Which Exhaust Housing Do I Have?
Diesel Enthusiast
Joined: Apr 2007
Posts: 210
Likes: 15
From: Geary Co. Kansas
If your talkin'to me, shoot me a pm w/details and lets talk!!
Diesel Enthusiast
Joined: Mar 2007
Posts: 350
Likes: 10
From: Port Crane NY
89-91&93had the 18.5 CM exhaust housing, 92 had the 21 CM exhaust housing. I threw a WH1C on mine last week, and the difference is absolutly amazing!!! For a 5 speed truck with the original 18.5, dont waste your money on a 16, pick up a 14CM wastegated. I have the 12CM W/G right now, and freeking love it, but some say its restrictive. I still lost 100 EGT's overall. Its all up to the person really. I'll keep my 12 for my drag racing purposes. (and it'll make a nice top turbo) 
Diesel Wrench
Joined: Mar 2007
Posts: 570
Likes: 63
From: Lake City, KS
Some, but not enough your going to notice the difference. A 16 is really laggy, not as bad on an auto, but still laggy enough. Lotta places claim a 16 cm housing will run 100* or so cooler than a 12 cm, but most everybody I know thats gone that route never sees that and end up ditching the 16 since it's laggy.
Diesel Bomber
Joined: Mar 2007
Posts: 3,910
Likes: 335
From: Capo Beach, CA
Well, a smaller housing will always restrict exhaust flow more than a bigger housing, unless it's wastegated.
The 16cm housing doesn't seem to restrict the exhaust to the point of unstreetable EGT's until you're pushing over 350 HP with only the stock intercooler, though. The 18.5 cm's, and 21 cm's especially, were utilized to make it impossible to melt an engine. Since all of us run pyrometers and are perfectly aware of the possibility of melting pistons and will cut off the fuel at 1250 degrees, we don't have problems with running more restrictive housings.
Now, I really don't understand why they went to the 21 cm the same year they added an intercooler and went to smaller injectors, which was also the same year they dropped the 3.07 rear end. How is an automatic truck with 160 HP engine, a 2400 RPM governor, 3.54 rear end gears, an intercooler and a maximum of 14 PSI of boost ever going to get to 1250 degrees? I never saw my stock non-intercooled 18.5 housing get above 1000, and that was pushing 20 PSI up a big hill for about 4 minutes.
The 16cm housing doesn't seem to restrict the exhaust to the point of unstreetable EGT's until you're pushing over 350 HP with only the stock intercooler, though. The 18.5 cm's, and 21 cm's especially, were utilized to make it impossible to melt an engine. Since all of us run pyrometers and are perfectly aware of the possibility of melting pistons and will cut off the fuel at 1250 degrees, we don't have problems with running more restrictive housings.
Now, I really don't understand why they went to the 21 cm the same year they added an intercooler and went to smaller injectors, which was also the same year they dropped the 3.07 rear end. How is an automatic truck with 160 HP engine, a 2400 RPM governor, 3.54 rear end gears, an intercooler and a maximum of 14 PSI of boost ever going to get to 1250 degrees? I never saw my stock non-intercooled 18.5 housing get above 1000, and that was pushing 20 PSI up a big hill for about 4 minutes.
