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Twin engine GTP project progress thread



Holy **** guys....

we worked all day on the car. Made some really trick suspension work on the bone stock suspension.
To completely get rid of the squat while still retaining some suspension and drivability. I can't believe how well it worked.

60 foot time 1.53 seconds on a dirt covered roads on cold sticky MT tires. (with a burnout on a sticky track it would be 2 tenth quicker no doubt).
0-60 mph in 2.6 seconds... it's unreal how well behaved it is yet. It is a violent acceleration but at the same time super easy to drive.
Easy low 10 second car right now on the street with little traction and still running 60% power.
I'm in love...

The sad news is by some freak accident the input shaft or chain broke in the rear transmission. It makes no sense as I'm not running a lot of boost at all.
My parts car with super sticky slicks on a glued track ran 100s of passes with no failure. Blue car 50 passes more HP and no failure either.
But the only difference is that I start in 1st gear and the 1st to 2nd gear shift is violent. I think that's what breaks the parts.

All my other drag cars I start in 2nd gear. I don't think it's a coincidence as I ran much more power (150HP more in the red parts car engine) with no failure.

anyhow we will replace the trans and do 2nd gear starts from now on and see how it goes.
In the meantime any shop wants to sponsor a transmission job on this car ?

 
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I think it's because they arent gonig the same speed all the time. The rear may peel out and be spinning faster and then when it catches it must slow down do to the front engine thats not going as fast. That sudden change has to hard on parts.
 
Fivefingerdeathpunch said:
I think it's because they arent gonig the same speed all the time. The rear may peel out and be spinning faster and then when it catches it must slow down do to the front engine thats not going as fast. That sudden change has to hard on parts.
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it doesn't work like that. They are truly independant of each other. I can shut off an engine and run single engine. I've tried it for fun and it's like having a 4500 lbs GTP.
Or a GTP with four Fat friends in it. Having two engines actually reduces the load on each engine/transmission, especially the front. The rear engine load is closer to a normal gutted GTP.
I've crunched the numbers and analysed the weight transfer.

With the new suspension mod the load of the rear is less which is why it peels off easier but now it acts more like an powerful AWD car with wheelie bars. Yet no wheelie bars !!
 


98GrandPrixIraqVet said:
Basically dragging or pushing the other transmission based on which one is moving the fastest?
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Neither. They are both moving weight according to their traction level and power level.
With the new suspension change my educated guess on the load factor for the rear engine is 60% and the front 40% off the line then going to 50% 50% when both engines have full traction.
This load factor can and will change depending on available traction. For example at a dragstrip with glue the rear will be doing 70% of the work vs 30% for the front but as the tires get their full traction again goes to 50/50
 


91parkave said:
I don't see how you come to that conclusion with different power adders and pumping efficiency of both engines.
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The numbers are not about pumping efficiency but about load carried by each engine. That means hiw much weight each engine has to drive.


Sent from my iPhone
 
I've always heard it was bad to spin a transmission in neutral at high speeds. When you shut one of the engines off, do you leave the transmission in neutral?

I still see a problem with the 2 engines being out of sync. They're not independent of one another because they are part of the same chassis. No matter what happens, one engine is dragging or pulling the other, because they are physically attached to one another. I don't know fit that is what caused your transmission issue, but time will tell. I would think it'd be odd to the PCM because the transmission is being drug through each shift. When a typical car shifts, acceleration stops during the shift...not here though.
 
Booba5185 said:
I've always heard it was bad to spin a transmission in neutral at high speeds. When you shut one of the engines off, do you leave the transmission in neutral?

I still see a problem with the 2 engines being out of sync. They're not independent of one another because they are part of the same chassis. No matter what happens, one engine is dragging or pulling the other, because they are physically attached to one another. I don't know fit that is what caused your transmission issue, but time will tell. I would think it'd be odd to the PCM because the transmission is being drug through each shift. When a typical car shifts, acceleration stops during the shift...not here though.
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When a car shifts under hard acceleration momentum keeps the acceleration going a second or two. It's nothing unusal. The fact the other engine helps keep more momentum going reducing the shock in the next gear.

The car shifted really incredibly well. I think it was a freak breakage because of the very high miles trans in the car. I think it's the chain that snapped, it was probably tired already. A fresh trans would go a long way.
 
Now that I think about it, I was wrong anyways...it'd be similar to a shift going down a steep hill...in your case a STEEP hill.

What do you shift the transmission into when the engine it's bolted to is off?
 


for the "idle" trans we use a flat towing trans circulation pump to keep the guts of the rear trans wet while in neutral with the engine off.

for short distances after being recently started and shutoff he should be fine since its mostly a racecar.

the Tq converters will stall as much as they need (slip) to equalize the load depending on the traction/load, that the beauty of a viscous tq multiplying drive. when launching the rear see's everything (one reason our 25.3 chassis is using 4x4 LCA hardware/heims and extra bracing)

so yer probably right the 1-2 did it in. but keep in mind that 400ftlbs is plenty to break a stock IS when the shock load can have the converter multiplying that up to 1000+ for a split second. plus without the rear driving a SC yer already 50+hp more than the front engine just from the crank not spinning it.

you may want to look into the 3.71fdr 80e though i dont think it will clear your unibody rails, thats just a mallet and a few licks away....

looking good guys.

kinda make me pissed we havent gotten more done on the 442 in the 14 year build/rebuild/rebuild lol
 
Pull tons of power at the 1 2 shift.. way easier than dealing with a second gear start or anything. On my drag car I run a touch of fuel cut on the 1 2 shift.
 
Booba5185 said:
Now that I think about it, I was wrong anyways...it'd be similar to a shift going down a steep hill...in your case a STEEP hill.
Click to expand...
Just thinking out loud...
On a normal setup, going down a "steep" hill, off the gas, there is no engine compression braking. If you pull it into a gear that is slower than the engine speed, then you have compression braking which would cause stress on trans parts. With both engines under power is the trans locked into that gear?


Turbocharged400sbc said:
the Tq converters will stall as much as they need (slip) to equalize the load depending on the traction/load, that the beauty of a viscous tq multiplying drive.
Click to expand...
Do not these torque converters have a clutch? Seems like one of the comments in the thread for the turbo project car, had a great link to transmission description. If I remember right, the PCM commands (don't remember the conditions) the trans and fluid is applied though the input shaft to the converter and it locks a clutch. Would this not be the same here? Could you turn that off on just the rear engine? How do AWD allow differential(ing)?

Again, just thinking out loud.
 
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