275/60/15 tires w/ a TA-49 - New converter needed?

[Speed_Dreamin']

I've recently upgraded to 275/60/15 tires, my car is now way slow to spool.

With 275/50/15 Nitto DRs, my best 60ft was 2.00, launching at 5 psi, blowing away the tires. With the taller, 275/60/15 MT DRs, my best 60ft is 2.3, launching at 5 psi, no tire spin and slow spooling. Seems to take longer to get from 5 psi to ~10 psi, once pressure reaches 10 psi, 25 psi is immediatley after. The car just rolls out, then Wham!, 25 psi like you flicked a switch. I don't think I have any exhaust leaks. I know I don't have any leaks between the turbo and intake ports.

I'm running the stock D5, stalling around 1800 rpm w/ a TA-49. Stock cam, intake, heads and rear gear. Should I be looking at a higher stall converter? Something in the 2500-3000 rpm range?

 

[Just a Six??]

Tires do not cause Slow Spool! You say yours is slow & then all of a sudden boost hits. That tells me you have an exhaust leak. Look & listen with 2ft of steel line (brake-fuel etc) attached to 3 ft of rubber hose (homemade stethescope)The header to turbo is where mine leaked. Also check headers, crossover etc.
I had a 49 turbo for years & they are great turbo's. With a 3000 stall you will fry the tires after 5lbs but it will spool that turbo instantly Unless you have a Leak. Its a fun combo but be careful as street tires will fry almost instantly on the street & with moisture on the road you have to be careful.

 

[1fast6]

what et and mph are you turning with that setup?

 

[Sweet6]

I have to launch about 2lbs higher with a 28" tall tire compared to a 26". I think a 3000-3200 stall would help a lot. At least make it easier. I am running a 3200 Vigilante with a DBB 6765 and it spools instantly. It is a blast to drive. My $.02.

 

[Speed_Dreamin']

If you launched with same boost for the 28s as 26's, does the turbo spool slow?

With the 26's and ~23 psi boost, 2.00 60ft, 12.66@109.
With the 28's and ~26 psi boost, 2.30 60ft, 12.75@112.

 

[Slow91z]

The problem has always been there, before it would spin the tires at a lower boost and as soon as the tires slipped the boost skyrocketed (spinning tires get the RPM's up fast just like a loose stall), now it's hooked up you get to see how slow it spools when it's actually under load at low speeds. Seen this many times on my cars, had street tires on and it was instant boost blowing tires off, I think everything is all good, go to the track put slicks on and all of a sudden spool up is slow. Investigate and find exhaust leak or whatever that I never would have noticed until I went to the track.

A different converter would help, but if you can get it to hold 10 psi or better at the tree it should work much better for the moment. As always with spool up you can play with the tune to try to make it as good as possible, and triple check exhaust leaks.

What exhaust housing?

 

[Speed_Dreamin']

Garret Exhaust housing. I think it say .63 A/R. Does that make sense? It's hard to read.

 

[forcefed3.8's]

What chip and fuel pressure?

 

[Slow91z]

Makes perfect sense, and for a stock converter car probably just right, as long as it's a true D5 you should be pretty well good to go just maximize the tune, and be for sure on leaks.

 

[BEATAV8]

I have a stock motor car with a TA49. It has always had a stock D5 in it but just a few weeks ago I swapped in a 3200RPM vigilante converter which I had laying around the garage.

With the D5 I could launch it with 8-10psi before letting it go. It always felt slow out of the hole until the boost would come up. With 28" tires, It was easy to pull 1.8's and even 1.7's with this combo, but it needed some time to wind up and like I say felt poochie until it got out a few feet. Car ran 12.0 @ 110mph with the D5. (No tire spin at all)

With the 3200 vigilante, it's a completely different animal. Spool up is super stupid fast as one might expect. I still need to take some data with it to see how much it slips through the traps, hoping that it's somewhat comparable to the D5's 12-15% since the car isn't making too much power.

To answer your question, it's true a stock D5 can spool up a TA49, but it's not impressive at all. My recommendation is to look into a PTC converter if you want really good results. The only reason I went with the vigilante is because I already had it laying around.

Here's a vid of the car with the vigilante in it....
GN Vs Trans Am at Jimmy's 2011 - YouTube

grand national vs trans am 7/30/11 - YouTube

 

[Speed_Dreamin']

Thanks everyone. It's a brand new TT chip, 43 psi rail pressure @ idle w/ vac line off. I did pull fuel out of first gear, which did help, but I don't have a wide band or a data logger, and the stored value of 600 mV @ 0mph in the scanmaster made me a bit nervous.

I'll triple check on the exhaust leaks.

 

[Just a Six??]

I'll triple check on the exhaust leaks.

Get a stethoscope & I bet you find a leak somewhere. No one could hear mine from the turbo to header but when I listened with my homemade stethoscope it was easy to hear then. The gasket was blown out on one side. Total about 1" gap, yet very hard to hear when the motor was running.

 

[usetaboost]

and if you have so many exhaust leaks you can tell where they are coming from, do a smoke test. That will really tell ya if you have a leak.

 

[bison]

Put a converter in that stalls to 2400@ zero boost/ vacuum and the problem will be solved. Otherwise you will need to raise the launch boost.

 

[Mr.Spool]

not only will a new converter put a better 60ft on the car but will also make the car much more fun to drive on the street.on a stockd5 ta49 i used to leave at 14lbs of boost to 60ft the car which did get worse from the 26 to the 28,the shorter tire took less boost at launch for the 60ft.

 

[Speed_Dreamin']

Thanks everyone. Just picked up a used PTS extreme 10.5 in, lock up, 2800 stall (believe it's just a re-stalled D5). Hopefully this helps.

 

[Dusty Bradford]

A restalled stock D5 would be a 12" converter. Yours should be a 2800-3200 stall. Check the rpm at 0-1# of boost and you'll know what it is.

 

[maxcom]

and if you have so many exhaust leaks you can tell where they are coming from, do a smoke test. That will really tell ya if you have a leak.

How do you perform a smoke test?

 

[usetaboost]

get a friend to watch for smoke. get a few quarts of cheap trans fluid, pull off a vac hose and stick it in the bottle. THe trans fluid burns off and will smoke like a train wherever exhaust leaks are. Park in the back yard so you can kill off those pesky bugs!

 

[BEATAV8]

Easy way to check for exhaust leaks while the car is OFF:
Connect a leaf blower or a shop vac (on reverse) to your exhaust pipe. Blow air into the exhaust and look for leaks. Cap off your other open tail pipe with some masking tape. A spray bottle with soapy water will be useful. Follow the bubbles.....