why not increase boost to reduce trq drop
10-17-2010, 06:37 PM
#21
It is a good post, and shows that tq can be held through in the upper RPM range. I only ask because of flow, as it plays a huge role. The 18g kit is well suited for the VQ, and you can tell this by looking at the HP curve, it never flattens out, it just keep going.
Last edited by Boosted Performance; 10-17-2010 at 06:39 PM.
10-18-2010, 06:43 AM
#23
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I think the torque drop probably has more to do with the VQ35DE's lack of VVEL thus restricting the engine's breathing at high RPM. If you push more boost it'll probably just be minimal gains but with a massive increase in AIT. If you look at the VQ37VHR's dyno charts from the 370Z subforum, their engines are able to keep a pretty flat torque curve all the way to redline.
https://my350z.com/forum/forced-indu...nt-inside.html
https://my350z.com/forum/forced-indu...nt-inside.html
10-18-2010, 10:00 AM
#26
lots of good comments. Obviously a properly setup boost controller is a must.
this thread wasnt for any car or turbo setup in particular, both TT and ST apply.
Knock and octane wouldnt really be much of a concern for most people's standard pump gas tunes as the turbos should be well within their optimal efficiency island.
Another example would be like Thom00001's car and his complaint that his trq took a dump after 6000 rpms bc of his stock cams. His turbos should have been able to easily carry his powerband out to redline with a just a little more boost once the trq started to drop. Not the most efficient way to alter engine VE, but its free.....
this thread wasnt for any car or turbo setup in particular, both TT and ST apply.
Knock and octane wouldnt really be much of a concern for most people's standard pump gas tunes as the turbos should be well within their optimal efficiency island.
Another example would be like Thom00001's car and his complaint that his trq took a dump after 6000 rpms bc of his stock cams. His turbos should have been able to easily carry his powerband out to redline with a just a little more boost once the trq started to drop. Not the most efficient way to alter engine VE, but its free.....
10-19-2010, 03:27 PM
#27
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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.
10-19-2010, 08:27 PM
#28
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if you are on something "cooler" like e85, u got more room, but no reason to then be more conservative on lower rpms, you jsut shoot for optimal range on turbo(s), of course you may have other limitations such as engine, clutchc, the turbo itself....
10-20-2010, 07:09 AM
#29
lots of good comments. Obviously a properly setup boost controller is a must.
this thread wasnt for any car or turbo setup in particular, both TT and ST apply.
Knock and octane wouldnt really be much of a concern for most people's standard pump gas tunes as the turbos should be well within their optimal efficiency island.
Another example would be like Thom00001's car and his complaint that his trq took a dump after 6000 rpms bc of his stock cams. His turbos should have been able to easily carry his powerband out to redline with a just a little more boost once the trq started to drop. Not the most efficient way to alter engine VE, but its free.....
this thread wasnt for any car or turbo setup in particular, both TT and ST apply.
Knock and octane wouldnt really be much of a concern for most people's standard pump gas tunes as the turbos should be well within their optimal efficiency island.
Another example would be like Thom00001's car and his complaint that his trq took a dump after 6000 rpms bc of his stock cams. His turbos should have been able to easily carry his powerband out to redline with a just a little more boost once the trq started to drop. Not the most efficient way to alter engine VE, but its free.....
10-20-2010, 07:35 AM
#30
too bad none of the pro tuners chimed in for a technical reason. If you look at the dynos of the fast cars, they have flat or increasing trq curves to redline. Surprising that more people dont wanna go faster and utilize their setups fully.
10-20-2010, 07:45 AM
#31
10-20-2010, 07:52 AM
#32
To add my two cents... very good topic str8dum1... I havent been around on Z in a while its good to get good post.
I think also the fact that our engines are open deck in design that vibration and bleed off internally could be a factor in stabilizing not only HP but TQ as in general the more volume of air the more TQ (in general). Like Greddy TTs on stock blocks put down more TQ than the APS, non-extreme, due to shear volume of turbos and piping.
I also asked this same question a few years ago and couldnt get a solid answer of adjusting the boost to solve. I think it can me done with about a weeks worth of tuning, but I think most tuners have a set number of hours they are willing to invest in a tune. Not that any one tuner halfazzes something but after 2 full days, the bills start to pile up with no revenue.
I think one could increase the over all curve and make it longer but end the end it will drop slightly due to physical airflow issues be it from the exit or entry side, not to rule out internal losses from the deck design.
good stuff
maybe if the motors get a Darton or similar sleeve this will help?!?!?! In reality boost will over ride all defects...LMAO
also with the ST set ups. smaller pipes being ran 8 and 9 foot in length create more volume than smaller pipes even those on a greddy kit, so the massive volumes of air being pushed aids in those TQ increases above.
I think also the fact that our engines are open deck in design that vibration and bleed off internally could be a factor in stabilizing not only HP but TQ as in general the more volume of air the more TQ (in general). Like Greddy TTs on stock blocks put down more TQ than the APS, non-extreme, due to shear volume of turbos and piping.
I also asked this same question a few years ago and couldnt get a solid answer of adjusting the boost to solve. I think it can me done with about a weeks worth of tuning, but I think most tuners have a set number of hours they are willing to invest in a tune. Not that any one tuner halfazzes something but after 2 full days, the bills start to pile up with no revenue.
I think one could increase the over all curve and make it longer but end the end it will drop slightly due to physical airflow issues be it from the exit or entry side, not to rule out internal losses from the deck design.
good stuff
maybe if the motors get a Darton or similar sleeve this will help?!?!?! In reality boost will over ride all defects...LMAO
also with the ST set ups. smaller pipes being ran 8 and 9 foot in length create more volume than smaller pipes even those on a greddy kit, so the massive volumes of air being pushed aids in those TQ increases above.
Last edited by 4SHIZZIL; 10-20-2010 at 07:59 AM.
10-20-2010, 08:03 AM
#33
its take 3 seconds to add more duty cycle at higher rpms. Thats how an open loop boost controller works. you set duty cycle vs rpms.
there is absolutely no flow limitations with any of the current turbos kits for the VQ at pump gas levels that would limit them from making flat trq curves all the way to redline. That is 100% a tuner based decision.
there is absolutely no flow limitations with any of the current turbos kits for the VQ at pump gas levels that would limit them from making flat trq curves all the way to redline. That is 100% a tuner based decision.
10-20-2010, 08:03 AM
#34
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.
or we are just seeing the flat spot that is a part of an overall curve just like the first dyno (4-5K rpms) posted by the OP.
If you have OVERKILL you can tune that larger sweetspot for the RPMs needed. Not saying you are wrong at all....
just asking the question if the engine ran to 50,000 rpms would we see the same TQ drop?
If so then we can say that in order to have a flat TQ curve one must back off the boost all together to balance it out. But since we want HP we sacrifice the loss in the end?
Last edited by 4SHIZZIL; 10-20-2010 at 08:05 AM.
10-20-2010, 11:41 AM
#35
overkill, what r you talking about?
RcDash is saying if you get rid of the big hump, it will make the curve look flatter. So instead of getting that 430 ft-lbs you only boost enough to make 375 ft-lbs. That way, by redline, you dont have that drastic drop. It would mimic a centrifugal supercharger at that point.
If you ran an engine out to 50,000 rpms and still had a turbo within its efficiency, then yes you could have a flat/rising trq line with increasing boost towards redline.
None of that is the issue, the question is, why dont tuners do it that way....
RcDash is saying if you get rid of the big hump, it will make the curve look flatter. So instead of getting that 430 ft-lbs you only boost enough to make 375 ft-lbs. That way, by redline, you dont have that drastic drop. It would mimic a centrifugal supercharger at that point.
If you ran an engine out to 50,000 rpms and still had a turbo within its efficiency, then yes you could have a flat/rising trq line with increasing boost towards redline.
None of that is the issue, the question is, why dont tuners do it that way....
Last edited by str8dum1; 10-20-2010 at 11:43 AM.
10-20-2010, 02:03 PM
#37
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i think a lot of tuners aren't chiming in because its just not a good idea. if you turned your boost up past 5k rpms, then you'd probably just get sick of all the good hp/tq up top and so little down low, that you'd want to adjust your boost controller to always give you that number from spool up to redline. hence why most people run the max amount of boost on their specific engine that they feel safest with. so basically, you're fighting with greed of more power.
10-20-2010, 02:37 PM
#38
well one thing on a stock block is that TQ is a beast. so the longer you stay in peak power (TQ) the more threat of BOOMB! Hence why boosting in 6th gear for long periods of time is a general no no on a stock block. Also boost and timing seems to be tuned to a fadding affect to redline on high TQ set ups (in my experiences), besides who has the space to boost in 6th to redline often?
maybe its a safety habbit that tuners develop due to doing so many stock motors vs built ones... like I said very good question that the only way I see being fixed is to have a huge tq curve from massive amounts of boost so that flattening is easier.
I agree with DEANFOOTLONG also.. prob wont get them to chime in.
maybe its a safety habbit that tuners develop due to doing so many stock motors vs built ones... like I said very good question that the only way I see being fixed is to have a huge tq curve from massive amounts of boost so that flattening is easier.
I agree with DEANFOOTLONG also.. prob wont get them to chime in.
Last edited by 4SHIZZIL; 10-20-2010 at 02:40 PM.
10-20-2010, 04:09 PM
#39
i think a lot of tuners aren't chiming in because its just not a good idea. if you turned your boost up past 5k rpms, then you'd probably just get sick of all the good hp/tq up top and so little down low, that you'd want to adjust your boost controller to always give you that number from spool up to redline. hence why most people run the max amount of boost on their specific engine that they feel safest with. so basically, you're fighting with greed of more power.
Have you ever setup a controller? Nothing before peak trq would change. Why would you think it would? People ARE NOT running progressive boost though. That's the entire point. AS your engine's VE goes down, 11psi is not max boost anymore.
Cars where the trq is dropping off are running the same duty cycle throughout the boost band.
like this
pic1
And to fix that, you set your BC up like this
pic2
Obviously, the power curve before 5500 rpms is absolutely the same.
The car still makes 432 ft-lbs peak trq @4500 rpms, but now makes 400 ft-lbs at 7000 rpms instead of 330.
Here's an example with a boost curve on it
See how the boost curve is completely flat. See how the trq take a dump? This a greddy kit with a TON more headroom. If the tuner were to bump the boost (ie flat boost curve til 5500 rpm) after 5500 rpms, the car would be significantly faster because the downshift would bring you into 75 ft-lbs more trq. You are using the turbo to increase the engines VE past the point where the cams, etc could carry it on its own.
If someone came out and said, past best engine VE, AITs, EGT's, cylinder pressure, etc go sky high when increasing boost to counteract. fine. But so far thats not the case...
Last edited by str8dum1; 10-20-2010 at 04:24 PM.
10-20-2010, 04:29 PM
#40
[QUOTE=deanfootlong;8733589 if you turned your boost up past 5k rpms, then you'd probably just get sick of all the good hp/tq up top and so little down low[/QUOTE]
You are not understanding what is going on.
Have you ever setup a controller? Nothing before peak trq would change. Why would you think it would?
Car where the trq is dropping off are running the same duty cycle throughout the boost band.
like this
pic1
And to fix that, you set your BC up like this
pic2
Obviously, the power curve before 5500 rpms is absolutely the same.
The car still makes 432 ft-lbs peak trq @4500 rpms, but now makes 400 ft-lbs at 7000 rpms instead of 330.
That is solely an rpm/load issue. When would you be driving full boost 5500+ rpms in 6th gear? Anything below 5500 rpms is the EXACT same power you'd be running by using a straight line boost duty cycle, as in pic 1. It would only be past 5500 rpms in this example that ANYTHING to do with trq or HP would change.
You are not understanding what is going on.
Have you ever setup a controller? Nothing before peak trq would change. Why would you think it would?
Car where the trq is dropping off are running the same duty cycle throughout the boost band.
like this
pic1
And to fix that, you set your BC up like this
pic2
Obviously, the power curve before 5500 rpms is absolutely the same.
The car still makes 432 ft-lbs peak trq @4500 rpms, but now makes 400 ft-lbs at 7000 rpms instead of 330.
That is solely an rpm/load issue. When would you be driving full boost 5500+ rpms in 6th gear? Anything below 5500 rpms is the EXACT same power you'd be running by using a straight line boost duty cycle, as in pic 1. It would only be past 5500 rpms in this example that ANYTHING to do with trq or HP would change.