48mm TB Flow Capacity
it sounds like a train commin, like bubrubb would say.. WOOWOO!!
04-02-2008, 03:19 PM
#33
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Well, let's see here... A stock throttle body with an airfoil will flow over 600cfm (from what I've read). This is good enough to feed a 350cid engine up to 6000rpm at 100% VE (volumetric efficiency). Plus, the ZZ502 (fuel injected version) makes over 500hp with a stock L98 throttle body.
With that being said, if you increase your displacement, rpms, or VE (heads, cam, exhaust, etc.), the bigger TB will benefit you. I have a book called "Small Block Chevy Performance" by Dave Emanuel that has a series of dyno tests on a Camaro LT1. They dynoed the engine with ported heads by CNC Cylinder Heads, CAI, and a stock 48mm TB. Everything else on the engine was stock. They bolted on a 52mm TB from TPIS; and gained 12hp and 6ft-lbs of torque. That's probably why you see so many people with bigger throttle bodies.
With that being said, if you increase your displacement, rpms, or VE (heads, cam, exhaust, etc.), the bigger TB will benefit you. I have a book called "Small Block Chevy Performance" by Dave Emanuel that has a series of dyno tests on a Camaro LT1. They dynoed the engine with ported heads by CNC Cylinder Heads, CAI, and a stock 48mm TB. Everything else on the engine was stock. They bolted on a 52mm TB from TPIS; and gained 12hp and 6ft-lbs of torque. That's probably why you see so many people with bigger throttle bodies.
04-02-2008, 06:15 PM
#34
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You are still missing a few key points.
Plenum volume is a resivoir of air the cylinders can tap into easily, this resivoir is pretty small on the LT1.
The 48mm TB was in the GM parts bin and as a rule if they can barely get by with something they already have as opposed to redesign, well they will save a buck barely getting by.
You are likely not understanding how that HP rating is achieved, start testing LT1s with no intake or ehaust restrictions or parasitic accessory loads and there are a LOT of LT1s over that HP number. One popular LT1 "specialist" offers a 520hp stroker known to put down 370-390rwhp. 500fwhp is not as bit a number as you think.
TBs also pose a RESTRICTION, it is not a magic number that gets hit and causes the HP to flatline, maybe the RamJet is pulluing 4" of vacuum and would substantially benifit from a bigger TB, guessing not a lot of guys are trying it though as last I heard the tuning software was not yet released.
Plenum volume is a resivoir of air the cylinders can tap into easily, this resivoir is pretty small on the LT1.
The 48mm TB was in the GM parts bin and as a rule if they can barely get by with something they already have as opposed to redesign, well they will save a buck barely getting by.
You are likely not understanding how that HP rating is achieved, start testing LT1s with no intake or ehaust restrictions or parasitic accessory loads and there are a LOT of LT1s over that HP number. One popular LT1 "specialist" offers a 520hp stroker known to put down 370-390rwhp. 500fwhp is not as bit a number as you think.
TBs also pose a RESTRICTION, it is not a magic number that gets hit and causes the HP to flatline, maybe the RamJet is pulluing 4" of vacuum and would substantially benifit from a bigger TB, guessing not a lot of guys are trying it though as last I heard the tuning software was not yet released.
04-03-2008, 09:43 AM
#35
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You are still missing a few key points.
Plenum volume is a resivoir of air the cylinders can tap into easily, this resivoir is pretty small on the LT1.
The 48mm TB was in the GM parts bin and as a rule if they can barely get by with something they already have as opposed to redesign, well they will save a buck barely getting by.
You are likely not understanding how that HP rating is achieved, start testing LT1s with no intake or ehaust restrictions or parasitic accessory loads and there are a LOT of LT1s over that HP number. One popular LT1 "specialist" offers a 520hp stroker known to put down 370-390rwhp. 500fwhp is not as bit a number as you think.
TBs also pose a RESTRICTION, it is not a magic number that gets hit and causes the HP to flatline, maybe the RamJet is pulluing 4" of vacuum and would substantially benifit from a bigger TB, guessing not a lot of guys are trying it though as last I heard the tuning software was not yet released.
Plenum volume is a resivoir of air the cylinders can tap into easily, this resivoir is pretty small on the LT1.
The 48mm TB was in the GM parts bin and as a rule if they can barely get by with something they already have as opposed to redesign, well they will save a buck barely getting by.
You are likely not understanding how that HP rating is achieved, start testing LT1s with no intake or ehaust restrictions or parasitic accessory loads and there are a LOT of LT1s over that HP number. One popular LT1 "specialist" offers a 520hp stroker known to put down 370-390rwhp. 500fwhp is not as bit a number as you think.
TBs also pose a RESTRICTION, it is not a magic number that gets hit and causes the HP to flatline, maybe the RamJet is pulluing 4" of vacuum and would substantially benifit from a bigger TB, guessing not a lot of guys are trying it though as last I heard the tuning software was not yet released.
1) Plenum volume effect on engine performance is independent from TB size.
2) 502 fwhp with a 48mm TB proves that the TB can flow at least 750 CFM, not the 600 CFM some aftermarket TB manufactures advertise. If the 502 Ramjet can produce more power with a larger TB, great.
3) 500 fwhp are equivalent to 400 rwhp conservatively, so a 390 rwhp pull would result in engine with 488 fwhp, not 520 fwhp. Furthermore a 520 hp engine has only 4% more power than a 500 hp engine, so both are pretty much in the same build category.
4) The difference between a 48mm and a 52mm TB in terms of restriction is 1% in density (refer to Fred's post). At 500 fwhp this could result in the loss of 5 fwhp.
04-03-2008, 11:32 AM
#36
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1) Plenum volume effect on engine performance is independent from TB size.
But the pressure in the plenum is a function of the pressure loss through the throttle body. A bigger TB provides denser air. That provides a larger mass of air in the plenum at any point in time. The lower pressure drop will allow the larger TB to maintain the plenum contents, particularly in "transition", when the blades are fully open and the RPM are increaing, and cylinders are demanding more air. While the plenum substantially decouples the throttle body from the cylinder volume, it's contents are still affected by the TB size.
2) 502 fwhp with a 48mm TB proves that the TB can flow at least 750 CFM, not the 600 CFM some aftermarket TB manufactures advertise. If the 502 Ramjet can produce more power with a larger TB, great.
I know from our correspondence that you know that a TB does not flow a specific or limited volume of air. And you know that a "flow" number is meaningless without stating the corresponsing pressure drop. Just because someone "advertises" that their TB will flow 600CFM, they haven't told you anything. Do you honestly believe that when you flow test it, it will suddenly stop flowing more air at 600CFM, no matter how large a pressure differential you apply? It will continue to flow air until the pressure loss approaches barometric pressure. It just reduces the density of the air in the cylinders. And reduces the HP you could make without the restriction.
3) 500 fwhp are equivalent to 400 rwhp conservatively, so a 390 rwhp pull would result in engine with 488 fwhp, not 520 fwhp. Furthermore a 520 hp engine has only 4% more power than a 500 hp engine, so both are pretty much in the same build category.
You can't use a 20% "rule of thumb". My TH400 drivetrain losses exceed that number under certain conditions, and I have seen other tranny setups that approach 25% total drivetrain loss. And it's just an attempt at obfuscation. I think Dwayne's point was that it may be "advertised" at 520HP, but may not make it for a variety of reasons.
4) The difference between a 48mm and a 52mm TB in terms of restriction is 1% in density (refer to Fred's post). At 500 fwhp this could result in the loss of 5 fwhp.
But this comes down to "what is that 5HP worth"? You have chosen to say "nothing".... others have said they would take it. Apparently GM felt that they were getting enough HP out of the RamJet 502 with the 48mm TB. That doesn't mean that a larger one wouldn't provide more power. Its just a matter of what you feel the "return on investment" is worth it. You appear to have made up your mind that you will try and make 500+ HP with a 48mm TB. You'll probably achieve that goal. But don't find fault with someone that says, backed by scientific knowledge, testing and common sense, I'll spend my money on a larger throttle body.
But the pressure in the plenum is a function of the pressure loss through the throttle body. A bigger TB provides denser air. That provides a larger mass of air in the plenum at any point in time. The lower pressure drop will allow the larger TB to maintain the plenum contents, particularly in "transition", when the blades are fully open and the RPM are increaing, and cylinders are demanding more air. While the plenum substantially decouples the throttle body from the cylinder volume, it's contents are still affected by the TB size.
2) 502 fwhp with a 48mm TB proves that the TB can flow at least 750 CFM, not the 600 CFM some aftermarket TB manufactures advertise. If the 502 Ramjet can produce more power with a larger TB, great.
I know from our correspondence that you know that a TB does not flow a specific or limited volume of air. And you know that a "flow" number is meaningless without stating the corresponsing pressure drop. Just because someone "advertises" that their TB will flow 600CFM, they haven't told you anything. Do you honestly believe that when you flow test it, it will suddenly stop flowing more air at 600CFM, no matter how large a pressure differential you apply? It will continue to flow air until the pressure loss approaches barometric pressure. It just reduces the density of the air in the cylinders. And reduces the HP you could make without the restriction.
3) 500 fwhp are equivalent to 400 rwhp conservatively, so a 390 rwhp pull would result in engine with 488 fwhp, not 520 fwhp. Furthermore a 520 hp engine has only 4% more power than a 500 hp engine, so both are pretty much in the same build category.
You can't use a 20% "rule of thumb". My TH400 drivetrain losses exceed that number under certain conditions, and I have seen other tranny setups that approach 25% total drivetrain loss. And it's just an attempt at obfuscation. I think Dwayne's point was that it may be "advertised" at 520HP, but may not make it for a variety of reasons.
4) The difference between a 48mm and a 52mm TB in terms of restriction is 1% in density (refer to Fred's post). At 500 fwhp this could result in the loss of 5 fwhp.
But this comes down to "what is that 5HP worth"? You have chosen to say "nothing".... others have said they would take it. Apparently GM felt that they were getting enough HP out of the RamJet 502 with the 48mm TB. That doesn't mean that a larger one wouldn't provide more power. Its just a matter of what you feel the "return on investment" is worth it. You appear to have made up your mind that you will try and make 500+ HP with a 48mm TB. You'll probably achieve that goal. But don't find fault with someone that says, backed by scientific knowledge, testing and common sense, I'll spend my money on a larger throttle body.
04-03-2008, 02:47 PM
#37
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By Grumpyvette from DigitalCorvettes.com Forum
I get asked frequently if installing a larger than the stock 48mm TPI throttle body will significantly help on a corvette engine, Ill save you some reading right off if you want, yes a 58mm can potentially increase hp if your engine is highly modified and you are still using a stock 48mm throttle body but the restriction a stock 48mm throttle body represents is not as significant and the gains to be had are not that large in most cases, your intake manifold and cam plus your heads are the major restrictions. The stock 48mm throttle body flows about 700cfm and has more than enough flow to support about 475hp-500hp, bored to 52mm it will support about 500hp,-525hp, a 58mm can support about 600hp, but keep in mind there are lots of factors other than just throttle body size that determine potential hp.
Those are APPROXIMATE GUIDLINES based on results seen from hundreds of engines, NASCAR engines make well in EXCESS of 600 hp and they use restrictor plates that in theory restrict air flow to under 700cfm. BUT YOUR GOING TO FIND THAT THE APPROXIMATE GUIDLINES HOLD BASICALLY TRUE, while your combo’s displacement and effective rpm range effect the results as does the efficiency of your headers scavenging the cylinders and assisting to fill the cylinders. The main thing I’m trying to point out here is that your throttle body is not the huge restriction to airflow and potential hp that the manufacturers would have you believe it is. I gained a few hp swapping from a stock throttle body to a ported 58mm throttle body . but not nearly the gains I got when swapping to a custom intake and aftermarket heads. just for grins I swapped back to the stock throttle body to test it out, throttle response was better with the stock throttle body but high rpm power was off only slightly, doing the math it was clear why, the stock throttle body was fine up to about 5800rpm on my 383 it was the intake runners and heads that were the larger restriction. true you gain something with the larger throttle body, but its mostly because the stock intake is so damn restrictive. use a less restrictive intake and the throttle body size change is less pronounced in its effect on engine performance.
Opinions from other forums, it's a coin toss at 500hp.....I'll do the 48mm and the 52mm and post the measured results (I have two stock TB's)....End of thread (from my part)
I get asked frequently if installing a larger than the stock 48mm TPI throttle body will significantly help on a corvette engine, Ill save you some reading right off if you want, yes a 58mm can potentially increase hp if your engine is highly modified and you are still using a stock 48mm throttle body but the restriction a stock 48mm throttle body represents is not as significant and the gains to be had are not that large in most cases, your intake manifold and cam plus your heads are the major restrictions. The stock 48mm throttle body flows about 700cfm and has more than enough flow to support about 475hp-500hp, bored to 52mm it will support about 500hp,-525hp, a 58mm can support about 600hp, but keep in mind there are lots of factors other than just throttle body size that determine potential hp.
Those are APPROXIMATE GUIDLINES based on results seen from hundreds of engines, NASCAR engines make well in EXCESS of 600 hp and they use restrictor plates that in theory restrict air flow to under 700cfm. BUT YOUR GOING TO FIND THAT THE APPROXIMATE GUIDLINES HOLD BASICALLY TRUE, while your combo’s displacement and effective rpm range effect the results as does the efficiency of your headers scavenging the cylinders and assisting to fill the cylinders. The main thing I’m trying to point out here is that your throttle body is not the huge restriction to airflow and potential hp that the manufacturers would have you believe it is. I gained a few hp swapping from a stock throttle body to a ported 58mm throttle body . but not nearly the gains I got when swapping to a custom intake and aftermarket heads. just for grins I swapped back to the stock throttle body to test it out, throttle response was better with the stock throttle body but high rpm power was off only slightly, doing the math it was clear why, the stock throttle body was fine up to about 5800rpm on my 383 it was the intake runners and heads that were the larger restriction. true you gain something with the larger throttle body, but its mostly because the stock intake is so damn restrictive. use a less restrictive intake and the throttle body size change is less pronounced in its effect on engine performance.
Opinions from other forums, it's a coin toss at 500hp.....I'll do the 48mm and the 52mm and post the measured results (I have two stock TB's)....End of thread (from my part)
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