why not increase boost to reduce trq drop
10-16-2010, 12:28 PM
#1
why not increase boost to reduce trq drop
So say you have a typical dyno like this
(just for an example Vas, not directed at your tune but just in general)
Assume the turbo is no where near out of breath, your fuel system is adequate, etc...
So why not add a couple more pounds of boost above 5000 rpms to give a flatter torque curve. The graph above is losing over 100ft-lbs in the prime driving area. Every boost controller should be able to do that. Trq are higher rpm is less "dangerous" on the motor ie: vortech.
Seems like tuners are leaving a lot on the table with turbo system that has alot more in it
Just curious, why its not done? Seems like everyone tunes for a flat boost curve once the turbo is spooled and you get the nasty trq drop as a result
(just for an example Vas, not directed at your tune but just in general)
Assume the turbo is no where near out of breath, your fuel system is adequate, etc...
So why not add a couple more pounds of boost above 5000 rpms to give a flatter torque curve. The graph above is losing over 100ft-lbs in the prime driving area. Every boost controller should be able to do that. Trq are higher rpm is less "dangerous" on the motor ie: vortech.
Seems like tuners are leaving a lot on the table with turbo system that has alot more in it
Just curious, why its not done? Seems like everyone tunes for a flat boost curve once the turbo is spooled and you get the nasty trq drop as a result
Last edited by str8dum1; 10-16-2010 at 12:30 PM.
10-16-2010, 12:34 PM
#3
ya that may help extend the powerband, but why not use what you already have...
The turbo is still well within its efficiency so AITs wont be a concern.
I think the dyno above was like 11psi, so why not bump to say 13 psi after 5000 rpms. Your peak HP will go up, but your max trq will still be the same, but you'll have maybe 410 ft-lbs at 7000 rpms instead of 330 ft-lbs
The turbo is still well within its efficiency so AITs wont be a concern.
I think the dyno above was like 11psi, so why not bump to say 13 psi after 5000 rpms. Your peak HP will go up, but your max trq will still be the same, but you'll have maybe 410 ft-lbs at 7000 rpms instead of 330 ft-lbs
Last edited by str8dum1; 10-16-2010 at 12:35 PM.
10-16-2010, 02:08 PM
#6
Adding headers or cams would probably be the best idea to increase TQ numbers. While bumping boost would do it to you'd also bump HP and probably not fix the 100+ TQ number drop. I rather like this Dyno sheet actually 
"auto magic" traction control past 4300 RPM's is great for street driving IMO keeps you out of trouble under "defensive" driving situations 
"auto magic" traction control past 4300 RPM's is great for street driving IMO keeps you out of trouble under "defensive" driving situations
10-16-2010, 02:40 PM
#7
Vas- lol, i just happened to see your dyno 1st
question is, why wouldnt you? People pay good money for turbos that are under utilized. trq is what keeps the car pulling. if your redline is 7200, why not shift back into more trq?
Who cares if you bump HP, HP doesnt break parts, trq does (obviously to an extent). And you've already hit peak trq at a much lower rpm so if there was gonna be damage it was done.
The dyno comparison would look like this (Vas's 9psi dyno- trq drops 80 ft-lbs)
why wouldnt you want the progressive curve?
Why spend all that money on headers, etc when your turbo can do the same thing...
I mean there must be a reason its not done that way...
question is, why wouldnt you? People pay good money for turbos that are under utilized. trq is what keeps the car pulling. if your redline is 7200, why not shift back into more trq?
Who cares if you bump HP, HP doesnt break parts, trq does (obviously to an extent). And you've already hit peak trq at a much lower rpm so if there was gonna be damage it was done.
The dyno comparison would look like this (Vas's 9psi dyno- trq drops 80 ft-lbs)
why wouldnt you want the progressive curve?
Why spend all that money on headers, etc when your turbo can do the same thing...
I mean there must be a reason its not done that way...
Last edited by str8dum1; 10-16-2010 at 02:50 PM.
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10-16-2010, 04:47 PM
#10
^aftermarket, but setup doesnt matter as I coulda grabbed almost any dyno from this forum. as any setup on pump gas is no where near pushing their turbos to their limits
that can be a concern with any setup...
and say it was tuned this way on a 9psi setup. wouldnt even matter as even 13-14 psi would still be safe. And who's to say its not safe. 400 ft-lbs at 6000rpms isnt the same thing as 400 ft-lbs at MBT
and say it was tuned this way on a 9psi setup. wouldnt even matter as even 13-14 psi would still be safe. And who's to say its not safe. 400 ft-lbs at 6000rpms isnt the same thing as 400 ft-lbs at MBT
Last edited by str8dum1; 10-16-2010 at 04:49 PM.
10-17-2010, 07:07 AM
#13
On a stock motor, it's safer to have torque drop off at high piston speeds to reduce stress on internal components. On a built motor, what you must essentially do to achieve a flat torque curve is to reduce the boost near peak torque. Boost is going to be limited by knock/octane, fuel delivery, and the turbos. Most folks with a built motor will run the maximum boost they can for their given set up. That usually means a torque curve that reflects the volumetric efficiency of the engine.
Last edited by rcdash; 10-17-2010 at 07:09 AM.
10-17-2010, 04:36 PM
#15
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first you need to see if you are actually holding the boost all the way through, this will be a function of the quality of the boost controller and the exhaust system being open enough to no cause the turbo to slow down.
Here is my graph at 10 psi, as you can see the boost holds all the way and the torque does as well not dropping much.
I have open dumps, 3 inch dual exhaust and also the Greddy profec e01 which allows you to adjust the gain at various rpm settings to straighten out the boost curve, at that chart it could be adjusted to be a little straighter but you can see it can be done if you have the right parts.
Here is my graph at 10 psi, as you can see the boost holds all the way and the torque does as well not dropping much.
I have open dumps, 3 inch dual exhaust and also the Greddy profec e01 which allows you to adjust the gain at various rpm settings to straighten out the boost curve, at that chart it could be adjusted to be a little straighter but you can see it can be done if you have the right parts.
10-17-2010, 05:30 PM
#16
^^^What turbo(s) and exhaust housings on them.
The dyno in the OP uses a 6262 T4 with a .58a/r housing. This is about equal to a GT35r turbo with a .82 T3 housing, and from testing done this is a very good turbo for a stock block, at about 400whp. Anything past that and the turbine becomes a restriction, cauising torque to drop in the upper rpm range.
I would say a .68 T4 would be good to about 480whp and anything past that a .81 T4 or even .96a/r for those that want to push a single turbo to it's limits.
I will have some test results soon with a T4 .68 housing on a stock block. Will share as soon as I get them.
The dyno in the OP uses a 6262 T4 with a .58a/r housing. This is about equal to a GT35r turbo with a .82 T3 housing, and from testing done this is a very good turbo for a stock block, at about 400whp. Anything past that and the turbine becomes a restriction, cauising torque to drop in the upper rpm range.
I would say a .68 T4 would be good to about 480whp and anything past that a .81 T4 or even .96a/r for those that want to push a single turbo to it's limits.
I will have some test results soon with a T4 .68 housing on a stock block. Will share as soon as I get them.
Last edited by Boosted Performance; 10-17-2010 at 05:32 PM.
1.02 with a T3 hot side, yes, but not a T4 that big.
10-17-2010, 06:32 PM
#20
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^^^What turbo(s) and exhaust housings on them.
The dyno in the OP uses a 6262 T4 with a .58a/r housing. This is about equal to a GT35r turbo with a .82 T3 housing, and from testing done this is a very good turbo for a stock block, at about 400whp. Anything past that and the turbine becomes a restriction, cauising torque to drop in the upper rpm range.
I would say a .68 T4 would be good to about 480whp and anything past that a .81 T4 or even .96a/r for those that want to push a single turbo to it's limits.
I will have some test results soon with a T4 .68 housing on a stock block. Will share as soon as I get them.
The dyno in the OP uses a 6262 T4 with a .58a/r housing. This is about equal to a GT35r turbo with a .82 T3 housing, and from testing done this is a very good turbo for a stock block, at about 400whp. Anything past that and the turbine becomes a restriction, cauising torque to drop in the upper rpm range.
I would say a .68 T4 would be good to about 480whp and anything past that a .81 T4 or even .96a/r for those that want to push a single turbo to it's limits.
I will have some test results soon with a T4 .68 housing on a stock block. Will share as soon as I get them.
I know the example was using an ST kit but it didn't seem to mean the topic was ST only but if it is disregard my post then