24/18's win.

 

^ thats what i needed to hear

 

How about throttle response? On and off the gas? Which one is best at darting in and out of traffic and still provide a fat top end??

I know GT28s can be ordered with ball bearings and can be fitted with water cooling. I understand they spool 300 RPM or so quicker?

Remember, If you already have K24s, the 24/18 is really the best financial choice. No selling your old cores, buying new ones, etc... just use what you have. That alone makes it worthwhile.

 

LOL...GT 28's win. Hybrid GT28's are unparalleled at these activities. Instant power on the track too. I tell people that my car is like driving a high displacement V8.

 

is anyone running true gt28's as opposed to the hybrids? i'd expect that they'd make more power than the k24/18g's

 

That would be an interesting comparison. I decided that as long as I was spending the money on all the adaptations that I would go with GT 30's.

 

I run the straight GT28s with open wastegates using the Vivid setup. Not sure how they fair against a 24/18gs since I haven't raced against one....

 

The numbers I have on the standard MHI 18G compressor wheel put it at:
Inducer: 50.5mm
Exducer: 68mm
Trim: 55

The two compressor maps I have seen differ slightly but put the compressor at a max flowrate of 590-600 cfm at a P/R (Pressure Ratio) of 2.0,
with a max P/R of 2.9-3.0

The Garrett GT2860RS has:
Inducer: 47.2mm
Exducer: 60mm
Trim: 62

And the “updated” Garrett comp map puts it at a max flowrate of 520 cfm at a P/R of 2.0 with a max P/R of ~2.6

Of course the comp wheel is only part of the equation. I don’t have any of the K24 turbine wheel measurements or maps to compare, but I would guess the GT2860RS turbine wheel is a bit more efficient since they seem to be capable of closer HP numbers then the compressor flowrates would lead you to believe, but with the K24/18G still edging out the GT2860RS. Of course stuffing either of these turbos into smaller housings will hurt/change their performance as well.

I used to run a pair of GT2860RS’ in a previous car (300ZXTT) years back when they were first released, and they were great turbos that were very responsive even on a 3.0L.

 

Where to the GT28-71 turbos fit into this discussion? Whould they have similiar numbers to the K28/18g ?

 

Brett,

Can I summarize? 24/18's flow much more so than hybrid 28's because the turbine and compressor on the hybrids are very small (which is why they spool so fast).

Standard GT 28's flow more than the hybrid GT28's but slightly less than 24/18's.

Am I correct?

 

A couple trims available, here is one. GT2871R:
Inducer: 51.2mm
Exducer: 71mm
Trim: 52
Max flowrate @ 2.0 P/R: 644cfm
Max P/R: 3.1

Seems like it could perform similar to the K24/18G if you ran it in the larger Garrett housings and not stuffed into K16 housings as all of the the hybrids I have seen do. Some people on other platforms have found the GT28 turbine wheel to be a bit too restrictive to take advantage of the higher compressor flowrate without running much higher boost levels. I think if you wanted to try the 71mm wheel the GT3071 would be a better match on the P-car for better turbine flow (lower backpressure) instead of having to run higher boost levels to get the same power.

I like Vivid's kit since it allows you to run any of these Garrett GT turbos using their original housings which should outperform the same wheels stuff into the smaller K16 housings.

 

Yes the Vivid kit looks excellent.

I am going w/ GT3076's but considered the 3071's.

 

This sounds like a pretty solid summary to me.

I look forward to your results. If you could do a before and after on the same dyno to compare spool up and power numbers it would be great.

 

Brett,

I will only be dynoing after...28's should be off as we speak (car has been in shop for 6 days now). The true measure is the 60-130. I am doing one on the 20th of Sep.

It will be hotter than when I ran my 6.68 but I should be close to 6 flat nonetheless.

 

sean, you have a stock bottom end yes ?