[Joshinator99]

So I went to the drag strip the last two weekends to knock the rust off (I had not gone since October 2023!). Starting out slow just to get reacquainted with driving fast lol… everything was going great. So after a 9.50 @149.9, I still had two more clicks to go up on my Smoothboost controller. So things were looking good for a new personal best despite 85 degrees and humidity! So I went up one more click and the car responded with a 9.6 at 148.9…and a VERY pronounced lull near 3/4 track… The A8 felt like it was slipping. …and the data log didn’t lie. The TCC slip was anywhere from 250 to 1200+ RPM virtually the whole quarter mile lol… so I’m guessing the still stock (!) A8 is finally calling it quits. Hard to complain about a transmission designed to handle a stock LT1 handling 1200+ HP for several years! Credit to KingLT1’s TCM tune!

So, the question is: If I’m going to keep turning up the power, do I drop big dollars into rebuilding the A8 with Pure, Tim King, etc OR just rip the band aid off and bolt in a built Turbo 400…? I rarely drive it on the street anymore and even then, I guess a cruise with a TH400 and 2.77 rear gears isn’t that big of a deal. I really like the idea of the built A8…the only question is if it will hold up under 1300-1500 HP…? Not sure who is still running the A8 in the 9 (and hopefully soon 8)second range.

Fire away with the comments my good friends.

[ZL14ever]

How do you know it's the transmission, not the lock up clutch in the converter itself? Does the reported engine torque look correct & similar to your runs from 2023?

Anyway to answer your question I would go with the built A8 route first. If that doesn't work well then you have an excuse to go with the TH400. My Tim King built A8 in my C7 has 15K miles and ~100 passes in the low 9/high 8

[Joshinator99]

Originally Posted by ZL14ever

How do you know it's the transmission, not the lock up clutch in the converter itself? Does the reported engine torque look correct & similar to your runs from 2023?

Anyway to answer your question I would go with the built A8 route first. If that doesn't work well then you have an excuse to go with the TH400. My Tim King built A8 in my C7 has 15K miles and ~100 passes in the low 9/high 8

Agree and had the same thought that it could very well be the converter. The thing that seems to be pointing to the transmission is it does need seem to be cutting spark during the shift at random times… full power during the shift is a sure way to terminate the stock A8 sooner than later lol… But great feedback, thank you.

Forgot to ask: are you launching in 1st or 2nd gear? Stock converter or aftermarket?

[jlaudio11]

I think it really comes down to what you really want out of the car. I’m in a similar situation where my stock trans just gave up randomly while cruising. How much street driving do you do and what do you want out of the car? I think that high 8 range is attainable and repeatable on a built overdrive trans. Into that mid 8 and lower I think the th400 shows itself as the better option. I personally just bought a used stock unit to replace mine and plan on fixing my original unit plus gpz clutches. If I were to go th400 it would be really hard for me not to go full on race car with it and start cutting weight everywhere. I have race only vehicles and don’t want that with this car. Oh and to really take advantage of the th400 you’re going to want a lot higher gear in the rear end.

[rcoe]

I sent my A8 to CircleD this winter and had them do a stage 3 build and a refresh on the converter. I am only around 800whp and more into tracking, but it has worked great all year.
CircleD was great to work with, good communication and had it done in the timeframe they quoted. If you are going the A8 route I would consider them.

[KingLT1]

Originally Posted by ZL14ever

How do you know it's the transmission, not the lock up clutch in the converter itself? Does the reported engine torque look correct & similar to your runs from 2023?

Anyway to answer your question I would go with the built A8 route first. If that doesn't work well then you have an excuse to go with the TH400. My Tim King built A8 in my C7 has 15K miles and ~100 passes in the low 9/high 8

It's doing some weird shit on the 4-5 now. There is a big swath of timing pull well before and all the way through the shift. Looks like slip based on the RPM curved around the shift. Plus it randomly decided to quit pulling timing on the shifts prior. It wasn't exhibiting any of this behavior before.

There is a possibility that the torque model might need some adjustment, I didn't tune the ECM. But if that is off then it could be causing this problem. It didn't dawn on me until you mentioned Torque reporting.

[ZL1Atlanta]

If your main goal is to go rounds and enjoy drag racing versus setting records, and if you don’t do a ton of street driving, just do TH400. You’ll be glad you did down the road.

[Joshinator99]

Originally Posted by jlaudio11

I think it really comes down to what you really want out of the car. I’m in a similar situation where my stock trans just gave up randomly while cruising. How much street driving do you do and what do you want out of the car? I think that high 8 range is attainable and repeatable on a built overdrive trans. Into that mid 8 and lower I think the th400 shows itself as the better option. I personally just bought a used stock unit to replace mine and plan on fixing my original unit plus gpz clutches. If I were to go th400 it would be really hard for me not to go full on race car with it and start cutting weight everywhere. I have race only vehicles and don’t want that with this car. Oh and to really take advantage of the th400 you’re going to want a lot higher gear in the rear end.

Originally Posted by rcoe

I sent my A8 to CircleD this winter and had them do a stage 3 build and a refresh on the converter. I am only around 800whp and more into tracking, but it has worked great all year.
CircleD was great to work with, good communication and had it done in the timeframe they quoted. If you are going the A8 route I would consider them.

Good feedback, thanks fellas.

Originally Posted by KingLT1

It's doing some weird shit on the 4-5 now. There is a big swath of timing pull well before and all the way through the shift. Looks like slip based on the RPM curved around the shift. Plus it randomly decided to quit pulling timing on the shifts prior. It wasn't exhibiting any of this behavior before.

There is a possibility that the torque model might need some adjustment, I didn't tune the ECM. But if that is off then it could be causing this problem. It didn't dawn on me until you mentioned Torque reporting.

I’ve been running a similar power level for nearly 4 years. I gotta think if my torque model is off I would have had problems a long time ago, no? Not sure if the logs I sent you will have the data you need to make that determination. Let me know what you need good sir.

Originally Posted by ZL1Atlanta

If your main goal is to go rounds and enjoy drag racing versus setting records, and if you don’t do a ton of street driving, just do TH400. You’ll be glad you did down the road.

Thanks Jason. So I guess the million dollar question is: how come you didn’t do the Th400 haha? At your power level you undoubtedly have a bunch of time and money into your 10L90.

[ZL1Atlanta]

Originally Posted by Joshinator99

Thanks Jason. So I guess the million dollar question is: how come you didn’t do the Th400 haha? At your power level you undoubtedly have a bunch of time and money into your 10L90.

A bunch of time and money for sure, but the only reason I have the car is to accomplish things with a 10L90, with a close second being accomplishments with a PD blower. I’d likely sell it if I got to where I wanted to leave the trans though. I’m in the middle of an odd issue now that is definitely testing me, but hopefully we’ll figure it out in the next 1-2 weeks.

[Joshinator99]

Originally Posted by ZL1Atlanta

A bunch of time and money for sure, but the only reason I have the car is to accomplish things with a 10L90, with a close second being accomplishments with a PD blower. I’d likely sell it if I got to where I wanted to leave the trans though. I’m in the middle of an odd issue now that is definitely testing me, but hopefully we’ll figure it out in the next 1-2 weeks.

Gotcha. Good luck sorting that out. Go get that 7!

[ZL14ever]

Originally Posted by Joshinator99

Forgot to ask: are you launching in 1st or 2nd gear? Stock converter or aftermarket?

2nd gear launch, stock converter

[Joshinator99]

Originally Posted by ZL14ever

2nd gear launch, stock converter

Thank you! That’s what I’m doing now currently as well.