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Just delivered today a 68-72 455 Olds with 11:1 flat top pistons.
Figuring the 11:1 is based on 72 cc chambers and I add my 77 cc aluminum heads (Edelbrock) what would the compression be (approximate).
If I add .040 thick Cometic head gaskets ( 4.125)
this adds 2.7 cc :
.04 X 4.125 X 16.39 cc/in3 = 2.7
taking the final chambers to 79.7 cc.
Would this allow regular gas with the aluminum heads?
Would the thicker gaskets be required for regular gas
or could I get by without the added expense?
If I had that engine, I wouldn't run regular in it, I don't run regular in my stock 283 power pack.
First off, you don't want to add any gasket thickness to lower static compression ratio. When you do that, you increase the squish, which increases the tendency of the motor to detonate.Quote:
Originally Posted by t0oL
Normally, when a builder puts a motor together, he figures the stack of reciprocating assembly components, cuts the block decks to whatever he needs to work with the gasket and chooses the correct combustion chamber volume and piston volume to establish the static compression ratio he wants. Then he chooses a camshaft based on being compatible with the static compression ratio. After that, he would choose the torque converter, rear tire and rear gear that would be compatible with the cam timing.
If you'll list the following, we'll try to help you figure it all out.
1/2 crank stroke
rod length
piston compression height
block deck height
If you have to run on pump gas, you never know when the formulations will change, so you want to design the motor so that it will run well on the lowest grade fuel. Those of us who lived through the Arab Oil Embargo know that this can and did happen.
With aluminum heads, I would not try to go beyond 9.7-10.0 static compression ratio. And I would engineer the squish at somewhere between 0.035" and 0.045".
Here's an article explaining squish. They're talking about motorcycle engines here, but it's the same thing no matter the make of engine.
http://www.rbracing-rsr.com/squishcalc1.html
upon removing the head the pistons look more like 10:1 with a ~3/16 dish
http://cgi.ebay.com/ebaymotors/Oldsm...item3a58d5df49
some1 said not to add a thicker head gasket to decrease static compression as it increases squish. this is NOT TRUE, a thicker head gasket will decrease both static AND mechanical compression ratio. This has been an age old method for folk with a lil too much engine for the street to tame said engine enough to have better drivabilty in a street situation. In point of fact i have a zero deck flat top piston( this means tha at TDC the top of the piston crown is dead even with the block deck surface, in my case actually .005 above since i took that off the deck of my block to b sure to have a straight true block deck) .030 over 400 SBC w/ 6" eagle H-Beam rods, knifed, tuft rided, indexed stock crank. Without givin exact specs i will say i have a flat tappet hydraulic cam in the engine that gives THIS engine a power band from 1800-5800rpm. I originally built this engine with a friend to go into a 74 Pontiac Ventura( which was on the Nova Platform like the 74 Buick Appollo and Olds Omega, but the car already had a healthy 373 SBC in it and sold with that leaving me with the engine. W/ stock head gasket thickness(.038 compressed) the engine had a mechanical compression ratio just a tad under 10.75-1 and with iron heads u could drive the engine on pmp gas but NOT race it and certainly not spray it on pmp gas even 94 octane sunocco. I invested in a set of .078 compressed thickness composite head gaskets which lowered the mechanical comp to jus about 10-1 and then put the engine in my work truck w/spray which i do on pmp gas(93 octane) and a max of 32* total timing and a advance curve that gives me all 6 possible degrees of distributoir advance by 1800 rpm.
Lest u think this is a chevy and may not apply to an Olds. I have been drag racing since my 1st on July 5, 1963 and i began my drag racing with an Oldsmobile, a 59 98 convert. Since then, tho i have delved into most all the domestic brands and RACED against the ones i have NOT delved into, i have been predominantly a GM Buick/Olds/Pontiac fanatic and had my most success in racing with these. I currently own a SBO powered 78 Buick Lesabre 4dr sleeper, I have owned 2 w30 4spd 442's a 67 and a 69 among other Olds Hot rods and built them all. Round here its said that if Mr Wizard can't make a Buick/Olds/Pontiac powered ride run quick in a street trim situation then Junk it and go to something else, that one jus ain't gonna run.
The SBO in my Buick is one that i built and using IRON heads. I raised the comp by going with a thinner steel sheet head gasket and shaving the iron heads by .030, to keep the static compression down to manageable i use a cam with a relatively HGH numerical duration which ALSO allows the use of more compression in any situation as hgh duration cams have hgh amounts of overlap and thus bleed off cyl pressure and lower static compression. Also, u can run even more mechanical as well as static compression ratio with alum heads on ANYTHING since alum has a hgher heat disipation rate than does iron.
Headers VS exhaust manifolds also decrease static compression as well since these allow a quicker heat disipation rate than does exhaust manifolds, not to mention a relief in back pressure that moves the power band up in the serviceable RPM range of the engine.
with the olds engine u can get away w/ nearly 11-1 if not 11-1 mechanical compression and the attendant static cyl pressure, even with a low overlap cam that does not bleed off so much cyl pressure and run pmp gas on spray thru a full exhaust w/tail pipes.
My lesabre is now an even 10-1 with iron heads and i run pmp gas thru a full exhaust and as much as 200bhp of spray in 2 stages to boot w/o a hint of detonation, the rule of thumb is that aluminum heads, all else the same will allow at least a 1 psi increase in comp ratio on the same octane fuel as would an engine wit iron heads.
with a 2.7cc increase in ur com chamber sizes u will lower the mechanica comp by approximately .25- .30 psi and get the attendant lowering in static cyl press a well. If ur cam has an adv duration above 290, especially above 300, say 304 x 316 int n exhaust respectively like i have in my Olds engine u'll b more than fine as long as u stay at or below 11-1 mechanical comp with the olds engine with aluminum heads. This isn't what i heard or what i think, i have actually built a 477 cube and a 491 cube stroker 455 Olds w/ Aluminum heads for other folk and both with a mechanical comp ratio of 11.1-1. both are street engines and both run on pmp gas with a full exhaust w/ tail pipes, also both are in HEAVY cars which also increases load and thus static cyl pressure under load by lowering the speed at which the engine will rev up thus containing more heat in the combustion process longer and how much heat u contain in the combustion cylce as well as how long u contain same is actually what has the final determination of static cyl pressure along with camshaft profile as much as does mechanical comp ratio.
BTW, as i say, my big 4dr lesabre has a SMALL BLOCK OLds V8. The mechanical comp ratio is aprox 9.99-1, the engine has IRON heads, the cam has adv duration numbers of 304* intake x 316* exh. I use 3" exhaust AND tail pipes with an X-Pipe and flowmaster 3" ID muffs. the car weighs in excess of 4400lbs sittin at the start line with 1/4 tank of fuel and me on board. W/ 3.08 Posi gear, a 3500 converter and TH350 trans on 275 x 60r x 15 BFG TA Radials the car runs low 13's hgh 12's on mtr and low 12's hgh 11's on 200 bhp of spray if i use the 26 x 10.5 x 15 MT ET Streets off my BUICK powered BMW.( I have an 88 3 series BMW Post Coupe powered by a 464" Stage b2 Buick 455 engine w/3500 verter, TH400 trans n Ford 9" rear axle, that runs 10's on mtr and 9's on spray. additionally i have a 77 455 H.O. 4spd( now a tremec TKO600 5spd) WS6 Pontiac Trans Am tha runs 11's on mtr and 10's on spray, all three cars use 3" exhaust w/ flow master muffs n 3" tail pipes and all three run on pmp gas as well as race on spray on it, all 3 are at or above 9.5-1 comp, all 3 have flat tappet cams and the Buick and BMW are hydraulic flat tappet at that. The TA has a really agressive solid lift cam but it too is flat tappet. Both the TA and the Lesabr are also standard bore engines and ALL use Iron heads and stock cranks and stock rods w/ forged alum pistons)
"some1 said not to add a thicker head gasket to decrease static compression as it increases squish. this is NOT TRUE, a thicker head gasket will decrease both static AND mechanical compression ratio."
A thicker head gasket will decrease both static and dynamic compression ratio, but it will also increase the tendency of the motor to detonate on the same fuel because it increases the width of the squish.
"I have been drag racing since my 1st on July 5, 1963"
You were a "johnny-come-lately". I started in the summer of '58.
"i use a cam with a relatively HGH numerical duration which ALSO allows the use of more compression in any situation as hgh duration cams have hgh amounts of overlap and thus bleed off cyl pressure and lower static compression."
First of all, you don't lower static compression ratio with cam timing. You lower dynamic compression ratio with cam timing. And it isn't the overlap that makes the difference. It's the intake closing point. There is insufficient cylinder pressure at overlap to make any appreciable difference.
Glad I stocked up on popcorn.:D:D
Don
I had "Static" once but I found that the radio was bad.
I'm with Don this could be pretty good. Go gettum Tech!!!
Roland
I was not a Johny come lately, i was drag racing before 1963, i only started doin it in my own rides in 63, which is why i only count till then...i don't count the time i spent being taught by the best in the St. Louis Mo area where i was born n raised and has always been a hot bed of drag racing activity both at the track and on the street.
Besides that i have run 10's with IRON HEADS and LESS than 11-1 comp on pmp gas with an olds engine in a big azz 4dr 84 98 regency and that was in the 80's nor was it a stroker engine and it retained all its amenities and accessories..How fast have u gone in anything Olds Powered that u may have built anytime in ur life, let alone thru mufflers on pmp gas in full dress street trim including tail pipes ?
Addditionally to all that drag racing experience almost exclusively with GM BOP engined cars, I am a graduate of GMI, General Motors Institute with a Mechanical Engineering degree in AUTOMOTIVE APPLICATIONS. Tho i was trained as a machinist during my degree program, i farm that out when i build an engine, even then i specify specs not rely on the machinist to decide.
Since 1977 i have lived in Flint, Michigan, the home and birthplace of GM, its parent and founding division as well as 2 of the only 3 divisions of GM that GM actually created, that being Chevrolet which was later divided into Chevrolet which remained and yet does remain under divisional control of BUICK, its creator, while the GMC division went to corporate, in fact the strike that attended said division led to the creation of the UAW, also born here in Flint. In fact for the past 22 years i have lived directly across the street from The Buick City assembly complex, which from the time it was completed till 1996 produced more vehicles and vehicle parts than any other place on the face of the Earth. Many of my best and closet friends are retired and or current BOP hourly workers and engineers and corporate types. i did my internship for my Mechanical engineering degree program 1/2 at the GM(milford) Proving grounds, formerly the PONTIAC proving grounds, the other 1/2 at Chevrolet assembly #36 , which is right down the street from GMI on Chevrolet Blvd, now renamed Kettering University in honor of its founding fellow Charles Kettering who was the founder and creator of the Dayton Electric Company, known as delco once aquired by GM, as well as CEO of GM's parent and founding division, BUICK, after the departure of Walt Chrysler from that positin to start his OWN company. Which he built the same way as William C. Durant Jr. did GM, predominantly by AQUSITION and incorporation of exiting auto COMPANIES. Dodge, Desoto, and Plymouth in Chrysler's case and all but Chevrolet, GMC and now GMAC finance for Billy Durant Jr.
YOU may b older than me, and u may have even started drag racing in ur own rides that u actually wrenched and built before i did, but u adhere to a number of the unfounded wives tales common among racers who have only some experience, no formal education in the field of engineering as it applies to automotive applications as i have. Wives tales which i once held as well, until they were factually dispelled in school at GMI, like that crap about a thicker head gasket makin for more squish. it doesn't and in fact it can't. In any internal combustion engine the piston crown stops at some point in the cylinder at TDC. in the case of the Olds engines with flat top pistons, domed or dished that would b w/ said base surface of the piston crown .045 into the cyl. unless u change the crown height of the piston and or the rod lenth w/o changeing the wrist pin position, u can not increase the volume above that point without lowering mechanical compression which will also lower static cyl pressure or static compression as its called.
the diff tween static and mechanical compression as u obviously do not comprehend is the pressure in the cyl at TDC when the engine is cold and NOT RUNNING and that when the engine is runnng at normal operatin temp, thas why same is CHECKED ONLY IN A HOT ENGINE. u simply can not increase the area in which the mixture is compressed without lowering the pressure w/o changing the position in the cyl at which the piston rests at TDC and BDC.
a thicker head gasket increases this, the same as shaving the block deck or the head deck decreases it.
I am a person who imparts only information that i actually KNOW from BOTH experience and education unless i preface or suffix same with i believe, i've heard, i have read or even i think.
Otherwise, if u analgolize, in this case Olds engines to a rooster and i told u a rooster dips snuff, u could find a fresh tin of skoal under his left wing, copenhagen under its right.
ur welcome to disgree with my assement on this subject, in fact i invite same, much of what i have discovered before and since school about this subject was born of someone disagreeing with me. However if u do so with such disrespect and antagonizm as u have u can expect same in return. in my vernaular, we call that playin the dozens, panning, capping, stinging on folk and i was better at that when i was a teenager than u'll b if ya live to b 200. In other words u got nothing coming on that tip. Better u remain respectful in whatever disagrement with me that u impart to me unless u enjoy gettin ur cap and or ur wig twisted with ur own BS rhetoric back in ur face. Thats in MY vernacular, in urs its likely ," unless u enjoy gettin laughed at and embarrassed".
Obviously u have yet to discern the difference between what ya think or believe and what u actually KNOW, and no matter when u began at this craft, until u do that as i have ur always goin to THINK that u KNOW things that just simply are not fact or so in any manner u can logically hold a position on and defend.
MY moto, before ya claim something u think u know is fact, make it make sense, and ur premise of increaseing com chamber volume in any way w/o changeing the piston position at top dead center does not and can not make sense, nor can u logicall defend such a position.
As i said, the idea of useing a thicker head gasket to lower mechanical and by association static compression is a ploy which i have used for decades with total success. in fact before the advent of really hgh compressed thickness head gaskets i used 1st indian head and later COPPER COAT spray contact sealant from 3M to bond a number of thin sheet steel or copper head gaskets together to achieve my desired chamber volume and by association my final mechanical AND static compression ratio. The 406 SBC i now have in my WORK truck indeed has a set of 125.00 a piece composite head gaskets from Fel-Pro that u like as not didn't even know existed let alone someone offered, and THATS JOBBER NET PRICE.
Since i retired in 2007 i do this of which we speak, as in drag race and build dedicated drag race oriented rides for street and strip for other folk, for bread and meat, if i don't win and do it right i don't eat and i love to eat, well i might add.
At the end of the day, keep this respectful and about the subject at hand rather than antagonistic and disrespectful when u post something to or about me. It isn't a gurantee, but 1st giving respect is the only way u can ever get any. YOU claim to B older and more experienced than myself in this field and u seem to want respect for that, which im more than willing to give ya, so long as with me u expect it with respect to me as u would have me do YOU.
The post that u made to which this is a reply is what folk like me consider to b playing, like i say, "playing the dozens"; unfortunately for that aim, I DO NOT PLAY, I never have, i jus like toys.
Hey wizard, Does FUJIMO ring a bell for you?
Dallas
Of all of your long winded posts---I have analized----first, you ramble on and on, jumping from one car you have to another, back and forth, change from static to dynamic, throw in numerous u, ur,jus,etc, and with many of your unneccessary words being mispelled, I have not been able to follow your line of thinking or keep up with what principal or theory you are exponding on without getting a headache.
One thing I have fiqured out is that you can't read or keep up any other persons post--
Tech was simply pointing out that using a thicker head gasket to lower the compression INCREASED the SQUISH (made the distance between top of piston and cylinder head greater) which will promote a more severe detonation-----
Now, I should point out that I also am older than you---If you truly did grow up in St Louis in those years and ever attended the drags at Alton, you have probably see me race when I was younger----and I will bet that you never beat me----
Over on another site there is a guy who says that if the facts don't support your theory, get another theory---Thats probably the kindest thing I can say to you, however,I believe that maybe you have just been around the GM corporate world, getting spoon fed BS and washing it down with GM Koolaid that you now think if you can ramble on and on and fill up line after line with words saying nothing that you have basicly learned more and more about less and less that you now know everything about nothing .
Jerry Clayton
Oh man!!!! Don't drink the Kool-Aid!!!!!!!!!!!!!!!!!!!:eek::eek::eek:
if u think my post are long winded and disjumbled then simply don't try to read them and keep ur negative comments and insults to urself unless u want em back in ur face in response. simple solution to the problem u claim to have wit my post
I speak on rides that i have as emphasis on what im speakin on, as i makin sure to make plain that im talkin what i KNOW from the experience of havin and actually BUILDING somethin rather than jus talkin about it.
as i said, i speak what i know unless i preface or suffix it otherwise.As for me jumping around that seems so to u because u obviously didn't have enough of a grasp of the topic to follow along in the 1st place.
hard to understand somethin when ya know nothin about it other than rumor an inuendo, stereotype and the like
as i said, i made a comment on the manipulation of compression both mechanical and static in specifically Olds engines, tho i spoke on the fact tha the same principles apply to ALL internal combustion engines. If any of ya don't know or want to know any better, fine, disregard, but when ya respond with childish BS animosity and ridicule u can expect to get same in return, as i say, that kinda playing the dozens crap im quite adept at, except, i ain't playin.
what i say about the OLDS engine in particular and engines in general is wha i KNOW, not what i heard or what i think, and the end game of the previous post is thart u can not increase the volume or area above the dome of the piston in an internal combustion engine and increase the saquish or the compression, meither static or mechanical, u can only lower same. simple as that
so, the addition of thicker gaskets that make for a 2.7 cc increase in the size of the area above the piston crown will decrease the mechanical and staic compression just as the questioner suspected i would, and this will b of gretater effect with aluminum heads than i wopuld b with iron heads.
don't hate cause u don't understand the principles and laws of physic which govern the operation of an internal combustion engine as well as ya thought ya did.
As for m spellin, tha is a lame and childish retort to throw out that has absolutely nothing to do with the subject a all, aftert all how could u KNOEW the word was misspelled unless ya
know what the word is or means ?
Right ya couldn't know. Besides, this is an informal text medium, the idea is to convey concepts, ideas and information by whatever keystrokes that surfice, the fewer the better, in the consideration that all participants have at least a rudimentary grasp of the text and language such that they can grasp said ideas and concepts without the aid of correct spellin, syntax, punctuation etc...Beside, some of m mispellins are obviously intentional, others are incidental and if ur concentratein on spellin n such ur missin the whole point of the post ANYWAY.
postin tha ur unable to do that is not an insult to me, its an insult to u, meanin u domn't even understand the medium in which ur tryin to rule and regulate whats posted to ur own idiosyncracies.
AGAIN, if u increase the volume bove the piston crown in an internal combustion recipricating engine u will lower both mechanical AND static compression.
Slow ur roll gents, i do not take kindly to insults and antagonism based on BS by folk whom i KNOW, let alone fools i don't'. u can't intimidate, embarras or silence me to my face in person, let alone in a settin such as this.
Again, as i say disagree with me, fine, i welcome that, come at me with disrespect and ridicle and thats the response u gonna get, rust me, im far better at that than any of u are ever goin to b and whatever i say here i will say and back to ur face. Best u keep this respectful and about automotives with me or don't post anything to or abou me at all. You folk do not RUN anything here any more than ya do in real time real life, least of all ME.
BTW, the fellow Brent, who created this forum is a long time friend of mine and THATS who invited me here, Brent and i have raced with and against each other both on the street and at the track, check with him and u'l find that i KNOW what im ta;lkin about and I DO NOT TAKE SMACK off anyone bout anything anywhere anytime. Again, in my vernacular, "YOU BETTER ASK SOMEBODY" cause ya obviously ain't got a clue.
Now post # 14 is much better---fewer keystrokes, fewer of those funny words,more concentration on the subject line and to the point.
You have a lot of experience and success, why don't you keep your posts more to the point and stay on the subject than rambling about 17 different cars you have and if you took the tires off this car and ran them on the other car it would lower the compression in the original posters car if he had iron heads but only if he was using rods that were original length with pistons that had the rings above the wrist pin??
Seriously why don't you forget who you are for a couple hours and go read your posts???
And just who would you recommend me to ask???and what do you think they could do for me???