Author Topic: Some math about 318is: choosing turbo and turbo maps... dreamming (Read 5682 times)

nuvolarossa · « **on:** March 17, 2007, 03:09:08 PM »

Hi, I've posted this on other forums, but It maybe helpful here too.

I've start to learn turbo maps because I've found a manifold for a 318is that is good for a low budget setup. The only problem is that it has a T3 flange, so I can't fit the GT-25/28 turbos without modify it.
So I started to know the specs of garrett t3 versions and I made some calculations...

All calculations are made for reach 200hp at sea level, supposing 2 psi losses between hoses/intercooler and 130�F, intake manifold temperature of 130�F, a generic BSFC of 0,50, a VE of 89,40 and a engine speed of 6500revs.

For now I've made the calculations for 200hp because of stock CR.
- Airflow needed for 200hp and a A/R of 12:1= 20 lbs/min
- Required manifold pressure required to meet the horsepower, or flow target: 22,46 psi absolute, 7,76 psi of boost
- manifold pressure with 2psi of losses: 24,46psia.
- Pressure ratio: 1,52 without losses, 1,79 with losses

Thanks to Garrett website. I've used the formulas from that Garrett link.

I think that the perfect T3 turbo is T3-60 trim.
This is what I've found:

I've calculated the airflow at 2500 and at 6500 and then plotted them in compressor map.
What mean the straight line? It means that from next 2500 to 6500 revs the car should have full boost with that 70% efficiency?

Who can help to analyze that map? Should be low lag time?

the GT28, GT25, T25, T28 cannot be fitted to the manifold that I maybe will buy. The GT30 can be fitted, but is too big for good driveability (lag) with only 7psi and stock internals with 10:1 CR...

here are some real data from M44 stock and from DASC at 7psi on M44 compared to data calculate from t3-50 at 7psi at sea level, supposing 2 psi losses between hoses/intercooler and 130�F, intake manifold temperature of 130�F, a generic BSFC of 0,50, a VE of 89,40 and a engine speed of 6500revs.
RPM   |318 HP........|turbo t3-50 7psi.....|318SC DASC
2000   |45..............|xx........................|.xx
2500   |50..............|.87.......................|..66
3000   |70..............|.107.....................|..81
3500   |80..............|.124.....................|..105
4000   |95..............|.141.....................|..124
4500   |100............|159......................|.140
5000   |120............|177......................|.158
5500   |125............|194......................|.169
6000   |130............|229......................|.183
6500   |138............|228......................|.xxx

What do you think?

Gunni · « **Reply #1 on:** March 18, 2007, 12:31:40 PM »

I�ve sat in a 2.0 SR20DET with a GT28RS turbo, there was NO lag to notice,
as soon as the throttle went to the floor there was instant boost, that turbo peaks to 320-350hp cirka.
You should be looking at something similar,

Same guy using a SR20DE(Not T) and 10:1 compression + 10psi = Crazy
Amazingly the Sunny GT 2.0 now passes Imprezza STI�s with stock engine and only 10psi boost.

Select something that starts to come on when the M42 is about to come on cam, helping it out a little bit and when it does come on cam the efficiency of the package will be alot better..

Don�t go for low end boost on the M42, you�ll need to cut timing alot and boost alot as the engine really isn�t breathing well down there.

sumyungguy · « **Reply #2 on:** March 18, 2007, 02:11:57 PM »

Yeah I'd say modify the manifold and put a GT28R or RS, its a perfect size turbo for our 1.8 motor (best for 1.5-2.5).

Theres nothing wrong with high compression (10-11:1) and 8-10lbs of boost.. It makes a very nice power band and with good tunning capabilities its very reliable. Take the Toyota 2ZZ (celica gt and lotus elise)11:1 motor for example, ForcedFed makes a turbo kit for it using the GT28R. The kit makes 250-260whp@7lbs, and the torque is so smooth and linear you think its supercharged.. If I where building a turbo kit for my car, it would be using a GT28R and stock compression hands down. But for the tunning end I dont know, maybe a custom harness and a AEM standalone..

Im actually gonna talk to my friend Shiv from Vishnu and see if he can make a piggyback for us at a reasonable price..

nuvolarossa · « **Reply #3 on:** March 19, 2007, 06:27:43 PM »

Thank you for replies. The engine will be a E36 M44, so it must be boosted to max 8psi. I want to be safe, I know that there are DASCs putting 10psi on M44 but I don't want to destroy my engine. I have a innovate lc-1 wideband for watch A/F ratio. I think that whatever will be the turbo I'll go for 5-6psi at start for see if I can fit my cartech begi RRFPR from another project. So who know if there will be a really difference in turbo-lag between a T3-60 and a GT-28R?
bye

Tonyb · « **Reply #4 on:** March 19, 2007, 10:19:45 PM »

Will this cost less then the DASC?

asubimmer · « **Reply #5 on:** March 19, 2007, 10:21:12 PM »

I have a gt28r waiting to go on...the dang manifold is still holding everything up

nuvolarossa · « **Reply #6 on:** March 20, 2007, 07:37:03 AM »

Quote from: Tonyb;21730

Will this cost less then the DASC?

For sure:D And it will be intercooled!

Alpine003 · « **Reply #7 on:** March 20, 2007, 08:51:50 AM »

Quote from: nuvolarossa;21706

So who know if there will be a really difference in turbo-lag between a T3-60 and a GT-28R?
bye

I've had both of these in my custom 2.2L Impreza and for that setup, they were definitely noticeable. I wouldn't bother with the T3 unless you're on a budget or if this will not be a daily driver.

sumyungguy · « **Reply #8 on:** March 20, 2007, 10:23:11 AM »

Quote from: nuvolarossa;21706

The engine will be a E36 M44, so it must be boosted to max 8psi. I want to be safe, I know that there are DASCs putting 10psi on M44 but I don't want to destroy my engine.
bye

You would be fine at 8-10, with no worries about destroying the motor, if you have decent management (timing and fuel). Im fresh on the bmw scene and dont know whats out there as far as tunning capabilities. I would try to stay away from the boost increasing fuel pressure regulators, their not perfect and the car starts to detonate you cant just simply add more fuel in that spot. I bet the Apexi SAFC work on our car's, it only adjusts fuel but you can fine tune it per 100 rpm.

I completely agree with Alpine003 about the turbo.... GT28R is great for DD..

vatos_p · « **Reply #9 on:** March 21, 2007, 01:04:33 AM »

i am going to use garrett GT2540R ( .70 A/R ) , get a look on this turbo...
with caclulations we made , this is the best..

Alpine003 · « **Reply #10 on:** March 21, 2007, 08:38:40 AM »

Quote from: vatos_p;21874

i am going to use garrett GT2540R ( .70 A/R ) , get a look on this turbo...
with caclulations we made , this is the best..

Yes this is sized better but leaves a little room for future upgrades. It might not apply to everyone though depending on their goals and setup.

nuvolarossa · « **Reply #11 on:** March 23, 2007, 05:34:33 AM »

It seems that you know more than me about turbo sizes.

So If I want a turbo that would have full boost from 2600-2800rpm with lowest lag possible, at 7-8psi, what turbo you advise me?

bye