Ok, I have been looking at loads of different threads where dynos have been posted and in many cases but not all cases, the torque curve starts to go downwards at the high end for turbo installations. I don't like that and I had a very slight effect of this myself with my previous car. In this thread I want some advice on how to improve the curve other than the tuning itself by changing or improving the setup.

I did a pic of how I like it to look like. TQ should be the same or increasing after the turbo starts to boost and the HP shall rise with the engine rpm.



It seems that it is exhaust restriction that causes the drop at high rpms, as turbo setups with small turbos or bad manifolds have a much worse torque up high than the bigger setups. Understandable.
However if we take the 3076r (.82a/r) for example, and intend a power of 350-400whp on stock compression, the turbo should not be too restrictive right? Several posts about it being good to about 500 before its time to go gt35.

Then we have the manifold and with my 330whp and ILP cast I had a very weak decay in tq at high rpms, was close to what I wanted but not quite. Would a real collector manifold solve the problems?

Also that car was fitted with a skunk 2 exhaust, and had the stock cat still. How would the stock 08 exhaust compare? Too restrictive?

Any other fixes to improve the overall efficiency without plowing big bucks into the setup?

 

my own experience with these cars tells me you are blaming the problem on the wrong thing.

have you ever seen an AFR plot on a chart? in most cases the closer you get to redline (usually somwhere around 8k on ap1's) the car tends to run extremely rich for safety reasons. upwards right around redline its common to see numbers in the low 10s. lots of tuners will leave the car like this to avoid any issues - at those engine speeds and for the amount of time you spend all the way up there it's usually not worth the risk to lean the car out for a prettier power curve.

i'm sure others will chime in but that's what i have noticed, and i've been told that's why it is not usually messed with.

 

I believe you're on the right track in regards to efficiency and exhaust restriction. First, best practice leads to a 3 inch or better exhaust - stock exhaust (regardless of year) and cat will not be very effective at sustaining power in higher rpms and will severely limit your power output.

As for the manifold...I don't think that is a major problem for what you're trying to accomplish, especially since you're trying to do this without braking the bank. The main characteristics affected by manifold design are spool time and overall power placement of the curve throughout rpm band, not necessarily only at the top end. Here's my backup on this theory:

[QUOTE=Full-Race Geoff;10605014][B]RESULTS:

 

Thats a very useful post Spectacle, thanks alot. I will definitely stick to my plan and build my own tubular, as it clearly increases the efficiency of the setup.

What about the exhaust then, whats the problem with stock exhausts? Is it the general size of piping or the sound dampeners or the cat? The stock cat + skunk 2 exhaust seemed to work well for what I did last time. Could just swap the cat for a pipe tho as I will be running E85, but I doubt it is needed.

@Teloshedge
Thanks for the heads up on the afr, will look into that some more. However my initial feeling is that this depends very much on the specific tune and setup. With a more restrictive setup where you have to boost more to gain power you will run into problems sooner aswell and will have to compensate with afr or ignition timing. Key word is efficiency I guess.

 

Combination of both. The name of the game here is backpressure, and you want to try to free up as much of it as possible to let the exhaust gases flow freely from the turbine housing. Free flowing = higher top end power

 

try playing with the WG

 

assuming the boost pressure stays constant boost is going to mimic the stock power curve, just move it up. if the results show something different then something is going on with the boost pressure.

for example most greddy turbo kits have a boost surge around 3500 rpm which is why they have an unnatural amount of torque for the amount of HP they have. the opposite end of that spectrum is the centrifugal blower kits that are boost by rpm and gain very little power down low and have peak power and torque right near redline. the SOT eaton blower kit is the most linear of any kit and the dyno results show super flat torque, like stock, just higher. a good turbo kit without boost surge or creep will do the same thing, it'll just have to be above a certain RPM before the turbo will give full boost.

 

I am using electronic boost control. Had no issues with boostcreep with the 38mm turbonetics WG from ILP in my last setup but maybe thats too restrictive aswell.... hmmmm....

Also remember I read somewhere that it can be important to angle the WG pipe in a "free flowing" angle (read less than 90 degrees) out of the collector of the tubular manifold. To avoid boost creep that is.

 

Good luck getting the torque curve to continue to increase all the way to redline..

 

only way would be to continue to add boost by rpm like a centrifugal blower does.