Tibbi

My drive in the Vt this weekend has made me a bit cautious about how to approach my beta build. For a long time I was pretty sure I wanted a GT-K 550 but never saw a compressor map one.

Even after talking with people from Turbonetics they agreed the 550 was probably the best fit. Today I finally found a compressor map....... and raged.

http://s14.postimage.org/78d73wuo1/GTK61.gif

Now if I am understanding things correctly most manufacturers rate their turbos at 15psi when they give HP ratings. And using the formula I found here (which has been confirmed by several other sites) at 15 psi and 6000 rpm a standard beta will be pushing 398.29 cfm or more importantly 27.55lb/min. That means that at our max curve, the car is, at best, just touching the tip of the available boost on the GT-K 550. I'm using 93% to calculate for Ve (volumetric efficiency) because I am doing a bunch of head work but the beta heads really don't flow all the great to being with.



Formulas:

CFM = (L x RPM x Ve x Pr) / 5660

CFM = (2 x 6000 x 93 x 2.02) /5660 ~ 398.29 cfm



Now convert to lb/min per this formula

lb/min = P(psia) x V(cu.ft./min) x 29 / (10.73 x T(deg R))

lb/min = (3.949 x 398.29) / (10.73 x 545) ~ 27.55



Numbers plotted on comp map:

http://s11.postimage.org/40n3843gj/15psi.png

The red line is at 6k rpm and 15lbs, the blue line is with revs raised to 7200.



So using the same map and formula I plotted a few more numbers:

@25lbs:

http://s9.postimage.org/3mh95zo4v/25psi.png

@40lbs:

http://s10.postimage.org/ay05af795/40psi.png



So, if I am reading this correctly, in order to get any kind of power out of this blower one needs to push 30psi and 55lb/min (or 795.1CFM). On a beta that means that power comes on around 3600 rpm and spool all the way up to 8k. I'm not trying to build a dyno queen but since my Tib has basically been retired to become another toy I am going to take my time and build an nice safe motor then boost accordingly. My power goals are ambitious but having to sacrifice drivablitiy is not an option. First of all are my calculations any where near accurate? 2nd is there a turbo out that that will push huge numbers but spool relatively low?





I'd like to see some power between 2500 and 3k, yet I want to push upwards 400 hp.





As for support mods:

I am still working on designs for the plenum and TB combo (that thread to be updated shortly.)

The head will be deck and full p&p with Ferrea oversize valves, Ferrea springs/seat/etc and 1.8L cam.

Crank will be WPC and cryo.

Forged rods and pistons (brand to be decided shortly)

Low mile Beta2 block from a 2008 Tib which I'm going to fill/debur/etc. Basically blueprinting.

Trans: if you recall my post from last fall I am sourcing a few options.

Fueling and cooling will be based on the turbo I go with and expected power.

faithofadragon

doin work to the crank other than balancing it is not needed, theyve seen upwards of 800-1000hp in korea with no issues



in fact, i dont think ive EVER heard of anyone having a issue with a beta crank so id save the cyro money for a mod elsewhere



as for the turbo, dont look at me, i was just given one and decided to roll with it

wheel_of_steel

You're on the right track with your equations man, but I think that turbo is a little huge:



27.55 lb/min is at 6000 rpm, and barely fits onto the bottom of the compressor map. You need to plot the CFM at idle speed, and draw a slope up to where you think you'll be making peak boost:







Now remember that in the real world, you won't have anywhere near 93% VE except at peak torque. At 6000 rpm, you might be getting 80%. At 2000 RPM with a hot cam, oversized valves, and a homemade plenum, the VE will be remarkably low. So your plot will end up looking somewhat like this:







You're on the right path though man. I'd go for a smaller turbo dude, look around the traps here and see what's popping. Also, get into some literature so you can get into further depth than my shitty memory can take you.

yellow01

I did all of these kind of calculations years ago bottom line is if your staying under 20 psi a 30r is the largest turbo you want to go with or 50lb min ideally I think you would be more happy with a turbo a bit smaller than that say around 42-45 lb min. find my t3t4 dyno under my profile it may help you get a better idea of what your shooting for. Hope this helps some

Tibbi

Thanks for the input guys!



Yeah, the 550 is insanely huge but I want power now and room for growth. I'm still pretty sold on the GTK model from everything I've read and seen, but the 350 uses a modified E50 comp wheel and with current power band maxing at 6k and running 25lbs it looks nice.

http://s11.postimage.org/l4q5lxarn/e50_25.png

(Yes that arc is a really bad guesstimate.)

It seems there's a lot of room to grow as well! One thing I forgot to take into account were changes in n/a power band with the new runners. Everything was calculated at the 6k mark the stoker gives, but beefier, shorter runners could pull the max power in or out a bit.





One question this still leaves is the turbine side. One of my main reasons for the 550 was the exhaust side looked like it was better for making bigger power but I don't know much about calculating that side of the event. If I go with the 350 I will be ordering it with the 450 turbine housing because it uses an F1-57 wheel and 0.65 A/R exhaust with 3" outlet. It might slow the spool a bit but will give me the opportunity to put more power to the ground. Does anyone know how to calculate how much trim and A/R affect the compressor side?









If I wasn't already sending off the contents of transmission and various motor components I probably wouldn't, but it only adds $30 to the over all cost and includes both treatments. $30 for piece of mind is money well spent imho.

wheel_of_steel

The 350 is better, but still huge. You want the turbo to be at peak efficiency by like 50% peak revs, those efficiency bands are basically determining your torque curve. So if you're reaching peak torque at peak revs, you will have an exponential-looking power delivery, like this:







As for turbine sizing, I can't help you there man. I've never had to do it myself, but it seems to rely heavily on word-of-mouth and rough guesstimates.

bmxer

Here's a site with a turbo mapper. Pretty cool with lots of input.



http://www.not2fast.com/turbo/glossary/turbo_calc.shtml

koreancorvette01

Here is a few I mapped for my own info when I was doing the same . I went with the GT2971R 52 trim 60AR





















the tool above is awesome by the way.

slow 2K2GT

I can only give personal driving impressions of the GT3076r AKA GT30r. Daily run at 18psi, CP low comp pistons, Ferrea oversize valves, valve seat throats open .75mm.



Boost builds around the 2800rpm range, full boost by 3500rpm and pulls all the way to redline. Builds boost launching hard but gets pretty squirrely if you arent ready.



While doing 1/4mile pulls there was no trouble spinning my tires all the way til mid 3rd gear (Bridgestone Potenza with 18psi)



Well thats my addition to this thread.

Tibbi

Thanks for the guys! Going to bookmark this and keep that in mind. That GT3071R looks great and after reviewing their products looks like that and some of it's companions might be the best bet. Sadly, I got news they're dropping the axe on us come Nov, so all Tib work is on hold until I find a new job





I know some of the people hear run GT35R's, I'm now curious what they see spool-wise.