What turbo would be a good match for my current stroker motor as a twin turbo setup. The RWHp is now 340 and my target would be to add 150 more Hp to the drive wheels. Particulars on the motor (it was not built with forced induction in mind):

395 cu.in.
AFR 190 cc heads
10.0:1 CR
SuperRam intake
I "burn" my own Eproms ( so I can reduce the timing and run richer AFR)
wide band O2 meter
all forged bottom end
new 42#/hr injectors (rated @ 43.5psi) in a box
new 340 l/hr fuel pump in a box
Holley AFPR

edit: I realize that I would be limited to about 7 to 8 psi boost with my CR at 10.0:1...

Would I have to run an intercooler for that Hp gain?

Are turbos rated for flow vs boost? (how do you rate/compare turbos?)

I have been checking over several sites and specifically BBSDesigns Products. Edgardo has some nice looking kits. The idea and look of twin turbos under the hood is very impressive to me. Thats where I am coming from.

 

Only look at compressor maps rated in lbs.
When you get ones rated in cfm, you have to do more math to fit them.

With only 8lbs, T04e 60's would fit the bill I think.
I'd have to look at the map again to see it they'll fit a 400.
at low boost.
You'll want one with a short center island on the map since your running low boost.
To see what I mean, look at a map for a T61 and a 62-1.
One is better suited to 2.0 PR (15psi) while the other is 3.0 or 25psi or more.

Or a single T70.

 

Thanks for the reply.

http://www.turbocharged.com/catalog/compmaps/fig16.html

In this link above can someone explain the maps,, for example the vertical axis is pressure ratio, what is that?

Then there are % curved lines thru the map, what are they?

 

The pressure ratio is simply that, the pressure ratio across the compressor section (intake or cold side) of the turbo. The pressure ratio is calculated by this formula (assuming sea level atmo conditions at the compressor inlet):

PR=(14.7+Boost pressure)/14.7

So at 10psi of boost (which should get you to your power goal), the PR is 1.68. With a few quick keystrokes on the calcultor, you can figure the PR for any boost pressure.

Once you have the pressure ratio, you need to figure your airflow, which is the horizontal axis (generally scaled on lb/min). As a very rough guide, you can take lb/min X 10 to get the HP that the compressor can support. This is quick and dirty, there are much more in depth calulations than this, but it will get you close. Read 'Turbochargers' by Hugh MacInnes for more info.

 

I made up this picture quick to help you out. It is the TO4E 60 trim compressor map as suggested by Z69.

The straight, heavy red lines plot the points for your application (about 600fwhp at around 10psi of boost). Note that I went up from 30lb/min, which is approx half of the airflow you will need for 600hp (30lb/min X 10 = 300hp X 2 turbos =600hp).

The % numbers on the map are the efficiency of the compressor. The higher the effieciency, the lower the charge air temp. You want a cool charge temp with high compression! The yellow area is called the max efficiency island. You want your torque to peak in that area for street cars (full on race may want the max effieciency closer to redline/max HP).

I also labeled the compressor speed numbers. A turbo spins very, very fast. I have seen turbos with design speed over 200,000rpm!

The blue line is the surge line. This is the point where the turbo
is moving too little air and the compressor becomes unstable (if severe enough, you can hear the chuggle noise through the intake). You can hear this surge condition sometimes whenbacking out of the throttle in a turbo car if there is no BOV or bypass valve in the charge air plumbing. Stay away from this line (if you are near it when plotting points, you need a smaller compressor).

Also stay away from the green line. It is known as the choke line, which is the point where the turbo is unble to keep up with the airflow demand. This line is identified by the quickly sloping speed lines, which indicates that even though the compressor is speeding up, it cannot support the required airflow. This will cause 1) the turbo to operate out of it's efficiency range and 2) the turbo will overspeed and possibly damage itself or (worse) the engine if the compressor wheel should burst. If you plot points close to this line, you need more turbo (a larger compressor).

 

I will buy that book this weekend.

At 7.5 psi boost, I will be running at a pressure ratio of 1.51,,, now back to that map you posted (thanks),,

if I follow across from 1.51, I will cross several % ellipses and another curved line labelled 69,640. What is this all about?

Or, as you said above, do I convert my engine flow rate from CFM to lb/min,,, and where 1.51 PR crosses with the lb/min flow,,, OK I dont know where I am going with this.

Read the book, Doc!!!!!

 

WOWWWWW

You snuck that in as I was typing,, now I'll read your last post.

 

I finished my above post and added some more info on that map. Hope it helps.

You still need to buy and thoruoghly read that book. Don't let anyone tll you it is out-dated. It is the best turbo book I have ever read.

BTW, that turbo is a pretty good match for your combo. In general, when plotting max HP on the compressor maps, try to get them just to the right of the max eff island. That way your midrange will be in the sweet spot!

**Note- I was assuming you will need 10psi to reach your goal. Thats why I plotted the points that way. If everything comes out well, you may reach your goal with a lot less boost, especially with good heads. FWIW, I added at least 100RWH with only 6psi of boost on my bone stock '89 L98 (dynoed at 328rwhp and 468rwtq).

 

Great stuff, thanks.

Now my motor makes 340 RWHp, so about 400 at the flywheel. Supposively, it takes 1.3 CFM to make 1.0FWHp (rule of thumb).
Therefore, I am flowing about 520 CFM or (x 0.0747 lb/cfm) about 38.84 lb/min.

Now, what do I do, divide the 38.84 by 2 (because of two turbos, one for each cylinder head?). So am I at 19.4 lm/min flow for the chart?

Also at 7.5 psi boost, I have a PR of 1.51...

 

You want to plot the points for supercharged airflow. Using your numbers, 19.4lb/min X 1.51PR = 29.3lb/min airflow under boost. Fairly close to the 30lb/min airflow per turbo I suggested.

Like I said, this isn't the engineering standard for turbo matching. You will see what I mean once you read the book. I use this method to get a rough idea of which turbo(s) will support my power goals. You then have fewer units to go through the more lengthy (accurate) calculations.

Also keep in mind that once you have the compressor selected, you still need to choose the turbine section (hot side, exhaust). This is the drive section and it has the most influence on the turbocharger's response, or lack of response (lag). You may want to go T3/T4 hybrid. Use the TO4E 60 trim compressors and T3 Stage 3 turbine wheels in either .63 A/R turbine housings (fast spool up, lower peak HP at high rpm) or .82 A/R turbine housings (slower response but increased top end).

 

http://www.innovativeturbo.com/pages...sor_images.asp

In the link above, there is a T04B-Strim compressor map. If I have a PR of 1.5 and flow rate of 19.4, it appears that I would be at about the 72% effeiciency curve and right of the center island.

Is this where I want to be?

 

You snuck another post in on me. You are awesome, thanks for the help, I see that I am plotting this wrong according to your last post.

A T03/T04 hybrid was BBSDesigns recommendation to me!!!!!!!!

Ok, its bedtime. 89JYturbo, thank you very much for your help.