[455-4+1]

Hi all

Just put together a spreadsheet to check a few numbers and got some conflicting results from a Turbo supplier over here

If you could please shed some light on this would be much appreciated
I have used the following parameters and formulas from SA Design book by Jay K Miler.

433.89 CID
100% VE at 6500 (I tried at 90 and 95 but turbo guy came back at 100% so used this to correlate with his numbers)

NA cfm at 100 % VE = 816.1
10 lb boost Pressure Ratio is 1.68
I used the after cooled/non after cooled graphs to determine density ratio
With 74% comp efficiency I got 1.46 PR with aftercool and 1.39 PR without

This gave me corrected boosted cfm of 1191.5/1134.4 cfm with and without aftercool

Converted this to 82.2/78.3 lb/min
converted to 0.622/0.592 kg/sec for their maps

For a twin turbo I would just divide these 2 numbers ?

This way I get 41.1/39.15 lb/min or
0.311/0.296 kg/s for 6500 rpm at 10lb per turbo

Am i doing something wrong here ?

Any help would be much appreciated
Turbo guy came up with allot higher kg/sec numbers (30-35% higher)

Maybe he isn't allowing for compressor efficiency (I went with 74% line which is definitely not linear as boost climbs for non after cooled )

Many thanks in advance

[455-4+1]

Screen shots form spreadsheet

[Tom Vaught]

How about a few more numbers?

a) Assumed Air Inlet Temperature F

b) Comp. Dischr. Temp. Ideal F (Calc)

c) Comp. Delta T. Actual F (Calc)

d) Ambient Density Lb./Cu.Ft (Calc)

e) Press Loss Thru Cooler PSIG (Use - for loss) (Given)

f) Charge Density WO Cooler (Lbs/Cu.Ft (Calc)

g) Charge Density W Cooler (Lbs/Cu.Ft (Calc)

h) % Change in density above ambient wo/cooler

i) % Change in density above ambient w/cooler

j) Need assumed Inter-cooler efficiency

I come up with 83 lbs min without inter-cooling and 95 lbs min with inter-cooling for engine
47 lbs per turbo with intercooling assuming twin turbos. .

Thanks

Tom V.

[455-4+1]

Thanks Tom, will add info when i get back to work.
I have some data logger info available so can look at inlet temps Vs boost.
Not currently running an aftercooler, but meth injection upstream and efi controlled methanol fuel.
Once i compare actual inlet temps vs ambient i can hopefully get an idea of how effective that is.
Was just running some initial numbers to see how current compressors matched up and they didnt look to good. Currently running 2x65mm and with my numbers 2x61mm looked great on the map in comparison. (remember max rpm is only 6500)
Looks like my 83 is spot on with yours, but possibly my aftercooled is a little light. Guess it depends on efficiency input?.
Still doesnt explain why the turbo guy here has numbers 35% higher which puts him right off the rh side of the map compared to mine?

[Tom Vaught]

Originally Posted by 455-4+1

Thanks Tom, will add info when i get back to work.
I have some data logger info available so can look at inlet temps Vs boost.
Not currently running an aftercooler, but meth injection upstream and efi controlled methanol fuel.
Once i compare actual inlet temps vs ambient i can hopefully get an idea of how effective that is.
Was just running some initial numbers to see how current compressors matched up and they didnt look to good. Currently running 2x65mm and with my numbers 2x61mm looked great on the map in comparison. (remember max rpm is only 6500)
Looks like my 83 is spot on with yours, but possibly my aftercooled is a little light. Guess it depends on efficiency input?.
Still doesnt explain why the turbo guy here has numbers 35% higher which puts him right off the rh side of the map compared to mine?

Agree, efficiency islands is what it is all about and getting the right size turbos so you are not so far off the map in either direction. Surge and choke are the "Mine Fields" where you really never want to be there.

My stuff does non inter-cooled and inter-cooled but you can work around the numbers if you have data so that the programs assume "Inter-cooled" but it is really "Charge Cooled" using the meth injection.

Tom V.

[455-4+1]

Agree "charge cooled" is more appropriate (I called it aftercooled)

I worked on Non aftercooled, and after and figured we would be in the middle somewhere until I got the logged inlet temps, then I could get a better idea of efficiency of the meth injection (main is 8x Siemens 220lb, aftercool is 2x Xspurt 1550cc (Bosh) in the inlet elbow, not sure on duty cycle for these yet until I get the logs.)

Additional info

Air inlet temp range is typically 10c to 28c (50-82f)
For ambient density could work on std air at this stage (for temp as well ?)
Allot of the other inputs could probably be answered once I have looked at the logs, but at this stage you non cooled 83lb is very close to my 78.3lb for non for evaluation purposes anyway .

Just cant figure why the local agent has 35-50% more

Is it possible hes just working of the PR of 1.68 instead of using an adjusted density ratio (@ 10lb I used 1.46 aftercooled and 1.39 non for DR) which got me very close to your 83lb. The difference between these 2 is 1.68/1.39 = 1.21 which could explain his higher numbers ?

We tried 15lb @ 6500 rpm and I got the following
(with 74% compressor efficiency as a start point)

816.1 NA cfm at 100% VE
At 15 psi I have a PR of 2.02
Density ratio of 1.72/1.56 for aftercooled and none
Turbo cfm of 1403.7/1273.1 for aftercooled and none

This calcs to 96.9/87.8 lb/min for aftercooled and none
For twins this roughly ½’s to 48.4/43.9 lb/min each
Convert to kg/sec and get 0.366 / 0.332 as a range for 6500 rpm at 15lb

Borg Warner calcs for airflow came in at .354 lb/min at 6500

So for non aftercooled we have me 43.9 lb/min 0.3319 kg/sec
BW calc 46.9 lb/min 0.3546 kg/sec

Average is about 0.343 kg sec
MP came up with 0.50 kg/sec almost 50% more which puts it off the chart for the turbos being looked at

Just seems like a very high number for that combo, unless I am totally missing something (been known to happen lol)

[Tom Vaught]

Except for the one typo here: "Borg Warner calcs for airflow came in at .354 lb/min at 6500 (units need to be like the rest of the post (0.3546 kg/sec) not lb/min, the math looks close.

Tom V.

[455-4+1]

Oops yes sorry bout that.
Was swapping between units and missed that one, well spotted 😉