PT54 & GN1s

[kidrick]

I've been running this combo for a couple years and can not run faster then a 124mph. Boost is 26psi timing is 26*. Just wondering if the turbo is not pushing enough air for the heads. It seems the iron head guys are running around 128mph with this turbo. My combo is:

PT54
PTE Front Mount
70mm TB
GN1s as cast
PTE 218/218
FAST
ATR headers & 3" downpipe
Siemens 55s (88%DC)
Single Walbro 307
Race weight 3420
Best time 10.83 at 124mph 1.52 60ft

 

[lazaris]

Have you tried increasing the boost?

 

[kidrick]

Yes, I tried to increase boost. On my FAST record the boost was bleeding off in third gear(29/30psi in first, 27psi in second and 25/24psi in third). I may be having puck sealing issues, I want to wire the puck closed next time, or I may have a small head gasket leak. I just bring this up because the car ran 118mph with 19psi and 18.5* three years ago, same combo. I would think that the boost and timing increase would give me more then 6mph. The down pipe is ATR(Houston style).

 

[lazaris]

Let us know what you find.

 

[ijames]

See http://www.turbobuick.com/forums/showthread.php?s=&threadid=138980 if you want to read some previous discussion on the limits of the 54.

 

[smokinttype]

I would run that 54 turbo to 30-35#'s in a heart beat. Since your heads are not ported you cant really expect a whole lot of power from them, especially since the turbo is unusually small for those heads.

Port your heads,buy a 70 GTQ, some 75's...and that thing would fly!

I am currently running this combo and it seems to do well.

 

[kidrick]

Thanks for the replies. I really think I have an exhaust leak somewhere eventhough spool up and vac. are all good. Have to test some things.

smokinttype,
Even though the GN1s are as cast, I should still expect more power out of them then any ported iron head, yet the iron headed guys are getting better mph. Yet some of the iron headed guys run a roller cam which is an advantage over my flat tappet. I would love to run over 30psi, Harry told me the turbo is good to about 33psi, just need to figure out why I can't so far.

 

[smokinttype]

you might have an exhaust leak? ....lol how would you not know that you had one?

 

[Grandnat]

Read the thread Ijames linked to.


I think that you have reached the limits of that turbo at 124 mph.
High tens is all you can realisticaly expect from that turbo.

Ask around and you will see that VERY few have gone faster with that turbo.

do you have a .63 exhaust housing or a .85?

if you only have the .63 then you are done. PERIOD

you can squeeze a couple more mph out if you have a .85

I have gone almost 127mph and I have the .85 housing

the fastest I have ever heard of with that turbo was Scott ATK at 128.8mph and I believe he has a pretty light car (A/C delete etc)