Can anyone answer the following----

1. What is the maximum RPM that you can safely rap a 351M up to?

2. What engine spins faster a 300-6 or a 351M

3. The guy I bought my pickup from put the wrong tach in. It is for 4 and 6 cyl engines. Is it reading too high or too low?

Any help is great

Fordman

 

FM, take the back cover off of the tach, most of the multi purpose tacks will set to 8s as well.

John

 

I already tried that. There is a little tag that says "For 6 & 4 cylinder engines only" So I dont think that it is usable for an eight cyl.

Fordman

 

It was worth a try. I have one from the early 70s that is switchable. I think that my new one is also.

John

 

Fordman

A properly built 351M should be able to easily withstand 5,000 to 6,000 RPM. If you build it to race you should be able to get to 7,000 RPM. The 351M has a 3.50" stroke just like the 351W and 351C.

Conversely, the 300 ci six has a 4" stroke and is designed to be a low-RPM truck motor. I have one in my '81 F-100 and I've never rev'd it past 3,000 RPM. At 3,000 RPM it sounds like it is really screaming and I don't want to blow it up.

Bruce

 

Fordman

I was thinking of this after my comments. I would imagine that you could build the 300 CI six to rev to 5,000 or 6,000 RPM. Blueprint and balance it and give it a good 4-bbl intake and headers and it should rev and make good power.

From the factory the 300 CI six has only a one bbl intake and carb and it can't get enough air. The straight-6 engine with the proper firing order in inherently balance which is why they (and thier V-12 brotheren) are so silky and smooooooth.

Hope this helps

Bruce

 

I stand corrected!!!

In addition to being a Ford truck fan, I am also addicted to classic Mustangs. My second car was a ’68 GT Fastback with a 302, 4bbl, 4-speed and a traction lock rear end. I loved that car and wish I never sold it. Many 327 Camaros and a few 400 Firebirds wish I never owned it.

I responded to this thread because I own an ’81 F-100 with a 300 CI six as well as a ’68 Mustang GT/CS with 289 and I am converting a ’71 F-350 from a 390 to a 400M. I have some experience with both 6 bangers and V8s. I also have a ’68 GT-500 KR that I bought without an engine that I need to restore.

I just got my September copy of Mustang and Fords magazine. Beginning on page 27 is an article about a company called Clifford Performance from Corona CA, (909) 734-3310. They specialize in Ford in-line six cylinder engine performance.

I did not realize that the 200 and 250 CI small block and the 240 and 300 CI large block six cylinder engines have seven main bearings and, properly built, can withstand 7,000 RPM and make mountains of HP and stump pulling torque.

I encourage you to buy the magazine and read the article. Small block V8s beware of the well built sixes. A 302 cannot touch the torque of a 300 and, according to Clifford Performance, they can build you a 300 six that will make 600 HP at 7,000 RPM.

Evidently many of us have underrated the humble in-line sixes.

I can’t wait until my ’81 F100 is exempt from CA smog laws (in 2011).


Bruce

 

The 351 M is pretty much a hybrid of the 300 and the 302 right? It has the potential to turn up to 7000 RPM but still retains the torque. What about the 400? It has the 4 inch bore and a 4 inch stroke. Does the extra half inch on the stroke(3.50 to 4.00) make a hiderance on the amount of RPM that you can get out of a 400?

Fordman