Big Blue24

Late 94 thru 98 have a 56mm 8 blade compressor with an 83mm outer diameter. 98.5-02 stick shifts and 98.5-00 auto shift have a 54mm 7 blade steeper pitched compressor with a 78mm outer diameter. All of the above have a "HX35W" turbo with a 12cm exhaust housing. Supposedly the older HX35's flow within 1% of what the new smaller compressor wheeled HX35's do. This is accounted for by newer blade design technology.

01-02 Automatics have an HY35 turbo with a 9cm exhaust housing and hard piped wastegate line. The specifics on compressor and turbine wheel size is information that I personally don't have.

HOHN

The problem with the difference between Holset turbine sizing systems and A/R is that the A/R scales linearly with the turbine size, while the Holset rating does not.

For example, if I have a 1.0 A/R housing on each of two turbines, one twice is large as the other in turbine wheel + section radius, then the housing will have twice the area, and hence flow twice as much.

The Holset sizing system refers to the sectional surface area at the area where the housing volutes end (the crease of the "6" or "9" as you look at the housing). Thus, a 14cm housing always has the same area, whether that's on a small turbo or a large turbo.

In some ways, the Holset system is more useful, but for the most part I think the Garrett system of A/R is superior.

kantdrive55

I know a lot of people are going to disagree with me on this one, but everyone seems to be so concerned with the wheel and housing sizes. Honestly all they do is tell you the physical size. The flow characteristics are really what is important. CFM is what you are really needing to know. How much air does it move, and through what rpm range does it move it. I have had maps that show a 57mm wheel flows more than a 62mm wheel. Use the different wheel sizes as a basic guide, but don't take it as the bible of information.

HOHN

To the contrary, Pat-- you are *exactly* right.

I think people have all but conceded that the BW compressor wheel is the de facto standard, thus they refer to inducer sizes only, to make relative comparisons from one BW wheel to another.

As long as they are confined as you describe-- "as a basic guide"-- I don't see the harm.

Any compressor wheel is a tradeoff between flow capability, pressure ratio capability, surge resistance, and efficiency. Some are better compromises than others.

For example, I personally feel that a gasser compressor wheel might work better in the top turbo of a compound setup, where ultimate Pressure ratio matters less. For example, the 56 or 60 trim compressor up top that typically won't have a very favorable PR capability might now be a good compressor option, delivering a more favorable ratio of flow to rotational inertia.

So all that to say that I don't doubt you for a second. Focusing on inducer size alone is a gross oversimplification and misses the importance of the whole package.

JMO

gwirehair

hate to just jump in, but since i just had a new turbo put in 2 days ago, and im somewhat turbo stupid, heres my quesion. 98.5 auto with stock hx35 - replaced it with hx35/40 hybrid (what invoice said) 14cm, 60mm/non-gated. it seems pretty much the same as the stock, although i havent gone to crazy on the pedal yet. i have bosch 300 injectors, afe, and genos straight pipe kit. should i have seen a real noticable difference? im planning on an edge ez pretty soon as well. what should/could i expect with this set up? anything i should be cautious about? i also plan to run boost/pyro/fp gauges as soon as funds are available. any info. would be appreciated. thanks.

HOHN

Turbos don't add noticeable power until you are well past the the limits of the existing turbo.

The 35/40 is an incremental upgrade, and while it's made 400hp, I don't think it's frankly that much of an improvement over stock because it's still the same hotside (turbine).

In my opinion, the hot side of the turbo matters a lot more for performance differences. If you want to make power and drop EGT, you have to step up to a larger turbine that will support more flow.

Otherwise your boost pressure starts to resemble a blown up balloon-- all pressure, no flow. We don't want pressure, we want FLOW. We simply use pressure to try and create that flow. The minute the pressure stops contributing to flow, we need to re-assess things to get back the flow.

With the injectors you have, I wouldn't expect to see any noticeable performance change with the 35/40 turbo. If you had larger injectors, the difference would be clearly noted.

jh

Big Blue24

You need that edge EZ or other boost fooling box so the engine computer will stop defueling. Once you get a boost fooling box, add a boost elbow or pinch the wastegate line. You will unlock the hidden power in that upgraded turbo once you start pushing 35 psi boost with it! Down at the pidly 20-21 stock psi range, you won't see a ton of difference between the two since the stock hx 35 is quite efficient at 20 psi.

HOHN

YOu think he can push 35psi with RV injectors?

Still, you know you are absolutely right about the defueling.

Remember that there are different factory defuel points, and they are different than wastegate setting. For example, the HOs are setup with 21psi wastegate point, but the ECM defueling is at 26psi. I don't know about the SO trucks on that defuel spec.

Honestly, this is a really good thing at times. For example, if you have RV injectors you can just plug the the wg port and ride that 26psi limit and be perfectly safe when towing. No EGT problems at all (unless lugging).

JMO

HOHN

Sorry, I didn't see this post earlier.

In short, it's emissions. The 12cm housing does provide more flow. The smaller housing on the 01-02 automatic transmission models has to do with emissions.

With the manual transmission, the direct mechanical coupling of engine to transmission means that it takes a little time for the engine to rev, even at light load.

But an automatic trans can flash to the stall speed and higher very quickly. This means that the turbo's response needs to be faster/earlier to keep emissions in check.

This is back in the old days where all a manufacturer had to do was tweak an ECM and maybe a little hardware to meet emissions. My truck doesn't even have a catalytic converter-- it didn't need one! Such was the advantage of electronic controls over the mechanical P-pumps.

Now, we have to go to more drastic measures.

jh

gwhammy

So Hohn, what do you feal would be the best turbo for a top turbo for spoolup. I agree with you on bottom end, I like the quickest spooling turbo I can get. I have a s 400 and a new 3b with a 26 cm housing for the bottom turbo. I have a couple of 351 ve off of late model truck and a hx35, a 35-40 and a hy.
You think a gas turbo, which would be in its range in the 25 to 30 lbs boost range would spool quicker? Which one do you think would be the best?

HOHN

Well, In a twins setup you can get away with a somewhat small turbo to help spoolup-- perhaps even a a little smaller than stock.

The Stock charger is, to me, a perfect starting point. It's 1) free, and 2) giving you known performance.

For max spoolup without choking, that means a Garrett BB charger up top. There are GT37 that are commonly marketed for our trucks.

But in a twins setup, you won't need that big of a turbo up top. I've been looking at the GT35, which will bolt to the factory manifold.

You can go even smaller and gain even more response, at the expensive of top-end power. The GT3076R is essentially a "stock replacement" Garrett that will make about the same power but spool WAY faster. Plus you have the option of some turbine housing that will bring the turbo in really early.

This smaller GT3076 will spool a whopping 30% faster than the already-quick GT37 that is marketed as the "performance" single turbo by Garrett. That type of low-end response all but eliminates smoke and in a twins application, can really help with EGT control when towing heavy.

If I was build a hi-dollar twins setup where response was the main priority, I'd build a GT3076R over a GT4508R, with the smallest housing on the small charger and the biggest housing on the big one. An external wastegate would be required.

JMO

RonA

Suppose your primary is putting out 120lbs per minute of air at a pr of 3.3. What pr is the 57mm secondary going to have to run at to move the air into the motor.

HOHN

What's the temp in the intake horn? What is engine RPM? VE?

A 57mm secondary would have to run the same PR as a 62mm secondary or any other secondary in that case.

If you can get the intank temps in horn down to 258F, you'll have to run a PR up top of 2.7 at 2700 rpm.

If you run higher rpm or can cool the intake charge more, the PR can drop as low as 1.9 (3200rpm, 130F intake temps)



jh

gwhammy

How would the hy or the he compare to the turbos you mentioned above. The he351 would be simple as the wastegate can be cut enough to not need a external gate.

HOHN

Stock CTD charger is comparable to GT30.

The later HE series stock chargers are tough to beat for all-around performance.