ccarlisi

I am considering 2 turbos for my 20B project: GT42 and TEC HT400 II.



I’m shooting for 600rwhp at less than 15.5psi. I have a 35R on my 2 rotor car and I am very happy with the power curve; near instant boost response from 3400rpms+ and pulls hard all the way to redline at 15psi. For the 20b I would like to duplicate and amplify the 35R curve. To put it another way I’m looking for 200rwhp per rotor. For the 2 rotor that required a turbo that flows about 60lbs/min at 15psi. To hit 600rwhp on a 20b I believe I will need a turbo capable of moving 85lbs/min at 15psi. I base this number on anecdotal information, a conversion factor that I derived based on a couple reliable dyno charts and one created by another forum member.



Among the turbos I am considering are the Turbo Engineering Corp (TEC) HT-400 II and the large Garrett GT42. Based on my initial read of the 2 compressor maps the TEC appeared to be the better choice; the TEC sweet spots ‘appear’ to be wider than the Garrett and the TEC map goes further up the airflow scale. However, after looking at the maps closely I have a couple observations.

1. The image of the TEC map is stretched wider than the Garrett map –meaning the difference in width between them is due not only to the Tec map having a larger scale (indicative additional capacity), but also because the picture itself is wider.

2. The Garrett map is cut off at 70% efficiency whereas the TEC map extends down to approximately 60%.

In order to compare the two units better I overlaid the maps and match their scales. After doing so, the GT42 looks like the better choice. The Garrett is more efficient at virtually every point above 60lbs/min at a pressure ratio of 2.2. While the Garrett map does not extend above 85lbs a minute as the HT400 II does I believe that the Garrett would also be able to get to this output level at around the same efficiency level as the HT400 II, considering their efficiency levels at comparable pressure gradients.



Finally, the leading edge of the Garrett graph extends down below a pressure gradient of 1.8, whereas the HT 400 II bottoms out at 1.8. While it is possible that TEC cut off their graph vertically in the same manner that Garrett cut the GT 42 graph horizontally, I don’t think it’s reasonable to expect much from the HT 400 II below 1.8 considering the shaft speed is under 56k.



Anyway, this is where I am with my thought process. If anybody agrees/disagrees with my analysis please feel free to make comments/suggestions.

qwester007

That map of the ht is all stretched out- If performance numbers are similar, I would always recommend Garrett. More all out race cars use them. Quality is important at 50,000+RPM.

rotor_dee

Check the compressor/turbine speeds. One thing to consider is that the ht has a slower compressor speed to flow equal amount of air.



one of the all out race cars that doesn't use garret gt turbos due too the high failure rate

ccarlisi

[quote name='rotor_dee' date='May 25 2005, 04:38 AM']Check the compressor/turbine speeds. One thing to consider is that the ht has a slower compressor speed to flow equal amount of air.



one of the all out race cars that doesn't use garret gt turbos due too the high failure rate


[/quote]



Hi Dee,



Thanks for the input. I noticed that at 2.2 the HT-400 II is near the lower-middle part of the shaft speed spectrum. That is one of the things I wanted to compare to the GT42. Unfortunately, Garrett does not list the shaft rpm on their map. Given where the HT-400 II is at 2.2 I'm concerned it may be moving too far down the shaft speed spectrum at lower boost levels -does this matter?



I'm definately not sold on ball bearing center sections. The 3 people I know that have used Garrett ball bearing center sections have had them fail. I have a plain bearing 35R on my 2 rotor. I spent a lot of time driving another FD with the same specs (even the same map), but with a ball bearing 35R. There was no appreciable difference in spool up or response.

supkilla

I like compressors that have lower shaft speeds usually a indicator effecient compressors.







[quote name='ccarlisi' date='May 25 2005, 07:31 AM']Hi Dee,



Thanks for the input. I noticed that at 2.2 the HT-400 II is near the lower-middle part of the shaft speed spectrum. That is one of the things I wanted to compare to the GT42. Unfortunately, Garrett does not list the shaft rpm on their map. Given where the HT-400 II is at 2.2 I'm concerned it may be moving too far down the shaft speed spectrum at lower boost levels -does this matter?

I'm definately not sold on ball bearing center sections. The 3 people I know that have used Garrett ball bearing center sections have had them fail. I have a plain bearing 35R on my 2 rotor. I spent a lot of time driving another FD with the same specs (even the same map), but with a ball bearing 35R. There was no appreciable difference in spool up or response.


[/quote]

rotor_dee

have to agree with sup on this one, lower compressor speeds tend to be a indicator of how effecient a compressor is.



Dee

Zero R

I would have to disagree on the high failure rate, not saying you didn't experience it. Just saying my experience has been different. I have had hundreds of these turbos go through my shop.These are all on everything from 12psi daily drivers to 32+psi drag cars. Piston and rotary. One has failed. This was due to the owner putting teflon tape on wrong and it getting into the bearings. They literally **** themselves out the drain along with nice stringy white tape.

ccarlisi

I have added the T-76 to the comparison. Surprisingly it looks very similar to the large GT42. I'm still not sure either of these will be good for 600rwhp @ 15psi so I am trying to find some real world success stories before making a decision.