With all the talk about the new HTA68 turbo, I thought it would be informative to post up a few results from the application of this turbo. It has been suggested that this turbo is somehow both a 16G with the power of a 20G. We had the opportunity to test the HTA on a 2.5L 08 STI, as well as a 2.0L WRX.
Before looking at the results, please save all of us the trouble of not posting up the obvious: Yes, the 08 STI test was not perfect as it was not a real stage 2. Yes I know it would be better on a complete stage 2. Yes I compared it with a real Stage 2 stock turbo. Yes it would be nice to have a 20G 2.0L to compare to. These results are just that: Results. They do not provide all of the information to make a complete conclusion. They do however contain some interesting insights for the more intellectually blessed. Please read on.
** We will have a HTA68 STI Full Exhaust Test later this week.
To start, letís look at the HTA68 on a 2.0L WRX.
This WRX was prepped with a complete stage 2 exhaust, external wastegate, and a set of equal length headers. Ported TGVs, DW850 injectors and 255lph fuel pump. On a 2.0L, I would consider this a bit of a laggy turbo. Power up top was fantastic, and on the 23psi Torco run power peaked at 348whp! 15psi at 4400 rpm, full spool at 4700 rpm.
A logical comparison would be an 18G or a 20G. I didnít have any 20G direct plots to compare with (on 2.0L), but I did have a good 18G comparison.
This comparison shows an 18G-5H-7cm compared to the HTA68 on a 2.0L WRX. Boost threshold with the 18G is obviously better by about 1000rpm. Once on boost however, at the same or similar boost levels the HTA68 performs better. While the 18G can hold 19psi to redline, it is clearly running out of efficiency compared to the larger HTA68. Had I not know what turbos were being compared here, I would have guessed an 18G and a 20G, perhaps even a 20G-6H.
On a 2.0L, this turbo makes great power, but it is a bit laggy (as a 20G might be). For many this would not at all be an issue, and the gains up top for a turbo of this price makes this a good choice if you are looking to make >330whp.
Turning up the boost a bit, let's compare a slightly higher boost level with the HTA68 and the 18G:
Here you can see with the boost at 22psi on the 18G 320-330whp is possible. With the HTA at about 23psi and with Torco added 350whp was touched on. That is pretty good power on a 2.0L with a nice bolt on turbo. The 18G outspools the HTA68 by about 600rpm here.
Summary for the 2.0:
Performance of the HTA68 seems similar to what a 20G might do on a 2.0L. Boost threshold is better with the 18G, but once spooled the HTA68 can outperform the 18G. Give the price point of the HTA68 ( it is at least a few hundred dollars less then the 20G ), it is a good alternative if you are looking for the 330+ whp range on your 2.0L. Obviously if lower end torque and boost threshold is a critical consideration, a 16G/18G might be a better choice.
Let's switch over to the 2.5L space.
For this test, we tuned an HTA on a 2008 STI with an aftermarket downpipe (single cat), and with the STOCK mid pipe and muffler. This is not a real stage 2 configuration, but something the customer wanted to try. As you can imagine the stock muffler is both quiet as well as restrictive. Fortunately we had a 20G customer who also tuned with a stock muffler.
We can start with the results of the HTA68 on the 08 STI:
Boost threshold is very good, stock level boost threshold in fact. Upper end power was not great, although based on the 2.0L results I would suspect this may be caused by the significant backpressure from the stock mufflers. While the turbo could hold a solid 20psi, power was the same rolling down to 19 at redline.
The overall results look similar to a 20G-7cm. Sure enough..
This is not a direct apples to apples comparison for a couple of reasons: First these are uncorrected results, and the 20G tune was done in 30 degree cooler weather. Second the 20G car had the perrin headers, which once hot can help spoolup a bit. If you factor in those differences, these two turbos perform about the same. Similar spoolup, similar power, similar torque.
It is possible that a difference might occur at higher power levels (and with a real exhaust), however I suspect the performance will be close. This new HTA68 is much like a 20G, but of course at a cheaper price level. Nice.
When comparing to a stock turbo, I consider both a more direct comparison with a car also with the stock muffler:
Here you can see how the stock turbo boost threshold was actually a bit worse, but this is comparing a stock downpipe vs an aftermarket one. Once the HTA is in the power, the stock turbo is significantly under the curve. Boost falls off up top, and power is down 50whp.
Switching to a Stage 2 STI setup:
This shows a real Stage 2 STI with downpipe compared to the HTA68 with downpipe but stock muffler. Obviously a real stage 2 to HTA with stage 2 exhaust would be a better comparison, but this is instructive. Consider the thought process here.. You have X dollars to spend on your bone stock STI. What should you do?
In this case, you could spend $1000 on the HTA68, plus perhaps $300 on the downpipe, or $1100 on a complete Stage 2 exhaust. With the HTA you get near factory noise level and a bit more power to boot. On the flip side if you are going to do a stage 2 anyways, the gains are pretty close. Clearly adding the HTA to the Stage 2 would give the best results.
Summary for the 2.5:
Good results on the HTA, but nothing spectacular. Performs like a 20G in this test case. Given the cost is less, it has an advantage. Boost threshold on the HTA is probably a bit better then the 20G in identical test cases (same headers, temp, etc). Clearly an 18G might spoolup a tiny amount sooner, but since this combo can get near stock spoolup in these test cases, why not get the extra headroom of the 20G/HTA68.
I am not sure why anyone would compare the HTA68 to the 16G. Yes it makes more power, but even the 18G outspools it on a 2.0L. The direct comparison would be with the 20G. A 20G 8cm will likely be a bit later in spooling, but might be a bit stronger at higher hp levels.