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Hey Guys,

I put about 5k miles on my rebuilt 4bt in a 71 K20 Chevy. Most systems were okay, but my motor got hotter then I was comfortable with. Boost seemed peaked out around 25 psi. I decided to roll the dice on a FB marketplace HY30. After making everything fit, I decided to go ahead and install my custom fabbed intercooler. NOW!! the temps are much better never going over 1k deg and the boost is as good if not better at the top end. Getting 28 max right now. NO drawbacks. I think I will advance the VE pump timing and get a Denny T pin to compliment the 3200 spring.

What I don't know and still don't understand is if the temp was from the restrictive turbo or non-IC. ?? The housings were both 7cm but exducer wheel is much larger on the HY30.
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I think the HY is very close to the HX30 with notable differences. I was thinking that I would change the 42mm compressor wheel and machine the housing to accept a billet 44mm wheel to pep up the HY30. The HX30 and HY30 have very similar comp wheels. Does anyone know about this Mamba wheel on Ebay? Mamba on eBay
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OR perhaps can suggest a good billet wheel. I think the extended tip helps whether or not the diameter changes much. You also see a radial series of holes drilled in the front of the compressor housings, any advice appreciated.

Lastly I have 6bt H1C hanging about and also an HX35, would these work fairly well as compounds over my hopefully modded HY30? I am head studded and would like to hit 40-50psi boost.
Thanks in advance.
Greg
 

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The HX30W and HY30W are essentially the same except for the turbine housing exhaust flange. T3 vs T28. The HE221W is an upgrade of the HX27W. It came with turbine housings ranging from 5.5-7.0 cm2. The one you have would have been the largest. Your heat issue was probably more due to the lack of an intercooler. Engines with these smaller turbos almost always had one. 25 PSI sounds a bit low for the HE221W. Those usually hit 30 or a bit more. A lot of that can be due to fuel setting on the injection pump and timing. Increasing the timing a little can also lower EGT. The compressor and turbine wheels on your HY30W are the same as the 42mm HX30W that came on 4bt's. As far as changing the compressor on your HY30W to 44mm that probably could be done. The exducer on the 42 and 44 is 73mm which would make it easier. There is really nothing bad about the 42mm and in a twin set it does OK. As far as a primary turbo in a twin set the HX35W would get the vote over the H1C. The HX35W usually has a 12 cm2 turbine housing and works better than the H1C. Now the WH1C was the same as the HX35W and it too works well. The ideal twin set is supposed to be a 44mm HX30W paired with a HX35W with the 14 cm2 turbine housing. That last item is kind of scarce in the used market and the 14 cm2 housing is kind of pricey. The 12 cm2 is as common as dirt and that works just fine. Be careful with twins. 40 PSI is about the limit on a stock head gasket even with studs. If you plan to push beyond that you may need the head O ringed. That's not fire ringed which is for all out high performance engines and not recommended for road use. If going to twins you'll need to upgrade injectors to 5x.012. That's about as big as a VE pump will handle. About 300 HP will be near the limits of the pump. In combo with that a larger oil pump and 7 plate oil cooler would be good options. Must also consider the radiator. At 200 HP and lower a stock radiator is generally plenty but at higher power you may need something bigger. Also, some type heat treatment to keep the heat in the exhaust system will improve boost whether you stay single or go twins. Ceramic coating the exhaust manifold, exhaust interconnect, and turbine housings can improve spool speed. Good quality ceramic is not cheap so most go with a turbine blanket(s) as a minimum. Anther add on can be a exhaust back pressure gauge. Can help in fine tuning the boost from each turbo and having more info on the engine when operating is always good. There are even dual reading boost gauges so you can see how much the primary is feeding the total. See photo below.
 

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