I was reading a thread in the small block forum in which Mike & Hector are discussing compression height & quench. In the reading I've done quench is often designed in for the sake of performance, but using the low dollar cast & forged pistons available these days means we get a dish across 95% of the crown, effectively killing quench except for the very edge. It's not until we step up to the higher-end pistons that we see flat-tops & semi flat-tops that allow us to control a larger amount of quench with gasket thickness. I know it's a long shot, but does anyone have experience with hp/torque differences with a switch to a flat-top & semi flat-top from the dished design without other significant changes? The problem with asking is that the piston switch alone will spike up the compression ratio & would taint the results, so I'm thinking a real apples-to-apples comparison might not have been done by anyone unless they were experimenting for just that reason. I thought I'd ask, anyway! o No: Devon
Devon,I hope that this thread becomes a very informative one.I'll give my very limited thoughts and hope that if my thinking is flawed someone can shed some light on the issues.It is my understanding that quench will promote turbulence of the air/fuel mixture as the piston aproaches and the charge is being ignited,it is also beneficial by reducing and/or preventing detonation.Regarding piston desing,my understanding here is that a dish is better than a flat top and the flat top is better than the dome when it comes to flame travel and propagation,the deal is that a higher compression gives the more bang,therefore, the dome.One could argue that a smaller chamber and a dished piston would be ideal,but then, depending on the dish one may need a very small chamber in order to achieve a compression on the 10-15:1 ratios needed to support radical cams and other hardware.That small chamber will create its own set of problems.So...we compromise.Please note that my build up is for a street car that I'll take to the track only to embarass myself while attempting to validate the expenditure of a small fortune :grin: .
another advantage to a small combustion chamber on the cyl. head is less valve shrouding, nextel cup motors have very small combustion chamber heads. i'm not sure of the milling limits on buick heads, you can also angle mill the head to tip the port into the cylinder for better filling, good luck
This guy: http://www.somender-singh.com/ Has a radical new concept (a groove) to promote squish, turbulence, etc. Very good reading.
in july popular hot rodding mag there's an artical where am&p builds a 700+hp pump gas motor w custom je pistons that are ideal,they have a close up picture of them.the top of the piston is flat only in the area where it meets the squish pad on the head and the rest of the piston is dished.unfortunatly i saw this after i purchased my generic speed pro dished pistons from ta.so i called ta to say what the f@#$,why cant you offer a piston like this and the told me that the speed pro was discontinued for a while and they just started making them again,before production started dave tried to convince them to do this and they showed no interest.the additional material on the piston is not that much so im not to worried,how much of a differance does it make? prob not much,but in my max iron head pumpgas combo every little bit counts.im trying to get away with close to 11-1 comp on pump gas,by following a few fundamental rules and with the right cam i thik i can get away w it.im just finishing the motor assembly and should have it in the car in a week,wish me luck! if i knew how to post pics on here i would do it but im a bit computer handicapped,the pic of my car on here was put on by a friend who had the pic and put it on for me w his computer. later chris.
Devon, Good question. It should make for some interesting reading. Street Rep, Did you see the Wiesco pro-tru forged 455 pistons? They have that type of dish (flat area matching the flat part of the head, open area where there is chamber), and are reasonably priced. ________ ALASKA DISPENSARIES
nope, wish i did about 6 months ago,i would have looked into them.where do you get em and i wonder why ta doesnt sell them.the speed pro,s are extremely reliable,my first set lasted almost 20 years and 4 rebuilds just sanded them and re-ringed em until the block finally had to be punched out.they are heavy and a little outdated though but i put lite pins in em.i know this sounds crazy but i was thinking about welding and machining a squish pad on but was worried about making them to soft. to late now there already in.if anyone out there has tried this or know anyone who has please let me know how it worked out,i know its ok to weld in the combustion chambers but there's alot more meat and heat is more easily dissapated.yes i agree,very good question,now all we need is some of the pro engine builders to comment,im just a hobbiest. ,chris
There are 2 schools of thought when it comes to the design of a piston dish, what is known as the inverted dome (pretty much a simple dish) and the reverse deflector (kind of like chamber matched). The Turbo6 crowd kind of goes both ways, most of the available pistons are inverted dome types like they are for the V8, however Diamond racing does make a reverse deflector piston that matchs what little quench area there is on the head. Since the V6 is an open chamber design, unless you go aftermarket, all you can really do for quench is have as much area around the perimeter as possible without compromising your crown thickness with too deep of a dish in the middle or shrouding your valves. From what I know the 67-74 heads are all closed chamber designs that lend themselfs much more to a taylored reverse deflector type of piston since there is a "quench pad" area inherant in the design. The mechanical qualities of each piston also have a role to play, since you can get hot spots in a reverse deflector due to its non uniform crown design and it can lead to a thinner crown thickness due to concentrating the entire dish into a smaller area. They also tend to be more expensive since they must be machined to fit the pattern vs a simple dish that just requires finishing. If I was building a 455 right now, I'd want to run as close to 0 deck as I could, closed chamber heads, reverse deflector pistons, and try for between 9.5:1 and 10:1 compression on a 0.040in gasket. Throw in some good cam dynamics to keep the low rpm cylinder pressure down and run it on pump gas with conservative timing on the street then add some for the track and put in the good gas. Or I'd just turbo it with around 8.3:1 compression and put the piston about 0.010in in the hole to keep a lurched headgasket from putting the slugs out of the hole after a deck cleaning.
Thank you all for the comments. I run the heavy, low-dollar dished Speed-Pros as well, with TA's valve reliefs. I've been wondering about a new piston design with a custom flat-top profile in the area away from the chamber, cascading into a deeper dish towards the chamber. Max quench where it counts. I'm running angle-milled '67 430 heads, don't remember the chamber volume off-hand...though it's small (don't have my notes handy). I'm at 10.8:1 now; this is a 6300 rpm max engine at the moment. I can run strong on 93 octane with *everything* in control. I'm interested in trying a different piston design, as described above. A switch to aluminum heads will most likely take place at the same time...so much for a good back-to-back comparison! The http://www.somender-singh.com site is interesting, to say the least. I'm like the vast majority of us, not in any position to do back-to-back research on my Buick. OK big dogs, I'm not looking for secrets here, but can you folks tell me if I'm going in the right direction? 93 octane, best WOT performance between 3800-6300 rpm. I'll take care of the lower rpm torque, got that covered. Devon
I got my wiescos from finishline motorsports. I think Jim Burek at PAE sells them too. Readily available... I think they're around $550 a set with rings and pins included, so a very good deal. ________ MICHIGAN MEDICAL MARIJUANA
Use the Wiseco pro tru -22cc dish reverse dome piston, deck the block to .010 ( .035 to .040 cut) Use a .030 blow resistant Head gasket & CC your head to around 62. This will give you an almost ideal .040 Quench distance with 11 to 1 compression allowing you to use an agressive enough cam (6200 rpm). Top it off with a nice set of Bulldog or Stage 2 al heads with polished chambers and you'll be in a horsepower range to run somewhere in the 10's, in a full weight, on pump gas. Maybe I can embarass myself at the track with this setup... later this year. It seems like its taking forever to get it there. Tom
a little cheaper though Summit. After checking around I got everything for something like $525.00. Don't go by what they list in their catalog sometime you have to do some searching (either online or call them)..
I used the wiescos reverse dome to try to keep the quench the best i could with iron heads and aluminum rods.Im down the hole 22 thou and a 40thou head gasket. 62 thou was alittle more than i would like but i wasnt sure how close u can go with aluminum rods compresion was lower aswell around 10 to 1 i would like 10.5 or 10.7 but i went on the safe side.Aluminum heads will give me a compresion bump but not easy to get the wife onboard for that upgrade.
What results did you get with this combo? (pinging etc...). Just curious as I have some stage one iron heads and have been wondering how much compression I can get away with if I utilize a quench pad type piston.
I have had no pinging sofar timing is 32 total on 94 pumpgas. I know its overkill but at the track i put half bottle of octaneboost in 8 gallons of fuel. I will try 34 timing in the spring. On the street i just run 94.
