Did you ever get a chance to put it back on the track again?
Dyno day
- Thread starter hemi24
- Start date
Just remember that DA isn't nearly as significant for a boosted vehicle as it is for naturally aspirated.
A great start and should be a high 11 on a quarter mile pass!
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A great start and should be a high 11 on a quarter mile pass!
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I always heard the opposite.. although usually the percentage of power drop is exactly the same just the boosted motor is making more power thus a larger hp drop at same percentage. Even worse if your mom intercooled or have a marginal intercooler. Of course you can add boost but that's besides the point.
It's a matter of ratios. A naturally aspirated motor is using 14.7 psia of pressure at sea level. This drops to 12.2 psia at 5000 ft. So, this makes for a difference of 17% in power between sea level and 5000 ft.
Same motor with a supercharger making 10 psi is using 24.7 psia of pressure at sea level, 22.2 psia at 5000 ft. This is a difference of 10%. The more boost, the less change because the ratio becomes less and less.
A turbocharged motor using electronic boost control gives up next nothing because the same absolute positive pressure is the same absolute positive pressure no matter the altitude.
All of this is why superchargers and then turbochargers became such a big deal on World War 2 fighter planes. They could maintain power at altitude far better than naturally aspirated motors.
Same motor with a supercharger making 10 psi is using 24.7 psia of pressure at sea level, 22.2 psia at 5000 ft. This is a difference of 10%. The more boost, the less change because the ratio becomes less and less.
A turbocharged motor using electronic boost control gives up next nothing because the same absolute positive pressure is the same absolute positive pressure no matter the altitude.
All of this is why superchargers and then turbochargers became such a big deal on World War 2 fighter planes. They could maintain power at altitude far better than naturally aspirated motors.
hemi24
Member
On blower motors tho you will loose boost unless you pulley swap. On my gt500 i usually was down 2-3 psi from 0 DA to 3800, which ended up being 3-4 tenths in the quarter.
We are planning to run next at the NMRA world finals in Bowling Green, hope to see some good cool air. I think the truck will go 11.6-11.7 at around 113-114
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We are planning to run next at the NMRA world finals in Bowling Green, hope to see some good cool air. I think the truck will go 11.6-11.7 at around 113-114
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Positive displacement blowers tend to lose boost fairly linearly, centrifugals don't because of the way they build pressure in relation to the RPMs. But yes, if you're seeing a change of 2-3 psi in the data logs, that is definitely going to slow you down!
I bet you'd easily run a personal best at Spookfest!
hemi24
Member
Definitely! When people used to run at Cecil and set best everyone would call it the “Cecil mod”.
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Your math is correct. But as others said you will lose boost due to poor air which factors in. If you lost 3 psi due to DA on a motor that has 400 base NA power at sea level then that would be big. You first lose the power from the base horsepower which would be 68 HP plus the loss of 3 psi Which is an additional 84 HP from a sea level engine. Again the boosted set up may lose even more if non intercooled or supercharged. Turbos will try and keep gate pressure which helps. Now which vehicle slows down more? The 400 hp NA motor that loses 68 HP or the boosted motor that loses 152 horsepower? Being around alot of built gen2 trucks I can definitely verify a 3psi boost loss from terrible DA to sea level. Was usually worth a 2-3 tenth loss in the 1/8 mile from dead of summer to winter... When my truck was NA I may lose 1/2 tenth between the two. This is why every vehicle needs boost! Just up the pulley or turn the boost controller up lol.
I almost wrote some of that into the original post, but we were talking about a mild centrifugal blown truck, not built positive displacement blower truck that loses 150 because it's a small percentage (remember this is a ratio) of a big number.
People correct boosted vehicles like they're naturally aspirated and it doesn't work that way, especially with centrifugals and even more so with turbos.
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People correct boosted vehicles like they're naturally aspirated and it doesn't work that way, especially with centrifugals and even more so with turbos.
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Centrifugals in my opinion are no different than a positive displacement. At a given pulley ratio and rpm a centrifugal will only pull in so much air. It will be directly related to the DA same as any other pulley driven compressor. A turbo on the other hand can be made to easier repeat passes from differing DA's but it is working harder to do it. I know it is a ratio of engine power but what I'm looking at is power to weight ratio.... The constant variable here is the vehicle weight. Does a 4000 lb lighting losing 68 HP lose more et than a 4000lb lightning losing 150hp?
We're coming at this from different directions. My point was that an 11 second naturally aspirated vehicle slows down more at a higher DA than an identical vehicle that runs the same 11 second ET with boost. You shouldn't use the same correction, not that there would be no correction.
Definitely a more powerful vehicle will lose more power and ET at higher DA.
So, if the point was the truck may lose more et/mph with the blower than it did naturally aspirated, yes, that's certainly possible. But it's going much faster!
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Definitely a more powerful vehicle will lose more power and ET at higher DA.
So, if the point was the truck may lose more et/mph with the blower than it did naturally aspirated, yes, that's certainly possible. But it's going much faster!
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Jamie V
Well-known member
Hmmm I need to ponder this.
Drag Times has a DA correction estimator that will demonstrate the difference.
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Jamie V
Well-known member
See that doesn’t make me believe it because it puts supercharged and turbocharged in the same category.
The supercharged engine will loose more then the turbocharged because the wastegate will bring the boost back up to where it’s set to on the turbo setup whereas the blower setup will just have less boost.
The supercharged engine will loose more then the turbocharged because the wastegate will bring the boost back up to where it’s set to on the turbo setup whereas the blower setup will just have less boost.
OK! I quit!
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