I had been noticing ever since i put the car together that i would hit 9psi around 4-5k rpm and then it would fall to about 5psi until redline. I thought it was a tuning issue since i was on my uberdata basemap.

Fast forward to last night-

I went to raceline tuning in cincinnati on a almost completely tuned map. They put me on the dyno and we ran it in 3rd gear. Well it came out to 170whp and 160 torque. The reason being right when VTEC hits, my boost falls off to 5psi and therefore causes the torque to fall off.

does anybody know why my boost would fall off like that when VTEC hits?

btw- i searched the archives, i found several threads however no real causes were named.


Modified by Del_Slowest at 8:11 PM 10/24/2004


Modified by Del_Slowest at 8:15 PM 10/24/2004

 

GReddy kit. Internal gate. It's not your VTEC causing it. Look at any GReddy kits pressure plot, even with the 18G kit and look what happens at 4-5k RPM.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HybridKOOP &raquo;</TD></TR><TR><TD CLASS="quote">GReddy kit. Internal gate. It's not your VTEC causing it. Look at any GReddy kits pressure plot, even with the 18G kit and look what happens at 4-5k RPM.</TD></TR></TABLE>

i'm running out of it's efficiency range? that was one of my thoughts, either that or a hair crack in my couplers.

 

Dammit, you're right......

**** on T3's :****:

 

also note: the car was dropping out of boost on the low cam too, but it took until 7000 RPM vs 5500-5800 on the vtec cam. As soon as the motor needed more flow, boost dropped off. My vote goes for bad/too small turbo because the setup was able to hold 9psi of boost at 4000 RPM when the dyno was setup to jsut generate load and hold the car at a steady rpm.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blundar &raquo;</TD></TR><TR><TD CLASS="quote">also note: the car was dropping out of boost on the low cam too, but it took until 7000 RPM vs 5500-5800 on the vtec cam. As soon as the motor needed more flow, boost dropped off. My vote goes for bad/too small turbo because the setup was able to hold 9psi of boost at 4000 RPM when the dyno was setup to jsut generate load and hold the car at a steady rpm.</TD></TR></TABLE>

turbo is being upgraded soon. If i get you a dirt cheap LS tranny maybe i can get a good deal on a tune too

 

Thats pretty weak, I havent heard of the greddy kits doing that until now

 

get me a dirt cheap LS hydro tranny and I'll finish tuning it for free y0.

 

and it wasn't a greddy kit...

 

type in "18g dyno" in honda-tech search and you can see all of the dyno graphs for the 18g greddy kits. they all fall off after about 4-5k. The HP stays constant and the torque falls linear

and yes, i don't have a greddy kit, but i do thave one small *** 50 trim T3 so it's about as bad

 

this is plotting my points on the graph you showed me rouge male. i did graph it correct....right? and remember honda engines are at 98% volumetric efficiency in vtec. The reason why DSM's can do it is because they run a lot more boost. So they hit the top portion of the graph. i'll graph a DSM right now and put it on there too. (edited dsm added) This means that i need to run more boost or get a turbo with a fatter efficiency range.

i graphed

honda = red
4k- 4psi
5k- 9psi
6k- 9psi
7k- 9psi
8k- 9psi

dsm = blue
3k- 9psi
4k- 19psi
5k- 19psi
6k- 19psi

 

my guess is the wastegate isnt closing more .. once you hit vtec ... the head starts flowing more and the wastegate is just staying at the same position ? that turbo should flow more then 170 whp

 

My car is doing this too. I have a b16a3 with a t3 60/63. I really believe it is the internal gate. My spool up is hella quick and boost hits REAL hard but then just dies off once vtec engages.....

 

yupp me too on my d16z6 with a greddy kit I drop boost after 5k...it happens to alot of people. I guess its cause of the internal wategate?

 

i'm betting its the wastegate too

 

why would the wastegate cause it? what does a sticking wastegate do? wouldn't a sticking wastegate mean that it builds more boost than you want?

 

I believe its the nature of an internal wastegate. They are kinda cheap and dont seem to hold boost like the externals. I think you can comp for this with an EBC like the greddy one that has a function to keep it from dropping off. I have not used one of these and I heard they are a total bitch to set so dont go run out and buy it...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Del_Slowest &raquo;</TD></TR><TR><TD CLASS="quote">why would the wastegate cause it? what does a sticking wastegate do? wouldn't a sticking wastegate mean that it builds more boost than you want?</TD></TR></TABLE>

well i can tell you they suck from personal experience. Mine works like **** and holds the flapper open a slight bit so all I can boost is 9-10psi and it spools up super slow for the tiny *** wrx turbo I have. I don't have a problem with boost dropping off anymore though...once it gets to 9psi it will hold it all the way to redline. It used to fall back though when I had the actuator adjusted differently.

 

it is most likely the actuator. I run around 16 psi on my 15G it doesn't drop off any more. I had to mess around with the threaded arm to eliminate the problem. I actually made it so at stock boost levels the actautor is good to 4.5 PSI I brought it down to around 4. I used my MBC to raise it to 16 psi. It still kind of drops off at vtec but maybe from 16 to 14.7? I also run the boost siganl from the IM not the compressor.

 

I'm having this problem as well...i'm hitting 5.2 psi at 4500, and then it levels off to 3.5 in VTEC. I was thinking this was because of my large-duration all motor cam that I have...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BauleyCivic &raquo;</TD></TR><TR><TD CLASS="quote">I'm having this problem as well...i'm hitting 5.2 psi at 4500, and then it levels off to 3.5 in VTEC. I was thinking this was because of my large-duration all motor cam that I have...</TD></TR></TABLE>


the only way to make it stop from falling off is to either

A. Rev less
B. Run more boost ie near 13psi

 

A MBC or retarding timing won't solve any of this? This is just how greddy kits (or turbo's with internal wastegates for that matter) are?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BauleyCivic &raquo;</TD></TR><TR><TD CLASS="quote">A MBC or retarding timing won't solve any of this? This is just how greddy kits (or turbo's with internal wastegates for that matter) are?</TD></TR></TABLE>


this is how this turbo is. Don't matter if it's internally gated. You have to know how to read a compressor map, otherwise you're screwed. I will post my excel spread sheet in a few so that you can easily read one.

actually, if you have a 1.6 you can just use the same points that i did. Just make sure you find a greddy map in lbs/min and not cfm

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by maddog20 &raquo;</TD></TR><TR><TD CLASS="quote">it is most likely the actuator. I run around 16 psi on my 15G it doesn't drop off any more. I had to mess around with the threaded arm to eliminate the problem. I actually made it so at stock boost levels the actautor is good to 4.5 PSI I brought it down to around 4. I used my MBC to raise it to 16 psi. It still kind of drops off at vtec but maybe from 16 to 14.7? I also run the boost siganl from the IM not the compressor.</TD></TR></TABLE>

Good point, I am going to mess with the actuator arm and see if that helps which way did you thread it?

 

its very easy actually...its just like a boost spike...just get a new wastegate...i had the same problem...initially the wastegate would open very slowly which is why you can get 9psi..but when your hitting vtec more air is being expelled into the turbo causing the wastegate to fully open which why your only seeing 6 at the end....i got a turbonetics wastegate and boost always holds strong now....another good way of checking if your wastegate is good is hook it up to a tire pump and see if the gate is holding boost...