Please, do not post here. As you might guess, I'd like to keep this pretty structured, to the point, and not filled with comments. It will be comprised of key info that the community has worked to document. If you feel you have found some info that should be in this, please PM me with the link to said info. I will take note. No guarantee it will be included, but will do my best to include info that is useful to everyone. This FAQ will also take some time to build, so please be patient. Like most people here, I don't live on the site 24/7. As it is, there is more info concentrated in 7 threads on Holsets than anywhere on the net. The concentration of information on these is far greater than any other turbo in the past here. We are all still on the learning curve even now with new setup info is being learned weekly/monthly as more and more people run them. So again, please be patient. This is a living document and everything can not be known about them right now. Meanwhile... as in the past, if you have general Holset questions, I'd invite you to do some reading in past threads. If your answer isn't found, please post in the current Holset thread, as there are more enthusiasts/users watching it than any other threads and the potential to get an answer will be much greater than creating a new thread. I'd like to also give a special thanks to those of you in the community that have helped make these threads what they are... the best Holset resource out there. Thank you. As a community, we should be proud. I'm going to start out gathering questions that people will ask or more/less catagorize the info. If you have suggestion for a "topic question", please PM me with your suggestion. These are in no special order right now and what comes to mind quickly (I will be removing them as they are posted below in the FAQ.): 3. What type of exhaust housing should I use? 6. What is the issue with the compressor cover and water pipe? 11. How much HP will I make with XX-XX Holset? 12. How quickly will I build boost and at what rpm? 13. What will a twinscroll manifold do for my XX-XX Holset? As this progresses, some of the above topics may get expanded or combined depending on flow of the explanations/info. ^^^ to be deleted at a later date. ************************************************* General links For more discussion history: Link to Part 1: Holset Turbos - DSM Forums Link to Part 2: Holset Turbos, PART 2 - DSM Forums Link to Part 3: http://www.dsmtuners.com/forums/turbo-system-tech/274459-holset-turbos-part-3-a.html Link to Part 4: http://www.dsmtuners.com/forums/turbo-system-tech/303969-holset-turbos-part-4-a.html Link to Part 5: http://www.dsmtuners.com/forums/turbo-system-tech/314629-holset-turbos-part-5-a.html Link to Part 6: http://www.dsmtuners.com/forums/turbo-system-tech/327647-holset-turbos-part-6-a.html Link to Part 7: http://www.dsmtuners.com/forums/turbo-system-tech/353498-holset-turbos-part-7-a.html Link to Part 8: http://www.dsmtuners.com/forums/turbo-system-tech/371627-holset-turbos-part-8-a.html For in vehicle results: Link to Results Only: http://www.dsmtuners.com/forums/tur...-results-only-complete-installed-systems.html Link to HX-52 setup; http://www.dsmtuners.com/forums/turbo-system-tech/307988-holset-volvo-hx-52-dyno-sheets.html For more specific component discussion: Link to Holset Part #'s: http://www.dsmtuners.com/forums/turbo-system-tech/312186-holset-part-thread-only.html Link to Holset oil feed discussion: http://www.dsmtuners.com/forums/turbo-system-tech/244467-holset-hx-35-oiling.html http://www.dsmtuners.com/forums/tur...turbo-users-your-oil-drain-may-too-small.html Link to Fake Holset Info: http://www.dsmtuners.com/forums/newbie-forum/306635-counterfeit-holset-turbos.html Summary provided by wiseman, DSM-onster HX35: The 8blade hx35 has a 56mm compressor inducer. This is found on 1995-1998 cummins manual pickups. The compressor flows 52 lb/min according to the compressor map. The bolton BEP housing (0.55 a/r) is enough to push the limit of the compressor. There's several 500whp 8blade hx35 cars out there with the bolt on housing. It reaches 20+psi by 3500rpms in 3rd with 272 cams. Smaller cams would equal a faster spool speed in most cases. The 7blade hx35 has a 54mm compressor inducer. This is found on the 1999-2002 cummins manual pickups. The compressor flows 60lb/min according to the compressor map and logged results from a member here. The bolton BEP housing with the hx35 turbine wheel do not SEEM to have enough flow to really reach the potential of 60lb/min. But many have logged over 50lb/min so far and seen 500whp. The stock hx35 12cm^2 twinscroll turbine housing is a t3 flange housing. This mated to a NON-divided runner manifold has produced a 132mph trap speed with a full weight 1g AWD. This is about 600whp. So the flow is there with the stock housing if you use a non-divided manifold. The spool speed of the 7blade hx35 is similar to the 8blade hx35 with 20+ psi by 3500rpms in the bolton housing and by 4000rpms with the stock housing with a non-divided manifold. HY35: The hy35 has a smaller turbine wheel than the hx35. And, it has a turbine housing connection that does not allow for a bolton housing to be used. It does not have a divided housing so any t3 manifold can be used effectively with this turbo. It has the same compressor as the 7blade hx35. We don't know if te hy35 turbine wheel and housing is enough to reache the 60lb/min potential of the 54mm 7blade compressor. Some one try it out already!!! It should at least be a faster spooling viable option to the full t3/t4 50-trim. H1C/WH1C: In 1994, there was the Wh1c which has pretty much the identical compressor as the hx35 but with a Vband compressor cover. The turbine wheel is the same. It will bolt into the BEP bolton hx35 turbine housing. It has 4 bolts at the housing instead of 6. So you will need to buy 2 more bolts and use 6 washers cut to make a flat side. Honestly, I just used bolts that were cut a little short and the bolt head was wide enough to pull the chra to the turbine housing. No sealing issues. Since the Wh1c is for all practical purposes an 8blade hx35 the spool and flow is the same too. I have the big h1c. It comes on the INTERCOOLED 1991-1993 cummins pickups. It has the webbing for MWE but no groove cut like the hx35/wh1c has. This turbo I term the big h1c because it has a 54mm compressor inducer and same exducer than the 8blade hx35/Wh1c. The other h1c is the small h1c found on the NON-intercooled cummins pickups. This has a 50mm inducer but only 7blades and has no webbing for MWE. Less blades helps flow, but so does a larger inducer diameter. The most whp ever recorded on a gas 4cylinder with the small h1c was done on a KA24 nissan: 411whp. Since the big h1c has a 4mm larger inducer and the same turbine wheel as the hx35, it is safe to say that it flows enough for between 411whp and 500whp. The diesel sources state that it flows SLIGHTLY less than the early hx35. So 4lb/min less than the 8blade hx35 puts the flow of the big h1c at 48-49lb/min right where a 50-trim or 20g is. The small bep housing is all that's needed to get the most from the compressor and the spool speed is 20+psi by 3500rpms. HX35-40 hybrid: Keeping the long tradition of the marriage of sportcompact and hybrid turbos, there is the hx35 turbine and the hx40 compressor. It is strongly recommended to use the large bep turbine housing or the stock hx35 turbine housing with an non-divided t3 manifold for this turbo. The small bep housing around a t31 size hx35 turbine wheel is probably not enough to merit any of the hx40 compressor wheel upgrades. 20+ psi by 4000rpms can be seen in the hx35/40 with the hx35 12cm^2 turbine housing with a non-divided t3 manifold. With the large bep housing, spool times are to be determined. But likely similar. HX40: The 8blade hx40 has a 58mm inducer and flows about the same as a 60-1 (around 60lb/min) with ALOT better high boost efficiency and spool speed. It is the most common hx40 out there. The small bep housing with the hx40 turbine wheel is plenty to reach the full potential of the 60lb/min 8blade hx40 compressor. 20+ psi by 4100rpms with 272s. The 7 and 6 blade hx40 is called the super40 and has the 60mm compressor inducer. This compressor flows around 69lb/min. You can get this wheel in billet style (think HTA). The non-billet wheel spools as fast as the 8blade hx40 in the bolton bep housing and has done 653whp at 40psi per the holset results only thread. Billet should spool even faster. The t3 .70 a/r BEP housing slows spool about 400rpms. But reports show a significant gain in flow per psi. So expect more power at lower boost with that turbine housing. H1E/WH1E: The Wh1e is like it's little brother the Wh1c. It mirrors the hx40 8blade in every way except that it has a v-band compressor cover and a 4bolt chra-turbinehousing pattern. It will consequently bolt into the hx40 bep bolton turbine housing and this is plenty of flow to max out its 60lb/min compressor. The h1e is like it's little brother the h1c. There are different size compressors. . . BUT there are also different size turbine wheels too. Check measurements before buying this turbo if you plan on running a BEP turbine housing. There are lower flowing compressors than the 58mm 8blade that are out there. So this turbo may not flow any more than an hx35 if get the wrong one. You need at least a 58mm compressor inducer for this to be a worthwhile turbo vs the proven hx35 or 8blade hx40. HX52: This is a big sucker. It is commonly found on the Volvo Semis and usually has a billet compressor wheel. It flows 88lb/min. There is no bolt on housing for it. If you want a bolton housing for this turbo, then you don't want this turbo. In fact if you want a t3 flange turbine housing for this turbo, then you don't want this turbo. You DO want this turbo if you're looking at a gt4294r or gt4202r. The turbine inlet is slightly different than a t4 bolt pattern. You can still get the t4 manifold to work just fine by enlarging the bolt holes. Misc.: Holset's don't spool slow. They spool faster than their garrett or mitsubishi counterparts. Diesel exhaust is cold and slow moving. The holset turbine wheel is a work of art. It has been shown to flow very well in a very small turbine housing. For example the hx40 turbine wheel in the small .55 ar bep bolton housing flows as much as a garrett gt35r turbine wheel in a larger .63 ar garrett t3 turbine housing. The hx40 with this configuration spools about 500rpms faster! You can upgrade to the .70 a/r BEP t3 turbine housing and have the same or slightly faster spool speed as the above gt35r with ALOT more flow per psi and consequently more horsepower per psi. This makes for VERY good pumpgas numbers. Holset patented map width enhancement. They do not have extended tip technology, but there compressors show more efficiency than their garrett or mitsubishi counterpart. They have superback technology witch leads to VERY, VERY durable compressors. The are designed to be overworked and underpaid. There are discrepancies all over the web concerning the compressor maps. Take what you hear/read with a grain of salt and a shot of tequila, and the worm. The holset is fine with stock 4g63 oil pressure from the oil filter housing. If you have no b shafts, you'll need a restrictor. The drain line is a garret bolt pattern. The feed line is different for different turbos.