Old Truck Turbos VS New Ball bearing turbos
 

Can anyone tell my why so many people use the ancient journal bearing truck turbos such as the TO4 on their roatires?

I wouls have to say it would be one of the most common aftermarket fitment Turbos on rotaries. Why is this?

I don't want to cahse massive power, but cool reliable power (by selecting a turbo via the compressor maps and using the most efficient part of the island for the average power).

I've been looking at a GT30R turbo and it would be able to deliver about 350 to 450hp with very high efficiency (cool boost), which would require less intercooling. Alos there would be a heap of power left in it by winding up the boost, ie getting about 500hp with over 70% efficiency.

Doesn't this make more sence than having an old narrow island turbo that only works efficiently in a very narrow power range.

Can anyone enlighten me why anyone would use a TO4?

Cheap, Proven, inexpensive to change ARs, or rebuild. At ~500.00 they are hard to beat, and are dead reliable. Carl

That is a good point, but rebuilding is becomming a possibility as Garrett are learning how to repair or service Ball bearing centre turbos (which they didn't do in the past).

I assume you mean US$500 right? Because you can get a GT30R for about US$800-900 (if you talk to the right people), and if you look at the compressor map of the GT30R and compare it to a GT40 (a modern version/relative of the T04) you can see that the compressor map of the GT40 isn't that much wider than the GT30R.

And here is the map for a GT40:

Garrett GT series turbos are rebuildable, it is not as bad as people want to make it sound.The GT 30R is too small if your looking to make descent power also the GT40 is not ball bearing, but the GT40R is.

-Sean

Sean, is it not true that at present you need to purchase a new cartridge, and that a new cartridge for the 40 is ~800.00 ?
Rtrpwrthe GT30R will not flow enough air to make more than ~400rwhp on a rotary. The 3540 is good for mid 400s, and the 40 is good for ~low 500s. As for cost, I would like to buy a GT40R, PM me with the best price you can get one for, if it's as good as you say, I'll pay you a 100.00 finders fee.
Sean, have any customers dyno'd the 40R kit? Thanks, Carl

It's a very simple answer to me... PRICE.

The MILD difference in performance between a regular turbo and an equivalent but ball bearing turbo just isn't enough to justify the HUGE price difference.

in ten years you'll be asking why we're all still using ancient ball-bearing turbos instead of electromagnetically-suspended-bearing turbos. ;)

price is a big deal. You can get a hybrid t04 that bolts to the stock manifold and stock-location downpipes for $600. Or, you can spend $4k on a ball-bearing kit.

This may be true but you get what you pay for your comparing two different things but implying the same results and that's way off.

well, yes, i know. but i am saying that price is a big deal. and when you're spinning your tires through second gear either way...

Questions:

1) What is the lbs/min of air to HP conversion for a rotary? (i.e., where on the compressor map should one look for, say, 475 FWHP?)

2) Does anyone carry a kit for a GT40R or GT30R?

Thanks,

-ch

Well i know CFM on a rotary is (CID x RPM x VE) / 1728

But your going to have to convert that to lbs/min

For ball parking, I have used 10 lb/min as a general rule, and it works out pretty damn close, if everything else is in order such as tune/engine/fueling etc... It was pretty much on right on the money from my last dyno...Max

I believe A-spec Tuning (IL) have a kit for the GT40R.

Try www.a-spectuning.com

If you can afford a ball bearing then you buy it. If not and you want a rebuildable turbo withoud spending more than 1K then you buy a journal bearing. Simple.

This is untrue I've rebuilt ballistic turbos for under 700 dollars.

-sean

...
 

I believe he was refering to the price of the turbo, not to have it rebuilt.

Alright maybe im just tired, but I cannot figure out what VE stands for. Haha

thanks
M-P

Ha, I wound up answering my own question:

BHP = (Airflow lbs/min) / ((BSFC / 60) * AFR)

So for a 500 FWHP rotary, the lbs/min of air would be:

500BHP * ((0.64) / 60) * 11:1) = 58.7

So a stock rotary (BSFC of .64) would make 500 HP at 11:1 AFR using 58.7 lbs/min of air.

Now what I don't understand is that this figure is WAY off the charts for even large turbos. So how do you properly size a turbo based on its compressor map?

I mean, since most humans are limited to less than 20psi (and probably around 15-17, or a pressure ratio of 2.2:1) the 500HP mark is outside the compressor map of everything smaller than a GT40...

-ch

And lemme add this question: after looking at the 60-trim TO4E compressor:

http://64.225.76.178/catalog/compmaps/Fig16.gif

it would appear that 400 RWHP (or about 475 FWHP, or about 54 lbs/min of air) is way outside the capabilities of this turbo as well. And yet there are those who have put down 400 RWHP with the HKS and XS kits at aroun 17psi.

What gives?

-ch

From reverse calculating my dyno number in combination with my air temps I figured out my t04e was running at about 66% at 400 rwhp, which was done at less than 15 psi, yes the turbo is getting off the map there, but now you have to factor in density recovery of the intercooler, which effectively gives you some of your efficiency back by cooling the intake charge, allowing the compressor to run somewhat out of the "eye" of the map, its very hard to size a turbo to run in the eye right through the rev range, its easier on limited rpm diesels than the engines like rotaries that have about 6000 rpm of range on boost... You can run outside of the eye , you just work the intercooler harder so its not wise to put up with a turbo just cuz the intercooler can mask it, but thats how shifting to a larger turbo gives you more power at lower boost levels in part as well, if you heat the air less initially, the intercooler has an easier time, and will deliver a cooler charge on a larger more efficient turbo, which makes more power...On a smaller turbo once you start to thrash the air you get on the downward side of the bell curve not only on compressor discharge temp, but also exhaust side backpressure...Max

Right, the I/C. Very good. Was your turbo a TO4E 60-trim? Your motor a streetport?

So, for someone who is sizing turbos for their car and valuing throttle response above all else, it sounds like you should look for a compressor map where your target FWHP is just off to the right of the map by 2-5 lbs/min, assuming that you've got decent intercooling?

And on that note, it also sounds like "flat" or "broad" maps are much better than "peaky" ones due to the relative low boost that rotaries like to see for reliability reasons...

-ch

Well the corrected airflow is actually less.

If you have an engine with 54lbs/min the corrected airflow at 60 degrees F would be about 50lbs/min.

Corrected flow= actual flow x sqrt([temp+460]/545)/(14.7/13.95)

PR=(Boost + Pressure Drop of (Intercooler + Air cleaner)+ Atmosphere)/(Atmosphere-pressure drop of aircleaner)

And if you work out the pressure ratio (taking into account the intercooler and air cleaner), you will find that 17psi is a pressure ratio of about 2.4. This corresponds to a point inside the map with a PR of 2.4 and a 50lbs/min flow.

These are some great responses. Thanks for the help here--it makes understanding the single turbo a lot easier,

-ch

I'm actually looking at getting a GT3540 after talking to my mate at Garrett.

It will be a realitvely simple installation with internal wastegate. Dial up 14-15psi use a decent exhaust and intercooler and 400hp isn't far off.

I'm looing at about 350hp using about 11 psi.