i've noticed that evo's running stock turbos have good torque to about 4-4.5k, however the torque starts to drop once the turbo spools...and the HP picks up.

is that because of the restrictive stock turbo?

 

thats a good question i have wondered that as well...

 

Look at some graffs from a v8 or 6 you'll see pretty much the same thing.

 

v8's or big v6's usually have very linear curves..well at least performance orientanted v8/v6 motors.

 

do you mean tq drops after 5500-6000rpm?

rather than after spool?



Its mainly because of the turbo.

You can put a bigger turbo in but at the cost of spool (ie low end tq)

 

is that stock turbo?

 

yes, mods are:
Cosworth filter
3port
3" frontpipe + 3" HFC
trick muffler

 

thats a very nice curve. what octane?

 

98RON = 92.5oct

 

ya thats a good lookin curve..

 

actually the car feels a but grumpy (like its drowning) just after spool, upto 4k... then there is a bit of a kick in the back..

so when I have time I will sort that out

 

It doesn't matter what size turbo you have...if you are pushing the turbo more down low than it can possible support up top as the engine is able to ingest more air you will get this drop off.

Basically the problem is we are all going for super fast spool and high torque spikes but the turbos cannot maintain them. To get a flat curve you need to get pretty much a 35r and run like 28psi flat and you should have a nice flat torque curve.

I could have a flat torque curve on mine if I ran really low boost but wheres the fun in that?



Notice how when boost starts tanking, so does your torque....

 

Boost = Torque

Murlo, you totally need go to a 20 psi tune. LOL!

 

In simplest terms for our cars...yes, lol. That is what I was trying to convey.

Double that and now you are talking...40psi for those slow math types

 

Torque will always drop off before 5250 on a engine. Doesn't matter how many cylinders it has. Even formula1 engines drop off but they do at much slower rate.