OMG!!! Twins Rock part II

[HoleshotHolset]

My experience with turbo gassers.....



I've worked on cars with anything from . 63 A/R to 1. 40 A/R... .

Anything from 15's in the 1/4 mile to 8's in the 1/4 mile.



Like I said... it's a ballpark figure.



Matt

 

[StakeMan]

Originally posted by KatDiesel

been waiting for someone to ask.



which turbo?

What ever you are running now is fine with me.



I don't think this will be a good comparison tho.



12 valve to 24 valve

 

[Mark_Kendrick]

Actually, the chargers shouldn't care what's driving them. There will be minor differences but it should still be an interesting comparison.

 

[Diesel Freak]

HoleshotHolset,



if I had a turbine with a 3. 63" exhaust exducer diameter, and a 3. 98" major diameter, what would you estimate a . 96 A/R, a 1. 15 A/R and a 1. 32 A/R



would the A/R change if I had a 3. 85/4. 23 turbine?

 

[HoleshotHolset]

DF:



You want me to do math? No thank you.



The A/R is a quantitative figure that determines the relative ratio between the internal area of a given cross sectional part of the turbine scroll and it's distance (radius) from the center line of the mainshaft.



The A/R ratio is a neat way of putting a number on how big or small a turbine (or compressor) housing is. Since the cross sectional area of the turbine housing is quite large at its inlet and slowly necks down towards the outer edge of the pinwheel... . it's kinda hard to quantify this relationship without a ratio that pinpoints the cross sectional area by using this numerical constant.



Since both turbine/compressor housings can be machined or extrude honed for different combinations, the resulting A/R ratio is something entirely new the minute you start doing any work like this.



As far as how A/R affects flow and spool... it's becoming more and more common to see . 96 and larger A/R ratio turbines on 3. 0L gasser engines... . and they spool quite nicely.



1. 40 and larger A/R's have been used for years on 4. 1L gassers..... so A/R and engine displacement relationships are still valid, yet not as critical as they used to be... due to ball bearing CHRA's, advances in turbine/compressor shape/pitch and lighter materials used in compressor/turbine wheels... . not to mention VGT/VNT... .



Matt

 

[StakeMan]

TTT



Still looking for those drive pressure #'s, kat.

 

[Jim Fulmer]

Drive Pressure

1 to 1 throught the band, no difference, no spikes and no changes when the wastegate opens, proves my theory, or guess that it would work, Now I'll try an 18 housing!



Jim

 

[J.R. Adkins]

 

[StakeMan]

TTT

 

[StakeMan]

Kat,

I guess we should assume that you don't have the drive pressure info that you said you had.

 

[KatDiesel]

Sorry was gone for about a week, until yesterday.



No I don't have the info sitting right here. Never claimed to. Kurt had some information on the B1 a while back which is what I was refering to. I was gonna test it for the heck of it but just haven't done so as of yet. Was asking which turbo people were interested in, I'll try to get Floor It's B1 (big one) and my B1 and test'em sometime soon. I have a 0 to 100psi Oil pressure gauge for drive pressure.

 

[StakeMan]

Originally posted by KatDiesel



I would imagine most poeple don't ask what drive pressure is like when buying turbos, because they either don't care or don't know what it is and how it is important. Drive pressure was discussed when I purchased my turbo.

 

[Mark_Kendrick]

I notice that the singles can get drive pressure down w/a big enough housing but have trouble with EGTs



you end up with a trade. more air out and less in. It causes an overfueled condition that drives up egts. If you get enough air in tho get the egts to drop then you have a diminishing return because drive pressure is up.



I still like the B1 as a single turbo but singles will never match the HP and driveability of twins unless you get exotic... like VGTs.



So Kat,

When are you gonna get to the drive pressures to give us something to compare to. Maybe you can get Kurt to help you out with a little data. If I had it I wouldn't post it w/o his permission.



Does anybody have any other turbos they want to compare them to?



I welcome it. I'd like to know if I'm doing as well(on drive pressure) as some folks say.

 

[StakeMan]

TTT



Still waiting. .

 

[BushWakr - RIP]

Ok, whistle on the play... . will you guys entertain a question from a relative virgin on this topic???



Is it possible to generalize on what an acceptable 'spread' is on a single? Specifically if your running 30 psi boost what is the 'acceptable' level of drive pressure beyond 30 psi. eg: 30 boost/ 35 drive, or 30/40 sort of thing.

Is this a situation were, for example 30/35 is 'acceptable but 25/30 is not?

Or is this not quantifiable in a general sense? I'm asking on behalf of the 1st Gen guys, who are trying hard to follow this thread, which by the way is top notch stuff. .



Bob.

 

[Diesel Freak]

Let me see if I have your question correct.



You are asking basicly. When does Drive pressure become to large of a factor?



the way I see it, I would like drive pressure to be equal to or less than boost pressure, but not higher than boost pressure. However this is not always possible when dealing with a stock turbo running at elevated boost pressures over 20 psi.



But to answer your question... . I guess it would be when you can no longer use higher boost pressure from the existing turbocharger to lower EGT. . or if drive pressure is 50% higher than boost pressure it is time for a larger housing, or possibly a completely different turbo.



But that is just a guess.

 

[Diesel Freak]

you also asked if it is quantifiable. well honestly it is not. here is why.



Assume you have a wastgated turbo set to limit boost to 20 psi. The turbo spools to 20 psi by 1500 RPM at WOT. For arguments sake drive pressure is 15 PSI.



Then we accelerate the engine to 3000 RPM at WOT. Air demand of the engine has basicly doubled. The turbo is still boosting to 20 PSI. Because of the higher air demand of the engine the turbo has to spin faster to maintain 20 psi of boost. To spin the turbo faster we need more exhaust energy... . in the form of drive pressure. Drive pressure is now 25 PSI.

 

[Steve Campbell]

This is not scientific....

... . but I checked my drive pressure a couple of months ago. DD1's and EZ ans stock HX35/12... ...

10/boost=10lbs/drive

20/boost=30lbs/drive

30/boost=45lbs/drive

..... I need a larger housing????? (knowing I will loose some low end response. )

 

[Diesel Freak]

Re: This is not scientific....

Originally posted by Steve Campbell

[B

..... I need a larger housing????? [/B]

only if you can not keep EGT down below 1200 on a long hard pull.



With DD1's and an EZ this "should" not be a problem.

 

[Mark_Kendrick]

Bush Whacker, DF,



From what I've been told drive <= boost is nirvana anywhere above 20-30 psi of boost. Less than boost being a realtively small amount. . 1-5 psi for instance at 60+ psi and be sure EGTs are in check.



Powerstrokes run 1. 5:1 on a regular basis. CTDs do too when turned up a bit.



The real trick is to keep drive pressure and EGTs down at the same time. getting drive pressure down can be done with a bigger housing but how much fuel can you burn at 50psi of boost and still keep egts in line? You will reach a HP level with a turbo and intake system after which some other power adder is necessary to keep EGTs down. Water/Alcohol injection, Nitrous, or something of the like to either add oxygen to the mix or get the temps down and make the charge denser.



On a single, >40psi makes compressor outlet temps soar. partly due to the heat of compression then the increasing lack of efficiency of the compressor.



Compund turbos combat temps on volume and tempreature. If properly tuned both compressors will stay in the efficient part of the map so all you have to deal with (for simplicity's sake) is the heat of compression. Hopefully the turbos won't add any unneccessary heat.



The heat generated by compressing 1000+ cfm of air to 60 or 80 psi is immense and the cooling systems on our trucks will become heat soaked in short fashion, limiting the duration of sustained extemely high hp exertions. EGTs don't rise much but coolant temps do.



FWIW,

Mark