Turbocharged400sbc
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See whaditellya!
Twin engine GTP project progress thread
- Thread starter TwinV6GTP
- Start date
Silver2kgtp
New member
In the 14 years owing and modding my GP and being on here. Only 3 GP's stood out to me as some of the best builds.
1 - Matt's TTGT
2- John T's MP112
3- JonBob's (now Greg's) Whipple
And now YOU!!!
One unique ride and a milestone for GP's
1 - Matt's TTGT
2- John T's MP112
3- JonBob's (now Greg's) Whipple
And now YOU!!!
One unique ride and a milestone for GP's
TwinV6GTP
New member
Looking good so far, still have to test that full throttle 2-3 shift.
TwinV6GTP
New member
thanks, I had some help from my guys at the shop but yes I think we did it very good time. It was a very complex project. The motor mounts are really strong too there is 5 times less movement then with the stock mounts. It is very stiff but yet has some give (not solid).
I also had some great tips and advice from the pioneers who did it first like James and Dave at TEP and Pontiac Jeff. That saved me a lot of research and messing around.
I knew what I had to do, what was involved. However nothing prepares you for the mount fabrication, it's VERY VERY VERY tight fit. Had to cut the Cradle in multiple areas and reweld it.
TwinV6GTP
New member
Thanks, and we are just beginning to scratch the surface of the car's potential. There is very little weight reduction so far, 200 easy pounds to remove then another 200-300 harder/more expensive pounds to remove. Built motors, built front trans and rear trans. The sky's the limit.
We are still running bone stock engines and trans (although the rear is a stock Cadi) everything is super cheap except for the turbo kits that we built.
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TwinV6GTP
New member
Get it working electrically I supposed ?
Yes it's very easy but I am running full manual at the moment.
At first I did it with push pull switches. The solenoid controls are just grounds and you need power to the solenoid (12V).
Now I have a TCM820 which as the ability to auto shift via RPM sensing. But the RPM sensing is erratic so I shift manually.
With the TCM820 I can control line pressure via a knob. I run full pressure because I don't drive the car on the street very much.
For making it work via the stock PCM I think you have to invert the signals but turbocharged400sbc could answer this better I have not attempted to do ECM control.
As for the Bonneville subframe it would have been probably a better choice but there are a lot of things to verify for compatibility for the knuckles and suspension. swaybars etc...
I had all my mounting points done it was quicker to redo the mounts. Also it was already a problem the factory mounts are too sloppy for high powered cars so that had to be addressed. Two birds, one stone.
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TwinV6GTP
New member
Getting ready for tomorrow's test N tune I found a major issue that needs to be addressed.
As suspected and also warned by guys who knows this trans. The 4.6L Northstar 4t80E converter is way too tight for a large turbo like a 6262.
I can barely make any boost off the line.
I didn't even think to check because of how hard the car got off the line. The front engine helps the rear get into the right RPM but right off the line, the rear engine has zero boost unless I stay full throttle on the torque converter for 5 + seconds and even then it's 4-5 psi, not nearly enough.
So we are starting right now a last minute change of the turbo setups front to back. Small turbo in the back and big turbo in front (unfortunately).
But the real solution is a looser stall in the back really... but I don't have time for that nor do I feel like taking out the trans just yet.
As suspected and also warned by guys who knows this trans. The 4.6L Northstar 4t80E converter is way too tight for a large turbo like a 6262.
I can barely make any boost off the line.
I didn't even think to check because of how hard the car got off the line. The front engine helps the rear get into the right RPM but right off the line, the rear engine has zero boost unless I stay full throttle on the torque converter for 5 + seconds and even then it's 4-5 psi, not nearly enough.
So we are starting right now a last minute change of the turbo setups front to back. Small turbo in the back and big turbo in front (unfortunately).
But the real solution is a looser stall in the back really... but I don't have time for that nor do I feel like taking out the trans just yet.
Turbocharged400sbc
New member
like I told you before that's the better setup... you want the quick spool and explosive torque in the rear and you want the more top end power up front where you can use it... this is a good problem bro...two birds. .. one slingshot
Problem could be same as I had. The RPM signal is more of a sawblade wave and usually the external electronics are looking for a square wave.
Possibly a MSD 8913 tach driver box or the sorts to convert it to the square wave.
TwinV6GTP
New member
Yes I was expecting this as well. But I was hoping the converter would let me boost until I find the perfect match converter for that size turbo. Ideally you want the big power in the back, not the front. Now my front engine is more powerful and that makes no sense. I will try it like that for now.
The turbos are switched. I will have to retune both setups now so lots of testing tomorrow before a real pass. It rained all day so I did as much testing in the rain that I could but with no load (low traction), it's hard to get the boost control right.
TwinV6GTP
New member
It could be but what is strange is that the signal looks good at times (stable) then will starting showing double more RPM or lower rpm erratically. Looks more like a dirty signal more than a signal type issue.
My AEM reads it to perfection. Normally the AEM can't read the RPM right on most other machines I had it on (Side by side and snowmobiles)
My HKS boost contoller reads RPM perfectly it seems. But the Aeromotive speed controller had issues. Even with a deal PRJ built to clean up square the signal, it would still switch to highspeed and back to low at idle every 30/40 seconds.
Removed it all together, and idles perfectly. So now just using a hobbs switch to toggle highspeed on the controller once boost hits.
I tried to do any little tricks, new twisted pair wires, ect to try and get it a clean signal.. and nothing would work like desired.
Figure its just the clunky device it self having the issue.
GTPpower
New member
If I were you, to prevent all that work, I would have just set up an antilag switch on the rear motor to pull timing way down to spool the turbo.
TwinV6GTP
New member
I already switched the turbos around. But going to the track only Friday, it's raining today.
But yes an antilag timing map in the low RPM full throttle range would help.
So far it seems the swap is just right. The 6262 spools about the same up front then the small GTX3076R in the back. So I can brake boost both at the same time which makes it easier to launch.
Turbocharged400sbc
New member
use the IAT for the anti lag, far better since you can also modify afr as well as the spark via iat
Turbocharged400sbc
New member
for some reason i recall dark horizon had a nice setup that i wanted to imitate on the TR but we spool too fast as is...
one thing i wanted to play with the oem pcm was to make a 2 step using the range switch input to fool the pcm into thinking your in R when your in 1st at the line by breaking the signal "b" circuit iirc...voila cheap 2 step
one of these days i was gonna play with it on my 97 gtp
while your front engine is more powerfull just remember that power is more usefull at the front past the 330
that rear with the smaller turbo is gonna start ripping right away, and id bet its tq curve is far fatter down low where you want it till the front can start pulling its fair share without rippin the tires off....
one thing i wanted to play with the oem pcm was to make a 2 step using the range switch input to fool the pcm into thinking your in R when your in 1st at the line by breaking the signal "b" circuit iirc...voila cheap 2 step
one of these days i was gonna play with it on my 97 gtp
while your front engine is more powerfull just remember that power is more usefull at the front past the 330
that rear with the smaller turbo is gonna start ripping right away, and id bet its tq curve is far fatter down low where you want it till the front can start pulling its fair share without rippin the tires off....
TwinV6GTP
New member
I thought about the same thing or the park signal. I'm sure it wouldn't be hard to do for us.
The next step once we have the rear trans proven reliable is going antilag on both engines for a quick spool. At the moment it would be hard to bracket race because it spools too slow. If the guy lights up the second set of yellows I'll have to spool up before I light my second set. And that's tricky because you lose brake power when pumping the pedal spooled up. That said I will install an electric vacuum pump for that reason. Also if the front engine quits on a 150mph pass I don't know if I can even stop the 4400 lbs car (now with the 4t80e)