Hot unrestricted air intake vs restricted cold air
Discussion
I'm trying to work out what sort of air intake + filtration to use in the capri. Engine is a standard (for now, eventually aiming for 500bhp+ ish) chevy v8. There is not a huge amount of space between the top of the carb and the underside of the bonnet.
So my immediate ideas are:
Traditional round pancake filter on top of carb, breathing in nice hot air from over the manifolds and blown in through the radiator..
Above but with ducts from front end blowing in cold air when in motion aimed at the filter..
Sealed filter housing on top of carb with ducts from front end, this will be restricted by the ducting taking a convoluted route to the filter, but will benefit from a ram air effect. If that makes any difference anyway..
A sealed filter housing on top of carb with intakes ducted from inside the wheelarch area, some kind of crud shield to protect against crap getting flung off the wheels. Much less restriction then front intakes, but no ram air. Also is this a positive or negative air pressure area?
Some kind of elbow on top of the carb, and a cone filter either in the arch or behind front valance, or two filters via a t-piece on the elbow
Cut a hole in the bonnet and stick a scoop on either the carb, hot rod style with internal filter, or a tall filter on the carb and a scoop on the bonnet pro stock style. This will cause problems at BIVA though most likely.
I guess any type of open filter will have unrestricted air flow, subject to filter size and clearance against bonnet and rocker covers etc, whereas ducted systems will be limited by the width and length of ducting, and any turns and twists that will need to be made.
What a long post. Sorry.
So my immediate ideas are:
Traditional round pancake filter on top of carb, breathing in nice hot air from over the manifolds and blown in through the radiator..
Above but with ducts from front end blowing in cold air when in motion aimed at the filter..
Sealed filter housing on top of carb with ducts from front end, this will be restricted by the ducting taking a convoluted route to the filter, but will benefit from a ram air effect. If that makes any difference anyway..
A sealed filter housing on top of carb with intakes ducted from inside the wheelarch area, some kind of crud shield to protect against crap getting flung off the wheels. Much less restriction then front intakes, but no ram air. Also is this a positive or negative air pressure area?
Some kind of elbow on top of the carb, and a cone filter either in the arch or behind front valance, or two filters via a t-piece on the elbow
Cut a hole in the bonnet and stick a scoop on either the carb, hot rod style with internal filter, or a tall filter on the carb and a scoop on the bonnet pro stock style. This will cause problems at BIVA though most likely.
I guess any type of open filter will have unrestricted air flow, subject to filter size and clearance against bonnet and rocker covers etc, whereas ducted systems will be limited by the width and length of ducting, and any turns and twists that will need to be made.
What a long post. Sorry.
Reverie make a nice carb cap.
Cap with 2 ports
Bloody expensive but you could make your own version in glass fibre.
Steve
Cap with 2 ports
Bloody expensive but you could make your own version in glass fibre.
Steve
Do the math to work it out!
Estimate the average upheat (proably in the region of 65-75deg whilst moving directly under the bonnet. (compared to 25degC air, that's a 14% reduction in density) (and remember on a highly tuned detonation limited engine, hot air also forces a spark retard to avoid detonation, which usually is responsible for a similar magnitude torque drop as well! (probably not soo bad on a failry low tune big cap V8 however)) (you might want to measure the temp under the bonnet to give yourself some ball park numbers under various diff driving conditions etc)
Then:
Work out the area you can provide for flow with the airbox, subtract say 10% area to account for wall drag (hydraulic diameter). Estimate the max airflow of your engine, this means you can then calculate the speed of the air in the intake, and hence calc the dynamic pressure of the system. Worst case is that all of that dynamic pressure will be lost in the intake system (0% pressure recovery) but in reality, even terribly dimensioned systems can recover in the region of 50% of the dynamic pressure.
My monies on even a small cold air pick up being better than an open filter.
Estimate the average upheat (proably in the region of 65-75deg whilst moving directly under the bonnet. (compared to 25degC air, that's a 14% reduction in density) (and remember on a highly tuned detonation limited engine, hot air also forces a spark retard to avoid detonation, which usually is responsible for a similar magnitude torque drop as well! (probably not soo bad on a failry low tune big cap V8 however)) (you might want to measure the temp under the bonnet to give yourself some ball park numbers under various diff driving conditions etc)
Then:
Work out the area you can provide for flow with the airbox, subtract say 10% area to account for wall drag (hydraulic diameter). Estimate the max airflow of your engine, this means you can then calculate the speed of the air in the intake, and hence calc the dynamic pressure of the system. Worst case is that all of that dynamic pressure will be lost in the intake system (0% pressure recovery) but in reality, even terribly dimensioned systems can recover in the region of 50% of the dynamic pressure.
My monies on even a small cold air pick up being better than an open filter.
Steve_D said:
Reverie make a nice carb cap.
Cap with 2 ports
Bloody expensive but you could make your own version in glass fibre.
Steve
That is rather stunning. I can see how they can justify the cost, beautiful piece of kit. Well out of my league! I reckon I could bodge something together of a significantly lesser quality, at a lower cost like you say though.Cap with 2 ports
Bloody expensive but you could make your own version in glass fibre.
Steve
Pumaracing said:
Hugely informative piece, that. Took a couple of reads to make sense but I think I got it now! Thanksdavepoth said:
?
Max_Torque said:
Do the math to work it out!
Estimate the average upheat (proably in the region of 65-75deg whilst moving directly under the bonnet. (compared to 25degC air, that's a 14% reduction in density) (and remember on a highly tuned detonation limited engine, hot air also forces a spark retard to avoid detonation, which usually is responsible for a similar magnitude torque drop as well! (probably not soo bad on a failry low tune big cap V8 however)) (you might want to measure the temp under the bonnet to give yourself some ball park numbers under various diff driving conditions etc)
Then:
Work out the area you can provide for flow with the airbox, subtract say 10% area to account for wall drag (hydraulic diameter). Estimate the max airflow of your engine, this means you can then calculate the speed of the air in the intake, and hence calc the dynamic pressure of the system. Worst case is that all of that dynamic pressure will be lost in the intake system (0% pressure recovery) but in reality, even terribly dimensioned systems can recover in the region of 50% of the dynamic pressure.
My monies on even a small cold air pick up being better than an open filter.
(my bold)Estimate the average upheat (proably in the region of 65-75deg whilst moving directly under the bonnet. (compared to 25degC air, that's a 14% reduction in density) (and remember on a highly tuned detonation limited engine, hot air also forces a spark retard to avoid detonation, which usually is responsible for a similar magnitude torque drop as well! (probably not soo bad on a failry low tune big cap V8 however)) (you might want to measure the temp under the bonnet to give yourself some ball park numbers under various diff driving conditions etc)
Then:
Work out the area you can provide for flow with the airbox, subtract say 10% area to account for wall drag (hydraulic diameter). Estimate the max airflow of your engine, this means you can then calculate the speed of the air in the intake, and hence calc the dynamic pressure of the system. Worst case is that all of that dynamic pressure will be lost in the intake system (0% pressure recovery) but in reality, even terribly dimensioned systems can recover in the region of 50% of the dynamic pressure.
My monies on even a small cold air pick up being better than an open filter.
I didn't realise it was that severe! Pretty much makes my mind up for me then, many thanks.
I now plan to use a calculator for the mathses. Wish me luck.
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