Blown 2 valves with 03-04 cobra shortblocks?

TonyG · Dec 6, 2008

I might be able to get a decent deal on a cobra shortblock for my 99 GT. My near term goal is to make 550+ with my intercooled vortech set-up. I am going to stay 2v, to avoid complications and excessive cost.

I heard that the dished pistons in the Cobra shortblock will raise my compression, so I have to choose my heads/cams carefully. Has anyone here gone through this path, and can make recommendations?

mustang50v8 · Dec 6, 2008

TonyG said:
I might be able to get a decent deal on a cobra shortblock for my 99 GT. My near term goal is to make 550+ with my intercooled vortech set-up. I am going to stay 2v, to avoid complications and excessive cost.

I heard that the dished pistons in the Cobra shortblock will raise my compression, so I have to choose my heads/cams carefully. Has anyone here gone through this path, and can make recommendations?

what kind of deal are we talking about here?

CobraRed_96_GT · Dec 6, 2008

I wouldn't be too happy about that set-up unless it was a insanely good deal. You're basically going from 52cc to 42cc (of the top of my head) cumbustion chambers. So now not only are your running boost (over spinning your vortech most likely depending on the set-up, making excess heat) on high compression (more heat), you're doing it on mahle pistons - which DO NOT like detonation. Detonation is more likely with the set-up you're talking about as well. My guess is you'll have to have a set-up capable of 600rwhp just so that you can pull timing and richen it enough to stay safe on those pistons (which can easily break the 2nd ring landing after one solid case of det.) while hitting the 500 range. Either that or just run only race-gas.

hotmustang331 · Dec 6, 2008

??? The cobras pistons are very stout....its just their piston to wall gap is a little too tight so they dont like high heat. They can take some detonation.... I have had detonation @ over 15PSI....low RPMs though but still they are fine.

His centri wont put out the heat like a eaton. Good timing map and tune, and he is golden Just keep the boost around 12PSI or under if you can.

joshjwc9 · Dec 6, 2008

Wouldnt it just be easier to assemble some 4v heads and swap blower mounting brackets for his blower and drop in the 4v? That way he doesn't have to worry about combustion chamber size, plus he can get more potential out of the stock 03 Cobra heads to meet his HP goal.

CobraRed_96_GT · Dec 6, 2008

hotmustang331 said:
??? The cobras pistons are very stout....its just their piston to wall gap is a little too tight so they dont like high heat. They can take some detonation.... I have had detonation @ over 15PSI....low RPMs though but still they are fine.

His centri wont put out the heat like a eaton. Good timing map and tune, and he is golden Just keep the boost around 12PSI or under if you can.

Not saying they're fragile - they are forged for god's sake. Just saying a 4032 grade forged aluminum is much more brittle (and has a lower melting point even if harder) than a 2618 piston. So detonation's going to be something you definitely want to shy away from even if it's capable of loads of power. In order to run normal gas you'll need to pull a good amount of timing and add fuel, so i'm thinking the set-up will need to be capable of more than 550rwhp to actually hit that mark.

TonyG · Dec 6, 2008

That's why I was asking about after market heads/cams.

Zoie_daGT · Dec 7, 2008

wouldnt that engine drop the compression??? His car should be at 9.5:1 and the Terminators are at 8.5:1. Or is that drop in the heads too???

CobraRed_96_GT · Dec 7, 2008

Zoie_daGT said:
wouldnt that engine drop the compression??? His car should be at 9.5:1 and the Terminators are at 8.5:1. Or is that drop in the heads too???

Don't look at the numbers - they alone don't tell you anything. The cobra being 8.5:1 doesn't tell you if it has deep pistons or large chambers. In this case it's large chambers, meaning the dish on the pistons is quite shallow. And his car stock is supposed to be 9.0:1 (although i believe 99/00's are closer to 8.8:1), not 9.5:1.

TonyG · Dec 7, 2008

According to the feedback I'm getting from other fourms, stock 2v heads on the 03-04 cobra shortblock gives a comp ratio of about 9.5-10. So with aftermarket/ported heads, I should be OK. I'm just looking for others who have actually gone through this already, so I can learn from their experience.

hotmustang331 · Dec 7, 2008

CobraRed_96_GT said:
Not saying they're fragile - they are forged for god's sake. Just saying a 4032 grade forged aluminum is much more brittle (and has a lower melting point even if harder) than a 2618 piston. So detonation's going to be something you definitely want to shy away from even if it's capable of loads of power. In order to run normal gas you'll need to pull a good amount of timing and add fuel, so i'm thinking the set-up will need to be capable of more than 550rwhp to actually hit that mark.

Hmm...interesting.

SVTPerformance - View Single Post - C6 Z06 vs. 03 Cobra

Just to give a gauge of how strong they are, that guy there blew the porcelain off of 5 plugs in his cobra and the pistons survived . But obviously a 2618 piston will handle more. They are not weak by any means....but there ARE better pistons out there

He also damaged #7 at some point...but it doesnt sound like it was from that event. #7 and #8 are common failures due to a design flow in the coolant routing with the 4Vs....and unless you get the cooling mod, those will be the first to go. But only when you do 150+MPH speed runs....which he did, at least while racing.

'03GTinFLA · Dec 8, 2008

I researched this also and came to the conclusion that it should work out well. I keep going back and forth about what engine combo to go with but I think I'm going to assemble the block and give it a shot. I'll check my bookmarks when I get home and report back with some more specifics about CR and such.

Blown 2 valves with 03-04 cobra shortblocks?

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