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Thread: The "epic" 430 rebuild caper!

  1. #11
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    Puzzled on compression

    Dear Carmantx,

    Quote Originally Posted by carmantx View Post
    On the compression deal.

    I don't think it would run well on 91.

    Depends on how you build the motor. Are you planning to zero deck the block? there is a difference in having a 10.25 piston, and having 10.25 compression.

    Just my .02 worth. I think, like the others have mentioned, you will have best power by matching up all of your components.
    I'm puzzled by this. 10.25:1 isn't a particularly extreme compression ratio. Both TA Performance and Orinda Motors thought it was acceptable. In fact, I thought somebody on Team Buick was running an engine with this compression ratio on regular gas. There are folks running with much more aggressive compression ratios on today's premium without complaints.

    Quote Originally Posted by carmantx View Post
    And I drink all the moonshine.
    Aren't you selfish!! Can't you share at least some with your car!!

    Cheers, Edouard
    Caretaker of a 1965 Buick Special "billy goat"!

  2. #12
    The static compression that can be used with a pump gas engine is dependant on the intake closing point determined by he camshaft. Engines with late closing intake valves generally need more static compression to function propperly, and engines with earlier closing intake valves will have a lower of tollerence for static compression. Choosing any camshaft for any pump gas engine should take into account this dynamic compression as well as the power range and type of the camshaft. There is a good explaination and a downloadable calculator for dynamic compression here: http://cochise.uia.net/pkelley2/DynamicCR.html. I would make sure the cam shaft selected for the pump gas engine keeps the dynanic compression between 7.5:1 and 8.0:1 for best engine function and performance. You can adjust your static compression to suit a particular camshaft if you find a cam profile you like that does not provide a good dynamic compression ratio with your planned static compression.

    I ran a few TA cams through the calculator with your planned engine perameters. The best one I found was the "sleeper" 288-94H. It can be used with stock rockers and provides 7.7:1 dynamic compression with 10.25:1 static compression with 66 cc heads, 14 cc dished pistons, .035" gasket, and .025" piston to deck clearence (total .060" quench is the max you would want to use). The 288-98H also was good at that static compression range, but seems more radical than you want to go.
    Last edited by Dr. Frankenbuick; 02-07-2011 at 05:49 PM.
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  3. #13
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    Wink But, but, but, . . . what happened to the mild-mannered wagon?

    To the most honorable Dr. Frankenbuick, Sir!

    With all due respect to your impeccable academic credentials. . . . .

    Quote Originally Posted by Dr. Frankenbuick View Post
    The static compression that can be used with a pump gas engine is dependant on the intake closing point determined by he camshaft. Engines with late closing intake valves generally need more static compression to function propperly, and engines with earlier closing intake valves will have a lower of tollerence for static compression. Choosing any camshaft for any pump gas engine should take into account this dynamic compression as well as the power range and type of the camshaft. There is a good explaination and a downloadable calculator for dynamic compression here: http://cochise.uia.net/pkelley2/DynamicCR.html. I would make sure the cam shaft selected for the pump gas engine keeps the dynanic compression between 7.5:1 and 8.0:1 for best engine function and performance. You can adjust your static compression to suit a particular camshaft if you find a cam profile you like that does not provide a good dynamic compression ratio with your planned static compression.
    Hitting a guy after dinner and a glass of wine huh! Okay, this will have to wait until tomorrow - you are *SO* over my head that the Space Station might collide with it!

    Quote Originally Posted by Dr. Frankenbuick View Post
    I ran a few TA cams through the calculator with your planned engine perameters. The best one I found was the "sleeper" 288-94H. It can be used with stock rockers and provides 7.7:1 dynamic compression with 10.25:1 static compression with 66 cc heads, 14 cc dished pistons, .035" gasket, and .025" piston to deck clearence (total .060" quench is the max you would want to use). The 288-98H also was good at that static compression range, but seems more radical than you want to go.
    However, I have enough cognitive function left (or so it appears) that I can pull out my TA Performance catalog and: . . . .

    The RPM range is 2500-5500 . . . so there is the 5000 pound trailer sitting there - how am I going to start moving that trailler it before I can tap into all that luscious horsepower? Nevermind the fact, $4.00 a gallon gasoline - it don't say good fuel economy! Now if you pay for my gas . . . . .

    Now to quote the TA Performance description:

    Good street/strip cam (strip? with a travel trailer? ). Gives 30+ HP over stock cam. Stock rockers ok (good thing too - I can't afford anything else!) TA valve springs recommended (ka-ching $$$) Small stall converter recommended (WHAT, stall converter required on my mild-mannered and faithful wagon!?!?!) Power Brakes okay (Well, I hope so, how you do expect me to stop the car and travel trailer - the flintstones way!!) Average idle, 1000 in park . . . (request denied! )
    Uh, still seems a little assertive for my tastes . . . ya'know, mild mannered, boring, unpretentious, . . . . a station wagon!!!

    What are you guys trying to do with my wagon!! Make a monster out of it!!?!?!???

    Oh sorry, Dr. Frankenbuick . . . . no offense intended.

    All appearances of humor in this posting were intended - so laugh!!

    Cheers, Edouard
    Caretaker of a 1965 Buick Special "billy goat"!

  4. #14
    It would not be a monster, but it would pull higher in RPMs then the RV cam. I put them both in comparison plotted over RPM using Dyno2003 below (green is the torque curve and red is the horsepower curve). You can see that even with great flowing heads the RV cam is all done pullig at 4500 rpm. The 288 is good to 5500+. There is less torque with the 288 at lower RPMs, but not enough to make a big difference. I just dont think you will be happy running out of steam at 4500 rpm, and your heads are made to breath at a higher rpm to make power.

    You would need to have your 200-4R built with a little more stall in the converter (about 500 over stock) to use the 288 at 10.25:1 static compression (7.7:1 dynanic compression). It would still have stump pulling torque, would have some impressive horspower (75 peak over the RV-12) and good economy when going easy on the pedal and in OD.

    Running the RV12 through the dynamic compression calcualtor at 10.25:1 static compression yielded 8.75:1 dynamic compression. That dynamic compression ratio is better suited to racing gas and would be very detonation prone in a pump gas engine. Reducing the static compression to 9.25:1 with the RV-12 gave us 7.8:1 dynamic compression. That would be a very good static compression ratio for that cam if you still want to use it. I used the lower static compression ratio (9.25:1)with the RV-12 in the Dyno2000 comparison below.


    Last edited by Dr. Frankenbuick; 02-11-2011 at 09:39 AM.
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  5. #15
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    The dr. there might have said this, but again, sticking a 10.25 piston in an engine doesn't necessarily net you 10.25 compression.

    Good luck, keep us posted on your progress.
    I have a 10.25 compression piston that ran a 10.24 in the 1/4. Trying for a 9 this season.
    I am building a 9:1 cast piston 455 for my convertible, with a custom ground cam, stock heads, SP1 intake, Qjet and headers. It will have enough torque to pull my house off the foundation. Your only pulling a 5000# trailer. Put a stock used 455 in it and work on the braking system. You could pull it 0 to 60 quicker than a prius can drive it.
    86 GN, all factory options, engine build in progress
    72 Skylark Convertible, 462, TH 400
    72 GSX Clone 464, TH400, 3:42. 10.71 @126mph best

    We build GM carburetors and specialize in custom built Quadrajets

    www.quadrajetpower.com
    mark@quadrajetpower.com

  6. #16
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    Thanks Steve for taking the time to present such valuable information and Carmantx for your replies also.
    Here is additional info that might help.

    The compression height on the Egge piston is 1.954. Egge didn’t have the dish volume available without actually going to the shelf and measuring it. Guessing it to be around 15cc.

    Waiting for verification on the stock deck height. Hopefully it is 10.57
    Depending on finished deck height, static compression can be as low as 9.6.

    This engine will spend most of its time between 1600 and 2000 rpm. The main goal is fuel economy so we want to push the limits of the DCR and be closer to 8.25.
    The lock-up converter will be activated during cruising.

    The heads will use 2.00 intake and 1.625 exhaust valves. There is no interest in power above 4500 rpm. The actual goal is a flat 500 ft-lbs of torque in the operating range stated.

    Thanks in advance for additional feedback.

    Paul

  7. #17
    I used the dimensions from these pistons in the DCR calculator: http://www.fastengineparts.com/products_view.php?id=1271. The .09 x 3.50 dish works out to 14 CCs and I used .025" down the hole with a .035" (felpro blue) gasket. Stock 430 pistons have been recorded as 16 CCs. You would be .058" down the hole with your pistons and predicted deck height. I would expect you will be reducing that to improve quench since you are going to press the limits of detonation and ignition timing with a high DCR. I also continue to think that an 8:1 DCR is all you want to do with today's gas and the chance that 91 octane is all that is available in a lot of locations (long cruises/vacations).

    I used the bigger valves in Dyno2003 as I have actual flow figures loaded for Gessler's stage-one comp port iron heads. The TA aluminum heads flow slightly better then Gessler's with the stage one valve, but I think the aluminum heads with smaller valves will flow similar to Gessler's iron heads with the bigger valves. I think those curves above will be very similar to the actual power produced. I have tested the Dyno2003 predictions against several motors that I have dynoed. Peak power is always close, and the shape of the curves are always very close.

    I could not own those heads and not let them do what they do best (let them live). I would trade off some low end torque for some fun and try to make it up with more vacuum advance in the distributor and the lock-up converter. But, that is just me.........................................
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  8. #18
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    Dr. Frankenbuick

    I would like your take on this.

    I would expect you will be reducing that to improve quench since you are going to press the limits of detonation and ignition timing with a high DCR.

    The trend seems to be that Quench is not important and Spherical dish is producing better results. Was talking to CP about a custom set of stepped pistons and they suggested spherical dish. HRD heads do some of our head work and Al reports as much as 20 HP gain on the 355 stock car engines using spherical dish. JE and others seem to be in agreement.
    I’m from the old school which says squeeze the mixture toward the spark plug and create some turbulence.


    What is your thinking on this?

    Thanks

  9. #19
    I think it is like being in Rome. When you have a large, funny shaped, combustion chamber with quench pads, you use quench to promote turbulance, cool hot spots and reduce detonation. When you have a small round combustion chamber that will still have good compression over a dish shaped piston top, the dish will promote faster flame travel requiring less spark advance and also reduce detonation. Each has its place, but I woud not try to change one into the other. When in Rome: do as the Romans do!
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  10. #20
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    Thanks - trying to balance those "intangibles."

    Thanks Steve, Paul, and everyone else who has contributed here!

    Sorry to have been "missing" from here yesterday. My Internet connection hardware decided to flip-out on me.

    I'm still trying to get my head around this whole discussion of dynamic compression ratio. However, I can see that pushing the engine toward a higher dynamic compression ratio will help the car's performance even for more "humble" tasks like towing. However, pushing too hard could cause knocking with today's 91 octane gas.

    Paul sent me an email pointing out that the TA Performance 112 cam would provide more "breathing room" on the DCR. When I look at the 112 specs, I see it would still provide good fuel economy and a mellow idle. The shift in peak torque RPM shouldn't be so extreme as a heavy load wouldn't be "tamed" with the 200-4R. So it may be time for me to shift the build specs yet again. Stay tuned . . . .

    Perhaps I should have given this thread: the great 430 build soap opera!

    Cheers, Edouard
    Caretaker of a 1965 Buick Special "billy goat"!

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