well the piston i found closest to the size "needed" for a 400 is a KB holden 308 pistons
kb numbers KB282/KB247/KB234
at 1.7 compression height its damn close to the 1.717 left between the pin and deck if you are gonna cut away at a piston
this would be a good "blank"

well hate to do this but a few numbers these are vauge numbers(and are usually charged per hour acording to how the shop works it may be much more) ...
20 to cut valves in
20 to bore the pin out(if needed)
10 to cut a round dish(more for funky shapes i suppose
pow you just added 400++++(500?) to the price of a set of cast pistons no including gas vent/ pin install/ oil modding/ polishing/ coatings
now i have yet to contact the manufacturers as i know some have(most of em most likely) have tooling for pistons that are not produced and can be had special order/semi-custom for a deicent price as compared to a full custom 1 of a kind piston
i can't recall the maker but one has these )some of them?( listed on site...

if not you are looking at 650 to buy and machine a piston to fit and you can get a custom set for 700-800 i have seen sooooo

if i can not fiind a piston to fit the 400 i will most likely go with a 400<427 budget stroker my self as the pistons are 250-300 for claimer series KBs with only? off set cutting the crank and narrowing the width of a 240 rod(da shot peen but thats gonna be done anyway)
as they will be coated either way and hopefully the combustion chamber too to keep hot spots down so i can boost the copression HOPEFULLY w/o detionation

 

I have the same concern with Aussie heads I just bought, and have another thread going along the same lines...before I found this one. I will be using Aussie heads on my 400 as well, and found some Sterling STL-427P30 pistons with .145 inch dish and 7.9:1 ratio (.030 over) at summit...do these sound like a good match to arrive at around a 10.25:1 ratio with the Aussie heads? Good enough for pump gas (92 octane)?

Thanks!

DiMora

Notes:

Edelbrock 2172 camshaft/lifters, Edelbrock 2171 intake Edelbrock 1405 carb, Edelbrock 7821 timing set will also be used.

 

Hello.

Thanks For the advice. Sorry for the delay in posts, lots of hours at work. The more I am reading, I think I might tone it down a bit. Instead of having cake I will go for the cupcake instead. Thanks again for the info. I will keep reading and and planning and probably be posting more questions later.

Thanks Chad

 

To get a compression ratio of 7.9:1 with stock heads, I get a dish of 22cc's. If you then use a 58 cc head, the compression ratio is 9.3:1. With that cam you will have 412 ft-lbs torque @3500 RPM and 332 HP@5000 RPM. The Dynamic compression ratio is then 7.3:1. You could stand 0.7 higher compression ratio, or less cam.

If I use 12 cc's for the dish, then your dynamic CR is 7.97:1. That should be good with 92 Octane.

In this case your torque is 427 ft-lbs@3500 RPM, and HP is 349@5000 RPM.

I recommend checking the cc's on both the pistons and the heads.

 

Danlee, you have been extremely helpful, and I think I am close to understanding what is going on here. Let me back up what the numbers you listed with some additional info to make sure we are on the same page - and this may indeed be a solution for carp1 (the original poster) as well. In my application, these are the 59cc Aussie heads I am using... Would you say the dynamic compression ratio is more of a factor for the detonation vs. the static compression ratio? I ask because 7.3:1 sound just fine for 92 pump gas...and even going with those pistons I mentioned and pulling off 412 ft-lbs and 332 HP is a HUGE improvement over what I had before, and I think would be just fine on the old led sled...but I'll see if I can't find some pistons with less dish to hit the perfect compromise. Anyone reading this thread with any ideas on pistons (please provide brand / model / source) please chime in, as I am about to go with those listed above.

 

Yes, dynamic CR is a better indicator than static CR for detonation.

Read the explanation and download the program at this website.

http://cochise.uia.net/pkelley2/DynamicCR.html

 

Thanks again danlee; great link. So it sounds like I am definitely OK using the aforementioned dished pistons, and would be on the "hairy edge" of detonation if I stick with flat tops and aussie heads, with a static CR of 10.75:1. Do you have an automated calcualator that can give me a quick dynamic CR on flat tops with the 59cc Aussie heads, and all the previously described edelbrock gear?

 

With flattop pistons (3cc) and 59cc heads and the Edelbrock 2172 cam, the dynamic compression will be 8.6:1. That is detonation territory. You could do this with a cam that has more duration or by retarding the 2172 cam 4 degrees. Even retarding 4 dregrees will be marginal for detonation.

 

Well, I called Federal Mogul (The maker of the pistons I mentioned above) and they said the dish in CC's of those pistons is 10.0 - fairly close to your previous post saying 12 might be just about right for 427 ft-lbs@3500 RPM, with HP at 349@5000 RPM...

Anyway, here is the final skinny on what I went with (the parts have been ordered). When it is built and running in a few weeks, I'll report back to everyone how well it works, and whether I have any detonation problems. Danlee, thanks for your help with all this, you have been invaluable.

Engine: Ford 400 bored .030 over (408 cubic inches)
Carb: Edelbrock Performer #1405 (600 CFM)
Intake: Edelbrock Performer 2171
Cam: Edelbrock Performer Plus #2172
Pistons: Federal Mogul 427P / Sterling STL-427P30 (same thing) 4.030 diameter, 10CC dish
Moly Piston Rings
Heads: Aussie 2V "quench" heads (59CC)
Timing Set: Edelbrock Performer #7821
Water Pump: Edelbrock Performer #8844
Federal Mogul / Melling High Volume Oil Pump
Brass Freeze Plugs
Fel-Pro Gaskets
Balanced, Line-bored, blueprinted

Can't wait to get her running...Danlee, if you have time to plug that into your desktop dyno, I'd be curious to find out what it predicts now that I have solid numbers on the piston CC and Aussie head volume. My builder knows some guys with real dynos, so maybe I can get it onto one to see how close the computer is vs. reality when it is all done. I tried to use the calculator myself, but I failed miserable when trying to figure out the dynamic stroke length calculator.

Best regards,

DiMora

 

Dimora,

Here are the numbers based on what you have given me.
HP= 345@5000 RPM
Torque = 424 ft-lbs@3500 RPM
DCR=7.81:1

This is slightly less than the previous because I added 3cc for valve relief to the 10cc for the piston for a total of 13cc instead of 12cc previously. If I don't add anything for valve relief then I get

HP=350@5000 RPM
Torque = 429 @ 3500 RPM
DCR=8.05:1

 

Dimora,

One more item that may have been overlooked is the Compression Height(CH) of those pistons. I used the factory CH in my calculations. Replacement pistons have lower CH (0.010?) to compensate for other work like shaved heads or decking. You can make up for this by shaving the heads by the same amount or decking the block.

If you give me the CH, I'll run the numbers again.

 

I appreciate it. I think it will be a nice balance of torque and HP for my heavy cruiser. I'll post pics when it is all done.

Thanks again, Danlee!

DiMora

 

yup most regulars have hashed and rehashed this so many times
the compressin height on the mogal pistons is 1.630 stock is ~1.650-1.670 so the pistons are compensating for a trued block and it is factored in the compression
IOW if you do not "true" your block the compression will be lower(and safer)
you can get 1.670 compression height 351C pistons cant recall the maker

basically they are reversing any improvemts from shaving he block or heads

well one tip for your machinist make sure he checks/ matches the angle of the intake and intake mount surface
as some 351m/400 shipped marginally (just barely matching/sealing) and when/if the deck or head is machined it could leak (known to happen)

see what u folks did ..got me to thinking amd looking at pistons again
found a EXELNT piston i didn't notice before
the KB148 4" bore 1.670 compression height 13cc D shaped dish and intended for the 351c so the intake valve lines up nicely
62cc heads is listed as 9.8:1
not too bad

ps the ENGINE's compression height(to zero deck) is 1.717
so 1.717 - 1.670 = 0.047 gap between the piston and deck(head mounting surface) this is where the knocking comes from too much of a gap causing problems..hot spots/not expelling enough of the exaust/no turbulence to cool the piston