some help with turbo selection

Skugulgurk · #1 11-22-2005, 07:30 AM

Okay, I know it's a little early to start planning out a turbo but... I couldn't help myself. I've been staring at flow maps all day

I can't seem to find a turbo that works "well" with what I'm trying to do. My goal is to make 500hp with a 420A stroker. According to my turbo calculator, it will take 8000rpm and 20 psi at 100% volumetric efficiency. I think these are obtainable. It won't be easy but it can be done.

I've been looking at all the flow maps on this page but none of them seem to line up for very long if at all, in the highest efficiency circle.

http://not2fast.wryday.com/turbo/maps/all.html#mitsu

Maybe I'm not doing it right. This is the information that the Turbo calculator is telling me.

20psi equals 2.36 atmospheres right?

If you guys have any suggestions they would be appreciated.

Thanks!

Thor06 · #2 11-22-2005, 07:14 PM

Sorry, this post wont help you at all, but where did you get that turbo calculator?

defiancy · #3 11-22-2005, 07:16 PM

Quote:

Originally Posted by Skugulgurk

Okay, I know it's a little early to start planning out a turbo but... I couldn't help myself. I've been staring at flow maps all day

I can't seem to find a turbo that works "well" with what I'm trying to do. My goal is to make 500hp with a 420A stroker. According to my turbo calculator, it will take 8000rpm and 20 psi at 100% volumetric efficiency. I think these are obtainable. It won't be easy but it can be done.

I've been looking at all the flow maps on this page but none of them seem to line up for very long if at all, in the highest efficiency circle.

http://not2fast.wryday.com/turbo/maps/all.html#mitsu

Maybe I'm not doing it right. This is the information that the Turbo calculator is telling me.

20psi equals 2.36 atmospheres right?

If you guys have any suggestions they would be appreciated.

Thanks!

Just remember that if you change the internals of the engine, pistons, lower compression pistons and you do a stroker kit or whatever. Your numbers will change and it might not take 8000rpms at 20psi. It's going to vary greatly on the power that your engine is putting out in addition to what boost/flow the turbo is giving you. So if you build a monster 420a then you are going to have waaay completely different numbers, And to make 500 horses you are definately going to have to make a monster 420a

Skugulgurk · #4 11-22-2005, 09:28 PM

Quote:

Originally Posted by defiancy

Just remember that if you change the internals of the engine, pistons, lower compression pistons and you do a stroker kit or whatever. Your numbers will change and it might not take 8000rpms at 20psi. It's going to vary greatly on the power that your engine is putting out in addition to what boost/flow the turbo is giving you. So if you build a monster 420a then you are going to have waaay completely different numbers, And to make 500 horses you are definately going to have to make a monster 420a

I have down the stroker numbers in those pictures. The stock bore is 3.444 and the stock stroke is 3.268. But you're right it doesn't take into account the compression ratios of the the pistons. as for other mods to the engine with all the head work and intake stuff I "plan" on doing it should be close to 100% efficiency maybe more

. This is only a tool and gives a rough guide. But if you plot those points on a compressor graph you can tell that a t-25 probably isn't going to cut it.

I was just wondering if anyone had any suggestions for turbo's that performed well in with these general plot points.

I got the Turbo calculator from Ray Hall Turbocharging. It is definatly fun to play with. It gives information like estimated quarter times and a bunch of other info. Here's the link

http://www.turbofast.com.au/freesoftware.html

Thor06 · #5 11-22-2005, 09:33 PM

Fuckin righteous, thanks!

kjewer1 · #6 12-02-2005, 09:23 AM

You wont be able to stay on the top efficiency island of any compressor. Airflow will always move off to the right as it increases. The points will go up with boost, and once that flatlines they will go off to the right as flow increases, then come back a little as flow decreases. This is real hard to visualize if you have never seen logged airflow data.

If you try to set it up so that at max HP you are at that high efficiency island, you will have a very laggy turbo

The trick is to balance lag with efficiency. Also note that as long as you are somewhere on the turbos map, efficiency plays a very small role. The example I like to use is extreme but illustrates my point: If intercooling efficiency is 100%, compressor efficiency is irrelevant. Consider that a typical FMIC is around 80% effient, any temperature changes due to the compressor efficiency will be cut down by the IC. Also consider that anyone holding a turbo record has run the turbo well off of it's map. You just have to tune accordingly.

My recomendation would be to use the 10hp per lb/min of airflow rule and add a little buffer so you aren't maxing out the turbo all the time. So your target is ~55 lbs/min IMO (50 lbs for 500 hp, plus a buffer). A 2.3 liter at 8000 rpm at 100% VE and 30 psi should be good for ~63 lbs/min. Now, you won't be at 100% VE at that rpm most likely, and you probably wont want to to use that much boost. So the 55 lb target seems acceptable looking at it that way as well. IIRC I used to get airflow in the 52-53 range at boost in the low 20s.

My belief for the turbo cars is that a 56 trim sized turbo is the smallest you would want on a 2.3/2.4, so you could look at it that way as well if it can apply equally to the 420s. My reasoning is that I am going to run 30 psi, so I need that 65 lb capacity, and it still spools so damn quick at ~3700 or so in my experience that I don't need any quicker spool making a smaller turbo useless.

When I maxed out the 65 lb turbo I Went to a 75 pounder (Otrim/T67), which started to push the limits of my lag tolerance. A 65 pound turbo would be a great street turbo with a little headroom for some track use at higher boost. Turbos in this size include the GT35R for reference.

Another thing to consider with a larger displacement motor is the turbine wheel and housing. With the ability to move 15-20% more air at the same boost pressure, some thought needs to be given to letting that extra air escape

Don't choke the larger motor using a hotside typically used on a 2 liter. It's a mistake I see being made all the time... When I chose my turbo (the T67) I set specific instructions for AGP. Not just enough capacity on the compressor wheel (which is easy since I have logged airflow data and know what I need), but the largest exhaust side that would still allow the turbo to reach full boost around 4500-5000 rpm. It came out closer to the 5k, but was within my range, and allowed for the maximum exhaust flow within my lag tolerance.

So the moral of the story is that real world flow numbers make theory and maps useless, and be sure to give equal thought to both the compressor and exhaust sides of the turbo given the application. Good luck.

Skugulgurk · #7 12-02-2005, 07:43 PM

Wow, Thanks for actually giving some useful advice. I had almost given up. Some other people I have talked to also suggested the GT35R. I have until the spring to figure it out, and hopefully then I'll have a better idea at how the engine is going to flow and such since it will be closer to complete then. Also I plan to try and find as much about what other people have done with a 2.2 liter engine as possible. This is my first turbo monster, so it has been and will be a learning experience. Again thanks for the help!!!!

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