Thread: 455 Olds 11:1 -> 10:1

Tweet

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)