Old School, how much boost will my old 89 head handle?

[Archive]

I know that the old big-bore head is prone to crack, but what induces the cracking? Overheating? Too much boost? Freezing temps?

------------------
http://coffeewithJesus. homestead.com/web1.html 89 1-ton, Amsoil System 3000 5-30,K&N air filter, cleaned-up exhaust, Dynomax straight-thru, rebuilt pump, 12cm wastegated turbo, thermostaticly controlled twin 14" electric fans, intercooler, modified 518 OD transmission, Gear vendors OD controler, R-134, louvered fenders, 93 aftermarket smoothe grille; 78 35'Avion, 93 Lance 900 slide in with generator and power jacks. Jesus saves!

 

[Archive]

I'd hedge a guess at the high internal temperatures from the high boost, both hand in hand, right? The cooling and instantaneous heat in that area may cause crack to develop. Distortion of the head from the install may also instigate the crack from boltdown stress. Also it may be just a certain amount of castings and machining tolerances at the factory.
$0. 02... . Anyone with some change for a $20??
Jason

 

[Archive]

Jsimpson!

While talking to 'Old School' on the tele about 'anti-freeze' and reading the TDR, I mentioned that you were asking him directly about boost for the old heads. He told me the answer and told me to convey it to you for fun. I told him you would rather hear it from the master himself and not Keen-O-Rama. I mentioned that I'm not worthy of such high powered knowledge & technically minded know-How.

I'll let you hear from the source, but a number between 29 PSI & 31 PSI were mentioned by our fearless 12 valve leader!

I think he still misses his old truck and needs a conjugal telephone visit on occasion. I think it's something about the manual hubs & cast iron transfer case!

 

[Archive]

Now that I'm at the PC,(thanks KEENO for the land line verbal relay) and can read the entire post, Your concerns about the head are justified. The earlier heads with the 9mm injectors were prone to cracking between the injector threaded bore and the valve seat. The later heads had 7mm threaded injectors, and more metal between the threaded bore and the valve seats. Rapid heat rise and cooling rates aggravate any areas suceptible to cracking. This means excessive fueling, high egt operation on a cold engine, or no cool down time after a long hard pull.
Boost values on a stock engine are really subjective. By that, you could go 30+ and expect great longevity from the head/gasket/block assembly.
The hot end housing (12cm, 14cm, 16cm) will determine the drive pressure at the turbo, that with the fueling availible, will max out the boost. Your EGT, driving style, and heat/cool down rates are most important.
Thanks for the reminder about the iron transfer case, KEENO.
Have fun.....