Need 351C stroker advice

Stock 4v heads on an M code '70 would be closed chamber. I believe the stock compression ratio is 10.7:1, but I've also seen 11:1 as the correct number. When you add displacement via a stroker crank, CR will go through the roof unless you use dish pistons. If you do that, you may regret it when you go to a better cylinder head.

If you have open chamber heads, you're still not out of the woods. I have a '70 Cougar with the OC 2v heads and it's a ping monster. In the years since the early '70's, it's been recognized that quench is the key to controlling ping. You need a closed combustion chamber with a quench everywhere else, in the neighborhood of 0.040" between the piston crown and the head surface. Since standard head gaskets compress to about 0.035", correct quench requires either flat-top pistons or a thinner head gasket.

I'm not saying you will have CR/ping problems, just that it's something to be aware of. Here's a great CR calculator to play around with: http://users.erols.com/srweiss/calccr.htm

You need to know your head's cc's to use the calculator. According to this web page http://www.canadianclassic.com/mi/specs.mv a '70 M code CC 4v head has a volume of 61.3-64.3 cc. A '72 Q code "Cobra Jet" 4v is 64.6-67.6 cc. A '72 R code "H.O." 4v is 73.9-76.9 cc.

My 408c is built with open chamber heads....10.7:1 and I do not have a detonation problem.
When you build the stroker you have to get new pistons anyway so you can simply match your compression to the heads you have.

bareje said:

dodgestang - does the 408c require more modifications to the block than the 393c?

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neither requires modifications to the block.

i would choose option 1 also. the stock 4v open chamber heads will be enough to feed that motor with no problem. as far as pinging goes, keep your compression ratio around 9.5:1, initial timing around 1degrees btdc with a total timing of 36-38 degrees, and keep the fuel mixture around 13.5:1-14:1 and you should have no pinging problems

keep in mind that if you swap heads later down the road your compression ratio is going to change. if you wind up with 9.5:1 with the 72cc OC heads then swapping to a smaller chamber "quench" head like most of the aftermarket heads are you'll end with closer to 10.5:1 compression, so keep that in mind. 10.5:1 will be fine with aluminum heads as long as you use 92-93 octane.

400-450hp is a pretty easy goal to reach even with a stock stroke cleveland. check out the latest issue of hot rod, they got 505hp and 565lb/ft from a 400M with e'brock cleveland heads, pretty impressive. they did increase the displacement slightly by offset grinding the crank and .040 overbore. they had a buch of oddball parts too, chevy rods, mopar 340 pistons and 5.0 late model flexplate and balancer to make it all work because the 400m doesn't have any aftermarket parts but it worked. point is if they get that much power from a 400m you should have no problems getting 450 from a stock stroke 351c with good heads.

bnickel said:

400-450hp is a pretty easy goal to reach even with a stock stroke cleveland. check out the latest issue of hot rod, they got 505hp and 565lb/ft from a 400M with e'brock cleveland heads, pretty impressive. they did increase the displacement slightly by offset grinding the crank and .040 overbore. they had a buch of oddball parts too, chevy rods, mopar 340 pistons and 5.0 late model flexplate and balancer to make it all work because the 400m doesn't have any aftermarket parts but it worked. point is if they get that much power from a 400m you should have no problems getting 450 from a stock stroke 351c with good heads.

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I have a mental picture of going into the local Kragen's for something for this combo and watching the poor counter monkey go into brain lock muttering "Make/model/year" in infinite loop.

BTW, that "400M" reference is fightin words in some quarters.

180 Out said:

I have a mental picture of going into the local Kragen's for something for this combo and watching the poor counter monkey go into brain lock muttering "Make/model/year" in infinite loop.

BTW, that "400M" reference is fightin words in some quarters.

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what do you mean 400m is fightin' words? i don't understand. the 400 and 351m use the same block and pretty much every other part except crank and pistons, so i'm kinda at a loss to what you mean. i have no personal problem against the 400, in fact i think it's a great engine actually. the 351m on the other hand is pretty much a dog or at least the one i had in my 74 ranchero was anyway. i only wish it had had the 400 instead.

bareje said:

Thanks for the replies everyone. Will the stock heads be able to stand up to the increased power from the stroker? Or will I need to get new valves, screw-in studs, guideplates, etc.?

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Bareje, I have a 72 Conv I've been working on restoring for a couple of years now and have been looking at a 408 stroker kit from Speed-O-Motive for about a year. Like you, I have the same 450hp/torque target and have been trying to work out the details on heads, cam, manifold, etc.

Here's a fantastic book on small block Ford strokers, and it has a great article on a 351C 408 stroker build >>> How to Build Big-Inch Ford Small Blocks

As for the heads, you should have new valve seats put in to handle the unleaded fuels. As for the rest of the moving parts on the heads, I would recommend the basic upgrades on springs, valves, rockers, etc. But, in this case I'm thinking of my 2V heads. Your 4Vs may have different requirements.

Best of luck!

AustinCobra

bareje said:

I’m looking into getting my short block rebuilt this winter and I need some advice. I’m kicking around two ideas and hopefully you guys can help me decide.

Option 1: Upgrade to a 393 stroker and keep the stock 4V OC heads.
Option 2: Leave the displacement alone and invest money in a good set of heads.

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I have a 393C stroker coming up for sale very soon. All the best parts used in the build, I never go cheap. Less than 900 miles.

4MuscleMachines said:

I have a 393C stroker coming up for sale very soon. All the best parts used in the build, I never go cheap. Less than 900 miles.

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is that the one from the Boss 351?

bnickel said:

what do you mean 400m is fightin' words?

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My reference is to the fact that there are purists who will jump on you for saying "400M"; they prefer just plain "400." That's all.

As far as the worthiness of the Ford 400, I want to be the first to predict that the Ford 400 will win the 2007 Engine Masters Competition.

As I understand the '07 rules, they will still measure torque at 300 rpm steps between 2500 and 6500 rpm and average the torque numbers, calculate hp at those same steps and average the hp numbers, then add the two averages. This formula has turned out to favor long strokes, provided that the bore must always be large enough to unshroud the intake valve.

The '07 EMC rules will also retain the 10.5:1 static CR rule from '06.

But for '07 there will be four new rules: (1) there will be no c.i. limit, except that (2) the shortblock must use a bore x stroke combo that was standard from the factory; (3) the score will also include an hp/ci component; and (4) they will accept only one version of a given combo, e.g., only one 4.00 x 3.48 small block Chevy, first come first served.

Since nearly every classic pushrod V8 is oversquare -- the 455 Olds (4.15 x 4.21) is the only exception I can think of -- the winning undersquare stroker combos of years past are illegal. After the Olds, the Ford 400 at 4.00 x 4.00 is as close to undersquare as you can get. Furthermore, as 6 of the top 7 finishers in the '06 EMC have demonstrated, the 335 series has an additional unfair advantage over the wedges: splayed and canted valves. Finally, an oversquare combo always produces more hp/ci than an undersquare combo of the same displacement and with the same heads, because of the valve shrouding issue and because shorter strokes have slower piston speeds and therefore can rev higher, cube for cube. If 335 series heads -- specifically the aftemarket CHI "3v" version -- were so dominant in this year's 434 ci stroker formula, with no hp/ci component in the scoring, they should be even stronger in a generally oversquare formula which also includes a hp/ci scoring component.

So write it down now: the Ford 400 will kill.

bnickel said:

is that the one from the Boss 351?

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Yes it is

4MuscleMachines said:

Yes it is

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going for a 408 next time around? or bigger?