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Tippy Tippy is online now
Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 8,477
Holset HX40 on a 3.4L results (LONG)

Thought I'd share my experience with the Holset HX40 on my 3.4L. I have poured hours of time searching the internet for comparable engines (since we are a small group with limited sample size) with different turbos trying to get a good set of data points to fall back on, when or if I were to buy another turbo. Just trying to give back to whomever may need another set of data points to base their decision on, on the exhaustive search for answers.

But first off, I have a Carrera 3.2 converted to 3.4, so although it shares the same platform as a 930, I have different heads (41mm intake ports), headers (1 5/8" with T4 flange), and intake. Most of you guys run SC cams, so my factory 3.2 cams are the exact same specs.

Holset's are not exact bolt ons, but you can easily machine a Garrett style turbine housing in a lathe in a couple of hours. I've done 2 of them myself easily. The Holset CHRA is a tad bigger in most of the dimensions over the Garrett's, so you simply take out a little meat on a few surfaces.

Now, for comparisons sake, I had a 60-1 HiFi previously. This is a 60mm compressor (equivalent to a K27 size?) with a smaller diameter compressor housing limiting about 5-10% of total airflow over the standard 60-1. The turbine is a "P" trim (65mm exducer) using a 0.81 A/R "open" housing.

With this turbo and the factory G50 using a 1 bar TiAL F46 WG, I made the following max boost per gear (reviewing datalogs):
1st - 4.5lbs/0.3bar
2nd - 12lbs/0.8bar
3rd - 14.7lbs/1.0bar
4th - 17lbs/1.2bar (boost creep due to elephant trunk WG circuit)

The car made 431whp around 1.2 bar of boost from the PO. In the 1/4 mile (for performance measurements sake), I managed a 12.4 @ 124 MPH best. Really slow elapsed time compared to the MPH due to lack of boost in the early gears and general lag.

Now the Holset. There are mainly 3 common versions of the HX40; 60mm 6-blade, 60mm 7-blade, and 58mm 8-blade. The 1st 2 are usually the most sought after. I have the 8-blade, 58mm (2mm smaller than the previous 60-1 HiFi); so pretty much the smallest, least flowing HX40 available and least desirable.

HX40's too use a "P" trim turbine. So, this is a somewhat apples to apples comparison. I machined a 0.84 A/R divided Garrett style housing and mounted it up. I maintained the 1 bar spring in the WG and tried it out. Initial results were that the car felt slower. It spooled around a 1000 RPM sooner to 1 bar, but it just didn't have the wallop/sledgehammer in the midrange. Hmmmm, I was little bummed, since I'd seen so many big hp builds.

So, reading and reading and reading more, I realized, this newer style compressor just needs to pushed harder to get the airflow needed to get back the missing power. The 60-1's are pretty much out of breath by 20 PSI (on ~3L engines), but a Holset does not really start to breath until at least 20 PSI, maybe even 25 (people have pushed these to 45 PSI!). So, I bought the biggest springs you can buy for the TiAL which are 1.4 bar. And wow, what a difference!

Where the car would normally feel like it ran out of breath with the 60-1, the Holset seems to keep pulling harder and harder. Very linear power delivery.

Reviewing datalogs, I get the following boost levels per gear:

1st - 9lbs/0.6bar
2nd - 15lbs/1.0bar
3rd - 17lbs/1.2bar
4th - 21lbs/1.4 bar

So, I don't have dyno sheet for this new configuration, but I can tell it makes a decent amount of extra torque due to the car squatting really hard in the 1st-3rd gears. Also, I reduced my 1/4 mile times to 12.0 and increased the MPH to 129.

One thing I've noticed about these higher flowing, modern compressors, are they come on to boost from my experience with a far linear feeling powerband. The older design compressors that seem to be out of breath up top seem to hit really hard, then taper off. I only have my Holset and my friends GT35R on a 965 to compare to though.

He too had a T66 (66mm) turbo with a "P" trim that hit really hard at 1 bar, but once he put the GT35R on, the car just pulled more like a naturally aspirated car; harder and harder to redline, but without the major sledgehammer to the back.

Next, I am going with the Borg-Warner S366 (66mm). This is a 830hp capable turbo that supposedly spools closer to a 62 to 60mm turbo of yesteryears. Although I'll never reach the capability of it's compressor and will be going backwards with slower spooling, I don't mind since the engine will see far less backpressure and far cooler inlet temps under boost. This will be good for bigger tracks I plan on hitting one day. I don't want a turbo that is instantly in boost since it will heat up big time on a big track in South Texas temps.

I hope to have a comparison of this bad boy soon!

Cory - turbo'd '87 C3.2 Guards/Blk, 3.4, 7.5:1 CR P & C's, soon to be 993SS cams and GSXR 750 ITB's fed by 964 intake, Borg-Warner S366 turbo @ 1.4 bar, Treadstone full bay IC, TiAL F46 WG, HKS 1 1/2" BOV, twin 044 pumps, MegaSquirt 2 (v3.57 board) w/EDIS, Tramont wheels (285's rr, 225's frt), Big Reds frt, 993 rr., tower brace, MOMO wheel
Old 04-14-2014, 06:45 PM
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