[Brian D'Amico]

I'm looking into putting a 4.21 / 4.25 stroker crank into my 400 when I rebuild my motor this fall and I was wondering does anyone make a dished piston that would get my C/R in the 9.5 to 9.8 range with 670 (72cc) heads?? I know someone on here has had to have done this... I looked in some old posts, but have found anything yet. Thanks!!!

[Jagtec1]

Looks like you'd need about a 25-28cc or so dished piston. You could have those chambers on the 670's cleaned up to deshroud the valves and gain 2 or 3 cc there. Any of the builders that post here can get, or have what you are looking for. Try Spotts Performance

[buwalda]

I had a similar combo & had Ross make a set of custom forged pistons with a 'D' shape 34cc dish.

[robscar]

in jim hand's book, pacific performance lists a couple combos that use dished pistons and small chamber heads. they are listed at 9.4 compression.
i've been reading the book yet again. soon i'll have it memorized. then i can quote it like some people quote shakspere.

[taalltheway]

I am also thinking about stroking my w72 400 with 670 heads. I would accept a 10,5:1 compression. Where could i find a complete strokerkit that works?

[taalltheway]

PS: Are there any downsides to using dished pistons? Some people told me you could lose power because dished pistons do not use the chamber architecture as efficently because the quench area gets lost??

[Jack Gifford]

T/A All the Way- A dish in the piston actually makes for a more efficient chamber- closer to a sphere (the ideal). But use a D-shaped dish, to maintain a quench area.

[taalltheway]

Thanks for the info. I did not know that. Well then i guess there are no good reasons left not to do it.....How many CCs would the dish have to be to reach not more than 10,5:1 with the 72 cc 670 heads??

[Brian D'Amico]

That's the same question I had.. how much to dish. The reason I said 9.5:1 was because I want to run pump gas (93 octane). Could I run 10.5:1 on 93??

[Rholmes]

Bada Bing running 10.5:1 c/r on 93 octane could be detrimental and not worth the risk for minimal (if any) power gain advantage(aluminum heads being the exception).I and many have tried all sorts of "voodoo magic",eg.(1) bigger cams,that only bleeds off the higher compression at low rpms and builds compression at higher rpm's,causing detonation and busting rings and sometimes pistons,(2)Retard timing, that ironically decrease performance and you may suffer some heat issues(3)Octane Boost(IMO look up "voodoo magic").(4) Custom Head gaskets(inferior combustion reaction:read decrease performance).So as you can see there are no cheap fixes.Get the iron headed engine,9.1:1 to 9.3:1,custom dished pistons,and you're engine will live for many a moons
PS Now about your sig.To quote the Godfather of soul "I don't know karate...but I know karazor"

[6567GTO]

I've got flat top pistons in my .040" 455/670 head combo and can't believe the difference a cam makes. The cam that I have now is a 290B-6 solid from Comp Cams and while at a cruise far away from my house I was forced (bad planning) to use some 93 octane gas to get home. I kept waiting to hear detonation but didn't. My last cam, a hyd Ultradyne 288/296 would have pinged like heck. Therefore, cam design can have a big effect on detonaton.

[taalltheway]

670 heads in a 455 with no dish??? You must have about 12:1 compression.....wow! What kind of fuel do you use? Are the 670s good enough for a 455?

[66GTO Jim]

If you go with one of the big name Pontiac Builders, such as Spotts, Butler, Pacific etc, to buy a stroker kit, they will put it together based on your what you want to end up with and your specific engine. They will ask questions like what is your deck height after milling? What compression ratio do you want to end up with? What heads are you using? Are they going to be milled and/or street ported? You will need to use a longer rod and a shorter height piston. Rods for a 4.250 crank would be 6.800 and are readily available. Pistons will have to be custom made anyway so they will order them based on what you want to end up with. Plus they are willing to provide phone support and answer questions. I would not recommend buying the parts piecemeal on your own. JMHO Jim

[6567GTO]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> 670 heads in a 455 with no dish??? You must have about 12:1 compression.....wow! What kind of fuel do you use? Are the 670s good enough for a 455? </div></BLOCKQUOTE>

Yes, it's around 12:1. I use a 50/50 mix of 93 octane unleaded and 110 octane Cam2 generally. I realise that it would ultimately harm the engine because there is inaudible detonation. But I was totally surprised that it hardly pinged at all with mostly a straight 93 octane in it. I'd say it was 80% 93 and 20% 110 when I was coming home from the cruise. For the heck of it I added even more 93 when I got home and it still barely pinged. I did end up hearing though and went back to a 50/50 mix.
Jim Butler helped me pick my cam for my combo. The other thing that changed with my newest combo is the heads were street/strip ported for the new cam. Probably lost a few CC's there too. They were basically untouched with the Ultradyne setup. I just cleaned them a little by removing casting high spots.