HX40-PRO arrives soon. It has the larger 18cm housing installed. Technically if this is a twin scroll, half of the scroll should be 9cm correct? So would there be any down sight to running my exhaust through one scroll? Would the inner or outer scroll be better in this setup? Does it matter?

How would 9cm compare to a .55AR BEP housing size wise? I’ve seen a few charts that compare CM2 sizes to AR sizes. Seems every chart I look at is a little different. The AR is a ratio and dependant on the wheel size in the turbo correct? Also does this not change with flange size t3-t3-t6…etc. Anyone have the actual equation to measure this? If the chart below is correct half a 9cm would be larger than a BEP housing. Also how heavy are the holset 18cm housings compared to a BEP?

6 cm2 = 0.41 A/R
7 cm2 = 0.49 A/R
8 cm2 = 0.57 A/R
9 cm2 = 0.65 A/R
10 cm2 = 0.73 A/R
11 cm2 = 0.81 A/R
12 cm2 = 0.89 A/R
14 cm2 = 1.05 A/R
16 cm2 = 1.21 A/R
18 cm2 = 1.37 A/R
21 cm2 = 1.61 A/R

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I was hoping to incorporate a spool valve in my setup. Although I don’t think the standard sandwich style “spool-valve” will fit. I would have to incorporate it into the actual housing. Similar to this…

Quick spool valve built into Turbine - YouTube


Any thoughts?

I spool a Hx40 pro with a 17cm^2 housing by 4800 rpms... But i have a high compression stroker on E85. The spool valve would work great if you were spooling a big turbo but the HX40 really isn't "that" big. If you can find one I would go with the smaller hx40 housing.

The way that guy is doing it in the video would be the best way to do but I would imagine that there would be issues. It seems easy but start throwing 1500* exhaust gas at it and see it if work effectively every time.

well the bolt on BEP housing are .55A/R but the T3 are .70A/R so half a scroll would be slightly smaller.

thats an interesting idea, did it work?

viperlp01 said:

I spool a Hx40 pro with a 17cm^2 housing by 4800 rpms... But i have a high compression stroker on E85. The spool valve would work great if you were spooling a big turbo but the HX40 really isn't "that" big. If you can find one I would go with the smaller hx40 housing.

The way that guy is doing it in the video would be the best way to do but I would imagine that there would be issues. It seems easy but start throwing 1500* exhaust gas at it and see it if work effectively every time.

Click to expand...

Well I guess it depends what you are use to. I don't want to sacrifice my top end with a tiny housing. I also don't rev my setup past 7k. Usually shift around 6800 or so. I like to run tons of boost and low RPMS, that is why I like my boost to build quickly. I've found Engines (and transmissions) will live much longer this way. This isn't a race car. I daily drive this pig, all options AC etc.

The .55 BEP housing is so small it scares me. I think my exhaust to intake pressure ratio would be crazy high. Although it may be fine at 6800 rpm? The 16cm housing may be the best bet as you said. But your stated 4800rpm to reach full boost is later than I'd like. Do you use a twin scroll manifold? I believe "Mr. Peepers" utilizes the twin scroll setup with a home built manifold and was seeing peak boost (28psi) by roughly 3400rpm (hx35). That is more the rpm I was looking for. I realize you don't always get what you want, and I may be chasing my tail here. If the variable vane turbos weren't so huge, they would solve all my problems!

As far as durability... I really don't see an issue? The Turbo II rx-7s had this technology right out of the factory. As long as you use thick steel and weld your "flapper" fasteners there isn't much to fail. The actuator would have to be strong to pull that gate open against exh flow, but I like the design. Just not sure if it's any better than having a proper twin scroll setup. Seems like if It was, OE manufacturers would be using them.

On a side note, maybe you could use a block off plate on each scroll and taper down the exhaust flow and bump up velocity for faster spool until you found a "happy place". No moving parts... no headaches

I know the 18cm housing weighs a fair amount more then the bep .55 one. My Holset came new with the t/s 18cm housing. Then I put the .55 a/r on.

An equation for converting AR to cm^2 doesn't exist because different turbo manufacturers will measure the area (cm^2) at different places in the turbine housing. The charts you find over the internet comparing the two will be, at best, estimates.

I bought my H1E with a monsterous T4 21cm2 housing and had a T3 16cm2 housing bored out to fit the wheel. Spools up nice!

"Nice" isn't very quantifiable.

Them'R'good spoolers riat ther...

massive turbulence before that little hole . but nice try, i like the idea.

just take a dremel and cut the divider out

no, seriousely, i bet you can find a smaller holset T3 housing on here for CHEAP if you just put up an add or ask around. So many people are chokin the crap out of their holsets with the little bolt on housings that there has to be more of the OEM holset units laying around than people know what to do with. if they haven't thrown em away some one would probably give you one to not have that chunk of cast taking up space inthe garage for no reason

yeah, i have one. you can have it

dsmcurse said:

yeah, i have one. you can have it

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see, the great DSM love being spread by the forum members' (what's kept me here 10 or more years )

HE351 is 60mm 7 blade has a 9cm2 single scroll there pretty cheap or maybe a HE351VE check them out

Yep I gotta 16cm,18cm T3's,19cm T4 left since I sold my hx40 so Im trying to move these.

DSMReviver said:

massive turbulence before that little hole . but nice try, i like the idea.

Click to expand...

Actually it's been done over on "the turbo forums" with mild success. There is no getting around some turbulence. If you use a venturi like entry it would greatly reduce it and force more flow through the other scroll. Something like so...



Thanks for the ideas all. I found a cheap BEP bolt-on housing with gated 02 . So for cost and convenience I may just jump on the turbo choking band wagon.

polarmoment said:

"Nice" isn't very quantifiable.

Click to expand...

Yes, I know but without posting up a log or some evidence that it worked I really didn't want make any claims. And I smoked the motor and in the middle of replaced it so I cant supply that.

I've got a hx35W gated housing, 12cm with a welded flapper and an outlet flange I'm looking to possibly trade for a 16cm with an outlet flange or at least enough cash to cover a new one.

dsmcurse said:

yeah, i have one. you can have it

Click to expand...

Well my BEP seller backed out on me. Is this am Hx40 16cm housing complete with WG? If so I'll take it let me know what I owe you for shipping.

Also your PM's are turned off?

Here are some results recorded from the quick spool valve above. Not bad!

Quick Spool Valve Dyno Tuned Comparison Test