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884 Views 4 Replies 5 Participants Last post by  Jurgen
Now i searched and found that a stock 4.6 birdie engine will handle about 6psi and will eventually die. But what about a mark 8 motor? is the pistons forged in it? how long will it handle the pressure? same thing with a 99-01 cobra engine. I want to get to about 350-400 range.

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Adding boost to any application will not help durability.
However I heard that block can handle up to 450/500 hp before the connecting rods go.

Here's a good page that you might want to look at:

Edit: I'm running 8 psi on my 4.6 SOHC
the mark 8 bottom end has the same hyperutectic pistons i belive with a 3cc dish? If you strap 2V heads to the mark 8 bottom end you will raise compression which isnt the way you wana go for boosted. 6psi is an ok level on a stock block. As long as it is tuned and fueled properly the stock block can be very durable. If you bolt NPI heads to a PI block you will lower the compression which will alow you to run more boost. 10 psi is about max for a stock block and thats pushing it!
6psi with a decent tune will last as long as your car will. The stock internals are certainly not ideal for boost, but not that weak. Detonation is the enemy, so as long as you stay a little on the safe side with the timing, you're good to go.

Sure, I've heard of/seen a handful of stock engines going out here and there with higher boost levels, but I'll guarantee you in all cases, it was due to the way it was tuned or previous condition of the engine that pushed it out the door.

Hell.....I know of several 4.6L Mustang guys running around with 9-11psi and 400+hp on the stock short block for years now without even the slightest hiccup. Again, keep the heat under control (conservative fuel and timing curve), maintain your engine and always run good quality fuel and you'll do alright.
Its mostly in the tune i am running about 8-9 psi it could blow up anytime but its been ok so far CobraRThunder (chris) is running like 11-12psi but i am not sure and hes been running that for a couple of years if you do plan on building a engine run whatever on a stock engine if it blowes up then big deal you are not gone reuse any of thouse parts on a new build.

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