PISTONS: Flattop or Dish for stoker....

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Haney

Haney

www.carsonandironmt.com
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What is the highest static compression that I can get buy with and still run pump gas (93 octane)? If you look at the particulars of my build, I am using a 360 block hopefully at .030 over and Ebrock heads. If I use a set of Probe flattops they have a 5.5 cc valve releiefs. Doing the math with the following assumptions:

Bore: 4.030
Head CC: 65
Bore of head gasket: 4.19
Thickness of head gasket: .039
Zero deck
piston volume: 5.5 (Probe flattops)

I get a 11.55 static Compression ratio.

I have always heard that due to heat disapation that you could run 1 pt higher with aluminum heads. This would mean 10.55 iron head equivalent.

Also, I know that these strokers like cam duration, so if I run a cam with at least 250 degress of druation @ .050 then I should bleed off some cylinder pressure.

So, do you think with this bottom end and cam, I could run pump gas or should I build with a set of dished pistions and get my compression down in the 10:1 static range?
 
I have a 360 with iron magnum heads that has 10.6:1 static compression. I have a 224/230 @ 0.050 cam that gives me 180-190 psi of cranking pressure. I run this engine on 89 octane and can get by on 87 if I am careful.

With a cam of 250 degrees duration @ 0.050" I would think you would not have a problem with 11.5:1.
 
One other point of data that I have is that I have a friend with a 416. He used the diamond flattops (6.6 cc) at zero deck, a set of x heads, and a MP 292/509 cam. He has no problem running 93 octane even at 34 degrees of timing. I know the X heads have a larger chamber on them than the E heads (72-74 cc's vs. the Edelbrocks 65 cc's) but they are iron. Plus the MP cam is really right at 240's duration @ .050.
 
going from say 8:1cr to 10:1cr will prolly get you a 60hp increase. from 10:1cr to 11.5:1 cr mabey 10-12hp.
worth it? mabey in a all out drag car. but for the street IMO not worth it.and yes, generally a 11:1 aluminum head
is equivilent to a 10:1 iron cylinder head engine. duration does not bleed off cylinder pressure, VO (valve overlap)
does, allbeit at lower rpms. upstairs there's not enough time to bleed off. but to answer your question. careful planning
and you can prolly get away with 12.5:1cr on 93 octane. now theres the dilemma of which piston design is better,
FT or dished. IMO, dished pistons make a more stable uniformed flame travel, with way less chance of detonation.
combine that with very good quench (around .040") and you'll get one hellava happy running street engine.
KB sell a "quench" dome dished piston for open/closed chamber heads in case your wondering. one other point,
for anything higher then 10:1 and pump gas.. you should go no further then 33degrees total timing.
 
With lets say 450 hp going from 8.5 to 10.5 will net you around 26hp.
You can run around 11.1 with 87 octane if you choose the right cam and use a quench dome piston or closed chambered head and the timing & curve will be very important here.
The .509 will turn a 10.5 340 into a low cylinder pressure pos, were talking 120psi or less cranking. That .509 cam is tried and true but I hate it, it's an OLD race piece, a light switch cam if you will, and I don't use hydros to race so it's worthless to me.

Go to engle cams site and check out the KV-3 AND KV-4 solid cams they are the next best thing to a roller.
 
I have read so much on how these motors (408-416 strokers) need big cams so they do not run out of air at the top end. I am concerned that If I shoot for 10:1 compression static and then put in a large cam (large duration, large overlap) that I will make a dog of a motor. Thus the reason for asking about flattops vs. dish.
 
360Z28 said:
u can't use the mathematical standard in some applications. i seen 60 horse gains on the dyno.
not tryin to start anything, just my experiance.
Click to expand...

I can agree with that.
A lot of times people don't have the enough compression for the cam, so matching those would yield more as opposed to being nuts on [cam/comp] and then raising it. More compression will pull harder on the valve/port and the closer that piston gets to the valve the sooner the signal initiates flow, in some cases engines with big port volume heads might respond more too.

Whatever the case may be, yep, thats true.
 
Are your heads open chamber 340 heads or the closed chamber 360 version? Reason I ask is the closed chamber version will have a better quench and quench engines resist detonation.

I went with the KB745 step dish, closed chamber Edelbrocks (360 version) milled to 62cc, zero deck pistons, and .039" gaskets for 10.3:1 compression. Cam is custom ground hydraulic roller with 236/242 duration @ 50 and 586/540 lift. Power band will be between 2,000 and 6,000 rpm. Engine was built for pump gas and a broad torque curve.

ShortBlockComplete_Shrunk.jpg
 
340sFastback said:
Are your heads open chamber 340 heads or the closed chamber 360 version? Reason I ask is the closed chamber version will have a better quench and quench engines resist detonation.

I went with the KB745 step dish, closed chamber Edelbrocks (360 version) milled to 62cc, zero deck pistons, and .039" gaskets for 10.3:1 compression. Cam is custom ground hydraulic roller with 236/242 duration @ 50 and 586/540 lift. Power band will be between 2,000 and 6,000 rpm. Engine was built for pump gas and a broad torque curve.
Click to expand...


The heads I have are the closed 360 version.....

Thanks for all the input.....
 
There are two ways I have chosen to go before...

The dish and tight quench is to me preferred for a street car and unknown fuel, and a small (under 250°@.050) cam. It will be able to run 87 cheapie fuel, but the high power numbers will not be there. Big torque, medium horsepower (500+tq, 400hp or so max, all done by 5K). I run the dish, and bring the piston proud (above the deck) by .005". I like Diamond's 20c version.

Second way is flat top and a bit more balanced power (and more of it). Flat top, in at zero deck, and a cam around 260°@.050. You will need to run 90 or better i it, but it will make that same 500+tq, but with 480-500hp with a decent carb and intake, and it will rev to 6500 easy.

That's how I do them.
 
moper said:
There are two ways I have chosen to go before...

The dish and tight quench is to me preferred for a street car and unknown fuel, and a small (under 250°@.050) cam. It will be able to run 87 cheapie fuel, but the high power numbers will not be there. Big torque, medium horsepower (500+tq, 400hp or so max, all done by 5K). I run the dish, and bring the piston proud (above the deck) by .005". I like Diamond's 20c version.

Second way is flat top and a bit more balanced power (and more of it). Flat top, in at zero deck, and a cam around 260°@.050. You will need to run 90 or better i it, but it will make that same 500+tq, but with 480-500hp with a decent carb and intake, and it will rev to 6500 easy.

That's how I do them.
Click to expand...


Thanks for the reply Moper.

One thing I would like to clairfy that even though my car is not a full time drag car, it is not a daily driver NOR do I make LONG hauls in it. It is mostly a car that gets driven on the weekends going to cruise-ins that are 40 miles or less from my home. Plus, I would like to start participating in our local street fights at the strip......

If I could build the "SECOND WAY" you described above and still be able to run 92-93 octane gas, I would be very happy. I just don't want to have to start mixing gas.

What pistons, cam and intake (more specificly) have you used in builds with good success in your second build. I am assuming that these would work well with a set of ported 360 style Ebrock heads.

Thanks alot!!!!
 
I think the heads you have are a good choice. One benefit to flat tops is they are generally a little lighter then the dished.
 
Haney said:
...If I could build the "SECOND WAY" you described above and still be able to run 92-93 octane gas, I would be very happy. I just don't want to have to start mixing gas...
Click to expand...

i'm runnin KB742 forged step dish piston, with aprox. 10.96:1cr w/ 57.5cc iron cyl.heads.
92 octane for drag racing, and 90 octane for general street cruising.
heres a very shitty drawing on FT vs DT piston...
the piston on the left, the flame is on a more linear path, reflecting off the sides of the cylinder
and chamber roof, increasing the chances of detonation ( having multiple flame fronts)
the dished piston on the right, has a more non linear, flame travel, rolling off the cylinder sides
and chamber roof. with a more complete and single flame front. hopefully it makes some sense lol.
heres a good example of flattop pistons and multi-flame fronts: http://www.youtube.com/watch?v=LZVnQeBek30

flametravel.jpg
 
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