Why so much boost??

[myblack98gst]

My friend and I were talking today and couldn't figure a legit reason for this.



Why does a DSM need so much boost to make decent power? for example he as a sr20det swapped 240 it is all stock except (t-25 turbo) with a greddy front mount. he is currently running 10 psi and we figure about 240-250 whp.. My car is 9.0:1 compression 6 bolt with a 14b @ 18 psi and I am probably about the same power???

both motors are the same displacement and everything, so why does the DSM require so much more to be the same? My car is tuned quite well and is running good for the turbo thats on it.. ( ran 84 mph in the 1/8 @ 18psi and pump gas(& broke the trans 3/4 of the way down the track)) and we are about dead even on a rolling run...


Discuss

 

[Black95TSIawd]

their t25's are a little different then ours and the have way less drivetrain loss then we do. A lot of other factors come into play here. How well do those SR heads flow? How about intake mani and throttle body? Do they have the same compression rating as our cars? A tuned 14b with a front mount on 18psi should make more then 250whp. His car is a lot lighter then yours too.

 

[ACKERSON]

First of all your friends 240 is about 500 lbs lighter than your dsm so you can't compare the two. Second you have more than 240 whp @ 18psi if you are tuned correctly and you have the supporting mods. There is no way you can compare the two you have a 3100 lb car and he has a 2600 lb car. Stock sr20det with 10 psi in a 240 is only going to make about 190- 210 whp.

 

[Totaled2Talons]

The key is not to be obsessed with pressure, but rather air flow. Its all a matter of how much air your turbo can move in a given period of time. If the turbo in his Nissan is bigger in anyway, it will probably move more air. If it can spin faster, then it will probably move more air. If his I/C piping is bigger, then it'll probably flow more air, so on and so on. That's why turbo companies put out "compressor maps" with their turbos. These complicated graphs tell you how much air a turbo can flow at a give speed, etc..

Here are some typical compressor maps:

14b
Big 16g
Small 16g

Recap: his turbo flows more air at a lower pressure than yours. try upgrading to a 16g and blow him outta the water...

 

[scottsee]

the physics of an engine are the same, every car opperates in the same way. calculated air mass density is recorded, compressed with fuel, and sparked creating combustion. imbetween you have air volume, compressor effeceny, pressure drop, exhaust pressure,02's and fuel maps and what not caculated into the equation. how do all of these things: A effect power: B when you start getting down to the caculated sicence of the diffrent cars, it all boils down to 2 things, how well the parts work in conjunction to how effecently the ecu reads and controlls the information provided buy such parts. ie, mafs, cas, knock, wideband, the more reliable the information, the better the performance provided. And how well the car responds to the information it recieves, and what it does with it. there is always the mecanical powertrain loss to caculate in as well. physics is basicly the answer. weigh, compression, power distribution, effecency.

 

[definitiveno]

1gen vs sr20

lower compression, larger turbo, better flowing head, superior maf

2gen vs sr20, superior maf

Here is a link to one of the guys on the 240 forums, he's makin 27X on his t25 to the rear wheels and 12.3, stock t25


http://www.240sxforums.com/forums/showthread.php?t=41858


the difference is staggering, I believe the fastest t25 eclipse is nearly a half second slower

 

[ACKERSON]

the fastest fwd dsm with a t25 that I know of is running a 12.4 and the dsm t25 flows around 80cfm less than the nissan t25. The 240 is about 500 lbs lighter than the dsm so it's not that impressive at all. The 14b flows about the same as the sr20 t25, and there are guys running mid 11's on 14b's with heavier cars.

 

[definitiveno]

I'd be interested to see a link to the 12.4 gst if you don't mind

 

[diambo4life]

the fastest fwd dsm with a t25 that I know of is running a 12.4

The fastest T25 on record is a 13.1. That was an AWD Talon. No way a FWD DSM is running a 12.4 with a T25. I will pull the BS flag on that. Prove me wrong.

 

[definitiveno]

also, gst and 240sx are only a hundred lbs difference 2750 to gst's 2850, and the sr20's garret t25 is rated the same 27lbs min as the mitsubishi t25. Housing seems to be the only difference.

 

[Endz0r]

you are on crack if you think our cars weigh less then 3000, unless you got some serious weight reduction done.

 

[definitiveno]

gsx, right?

here is a gst http://autos.msn.com/research/vip/spec_Exterior.aspx?modelid=2052&trimid=-1&src=VIP&tab=2&sub=3

and a 240sx of equal year http://autos.msn.com/research/vip/spec_Exterior.aspx?modelid=2151&trimid=-1&src=VIP&tab=2&sub=3

 

[Mirage2LTurbo]

A close friend of mine went 12.9 on 10lbs w/exhaust and small top/bottom FMIC in his SR20 swapped 89 240. Yes, I said 10lbs, and have the logs to prove it. He didn't re-adjust his mbc once he got to the track, and never checked his gauge all day long. He was trapping 103-105mph.

 

[mlopez]

The fastest T25 on record is a 13.1. That was an AWD Talon. No way a FWD DSM is running a 12.4 with a T25. I will pull the BS flag on that. Prove me wrong.

A good buddy of mine has the fastest T25 powered FWD. 11.1@127. His user name is hsr98gst. You can look in the fastest 1/4 mile times on this site. The car has alot of weight reduction and nitrous. I think his best time off the bottle was a 12.4

 

[DSMJim]

There are a few things that make the difference.

They can rev to 9000 we can only till 7500. That makes a huge difference to start
They are RWD with low drive line loss, were AWD with much more (or FWD with less)
The 1G has lower compression, not sure of SR20 vs. 2G at 8.5:1 probablly pretty close.
Their heads flow much better than ours
Their stock cams have much more lift and duration than ours do
Their T25 is like our 14B on 1G and WAY better than our T25 on 2G.

Basically they can make more power at lower boost due to engine design because their engines from a very basic starting point are better to make power on. Once both engines are built with aftermarket cams and ported head etc, they are pretty well the same for power production at boost vs. WHP.

 

[ACKERSON]

http://www.dsmtimes.org/fwd.htm Its # 35 on the list, for the 12.4 fwd
DSMJIM, are you sure about the sr20's being able to rev to 9k, or are you thinking of the ca18? Also, I don't think there heads flow as well as ours do. From what I have read they flow about 180cfm at max lift (10.5mm on the highport head and 11mm on the lowport head). I believe the 4g63 flows around 190 at max lift. There intake manifold flows 205 cfm ours about 240. Sr20det compression is 8.5:1. They have our 1st gens beat in that category. There cams do have way more duration and lift than ours do.
The bore and stroke being square at 86mm is an advantage over the 4g63's undersquare 87.9mm stroke and 85mm bore, but with a worse r/s ratio 1.54 vs 1.64. It's a trade off, I think if you bolted the same turbo to each engine and put them on an engine dyno (not chassis dyno) the numbers would be very similar. Who know maybe all of my info is wrong and I wasted all that time doing the research for nothing.

 

[ACKERSON]

Oh yeah for definitiveno, the dsm t25 is not the same as the nissan t25. I'm not exactly sure about the specs of the turbo's but I do know the red top sr20 comes with a 50 trim t25, that flows 28 lb/min (405cfm) and the dsm t25 flows about 24-25 lb/min (295 cfm). That is about the same difference as the dsm 2nd gen t25 and the 1st gen 14b, and everybody knows the 14b kills the t25. When they get an sr20 powered car into the 7's they'll get my respect, maybe they already have????

 

[Mirage2LTurbo]

DSMJim: Are you kidding? An sr20 might rev to 9000, but beware of launching rocker arms. They are well known for this. Definitly not stock, but with stops, they can with a chipped ECU