boosted 454 vs same 502 ?
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boosted 454 vs same 502 ?

  1. #1
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    Default boosted 454 vs same 502 ?

    Just a discussion we have been having on a setup
    for my buddys new project boat

    If you had a 454 with a 5psi roots blower making lets say
    600hp and changed the shortblock to a 502 shortblock but used
    same cam,heads,blower,everything from the 454 what would the gain of the
    50 extra cubic inches actually be.
    My guess is around 65hp and 75lbs tq due to the cubes and the unshrouding of
    the valves due to the bigger bore
    my buddy says because of the loss of boost on the bigger shortblock
    it would actually be a smaller difference to the tune of 50hp and 50lbs tq
    to where it would not be worth doing ..

    Any real life experience with this swap anyone?
    If it makes you say DAMN it must be a CARRERA
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    Senior Member steele211's Avatar
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    This should be interesting I have wondered the same thing. Not that I have any idea but I would think that it would matter somewhat as to how the parts were for the smaller motor. What I mean is if the heads cam and such were on the big end of what was needed for the 454 it might be in the sweet spot for a 502? Maybe?

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    Or Seth, either one Budweiser's Avatar
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    Default I like a good hypothetical debate

    I can't envision a roots supercharger (positive displacement) magically displacing appreciably more or less volume of air (aka horsepower) if it's spinning the same speed, same drive ratio.

    And the same cam on a larger engine typically peaks at a lower RPM... Doesn't it?

    My guess is... ALL THINGS EQUAL, EXCEPT SHORT BLOCK... Nearly the same HP at a lower RPM, Max boost will be less, more peak TQ also at lower rpm.

    I'm curious what the guys who have been down the road before have to say.
    Last edited by Budweiser; 07-11-2012 at 05:46 PM.

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    steelcomp was here
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    Too little information. What heads, what cam, what size blower, what rpm, etc? The 502 has way more potential, but I know that's not the question.
    You have a basic hp/ci available, so jus the increase in displacement should net more power. Again, too many variables to really say.
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    Default

    Gen 6 stock rec port heads
    Predator Custom Cams, gen6 roller , 570/580 with 1.7rr [email protected] 230int 236exh 114lsa
    with a powerband of 2000-5200 on a 454
    springs 1.540 dia 140lbs at 1.940 and 425lbs at 1.250
    9-1 comp ratio on both 454 and 502
    stock GM roller lifters
    twin holley 750
    weiand 256 making 5lbs boost at 5000rpm on the 454 with above parts
    like I said it would all be exactly same except for shortblock for both 454 and 502
    Last edited by HTRDLNCN; 07-12-2012 at 11:56 AM.
    If it makes you say DAMN it must be a CARRERA
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    Senior Member ICECREAMAN's Avatar
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    I don't know what it is, but there is a math formula that will calculate HP potential for the motor. When mine was built the builder showed me what the difference would be if it was a 671 @ say 6lbs of boost on a 454 vs same thing on a 540. Then same for 871 and so on. Don't crucify me if I'm saying this wrong, but it's all math.

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    steelcomp was here
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    Quote Originally Posted by HTRDLNCN View Post
    Gen 6 stock rec port heads
    Predator Custom Cams, gen6 roller , 570/580 with 1.7rr [email protected] 230int 236exh 114lsa
    with a powerband of 2000-5200 on a 454
    springs 1.540 dia 140lbs at 1.940 and 425lbs at 1.250
    9-1 comp ratio on both 454 and 502
    stock GM roller lifters
    twin holley 750
    weiand 256 making 5lbs boost at 5000rpm on the 454 with above parts
    like I said it would all be exactly same except for shortblock for both 454 and 502
    One thing I can tell you right off the bat is you need to replace those lifters. You're running an OEM lifter with a .700" dia. wheel on an aftermarket cam designed for an aftermarket lifter with a .750 dia. wheel. With those valve springs and that small wheel (which increases the intensity of the lobe) you've more than likely got some valve train issues you're not aware of. Get a set of quality hyd. roller lifters and put some spring pressure on it before you tear up your valve train completely.
    That little 256 is going to have to spin about another 10-12% over to get the same boost on a 500" engine, as compared to a 454. According to Weiand/Holley, you need to run about 53% over to get 5.3# boost on a 502.

    This might come in handy, especially page 10:

    http://www.holley.com/data/TechServi...ech%20Info.pdf
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    Or Seth, either one Budweiser's Avatar
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    Steel... You're getting too technical on this. It's a bench racing "what if" scenario. If you simply took everything off a 454 and put it on a 502, without changing a single thing. The only assumption I'm making in my guesstimate is that the compression ratio is maintained in the swap.

    I still believe the peak horsepower would not significantly change because the bolwer is still spinning the same speed... moving the same amount of air.

    However, peak torque may be higher and lower in the rpm's due to the increase in cubes/same cam timing.

    Would the power increase at all if the blower is still moving the same amount of air? Would the blower move more air?

    Not a challenge. I'm curious. I don't know all that much about the intricacies of roots supercharging. I could totally be missing something altogether.

    Good info on the lifters.
    Last edited by Budweiser; 07-12-2012 at 12:52 PM.

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    Quote Originally Posted by Budweiser View Post
    Steel... You're getting too technical on this. It's a bench racing "what if" scenario. If you simply took everything off a 454 and put it on a 502, without changing a single thing. The only assumption I'm making in my guesstimate is that the compression ratio is maintained in the swap.

    I still believe the peak horsepower would not significantly change because the bolwer is still spinning the same speed... moving the same amount of air.

    However, peak torque may be higher and lower in the rpm's due to the increase in cubes/same cam timing.

    Would the power increase at all if the blower is still moving the same amount of air? Would the blower move more air?

    Not a challenge. I'm curious. I don't know all that much about the intricacies of roots supercharging. I could totally be missing something altogether.

    Good info on the lifters.
    The amount of air the blower is moving is not independant of the engine it's trying to feed. They're directly related. If you have a hose filling a 5 gal bucket, is it going to fill a 6 gal bucket in the same mount of time if you don't change anything?
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    Senior Member SoldHondaBoughtHondo's Avatar
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    How much less hp would the blower use because of the reduction of
    boost pressure?
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    Or Seth, either one Budweiser's Avatar
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    Quote Originally Posted by steelcomp View Post
    The amount of air the blower is moving is not independant of the engine it's trying to feed. They're directly related. If you have a hose filling a 5 gal bucket, is it going to fill a 6 gal bucket in the same mount of time if you don't change anything?
    No. It will fill the six gallon bucket with only 5 gallons in the same amount of time.

    Sounds like you're supporting and debunking my theory at the same time. Am I missing something?
    Last edited by Budweiser; 07-12-2012 at 01:14 PM.

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    Quote Originally Posted by Budweiser View Post
    No. It will fill the six gallon bucket with only 5 gallons in the same amount of time.

    Sounds like you're supporting and debunking my theory at the same time. Am I missing something?
    But then you're only 5/6 full.
    Yes, I think you're missing something but I'm not sure how else to explain it. You can't fill 500ci with the same amount of air/fuel as 450ci and get the same results. If you could, you could run that same little 256 blower on a 600" engine.
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    Or Seth, either one Budweiser's Avatar
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    Quote Originally Posted by steelcomp View Post
    But then you're only 5/6 full.
    Yes, I think you're missing something but I'm not sure how else to explain it. You can't fill 500ci with the same amount of air/fuel as 450ci and get the same results. If you could, you could run that same little 256 blower on a 600" engine.
    Hmm, I'll have to think about that for a few. What is your prediction on the hypothetical scenario? Absolutely no changes except 48 more cubes. That may help me understand.

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    Quote Originally Posted by Budweiser View Post
    Hmm, I'll have to think about that for a few. What is your prediction on the hypothetical scenario? Absolutely no changes except 48 more cubes. That may help me understand.
    I think I thought of a better way (the right way) to explain this: think of it in terms of volumetric effeciency, which is all a blower does is increase VE. Say with the 454 you have 110%ve @ 5# boost. With no change in the blower and adding 50ci, the VE can only be less. The blower isn't going to move any more air (all else being the same) but it's trying to fill more volume. Less VE = less cylinder filling.
    My prediction? There will be some loss in power due to less VE, but regained by the increase in displacement. There may be a net gain, but it won't be much. If the 5# of boost is maintained, then there will be whatever net gain in tq/HP that the VE will allow. I would say at least 1hp/ci.
    Last edited by scott foxwell; 07-12-2012 at 02:03 PM.
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