Why's my turbo car so slow?? 6.9@104
08-18-2009, 02:54 PM
#1
Why's my turbo car so slow?? 6.9@104 Well here's a little bit of background on my car...
2004 GTO, 370 iron block forged internals, 9.5:1, basically stock heads, LS6 cam, TC76 turbo in an STS setup, 4L80e with TCI computer, 3600 stall (don't want to say the brand just yet, but they are widely respected on this board)
I've been working on this car since I bought it new. It was a 6 speed car and the best I ever went with the manual trans was 10.96@136 with a 1.81 60'. Power is about 650rwhp.
Because I was tired of playing with clutches and didn't want to damage the 6 speed, as well as it being hard to launch, I decided to do a 4L80e swap. I am using the TCI standalone computer and the trans is basically a HD rebuild with the TransGo shift kit.
I figured that between launching the car better and not losing boost between shifts that I would gain some pretty good ET and keep my trap even pretty close to where it was at.
So far I'm having the best results launching the car at about 3000 rpms and just foot braking it. I haven't tried holding it with the ebrake or anything and going higher. It doesn't come out on boost and the best I can get is 1.7x 60's.
So far my best run has been 6.9@104 in the eighth... I couldn't stay in it for the 1/4 due to no cage. The one or two times I did do a full pass I could only get about 10.9@130mph in the 1/4 with a 7.1 in the eighth. It also seems to me like the converter is eating up a ton of power up top. I'm also wondering if it is too loose for launching the car as well. Just seems to me that it should be getting out harder and also trapping higher.
Here's a vid http://www.youtube.com/watch?v=xJDoSYM8NKs
Any thoughts? I can provide more info just let me know what you think.
2004 GTO, 370 iron block forged internals, 9.5:1, basically stock heads, LS6 cam, TC76 turbo in an STS setup, 4L80e with TCI computer, 3600 stall (don't want to say the brand just yet, but they are widely respected on this board)
I've been working on this car since I bought it new. It was a 6 speed car and the best I ever went with the manual trans was 10.96@136 with a 1.81 60'. Power is about 650rwhp.
Because I was tired of playing with clutches and didn't want to damage the 6 speed, as well as it being hard to launch, I decided to do a 4L80e swap. I am using the TCI standalone computer and the trans is basically a HD rebuild with the TransGo shift kit.
I figured that between launching the car better and not losing boost between shifts that I would gain some pretty good ET and keep my trap even pretty close to where it was at.
So far I'm having the best results launching the car at about 3000 rpms and just foot braking it. I haven't tried holding it with the ebrake or anything and going higher. It doesn't come out on boost and the best I can get is 1.7x 60's.
So far my best run has been 6.9@104 in the eighth... I couldn't stay in it for the 1/4 due to no cage. The one or two times I did do a full pass I could only get about 10.9@130mph in the 1/4 with a 7.1 in the eighth. It also seems to me like the converter is eating up a ton of power up top. I'm also wondering if it is too loose for launching the car as well. Just seems to me that it should be getting out harder and also trapping higher.
Here's a vid http://www.youtube.com/watch?v=xJDoSYM8NKs
Any thoughts? I can provide more info just let me know what you think.
08-18-2009, 03:01 PM
#4
You didnt say how much boost you are running. I think your times are actually right on par for your set-up. Here are your "weak links" to faster times IMO: Stock heads, small cam, small turbo, rear-mount, heavy power-robbing trans, no-trans brake.....and what sounds to be a wrong converter for your HEEEEEAAAAAAVY car.
I think high tens is actually very respectable for your set-up!
I think high tens is actually very respectable for your set-up!
08-18-2009, 03:06 PM
#5
It dynoed 650rwhp with the 6 speed... has not been dynoed with the auto. I am running 15psi on 93 and meth.
What would you change with the converter? I do think that is the biggest power drain right now. And you are correct I would estimate my car around 4200 lbs....
What would you change with the converter? I do think that is the biggest power drain right now. And you are correct I would estimate my car around 4200 lbs....
08-18-2009, 03:26 PM
#6
It dynoed 650rwhp with the 6 speed... has not been dynoed with the auto. I am running 15psi on 93 and meth.
What would you change with the converter? I do think that is the biggest power drain right now. And you are correct I would estimate my car around 4200 lbs....
What would you change with the converter? I do think that is the biggest power drain right now. And you are correct I would estimate my car around 4200 lbs....
You'll get your some of your MPH back when you get better 60s. My car will trap 133mph on a 1.8 60' and 136 with a 1.5 - low 1.6 60'. You need to data log your RPM and calculate your converter slip at the end of a full pass. If it's slipping a large amount such as over 15% you might be pushing through it too much (this can vary, i've seen some guys say they have had better ET's with this much slip). You also need to figure out what your shift extension is. I've been told that ideal is around a 800 rpm drop on a shift. Getting a good converter on the first shot with a turbo car take a lot of luck or someone with a lot of turbo experience to build it correctly for your combo. I'm on my 3rd and it's a bit too tight on the shifts, I need to make more power to loosen it up.
Your missing 0.5 sec in the 1/8 just due to your 60'. With a low 1.6 60' you'd should go pretty close to 6.5 @ 106. If you are pushing through the brakes when building boost a 2 step might help.
Another thing to look at is where your car is making peak power and where you are shifting at. If your peak power is 5600 (most likely with a 370 and a tiny turbo like you have) and you are shifting at 6500, you are going to run quite a bit slower. If it feels sluggish up top it's probably due to back pressure, the higher your rev the worse it gets.
08-18-2009, 05:54 PM
#7
First of all, forget dyno numbers, they often times aren't even close to accurate If you dyno your auto you'd probably be lucky to put down 500 rwhp with the Th400. It's just a tool for tuning.
You'll get your some of your MPH back when you get better 60s. My car will trap 133mph on a 1.8 60' and 136 with a 1.5 - low 1.6 60'. You need to data log your RPM and calculate your converter slip at the end of a full pass. If it's slipping a large amount such as over 15% you might be pushing through it too much (this can vary, i've seen some guys say they have had better ET's with this much slip). You also need to figure out what your shift extension is. I've been told that ideal is around a 800 rpm drop on a shift. Getting a good converter on the first shot with a turbo car take a lot of luck or someone with a lot of turbo experience to build it correctly for your combo. I'm on my 3rd and it's a bit too tight on the shifts, I need to make more power to loosen it up.
Your missing 0.5 sec in the 1/8 just due to your 60'. With a low 1.6 60' you'd should go pretty close to 6.5 @ 106. If you are pushing through the brakes when building boost a 2 step might help.
Another thing to look at is where your car is making peak power and where you are shifting at. If your peak power is 5600 (most likely with a 370 and a tiny turbo like you have) and you are shifting at 6500, you are going to run quite a bit slower. If it feels sluggish up top it's probably due to back pressure, the higher your rev the worse it gets.
You'll get your some of your MPH back when you get better 60s. My car will trap 133mph on a 1.8 60' and 136 with a 1.5 - low 1.6 60'. You need to data log your RPM and calculate your converter slip at the end of a full pass. If it's slipping a large amount such as over 15% you might be pushing through it too much (this can vary, i've seen some guys say they have had better ET's with this much slip). You also need to figure out what your shift extension is. I've been told that ideal is around a 800 rpm drop on a shift. Getting a good converter on the first shot with a turbo car take a lot of luck or someone with a lot of turbo experience to build it correctly for your combo. I'm on my 3rd and it's a bit too tight on the shifts, I need to make more power to loosen it up.
Your missing 0.5 sec in the 1/8 just due to your 60'. With a low 1.6 60' you'd should go pretty close to 6.5 @ 106. If you are pushing through the brakes when building boost a 2 step might help.
Another thing to look at is where your car is making peak power and where you are shifting at. If your peak power is 5600 (most likely with a 370 and a tiny turbo like you have) and you are shifting at 6500, you are going to run quite a bit slower. If it feels sluggish up top it's probably due to back pressure, the higher your rev the worse it gets.
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08-18-2009, 08:44 PM
#8
I only gain about 1mph from 1.60-1.50. It's about having a higher average HP because you are leaving with more boost to get the good 60's so it takes less time to reach full boost.
Not every vehicle is the same either. My friends NA Busa gains MPH as his 60' goes down as well.
08-18-2009, 10:01 PM
#9
I think I have some things I can do for little to no money that will help. I have a set of new 317 heads that I can give a little love to and bolt on. I also have a bunch of 2.5" and 3" mandrel bent tubing so I could move the turbo up front or at least redo the STS exhaust with better and larger tubing. I'm still wondering about the converter though...
If I redo the STS exhaust, switch from my .81 to a .96 housing, and put my 317s on with ARP studs (only ARP bolts right now) I wonder how much more power I could make. I imagine it'd make a decent amount more at the same boost level...
If I redo the STS exhaust, switch from my .81 to a .96 housing, and put my 317s on with ARP studs (only ARP bolts right now) I wonder how much more power I could make. I imagine it'd make a decent amount more at the same boost level...
08-19-2009, 12:38 AM
#10
Calculate and log what the converter is doing to see if it is in fact a problem or not. You want to look at the percentage of slip which is calculated by your speed vs rpm. You really need a transbrake to get the car to leave, if it could make more boost on a footbrake with it being rearmounted it would be slipping going down the track, so that is kind of a good sign.
Being a rear mount turbo car is one step harder, at that point you need a killer converter or one that is loose enough to spool on the transbrake and then u can lock it up going down the track to prevent massive slippage.
If you have the skills move the turbo up front it might have a chance of making decent launching boost on a footbrake. It will also make the car as a whole more enjoyable.
I have seen alot of turbo car trap better when they hook better...they like to be loaded right?
I dont know that it will make much more power. The .96 will help some, the heads will lower compression and probably hurt it alittle with the same tune/boost, and re-doing the piping may help some. If you are worried about trapping high focus on the power, if you want it to E.T. better focus on improving the 60'.
Being a rear mount turbo car is one step harder, at that point you need a killer converter or one that is loose enough to spool on the transbrake and then u can lock it up going down the track to prevent massive slippage.
If you have the skills move the turbo up front it might have a chance of making decent launching boost on a footbrake. It will also make the car as a whole more enjoyable.
I dont know that it will make much more power. The .96 will help some, the heads will lower compression and probably hurt it alittle with the same tune/boost, and re-doing the piping may help some. If you are worried about trapping high focus on the power, if you want it to E.T. better focus on improving the 60'.
Last edited by black98ws6ta; 08-19-2009 at 12:44 AM.
08-19-2009, 08:11 AM
#11
I can do that... so basically log rpm vs mph, do the calc with the gear ratio, rear end and tire size, and see how much higher my rpms are than they should be. I will do that and post the results. Does it matter how fast I go? Say if I just do like a pull to 120 so I know I'm into 3rd will that be OK?
08-19-2009, 08:16 AM
#12
My thinking on the 317s is that although they will drop the comp some, if I do the .96 housing and piping, and with the slightly larger runners of the 317s, I think it would make around the same power with the same boost level bc it's flowing more volume. From what I've read it sounds like I wouldn't want to run more than 18-19psi on stock casting GM heads. I can always play with C16 or Q16 too.
OOO one more thing. One of my good buddies has a Mustang dyno... but with the converter not being locked it seems like if I dyno it to tune it, I'm only going to see like 5000-6500 rpm with how it rides the converter. Is there any trick to this or is that just the way it is?
OOO one more thing. One of my good buddies has a Mustang dyno... but with the converter not being locked it seems like if I dyno it to tune it, I'm only going to see like 5000-6500 rpm with how it rides the converter. Is there any trick to this or is that just the way it is?
08-19-2009, 08:43 AM
#13
My thinking on the 317s is that although they will drop the comp some, if I do the .96 housing and piping, and with the slightly larger runners of the 317s, I think it would make around the same power with the same boost level bc it's flowing more volume. From what I've read it sounds like I wouldn't want to run more than 18-19psi on stock casting GM heads. I can always play with C16 or Q16 too.
OOO one more thing. One of my good buddies has a Mustang dyno... but with the converter not being locked it seems like if I dyno it to tune it, I'm only going to see like 5000-6500 rpm with how it rides the converter. Is there any trick to this or is that just the way it is?
OOO one more thing. One of my good buddies has a Mustang dyno... but with the converter not being locked it seems like if I dyno it to tune it, I'm only going to see like 5000-6500 rpm with how it rides the converter. Is there any trick to this or is that just the way it is?
what are you logging with?
08-19-2009, 10:34 AM
#15
you need to get a VSS feed back to the PCM.... are you even getting out of idle spark tables (in your logs)? I wouldn't think so if the PCM always sees 0 MPH... get a VSS back even if it's wrong so that the PCM knows you are moving. You can use a wheel speed sensor if you have nothing else handy.
08-20-2009, 10:30 AM
#18
The first time I ran my car, I was lean, but programmed the PCM to pull timing if it lost meth, so I didn't knock. I resolved the problem, picking up a full point on the AFR's. I instantly picked up 1 second and 10mph from it. The next time I went to the track, I logged the car and noticed that I wasn't spraying enough meth and the IAT's got to my programmed threshold, removing 5° timing. Again killing my MPH and ET. They wouldn't let me run another 1/4 due to safety items, but I picked up 3mph and 3 tenths in the 1/8th by adding meth and keeping my timing.
08-20-2009, 10:31 AM
#19
+1. If I were you I wouldn't go changing anything until you find the problem. If EVERYTHING is the same (including the weather) before and after the trans swap, something is definetly not right. I would expect the car to drop atleast a 1/2 second in the 1/4 from this trans swap alone.
08-20-2009, 01:57 PM
#20
[QUOTE=HydroStream6;12090049]It dynoed 650rwhp with the 6 speed... has not been dynoed with the auto. I am running 15psi on 93 and meth.
What would you change with the converter? I do think that is the biggest power drain right now. And you are correct I would estimate my car around 4200 lbs....[/QUOTE]
looks like NYI in your video.. there is a scale right at the end of the track
What would you change with the converter? I do think that is the biggest power drain right now. And you are correct I would estimate my car around 4200 lbs....[/QUOTE]
looks like NYI in your video.. there is a scale right at the end of the track