Twin engine GTP project progress thread

[SnowTh1ef]

It almost scares me how fast you got the 4t80 in and running like it's a bolt in procedure. You're amazing.

[TwinV6GTP]

It almost scares me how fast you got the 4t80 in and running like it's a bolt in procedure. You're amazing.

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.

[Silver2kgtp]

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

[TwinV6GTP]

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

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.

[91parkave]

2 things

1. All in all would it better trying mount a bonneville subframe or something with a 4t80 already?

2. Do you ever plan on releasing the info from what you did specifically to get the 4t80 working?

[TwinV6GTP]

2 things

1. All in all would it better trying mount a bonneville subframe or something with a 4t80 already?

2. Do you ever plan on releasing the info from what you did specifically to get the 4t80 working?

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.

[TwinV6GTP]

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.

[jdredd]

Get it working electrically I supposed ?
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.

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]

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.

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)

[jdredd]

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.

[Turbocharged400sbc]

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

[TwinV6GTP]

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

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.

[GTPpower]

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.

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]

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.

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.

[TwinV6GTP]

Ready !

[Turbocharged400sbc]

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....

[TwinV6GTP]

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....

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)

[Turbocharged400sbc]

use the IAT for the anti lag, far better since you can also modify afr as well as the spark via iat

[SlowFiero]

Factory rpm limiter is too slow to use as a two step. I tried, all it did was destroy the input sprag. Two step is very helpful for spooling the turbo though. I have one I adapted from the turbo buick guys. Without it there is no way I could hold my car on the line. Now I can sit at 3000-3200 rpm make as much boost as I want and not push through the brakes. Just break transmissions instead lol. I think I ran into the same rpm signal issues you guys are seeing with the two step. It would kick in at idle. Ended up getting past that when the designer put a opto isolator on the input circuit. Now works flawlessly.

Talking to Terry at precision, he said not to run against the converter spooling up for more than 3 seconds. It will pump itself out of fluid and start chewing itself up internally. Pump also can't refill the converter by the end of the run and you end up with excess slippage in third due to lack of fluid.



Cool project, going to be interesting to see how far you can push it.

[TwinV6GTP]

Thanks for the suggestions. It's not super lazy. It needs at least 3 seconds to get a solid boost number.

Here's a video of our testing during the rain. We waited until it got dry but it never did.
So we tested in the parking lot of shop on the wet cement.

The 1st video shows the big turbo in the back and the other is with the big turbo in front.
You can clearly see how loose the stock 4t65-HD converter is vs the 4.6L Northstar converter in the back.