BaileyPerformance
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| posted on 24/11/12 at 09:35 PM |
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quote:
Originally posted by jeffw
I should say that 15psi comes out of the Rotrex but only 9psi arrives at the plenum as 6psi is eaten by the intercooler (which is rubbish I know).
The car makes 300HP/250 ft lb at the wheels.
Thats really really good power for that boost, you must have decent cams to make that sort of power. We see around 330BHP (at engine) at 20PSI but
that's with stock head and cams, we normally see more torque than power (this is due to the stock cam profile)
As you say the intercooler seems to be dropping alot, but a cool charge maybe worth more to your engine than boost, considering you have a high CR.
On a zetec a 10deg drop in air temp is worth the same as a couple of pounds of boost, so if you replaced your intercooler with a free-flow version the
chances are the boost would go up and so would the air temp, you could end up with less power!!
Have you got the cam spec please? just out of interest.
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MRLuke
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| posted on 24/11/12 at 10:00 PM |
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quote:
Originally posted by BaileyPerformance
quote:
Originally posted by MRLuke
quote:
Originally posted by BaileyPerformance
Decent engine such as a cosworth YB the head design is very good as standard, so the engine will make good power at low boost pressures, as the boost
pressure is increased (in the hope of gaining more power) the law of diminishing returns comes in, for example a stock YB will make around 270BHP at
15PSI but it will not make 540BHP at 30PSI (without further breathing mods) so it is clear not all the boost is finding its way into the cylinders.
Do you not have to consider that 15psi is actually 15psi above atmospheric (as at 0psi boost engine will still make power) Therefore you are going
from circa 30psi total to 45psi total. Gives power of about 400bhp which probably isnt far off what a cossie makes on 2bar?
Your probably right, a cossy would make 400BHP ish at 2bar, but that's what i said - 30PSI (2bar) it would not make twice the power it did at
15PSI (1bar).
The term "boost" infers extra air over an above what the engine can pull in on its own "naturally aspirated". I good race
engine will achieve a VE of 95%, F1 maybe over 100% due to cleaver ram effect, average production car engine probably around 80%. The higher the VE
the higher the effective compression and more power. So its not true to say 15PSI of boost is actually 30PSI as that would suggest the engine has a VE
of 100% before you turbo charge it, which is not likely.
Boost is always quoted gauge not absolute - but the engine management measures absolute (MAP) as it needs to read vacuum for load purposes when off
boost as well as on boost.
At 0psi boost the engine is making around 130bhp. You are increasing the mass of air by 50% so the power should increase by 50% as well not 100% as
your post reads.
There will be losses whether its is FI or not but I think that talking about VE is just over complicating something that doesn't warrant it.
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BaileyPerformance
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| posted on 24/11/12 at 10:18 PM |
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quote:
Originally posted by MRLuke
quote:
Originally posted by BaileyPerformance
quote:
Originally posted by MRLuke
quote:
Originally posted by BaileyPerformance
Decent engine such as a cosworth YB the head design is very good as standard, so the engine will make good power at low boost pressures, as the boost
pressure is increased (in the hope of gaining more power) the law of diminishing returns comes in, for example a stock YB will make around 270BHP at
15PSI but it will not make 540BHP at 30PSI (without further breathing mods) so it is clear not all the boost is finding its way into the cylinders.
Do you not have to consider that 15psi is actually 15psi above atmospheric (as at 0psi boost engine will still make power) Therefore you are going
from circa 30psi total to 45psi total. Gives power of about 400bhp which probably isnt far off what a cossie makes on 2bar?
Your probably right, a cossy would make 400BHP ish at 2bar, but that's what i said - 30PSI (2bar) it would not make twice the power it did at
15PSI (1bar).
The term "boost" infers extra air over an above what the engine can pull in on its own "naturally aspirated". I good race
engine will achieve a VE of 95%, F1 maybe over 100% due to cleaver ram effect, average production car engine probably around 80%. The higher the VE
the higher the effective compression and more power. So its not true to say 15PSI of boost is actually 30PSI as that would suggest the engine has a VE
of 100% before you turbo charge it, which is not likely.
Boost is always quoted gauge not absolute - but the engine management measures absolute (MAP) as it needs to read vacuum for load purposes when off
boost as well as on boost.
At 0psi boost the engine is making around 130bhp. You are increasing the mass of air by 50% so the power should increase by 50% as well not 100% as
your post reads.
There will be losses whether its is FI or not but I think that talking about VE is just over complicating something that doesn't warrant it.
My power example was based on a cosworth YB, which will not make more than 100BHP in NA form assuming the engine is stock, we have seen a stock YB in
a car just with turbo removed and carbs fitted and they make less power than a pinto.
So, the folks at Ford designed the cosworth YB to make around 210BHP, at 8psi so the turbo doubled the engines power output at only half a bar, at
1bar you only get another 60BHP.
So to state "You are increasing the mass of air by 50% so the power should increase by 50% as well" is wrong, it all depends on the
engines VE. The VE depends on engine breathing and CR.
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jeffw
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| posted on 25/11/12 at 05:22 AM |
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quote:
Originally posted by BaileyPerformance
quote:
Originally posted by jeffw
I should say that 15psi comes out of the Rotrex but only 9psi arrives at the plenum as 6psi is eaten by the intercooler (which is rubbish I know).
The car makes 300HP/250 ft lb at the wheels.
Thats really really good power for that boost, you must have decent cams to make that sort of power. We see around 330BHP (at engine) at 20PSI but
that's with stock head and cams, we normally see more torque than power (this is due to the stock cam profile)
As you say the intercooler seems to be dropping alot, but a cool charge maybe worth more to your engine than boost, considering you have a high CR.
On a zetec a 10deg drop in air temp is worth the same as a couple of pounds of boost, so if you replaced your intercooler with a free-flow version the
chances are the boost would go up and so would the air temp, you could end up with less power!!
Have you got the cam spec please? just out of interest.
The cams are designed by CNC Heads (http://www.cncheads.co.uk/?p=755) to work with their head. The cams have the maximum lift you can get away with
on stock pistons so something more than Piper 285 but not full race cams. The engine made 190HP at the wheels NA.
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BaileyPerformance
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| posted on 25/11/12 at 03:45 PM |
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Thanks for that, i'll have a look.
Your using stock pistons? the standard Ford items? that surprises me.
I think the most we have seen out of a NA 2.0L zetec is about 190BHP at the flywheel, so you are doing well to get 190 at the wheels - that must be at
least 210 at the engine? did your tuning give you a engine and wheel printout?
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jeffw
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| posted on 25/11/12 at 06:03 PM |
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NA was stock pistons and rods...it now has forged pistons and rods as you would expect as well as ARP studs.
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