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Thread: 588 pump gas, whats a good compression number to use

  1. #1
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    588 pump gas, whats a good compression number to use

    I`m redoing my 588, with new 121 cc heads and a 268 278 750 lift cam 112 center line, typical .040 head gasket, and probably about a .020 piston in the hole, I know there are not a lot of piston combos out there to buy for a max`ed out pump gas engine. but any one know how much dome I could run, with out running into detonation problems,or what the max number is for pump gas,I could do the math. I`m not sure if advancing or retarding the cam makes any diff, but I might as well get the right piston first.

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    max compression

    I assume you will run street-strip. with aluminum heads you could go to 10-1. watch the timing. will you use NOS? just a thought, with all the money you spent on building the engine and setting up the car to handle the power. why not buy some good fuel?

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    Re: max compression

    Quote Originally Posted by mark6052
    I assume you will run street-strip. with aluminum heads you could go to 10-1. watch the timing. will you use NOS? just a thought, with all the money you spent on building the engine and setting up the car to handle the power. why not buy some good fuel?
    Well with the the price of fuel,,20.00 a gal for race fuel as opposed to 5.00 for pump gas,,big difference,,and yes alum.heads,,and no nitrous,,car should handle 800 hp,,runs mid nines now,on 11 inch tires,,hooks hard on our shit track,,and I`m running 10.3 - 1 now,,and was running 10.1 - 1 with steel heads,,I thought I could go to around 11 - 1 with aluminum heads??? any one else running a pump gas engine,,,how much compression you running ???

  4. #4
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    Ok, what are you calling pumo gas? Do you know the RON and the MON or at least the advertised Octane numbers of what you are wanting to run?

    What is the principle and secondary application for this engine? Is it race only? Street drivable and race?

    Do you know what your current valve to piston clearance is with current setup?

    If your piston is in the hole .020 and your gasket is .040? .042? Then for your bore size you do not have much squish ability built in. If anything you may be having some pre-ignition and minor detonation problems if you are driving it on the street at low rpm part throttle operation.

    If your valve to piston clearance can stand it, put in a thinner head gasket. Be certain just what your piston in the hole deck ht is first. Then you can safely shoot for a minimum squish/quench distance of .040 as long as you have enough valve to piston clearance. Yes' it will bring your compression ratio up but at the same time should give you a better burn pattern with a more efficient combustion fire chamber. (My term which includes cylinder head and piston all together at TDC.) That engine needs to benefit from the squish of air/fuel mixture that is only possible when the piston is near the cylinder head.

    I disagree completely with the info of you only being able to run 10.00 -1 compression with pump gas. My 10.00 -1 street engines work great with 89 octane pump gas and my 10.00 -1 SB engines work great with 87 octane. My Steel head daily driven bb HEVYS AND mOPARS WORK VERY WELL AT 10.75 -1 COMPRESSION AND WITH ALUMIUM HEADS WE BUMP IT UP ANOTHER 1/4. and at times, slightly more. (Sorry about caps lock).

    I am not telling you to run out and make your BB Chevy 11.00 -1 and higher just becuase I have good results though. Too many have tried and have burned up their stuff. To run high compression with station available pump gass it does take a little planning and a little extra work on the part of the engine builder. I have street/strip SB Chevys running as much as 11.30 -1 compression and they drive them on 92 octane pump gas.

    You can do it if you do things right. I see no reason at all that with your cam specs, if you have a good quench/squish clearanced set-up, You shouldn't be able to run it above 10.50 - 1 and even up to 11.00 -1 if you watch and be careful in the assembly and get no more than a .045 quench/squish in it, with carefully sanding down by hand any sharp and rough edges on the piston, around the valve notches etc.

    I am now in the beginning process of building a barn burner that will be capable of running on the street at 12.00 -1 measured static copression but will be using an av gas mix with other gas.

    So do you need any different pistons to get more compression? I think you don't. Now' if you want to go further and make more power with what you already have and are buying new pistons, here is my suggestion. Buy them from me. lol. No' seriously I do some tricks in design and in dome shapes that if you will angle mill your heads to reduce the chamber size, we can get you more power even at the same compression ratio, but will use a small dome, flat top or even a reversed dome if needed and you will need less total ignition timing becuse it will be a more efficient design. Oh' I was sorta joking about buying them from me. If you call to BRC Performance you can still get my dome by asking for the EW Dome profile. If you need a dome. If not then we will need to design whatever it is you need to make it work like you want.

    Still I think you can do just fine without buying new pistons.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

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    Thanx Ed,,,I`ll give you some info on first setup I had,,pump gas 92 octane,,brodix alum block,,afr 305 heads shaved to 114 cc, I think they took .050 off them,,264/272 715 lift @108 L.S.,,flat top piston -3 dome,,piston in the hole .009 cold,,,.019 hot,,,.040 head gasket,,valve to piston int.-.200,ex.-.080,,, (no relieve for ex. in piston) Car ran great at 30 timing never dyno ed but ran 9.50s w/2900 @ 3500 air...Needed new cam(wont tell you how I wrecked other one,,,) anyway new combo will be..same block,,,afr 357 cc heads w/121cc chambers,,,.040 head gasket 4.630,,,cam 268/278 750 lift,,,piston lets say still in the hole .009-c/.019-h...I need to get a piston where I can max out on compression and still run 92 octane pump gas ( I heard a while ago that you could run 10-1 on steel heads, and 11-1 on alum,,but you don`t see that coming from engine builders anymore,,thats why I`m asking the question, about compression,,maybe its from the old days when we had leaded gas and higher octane??? So any way I see Wiseco is making a 15 cc dome piston now for BBC,and thats were I thought I would go,but I don`t want to exceed my compression limit here,,you mentioned piston designs you have-may look into that! so here I am with the compression ratio issue,,I don`t much like getting my hands dirty that much anymore( getting to old for that) so I want to get it right this time and spend more time driving it. I`ve had the car for some 30 years now and started out racing around in the 14 sec range and I`ve been changing combinations since..Time to leave it alone and just race,,I`ve won 2 championships lately,and even a Wally.but with changing things all the time, It`s hard to stay consistant...any way enough jabbering!!! heres where we are,,on the PISTON issue

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    pump gas

    thanks for more information. yes you can run 11-1 with aluminum heads on the street. theres always somebody that will say they are running 12 or 13-1 comp on the street and have no problems. first is to know what the "true" comp really is. If race fuel is that high you might want to buy some in the states. I know of a shop in greatfalls montana. again I ask you, with all the money you have spent on your engine and drive train, why cheapen up on fuel? one final thought, av-gas is made to work in modern airplanes that have 7-1 compression and run at 2300rpm. does that sound like your motor? :roll: for every guy I hear says they run "it" with no problems I have seen broken parts, rings that dont seal,etc. the dyno doesnt lie, race fuel builds more power. :!:

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    am now in the beginning process of building a barn burner that will be capable of running on the street at 12.00 -1 measured static copression but will be using an av gas mix with other gas
    Mark did you miss the part about it will be mixed with other gas?

    Straight Av Gas is not real good on an automobile engine. At least I don't think it is.

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

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    Re: pump gas

    Quote Originally Posted by mark6052
    thanks for more information. yes you can run 11-1 with aluminum heads on the street. theres always somebody that will say they are running 12 or 13-1 comp on the street and have no problems. first is to know what the "true" comp really is. If race fuel is that high you might want to buy some in the states. I know of a shop in greatfalls montana. again I ask you, with all the money you have spent on your engine and drive train, why cheapen up on fuel? one final thought, av-gas is made to work in modern airplanes that have 7-1 compression and run at 2300rpm. does that sound like your motor? :roll: for every guy I hear says they run "it" with no problems I have seen broken parts, rings that dont seal,etc. the dyno doesnt lie, race fuel builds more power. :!:
    Thanx Mark,,but to keep buying race fuel for something I drive on the street is not only expensive but inconvenient,and this thing go`s through quite a bit of it , AV gas is not sold here to the public anymore, I`m ok with pump gas, keeps my cost down in that area,and I`ve been building decent power with it, and I`ll stick with it, I just wanted some feedback on a safe compression ratio to run it.
    P.S. Ed, I checked out the pistons on the BRC web page,and they look pretty good,,Any idea what the CC is for the dome?

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    Hi again,
    Like with any other brand, the cc is different depending on what you need. That one in that pic had a very small dome but it looked bigger becuase we cut some deep notches in for valve reliefs. It actuallu masures to be a 1 cc but is making up for some hefty valve notches.

    Currently the ones we are now doing for the 24 degree Edlebrock from Curtis Boggs' Race Flow Devolopment is being made with a 9 cc dome of the same profile but different valve arrngements to fit the head and the .846 lift cam.. That will stick up appx .125 tall is all. I will be angle milling that head when we get it.

    We are also currently doing another set that will have a -15 cc reversed dish, but will still be using the same basic piston design of mine with all the internal custom milling. That set will be for an engine using a 1.026 lift cam.

    You can clik on the sticky at the top of this page and see the internal appearance of my nitrous pistons by scrolling way down the page. I posted several pics there.

    The non-nitrous design is much lighter and not as beefy.

    That dome profile may not look like much to most of you, but it has already shown very good complete burn pattern results which means a more efficient combustion process. I hate mountains on top of a piston. lol

    Ed
    " Let all things that hath breath, praise the Lord. Praise Ye the Lord" Psalms 150 vs 6.

  10. #10
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    Sounds like most of your stuff is custom tailored to the heads you are using,they don`t have a piston to fit most aftermarket heads? like mine?


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