I got a 2003 Mustang Gt with light mods(Mac Cold Air Intake, Professional Products 75T.B. & Plenum combo & duel flows). I was wondering how it was possible if posssible to swap the 2V heads out for 4Vs and have it bored from a 281 to a 302 and still be passable for smog. Im sort of new to all of this and any advice would be kindly welcomed. Also, would swapping out the stock 3.27 gears for 3.73s make a big difference?
Wondering how to keep it all street legal and smog passable
- Thread starter Pinky's2003GT
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trinity_gt
10 Year Member
Welcome.
First, search is your friend. The 2V->4V discussion has been had many times before and you can learn a lot by perusing those threads. Also, you'll never bore a modular engine to 302cid. Because of cylinder wall thickness and bore spacing issues there's simply not enough meat there; you need to get that displacement with stroke.
A couple of thoughts on smog compliance: A lumpy cam is not your friend. They tend to pass a lot of unburned HCs into the exhaust because of high overlap numbers. If you need to pass emissions sniffers, carefully consider any cam upgrade... By and large, displacement isn't a problem so a 302-in mod would be fine. Leave the EGR functional. Most important for smog is keeping (or having access to for the purpose of checks) the factory H pipe with its high quality cats. While single-cat-per-bank aftermarket midpipes usually flow well they don't generally catalyze nearly as well as the factory cats on the OE mid. Certainly, an O/R midpipe is out of the question from the perspective of emissions compliance.
NOx emissions climb with cylinder pressure and temperature. Keep some timing out of the tune and make sure the EGR functions as intended. With a good tune and O2 sensors in good condition, there's no reason, after all this, you shouldn't pass emissions.
02nightmaregt
To hell with your Mustang, I want to see your HOG!
FWIW i would skip the 4v swap and go FI or spray. You'll still pass smog and make great power. You'll also save a TON of money doing that. Yes i recommend the 3.73's i've had them for about 3 years and love 'em.
:OT: But why is everyone seeming to lately ask about swapping 4v heads onto a 2v car????? What the world?
