18.5cm exhaust housing

[formula]

Well, I finally got around to trying out my 18. 5cm exhaust housing. Oo. Oo.



Bottom end lag is slightly more. Boost at cruise is down about 4psi. EGTs at cruise are up about 50 deg. EGTs in the 20 to 35psi boost range are down a good 200deg.



Now for the fun part... ..... midrange and top end power and throttle response is up considerably. Max boost was 36psi with the 14cm gated housing with the wastegate open full. Max boost now is 40 psi. EGTs don't climb as fast as they did with the 14cm but still can get pretty darn toasty with a lead foot. It appears that the 14cm housing was too restrictive and was choking down the exhaust flow in the 1800+ rpm range.



Sean

 

[Midnite]

Well, no one else has posted any replies, so I'll do one...



It almost sounds like you could put a PDR HX40 to good use. Obviously that's quite a bit more expensive than just trying out your old stock housing though. Do you plan on going the HX40 route down the road? I'd love to hear how it works for you if you do.



Mike

 

[nascar mark]

Originally posted by nascar mark

Sean, Actually if I was running a 16cm NW housing I would have 43-44 psi with my setup. The 12 is wastegated and I am dumping allot of boost as the wastegate is fully open at 30 psi. I can hear it screaming help. :{

Sean, your findings are why Piers has always said the n/w 16 is the best all around exhaust housing for our 1st gens because it has the fine balance of good responce at all rpm ranges. The 18. 5 is just that, alittle boggy even with the power turned up. The 12 and 14 restrict alittle and the 16 is just right.

 

[RGT]

would you have to modify the downpipe to put on a 16cm nw? is there any disadvantage to going to a gated 16?

 

[nascar mark]

The n/w 16 is a direct bolt on. The 12 or 14 would require 1. 25" cut off of down pipe to bolt up properly. I have never heard of a w/g 16.



mark

PDR - Black Sheep Racing

 

[formula]

Mark,

I am aware of the 16cm housing being recommended as the best for all around performance. The lag really isn't bad at all, only a little more than the 14cm I was running. It's also way more responsive off the line than the stock setup, even with my new torque convertor.

Originally posted by formula

This may be a bit confusing at first. But, I'm posting this here because it is potentially very useful information for anyone thinking of making power modifications to their truck.



These results are based on measurements I took from the stock H1C turbo with a Banks 14cm wastegated exhaust housing. From 0 - 20 psi boost, the drive/boost pressure ratio stayed just about 1:1. At 22psi, drive pressure was 25psi. At 24psi, drive pressure was 30psi. Couldn't get a drive pressure reading above 30psi because that was the limit of the gauge I was using. When increasing boost from 0-20psi, the EGT rose slowly and steadily from 300 to 750. When going from 20-26psi, EGT rose much faster going from 750-1200 in just a couple of seconds.



This is a delicate balance that is very much dependent on the efficiency range of the compressor (the cold side of the turbo that acutally pressurizes the air). This can't really be changed without changing or modifying the compressor. It appears that when staying within the compressor's efficiency range it will produce cool boost and and a drive/boost pressure ratio of about 1:1. When you start to fuel the engine and produce boost and exhaust gas volume that exceed the efficiency of the turbo, the drive/boost pressure ratio will start to shoot up along with your EGT. Compensations can be made by changing the exhaust housing of the turbo to keep the boost and drive pressures in check. Boils down to: throttle response = smaller 12-14cm wastegated exhaust housing, more fuel = larger (wg or not) 16 exhaust housing, lots-o-fuel = new turbo.



As for the exhaust housing sizes:



For the same compressor, increasing the size of the exhaust housing will... ... increase spoolup time, decrease throttle response, make more bottom end and acceleration smoke, require more rpm and load to produce the same boost as a smaller housing, flow more exhaust gas, lower EGT when under load such as towing (better drive pressure), increase EGT under low throttle, operate more efficiently under high loads, allow heavier fueling while keeping EGT under control.



Decreasing the size of the housing will: decrease spoolup time, increase throttle response, reduce low end and acceleration smoke, make more boost at lower rpm, flow less exhaust gas, increase EGT under high load (excessive drive pressure), decrease EGT under light load, operate more efficiently when under lighter loads such as driving around town and cruising down the highway.



Hope this helps





Cheers,

Sean

I'm not particularly concerned with off-the-line throttle response. If I have the desire to do a hard launch, I can just powerbrake it to spool the turbo (in 4x4 ). Once I'm rolling a bit and have about 5psi boost there is no more lag. It doesn't take much to get to that level, thanks to the new turbo I'm mostly concerned with performance in midrange and top end. The 18. 5cm performs very well in that area.



I originally bought the gated 14cm housing a couple of years ago to improve throttle response. At that time, I hadn't planned on changing my injectors, getting my transmission modified, or putting on a PDR HX35.



I started this thread to provide other readers with some information on the performance of the 18. 5 cm housing with the particular mods that I'm running.



Cheers,

Sean

 

[formula]

Originally posted by RGT

would you have to modify the downpipe to put on a 16cm nw? is there any disadvantage to going to a gated 16?

If you're gonna change from a gated housing to a non gated housing, then you'll have to add 1. 25 inches of length so it'll connect up to the housing. This is easier, because you don't have to deal with the pipe hitting the firewall or the a/c ducting as is the case when you change from a non gated housing to a gated housing.



I just got a piece of 3" tailpipe extention from autozone, cut it to size, and put it at the bottom of the downpipe where it connects to the transfer case pipe.



The non gated housings (16cm, 18. 5cm and the 21cm) are interchangable and will not require any modifications of the downpipe.



I'll second Mark on the 16cm gated housing unavailability/non-existence. I looked for one, and could not find one anywhere. Also, a wastegated housing will cost you 3x's more than a non gated housing (new).



Sean

 

[formula]

Originally posted by Midnite

Well, no one else has posted any replies, so I'll do one...



It almost sounds like you could put a PDR HX40 to good use. Obviously that's quite a bit more expensive than just trying out your old stock housing though. Do you plan on going the HX40 route down the road? I'd love to hear how it works for you if you do.



Mike

Thanks, Mike



I've thought about putting on a HX40. But I probably need to find a bit more fuel and some airflow (cam) before I go that route. For now, I'll be waiting for springtime to roll around so I can get in on the next dyno day and see where I'm at. Also, I'd like to do some towing and see how I like the performance of things in that area.



Sean