HOHN

I'm considering having HTT upgrade the cold side of my turbo using a 60mm wheel. This would give me an HX40 compressor mated to my oem 35 turbine side with the 12 housing (it's cheaper than buying a new 14wg to go with it).

Now, my gut tells me that the 12 hsg is too small even with the stock 35 compressor, and putting on the 40 wheel will only make things worse.

Then I get to thinking that this might not be the case. Follow me, here.

First, I live in altitude. Spoolup is the SINGLE most important factor to driveability, low smoke, and fun. This points towards a smaller housing.

The thin air of higher altitude makes the job of a smaller 56mm wheel tougher. The little wheel has to spin faster to make X amount of boost, and this pushes it off its efficiency map much sooner. For example, the 60mm wheel should have much lower discharge temps @ 30psi boost than would the 56mm wheel, especially in high altitude!

But there are drawbacks, here.

1) the heavier 60mm wheel MUST spool slower than the 56mm 35 wheel.
2) If the turbine housing is on the small side for the 35 compressor (and it is, due to emissions), then the mismatch would seem to be even worse pairing the tightest 35 housing with a 40 compressor.


Holset's smallest housing for the Full HX40 is 16cm. There's probably a reason for that. Keep in mind that this is also paired with the 40s larger (and failure-prone) turbine wheel, so the 16cm turbine section of an HX40 flows a LOT more than would a 16cm housing would on a 35's turbine, because the wheel is so small.

So here's what I would expect from a 35/40 with my 12 hsg:
1) slightly slower spoolup
2) Lower boost@ cruise, w/ higher EGT on average
3) Slightly lower WOT EGT for a given boost. IOW, at 35psi, the big wheel is moving more air.


I'd like to upgrade my turbo, but I'm afraid of taking a step backwards. Why? Well, slower spoolup is one thing, but I also think EGT may get higher because of the tight housing and small overall turbine section. It stands to reason that the 60mm wheel would take more turbine hp to drive, increasing drive pressure. This higher drive pressure may only make EGT worse on the top end.

So, if a stock 35 can get CRAZY high drive pressure once you get to the outer limits, would a 40's larger compressor wheel make it better or worse? I don't want 50psi drive at 30psi boost.

Please help me out if you have experience with this upgrade (or a Dodgezilla).

jh

Ponci

The 35/40 with a 12cm housing works great with lower fuel settings. On the higher fuel settings the drive pressure will go through the roof. I have found that the most effecient boost level with lower fuel setting is 38psi. At that level the intake charge is still fairly low. At 38psi of boost the drive pressure is around 57ish. That is with some modifying of the wastegate flapper on how you control it. Hope this info helps!.............Brad

sleds

I'm pretty sure the compressor wheel is 54mm on the 24v's and 56 on the older 12's. This was the first turbo upgrade I did and I couldn't beleive the difference in power and egt, but I was running a 16 nonwastegated housing. Low rpm egt's didn't change but they were alot cooler up higher. Spool up wasn't much slower than the stock charger and I also live at 5000ft. I think the setup your thinking about would be awesome with an external wastegate to properly vent all six cylinders to keep drive pressure down and not use your existing wategate on the turbo.

WideOpenThrottl

Well I will be able to get you some results on the 60mm conversion this weekend. I have the 60mm wheel and housing with me and will be installing them this weekend, i have a 14mm w/g exhaust housing on it already though.

But I would think that your spool up speed should not change much at all if you do not change your exhaust housing. Since the compressor wheels are directly connected to each other they spin at the same speed no matter what, so spool up should be affected by the exhaust side only i would think.
Your boost should not be more because it is limited to your wastegate setting. the 60mm housing will move more air but should not achieve more boost pressures if your waste gate is working properly, at least thats what i would think, someone fill me in if i'm a little off.

I will respond this weekend once i get it installed, it does require some minor lathe machining to fit the bigger wheel.

HOHN

I've modified my OEM wg to vent all 6 cylinders. The housing's also been ported a bit, so it's probably more like a 13 housing.

Before I modded my turbo, I could hit max boost (32 psi at the time) in 4th, 5th, and 6th gears. Now I can only hit max boost in 6th.

I don't see a need for an external gate yet-- not at my power level. Certainly, the cost/benefit isn't favorable just yet.

HOHN

Spoolup WILL be slower. It has to be. You are spooling a larger, heavier compressor wheel. More mass means more inertia. More inertia means slower spool.

It's probably won't be MUCH slower, though.

HOHN

As posted, I've modified my WG flapper to gate all 6 cyl, but I'm still intruigued by the Hobbs-based WG control.

I can't say I'm really happy with 57# drive @ 38psi boost! If anything, it just seems to prove that the turbine section is too small for the compressor wheel.

Do you have boost/dp figures for lower boost levels? I'd probably dial this thing down as low as I can and still have EGTs be reasonable. How about 35psi? 32psi? 30psi? I'm guessing that boost and drive track pretty close to 1:1 until about 27-28psi, where drive starts to outpace.


The other element to this is that I'm considering twins down the road, and I think that a 35/40-12WG would be a VERY good, quick top charger in twins, because you'd be gating it before the drive pressure got crazy. It should spool VERY well on top.

G1625S

I'll be trying that setup soon myself. I think Wannadiesel ran it for a while, only he was using the HTT stage IV, which is 62mm, I believe. That is the size that needs the backing plate modified. Paul from HTT said that the stage III (60mm) will bolt up to my H1C or an HX35 without modification. He also recommended against the 12cm. I would say that after a slight lag it would probably spool too fast with a 12 at lower revs, leading to the dreaded bark. Even then, with moderate fueling and thin air my gut says it'd be a great daily driver combo.

RowJ

Justin
Just to give some comparison data...

As best as I could ever determine, the KSB-1 I had was a non WG 12cm2 housing on a 60 or a 62mm compressor bore. I picked these bits of info up from several different threads....for, as you know, the B-1 manufacturers are very tight with info....and do not use Holsets measuring system.

Anyway, with a bullet proof shaft and oiling system...this was/is one hell of a turbo! TIP was 45# at 45 psi.

Based on these ball park facts, I would think you would love your new turbo...as you describe it....if not overloading the stock shaft??

Based on what you have already done to your housing, I think your idea sounds worth trying.

RJ

WideOpenThrottl

Well i'll soon find out how much slower it spools even if it is noticable, i don't think there will be much difference, but i will be adding more fuel at the same time(different plate).

WideOpenThrottl

I just recieved the 60mm housing and wheel from HTT last week and there is some machining required for the hx35 (given in the provided directions), i does not bolt up, its just minor machining though, manual lathe work.

RowJ

I don't think this is accurate. The "little wheel" does not spin as fast as it has to to reach a certain boost level....It spins based on available pressure...and reads what ever boost results! HP and boost is less at altitude, but discharge temps per a given boost level are no more. That's the way my mind see it, anyway.

RJ

HOHN

RJ-- the only problem I see is that we can't draw comparisons between the Holset and B1 sizing systems. The "size" of the B1s is just what some guys like Rod Snaith (Wildcat diesel) came up with based on how it seemed to perform. AFAIK, there was no measurement actually made.

And even if the housings WERE the same size, they would STILL performance differently because the B1s have a larger (much larger) turbine wheel. This means that the SAME turbine housing size on a B1 will yield a larger A/R than it would on an HX35.

This is why the 16cm housing for an HX40 flows a LOT more than 16cm housing for the 35-- the larger pinwheel of the 40's turbine side makes it flow more even with the same housing size.

SHARPMACHINE

At what altitudes do things change? I am only at 600' above and am thinking about doing the same thing as soon as I add some sticks and a #100 plate. I want to take my little 35 as far as it can go to maintain a great street truck as others are saying.
Sorry I don't have much to add. thanks

G1625S

''I just recieved the 60mm housing and wheel from HTT last week and there is some machining required for the hx35 (given in the provided directions), i does not bolt up, its just minor machining though, manual lathe work.''

oops, sorry about that. Must be H1C specific information. Thanks for the correction.