Ported head + Boost
03-11-2003, 12:50 PM
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Ported head + Boost
If you port the head, does that mean you have to run less boost because of the amount of air the engine can consume? more boost = more air sent mixed with the same amount of fuel = running lean?
Also would cams affect the boost pressure that you could run too?
Also would cams affect the boost pressure that you could run too?
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03-11-2003, 03:40 PM
#8
Boost pressure DOESNT equal airflow, but people dont get that.
Cams and Headwork (and bigger exhaust housing, and loadsa stuff) does mean the car flows more air, so more power, at same boost reading, so yea, the car would need more fuel too.
Cams and Headwork (and bigger exhaust housing, and loadsa stuff) does mean the car flows more air, so more power, at same boost reading, so yea, the car would need more fuel too.
03-11-2003, 03:43 PM
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so without the extra fuel, would the car run lean?
if the car was running 28psi on greys before the headwork, would it still be able to run 28psi or would you need to back the boost off to stop it leaning out?
if the car was running 28psi on greys before the headwork, would it still be able to run 28psi or would you need to back the boost off to stop it leaning out?
03-11-2003, 03:43 PM
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Surely a ported and flowed head won't increase boost, it'll smooth the air's path but if you running say 21psi and fueling for 21psi then surely it'll remain the same?
Surely porting and flowing the head only becomes an advantage when it can't flow the air that your trying to force through it!?
Also i can't see how cam's can affect the boost pressure that you can run either, but they affect power by managing the air flow in and out of the engine?
Surely the determening factors to the boost pressure you can rum are weather the head/exh/inlet/turbo can handle it and also wether you can fuel correctly for it and mainain sensible ACT's?
PJay
Surely porting and flowing the head only becomes an advantage when it can't flow the air that your trying to force through it!?
Also i can't see how cam's can affect the boost pressure that you can run either, but they affect power by managing the air flow in and out of the engine?
Surely the determening factors to the boost pressure you can rum are weather the head/exh/inlet/turbo can handle it and also wether you can fuel correctly for it and mainain sensible ACT's?
PJay
03-11-2003, 03:49 PM
#12
Surely its whatevers MOST restrictive?
Most the time its the turbo exhaust housing, but could be head, cams, manifolds, exhaust, anything.
But IMO once the most restrictive thing is made less restrictive then you got more airflow at the same boost level, so need more fueling.
Remember when Stu said about they needed to remove 10% or somthing of the fueling on Seans car when they went back to a mongoose from the 4" bore drainpipe he was running.
This is another "need Stu or Karl to confirm/explain properly" type post, as its hard to put into words.
Most the time its the turbo exhaust housing, but could be head, cams, manifolds, exhaust, anything.
But IMO once the most restrictive thing is made less restrictive then you got more airflow at the same boost level, so need more fueling.
Remember when Stu said about they needed to remove 10% or somthing of the fueling on Seans car when they went back to a mongoose from the 4" bore drainpipe he was running.
This is another "need Stu or Karl to confirm/explain properly" type post, as its hard to put into words.
03-11-2003, 03:55 PM
#13
Also i can't see how cam's can affect the boost pressure that you can run either, but they affect power by managing the air flow in and out of the engine?
If as you say cams manage air flow in and OUT of the engine, surely this is going to affect boost pressure, as it is air flow out of the engine that spins up the turbo .
03-11-2003, 03:58 PM
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Bit of a contradiction there surely? If as you say cams manage air flow in and OUT of the engine, surely this is going to affect boost pressure, as it is air flow out of the engine that spins up the turbo .
PJay
03-11-2003, 04:05 PM
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Boost pressure DOESNT equal airflow, but people dont get that.
Cams and Headwork (and bigger exhaust housing, and loadsa stuff) does mean the car flows more air, so more power, at same boost reading, so yea, the car would need more fuel too.
Cams and Headwork (and bigger exhaust housing, and loadsa stuff) does mean the car flows more air, so more power, at same boost reading, so yea, the car would need more fuel too.
Also would cams affect the boost pressure that you could run too?
PJay
03-11-2003, 04:07 PM
#18
Norris Motorsport
When you fit a ported head and/or cams it is wise if not essential to remap the car or at least confirm the fuel map is correct.
Lets take a cosworth mapped as standard by speed/densisty.
Based on a given rpm and map sensor input (i..e boost) (lets assume WOT) the car will be mapped for the engines actual airflow. This means we are saying that at X rpm and X boost the engine consumes X amount of air and hence requires X amount of fuel. This is fixed by the map in the ecu.
If we now fit a ported big valve head for the same rpm and map sensor output we are flowing more air due to the lower resistance the ports/valves offer to the air. The map will have X injector duration at this point which as it was specced for the std head will now be insufficient for the increased airflow at those same conditions resulting in the engine running lean.
On some engines the head makes little difference if say for example the turbo is the main restriction.
However if you take my engine capable of making 600bhp on 26psi at 7200rpm, imagine the consequence of putting in a normal 403 (grey's) map in. A normal grey map might have an injector on time of 16ms at 26psi@7200rpm and be sufficient to fuel for 380bhp. given my 600bhp potential I would be underfueling by about 35% with disaterous consequences!
so you see the answer is it's not about plenum pressures and rpm, its about actual airflow for a given plenum pressure and thats where ported heads and cams effect things and hence usually need remapping.
Lets take a cosworth mapped as standard by speed/densisty.
Based on a given rpm and map sensor input (i..e boost) (lets assume WOT) the car will be mapped for the engines actual airflow. This means we are saying that at X rpm and X boost the engine consumes X amount of air and hence requires X amount of fuel. This is fixed by the map in the ecu.
If we now fit a ported big valve head for the same rpm and map sensor output we are flowing more air due to the lower resistance the ports/valves offer to the air. The map will have X injector duration at this point which as it was specced for the std head will now be insufficient for the increased airflow at those same conditions resulting in the engine running lean.
On some engines the head makes little difference if say for example the turbo is the main restriction.
However if you take my engine capable of making 600bhp on 26psi at 7200rpm, imagine the consequence of putting in a normal 403 (grey's) map in. A normal grey map might have an injector on time of 16ms at 26psi@7200rpm and be sufficient to fuel for 380bhp. given my 600bhp potential I would be underfueling by about 35% with disaterous consequences!
so you see the answer is it's not about plenum pressures and rpm, its about actual airflow for a given plenum pressure and thats where ported heads and cams effect things and hence usually need remapping.
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