Exhaust/Header Size 3.2 Carrera
 

I noticed the recommended pipe diameter is 1 3/4" for a 3.2 engine. Is that absolute or is it possible to use 1 5/8"?

The recommendation when I bought mine years ago was 1 5/8 from George Narbel European racing headers.

Most will advise 1-1/2" or 1-5/8"

Really? I was looking at b&b headers to be specific. Looks like their website specs 1 5/8pipe for SC's and 1 3/4 for Carreras. Then again the difference between the two is 0.125", which is not much.

For almost any "I want to go fast" use 1-3/4" is 3.6 territory. I could see it if you are going to just try to get the biggest HP numbers on a dyno or are going to run for extended periods flat out in 5th but you will lose mid range.

In other words 1-5/8"...

+1
yes, it depends on how you plan to use your Carrera. Either are far better than stock. If you plan on installing PMOs and racing then go bigger.

Displacement is only part of the formula for header primary size and length. C/R, camshafts, induction, and peak rpm must also be considered. For a bone stock 3.2L engine 1 5/8"OD is a good size if ID is no less than 1 1/2".
This leads to discussion on materials choice. Cheap materials (steel or 304 stainless) must be thick and heavy to last any length of time. We use 321 stainless with a wall thickness of 0.049". This yeilds a larger ID and lighter weight with also longer life. ID should never be <1.50" for a stock Carrera engine. Dansk/SSI for example have 1 1/2" OD but only 1 3/8" ID.
Always check ID when choosing headers.

That's actually huge. Torque is greatly affected by primary size.

I went from 1 5/8" to 1 3/4" on a normally aspirated 3.2 and the car was noticeably slower and less responsive. Switched them back to the 1 5/8 and the car ran great again.

Thanks for all the replies - good info!

Best advice by far.

What would be ideal header ID for a 3.0 with carbs then?

If your street 3.0L also has cams and/or a bump in compression 1 5/8" is good, if it is stock with carbs 1.5/1.63 step headers might work best, next is thin walled 1.5" headers. Thick walled 1.5" headers are 1 3/8"ID which is marginal at 3.0L displacement. The difference in all of these is a few HP on the top end. Staying on the conservative side preserves torque which is more valuable for a street car.

As Rod stated 1 5/8 is right sized for a 3.2L, 1 3/4 is right sized for 3.6L engines. We are working on 2" headers for a 3.9L engine.

what he said

all the copies of the original 911 header are 35mmID, that includes SSI and Dansk

these work well on 2- 2.7 liter engines up to and including 2.7RS, for 3.0 they are better than the smog exhausts used through '89, but would be on the small size for 3.0RS due to the cams and rpm, on a stock 3.2 they will be fine for around town use <6k rpm but somewhat restrictive if all you driving is from 5500 to 7000.

The best compromise for stock 3.2s is usually 1 5/8"OD(1 .5"/38mm ID) it's interesting to note that the 993 headers are 1.5"/38mm ID

just a side note to add to Brians response 304 is actually very good but in high heat applications can crack with improper welding techniques and thats why it has the bad wrap out there. a good portion of head manufacturers do a 2 pass weld constituting a root and a cover pass. when dealing with stainless (welding it) you want to keep it as cool as possible and on thin wall .080 and less single pass is all that is required. multipass is very common in the pipe industry and sometime manufactures dont understand the difference between tubing and pipe which leads to the in correct welding methods.

Now on topic 1.750 is pretty big for a stock 3.2 I would suggest 1.625 remember improved TQ down low comes from smaller primaries but that can count against you up top so it needs to be balanced out

Use 1 5/8" O.D. headers or larger on a 3.2. Anything less is an automatic 10-15 hp governor on the motor.

What is the consensus on using 1 5/8 ID George's headers on a stock 3.2 with a sport muffler and matched Steve Wong chip? Or Euro DME?