does the quench theory hold true for dish,flat,and dome pistons equally? or are there varying degrees of benefit per piston type?

thanks,
kip

Holds true for flat and some dish pistons. Dish pistons that still have a quench area will have a quench effect (-12, -18cc KB pistons for example). I suppose there would be some quench effect on a dome piston as well, but I'd think a big dome would kind of "get in the way"

If I had the choice I would much prefer a small combustion chamber with a flat top piston making 12:1 than a big chamber small dome piston making 12:1 on a small block. Faster flame propogation with the FT piston too --- you don't have any domes in the way . . .

Let's see..

First, true flat-tops with small valve notches and small combustion chambers.

Next, mirror combustion chamber shaped dished pistons to lower the CR. with small chambered heads.

Next, round dished and small chambers.

Next, round dished with a 45 degree chamfer around the circumference and small chambered heads.

Finally, tall domes and either the sky's the limit CR. amd small chambers or decent CR., tall domes and big chambers!!

The ineff's. of the last two are kinda made up by the hp increase due to higher CR.!!!

Plus you can massage the top's of the domes to help the flame front travel thing!!

As alway's, jmho... pdq67

thank you both,

i was thinking any part of the piston that is not on the same plane as the 'top' would take away somewhat from the quench effect. the top being where you take your quench measurement from.
so the closer to a true flat top, the better for quench. the more area that is not in the same plane as the top, the less the quench effect.

reason i ask.. i was planning to re-build my 383 as a quench engine with flattops, but two 400 engines came up for sale locally at very good prices. with my 64cc heads i need to run a dish to keep CR reasonable.
shooting for 10.2-10.5-ish with aluminum heads.
thanks again for the input, goin to look at the 400 engine tonight...

kip

Yes, a 400 motor will need dished pistons like you say in it to lower the CR. to a usable range. I have the #4 piston type in my 406 along with double hump heads.

Not the best in the world, but it will get out of it's own way quite well, at least for me..

I figure a true flat-top and a set of smogger big valve 76, or maybe even 80 cc'ers, (if they are made?), should be about right and I do believe for stock heads it will run better.

Now remember this is my brand of "shade-tree" so may not suit you.. pdq67

PS., I built my 406 way back in '84 so it was put together before there were any CR. calculating programs. Now I would run everything through one so I would at least know theoretically what my CR. should be... And set/make it accordingly...

You're gonna need -15 to -20cc pistons to get your CR down in a managable range (low 10's). There isn't gonna be any quench - those are blower pistons. The little bit of squish you get off the 1/4" to 3/8" perimeter at deck height just isn't going to amount to much. So you're gonna be at 10:1 to 10.4:1 with no effective quench. But with the aluminum, you might be o.k. (Think I'd stay closer to 10:1 and the -20cc end of the spectrum.)

If I were in your shoes, and was going to build it the way I really wanted it, I'd shoot for the flattops and the tight quench and try to sell/trade my existing heads for a pair of aluminum performance heads with 74-76cc chambers. But that's a little more expensive (what do AFR's run...$1200 a pair, new?!) On a trade, if you trust what you're getting, it might not cost you too much, though.

Good luck! I'm sure others have thoughts on how to approach it as well. Quench is out the window, though, with those heads.

thanks guys,

i picked up that 400 shortblock last night. so i'm goin to look into swappin my heads, they are brand new pro toplines in the box, they make a 72cc chamber that would work out better for the 400 block...hope they'll swap them.

yea huck, a 12cc dish and a .049 quench still puts me at 10.6ish CR...too much with no quench. i had it all worked out for the 383 with flats, but i just couldn't pass up this 400!

kip

Kip,

Sounds like a good deal. I'd think they'd let you exchange them, if they're still in the box. Could be you'll be faced with a re-stocking fee...but I'd eat that and optimize the engine, rather than take your chances. Any extra margin helps. I'd much rather be able to run pump gas than not...and if I had more room for error, I'd rather be able to run ANY pump gas, than be stuck with only premium and little margin to avoid detonation.

All that said...I'm kinda pushing it myself - 10.3-10.4:1 with iron heads...but I cut the quench down to .037 or so, massaged the pistons a little to both increase inverted dome volume and remove the rough edges (smoothed and deepened the valve pockets a little bit), and knocked down the rough edges on the heads. All so I could run 64cc Vortec heads, which are also supposed to be a little better than your run-of-the-mill factory iron heads in the anti-knock department. So far no problems...but I've never dared run anything but premium either (sometimes the best "premium" around here is 91 octane, though). With 72cc aluminum heads, you oughta be in o.k. shape if you keep the quench fairly tight - a lot better than 64cc and high volume inverted domes - probably about 10.7:1 to 10.8:1. Should be o.k. with a tight quench and aluminum heads.

Have fun! :D

Keith Black makes a -18cc and a -22cc D dish piston for a 406 (5.7" rods) which DOES create a fairly normal sized quench area.

Look in the KB catalog at KB168 (-22cc) and KB147 (-18cc).

One word of caution. If you choose KB pistons make sure your ring end-gap is set to .030" regardless of application. I learned this the hard way (long story) and the KB rep (not tech support, but the area sales rep) confirmed that .030" is what you want for the TOP compression ring.

PS. And don't be afraid to go with a "D" dish piston!! They have very good combustion characteristics - comparable to a flat top from a performance standpoint IMO. Modern D dish pistons are much better than the old style saucer-shaped dish pistons on 70's smogger engines . . .

Ya know...Eric's right. I haven't looked at a piston catalog recently enough. The D-dish pistons DO look like they create a decent quench area. And you'll push the CR down into the 9.8-10.3:1 range (if the block's .030 over). I WAS thinking of the old smogger and blower pistons with a full relief, instead of a D-dish.

Now I feel stupid.... :rolleyes: Oh well. Hopefully you've not had time in the last couple hours to go out and exchange your heads.

Of course, if it's already got flat-tops, and you have no reason to change pistons, it might still make sense to go with the larger chambers.

hey guys,
thanks for the feedback. good news, i can exchange the heads. the 72's will give me some cushion. yea huck, i wanted to run flats for the max quench effect. i dont have pistons yet.
i was looking at those pistons eric, KB147 and 168. they do have a portion that is flat.
now compared to flat tops, the quench effect would be compromised somewhat, correct?
is there a proportional relationship with this or is it as long as you have some portion of the piston as a flat top, you will have a good quench effect??

eric, interesting what you said in your PS. brings to mind another related topic i have heard, and this could be totally incorrect, old wives tale sorta thing...
dish pistons have a potential to make more power over flattops due to their shape resembling a hemisphere. so sorta like a hemi chamber turned upside down. now i realize there are many dish shapes... and there may be no real way to prove this... just something i heard years ago at the local machine shop... and this was in regard to old school bathtub chamber design.
but now with the quench effect in the picture, and modern chambers-swirl and scavenging...
i would think that would give flattops an advantage... or maybe there is no advantage over the modern D-dish ??
thanks for the heads up on the KB's top ring.
huck, thats one cool sleeper you built there. i bet you surprise a bunch of people with that !
eric, sick 1/4 time with a 383.. whats your ride weigh in at?

kip

No, a D-dish piston should not compromise the quench effect at all. The quench area on the piston is shaped the same as (like a mirror image kind of) the flat spot on your head (cylinder head that is ;) ). The two flat spots should basically line up with each other which allows for the near miss and the squish effect. The important part is just that one section of the combustion chamber . . .

I've also heard the same thing about a dish pistons larger surface area having advantages - but I sure as heck couldn't explain why or if its true.

I assume "sick" is a compliment, so thanks. It weighs in at 3340 race weight. You might add another 20 lbs or so for my tool bag in the trunk.

I believe it is spelled "sik"

smile.gif

Yeah...I kinda lost the sleeper effect with the 2.5" dual exhaust and 40-series Flowmasters, though!! :D But it does kinda surprise people when this sporty, Japanese-looking car pulls up and rumbles like a stock car. I haven't run into many people interested in finding out what it'll do! Actually, I don't know what it'll do. I've got a couple bugs to work out in the drivetrain and chassis (I think the differential needs rebuilding), and it's not really a track-ready car. Kind of a work in progress - still needs body work, too...and I never really intended it to be a drag car. The stock independent rear and the T-5 are fine for the street...but a little weak for heavy track use. I know it'll get to 90 in one hell of a hurry!! :D The one time I tried timing it 0-60 on a rural (empty) highway, I was trying to coordinate holding a stopwatch myself and launching the car. It read a little over 6 seconds, but I'm pretty sure I hit the stopwatch a little before I took off, and didn't catch it at 60 when I stopped it - was probably up to 65 or close to 70. And I didn't have the launch technique down very well - never been very good at feathering the clutch - never done any serious drag racing. I dumped it about 3000 rpm and simultaneously planted the gas pedal. Pretty much slid sideways for the first 50-100 ft.

But it IS kind of a fun car! :D

Good luck with your engine! If there's no real penalty to exchanging the heads, I'd still go with the flat-tops, like you suggested. I've "heard" that dished pistons just don't give you as good a quench effect...but maybe that advice was based on similar misconceptions like mine of the old full dish designs. In any case, better safe than sorry - if the head change is easy enough. Plus, flat-tops are more readily available, and cheaper. (Eric's right, in his post above, that the primary concern is the area of the piston under the "non-chamber" (flat) portion of the head, though. That's what creates the quench - the air/fuel mixture being squeezed out of this small area at high velocity - the bigger the gap, the lower the velocity, the less the effect. Much over about .045-.050 and there isn't much effect.)

Here is what I used to get my compression low on a SBC 400.

My SBC 408

Engine: 400 SBC ID# 330817/14y139664/ T0508CSU
(4.125 bore X 3.750 stroke) after .040 bore (4.165 bore x 3.75 stroke =408)

Crank: Scat 9000 Crank 3.750 6.00, Internally Balance, Part# 400-3750-6000

Bearing: Clevite– MS1038P Mains and CB663P Rods

Piston: Wiseco Flattop Pistons, .040 over, 5.4cc; 430 grams, Part# PT020H4

Rods: Eagle ESP 4340 H-Rods 6.0, Part# CRS6000B3D

Block: Zero Deck: 0.000

Compression Ratio: Static-10:48 Dynamic-8:30

Cam: Grind:
http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=114681+&B1=Display+Card

Heads: AFR 195 Part# 1035 w/23º valve angle, 74cc, drilled steam holes

Head Gasket: Fel-Pro-1014 / 0.039

Intake: Edelbrock RPM #7101

Carb: Holley 750

Rear End Gear: 3:73

Transmission: Pro-Built Street/Strip 700R4

Stall Converter: A.C.T. 3000 Stall

Exhaust: Hooker Super Comp headers 1 5/8 Headers part # 2460-1 ceramic coated;
Hooker Super Competition high flow cat-back exhaust system, Intermediate pipe: 3 in.
* Tail pipe diameter: 2 1/2 in.
* Dual tail pipes out the rear under the bumper

FWIW, Mine are TRW, 22cc dished, and heads were big valve -461's at a measured 66cc and I ran steel shims and just whatever leaded regular I could find back in '86 when I last drove it.

The old sucker ran fine, imho...

pdq67

According to professionals like David Vizard, a d-dish/small chamber head is as good as or better than a flat top piston. I think someone hit on the reason why...it creates a "spherical" combustion chamber which supposedly is very efficient and effective. I do know that with factory type heads Vizard has proven repeatedly that a d-dish/64cc chamber is much, much stronger below about 4000 rpms or so than a flat top/76cc chambered head, with them running about equal after that point. But, remember that this is with factory style non-fastburn style chambers...I couldn't find anything on the newer aftermarket heads with the heart or kidney shaped chambers. You will find that typically a flat top piston is considerably lighter than a dished piston. In your case, since the engine is already built, I would swap the heads...easier than changing pistons and cheaper if all you will be out is shipping. And, you won't have to rebalance the low end. Or yank the motor. Or rehone the cylinders. smile.gif

thanks again guys,

DTL, thanks for listing your combo. i'm shooting for 10.5 with the alum heads... thinking a single pattern cam. have you fired your 408 up yet? just curious how that cam behaves....

travis, the engine isn't built yet, basically a standard core that has to be gone through. so im debating the dish/small chamber vs the flat/large chamber route now. and yea i had heard years ago that a dish had a greater potential due to its shape resembling a hemisphere(at least more than a flat does). but that was in regard to the old style bathtub chambers... the pro topline chambers are really a sweet lookin kidney shape.
so who knows if that holds true with them.

"I do know that with factory type heads Vizard has proven repeatedly that a d-dish/64cc chamber is much, much stronger below about 4000 rpms or so than a flat top/76cc chambered head, with them running about equal after that point. But, remember that this is with factory style non-fastburn style chambers...I couldn't find anything on the newer aftermarket heads with the heart or kidney shaped chambers."

travis, how much stronger below 4K was visard finding? which book is that in?

pdq, thanks for your input... i probably wouldn't be able to tell the difference whichever route i go.. this should be the most powerful smallblock i've ever built(my first 400). and how much power diff are we talking between flat/large chamber and dish/small chamber anyway?

eric, sick or 'sik' is definitely a compliment! i'm hopin for high 11's with this 400, but its mainly a 3 season daily driver, has to get me to work and will see autocross courses all through the summer. so who knows...

i'm goin to talk to pro topline and see what they suggest with their combustion chamber.

anymore thoughts or experiences?
i appreciate the responses....

The article off the top of my head was back about 10 years ago, where Vizard tested a 383 with flat tops/441 heads vs. d-dish/186 heads...the d-dish combo was worth about 50 ft-lbs more torque at 2500-3000 rpms over the open chamber factory heads. Interesting too was that the 441's flowed almost identical numbers to the 186's under about .400 lift, and actually flowed 10-15 cfm more above .400 lift. This was on a 9-1 engine with a 270 comp magnum hydraulic. He ran a similar test with a 9-1 383 with a 252 high energy cam and the results was the same. I will have to look and see if I can find those articles for more details.

I went thru exactly the same thing you are going thru trying to get about 10.3-10.5 compression out of my 388. I wanted a forged piston, which really limited my options on pistons to get this compression range because it seems nobody makes a d-dish forging between a -20cc dish and a flat top. If you want a hypereutectic piston, then KB makes a -12cc dish piston that would put you right in the 10.3-10.5 range with a 64cc head. Thats why I ended up ordering the 72cc pro topline heads and flat top wiseco pistons. Heads should be here today.

thanks travis for that info,
i want the engine to be a low-mid range engine, so an extra 50ft/lbs in the 2500-3000rpm area would definitely be welcomed.
the variable is the new head design, cant really compare them to the old castings.
i have an email into pro topline for their take on it.
FYI, with the pro toplines 200 cc runner, you may need to trim the bottom of your rocker arm studs as they protrude into the runner, blocking some flow. here's what they said,

"Thank you for your email. The threaded holes do protrude into the intake runner due to the shape of the port. You may be required to machine the studs down so they do not interfer with the flow."

Thanks and regards,
Greg Stokes
Sales/Technical/Marketing
Pro Topline Limited