Massive Lag with 6780S

[MNwe4]

Hey guys, looking for a little insight on how to reduce my horrible lag. Just to give you an idea, the best I've run is 12.024 at 120.27. Sixty foot was 2.155. This was at 22psi with alky and pump gas. I just can't get the car to leave hard. Turbo is a precision 6780S compressor housing and the exhaust housing has THB3- cast in it with a hand engraved 80 following. I'm also running a PTC converter with a 3800 stall. I guess what I'm after is finding out if my turbo is just not right for my combo. How different is this turbo from a 6776?

Thanks, Dave

 

[DCVING 6]

How's your tune up look? Alky coming on too early and causing it to be too rich?

When footbraking the car, what RPM are you at to get 0 psi boost?

Any exhaust leaks? Do those knock off headers seal up good?

 

[Royal-T-Ltd]

yeah, it might be wayyyy too fat down low... especially if your alky is coming on ...... post some logs

 

[Dusty Bradford]

Hey guys, looking for a little insight on how to reduce my horrible lag. Just to give you an idea, the best I've run is 12.024 at 120.27. Sixty foot was 2.155. This was at 22psi with alky and pump gas. I just can't get the car to leave hard. Turbo is a precision 6780S compressor housing and the exhaust housing has THB3- cast in it with a hand engraved 80 following. I'm also running a PTC converter with a 3800 stall. I guess what I'm after is finding out if my turbo is just not right for my combo. How different is this turbo from a 6776?

Thanks, Dave

I'm betting that 10" converter is no where near 3800 stall. Maybe 2800-3000. It's most likely time for a non lock with a turbo that size.

 

[MNwe4]

Here's my best run. AFR is close, but not exact to what my gage was reading.

 

[MNwe4]

Oh, my alky comes on around 13 psi also.

 

[TurboBuRick]

Is that a PLX wideband?

What kind of wastgate? Are you sure it's sealing?

 

[TurboBob]

what wastegate setup are you running? (Rick and I think alike it seems)

How much boost can you hold at the line?

What are the RPM's at 0psi, and 5 psi?

No wheelspin I assume on your runs?

Bob

 

[TurboBob]

I looked at the log, It looks like the wastegate may not be closed properly.

Your converter seems to be about 2900 RPM at 0 psi. But you did not launch with any boost. Considering how long it took for the boost to 'hit', you should look at the wastegate.

But try brake-torquing to 8 psi, and then launching. If you can build any boost it should launch harder.

B

 

[MNwe4]

Thanks for the quick responses guys.

-I'm using a Tial 38mm wastegate. The sealing ring is in correct. I checked. It has the ~15psi spring in it.
-I can't hold any boost on the line. Pushes the nose at the track and spins on the street. I wasn't trying much on the line here because it was the final round race and I needed to get the RT, which I did and won against a 12.008. His 60' was 1.7 though so I had to run him down.
-If I'm on the brakes and stab it quick it will flash to around 3000 rpm.
-You got it, no wheel spin on the line, but hold on at the 1-2 shift.

This is just so frustrating when I know the car makes a good deal of power. I appreciate the help.

 

[MNwe4]

Is that a PLX wideband?

What kind of wastgate? Are you sure it's sealing?

AEM wideband with gage. Tial 38mm wastegate and I checked the direction of the sealing ring and it's correct, so I assumed it's working. I could try pulling it off and making plates to block the two open holes. I would just have to be careful in testing to not overboost.

 

[WSLN 6]

Sounds like you should focus more on your rear brake problem, then go back and see how your launch is with some boost.

 

[Slow91z]

Doesn't sound like a 3800 stall to me, more like 2800.

 

[TurboDave]

I'm in agreement with WSLN6! Holding good boost on the foot brake is a battle that many turbo regal owners have had over the years, but can be done. Unless there are certain mods done to the rear brakes.

If you have disk brakes on the rear, or are running vacuum brake system you will never be able to hold substantial if any boost on the brakes. Just the nature of those beasts.

If, however you have drums on the rear and are still running a powermaster or similar system there are tricks that can be done to gain huge boost numbers on the foot brake. Even my old 86 can still solidly hold 15# of boost on the foot brake (although I could never launch with that much, just spun), but I could get some pretty solid launches with upwards of 8-10# of boost.

 

[BEATAV8]

a 6780 HPQ and a 218/218 cam are gonna need a loose converter to get going no matter how you cut it. I think you would be better off with a P trim turbine.

 

[notacarlo]

12.0 @ 120! - Nice top end surge! I ran 12.0's at 108.

Agree, way too fat down low. 3000+ stall would do you some good. Hate to see what that thing will do when it 60's good.

 

[MNwe4]

I have new (stock) cylinders and shoes in the rear along with drilled and slotted rotors up front. The converter is also brand new and my third one, so I'm pretty set on leaving it in. It is what PTC recommended being a true street car and all. Would moving to a 6776 P-trim make that much of a difference? Both have the .63 a/r exhaust housing dont they? Another curiosity, how does oil pressure affect turbos, meaning will high pressure slow them down significantly?

 

[WSLN 6]

I would talk to Dusty about your converter options, I know you don't want to swap it again, but it sounds a bit mismatched even for a street car. I absolutely love my 9.5 n/l and it only gained 200rpm on highway cruises.
Some things that have helped me hold more boost on the footbrake:
- Boxed lower control arms with new bushings (gained 5psi holding power)
- Vacuum resevoir as I have vacuum brakes
- Line lock to save the rear brakes during burnouts
- S-10 rear brake cylinders

 

[Dusty Bradford]

I have new (stock) cylinders and shoes in the rear along with drilled and slotted rotors up front. The converter is also brand new and my third one, so I'm pretty set on leaving it in. It is what PTC recommended being a true street car and all. Would moving to a 6776 P-trim make that much of a difference? Both have the .63 a/r exhaust housing dont they? Another curiosity, how does oil pressure affect turbos, meaning will high pressure slow them down significantly?

I see you have two options.

A 9.5 non lock will spool the turbo with around a 3200 stall, still drive well and won't loose any top end charge.

If you stick with the current converter, you need to step back to a 6262 or something along those lines. Even with great brakes, that's ALOT of turbo for a tight converter to spool.

 

[Alky V6]

Sounds like a perfect candidate for a small, half second shot of go juice.