351M to clevland changes
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From: Taylorville, IL
351M to clevland changes
i found out that you can bolt up a set of 351c 4 vavles heads to a 351m, and that you can bolt up a 351c intake, but you need to use a spacer. What kind of spacer, do they make one or do i have to make one, should i get a bigger carb? I was told that this makes the engine breathe better, therefore making more hp. Anyone have a bit of advice? thankx-Jason
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From: PacNW
A set of 351C 4V heads (the V stands for venturi as in 4V carb, not valves) will bolt to a 351M with no modifications. Weiand used to make the spacers for the 351C intake manifold but I've heard they don't make them anymore. I believe DSC Motorsports still makes a spacer, you might want to check on their website. You will have to modify the spacers to match the large ports on the 4V heads and also make sure you get a manifold designed for 4V heads as well.
Depending on the style of 4V heads you get, open or closed chamber, you need to be aware of the increase in the compression ratio particularly with the closed chamber heads.
Overall I don't think you'll find a lot of positive feedback on this swap simply because the large ports on the 4V heads cause a serious loss of bottom end torque so depending on what vehicle you plan to put this in you might not be too happy with the results.
Depending on the style of 4V heads you get, open or closed chamber, you need to be aware of the increase in the compression ratio particularly with the closed chamber heads.
Overall I don't think you'll find a lot of positive feedback on this swap simply because the large ports on the 4V heads cause a serious loss of bottom end torque so depending on what vehicle you plan to put this in you might not be too happy with the results.
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From: Delaware
You will be much better off with a set of Aussie heads. They will bolt on and you can use any manifold for a 351M/400 motor. You do not need spacers. This mod will be a lot cheaper, and it will run better.
The DSC spacers are expensive and will raise your carb at least 1 inch.
The downside is the Aussie heads have 58cc chambers, where yours have 78.4cc chambers. The compression ratio may be too high for pump fuel unless you take steps to reduce the cylinder pressure.
The DSC spacers are expensive and will raise your carb at least 1 inch.
The downside is the Aussie heads have 58cc chambers, where yours have 78.4cc chambers. The compression ratio may be too high for pump fuel unless you take steps to reduce the cylinder pressure.
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From: Taylorville, IL
The main thing I'm looking for is increase in airflow. I was told the clevland has four valves, I take it I'm wrong. Do they make any kind of oversized valves for this kind of thing? I was told the main limitation on the m motors is the 2v head. This engine is in a 79 f150 4x4. It has 31" tires for now (a set of 38's in the near future) and a 2v carb. I know the swap to a 460 is popular, but for the same money I'd rather put it into what I already have. I have an almost complete second 351m motor, but I'm not sure if it's good. I'm going to the 400 set up, and I want to keep good torque. Also, I have the 4 speed in this truck and an auto (not sure which one) in a 79 2wd short bed. I like the low first gear in the four speed, but what will be better on the highway. I take the interstate to work everyday (65mph +) and I go through fuel. Help???????
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From: PacNW
The heads are absolutely not the limiting factor on the 335 series (351M/400 & 351C) engines. While the 4V heads do have very large valves (larger than a stock 460) the 2V & M heads still have relatively large valves (2.04/1.66). The biggest reason for the lack of grunt in the 351M/400 engines is the low compression ratio, 2V carbs and severely retarded timing built into the factory camshafts. If you focus your time & $$$ on improving the induction, C.R. & timing on the 400 you'll fnd you can build a very respectable engine for less than the cost of a swap to a 460.
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Bill, don't you mean "...severely retarded timing built into the factory timing set". Rather than "...severely retarded timing built into the factory camshafts". 
All of the 335 series engines have "Cleveland" heads. There are slight differences with different production years. Check out this tech paper here:
https://www.ford-trucks.com/article/...00_Engine.html
All of the 335 series engines have "Cleveland" heads. There are slight differences with different production years. Check out this tech paper here:
https://www.ford-trucks.com/article/...00_Engine.html
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From: PacNW
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From: chicago burbs
waldens pond data shows that the 2V heads outflow the 4V's up to about .400" of valve lift. do a little blending in the bowls and you'll see more flow from the 2V's. http://web.archive.org/web/200206100...s/fmotorsp.htm
Last edited by grclark351; Dec 10, 2004 at 11:34 PM.
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From: Taylorville, IL
You guys have a little more tech info than I have. I'm a suspension man who loves engines that go fast, but I'm still learning about specs. I'm gonna change to the 400 crank and pistons (which should be all to make it a 400, right?) what else do I need to increase the cr? I want to go with a mild cam, and edelbrock intake and a 600 carb. I was told if you run high octane, you can retard the timing, but what are you talking about with the bowls of the head? I also want to thank ya'll. this is the first time I've been on a forum where people knew what they were talking about. Any other related help that I may not know to ask would be great too. Thanx-Jason
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From: PacNW
Read the thread on 351M>400 build up:
https://www.ford-trucks.com/forums/s...9&page=1&pp=25
We've been having a discussion on the different heads, valve sizes, airflow & head porting. There's also a link to a 382 HP 400 build up article that Hot Rod magazine did back in 1999.
As far as turning a 351M into a 400 all you need is the crank & pistons. I'd suggest you look at the pistons that Tim Meyer sells, they're designed to help eliminate the problem of the pistons being too far down in the bore that plagued factory 400s. Be sure to get the entire rotating assembly (crank, rods, pistons, flywheel/flexplate & harmonic balancer) balanced before you install it in the block.
Running higher octane gas actually allows you to advance the timing which gives you more power.
https://www.ford-trucks.com/forums/s...9&page=1&pp=25
We've been having a discussion on the different heads, valve sizes, airflow & head porting. There's also a link to a 382 HP 400 build up article that Hot Rod magazine did back in 1999.
As far as turning a 351M into a 400 all you need is the crank & pistons. I'd suggest you look at the pistons that Tim Meyer sells, they're designed to help eliminate the problem of the pistons being too far down in the bore that plagued factory 400s. Be sure to get the entire rotating assembly (crank, rods, pistons, flywheel/flexplate & harmonic balancer) balanced before you install it in the block.
Running higher octane gas actually allows you to advance the timing which gives you more power.
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From: chicago burbs
the valve bowl is the area under the valve in the head. here is a link to some pics of some nice bowl work.
http://raceabilene.com/kelly/hotrod/newmotor2.html
http://raceabilene.com/kelly/hotrod/newmotor2.html