Hi.

I've been trying to decipher what kind of turbo would be the best match-up for my h22a, with moderate (around 5 or 6 psi) boost, and one having a boost threshold at around 4,000rpm, give or take.

I bought "Maximum Boost" by Corky Bell, and it has been quite helpful, but I get a bit lost in the "turbo selection" chapter..

Thanks in advance..

 

The short answer: Garret GT30R.

The long answer: here's a few tools on how to pick a good turbo for any engine.

http://www.turbofast.com.au/javacalc.html

The best resource there is the "TurboPower" calculator. You enter in the bore, stroke, number of cylinders, rpm, boost, level, etc and it calculates an estimated air flow level. From there you can use the data to read a compressor map. This is what a compressor map looks like:



Air flow in lbs/min is spit out by the calculator. Your pressure ratio is just boost level. Take whatever your boost level is and add 14, then divide by 14. So 6 psi plus 14 is 20, then divide that by 14 and you get a pressure ratio of about 1.43. Then you find what compressor efficiency level that puts you at for that map and figure out if it's a good match. So for this particular turbo, if you were flowing about 25 lbs/min at a pressure ratio of 1.7 that would put you right smack dab in the middle of the compressor map.

Most turbo manufacturers have compressor maps on their websites.

 

What about the Garrett GT25 with a 0.82 A/R trim?

Am I using the terminology correctly?

 

What numbers are you using in the turbo calculator?

Here's what I plugged in.

Bore - 3.425 in
Stroke - 3.57 in
Number of cylinders - 4
RPM - 7000
Ambient air temp - 25 celsius
Engine VE - 110
Boost pressure - 6 psi
Compressor efficiency - 75
Intercooler efficiency - 70

That produces an air flow of 26.7 lb/min at a pressure ratio of 1.43, which is way off the map for a GT25R (there's no plain GT25--the R at the end means it has a ball bearing center section).

The H22 flows a lot of air even at low boost levels so the GT30R is the way to go to insure you don't totally fall out of the compressor's efficiency range at higher rpm.

Oh and I guess I failed to mention that Garrett GT turbos are really freakin expensive. For something more affordable both a T3/TO4E 57 trim and T3/TO4E 60 trim will do the job with efficiency but they won't spool quite as quickly as the GT30R. Of those two, the 57 trim will spool quicker than the 60 trim.

 

Cost aside, do you think that the GT30R 84 trim, 1.06 A/R is better suited than the 0.82 A/R?

 

1.06 is probably too big for an H22 to spool up nicely. The thing about a GT30R on an H22 is that while it is in fact right in the middle of its efficiency range at low boost levels, you're really not making the turbo do much work at all. Better to stick with the .82 a/r for the exhaust housing.

As for where to buy it, I really like ATP Turbo as they were very helpful when I emailed them about some various things I was just curious about.