Which stroker crank/rod/piston combo? (351)

[Jason 302]

1969 351w block w/9.48" deck height
383 stroker kit. 1.875" throw/6.25" rod/1.35" piston= 9.475" 1.667 rod ratio
393 stroker kit. 1.925" throw/6.20" rod/1.35" piston= 9.475" 1.610 rod ratio
408 stroker kit. 2.000" throw/6.20" rod/1.28" piston= 9.480" 1.550 rod ratio
408 stroker kit. 2.000" throw/6.125" rod/1.35" piston=9.475" 1.531 rod ratio

What do you guys think? I think the first 408 combo looks awesome, but I have to have some deck clearance to true it up. I really like the 383, but hate saying it cuz it's Chevy lingo.

Motor will be street/strip blah blah, you know, the usual. Hydro roller cam, good heads, EFI, 6500 rpm.

 

[tjm73]

I liek the 408 with the 6.2 rods myself.

Did you know a .020" over 408 stroker is exactly 405.9 inches or a 406. A 406 Ford has history in it's name. Only Ford had a HiPo 406.

 

[Jason 302]

I liek the 408 with the 6.2 rods myself.

Did you know a .020" over 408 stroker is exactly 405.9 inches or a 406. A 406 Ford has history in it's name. Only Ford had a HiPo 406.

The only thing I don't like about that combo is the pistons will stick about .005-.008 out of hole after having the block decked. That would probably put compression close or over 11:1, which I don't want. I might put about 5-7# of turbo to her one day.

 

[Rick 91GT]

Have the block measured, you would be surprised how much meat can be there on an old block. I milled one .014" once and the piston was only .003" out of the hole.

I'd go 408 4" stroke, 6.2" rod

 

[Vipersix]

Did you know a .020" over 408 stroker is exactly 405.9 inches or a 406.

How is it that you can overbore a 408 and come up with a smaller displacement? I need to find that kinda math come tax time!

If you're worried about compression and know that you are going to run some sort of boost down the road, go with some low compression dish pistons. This will help not only with your compression woes but also assiste with clearance at the heads.

 

[tjm73]

How is it that you can overbore a 408 and come up with a smaller displacement? I need to find that kinda math come tax time!

Easy instead of overboring the stock 4.00" bore by .030" to get a 408 you overbore it .020" and get a 406. No funky math involved. You gotta remember that the 408 stoker is a 4.00" bore and 4.00" stroke bored .030". Reduce the overbore and you reduce the cubic inches. A 4" bore and 4" stroke is a 402.

The only thing I don't like about that combo is the pistons will stick about .005-.008 out of hole after having the block decked.

That depends on the actual deck height you are working with, the piston pin height of the pistons you plan to use and the ammount of material you plan to remove when you deck the block.

The rod plus 1/2 stroke equals 8.2". Add that to the pisotn pin height you have and then deduct that from planned deck height. Keith Black forged pistons for a 408 stroker example have a 1.28" PPH. That 9.48" total height. Yoiu can take about .025" of the block for zero deck height. Plenty to sqaure the deck up. And it wouldn't stick out.

There are 2 351W block heights to look at. '69-'70 = 9.480" and '71-'96*= 9.503".

On a '69-'70 block you can't deck with out the pistons coming out of the bore. "71-'96 you can. There is no significant difference in the blocks until the F4TE block showed up in mid-1994. It's a roller cam block.

Compression can be compensated for by choosing the right cylinder head for the job. You should decide what head gaskets you plan to use also and calculate your actual compression ratio. Head gaskets have an impact on your C/R too.

Don't go by what's advertised, as it is often not correct.

If you think you might go turbo someday I'd shoot for a 9:1 compression ratio with aluminum heads. It'll deliver good power naturaly aspirated and great power turbo'd.

 

[Vipersix]

Cylinder heads normally have a very small impact on compression ratio unless you get into the race specific or more spendy pieces. Otherwise, the thickness of your gasket and your piston will determine the compression.

I guess I'm the only one who sees the humor in overboring an engine and getting smaller displacement. I guess it's just how you worded it. If you are only going .020 over then it's not a 408 stroker... all I'm saying.

 

[tjm73]

Cylinder heads normally have a very small impact on compression ratio unless you get into the race specific or more spendy pieces. Otherwise, the thickness of your gasket and your piston will determine the compression.

WRONG! The combustion chamber of a cylinder head has a VERY BIG impact on your compression ratio.

Take the AFR 185 for example. on the exact smae engine you can mount them and with the 61 cc or the 58cc. The difference in c/r will be almost .5 of a compression point. Or more simply, you can go from 10:1 to 10.35:1. (yes I calculated that)

.35 is a significant ammount in my book. Top that same combo with Edelbrock Heads with a 70cc chamber and it drops to just 9.09:1, over a 1.25 point drop. So head cc volume is importent and has a big impact on compression ratio.

 

[Vipersix]

Most street heads have virtually identical combustion chambers. As I said, unless you get into race heads or the spendier types (i.e. AFR 185+ or the larger ones from Edelbrock or Trick Flow or whoever) the compression will not change more than .15 or so. Small in my book. For most of the people who look for help on this forum a piston design will affect their compression more than head choice. IMHO anyway...

 

[ExplodingGopher]

Everything adds up together, chamber cc, milled block or head, deck height, head gasket thickness, head gasket bore, amount of quench, compression height, cc of pistons, it all adds up to what the STATIC COMPRESSION IS, you also have to consider the camshaft, a bigger cam will help with high compression making the dynamic compression lower thus helping with detonation. Im in the middle of assembling my 466 big block and i did my homework, i had to go with a .060" thick headgasket to get some decent clearance between the deck and head because the pistons have a higher compression height and poke out .016" which is still ok to run. With my combo i will end up with 10.35:1 compression.

If you have any questions about anything mentioned above, feel free to inquire.