What does the HTT compressor actually do?

[Begle1]

I've never actually learned...

What's the difference between aftermarket and stock, and what does the difference result it?

[wannadiesel]

Blows more (higher volume) air.

The II an III upgraded compressors have a larger inducer (small part you can see with the intake off) than stock, which allows them to pull in more air. The IV has a compressor wheel that is larger than stock.

They all flow more air than stock, and because they have MWE slots they don't surge at low RPM and high boost.

[Begle1]

Wouldn't a larger inducer make the spool up slower?

It has to have some sort of downside, right?

[90firstgen]

I went from a 50mm wheel to the 56mm wheel. I didn't go for anything bigger because I was planning on intercooling it at the same time. I knew the intercooler would add some lag and I also thought that the bigger the wheel, the more lag. Turns out, I didn't go the I/C route and just changed the wheel. The turbo actually spooled faster. It's a trade off between the added weight of the wheel and the more air it pulls in per turn. I was reading one of corky bell's turbo books and he mentioned how the compressor wheel doesn't really change lag that much. Most of the weight is in the turbine wheel. I don't know if the bigger uprgades add any lag or not. I'm guessing you could at least go to the stage 3 and not feel any more lag. The stage 4 might be a bit different since the exducer is bigger... but I don't really know. That's for the people that have them to decide

[JLeonard]

I modified my baby H1C by replacing the compressor wheel with a larger one and housing (with MWE slot) from a 94 WH1C. At the same time I also built a custom 3 inch crossover pipe.
I got a little more lag by doing this, but then added some fuel (via the fuel screw) and that got it back to where I was.
The benefit for me is that the truck really likes to run at highway speeds now...much better than before and I have instant power in the mid to upper rpm range, hich suits the type of driving I do.

[CAJUN 93]

I installed my stg iv at the same time as the 16cm housing. it actually spools faster than the stock turbo with the 18.5. what amazes me is the rate of climb for the boost. 35mph in 4th gear @ 5 lbs boost, stab the throttle and boost jumps to 25 almost instantly (i'm not exaggerating, it really climbs fast) then continues to climb to 30 lbs @95 mph. makes it really fun to drive in traffic. btw, the pyro will hit 1300 on the above run, it would bury it with the stock housing.

daryl

[Begle1]

Alright, so now that we've reaffirmed that I want one...

A HX-35 essentially has a Stage IV intake from the factory, right?

So it wouldn't make any difference if I got an intake and 12 cm w/g exhaust on my H1c, or if I got an HX-35?

[gman07]

The HX35 basically has a Stage I upgrade. It has the 56mm inducer versus the stock 54mm (intercooled) or 50mm (non-IC) wheels, and it has an 83mm exducer (same as stock). The Stage IV is a 60mm/86mm wheel.

[Begle1]

One more thought then before I get a stage IV...

What compressor would be best in combination with the HT3B that I'm going to add in a couple years?

[dazedandconfused]

One more thought then before I get a stage IV...

What compressor would be best in combination with the HT3B that I'm going to add in a couple years?

I would like to know this as well. I need to get other things done to my truck first though

[MikeThomas]

Would mounting the components left over from a stage 4 upgrade (backing plate, impeller, housing) from my H1C truck be an "upgrade" for the "baby" H1C?

[90firstgen]

One more thought then before I get a stage IV...

What compressor would be best in combination with the HT3B that I'm going to add in a couple years?

Well you need to have an idea of how much boost you'll be running with that turbo. There's obviously some exponential equation when it comes to figuring out how much the boost is multiplied by the second turbo. One thing I'm not sure on is whether you'd say you're running 50 psi out of that turbo, or whether you'd say that you're compressing 15 more psi to make "x" amount of boost. Somebody smarter than me can clarify. But once you've established that, you get printouts of the compressor maps and see which one is pulling more lbs./min. in at that certain boost level (whether its 50psi or 15psi). That needs to be the determining factor on choosing wheels. Does that make sense? It's kind of hard to explain it on here.

[90firstgen]

Would mounting the components left over from a stage 4 upgrade (backing plate, impeller, housing) from my H1C truck be an "upgrade" for the "baby" H1C?

Yes sir.

[gman07]

Well you need to have an idea of how much boost you'll be running with that turbo. There's obviously some exponential equation when it comes to figuring out how much the boost is multiplied by the second turbo. One thing I'm not sure on is whether you'd say you're running 50 psi out of that turbo, or whether you'd say that you're compressing 15 more psi to make "x" amount of boost.

The turbo isn't really "adding" pressure, it's multiplying the atmospheric pressure that is already there. With most turbo maps, you'll see a PR on the left side instead of psi. The pressure ratio (PR) is just the ratio of the pressure after the compressor to the pressure before it. For example, let's say a compressor is efficient to a pressure ratio of 3:1. Atmospheric pressure is 14.7psi; that compressor is efficient to 44.1psia, or 29.4 psig.

With twins, you're basically just multiplying the pressure... twice. If the primary is operating at a pressure ratio of 2 and the secondary operates at a pressure ratio of 2 as well, then you'll end up with a pressure ratio of 4, or 58.8psia (44.1 psig). This way you can achieve higher pressure ratios while still not exceeding the compressor map of either turbo.

So if you want to end up with an efficient 60psi boost (a pressure ratio of 5.1) and you have a primary that will efficiently provide a pressure ratio of 2.2, you'll need a secondary that's in it's map at a pressure ratio of 2.3 (which isn't hard to find).

The advantage of the HTT upgrades is found more in flow than in pressure. The wheels are taken from H1E's, which are on 8.3 L Cummins engines. They're more efficient at higher flow rates, which is why they're good at higher RPM's on 5.9's. As for picking a wheel for twins flow-wise, I'm pretty much lost...


This is the "basic-est" of basics on twins, based on what I've learned from reading. I ignored efficiencies as well. Feel free to correct any inaccuracies you find

[90firstgen]

Good explanation gman. I'm on the same page as you, just having a hard time explaining it. If I were to build a set, I would look at how many pounds of air per minute the wheel would pull in. That's just because its easier for me to see which wheel will be pulling more air in at the boost level I set the wastegate to. So if the stage 3 pulls in more pounds per minute at 15psi than the stage 4, for example, then I would use the stage 3. But I do not know which is more efficient in that range without looking at a compressor map. Of course I could be a complete idiot for doing it this way instead of looking at the pressure ratios