[LM93]

I'm just exploring options for a street-driven '79 Firebird with a Pontiac 350 in it. I'm not sure about all the inputs I'm punching in because I'm not familiar with what the differences between N/A and blown engines would be for these numbers. Am I close, or any of these numbers way off? I really don't have any experience to know, although from what I gather a blow-through carb acts like an intercooler, so that's what I've entered for the intercooler stat row.

I haven't gotten around to comparing a stroker vs a turbo build. With either a blown or N/A engine, I want to be able to put a manual transmission behind it because I think they're more fun.

[Tom Vaught]

Not close at all.

1) assume about 90% on the engine efficiency. You are increasing the mass flow with boost, not the volumetric efficiency.

2) A Blow thru carb does NOT act like a Inter-cooler Set the Inter-cooler efficiency to 0

3) Your exhaust temps with any boost are typically in the 1300-1400 degree range unless you are just cruising down the road. Even at cruising they are over 1000 degrees.

4) Turbo compressor efficiency is rarely, if ever over 78% and more likely in the 72 to 74% range.

5) Normally on a street car (with a filter) you would assume 1 psi across the air filter element. Running without a air cleaner or screen before the turbo usually comes back and bites you at the track (when a stone finds its way into your turbo vanes). Bye Bye Turbo. A draw thru carb set-up would have a air cleaner mounted on the carb BEFORE the turbo.

Tom V.

[LM93]

How are these?

[Tom Vaught]

THAT LOOKS BETTER, POST UP THE REST OF THE INFORMATION BASED ON THE INPUTS YOU MADE IN MATCHBOT.

TOM V.

[LM93]

Is the Turbine Wheel Diameter for the third chart the same as the turbine wheel outer diameter listed in the product PDF?

[Tom Vaught]

You really need to assume that the 2.0 pressure ratio does not come in at the 6th column.
You need to assume that the pressure ratio is 2.0 at the #3 column and then a waste gate
allows it to not go higher at columns 4 & 5 & 6.

So change the pressure ratio to 2.0 for those columns. 3,4,5,6 and see what the compressor curve looks like.

Tom V.

[LM93]

By Pressure Ratio do you mean the Turbine Expansion Ratio?

[Tom Vaught]

No I mean the Compressor Pressure Ratio.
Post #5, THE FIRST PICTURE. Top Line Change the values in #3,#4,#5,#6
to 2.0 PRESSURE RATIO. Then re run program and post Compressor flow line again

Tom V.

[LM93]

Will column #1 and #2 take care of themselves?

[Tom Vaught]

POST UP THE COMPRESSOR MAP AS WELL AS THE POST #9 INFO WITH THE 12.9 BOOST PRESSURE.

Tom V.

[LM93]

Point #3 on the turbine graph can't move up any higher with a 12.9 boost.

[Tom Vaught]

To Have a good turbo match, you would like:

Lower Exhaust Pressure vs Boost Pressure or the same boost pressure (Pressure Ratio is 1 to 1 ).

The Boost Pressure rising fairly quickly but still to the right of the Surge Line

A very good Horsepower number is shown for the size of the turbo and and the boost pressure planned.

So dialing in your numbers on the Borg Warner Matchbot program:

a) Your Boost Pressure IS HIGHER VS YOUR EXHAUST PRESSURE.

b) Your Little 350 cid engine could make BSFC numbers in the .48 to .56 range.

c) Your Turbo is performing very well with the points to the right of the Surge Line &
centered (all points inside the map) for the whole performance curve.

d) The turbine size and its map line is clearly documented for you. You could order that Turbine Housing for your turbo Compressor to get the correct performance. I can't read the turbine size on your screen shot.

e) A 91S74 BW Compressor Wheel/Turbo EFR 9180 is a good match.

f) If you look at the turbine map and follow the line where the 3 dots are on the SAME LINE you will have the correct size turbine housing for the 350 engine. Can't read the Part Number

g) Your little 350 cid engine is capable of making 560 hp with that little turbo at only 15
psi of gage boost pressure. You are at the limit of a street system without a Inter-cooler.
A Intercooler would drop the charge temp by 100 degrees and add even more power to the engine.

h) Your little turbo will use only 43.6 lbs of air mass Exhaust Flow to power a compressor wheel that moves 64.37 lbs of air mass flow on the compressor side so the little turbine wheel will be doing outstanding work for the size of the turbine wheel.

All you needed to do was request the right information in the program to get the numbers.

Tom Vaught

[turbo69bird]

Use an s475 works just fine. I’ve done it myself w a dead stock 350 ran 11 flat at 10 psi. Worked great on the street. 70 350 2bbl motor out of a lemans. Raced it for a full season that way. Ran good yanked it out and put it in a 67 bird n/a ran well for another 6 years before I lost track of the car.

[Tom Vaught]

Can't disagree with that as I own a pair of the S475 Turbos my self.
They are scheduled to go on a short deck 366 Pontiac engine with Ported SD aluminum heads.

Tom V.

[LM93]

That map is for a BW 91S74, actually. The turbine size is 91 EFR, 67.8 inducer, 92.2 exducer. Which of the four Product types(B,C,D,H) is the best match?

[LM93]

I hit the compressor map for a BW S475SX with MS paint. Are these points accurate? Matchbot doesn't have that model. The S475 efficiency points peak at 5000-6000rpm, as opposed to the 91S74. which peaks at 4000rpm. Will that early peak cause power to 'nose off' or is efficiency more temperature related? I can weld up an intercooler no problem.

[Tom Vaught]

Notice how the Pressure Ratio curve is to the right of the Surge Line nicely, even at a low
26 lbs of air mass flow. And this is at a 2.0 pressure Ratio.

Notice with the boost regulated by a wastegate for a 2.0 Pressure Ratio across the curve.

Notice how the mass flow line at 2.0 pressure Ratio is at the very good 76 % efficiency
Island twice and at the highest Efficiency line 78 % during the curve.

If you plotted one more point on the curve you would still be in the 74% island even at
71 lbs per minute of compressor air flow. That is 710 hp assuming 10 hp per lb of air
mass using the normal rule of thumb. 72% is considered acceptable for a compressor flow curve.

The other turbo is capable of about 63 lbs/min or 630 hp.

The BW 475 is capable of 710 HP with the given maps at the same boost pressure.
So it would be a better turbo by 80 HP vs the other one.

Tom V.

My two BW 475 type turbos should make over 1500 hp with a inter-cooler.

[Tom Vaught]

A bit more information on KG/sec and Lbs/Min:

.1 KG/sec is equal to 13.23 lbs/min.

1.0 KG/sec is equal to 132.28 Lbs/Min.

Using this converter: http://www.kylesconverter.com/mass-f...nds-per-minute

.48 KG/sec is equal to 63.49 lbs per minute using Kyles Converter or 630 HP.

Formula is 132.28 times .48 = 63.49

Tom V.

[Tom Vaught]

Originally Posted by LM93

I hit the compressor map for a BW S475SX with MS paint. Are these points accurate? Matchbot doesn't have that model. The S475 efficiency points peak at 5000-6000rpm, as opposed to the 91S74. which peaks at 4000rpm. Will that early peak cause power to 'nose off' or is efficiency more temperature related? I can weld up an intercooler no problem.

Where did you get engine rpm info from the compressor map you posted?

Tom V.

[LM93]

I just guesstimated the points from the corrected airflow rates given in the calculated outputs chart in lbs/min.