 1/2 (think he meant 1 3/4)
3.4-3.5 = 1 3/4
3.6-3.8 = 1 3/4 or 1 7/8

Your largest target would be 1 5/8 for 2.0-3.2

Who needs heat?

You and i for sure.. I need to come pick up that engine shortly so I can get working on this..



As to what they look like with heat this will be again a little trial and error.. I probably need a true 914-6 bracket to set height for the muffler and put the engine trans assembly together and start mocking up.. They won't look oem but won't look like b&b either..

Mark I will surely put you on the list for the first set..

1-1/2" up to 2.7
1-5/8" or 1 3/4" for 3.0 and 3.2, stock I'd use the 1 5/8" and use the bigger for HP.

But that said, although there would obviously be a bit of power loss, even a stock 3.2 runs fine on factory heat exchangers with are IIRC only about 1 3/8".

My 2.7 was spec'd out at 1 5/8 by MSDS.

I'm quite interested in your project!!!

BTW if someone has some SSI 911 heat exchangers and/or some stock 914/6 or the new reproduction units, get them to mb so he can use them for setup

Come by and get it. It's on an engine stand right by the garage door.

I also ran 1 5/8" MSDS headers on my 2.7. Ran awesome. It was a stock 2.7 with webers.

Is there an accepted ratio between exhaust port size, and header pipe size?

Looking at the chart posted above the 1 5/8 pipe is used for 2.0 to 3.2 head sizes, yet the port sizes vary considerably.

1 5/8 is 41.275 mm.


Exhaust ports run from 32 mm to 38 mm for those engine sizes. I have heard if you oversize, you can kill performance but obviously some oversizing is prefered. What is considered optimal?

I'm no engineer but I'd think cylinder volume & RPM would be more relevant.

Yes and yes so camshaft could dictate allot. Ssi use to only make one size primary but changed flanges based off engine requirement. I always saw great performance out of 1.5" primary 1.375 id on 2.0-3.0 on 3.2s you have to go 1.625.. I personally liked the 993 heat exchanger the best for this application.. In fact that would be a good fit for 914-6 but useing the Gillette style not bischoff like I preferred for the 911 setup because of flange location and adaption. Though the 993 heat exchanger is not equal length they are 1.625 and are very close to equal length..

I will probably go with 1.625 as my base but I worry about loss of low end torque on the smaller engines

Smaller engines already have the stock he's. The large engines have been waiting on a solution.

Good point.. Well guess I will have to solve that.. ..

Anyone know what the difference between a 1.7/ 1.8 muffler bracket? I remember they can simply be redrilled but been 15 years since I have done that..

At $3K a pair.

Many (too many) years ago I had a Euro 3.2 and standard 914 HEs on a rolling road. From memory peak power was down about 20hp and 800 rpm compared to mild steel headers.
Also for a Q&D solution a friend who messed about with engines said a good rule of thumb was the "pipe should be the same size as the valve". Without looking it up I've no idea what that equates to, but at the time the comment was "hmmm, he's not wrong...".

One thing I haven't seen discussed is the other half of the exhaust equation...what are you going to run for a muffler?

1 3/4" pipes on a stock banana? then you may as well stuck to a smaller tubes anyways.
Zero backpressure then you are likely very loud and may lose some bottom end torque.

Like everything in the high performance engine world there is no perfect combo, everything is a trade off. Too much of a good thing is usually bad for street drivability. Getting the drivability back for the street and you will lose the peek HP.
Hot street with driveability is a balancing act and with this type of engine I'm looking more at torque curve than peek HP.


One thing I was always seeing was peeps building full race tuned engines, then not being happy with the end result, because they only ever drove on the street.
Also here's a rub, in the 90's friend and I built same size 2.0 bug engines (78mm X 90.5). His had 044 big valve head's and mine had ported and polished stock valve heads, his had a w-120 cam and mine the slightly smaller w-110, his a 1 5/8" header and mine a 1 1/2", other than that I'd say everything else was equal. We drag raced (yes illegally) countless times, he never could catch me, I beat him off the line every time. He would be catching up to me, but he could never match my bottom end torque.

Now this is more experience with Type 1 vw performance engines and I build T4 engines with the same premise, but at 2.0 (78X 90.5mm) each cylinder has the same volume as a 3.0/6.*
I always noticed smaller (1 1/2") tube headers provided more bottom end grunt, where bigger tubes gain top end at the cost of the bottom end torque. As many know this is also true with cam selection, mild to wild what you gain with one you lose with the other. Same when added a bit of backpressure with the muffler compared to a megaphone straight out pipe stinger.

Since 95% of the engines I've ever build were for the street, I've always strived for the balance of an acceptable idle (a little loppy is OK as long as it will idle at 900rpm) with good bottom end torque and acceptable top end.

What I'm getting at is a bit of loss in exhaust flow may be worth it, you have to be truthful to yourself as to what are you using the car for.
Racing? you want the biggest baddest straight through loud pipes.
Quiet or semi quiet? with street drivability? Then the muffler is likely killing (at minimum effecting) any larger tube advantage anyways. Plus personally I'd be more interested it bottom end torque then the top end HP.

*Even with VW t1 big valves they're are still smaller valves then /6, etc. I know VW t1 references it's not a true apples to apples example but IMHO and just an FYI I've build a lot of T1&4, plus a few /6 motors, so it's close enough.

Good information, those heads have 40mm exhaust valves, so that would make sense.

These. Open pipe. No baffle. No exhaust. Turn the volume up to 11 and piss off the neighbors.


But i want heat.

After the headers with heat are done. I will be working with m&k to build a quiet version very similar to the stock internals just out of stainless..

My short list of products and will be introduced in 2016 are oil tanks, oil filter consoles, oil filler necks, headers with heat exchangers, and a quiet muffler.. Most of this I have developed before just for 911s..

Any idea what the cost will be for 1 5/8" heat exchangers? I am currently running stock 914-6 heat exchanges on a 3.2 motor. I know its choking the motor a bit, but it runs fine.

I can't wait to see them and the cost also
I'll start saving now..
will need one set and love your work!!!

Just a quick costing exercise would be per header 1 burns style merge collector $175, each flange $10, each bend is about $20 along with the heat exchanger which will not look stock but more similar to b&b.. Probably in 200 per heat exchanger in stainless steel and non polished.. I have also considered making heat exchangers for the headers that are already out there in the aftermarket..

I think my target would be 1500 for a set of complete headers/heat exchanger.

At that price you would have /6 customers lined up around the corner, that is if you can come up with a product/design that works.

nice price!

Sounding good.

Would a rounder style heater box like the stock design or at least if the tops were rounded tend to stay cleaner?

I hope I can make it happen the b&b are very simple but cost way to much.. The factory ones are a great design again was at to costly.. If people don't want factory look but want nice design and cost effective then I guess mine will fit the bill

Yes but then your talking stamping dies $$$$$

Got it.

Any feed back on the 914-6 vs 4cyl muffler bracket..??

914-6 headers and OE heat exchangers can use the 2.0 exhaust bracket, from what I hear

Make up something cool from ss. I have an England hanger if you want a pic.

and by 2.0, I mean the 4 cyl 2.0 bracket

If you wanted to do something cool, one that would incorporate the muffler straps would be cool

I'm running factory six heat exchangers, with a 2.0 four muffler hanger. Works fine. I've been running this combo with my 3.2 for over 15 years.

Here's and old pic from the board:

Looks like making a SS bracket like a 2.0 hanger and/or straps would be a better solution.

England hanger

I'd ditch the welded-on stiffener and use dimple dies instead reduce flexing in that part.

Looks like I have c.. So the question is the height the same for b and c from mounting on the trans axle to the muffler bolt location so that all I need to do is still new holes in my 1.7, 1.8 bracket..

My method for locating everything is the engine being point a and the bracket is point b that way I I can build from a-b.. So the bracket is really important for mocking up. I will develop something like the 911 has for the finished product.

Any chance you can make some simple ones like these in stainless ?

Click to view attachment

Yup and then heat exchangers would be a breeze.

Who made this originally?

Not entirely sure who made them..
They were a backup set of headers for a 914-6 GT .
They were made in the early 70's. I bought them in the mid 70's
They had never been on a car, so.. new when I got them.
they look like they were hand made.

They were part of a big parts stash that got bought by someone I knew.
The Race Team moved and sold off a lot of parts before moving.

I can PM you more details if you like ?

I got this shift rod at the same time, it allows for an early 911 aluminum
case engine to fit in a 914-6 and clear the casting on the bottom of the engine.

Click to view attachment

I may have a B laying around. I'll take a look. I'm also interested in a simple exhaust that bolts to a nice 2 outlet muffler. Something that'll make my little 2.2 sound like an IMSA car.

Wouldn't help. The part would still flex in between the dimpled holes.

GT Racing Headers, in SS with heat, for $1500.00. Now we are talking!

I still think I can make it happen for that or darn close

I definitely interested please more details.