351 swap

Insayne · Dec 17, 2011

I've come to ask the mustang gods. I was going to get another block and build a 347 but the I started thinking why don't I throw my 351 at the pony. I have a 351 block ready to build. So I was thinking 408 and be done with it. A set of nice high flow heads cam to match rpm 2 intake. Here's the hitch. I live in Cali. While most of the smog techs won't know the difference between the 302 and 351 will it blow clean enough? Also how would it work with aftermarket carb exempt numbers? I mean aside from the stroke and can profile(both of which I can lie about) the only 351 specific part would be the intake manifold?

BLOWN 95GT · Dec 17, 2011

Wish I could help but I don't have smog test down here in the stix ALABAMA!

Insayne · Dec 17, 2011

You lucky sob!

CC'S95GT · Dec 18, 2011

you should definately call a tuner to see if they can get it to smog as clean as a stock motor. I would think they could since there are OBD2 351's out there. Probably not gong to be cheap though.
I wonder the same thing can be done with a 306, 347, etc. in ATL too.. It still has to smog as clean as stock, although not as tight as Comifornia

Insayne · Dec 18, 2011

Well a 306 should be no problem what so ever. I know people get by with the 347's too all the external bolt one can easily come with air resource board exempt numbers. The 408 on the other hand is another 60 cubes over the 347 and is a bit of a different animal. I still think they could tube it down but the 351 intake is going to be hard to get around smog with.

framda · Dec 18, 2011

Just out of curiosity, how do they test in California? I assume from your post that they do a tail pipe sniff as well as visual inspection. Do they hook up to your computer to check any kind of programming or tuning?

Insayne · Dec 18, 2011

On obd1 I don't think they hook up to computer. They do a visual and are going to ask about every visible modification then they run a sniffer on a 2 speed dyno test

rz5.0 · Dec 18, 2011

Tune and cam will make the most diffrence not sure if you can find big heads like that with smog ports on the back.

Paul · Dec 18, 2011

There is almost no way you'll get the 408 to pass the sniffer. I tried and tried and tried and tried to get my 418 to pass emissions with a very small cam, mild heads and intake, and extensive tuning via an AEM EMS with dual widebands running speed density. By running 50% alcohol in the tank, shutting injectors off, running the motor ULTRA lean to the point where it would barely stay running at all, and more, it could get it to pass two out of three components of the nest a time. (CO, HC, or NOX) However, when I would adjust the tune, for example, to pass NOX, I'd fail HC. Adjust to get HC in the clear, and fail NOX.

Remember, it's just simple numbers physics here. You're trying to get a motor that is 40% larger than a 302 to pass on 302 standards.

I don't recommend it. Put an emissions-legal blower on your 302.

Paul.

Insayne · Dec 19, 2011

My only concern is my tired bottom end. I'd have to build me a forged bottom end and get some big smog heads

Paul · Dec 19, 2011

You don't need a forged bottom end to run boost. Keep the boost sane, add a good tune, and you'll be fine. It is 100% internet mythology that you must have a forged bottom end to handle boost, or that hypereutectic pistons will asplode like glass as soon as you apply something greater than atmospheric pressure. Hypereutectic pistons are less resistant to detonation that forged; however, the simple solution there is DON'T DETONATE which can be accomplished through a good tune and a safe AFR.

Paul.

evilcw311 · Dec 20, 2011

all this is easy to surpass...........Move out of california!!!!! lol

im so glad that we dont have that crap here, you guys can have it!!!!

Insayne · Dec 20, 2011

Good point Paul. My motor just worries me. I have to run another leak down but the first time I had 15% loss in one cylinder and 20% in another. I mean it could be valve issues but I don't know. That plus a miss I can't get rid of and I'm just thinking boost will compound the issues. I do have some gt40p's to port and I can get an aftermarket or slap the explorer intake that I have on and while I'm in there I can get a bit of a look at what's going on.

Sludge805 · Dec 20, 2011

I'm in Cali and run into the same problems, do you have any smog techs in the are that will you know look past the visual part as long as you blow clean?

Paul · Dec 20, 2011

If you have compression issues or other significant mechanical issues, then significant upgrades (in my opinion) performance-wise are simply off the table until the engine is mechanically sound. However, you'll want to make absolutely certain that your issues are real and significant before you go tearing motors apart and spending big bucks.

Paul.

Insayne · Dec 20, 2011

I'm sure I could find a tech but the big stroker won't blow clean. Yeah Paul that was why I was thinking of building another motor. I need to do the compression and leak down to see what's what.

MustangChris · Dec 20, 2011

my buddies say anything on E85 will pass..... have you thought about an E85 tune, then simply switch it back to unleaded after the inspection? Not sure what an "E85" tune entales on a carb set up. just trying to throw some ideas into the kettle, ya know?

buscg · Dec 20, 2011

You will have to use two smog pumps to pump air right into the exhaust. Thats your cheap route, haha. Like the other guys said its gonna come down to how much money you have to make everything perfect including the tune.