HTT Stage 2 issues

[moparguy]

This is a bit long winded, my aplogies. I installed the subject HTT upgrade to my 16cm non-wastgated stock turbo a couple of years ago. I was pleased with the 100deg. or so drop in egts I saw and it seemed to help power. I didn't extablish a baseline so the power bit is subjective.



The turbo works fine at my normal low altitude homebase (200 or so ft. above sea level). However, when we go out West pulling a trailer in the Rockies, I get a really bad case of the barks. Since this is a once a year trip, it took a second trip after the upgrade to figure out what the bearing failure kinda noise was.



Anytime the truck is working in 5th gear in a range of 2200 to 1900 rpm, under a constant pull up most grades, the turbo starts barking, boost drops to zero, then right back up to boost. The only solution is to back out of the fuel or drop a gear and bump the rpm up to 2500 or so, then no problem.



Boost levels don't seem to affect the barking much, it can happen at 12 lbs. headed north on I 25 out of Raton NM, or 20lbs if the rpms drop. RPM is the main culprit, let it drop and it seems the back pressure overcomes the boost and instant bark.



I'm considering porting the stock 12cm exhaust housing, drilling the divider out so it'll relieve the front 3 cylinders and trying to adjust the wastegate so it starts dumping sooner. That and prehaps a 4" exhaust upgrade.



So, what do you'all think, will my changes help and has anyone else experenced this problem.



Thanks, RJR

 

[jwilliams3]

The ported 12cm housing is a good idea.

Or even better I would consider installing a 14cm2 wastegated housing.



I have a buddy who installed a 16cm2 on an HTT like you have and was not very happy; lag and power etc.



On my advice, he switched over to the 14cm2 wastegated and could not be happier.



I think the 16cm2/35/40 combo is too large when you tow with lower rpm's.

 

[BradyWilliams]

RE: 16cm Housing

I agree you need to be using a Waste gated 14cm housing. I have used a HX35/40 with 14cm turbine housing for years, pulling at altitude. No problems! However I use a Phat Shaft Turbo now and that is a lot better. Thanks

 

[CRoth - BD-Power]

What's happening is called compressor surge and it will destroy your turbo. A larger exhaust housing may help as it will lower your boost at a set fueling level and pull the wheel away from the surge line. The problems is casused from the engine not conusming enough air from the turbo, this causes the compressor wheel to stall. A lot of the larger big single turbos have this problem as well, it all comes down to turbo matching.

 

[moparguy]

Thanks for the help. CRoth, I can see a new turbo on the horizon. I did do a gasket match port job on the stock 12cm housing yesterday and drilled out the divider using a 1 1/16th bit which hopefully will waste enough pressure to help.



I'd be open to trying a 18 or 21 cm housing except for the fact that in the past I haven't been able to duplicate the surge at my low altitude. It's only been a problem above 4 or 5000' or so. Not sure I want to live with the lag for a solution that's only needed a few days out of the year.



RJR



added in edit;



Croth, I just reread your comments. And from what I've experenced I agree, the engine when working in the low 2000 rpm range isn't able to consume (flow) the air supplied by the compressor. Having said that, it would seem that the only solution is to supply less air, use a smaller compressor wheel (or port the head, change the cam,,,). No?



I've been thinking that reducing the exhaust side pressure would help since the compressed air charge as well as the engine generated gases would exit with less restriction hence preventing that balanced or overbalanced condition from developing that's upsetting the compressor side of things. I'm starting to think the stock compressor wheel may be best in this application.



RJR