Best exhaust size for a B20

[AndrewNance]

I'm looking into exhaust options for my 122. It's about to have a B20F from a '74 142 but with SUs. I have a Double S 2" muffler that I had thought about using but I'm kinda just wondering if I should go bigger. I definitely want the best flow since I have a decent flowing head on it but I figure at some point you get too large to supply enough back-pressure and power would begin to decline.

Basically, my question is what is the best exhaust diameter for the B20 with FI head?

[Canuck]

Look into the sport exhausts - 2" is pretty small and 2.25" is better. You don't want any of this back pressure nonsense. If you're staying with the stock manifold (I'm guessing yes) - then 2" is fine and without other engine modifications you're OK. Don't go looking for a big power increase - you won't get one.

[gsellstr]

I'd go for a 2.25" if I were to do it again. I actually have a 2.25" on the 140 with a header, cam, VPD type II head, etc. and it runs out pretty darn well. Went from the stock system to the 2.25" and lost a little low-end but that's been made up as the rest of the build came along. If you can source a true mandrel-bent 2" that would be pretty decent for a stock-mild build as well.

[Redwood Chair]

^

Grab the 60mm exhaust from a 240T in the jy and rework it or get some 2.25 bends from columbia river mandrel bending.

[AndrewNance]

For the header, i'm going to be using either a Stahl or Ipd. Not the stock downpipe. Im thinking of going with a 2.25" with either a single glasspack or magnaflow straight-thru. Just something for a nice throaty tone and increased flow.

[gsellstr]

I've got a dynomax turbo muffler on mine and it's actually a bit much if you plan any kind of highway jaunts, so I ended up with a summit bullet muffler on the end as well to tame it a bit. If you're doing the header, go for the 2.25".

[mitch1971]

You need a pretty decent B20 to warrant a large header and exhaust. Too large a header is going to kill your bottom end power and the gases will flow slower, too small a diameter and you'll get less flow. 2.25" is 26% larger than 2" and unless you have a high performance B20 a 2" is a better choice. A larger exhaust just pushes the max power up the rev range and I doubt if there would be any power gain and it could well be worse. I have a moderately worked B20e head and KG trimming recommended his stage 1 header and I have one of his stage 3 headers and he said that was much too large for my engine. I went with the E manifold and 2" Simmons exhaust in the end and it is a good combination.

[vvpete]

Originally Posted by Redwood Chair

^

Grab the 60mm exhaust from a 240T in the jy and rework it or get some 2.25 bends from columbia river mandrel bending.

This, and weld it up to the stock downpipe, the header is a waste of money IMHO for a motor not much more hp than stock. Even aftermarket 240T parts are cheap, get the under axle, front pipe, turbo can and make up a tailpipe or use a 90 deg (not S) tailpipe from a later B21F. I used this in a '68 144 for 18 yrs, but added the Pacesetter 3" single glasspack resonator tip to quiet it down. Without it I found it too loud.

[AndrewNance]

I got a good deal on MikeJr's Stahl header so I went for it. My stock system now is less than two inches. It's one of the mild steel kits from Swedish Treasure. It also has a super restrictive muffler with another can behind it. It sounds like a straw. Anything will be better than what's on it.

[lummert]

I looked into this years ago when I owned a 1980 VW Dasher. Seems that the exhaust pipe needs to be the diameter of one of the two downpipes times 1.5. Example: 1.5 x 1.5 = 2.25.

Sounds like you're on the right track at 2.25 inch.

[vvpete]

Originally Posted by andrewnance21

I got a good deal on MikeJr's Stahl header so I went for it.

What is the output flange size on the header?
Probably 2 1/2 "
The 240T 60mm is a good compromise size, 2.36".

I had a Bosal Big Bore muffler system on my 144 for a while, complete 2 1/4 system end to end with basically a 240t rear muffler and bigger resonator in the tailpipe, nice throaty sound to my modified B20 w/SU's but when the complete 240T system went in with the single rear turbo muffler the flow and performance improved a lot.

[AndrewNance]

I'm not sure. The outlet tapers off so it really can be cut to pretty much any diameter up to probably 3". I'm thinking I try 2.25" and if I hate it, I'll put a little more restrictive muffler on it.

[lummert]

Just measure the outside diameter of each of the primary tubes of the downpipe and post here.

[AndrewNance]

Originally Posted by lummert

Just measure the outside diameter of each of the primary tubes of the downpipe and post here.

I will when it gets here

[smokeyfan1000]

Originally Posted by andrewnance21

I'm not sure. The outlet tapers off so it really can be cut to pretty much any diameter up to probably 3". I'm thinking I try 2.25" and if I hate it, I'll put a little more restrictive muffler on it.

2.5" or the OEM volvo turbo exhaust, use two lo back pressure/straight through type mufflers and it'll be quiet enough but a sporty sound over stock.

[smokeyfan1000]

Originally Posted by andrewnance21

For the header, i'm going to be using either a Stahl or Ipd. Not the stock downpipe. Im thinking of going with a 2.25" with either a single glasspack or magnaflow straight-thru. Just something for a nice throaty tone and increased flow.

The IPD header (if it's the same one for B20 they've had for years) isn't much good. Bad collector design/execution.

Not as good when compared to other, better designs. Go with the Stahl, or one of the Swedish header for b20. It'll be a higher qulity, and make better/more power than the old style IPD one.

I'd look for(and recommend) a hi quality 4-2-1 design header, as opposed to 4 into one V8 design collector if it's good road/street performance you're wanting

[Dauntless]

I'd go 2.25"

[AndrewNance]

Originally Posted by smokeyfan1000

The IPD header (if it's the same one for B20 they've had for years) isn't much good. Bad collector design/execution.

Not as good when compared to other, better designs. Go with the Stahl, or one of the Swedish header for b20. It'll be a higher qulity, and make better/more power than the old style IPD one.

I'd look for(and recommend) a hi quality 4-2-1 design header, as opposed to 4 into one V8 design collector if it's good road/street performance you're wanting

Yeah, the Stahl is the one I've got but I believe it is 4 into 1, unless I modify it, though I won't. I'm thinking of starting with one Magnaflow like yours and if it's too loud, I'll add another at the back.

[lummert]

I tried a generic straight through 14 inch long oval muffler. Too loud. Ended up replacing the 14 with an 18 inch long. Now my ears thank me.

[smokeyfan1000]

Originally Posted by andrewnance21

Yeah, the Stahl is the one I've got but I believe it is 4 into 1, unless I modify it, though I won't. I'm thinking of starting with one Magnaflow like yours and if it's too loud, I'll add another at the back.

Gonna take 2 magnaFlow mufflers if you're wanting close to being quiet, with no "drone" inside the car. One alone is going to be loud if in 2.25-2.50" pipe system and one MF muffler.

I can hear my car's "exhaust note" inside the car, but there is no bothersome/headaches causing drone

Before I had the 2.5" system made, I did try a stock header pipe , pipe to rear, with a (18" IIRC) CherryBomb glass pack in the passenger floorboard area, and turned it down in front of rear axle, but it was noisy & droned like hell inside the car.

The two magnaflows cured that obnoxious noise.

[iwannadrive]

Originally Posted by Redwood Chair

^

Grab the 60mm exhaust from a 240T in the jy and rework it or get some 2.25 bends from columbia river mandrel bending.

about how much "reworking" does the 240T exhaust require?

my 122s is running just a small single thrush glasspack on the stock exhaust right now, and, although it's got an alright tone when it doesn't "blat" (which it unfailingly does at almost any throttle position around 2-3k rpms), and sounds pretty nasty while revving, it's just waay too loud and droney. I kind of want to keep the glasspack and throw a turbo muffler in the system somewhere.

[AndrewNance]

I've got the interior floor soundproofed so the sound on the inside isn't really my biggest concern.

[JohnMc]

I've got some old 4:1 header on my well warmed B20, with a 2.25 exhaust with 2 16" glass packs.

It's really too loud. It's fun in small doses, but anything over about 15 minutes and you need ear plugs or your ears are going to ring afterwards, and you've probably done some amount of hearing damage. I have a bit of tinnitus now, probably half from that old thing.

[lummert]

Originally Posted by andrewnance21

I've got the interior floor soundproofed so the sound on the inside isn't really my biggest concern.

I have a 1988 Volvo 760 Turbo Wagon with plenty of factory sound deadening. Trust me, if the exhaust is too loud, you will hear it. Even with the windows rolled up.

[gsellstr]

I wonder if you've got one of the old Clifford's IPD used to sell John? Got one of those on mine, circa 1996-ish.