I have a 351m/400 my crank is at my local speed shop being turned. I want to do a mild build to this motor. I don't want to stroke it. I plan on doing a roller cam and some head work. Along with aluminum intake and headers. I messaged Tim on here for some help but no response back. What do I need to have my machine shop do to my heads to set them up for a roller cam? Also which is a good cam for my use: pump gas 91/93 octane, driving to work and back (don't care about gas mileage), off road use, and truck pulls. I run 37 inch tires. So I need some more torque and hp. When I pull in truck pulls I currently pull around 5600 - 6800. This rpm range I'm fine with. Maybe a little higher is fine. Rods and pistons are stock. Should I port the exhaust side of heads and polish? What about intake side? Hardened push rods? Bigger valves? I do plan on a 3 angle valve job.

 

So what crank is it? 3.5 or 4.0 inch?

Turning 6800 rpm with stock pistons and rods?

Those stock heads won't make power at those engine speeds even with a 3.5" crank.

Sounds to me like there's some confusion, at least I'm confused.

R.

 

No confusion. Low range 1st gear, sometimes low range 2nd gear. Pulls high rpm all the way down the track.
Once I pull my heads off I will measure the stroke. Pulling isn't about power per say, more about wheel speed. Faster I spin the tires, longer I go before the sled stops me.

Like I said I want to go with a roller cam and some mild porting while still running pump gas. So I want to know which roller cam to go with. And what else to do to the heads.

I have a street mod truck with a 460. Stock crank, rods, pistons and a cheapo roller cam. Runs c12. I did tons of porting to those heads. They are not scj heads. Stock 460 heads. I can fit a golf ball inside of the exhaust ports. But its street mod. I want to build my 400 up a bit for stock class.

 

Your crank is at the shop being turned but you don't know the stroke?

If you have and are going to stick with a 351M, save your money. It is a low compression engine, which will limit your choice of cams to short duration, high lift jobs. No 6800 RPM power with those afaik, I think they are listed as 4500 or 5500 RPM limit.

If you have a 400:

--porting would be a rough finish on the intake, smooth on the exhaust. You can probably google a port and polish video.

--whoever you buy a cam from will tell you all about it and what you need. Roller = $$. Since the roller set up is all different, you will be buying pushrods, springs etc.

--if your heads need work like valve guides, consider aftermarket heads

--look on the TMI site for the piston you need to get into the 9s compression wise.

--look at the builds on the TMI site and pick and choose from that formula as your budget allows.

Again, forget any notion of making real power out of a 351M. Donate your cash to a worthy cause instead.

 

No I don't know the stroke at this moment. I blew a rod bearings to peices at my last truck pull. That's why crank is at the shop being turned.

My compression ratio is in the 9's my heads were plained before. Cam that's in it is flat tappet but not stock. Crank, rods and pistons are stock besides a previous .010 turn on the crank.

Once I get the crank back and heads off I will check the stroke. As far as porting the shop will be doing it for me, I don't want to run higher than 93 octane. I'm not looking for a 800hp motor. I have my 460 for that. I just want some more get up and go without stroking the 351m/400. Can't run aluminum heads in stock class. That's why I'm working these heads. I will check tmi site.

 

Do you know the casting number of the heads?

If they have the water jacket all the way around then you really do need to port them. Just rounding off the plateau around the exhaust valve helps a lot. Ported the exhaust they can be made better than a stock BBC exhaust. I'm sure if you really ported the whole head 500+ HP is possible. Stock valve sizes are just fine. Porting yourself will save a bunch of money.

As far as other modifications, rocker arm studs would be nice, but costly on a canted valve head because each pedestal is canted. I, and many others are using Scorpion bolt on roller rockers. Their customer service is fantastic.

Get the Keith Black hypereutectic pistons from Tim Meyer, he's great... Just swamped right now I'm sure. He's got a Project going for NEW 351C based race blocks going.

I would polish the rods and get ARP bolts installed. I'm using the smallest Howards hydraulic roller cam, but don't have enough time to know if I could recommend it or maybe the next larger one for your application. If you run a roller cam - use hardened pushrods for sure. They are really long in the tall deck of the 351M/400.

 

You realize you either have a 351M OR a 400.

The Keith Black pistons work for the 400, will not work in a 351M.

How did you figure 9:1 just based on cutting the heads? That's almost a full point.

351M/400 Performance Build Up

 

What are the crank differences between the 351m and 400? I assume the rod journals are smaller with taller pistons on the 400 to get a longer stroke? I need the exact diameters of the crank if anyone knows.

 

Rod and main journals are the same.

Rod is the same for both motors at 6.58".

Piston compression height on the 351M is listed at 1.947" or 1.921" --other variations probably exist depending on the piston supplier. The smaller that number, the lower the compression and poorer performance will be, as that will mean the piston is further down the hole.

Piston compression height on the 400 is 1.65", close to the same as the 351C. More info here, although I think some of the pistons he mentions for the 351M are no longer available based on other posts here:

M-Block 351M/400 Performance

Stroke for the 400 is 4", thus the crank arm is 2".

Stroke for the 351M is 3.50", so the crank arm is 1.75".

 

So to turn a 351m into a 400 you need a 400 crank and pistons. Rods are the same? No block work needed right? 400 crank bolts up fine?

I will call the speed shop to see which crank it is

 

Crank and pistons. Stock pistons will give you 8ish compression. 9.3-9.5 pistons are available. Those and mildest of RV cams will put you into the mid to high 200s HP wise and probably burn no more gas than you do now.

 

I'm not changing my current pistons just trying to figure out if I have a 400 or 351m. Not sure if speed shop will know. If not then I have to wait till crank is done. Old rebuild was .020 rods, .010 mains, headsplained (not sure how much), stock or cheapo flat tappet cam.

New build currently: .030 rods, .020 mains. Weiand plus non egr 4bbl intake, Holley 750 4bbl vacuum secondaries, 1 inch carb spacer, long tube headers, exhaust ports ported, gasket matched and polished, intake ports ported, new valves with 3 angle valve job, fuel pump delete plate, new oil pump and rod.

Still might do a roller cam 2,000-6,500 rpm. Not sure yet. Alot for a cam kit when I have a 460 sitting on my garage floor.

When I'm done porting heads with everything else I will be near 350-400 hp easily. On pump gas. Will put 1,000 to 2,000 miles on motor then test is at truck pulls. She's either going to pull hard or she's going to blow. We will see.

 

Since you're going to be doing truck pulls with it....

I'd suggest you make sure you have 9.5:1 or better compression, upgrade to ARP rod bolts and THEN a roller cam. Something like the Howards P/N 230245-10 - 225/229 degrees duration at 0.050" lift, and .576"/.600" lift, this should put you over 400HP if you've got even a moderate port job on the heads. I say Howards only because I've got their catalog in front of me, any cam company can set you up with something similar. You'll need a properly prepped rod for sure.

Like a lot of people here I'd say it would be worth the effort on a 400, but probably not on a 351M. Your call on that one, if you want to do the 351M just to see what it can do - I can respect that!

 

I plan to use arp bolts on everything. They have head bolts, rod bolts and a bolt set that does valve covers, intake etc.. So I'm ordering all 3. As far as compression, I can't go to high. Only allowed pump fuel in stock class. The 351m vs 400 debate is the same as the 302 vs 351w debate. Obviously nothing replaces replacement. My goal is to achieve a good running street motor that I can drive to work or the grocery store while still kicking a stock 460s *** in truck pulls. Impossible? No. Head jobs create a ton of power. Can I go far on 351m/400 heads? Not as far as scj but I can make power out of these heads. Don't plan on bringing this engine to the dyno. But I will promise when I'm done it will be over 400hp, not stroked, pump gas and be able to be driven on the road.

One question I do have. My 460s dissy I had to install a bronze or brass gear because I was shearing the stock one up. Should I do this on this motor or is the stock safe for 400hp?

As far as the cam I'm not sure what I'm doing yet. I want to keep this under 3grand. I have 450$ invested into my crank, bearings and gasket set so far. Still have to order my weiand intake and headers. That will be around 500$ or so. 300$ or so for all the arp bolts. Hardened push rods(dont have a price yet) Then pay the speed shop to do a 3 angle valve job. When I'm done doing this much I will decide if I'm doing a roller cam or not as the speed shop will need to setup my heads for it.

 

I have a set of stock 2V cylinder heads that I gasket matched intake and exhaust and port polished every exhaust runner, removed the stupid EGR humps and matched the valve seat to bowl, smoothed and cleaned up all transitions and slightly cleaned up the chambers, I didn't want to remove too much and drop compression a lot they measured 78cc I am building a 500hp 400 and wanted to use these heads for a "stock" looking street thumper but, there is one crack in the #8 exhaust just under the exhaust valve seat and goes just between intake and exhaust seat. If you want to have stock heads, fix these and they will work well for you, all other things are within spec so you can just throw in good valves and springs etc. and these will flow good for you. Let me know