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now what?
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Discussion Starter #1
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?
 

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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
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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.
 

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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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now what?
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45 Posts
Discussion Starter #5 (Edited)
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
 

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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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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/TechService/Technical/Supercharger Tech Info.pdf
 

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Or Seth, either one
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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.
 

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steelcomp was here
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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.
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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How much less hp would the blower use because of the reduction of
boost pressure?
 

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Or Seth, either one
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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?
 

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steelcomp was here
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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
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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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steelcomp was here
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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.
 

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Or Seth, either one
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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.
So, I get it. All of it. We're saying the same thing. Not much gain, all things the same. I think the OP (and his friend) are very optimistic thinking 50+ HP gain. Which would be more accurate if it were a naturally aspirated scenario. Just because the engine is bigger doesn't mean the blower is going to move any more air.

In theory, wouldn't the HP peak at a lower rpm in this scenario?
 

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steelcomp was here
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So, I get it. All of it. We're saying the same thing. Basically, yes. ;) Not much gain, all things the same. I think the OP (and his friend) are very optimistic thinking 50+ HP gain. Which would be more accurate if it were a naturally aspirated scenario. Just because the engine is bigger doesn't mean the blower is going to move any more air.

In theory, wouldn't the HP peak at a lower rpm in this scenario?
Probably, since in relation to the displacement, everything will be "smaller".
 

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How much less hp would the blower use because of the reduction of
boost pressure?
The HP difference would require the worlds most accurate dyno. Boost pressure has very little effect on HP consumption. AIR FLOW does. How much pressure the blower makes moving X air into a space has little effect on the power requirement. If the size of the space changes to cause the pressure drop, the power requirement is still mostly linked to the CFM of air moved, not the pressure that results from the volume of air moved. Bottom line, blower SIZE and SPEED determine the power required to drive it. The other misconception is that a 14-71 requires more power to turn than a 6. BULLSHIT. At the same air delievery, they HP required is almost the same. 4 additional inches of aluminum rotor is not that much harder to turn. Its the amount of work you ask it to do that eats power. The same air flow thru them requires the same power.
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.
I think what you and Budweiser are not coming to terms with the AMOUNT of air moved.
Of course a move the same amount of air/fuel into a 500 as you do a 454 with the same 256 blower at the same exact speed. In fact, it may move ever so lightly MORE air into the 500 incher due to lower back pressure(boost).

Lets change the blower to a 6-71 because the rotor speed of a 256 is almost double that of a 10-71 at the same air flow and I'm not really that familiar with the flow curve.
With a 6-71 the 454 driven to produce 5lbs of boost, will produce 2 lbs on the 502. Its almost a waste to discuss 2 lbs of boost. The HP to drive the blower is virtually identicle(again, its pumped air, not pressure that has the biggest effect on the power requirement).
The both engines will recieve almost the exactly same amount of air/fuel. Not enough back pressure on either to throw the delievery off that much. Not enough rotor speed to make either to make the blower efficiency change alot. Although the roots is not 100% efficient, it is a postive dispalcement pump that is simply feeding another positive displacement pump. The engine can only recieve as much air as the blower can supply, and no more. Assuming the blower at that speed is equally efficient, both engine will see the same CFM delievered.
But with the same exact compression ratio, the 454 will have an effective CR of about 12 to 1, and the 502 about 10.2. The 454 will exert a higher pressure across a smaller square inches than the 502. Does the additional square inches of piston offset the additional PSI of the 454? Hard to say.
I would lean towards the 454 slighty, but only from the experience of doing exactly the same thing between a 440 and a 470, with the 440 winning out. But there is a stroke difference instead of bore, which I think may play a bigger part in the comparison. The CID was also only 30 difference not 50.
We built 440s that would bury our 470 AT THE SAME BLOWER SPEED, which was governed by rules. It was able to do it due to higher cylinder pressures and some additional RPM.
BUT, when we rethought our program, made some changes to the 470s static compression ratio, the 440s lost out. But the 440 could out run the 470s because it had the same amount of air/fuel to deal with, but it made higher cylinder pressure due to the small confines of the same amount of fuel. Basically, it had a higher final effective CR.

Still no convinced the 440s can make more with the same air/fuel delievery. Just haven't had the time to rework it to the point we have the 470.



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So, I get it. All of it. We're saying the same thing. Not much gain, all things the same. I think the OP (and his friend) are very optimistic thinking 50+ HP gain. Which would be more accurate if it were a naturally aspirated scenario. Just because the engine is bigger doesn't mean the blower is going to move any more air.

In theory, wouldn't the HP peak at a lower rpm in this scenario?
If the blower puts out 6lbs of boost on both motors the bigger cube motor would have to produce better horse power #'s wouldn't it? If you have 110% VE on a 454 and 110% VE on a 502, I would think the 502 could produce 50hp or more than the 454.
 

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steelcomp was here
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If the blower puts out 6lbs of boost on both motors the bigger cube motor would have to produce better horse power #'s wouldn't it? If you have 110% VE on a 454 and 110% VE on a 502, I would think the 502 could produce 50hp or more than the 454.
Yes, "if"...but we're not talking about equal boost. We're talking about the same blower, same everything, just increase the displacement. The same blower will not produce the same boost on a bigger engine unless you increase the amount of air the blower is delivering.
 

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Or Seth, either one
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If the blower puts out 6lbs of boost on both motors the bigger cube motor would have to produce better horse power #'s wouldn't it? If you have 110% VE on a 454 and 110% VE on a 502, I would think the 502 could produce 50hp or more than the 454.
Yes, but you would have to spin the blower faster. The original post was a hypothetical "what if" the ONLY change made was added cubic inches. Making up the difference you're speaking of would require a pulley change (big woop :) ) but, doesn't answer the question. I find the question intriguing and am glad it came up.

-Seth-
 
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