I'm wondering how much stock to put into the compressor map. The rule of thumb on Turbonetics' site is that it takes 1#/min of airflow to make ~10 HP (at the crank). So one turbo flowing 45#/min would make ~450 HP. Since I have two turbos, each one will need to support ~45#/min to make 900 crank HP. The compressor map pretty much stops at ~43#/min. So it would seem that regardless of what boost I run they are going to be way out of their ideal efficiency range.

Turbonetics T04E 57 Trim Compressor Map:

 

It looks like they don't like your big 402. Wouldn't you be lucky to see 15psi with these on the 402? That puts you right around the 2 of the left axis and 40-45 on the bottom. 50% efficiency.

 

I don't know why I couldn't run more than 15# technically. I'm sure if I keep the gates closed it will make a lot more than that. Question is do I want to? It looks like 2 bar would support 800 crank HP, just far from efficiently. I'm SWAG'ing ~800 RWHP from 14# based on the UPP results on an 11:1 402: http://forums.corvetteforum.com/c6-f...w-results.html so thats ~900 at the crank with similarly sized turbos so clearly 57's can support more than the map suggests.

 

If I'm reading the maps correctly it seems like you'd want to run something more like twin 76's to support 800-1000 HP efficiently.

Turbonetics HP 76 Compressor Map:


Actually their T66 seems to fit the bill well also. Two of those have a nice sweet spot from ~800-1200 HP!

 

It looks kind of small for 402 depending on what kind of power you are looking to make. I have 402cid with C6 APS kit and it is fantastic on the street and track but it runs out of air avow 13-15 psi ( 7-800 RWHP ) I’m looking to change those to bit bigger turbo or something flowing ~56-60#/min. that should be grate for +-900 RWHP and with grate low end TQ and instant throttle response. For me the street is number one and drag racing for additional fun.

 

Hello Bill,
I will be able to let you know first hand how twin T76, HPC billet wheels and ball bearing turbos work.

 

I think those will work very well Nick!

A friend pointed out that real world results often differ from "on paper". Example: My old Novi 1500 is only rated to 825 HP max. Mark (winters97gt) is making 825 RWHP from it on his 402 which is ~950 crank. From the looks of it I'm way off the map efficiency-wise but they'll still be good for low to mid 800's RW and possibly more if I swap out the exhaust housings (.62 to .82 AR).

 

Goals. What are they? First question.

What Fuel? Second question. ( Pump, IIRC?)

 

End goal is 900RWHP but I don't think thats going to happen. I think a reasonable goal for these turbos would be 825.

93 octane with dual nozle straight meth.

 

if you didnt get the turbos yet step up to the precision units!

 

Note: 57 trim is not the same as 57mm

 

True, I'm not exactly sure that is my actual compressor map, it's just the only 57 mentioned on the Turbonetics site. Sure wish turbo manufacturers didn't use so much pixie dust, smoke and mirrors. Why is it too much to ask to publish the wheel size(s), trim and AR rather than come up with fancy names to make it sound cool, never mind publish a compressor map.

 

oh, and lets not go into the effect of the turbine's a/r has on the compressor map itself.

 

[QUOTE=5 Liter Eater;1579576780]I think those will work very well Nick!

A friend pointed out that real world results often differ from "on paper". Example: My old Novi 1500 is only rated to 825 HP max. Mark (winters97gt) is making 825 RWHP from it on his 402 which is ~950 crank. From the looks of it I'm way off the map efficiency-wise but they'll still be good for low to mid 800's RW and possibly more if I swap out the exhaust housings (.62 to .82 AR).[/QUOT

Bill without a doubt start off .82 AR. Don't use bother with .62

 

A little bit of everything. Yes, it can be slightly different in the real world than on paper, but paper gets you close trial and error will finish you off. Yes technically you can flow a bit more than what's on the paper, but you'll do so outside the efficiency range. AND Yes, 57 "trim" is different than 57mm. Infact the 57mm side is even misleading because that's only the inducer size, stating nothing about the exducer.

Correct on the 76's...well partially. I have not doubt that they've been used with great results, AND if you map out the compressor map at 15psi and redline, that will put you smack dab in the peak of the efficiency, beautiful! However, I'm going to assume that your car doesn't have a variable geometry transmission, and isn't going to spend it's life at redline. I run a single T76 on my 3000GT pushing 800whp. I'm going to have to say for what you're looking for the twin 76's are just a bit too big.

Here's what you want to look for when mapping the compressor. First, what's the power you want to make, and aprox (based off others) what is the required boost to achieve that. Obviously fuel, compression, cam, etc all play a vital roll, but just to narrow it down. The 57 trim you posted I would call a 425hp max from each turbo, so 850 total. Now where do you assume that you'll be spooled by? Generally fully spooled by ~4K isn't alot to ask for, so we'll assume that. Now plot your lb/min requirements at 14psi @4K and then at 14psi @ redline (or what ever boost you choose). Draw a line. Try to get the majority of that entire line as efficient as possible when comparing turbos, and cap it on the right side of the map, because it's pretty good assurance that the turbo isn't going to support much past what's drawn on the map.

Looking at the 57 trim map posted, I would say that's a really efficient setup for 600-700hp on our cars, and maxed out by 850. Comparing that to a SH-trim (58mm)

57 Trim- Inducer 56mm Exducer 74mm
58mm - Inducer 58mm Exducer 76mm

And those 2mm on each are good for anther 75hp each.

Oh, and one last thing, if for whatever reason you find any point of your plot off the left side of the map (surge limit), that's very bad too. That's where the turbo is too big and trying to flow too much air for what little shaft speed it has and isn't able to maintain pressure. It causes back flow, which can damage the shaft/bearings.

Hope this helps.

CK

 

Good info, thanks CK. Yea I think the 57's were chosen for those who would want to run on wastegates and stock cubes. They are most efficient between 400-625 HP. If I push them over 800 they will be on the verge of choking out. It is what it is.

 

Changing turbo's already Nick!?!

Your a mad man!!

 

Its winter....can u tell I get bored easily? To be honest though I hurt one of my turbos. Seems that standard journal bearing couldn't handle thrust load plus I was able to get good money for the other turbo. Jz@forcedinductions.com hooked me up on new bird suckers. Ball bearing and billet 76 should be very interesting. LOL.

 

Bill,
Sorry I haven't been able to reply yet to this thread. I went back through some of my notes from when I started my build. I ran across an email where TTi stated that the turbo had an SH wheel which stands for Super H. If you download the compressor map from turbonetics, it looks like this:



Knowing what I know about the kind of power that people have made with the 57mm turbos, this is a better fit. I know early on there were even a few guys that used these "standard small turbos" on 402's and 427's and they weren't disappointed. Did they make 1000 rwhp, no, but they did eclipse 900 rwhp.

 

Same turbos as in our kits. And they're 58mm, not 57mm.

And I've personally pulled 550whp out of a single one by itself.