1973 455 Stage 1: now 8.5:1 compression, how much higher possible for 2018 Premium fuel?

Discussion in 'Street/strip 400/430/455' started by Warren Jarrett, Feb 26, 2018.

  1. Warren Jarrett

    Warren Jarrett Well-Known Member

    My 1973 Buick 455 Stage 1 is getting completely rebuilt. Nothing too fancy, nothing very high performance. The cam is going to be TA .468 exh lift, 215 exh dur, 112 lobe center, "1100-5500 rpm, 8.0 to 10.0 CR". Customized original Stage 1 dist and carb, performance muffler and exhaust.

    So, now that the whole engine is comping apart, my feeling is that boosting compression ratio is the best way to gain performance with no compromise... except for the fuel that I will need to use.

    What is the easiest way to raise compression ratio? I think it is probably pistons, but which ones do you recommend? And what compression ratio is about the max to still use current Premium pump fuel (in California)?

    I would rather err on the too-high compression side, and have to add a little high lead/high octane racing gas to each tank-full. If too low compression, and not providing the FULL benefit from pump 92 0r 93 octane, would be dissappointing. I am thinking about 9.5:1, what do you think?
     
  2. hugger

    hugger Well-Known Member

    Performance increase will be minimal, I would go with more cam and the 9.5/9.85 comp
     
  3. 8ad-f85

    8ad-f85 Well-Known Member

    I would do the exact opposite of the proposed plan. Keep compression modest and safe.
    Even modest airflow improvements, along with the above mentioned slightly larger cam, will by far and large obliterate what perceived or minimal gains would be had by squeezing a little bit more compression from an already dangerously high cylinder pressure/octane condition.
    Assuming that gasoline is the same from every refinery, always meets specs, never a station switcheroo, and also goes for around the nation?
    Why use your engine as the test bed for that theory?
    The other thing to consider is that the 1/2 to full point compression might help to the tune of 2-4% hp and mileage, so 7.5 to 15 hp that you'll still likely have to detune your engine away from to avoid spark knock. Or don't and probably pound out your bearings quickly.

    As an example, a 20 cfm gain in the induction would allow over 40 hp, and 40 cfm over 80hp, with the appropriate cam of course. Factory intake and related parts support this, compression and octane tolerance are now pushed safer.
    Why do the opposite?
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Warren,
    First thing you need to understand is that an engine does not run at the static compression ratio. You need to read this article.

    http://www.empirenet.com/pkelley2/DynamicCR.html

    The static compression ratio is calculated from the physical measurements of the engine. If the volume above the piston at the bottom of the stroke is 50 cubic inches, and then 5 cubic inches at the top of the stroke, then the compression ratio would be 10:1. Dynamic compression takes into account cam timing. If the intake valve closed at the bottom of the stroke, then Static Compression would = Dynamic Compression. That is never the case, the intake valve always closes as the piston is moving up the cylinder on the compression stroke. Different cams, close the intake valve earlier or later. No compression can be built with an open intake valve. Dynamic compression is calculated from the stroke remaining AFTER the intake valve closes. That is why you see recommended static compression ratios in a cam description. To keep the DCR in pump gas territory. Smaller cams close the intake valve earlier. High static compression ratio combined with a smaller cam will result in an engine that can't run on pump gas without detonating.

    I'm not sure which TA cam you want to run because you haven't described it well. Looks like the TA RV-12 or TA112?. Those are small cams. Keep the static compression lower. You want the DCR around 7.5-7.8:1 to run on pump gas. The above linked article has a DCR calculator at the end. Download it and play with the numbers

    Zero deck gives the best detonation resistance and engine efficiency. With the affordability of custom pistons, you can get zero deck and the desired static compression for the cam you choose to run. Autotec and Diamond pistons are 2 choices. Contact Jim Weise about that.
     
    Last edited: Feb 27, 2018
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  5. Bigpig455

    Bigpig455 Fastest of the slow....

    Jim Weiss spec'd a Comp cam for me to increase DCR on an 8.5 SCR engine, and the car runs very strong without much else involved. If your just gonna cruise and get on it once in a while, call Jim for cam advice and leave the bottom end alone unless you have to change something.
     
  6. BuickV8Mike

    BuickV8Mike SD Buick Fan

    California Premium is 91 octane where I live. My stock 10:1 but 0.045 in the whole pistons and stock cam seems to be just capable of using this low octane Premium fuel for reference.
     
  7. StagedCat

    StagedCat Platinum Level Contributor

    x2....that was my question, where you getting 92-93, I'm in SoCal with 91 avail....
     
  8. 8ad-f85

    8ad-f85 Well-Known Member

    Noting for reference, a mild performance cam is going to make more cylinder pressure than a stock engine in most cases.
    Some are going to question how accurate the 10-1 spec is, as well as if full timing is dialed in (detuned).
    A 1000lb heavier car isn't going to get by as easily.
     
  9. KenneBelle455

    KenneBelle455 Well-Known Member

    These guys here give some great advice and clearly really know their Buicks.. I just want to add this thought to the discussion.. I wouldn't just think about the gas that's available today in 2018, I'd think about what might be available 5, 10, 20+ years from now. With all modern cars being capable of running on 87 octane, and the move to all new car production being all-electric in another decade or two, I see it as very possible that 91 octane will no longer be readily available at the pump in the foreseeable future, as few people will need it. In a potential world of 87 octane only at the pump, I'd want to be able to run that rather have to buy expensive race gas all the time just to drive my car on the street. But I'm looking at it from the standpoint of, if I'm building an engine I want to do it once and do it right, because I don't want to have to do it again in 5-10 years. It sounds like your car is going to be more of a cruiser than a racer, so you may want to think about that.

    As others have mentioned, erring too high on dynamic compression will require detuning to compensate for pump gas, which completely negates any slight benefit from the extra compression. An engine is a complicated system where all parts have to work well together for the best results, so rather than focusing on just static compression ratio, focus on putting together an engine where everything is well matched. From what I've seen here so far, there's a lot of guys here that really know these engines well and have long since figured out which combos work well. I'm a Pontiac guy myself, and while I'm not at the same level a lot of these folks are with their Buicks, I can certainly tell you all the same rules apply with a Pontiac as well. I've seen a lot of Pontiac 455s built with 6X-4 heads with pounded rod bearings and beat up ring lands because they can't get them to stop detonating, whereas my lower compression 455 with 6X-8s makes nearly as much power but runs fine most of the time on 87 octane. I'm sure it's the same for a Buick, just as it is for an Olds, or any other engine out there.

    Be realistic about your intended use for the motor and build it accordingly. A lightweight car with a manual trans can usually get away with a bit more compression than a heavy full size car with a stock convertered automatic. Don't build a high strung race engine and stick it in a LeSabre with an automatic, you know? Build it right and you'll be able to just enjoy it and know you can buy gas anywhere.
     
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  10. 70 GMuscle

    70 GMuscle Plan B

    Im using a 73 455 in my 70 GS.
    I had the bowls cleaned up and left stock original valves as it was in excellent condition.
    Cylinder head guy said best bang for the buck.
    The turn down under the valve was small and sharp.
    Now cleaned up and smooth.
    Have speed pro pistons w claimed 10.0 to 1
    Actual compression measured is 9.3 to 1. Block is .040 over.
    Edelbrock extreme energy n performer intake has it running sweet for a cruiser.
     
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  11. NealWright

    NealWright Active Member

    Other thing to keep in mind ... my stock ‘73 455, measured closer to 7.8:1 compression

    If you’ve got a blank slate ... pistons are best way to get compression ... decking block/heads can do it too, but pistons are #1 choice

    Simple 9.5:1 & TA212 can seem popular choices ... read, and understand DCR, you’ll see Int Valve closing timing is critical to fuel requirements

    Call TA too ... they’ll help you with your goals
     
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  12. BuickV8Mike

    BuickV8Mike SD Buick Fan

    I'm starting to think the starting point is measure your blocks piston depth in the hole and get pistons to get zero deck equivalence. Possibly Pontiac rods which are 0.025" longer best I remember. Then, you could set combustion chamber size and cam? Am I on the right track?
     
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  13. Stevem

    Stevem Well-Known Member

    I would not go over 9.4 comp if you want to drive the most anywhere and run on 91 octane if need be !
    Having the ability ( low enough comp) to add in 8 to 10 degrees of vacuum advance affords far better part throttle drivability then a added full point of compression any day, especially with a automatic Trans car!!

    With a 9.4 comp and 455 cubes you will need more than a Intake duration of 215@.050" to keep the cylinder pressure under 190 psi .

    With your heads I would take advantage of there air flow levels and run something in the .500" to .525" lift range by means of a higher then stock rocker ratio so your idle and low end cylinder pressure affords good bottom end power with greater top end thrown in as icing on the Cake!

    And another thing in regards to the heads, polishing out those as cast ruff chambers so they are not Carbon collectors that make for glowing hot spots after a few thousand miles would be on my to do list also!
     
    Last edited: Mar 1, 2018
  14. Harlockssx

    Harlockssx Brother Graw Mad

    I don't think we'll be seeing less than 91 octane within our lifetimes, as many newer cars run in the 11:1 compression ratio range without direct injection. I do like the idea of E-85, but I think it stands a good chance of going away first, due to the awful mileage it gives. I had a methanol/water injection setup on one of my previous turbocharged cars (600hp 2.0L) for those times I needed to run pump gas...I think that would be a decent investment in a built 455, provided you drove it enough to use it. The downside is the nozzles can clog over time.
     
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  15. KenneBelle455

    KenneBelle455 Well-Known Member

    What the future holds is anyone's guess, but regardless, if I were building a hot cruiser that I wanted to put some real miles on, I would make sure that it can run just fine on today's pump fuels at least. With today's technology and decades of experience, you can build a big cube V8 to make a ton of power and run easily on pump gas. If you're not building a race car, the question you have to ask yourself is this: Is the little bit of extra power you'd get from pushing your dynamic compression beyond what you can run on pump gas worth the expense and significant limitation of having to run race gas in it and thus not be able to drive it wherever you want without worry? If your cruising methodology really only involves local weekend drives within the range your fuel capacity allows, then maybe that's not so much of a factor for you, but if you want to really put some miles on and drive a ways from home, that restriction could very easily start to get very, very annoying, and make you not want to drive as much, thus harming your overall enjoyment of the car. Every enthusiast is different, but I'd get very annoyed very quickly if my formerly favorite cruiser turned into a hassle just to feed it. Not to mention, think about the times you might get stuck in traffic on a hot day, or creeping through a car show or downtown cruise on blazing hot asphalt in the summer.. those are not the times that I want compression demons to show themselves.

    Does a street cruiser really need more than 450-500 reliable horses? That's not that hard to make on pump gas if you build it right. Is the extra couple dozen HP you'd gain from boosting the compression worth the hassle and expense of race gas? Pulling back timing to compensate and making an engine that responds lazily to throttle input and runs hotter is not my idea of a good compromise. The better compromise would be to shoot for a few less HP, but end up with a snappy, responsive engine that you never have to worry about that runs on gas I can find anywhere and can still just as easily turn the tires into atmosphere any time I want.

    Just my opinion, some food for thought. I know a lot of people dream of big HP numbers and they get so focused on that that they forget about the fact that the vast majority of their driving in a street cruiser is light throttle cruising. I personally don't think a few extra HP when I stand on it is worth compromising all the rest of that cruising time.
     
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  16. Warren Jarrett

    Warren Jarrett Well-Known Member

    Wow, everybody, thank you. You've given me a lot to consider.

    So, for 2 days I drove my car with a new cam, timing chain, oil pump, rebuilt carb and distributer, exhaust system, and cleaned-out fuel tank. Just for 2 days. Then wammo, it overheated and lost oil pressure. I towed it to the mechanic, and he found the connecting rod bearings were breaking. Probably the main bearings are not far behind. So the whole engine is coming out for "freshening". Thus my ability now to make more changes and increase performance from some other improvements.

    From what I remember, well, in high school auto shop, which was a LONG time ago, the two best ways to get improved performance across the entire RPM range are displacement and compression. Well, 455 satisfies the displacement department. And I think 9.5:1 will satisfy the compression concern, compared to 8.5:1. So, I am ripping out the deeply dished 1973 pistons, and putting in slightly dished 1970/71 pistons. That is it. Everything is already settled, including my cam, which I just bought from T/A, the TA-112-455. I think I will polish the head ports, too. And, I already sent my distributor and carburetor to Everyday Performance for cleaning and recalibration, along with some other improvements he makes.

    I don't want a lope and a lot of high RPM power, that is for sure. I want strong torque, smooth idle, and driveability like butter. If someday I have to add a little bit of race gas to my tank of pump gas, I don't mind. I actually like the idea of running real lead past the valves. A little bit of authentic tetra-ethyl lead added to unleaded gas supposedly activates the octane more than a simple calculation would imply.

    In my 1973 Pontiac 455, with 1969 400 heads, I really DO need about 2 gallons of high-octane, high-lead racing gas per full tank of 91 octane pump gas. And this allows me to have complete flexibility for optimum ignition timing. THAT is a great engine (as long as I don't drive far from home) !
     
  17. Stevem

    Stevem Well-Known Member

    The Pontiac 455 is a bit of a different case then the Buick when it comes to tuning and octane needs as the Pontiacs stoke is bigger then its Bore while the Buick is the opposite and this makes for much faster cylinder pressure rise and much different Cam needs, and a faster need for high levels of Intake air flow on the induction stroke.

    The fully machined smooth chamber of the Pontiac is a blessing in this case!
     
  18. Mark Demko

    Mark Demko Well-Known Member

    I agree, 91 and (around here) 92 octane will be around for awhile.
    Reason for people using 87 octane in their newer high performance cars is the computer just retards timing for the lesser octane.
    Yes you can use 87 octane, but their performance will suffer.
    You can only achieve so much power from 87 octane.
     
  19. Warren Jarrett

    Warren Jarrett Well-Known Member

    So practically speaking, how do we "build" a Buick 455 differently than a Pontiac 455 for just fun street use and a noticable performance increase (to zip onto the freeway, and zoom around at 100 to 120 mph), without going crazy? Well, I guess driving at 100 to 120 on the freeway would be considered "crazy" by many, particularly the police.

    I mean "without going crazy" with performance parts: no roller cams, stroked crankshafts or high-rpm stall convertors.

    It seems to me that, reading the many comments here and my other posts, for the Buick 455, choosing the right cam for the performance I want to achieve is really key. I have the Stage 1 larger exhaust valves, so maybe they come into play. And now I am going to have the higher compression pistons. I don't feel there is much more I can do, compared to the Pontiac 455, which had a lot more options to consider, for example various heads from earlier years and the 400 engines.

    By the way, the guys at TA Performance like my plan to use the 112 cam with higher compression (1970-71) pistons. They think that is about the only things I can do, for a noticable increase in power from low RPM to high RPM, and a smooth idle. Come-on, this is a Buick Century, not anywhere near a hot-rod candidate.
     
    Last edited: Mar 4, 2018
  20. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    3 words, better cylinder heads.
     
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