351M OH NO! What direction do I go now?

Steelcityfan29 · Oct 14, 2010

So through the help of some people on this forum we have found out that I have a 351M in my car... yuk!

So now what do I do?

I've been told its pretty easy to get back into a 351C or W but I have to buy some parts.. and obviously and engine and transmission. The 460 option wont fit and I want a car I can corner in when Im done.

Right now I have these options or I can wait.

A 302 boss with no heads I can get on a trade.

A 351 Cleveland with cobrajet intake manifold with two 650 hollys and cobrajet heads. This is the more expensive option. The heads need to be rebuilt and the carbs need work. I think a complete rebuild here would be likely.

A 302 HO out of a mid 80s mustang... I know nothing about these engines and they dont seem too popular.

I'm building a 69 mustang and I want it fast and I want to show off.. basically its my fun car and if I feel like tearing rubber off the tires.. I want that ability.. though.. I don't want to drag it or anything. I want to be able to go cruise in it too.

So please give me some suggestions on.. transmission and engines. Its an automatic currently and thats fine I'm impartial that way. It has a 9 inch rear end now. I assume the previous owner put this in. It feels super torquee if thats a word LOL with the 351M thats in it now. But the brakes are too crappy to go over like 35 safely.

Any suggestions are appreciated. I'm an old jeep gy I know nothing about fords other than what I read on forums.. so I'm here for help.

2+2GT · Oct 14, 2010

Steelcityfan29 said:
The 460 option wont fit and I want a car I can corner in when Im done.

Any suggestions are appreciated. I'm an old jeep guy I know nothing about fords other than what I read on forums.. so I'm here for help.

Um, actually with the right motor mounts and shorty headers a 460 will just about bolt in. With an aluminum intake, aluminum heads, and headers it'll probably weigh less than the stock 428, too.

horseballz · Oct 14, 2010

Steelcityfan29,
From all that I've read/heard the, 351M is a turd in stock form, but much can be done to wake it up. If the engine runs well and dependably, spend your $$$ first on your brake system and then work on waking up what you have. If you're not going to race competitively, it will likely be the best bang for your buck. Remember that performance differences are often in small degrees. Whereas, similarly built 351C and 351M may always/usually have the 351C winning at the track, the seat of the pants difference on the street may not be that dramatic. In other words: "If it ain't broke, don't fix it." FIX THOSE BRAKES", that's the biggest priority before you can even judge the engine's suitability.
Just My $.02,
Gene

68RCodeConv · Oct 14, 2010

I'm wondering how you got a 351M to fit in a Mustang engine compartment. It will go in if you remove the exhaust manifolds but no way to get a header in there, much less the manifolds. I would take another look at it.

As for power - note that an engine is a balanced combination of parts. Throwing dual carbs or different heads on something is not necessarily going to make it any faster. And power costs money - how fast to you want to go?

I've got a stroked FE motor with aluminum heads, intake and water pump. Weighs about the same as a stock 351W. Best of everything in the motor AND it was built by a guy that really, really knows these engines. 580 ft/lbs of torque at 3900 rpm. But it cost me $10K turnkey.

Steelcityfan29 · Oct 14, 2010

Thanks for the suggestions and I agree on the brakes. The 351M runs amazing.. the transmission however feels shot. So either way I have to get a major component. I hear 351Ms dont have much for get up and go components as they're usually pulling a tailor not burning rubber. But I don't really know.

As for the 460 I have to cut my mounts where my struts are now from what I read to squeeze it in there and I need a special radiator. So I didn't want to go that route. The 351M BARELY fits.. its SUPER close and already I don't think I can change spark plugs without removing the engine unless i'm really lucky.

So In this situation I want something fast.. I will drag race against my buddies at fire bird raceway here on occasional weekends but not like for real competition. I need to smoke my friends wrx.. which might be rough. its a fast little bastard LOL.

Though I want to be able to drive it on the street as well... Am i asking too much there or whats the bet approach on this? Should I look for another C6 and keep the 351M? or because i need a tranny anyways should I look for a 3561C or W? or something else?

Thanks again for taking the time to help me.

Im pretty open to anything, I'm new to this and doing a majority of the work myself. I just need some good advice which I received before but I forgot to mention the 351M transmission is crap and I don't think power brakes... or a brake booster will fit.. with the 351M which is why I'm guessing the PO took out the power brakes and steering unless it was for the vacuum off the engine.

69gmachine · Oct 14, 2010

Since you already have the engine in and running, I'd save that for last. Improve the brakes, steering and suspension first to minimize down time.

Next I'd change the transmission out to either a TKO 5 speed or Magnum 6 speed depending on your budget. Whenever you decide to put a different engine in, you'll need to replace the bell housing and flywheel, but if you use an 11 inch clutch and pressure plate and a 164 tooth flywheel on the new Windsor or Cleveland, you should be able to re-use the clutch and pressure plate.

You could also replace the heads with aluminum versions to knock some weight off. That may be a good opportunity to change spark plugs . Later you can swap the heads on either a Windsor or Cleveland stroker short block.

CGarris70 · Dec 25, 2010

For a driver where originality is not a concern, stroke the mid 80's 5.0L to a 347. You end up with a cheaper solution to build, less weight, better driver and better fule economy. The 351M shares it bellhousing patern with the 400M and 429\460 big blocks. The 289, 302, 351W and 351C all share the small block pattern. Good Luck!

Realmongo · Dec 26, 2010

What is the casting number on the mid '80s 5.0? The 5.0 is a decent build if it is the later design roller engine from about the 1987 model year up. The earlier blocks from the '80s were poorly built (thin with lots of core shift) and lacked roller cam ability.

rbohm · Dec 26, 2010

if you really do have a 351m in your mustang now, a 460 will go right in place of it as they are the SAME width. both blocks have a 10.3" deck height, the only difference is that the 460 is longer. if you dont want a 460 though, your choice but you are a fool imo, oyu can build a 400 from the 351m block since the 351m is basically a 400 with a 351w crank installed, and longer rod and taller piston. you can get a 400 rotating assembly from PAW for a reasonable cost. personally i would get the rest of the car up to par, then grab a 460 and C6 trans from a mid 70s full size car, and drop it in place of your current engine/trans, after building a little more power into the combination of course.

2+2GT · Dec 26, 2010

MR.Speed said:
The 351M shares it bellhousing patern with the 400M and 429\460 big blocks.

True, which means if you go with a 460, you won't have to buy a trans.

Rusty67 · Dec 27, 2010

The 400M is one of the best motors on the planet in terms of potential. You can build the absolute hell out of it and it will take punishment like no other. It is also really different. No one seems to use them because no one seems to understand them.

Its really all about what you want.

How much are you going to modify the chassis and suspension ? How good do you want it to handle ? Are you going to drag it or auto cross it ?

woodsnake · Dec 27, 2010

I live in Nampa, when I'm not over seas, it's good to see another Idahoan reaching out. looking at what you've listed for goals, (quicker than the WRX)
You have some decisions to make. If the Cleveland motor is a serious option, I'd get that, and sell the intake and carbs to help pay for what you need. You are going to need rear end gears to be "quicker" than the wrx, and then an overdrive to leave the city.
This guy is actually out by Caldwell,

Modern Driveline T5 transmission parts & conversion packages

So, short answer, 351C bottom end, good .525~ cam, 650 Holley, 5 speed, 3.73 gears, and 17 inch wheels and tires.

Hack · Dec 28, 2010

You could always stroke the 351M to 434 if you want more power. There are a lot of parts required for an engine swap, so even an inexpensive engine can add up once you buy all the pieces (think exhaust, cooling, etc.). Tim Meyer sells all sorts of parts for the 351M / 400. The stroked 351M probably isn't the best choice unless you like the motor, but it's another option. I myself like the 335 series engines, but I can understand wanting something lighter in a Mustang. I would also probably stay away from a big block in a Mustang.

351M OH NO! What direction do I go now?

Steelcityfan29

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